HK1024820B - Driver circuit and method of operating the same - Google Patents

Description

Driving circuit and operation method thereof

Technical Field

The present invention relates to a driving circuit. The invention also relates to an operating method of the driving circuit.

Background

Drivers for light emitting diodes, LEDs, are well known in the art.

A first type of LED driver comprises a resistor connected to a voltage source, an LED and a switch. The first electrode of the resistor is connected to the anode of the LED. The cathode of the LED is connected to the first electrode of the switch. The voltage source electrode with the highest positive potential, the "anode", is connected to the second electrode of the resistor, and the voltage source electrode with the lowest negative potential, the "cathode", is connected to the second electrode of the switch. The switch may be an n-type bipolar transistor wherein the first electrode of the transistor is the collector and the second electrode is the emitter.

In operation, when the switch is closed, i.e., energized, a current flows from the "anode" of the voltage source, through the resistor, the LED and the switch, to the "cathode" of the voltage source. If the resistance value of the resistor and the voltage of the voltage source are properly selected, the LED emits light. The LED emits light when the voltage across the LED is greater than the threshold voltage of the diode when forward biased. This voltage is called V_FAbout 1 to 2V. The resistor is used to limit the current in the circuit. The switch may be implemented, for example, with a bipolar transistor or a field effect transistor FET.

A disadvantage of the first LED driver is that the LED requires a small forward voltage to emit light. In addition, the current limiting resistor consumes energy, which causes waste. These drawbacks become more pronounced when the voltage source is a battery, in which the maximum voltage provided is limited and the energy stored in the battery is a limited resource. If V_FA bipolar transistor of 1.4V and a collector-emitter voltage of 0.2V when turned on is used as a switch, the voltage of the voltage source needs to be greater than 1.6V (1.4+ 0.2). In this case, it is impossible to use a battery that supplies a voltage of 1.5V. This situation becomes worse if two or more LEDs are connected in series. Even if the voltage of the voltage source is high enough to cause the LED to emit light, energy is wasted in the resistor. It is undesirable to waste energy due to the limited amount of energy available for storage in the battery.

A first solution to the above-mentioned problem is shown in DE-a-2255822. Therein a driver is disclosed comprising an LED connected to a voltage source, a bipolar transistor acting as a switch and an inductor. The LED is connected in parallel with the inductor. The anode of the LED is connected to the collector of an n-type bipolar transistor. The voltage source electrode with the highest positive potential- "anode" is connected to the cathode of the LED, and the voltage source electrode with the lowest negative potential- "cathode" is connected to the emitter of the bipolar transistor.

In operation, the transistor acts as a switch that alternately closes and opens. This is achieved by applying an appropriate signal at the base of the transistor. During the switch closure, energy is stored in the inductor. When the switch is then opened, the stored energy is released through the LED. If the parameters of the inductor are chosen appropriately, the forward voltage across the LED will reach the threshold voltage V_FThe LED emits light. Then, the switch is closed again to repeat the above procedure. It should be noted that the maximum forward voltage across the LED may have a larger nominal value than the nominal value of the voltage supplied by the voltage source. Thus, an LED can be driven by a voltage source which provides a rated value smaller than the LED threshold value V_FThe voltage of (c). In addition, the scheme does not contain a current limiting resistor for energy consumption.

A second solution to the above problem is disclosed in US-A-3,944,854. Therein a driver is disclosed comprising an LED connected to a voltage source, a bipolar transistor acting as a switch and an inductor. In this case, the LED is connected in parallel with the switch. The operation of the drive is thus similar to that of the drive disclosed in DE-a-2255822 above.

In US-A-5,313,141A driver for an EL lamp is disclosed, the driver comprising A switching circuit and an inductor.

Drivers for buzzers are well known in the art.

A buzzer includes an inductor and a vibrating plate. In operation, a periodically alternating electrical potential is applied across the inductor, thereby generating a magnetic field of periodically changing strength in the vicinity of the inductor. Due to these changes in the magnetic field strength, the vibrating piece disposed substantially adjacent to the inductor vibrates. These vibrations of the membrane generate an acoustic signal. Thus the operation of a buzzer is similar to the operation of a loudspeaker.

One prior art buzzer driver includes a buzzer, a transistor, a resistor, a diode, and an n-type bipolar transistor connected to a voltage source. The first electrode of the buzzer is connected to the first electrode of the resistor and the anode of the diode. The second electrode of the resistor is connected to the collector of the transistor. The electrode of the voltage source with the largest positive potential- "anode" is connected to the second electrode of the buzzer and the cathode of the diode. The electrode of the voltage source with the least negative potential- "negative" is connected to the emitter of the transistor.

In operation, the transistor may act as a switch that alternately closes and opens. This is achieved by applying an appropriate signal to the base of the transistor. When the transistor is turned on, a current flows through the inductor of the buzzer, and energy is stored in the inductor. When the transistor is non-conductive, the stored energy is released as a current flowing through the diode. The current flowing through the buzzer inductor will generate a magnetic field around the inductor. The actual position of the membrane in the buzzer depends on the magnetic field strength. Since the strength of the magnetic field varies periodically as a function of time in connection with the switching of the transistor, the membrane vibrates, thereby generating acoustic waves. The frequency of the acoustic wave depends on the switching frequency of the transistor. Other types of periodic signals, such as a sinusoid, may of course be used when driving the transistor.

To fully understand the background of the present invention, some prior art circuits will now be described.

An LED driver may be used to drive a number of LEDs. This is commonly used in the prior art where LEDs are used to backlight, for example, a Liquid Crystal Display (LCD) or a keypad panel. One prior art LED driver for multiple LEDs includes a constant current generator (constant current generator) connected to a voltage source and multiple LEDs. A group of LEDs may be connected in series or in parallel. A number of groups of LEDs can then be connected in series or in parallel.

Many voltage converters (voltage converters) that utilize an inductor and a switch are well known in the art. The common operating principle of these converters is that the inductor alternately charges and discharges. This is achieved by alternately closing and opening the switch.

One problem with prior art drivers is that if there are more than one driver in a common system, the overall space required for the driver circuitry on a printed circuit board, PCB, is large. This problem becomes even more pronounced when there are several drive circuits in a system that actually requires very small dimensions. A system requiring such small size is a handheld system (e.g., a cellular telephone).

Another problem with prior art drivers when used in a shared system is that it takes at least a period of time, for example, to secure components to a PCB with a pick-and-place machine, during which all of the components of each driver are secured in turn. The time taken to attach a component to a PCB corresponds to a certain cost since a resource such as a mounter will be occupied during the time period for attaching the component.

Another problem with prior art drivers when used in a shared system is that each driver requires a separate control signal that is used to control the operation of the driver. The control signal is typically generated by a control unit, such as a microprocessor. Each control signal occupies an output port of the control unit. In many systems, the number of control unit output ports is limited. This problem becomes particularly acute when the control unit is incorporated into a physically small device, such as a handheld system, since each output port occupies a certain minimum area on the PCB.

Fig. 1 shows a first prior art LED driver 100 comprising an LED120 connected to a voltage source 150, a switch 140 and an inductor 130. The voltage source 150 includes a first electrode of maximum positive potential-the "anode" and a second electrode of minimum negative potential-the "cathode". The voltage source 150 may include one or more batteries or be constructed of other devices known to those of ordinary skill in the art. The LED120 and the inductor 130 are connected in parallel. The anode of the LED120 is connected to a first electrode of the switch 140. The electrode of the voltage source 150 with the largest positive potential- "anode" is connected to the cathode of the LED120, and the electrode of the voltage source 150 with the smallest negative potential- "cathode" is connected to the second electrode of the switch 140.

In operation, switch 140 is alternately closed and opened. During the time that switch 140 is closed, energy is stored in inductor 130. Thereafter, when the switch 140 is open, the stored energy is released through the LED 120. If the parameters of inductor 130 are properly selected, the maximum forward voltage across LED120 will reach the threshold voltage V of the LED_FAnd the LED120 emits light. Then, the switch 140 is closed again to repeat the above procedure. It should be noted that the threshold voltage across LED120 may be rated more than the voltage supplied by voltage source 150. Thus, the LED can be driven by a voltage source which provides a rated value smaller than the threshold voltage V of the LED_FThe voltage of (c). In addition, the scheme does not include any current limiting resistor which consumes energy. However, a resistor is sometimes included to limit the peak level of current from voltage source 150.

Fig. 2 shows a second prior art LED driver 200 comprising an LED220 connected to a voltage source 250, a switch 240 and an inductor 230. The anode of LED220 is connected to a first electrode of switch 240 and a first electrode of inductor 230. The electrode of the voltage source 250 with the largest positive potential- "anode" is connected to the second electrode of the inductor 230, and the electrode of the voltage source 250 with the smallest negative potential- "cathode" is connected to the second electrode of the switch 240 and the cathode of the LED 220.

In operation, switch 240 is alternately closed and opened. During the time that switch 240 is closed, energy is stored in inductor 230. Thereafter, when the switch 240 is open, the stored energy is released via the LED 220. If the parameters of the inductor 230 are properly selected, the maximum forward voltage across the LED220 will reach the threshold voltage V_FThe LED220 emits light. Then, the switch 240 is closed again to repeat the above procedure. It should be noted that the maximum forward voltage across the LED220 may be rated more than the voltage supplied by the voltage source 250. Thus, the LED can be driven by a voltage source which provides a rated value smaller than the threshold voltage V of the LED_FThe voltage of (c). In addition, the scheme does not include any current limiting resistor which consumes energy. However, a resistor is sometimes included to limit the peak level of current from voltage source 250.

Figure 3 shows a circuit diagram of a prior art buzzer driver 300, the driver 300 comprising a buzzer 360 including an inductor 330 connected to a voltage source 350, a transistor 380, a resistor 390, a diode 370 and an n-type bipolar transistor 380. A first electrode of the buzzer 360 is coupled to a first electrode of the resistor 390 and to an anode of the diode 370. The second electrode of resistor 390 is connected to the collector of transistor 380. The electrode of the voltage source 350 having the most positive potential, the "anode", is connected to the second electrode of the buzzer 360 and the cathode of the diode 370. And the "negative" electrode of the voltage source 350 having the least negative potential is connected to the emitter of the transistor 380.

In operation, transistor 380 may function as a switch that is alternately closed and opened. This is accomplished by applying an appropriate signal to the base of transistor 380. For example, the potential V varying according to a square wave or a sine wave_BUZZThrough a current limiting resistor 391 to the base of the transistor 380. When the transistor 380 is turned on, a current flows through the inductor 330 of the buzzer 360, and energy is stored in the inductor 330. When the transistor 380 is non-conductive, the stored energy is released as a current flowing through the diode 370. The current flowing through the inductor 330 of the buzzer 360 creates a magnetic field around the inductor. The actual position of the membrane (not shown) within the buzzer 360 depends on the magnetic field strength. Since the magnetic field strength varies periodically as a function of time depending on the switching of the transistor 380, the vibrating plate vibrates, thereby generating a sound wave. The frequency of the acoustic wave depends on the switching frequency of the transistor. Other types of periodic signals may also be employed when driving the transistor.

Figure 4 shows a circuit diagram of a prior art LED driver 400,the driver 400 is for a plurality of LEDs and includes a constant current source connected to a voltage source 450 and a plurality of LEDs 420-427. The three LEDs 420-422 in the first group are connected in parallel by tying their anodes together and tying their cathodes together. The five LEDs 423-427 in the second group are also connected in parallel by tying their anodes together and tying their cathodes together. The two groups of LEDs are connected in series by tying together the cathodes of the three LEDs in the first group and the anodes of the five LEDs in the second group. It should be understood that the first and second sets of LEDs may include any number of LEDs, and the number of sets may be one or more than two. The LEDs are connected to a current source comprising an n-type bipolar transistor 480, three resistors 490, 491, 492 and two diodes 470, 471. The cathodes of the five LEDs in the second group are connected to the collector of the transistor. The emitter of the transistor 480 is connected to a first electrode of the first resistor 490. The base of the transistor 480 is connected to the anode of the first diode 470, the first electrode of the second resistor 491 and the first electrode of the third resistor 492. The cathode of the first diode 470 is connected to the anode of the second diode 471. The cathode of the second diode 471, the second electrode of the first resistor 490 and the second electrode of the second resistor 491 are connected together and to the electrode of the voltage source 450 having the smallest negative potential- "cathode". The electrode of the voltage source 450 with the largest positive potential, the "anode", is connected to the anode of the first set of three LEDs. By applying a potential V_LEDThe second electrode applied to the third resistor 492 feeds a constant current source.

In operation, when a sufficiently high potential V is applied_LEDWhen applied to a current source, the potential at the base terminal of the transistor 480 is equal to the threshold voltage of the first diode 470 and the second diode 471 (typically 2 × 0.7V — 1.4V). Since the potential is nearly fixed and the potential between the base and the emitter of the transistor 480 is also fixed (typically 0.7V), the potential across the first resistor 490 is fixed (1.4V-0.7V — 0.7V). Thus, the collector-emitter current may be determined by selecting the value of the first resistor 490. This current is independent of the load on the collector of transistor 480. Thus, the structure acts as a constant current source. A current then flows through LEDs 420-427. If the potential of the voltage source 450 is sufficiently high,whereby the voltage across each LED420-427 is greater than the threshold voltage V of the diode_FAnd then the LED emits light. Because of the different number of LEDs used in the first and second groups, the current flowing through each of the three LEDs 420-422 is greater than the current flowing through each of the five LEDs 423-427. Thus, a first group of three of LEDs 420-423 emits more light than a second group of five of LEDs 424-427. When the potential applied to the current source is low enough (e.g., zero volts), no collector-emitter current flows through transistor 480 and the LED does not emit light.

Fig. 5 shows a circuit diagram of a prior art forward buck (also referred to as "buck") circuit 500. The circuit includes a first switch 540, a second switch 541, an inductor 530, and a capacitor 510. The circuit is connected to a voltage source 550. The electrode of the voltage source 550 having the most positive potential, the "anode", is connected to the first electrode of the first switch 540. A second electrode of the first switch 540 is coupled to a first electrode of the inductor 530 and a first electrode of the second switch 541. A second electrode of the inductor 530 is coupled to a first electrode of the capacitor 510 and a first electrode of the buck circuit load 599. The "negative" electrode of the voltage source 550 having the smallest negative potential is connected to the second electrode of the second switch 541, the second electrode of the capacitor 510, and the second electrode of the buck circuit 500 load 599.

During a first time period, the first switch 540 is closed and the second switch 541 is open. A current flows from the voltage source 550 through the inductor 530. Thereby storing energy in inductor 530. During a second time period, the first switch 540 is open and the second switch 541 is closed. The energy stored in inductor 530 is released into capacitor 510 and load 599. By alternately repeating the first time period and the second time period at a predetermined duty cycle, the output voltage, i.e., the output voltage across capacitor 510 (and load 599), will be a positive voltage, which is less than the input voltage of voltage source 550. Capacitor 510 attenuates the amount of ripple voltage in the output voltage.

A negative buck circuit, also known as a negative cancellation (buck) circuit, converts a negative input voltage to a negative output voltage that is less negative than the input voltage. The negative step-down circuit can be implemented by using the same type of circuit as the positive step-down circuit, but with appropriate modifications to the polarity of the potential in the circuit.

It is understood that the first switch 540 and/or the second switch 541 may be implemented using bipolar transistors or FETs. The second switch 541 may be replaced by a diode. In the case of the forward voltage step-down circuit, the cathode and the anode of the diode are connected to nodes, respectively, and the first electrode and the second electrode of the second switch 541 are connected to the nodes, respectively. The direction of the diode is opposite to that of the diode in the case of a negative buck circuit.

Fig. 6 shows a circuit diagram of a prior art forward boost (also referred to as "boost") circuit 600. The circuit includes a first switch 640, a second switch 641, an inductor 630, and a capacitor 610. The circuit is connected to a voltage source 650. The electrode of the voltage source 650 having the most positive potential- "anode" is connected to the first electrode of the inductor 630. A second electrode of the inductor 630 is coupled to a second electrode of the first switch 640 and a first electrode of the second switch 641. A second electrode of the second switch 641 is coupled to a first electrode of the capacitor 610 and a first electrode of the load 699 of the voltage boost circuit 600. The "negative" electrode of the voltage source 650 having the minimum negative potential is connected to the second electrode of the first switch 640, the second electrode of the capacitor 610, and the second electrode of the load 699 of the voltage boost circuit 600.

During the first time period, the first switch 640 is closed and the second switch 641 is open. A current flows from the voltage source 650 through the inductor 630. Thereby storing energy in inductor 630. During a second time period, the first switch 640 is open and the second switch 641 is closed. The energy stored in inductor 630 is discharged into capacitor 610 and load 699. By repeating this operation for a first time period and a second time period at a predetermined duty cycle, the output voltage, i.e., the output voltage across capacitor 610 (and load 699), will be a positive voltage that is greater than the input voltage of voltage source 650. The capacitor 610 attenuates the amount of ripple voltage in the output voltage.

A negative boost circuit, also referred to as a negative boost circuit, converts a negative input voltage to a negative output voltage that is more negative than the input voltage. The negative boost circuit can be implemented by using the same type of circuit as the positive boost circuit, but with appropriate modifications to the polarity of the potential in the circuit.

It is understood that the first switch 640 and the second switch 641 may be implemented using bipolar transistors or FETs. The second switch 641 may be replaced by a diode. In the case of the forward boost circuit, the anode and cathode of the diode are connected to nodes, respectively, and the first electrode and the second electrode of the second switch 641 are connected to the nodes, respectively. The direction of the diode is opposite to that of the diode in the case of a negative boost circuit.

Fig. 7 shows a circuit diagram of a prior art positive-negative polarity conversion (also referred to as "buck-boost") circuit 700. The circuit includes a first switch 740, a second switch 741, an inductor 730, and a capacitor 710. The circuit is connected to a voltage source 750. The electrode of the voltage source 750 having the most positive potential, the "anode", is connected to the first electrode of the first switch 740. A second electrode of the first switch 740 is connected to a first electrode of the second switch 741 and a first electrode of the inductor 730. A second electrode of the second switch 741 is connected to a first electrode of the capacitor 710 and a first electrode of the load 799 of the positive-negative polarity inverter circuit 700. The "negative" electrode of the voltage source 750 having the least negative potential is connected to the second electrode of the inductor 730, the second electrode of the capacitor 710, and the second electrode of the load 799 of the positive-negative polarity inverter circuit 700.

During a first time period, the first switch 740 is closed and the second switch 741 is open. A current flows from voltage source 750 through inductor 730. Thereby storing energy in inductor 730. During a second time period, the first switch 740 is open and the second switch 741 is closed. The energy stored in inductor 730 is released into capacitor 710 and load 799. By repeating this operation for a first time period and a second time period at a predetermined duty cycle, the output voltage, i.e., the output voltage across capacitor 710 (and load 799), will be a negative voltage rated at a value greater than or less than the input voltage rating of voltage source 750. The capacitor 710 attenuates the amount of ripple voltage in the output voltage.

A negative-positive polarity conversion circuit, also known as a buck-boost circuit, converts a negative input voltage to a positive output voltage having a voltage rating that is greater than or less than the voltage rating of the input voltage. The negative-positive polarity conversion circuit can be realized by using the same type of circuit as the positive-negative polarity conversion circuit, but by appropriately modifying the polarity of the potential in the circuit.

It is to be understood that the first switch 740 and the second switch 741 may be implemented using bipolar transistors or FETs. The second switch 741 may be replaced by a diode. In the case of the positive-negative polarity conversion circuit, the negative electrode and the positive electrode of the diode are connected to nodes, respectively, and the first electrode and the second electrode of the second switch 741 are connected to the nodes, respectively. The direction of the diode is opposite to that of the diode in the case of the negative-positive polarity conversion circuit.

Disclosure of Invention

It is an object of the present invention to provide a driving circuit for driving at least two functional devices, such as an LED, a buzzer, a voltage converter or an EL lamp, which requires little space on a PCB when in use.

Another object of the present invention is to provide a driving circuit for driving at least two functional devices, which requires little time for fixing components to a PCB with resources such as a mounter when fixing the components to the PCB.

It is still another object of the present invention to provide a driving circuit for driving a plurality of functional devices by controlling a small number of control signal lines. The object of the invention is to have fewer control signal lines than the number of functional devices, so that a small number of output ports of the control unit can be used, as a result of which the output ports and the control signal lines require less space on the PCB when implementing the invention.

The object of the invention is achieved by providing a driving circuit for driving at least two functional devices, such as an LED, a buzzer, a voltage converter or an EL lamp, the circuit comprising: an inductor; a first connection point and a second connection point for connecting a voltage source; a switching device which, when in a first state, enables current to flow from the first connection point through the inductor thereby charging the inductor, and which, when in a second state, substantially prevents current from flowing from the first connection point to the inductor; and at least two functional devices that function when energy is released from the inductor to the at least two functional devices.

The present invention also provides a method of operating such a drive circuit, the method comprising the steps of: firstly, setting the switching device to be in a first state for controlling current to flow out of the first connecting point and flow through the inductor, thereby charging the inductor; the switching device is then set to a second state for releasing the energy stored in the inductor to the functional device.

This structure has following advantage: the space required on the PCB for two or more drivers is less than when the same number of drivers are implemented separately, since fewer components are required.

In addition, this structure has the following advantages: when the components of the drive circuit that drives at least two functional devices are fixed to the PCB, less time is required by resources such as a chip mounter that fix the components to the PCB because the structure requires fewer components than when the same number of drivers are separately implemented.

In addition, the structure has the following advantages: this configuration requires fewer signals to control the drivers than would otherwise be required if the same number of drivers were implemented separately.

Less space is required on the PCB because the driving circuit of the present invention requires fewer components (inductors and switches) than the number of components required by prior art drivers when the same number of drivers are employed. In addition, the space required on the PCB is also reduced because when the control signal lines are generated by the output ports of, for example, a microprocessor, the number of control signal lines required to be used on the PCB is smaller, and the required PCB space is further reduced because the number of output ports required to be used on the PCB is smaller. And the number of required control signal lines and the number of possible output ports are smaller due to the operation method of the driving circuit of the present invention in which the operation of one or more functional devices can be controlled by changing the frequency of one control signal.

Drawings

The foregoing and other objects, features and advantages of the invention will be more readily understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 shows a circuit diagram of a first prior art LED driver employing an inductor;

FIG. 2 shows a circuit diagram of a second prior art LED driver employing an inductor;

figure 3 shows a circuit diagram of a prior art buzzer driver;

FIG. 4 shows a circuit diagram of a prior art LED driver;

FIG. 5 shows a circuit diagram of a prior art voltage step-down circuit;

FIG. 6 shows a circuit diagram of a prior art boost circuit;

FIG. 7 is a circuit diagram of a prior art positive-to-negative polarity conversion (positive-to-negative polarity) circuit;

figure 8 shows a circuit diagram of an LED and buzzer driver according to a first embodiment of the invention;

figure 9 shows a circuit diagram of an LED and buzzer driver according to a second embodiment of the present invention;

figure 10 shows a circuit diagram of an LED and buzzer driver according to a third embodiment of the present invention;

figure 11 shows a circuit diagram of an LED and buzzer driver according to a fourth embodiment of the present invention;

fig. 12 shows a circuit diagram of an LED driver and a forward voltage step-down circuit according to a fifth embodiment of the present invention;

fig. 13 is a circuit diagram of an LED driver and a positive-negative polarity conversion circuit according to a sixth embodiment of the present invention;

fig. 14 shows a circuit diagram of an LED driver and a forward boost circuit according to a seventh embodiment of the present invention;

FIG. 15 is a signal diagram showing the operating performance of an LED and buzzer driver in accordance with an eighth embodiment of the present invention;

fig. 16 shows a circuit diagram of an EL lamp and buzzer driver according to a ninth embodiment of the present invention.

Detailed Description

In the following description, for purposes of explanation and not limitation, specific details are set forth, such as particular circuits, circuit elements, techniques, etc. in order to provide a thorough understanding of the present invention. However, it will be apparent to one of ordinary skill in the art that the present invention may be practiced in other embodiments that depart from these specific details. In other instances, detailed descriptions of well-known methods, devices, and circuits are omitted so as not to obscure the description with unnecessary detail

Description of the invention.

Fig. 8 shows a circuit diagram of an LED and buzzer driver 1000 according to a first embodiment of the present invention. The driver includes: a voltage source 1050 connected to first and second connection points (not shown); a buzzer 1060; a switch 1040 and four LEDs 1020-1023. The buzzer 1060 includes the inductor 1030 as described above. The first electrode of inductor 1030 is connected to the electrode of voltage source 1050 having the most positive potential, the "anode". A second electrode of the inductor 1030 is coupled to a first electrode of the switch 1040 and to anodes of the first and third LEDs 1020, 1022. The cathodes of the first LED1020 and the third LED1022 are connected to the anodes of the second LED1021 and the fourth LED1023, respectively. The cathodes of the second LED1021 and the fourth LED1023, and the second electrode of the switch 1040, are connected to the "cathode" of the voltage source 1050 having the minimum negative potential.

In operation, switch 1040 is alternately closed and opened. During the time that switch 1040 is closed, energy is stored in inductor 1030. Thereafter, when the switch 1040 is open, the stored energy is released through the LEDs 1020-1023. If the parameters of the inductor 1030 of the buzzer 1060 are chosen appropriately, the forward voltage across the LEDs 1020-1023 will reach the threshold voltage V of each LED_FEach LED emits light. Then, the switch 1040 is closed again to repeat the above procedure. It should be noted that the maximum forward voltage across the LED may be rated more than the voltage supplied by the voltage source 1050. The closing and opening of switch 1040 also creates a magnetic field around inductor 1030 of buzzer 1060. Thereby, as described above, a sound wave is generated by the vibrating plate (not shown) in the buzzer 1060. The frequency of the acoustic wave depends on the frequency at which the switch 1040 is closed and opened, i.e., the operating frequency of the switch 1040.

Fig. 9 shows a circuit diagram of an LED and buzzer driver 1100 according to a second embodiment of the invention. The driver includes: a voltage source 1150 connected to first and second connection points (not shown); a buzzer 1160; a switch 1140 and four LEDs 1120-1123. Buzzer 1160 includes inductor 1130 as described above. The first electrode of the switch 1140 is connected to the electrode of the voltage source 1150, the "anode", having the most positive potential. A second electrode of the switch 1140 is coupled to a first electrode of the inductor 1130 and to the cathodes of the first LED1120 and the third LED 1122. Anodes of the first LED1120 and the third LED1122 are respectively connected to cathodes of the second LED1121 and the fourth LED 1123. The anodes of the second and fourth LEDs 1121, 1123 and the second electrode of the inductor 1130 are connected to the "negative" electrode of the voltage source 1150 having the smallest negative potential.

In operation, switch 1140 is alternately closed and opened. During the time that switch 1140 is closed, energy is stored in inductor 1130. Thereafter, when the switch 1140 is turned off, the stored energy is released through the LEDs 1120-1123. If the parameters of inductor 1130 of buzzer 1160 are properly selected, the forward voltage across LEDs 1120-1123 will reach the threshold voltage V of each LED_FEach LED emits light. Then, the switch 1140 is closed again to repeat the above procedure. It should be noted that the maximum forward voltage across the LED may be rated more than the voltage supplied by voltage source 1150. The closing and opening of switch 1140 also creates a magnetic field around inductor 1130 of buzzer 1160. Thereby generating a sound wave by the vibrating plate (not shown) in the buzzer 1160, as described above. The frequency of the acoustic wave depends on the frequency at which the switch 1140 is closed and open, i.e., the operating frequency of the switch 1140.

Fig. 10 shows a circuit diagram of an LED and buzzer driver 1200 according to a third embodiment of the invention. The driver includes: a voltage source 1250 connected to the first and second connection points (not shown); a buzzer 1260; a first n-type bipolar transistor 1280; a second n-type bipolar transistor 1281; three resistors 1290, 1291, 1292 and four LEDs 1220-1223. The buzzer 1260 includes an inductor 1230 as described above. The collector of the second transistor is connected to the electrode of the voltage source 1250 having the most positive potential-the "anode". A first electrode of the inductor 1230 is connected to an emitter of a second transistor 1281. A second electrode of inductor 1230 is coupled to a first electrode of first resistor 1290. A second electrode of the first resistor 1290 is connected to a collector of the first transistor 1280 and anodes of the first LED1220 and the third LED 1222. Cathodes of the first LED1220 and the third LED1222 are connected to anodes of the second LED1221 and the fourth LED1223, respectively. The cathodes of the second and fourth LEDs 1221 and 1223 and the emitter of the first transistor 1280 are connected to the "cathode" of the voltage source 1250 having the minimum negative potential. First electrodes of the second resistor 1291 and the third resistor 1292 are respectively connected to bases of the first transistor 1280 and the second transistor 1281. A second electrode of the second resistor 1291 is connected to a resistor designated V_BUZZ/LedOn the signal ofA second electrode of the third resistor 1292 is connected to a resistor designated V_refOn the signal of (c).

In operation, a voltage source 1250, which may be two nickel mh (ni mh) cells connected in series, provides + 2.4V. One +1.6V was applied at atmospheric pressure to a standard V_refOf the signal of (1). A second transistor 1281, a third resistor 1292 and a resistor labeled V_refTogether, act as a constant voltage source (constant voltage generator), thereby stabilizing the voltage at the emitter of the second transistor 1281. The first transistor 1280 is rendered alternately conductive and non-conductive between the collector and emitter. This is done by applying a voltage designated V to the second electrode of the second resistor 1291_BUZZ/LedA square wave signal of the signal with appropriate voltage fluctuations. During the time that the first transistor 1280 is on, energy is stored in the inductor 1230. Thereafter, when the first transistor 1280 is non-conductive, the stored energy is discharged through the LEDs 1220-1223. If the parameters of the inductor 1230 of the buzzer 1260 are properly selected, the forward voltage across the LEDs 1220-1223 will reach the threshold voltage V of each LED_FEach LED emits light. Then, the first transistor 1280 is turned on again to repeat the above procedure. It should be noted that the maximum forward voltage across the LED may be rated for a voltage greater than the rated voltage supplied by the voltage source 1250. The changing state of the first transistor 1280 between conducting and non-conducting also creates a magnetic field around the inductor 1230 of the buzzer 1260. Thereby, as described above, a sound wave is generated from the vibrating plate (not shown) in the buzzer 1260. The frequency of the acoustic wave depends on the switching frequency of the first transistor 1280, i.e. is applied to a frequency denoted by V_BUZZ/LedThe signal frequency of the signal.

Fig. 11 shows a circuit diagram of an LED and buzzer driver 1300 according to a fourth embodiment of the present invention. The driver includes: a voltage source 1350 connected to first and second connection points (not shown); a buzzer 1360; a first n-type bipolar transistor 1380; a second n-type bipolar transistor 1381; three resistors 1390, 1391, 1392 and four LEDs 1320-1323. The buzzer 1360 includes an inductor 1330 as described above. The collector of the second transistor is connected to the electrode of the voltage source 1350 having the most positive potential- "positive". InductanceA first electrode of the device 1330 is connected to an emitter of the second transistor 1381 and to cathodes of the first and third LEDs 1320, 1322. Anodes of the first LED1320 and the third LED1322 are respectively connected to cathodes of the second LED1321 and the fourth LED 1323. A second electrode of the inductor 1330 is connected to a first electrode of the first resistor 1390 and to the anodes of the second and fourth LEDs 1321, 1323. The second electrode of the first resistor 1390 is connected to the collector of the first transistor 1380, and the emitter of the first transistor 1380 is connected to the "negative" electrode of the voltage source 1350 having a minimum negative potential. First electrodes of the second resistor 1391 and the third resistor 1392 are respectively connected to bases of the first transistor 1380 and the second transistor 1381. A second electrode of a second resistor 1391 is connected to_BUZZ/LedAnd a second electrode of third resistor 1392 is connected to a terminal labeled V_refOn the signal of (c).

In operation, a voltage source 1350, which may be two nickel MH batteries connected in series, provides + 2.4V. One +1.6V was applied at atmospheric pressure to a standard V_refOf the signal of (1). A second transistor 1381, a third resistor 1392 and a reference V_refTogether, act as a constant voltage source, thereby stabilizing the voltage at the emitter of the second transistor 1381. The collector and emitter of the first transistor 1380 are alternately rendered conductive and non-conductive. This is done by applying a voltage designated V to the second electrode of second resistance 1391_BUZZ/LedA square wave signal of the signal with appropriate voltage fluctuations. During the turn on of the first transistor 1380, energy is stored in the inductor 1330. Thereafter, when the first transistor 1380 is non-conductive, the stored energy is discharged through the LEDs 1320-1323. If the parameters of the inductor 1330 of the buzzer 1360 are properly selected, the forward voltage across the LEDs 1320-1323 will reach the threshold voltage V of each LED_FEach LED emits light. Then, the first transistor 1380 is turned on again to repeat the above process. It should be noted that the maximum forward voltage across the LED may be rated for a voltage greater than the rated value of the voltage supplied by the voltage source 1350. The changing state of the first transistor 1380 between conducting and non-conducting also generates a magnetic field around the inductor 1330 of the buzzer 1360. Thereby generating a sound wave by the vibrating plate (not shown) in the buzzer 1360 as described above. The sound waveIs dependent on the switching frequency of the first transistor 1380, i.e. applied to the reference V_BUZZ/LedThe signal frequency of the signal.

With reference to the third and fourth embodiments described above, the constant voltage source may be omitted. The advantage of including a constant voltage source in the circuit is that the sound produced by the buzzer is independent of the voltage provided by the voltage source. For example, the voltage provided by a nickel MH battery depends on, for example, the energy stored in the battery. Instead of using a constant voltage source, the voltage supplied by the voltage source can be measured and this information can be used to compare the values denoted V_BUZZ/LedIs pulse width modulated to compensate for variations in the supplied voltage. Further, one of ordinary skill in the art will recognize that the voltage sources 1250, 1350 may be selected to provide voltages different than those used in these embodiments. May also be labeled V_refThe potential of the signal is chosen to be different values.

In the case of the third embodiment, it is noted that the voltage provided by the voltage source 1250 and the number of LEDs connected in series are preferably selected such that substantially no current flows from the voltage source 1250 through the LEDs when the first transistor 1280 is non-conductive and after the inductor 1230 is discharged.

Referring to the first, second, third and fourth embodiments described above, it will be appreciated by those skilled in the art that the acoustic frequency of the buzzers 1060, 1160, 1260, 1360 may also depend to some extent on the ratio of the time period during which the switches 1040, 1140 are closed to the time period during which they are open, or on the ratio of the time period during which the first transistors 1280, 1380 are conductive to the time period during which they are non-conductive. By selecting the operating frequency (e.g. 500Hz) of the switches 1040, 1140 or the first transistors 1280, 1380, which frequency corresponds to the frequency of the sound waves generated by the buzzers 1060, 1160, 1260, 1360 (e.g. 500Hz), which sound waves are within the audible frequency range, the LEDs 1020-1023, 1120-. (the acoustic frequency range is sometimes defined as 20-20000 Hz.) conversely, the LEDs 1020-1-23, 1120-plus 1123, 1220-plus 1223, 1320-plus 1323 can be illuminated while no audible sound is generated in the buzzers 1060, 1160, 1260, 1360 by selecting the operating frequency (e.g., 40000Hz) of the switches 1040, 1140 or the first transistors 1280, 1380, which corresponds to the frequency of the sound wave generated by the buzzers 1060, 1160, 1260, 1360 (e.g., 40000Hz), which is in the non-acoustic frequency range. It should be noted that most buzzers produce sound waves only at frequencies below 10000 Hz. Thus, frequencies at which the buzzer does not produce sound can be used when the buzzer should be silent. When the switches 1040, 1140 are kept normally open or closed, or the first transistors 1280, 1380 are made normally non-conductive or normally conductive, the LED is prevented from emitting light and the buzzer does not generate any sound wave.

Fig. 12 shows a circuit diagram of an LED driver and a forward buck (also referred to as "buck") circuit 1400 according to a fifth embodiment of the present invention. The circuit includes: three FETs 1480, 1481, 1482; an inductor 1430; four LEDs 1420-1423; and a capacitor 1410. The circuit is connected to a voltage source 1450, the voltage source 1450 being connected to first and second connection points (not shown). The electrode of the voltage source 1450 having the most positive potential, the "anode", is connected to the drain of the first transistor 1480. The drain of the first transistor 1480 is coupled to the first electrode of the inductor 1430, the source of the second transistor 1481, and the cathodes of the first LED1420 and the third LED 1422. Anodes of the first LED1420 and the third LED1422 are respectively connected to cathodes of the second LED1421 and the fourth LED 1423. Anodes of the second LED1421 and the fourth LED1423 are connected to the source of the third transistor 1482. A second electrode of the inductor 1430 is coupled to a first electrode of the capacitor 1410 and a first electrode of the buck circuit load 1499. The "negative" electrode of the voltage source 1450 with the least negative potential is connected to the drain of the second transistor 1481, the drain of the third transistor 1482, the second electrode of the capacitor 1410, and the second electrode of the LED driver and buck circuit 1400 load 1499.

The voltage source 1450 provides a voltage (e.g., + 4.8V). Each of the transistors 1480-1482 may be operated to make or break conduction between its source and drain by applying an appropriate signal to the gate of the transistors 1480-1482. The operation of the circuit when the LED should not emit light will now be described. In this mode, the third transistor 1482 is not conductive. During the first time period, the first transistor 1480 is conductive while the second transistor 1481 is non-conductive. A current flows from the voltage source 1450 through the inductor 1430. Thereby storing energy in the inductor 1430. During the second time period, the first transistor 1480 is non-conductive and the second transistor 1481 is conductive. Because the second transistor 1481 forms a closed loop, energy stored in the inductor 1430 is released into the capacitor 1410 and the load 1499. By alternately repeating the first and second cycles at a predetermined duty cycle, the output voltage, i.e., the output voltage across the capacitor 1410 (and the load 1499) will be a positive voltage (e.g., + 3.0V). It should be noted that the value of this output voltage is lower than the voltage of the voltage source 1450. The capacitor 1410 attenuates the amount of ripple voltage in the output voltage. In a mode when the LED should emit light, the second transistor 1481 is kept off, and the third transistor 1482 is alternately turned on and off, corresponding to the switching of the second transistor 1481 in a mode when the LED should not emit light. The closed loop formed by the third transistor 1482 upon release of the energy stored in the inductor 1430 now includes the LEDs 1420-1423. During at least a portion of the cycle, the forward voltage across the LEDs 1420-1423 reaches the threshold voltage of the diodes, which then emit light.

In another embodiment, an LED driver and a negative-going buck circuit are formed. This is achieved by using the same type of circuit as in the fifth embodiment, but with appropriate modifications to the polarity of the potential and the orientation of the transistors and LEDs in the circuit.

In the case where the LED is to emit light at all times, the second transistor 1481, and even the third transistor 1482, may be eliminated.

Fig. 13 shows a circuit diagram of an LED driver and a positive-negative polarity conversion (also referred to as "buck-boost") circuit 1500 according to a sixth embodiment of the present invention. The circuit includes: three FETs 1580, 1581, 1582; an inductor 1530; four LEDs 1520-1523; and a capacitor 1510. The circuit is connected to a voltage source 1550, and the voltage source 1550 is connected to first and second connection points (not shown). The electrode of the voltage source 1550 with the most positive potential, the "anode", is connected to the drain of the first transistor 1580. The source of the first transistor 1580 is connected to the first electrode of the inductor 1530, the source of the third transistor 1582, and the cathodes of the first LED1520 and the third LED 1522. Anodes of the first LED1520 and the third LED1522 are connected to cathodes of the second LED1521 and the fourth LED1523, respectively. Anodes of the second LED1521 and the fourth LED1523 are connected to the source of the second transistor 1581. The drain of the third transistor 1582 is connected to a first electrode of the capacitor 1510 and a first electrode of a load 1599 of the circuit 1500. The "negative" electrode of the voltage source 1550, which has a minimum negative potential, is connected to the second electrode of the inductor 1530, the drain of the second transistor 1581, the second electrode of the capacitor 1510, and the second electrode of the circuit 1500 load 1599.

The voltage source 1550 provides a voltage (e.g., + 4.8V). Each transistor 1580, 1581, 1582 may be operated to make or break conduction between its source and drain by applying an appropriate signal at the gate of the transistor 1580, 1581, 1582. The operation of the circuit when the LED should not emit light will now be described. In this mode, the second transistor 1581 is not turned on. During a first time period, the first transistor 1580 is turned on, and the third transistor 1582 is not turned on. A current flows from the voltage source 1550 through the inductor 1530. Thereby storing energy in inductor 1530. During a second time period, the first transistor 1580 is non-conductive and the third transistor 1582 is non-conductive. The energy stored in inductor 1530 is released into capacitor 1510 and load 1599. By alternately repeating the first and second cycles at a predetermined duty cycle, the output voltage, i.e., the output voltage across capacitor 1510 (and load 1599), will be a negative voltage rated at a voltage greater than or less than the rated value of the input voltage from voltage source 1550 (e.g., the output voltage may be-5V or-3V). Capacitor 1510 attenuates the amount of ripple voltage in the output voltage. In a mode when the LED should emit light, during the second time period, the second transistor 1581 is sometimes turned on instead of the third transistor 1582 which is not turned on at this time. The energy stored in inductor 1530 is then discharged through LEDs 1520-1523, rather than into capacitor 1510 and load 1599. For example, during the second time period, the third transistor 1582 may often be turned on 3 more times than the second transistor 1581. The ratio of the number of conduction times between the second transistor and the third transistor during the second time period may be selected according to the requirements of the associated circuit 1500. Such a requirement may be the intensity of light that the LED should emit and/or the amount of current that needs to be delivered to the circuit 1500 load 1599.

In another embodiment, a negative-positive polarity conversion circuit is formed. This is achieved by using the same type of circuit as in the sixth embodiment, but with appropriate modifications to the polarity of the potential and the orientation of the transistors and LEDs in the circuit.

Fig. 14 shows a circuit diagram of an LED driver and a forward boost (also referred to as "boost") circuit 1600 according to a seventh embodiment of the present invention. The circuit includes: three FETs 1680, 1681, 1682; an inductor 1630; four LEDs 1620-1623; and a capacitor 1610. The circuit is connected to a voltage source 1650, the voltage source 1650 being connected to first and second connection points (not shown). The electrode of voltage source 1650 having the most positive potential, the "anode", is connected to the first electrode of inductor 1630. A second electrode of the inductor 1630 is connected to the source of the first transistor 1680, the source of the second transistor 1681, and the anodes of the first LED1620 and the third LED 1622. Cathodes of the first LED1620 and the third LED1622 are respectively connected to anodes of the second LED1621 and the fourth LED 1623. The cathodes of the second LED1621 and the fourth LED1623 are coupled to the drain of the third transistor 1682. The source of the second transistor 1681 is coupled to the source of the third transistor 1682, a first electrode of the capacitor 1610, and a first electrode of the circuit 1600 load 1699. The "negative" electrode of the voltage source 1650, which has a minimum negative potential, is coupled to the source of the first transistor 1680, a second electrode of the capacitor 1610, and a second electrode of the circuit 1600 load 1699.

Voltage source 1650 provides a voltage (e.g., + 4.8V). Each transistor 1680, 1681, 1682 can be operated to make conduction or non-conduction between its source and drain by applying an appropriate signal to the gate of the transistor 1680, 1681, 1682. The operation of the circuit when the LED should not emit light will now be described. In this mode, the third transistor 1682 is not turned on. During the first time period, the first transistor 1680 is conductive and the second transistor 1681 is non-conductive. A current flows from voltage source 1650 through inductor 1630 and first transistor 1680. Thereby storing energy in inductor 1630. During the second time period, the first transistor 1680 is not conductive and the second transistor 1681 is conductive. The energy stored in inductor 1630 is discharged into capacitor 1610 and load 1699 because second transistor 1681 forms a closed loop. By repeating the operation during the first and second periods at a predetermined duty cycle, the output voltage, i.e., the output voltage across capacitor 1610 (and load 1699), will be a positive voltage (e.g., + 6V). It should be noted that the value of this output voltage is greater than the voltage of voltage source 1650. Capacitor 1610 attenuates the amount of ripple voltage in the output voltage. In a mode when the LED should emit light, corresponding to the switching of the second transistor 1681 in a mode when the LED should not emit light, the second transistor 1681 is kept non-conductive, and the third transistor 1682 is alternately turned on and off. As the energy stored in the inductor 1630 is discharged into the capacitor 1610 and the load 1699, the current flowing through the third transistor 1682 also flows through the LEDs 1620-1623. During at least a portion of the cycle, the forward voltage across the LEDs 1620-1623 reaches the threshold voltage of the diodes, which then emit light.

In another embodiment, an LED driver and a negative boost circuit are formed. This is achieved by using the same type of circuit as in the seventh embodiment, but with appropriate modifications to the polarity of the potential and the orientation of the transistors and LEDs in the circuit.

In another embodiment, the second transistor 1681 is replaced by a diode having an anode connected to the second electrode of the inductor 1630 and a cathode connected to the first electrode of the capacitor 1610.

In the case where the LED is to emit light at all times, the second transistor 1681 may be eliminated.

With reference to the fifth, sixth and seventh embodiments described above, it should be understood that the transistors 1480-1482, 1580-1582, 1680-1682 may be implemented with bipolar transistors.

An eighth embodiment of the present invention comprises: an LED driver; a buzzer driver; and a forward buck (also referred to as "buck") circuit. In this case, the circuit in fig. 12 of the fifth embodiment is modified in such a manner that the inductor 1430 is an inductor (not shown) of a buzzer. The operation characteristic of the eighth embodiment is described with reference to fig. 12, and in fig. 12, the inductor 1430 should represent the inductor of the buzzer. Fig. 15 is a signal diagram showing the operation characteristics of the eighth embodiment. The states of the first, second and third transistors 1480, 1481 are shown as a function of time. These states are referred to as "conducting" or "non-conducting". This in turn refers to the conductivity between the drain and source of the transistor. Four modes of operation will be discussed below. During all four modes, the voltage reduction circuit operates. The first operating mode is shown between time points t0 and t 1. During this phase, the buzzer does not produce audible sound, and the LED does not emit light. The second mode of operation is shown between time points t1 and t 2. During this phase, the buzzer does not produce audible sound, but the LED is illuminated. The third operating mode is shown between time points t2 and t 3. During this phase, the buzzer produces audible sound, but the LED does not emit light. Finally, a fourth mode of operation is shown between time points t3 and t 4. During this phase, the buzzer produces an audible sound and the LED emits light. As discussed above in connection with the fifth embodiment, energy is stored in inductor 1430 during the on-phase of first transistor 1480. Then, the first transistor 1480 is not conductive, and the stored energy is discharged through the second transistor 1481 or the third transistor 1482 through the capacitor 1410 and the load 1499. The LEDs 1420-1423 emit light only when energy is released through the third transistor 1482. In the first and third modes of operation, the LED should not emit light. Therefore, as shown in fig. 15, the second transistor 1481 is turned on during the time periods t0-t1 and t2-t3, when the energy of the inductor is released into the capacitor 1410 and the load 1499. Conversely, when the LED should emit light as in the case of the second and fourth modes of operation, the third transistor 1482 is turned on when the energy of the inductor is discharged into the capacitor 1410 and the load 1499. This is shown in FIG. 15 for time periods t1-t2 and t3-t 4. The frequency at which transistors 1480, 1481, 1482 transition between the conductive and non-conductive states will determine whether the buzzer produces a sound wave in the audible range or the non-audible range. If the frequency is high enough, the frequency of the sound wave is higher than the highest frequency that can be heard by a person. The buzzer is perceived to be silent. On the other hand, if the buzzer stops generating sound waves at a certain frequency, for example 10000Hz, the frequency is sufficiently high. Such high frequencies are shown in FIG. 15 in time periods t0-t1 and t1-t2, which correspond to the first and second modes of operation. The buzzer generates a sound wave that can be heard by a person if the frequency is within a range corresponding to a range of audible frequencies that can be heard by a person. Such frequencies are shown in FIG. 15 in time periods t2-t3 and t3-t4, which correspond to the third and fourth operating modes. It should be noted that fig. 15 only schematically shows: the frequency of switching the transistors 1480, 1481, 1482 is higher in the time periods t0-t1 and t1-t2 than in the time periods t2-t3 and t3-t 4. It will also be appreciated by those skilled in the art that the empirical frequency generated by the buzzer may also depend on the duty cycle between the conductive phases of transistors 1480, 1481, 1482 and the non-conductive phases of transistors 1480 and 1482.

In other embodiments, the inductors 1530, 1630 of the sixth and seventh embodiments, respectively, may be replaced with a buzzer inductor, in accordance with the fifth embodiment as modified from that described in the eighth embodiment.

In the case where the inductors 1430, 1530, 1630 of the fifth, sixth or seventh embodiment are replaced with the inductor of the buzzer, the LEDs 1420-1423, 1520-. The operation of these embodiments is similar to that described in connection with the eighth embodiment.

With reference to any of the foregoing embodiments, it should be understood that the number of LEDs may be other than four. Instead, groups of LEDs, each group comprising LEDs connected in parallel, may be arranged in series. Of course, the parameters of the inductor and the operating frequency of the switch/switches or transistor/transistors and the voltage supplied by the voltage source must be adjusted according to the number and configuration of the LEDs used.

Fig. 16 shows a circuit diagram of an EL lamp and buzzer driver 1700 according to a ninth embodiment of the present invention. A high frequency oscillator 1701 and a low frequency oscillator 1703 are connected to a control logic device (control logic) 1702. The output signals from the control logic device 1702 control a first switch 1740, a second switch 1741, a third switch 1742, a fourth switch 1743, and a fifth switch 1744, respectively. The first pole of the first switch 1740 is connected to the pole of the voltage source 1750 having the most positive potential- "positive". The second electrode of the first switch 1740 is connected to the first electrode of the second switch 1741 and the first electrode of the inductor 1730. The second electrode of the second switch 1741 is connected to the cathode of the first diode 1770. The anode of first diode 1770 is connected to the cathode of second diode 1771 and to a first electrode of EL lamp 1721. The second electrode of EL lamp 1721 is connected to the "negative" electrode of voltage source 1750, which has a minimum negative potential. The anode of second diode 1771 is connected to the first electrode of third switch 1742. A second electrode of third switch 1742 is connected to a second electrode of inductor 1730 and a first electrode of fourth switch 1743. The second pole of the fourth switch 1743 is connected to the "negative" of the voltage source 1750. The cathode of the third diode 1772 is connected to the first electrode of the inductor 1730. The anode of the third diode 1772 is connected to the first electrode of the fifth switch 1744. A second electrode of the fifth switch 1744 is connected to a second electrode of the inductor 1730. The inductor forms part of the buzzer 1760.

During operation, when EL lamp 1721 is assumed to emit light, a potential is generated across the first electrode of EL lamp 1721 that alternates between positive and negative. The positive potential is achieved by: the first switch 1740 and the third switch 1742 are set in the closed state, the second switch 1741 and the fifth switch 1744 are set in the open state, and the fourth switch 1743 is alternately closed and opened. This corresponds to a boost regulator (boost regulator). When the fourth switch 1743 is closed, a current will flow from the "positive" of the voltage source 1750, through the first switch 1740, the inductor 1730, and the fourth switch 1743, to the "negative" of the voltage source 1750. Thereby storing energy in inductor 1730. When the fourth switch 1743 is open, the energy stored by the inductor 1730 will be released to the EL lamp 1721 through the third switch 1742 and the second diode 1771. By alternately closing and opening fourth switch 1743, a high potential will be created across the first electrode of EL lamp 1721. The negative potential is generated by: the second switch 1741 and the fourth switch 1743 are set in the closed state, the third switch 1742 and the fifth switch 1744 are set in the open state, and the first switch 1740 is alternately closed and opened. This corresponds to a buck-boost regulator (positive-negative potential converter). When the first switch 1740 is closed, a current flows from the "positive" terminal of the voltage source 1750, through the first switch 1740, the inductor 1730, and the fourth switch 1743, to the "negative" terminal of the voltage source 1750. Thereby storing energy in inductor 1730. When first switch 1740 is open, the stored energy is released as EL lamp 1721, first diode 1770, second switch 1741, inductor 1730 and fourth switch 1743 form a closed loop. By alternately closing and opening first switch 1740, a high negative potential will be generated across the first electrode of EL lamp 1721. The frequency at which the fourth and first switches are opened and closed, respectively, is selected to be high enough to bring the potential of EL lamp 1721 to a value high enough to cause it to emit light. If the frequency is chosen to be greater than the maximum frequency of the audible frequency range, for example 20000Hz, no sound waves are generated from the buzzer 1760 when the inductor 1730 is charged or discharged. This frequency is provided by the high frequency oscillator 1701. A positive potential and a negative potential are alternately generated at the first electrode of EL lamp 1721 at a lower frequency, such as 100-. This frequency is provided by a low frequency oscillator 1703.

During operation, when it is assumed that the buzzer generates a sound wave, the first switch 1740 and the fifth switch 1744 are closed, the second switch 1741 and the third switch 1742 are opened, and the fourth switch 1743 is alternately closed and opened. When the fourth switch 1743 is closed, a current flows from the "positive" of the voltage source 1750, through the first switch 1740, the inductor 1730, and the fourth switch 1743 to the "negative" of the voltage source 1750. Thereby storing energy in inductor 1730. When the fourth switch 1743 is open, a part of the stored energy is released due to a vibration plate (not shown) generating an acoustic wave, and a part passes through the closed loop of the inductor 1730, the fifth switch 1744 and the third diode 1772.

In another embodiment, third diode 1772 and fifth switch 1744 are removed. During operation, when it is assumed that the EL lamp 1721 emits light, the first, second, third, and fourth switches are controlled as described above. However, during operation, when it is assumed that the buzzer 1760 generates an acoustic wave, the frequency of the high-frequency oscillator 1701, which controls the opening and closing of the fourth switch 1743 and the first switch 1740, is lowered to a frequency within the audible frequency range. Then the buzzer 1760 will produce an audible sound wave.

It should be understood that any one of the first switch 1740, the second switch 1741, the third switch 1742, the fourth switch 1743, and the fifth switch 1744 may be implemented using any kind of transistor, such as a bipolar transistor or a field effect transistor, respectively.

The structure of the driving circuit in the above embodiment has the following advantages: the space required for two or more drivers on a PCB is less than the space required to separately implement the same number of drivers. In addition, these structures have the following advantages: these structures require fewer signals to control the drivers than the number of signals to control the drivers when the same number of drivers are implemented separately.

Less space is required on the PCB because the driving circuit of the present invention requires fewer components (inductors and switches) than the number of inductors required by prior art drivers when the same number of drivers are employed. Furthermore, when components of a drive circuit that drives at least two functional devices are mounted on a PCB, resources such as a chip mounter require less time to mount the components on a PCB because fewer components are required than when the same number of drivers are implemented separately. In addition, the space required on the PCB is also reduced because a smaller number of control signals need to be used on the PCB when, for example, the output ports of a microprocessor generate control signals, and the PCB space required is further reduced because a smaller number of output ports need to be used on the PCB. And the number of required control signals and the number of possible output ports are smaller due to the method of operation of the inventive drive circuit in which the operation of more than one functional device can be controlled by means of a control signal by changing the frequency of the control signal.

Claims (9)

1. A driving circuit for driving a functional device such as an LED, a buzzer, a voltage converter or an EL lamp, the circuit having: an inductor (1030; 1130; 1230; 1330; 1730); a first connection point and a second connection point for connecting a voltage source; a switching device (1040; 1140; 1280; 1380; 1740) for allowing current to flow from the first connection point through the inductor when the switching device is in a first state, thereby charging the inductor, and for preventing current from flowing from the first connection point to the inductor when the switching device is in a second state, wherein the at least two functional devices (1060, 1020-,

characterized in that one of said functional means is a diaphragm generating a sound wave when energy is released from the inductor, the inductor and the diaphragm forming part of a buzzer (1060, 1160, 1260, 1360, 1760).

2. The driver circuit according to claim 1, wherein one of said functional means is at least one light emitting diode (1020-1-23; 1120-.

3. A driver circuit according to claim 1 or 2, wherein one of said functional means is a voltage converter (1481, 1410; 1582, 1510; 1681, 1610) which generates a predetermined voltage when energy is discharged from the inductor.

4. A drive circuit according to claim 3, wherein the voltage converter is a step-down converter (1481, 1410) in which the value of the predetermined voltage is less than the value of the voltage applied between the first connection point and the second connection point.

5. A drive circuit according to claim 3, wherein the voltage converter is a step-up converter (step-up converter) in which the value of the predetermined voltage is greater than the value of the voltage applied between the first connection point and the second connection point.

6. A drive circuit according to claim 4 or 5, wherein the predetermined voltage has a polarity opposite to a polarity of a voltage applied between the first connection point and the second connection point.

7. A drive circuit according to claim 1 or 2, comprising at least one switching device for controlling the release of energy from the inductor to a selected number of functional devices.

8. A method of operating a driver circuit according to claim 1, wherein:

i) the method comprises the following steps

a) Setting the switching device in a first state for controlling a current to flow from the first connection point through the inductor, thereby charging the inductor; after that

b) Setting the switching device to a second state for releasing the energy stored in the inductor to the vibrating plate to generate a sound wave;

ii) wherein an audible sound wave or a non-audible sound wave is selected by selecting the first or the second frequency, wherein step a) is repeated alternately with step b) such that the membrane vibrates at a frequency corresponding to the audible sound wave of the first frequency and the membrane vibrates at a frequency corresponding to the non-audible sound wave of the second frequency.

9. A method of operating a driver circuit according to claim 8, as far as the driver circuit relating to claim 7 is concerned, further comprising the steps of: at least one switching device is controlled in a predetermined sequence for controlling the release of energy from the inductor to a selected number of functional devices to release energy to at least two of the functional devices during two different time periods.