JP2012160287A - Light-emitting diode lighting circuit - Google Patents

Abstract

EMI noise of a light emitting diode lighting circuit is reduced.
A constant current circuit includes a drive transistor for controlling a drive current of an LED array, and an LED drive circuit for controlling the drive transistor. The LED drive circuit has a voltage based on the drive current. The operational amplifier 7 supplies a control pulse for controlling the driving transistor 6 based on the reference voltage, and the operating current control circuit 2A controls the rise time and the fall time of the control pulse supplied by the operational amplifier 7.
[Selection] Figure 2

Description

  The present invention relates to a light-emitting diode lighting circuit in which a plurality of light-emitting elements such as LEDs (light-emitting diodes) are assembled to form one light source, and the light source can be controlled to be controlled to an arbitrary brightness as an illumination lamp.

  In recent years, the performance of LEDs has been rapidly improved, and white LEDs that are indispensable for illumination have been developed, and it has become possible to emit light with a brightness that can be used sufficiently as illumination.

  FIG. It is a circuit diagram which shows the structure of the conventional light emitting diode lighting circuit. The light emitting diode lighting circuit is connected to an LED array 95 in which six LEDs are connected in series, a power supply Vdd1 connected to one end of the LED array 95 to light the LED array 95, and the other end of the LED array 95. And a constant current circuit 91.

  The constant current circuit 91 is composed of a power MOS transistor connected to the other end of the LED array 95, and a driving transistor 96 that controls the driving current of the LED array 95, and the opposite side of the LED array 95 with respect to the driving transistor 96. And an LED drive circuit 97 that is configured by an integrated circuit and controls the drive transistor 96.

  The LED driving circuit 97 has various functions such as LED brightness control, driving of a plurality of LED arrays, LED open detection, and short detection. However, FIG. 13 shows only the operational amplifier 98 that controls the constant current value flowing in the LED array 95 and the PWM control circuit 78 for luminance control.

  The LED drive circuit 97 has an operational amplifier 98. The operational amplifier 98 sends a control pulse for controlling the drive transistor 96 to the drive transistor 96 via the switch circuit 77 based on the voltage V0 based on the drive current supplied to the LED array 95 by the drive transistor 96 and the reference voltage Vref. Supply.

  As shown in FIG. 13, the operational amplifier 98, the drive transistor 96, and the resistor 76 in the LED drive circuit 97 constitute a constant current circuit. The LEDs of the LED array 95 are turned on by a current determined by the reference voltage Vref input to the Vref terminal and the resistance value of the resistor 76.

  Further, the LED drive circuit 97 has a function of adjusting the brightness of the LED by the PWM waveform input from the terminal PWM_IN. The LED drive circuit 97 includes a PWM control circuit 78 and a pull-down transistor 79. The PWM control circuit 78 controls the switch circuit 77 and the pull-down transistor 79 based on the PWM waveform input to the terminal PWM_IN.

  Specifically, the PWM control circuit 78 turns on the switch circuit 77 and turns off the pull-down transistor 79 when the PWM waveform input from the terminal PWM_IN is “H”. At this time, the constant current flows through the driving transistor 96 and the LED is lit. When the PWM waveform is “L”, the switch circuit 77 is turned off and the pull-down transistor 79 is turned on. At this time, the transistor 96 is turned off and the LED is turned off. As described above, the brightness of the LED can be adjusted by repeatedly turning the LED on and off.

  In such an LED lighting circuit, in order to cope with an on / off period in which the flicker due to the on / off of the LED is not felt, and to prevent flicker from being affected by fluctuations in the power supply voltage, etc. The driving capability of the driving transistor 96 needs to be increased.

  However, when the voltage difference between the reference voltage Vref and the voltage V0 based on the drive current is large, the drive transistor 96 is strongly biased to eliminate the voltage difference between the reference voltage Vref and the voltage V0, and the voltage V0 is set to the reference voltage Vref. It tries to start up suddenly. Such a steep change in the voltage V0 generates EMI (Electro Magnetic Interference) noise and affects other devices.

  In order to prevent the occurrence of such EMI noise, as disclosed in Patent Document 1, two transistors corresponding to the drive transistor 96 are prepared, and the drive capability of one of the transistors is lowered, and the power supply When the voltage fluctuation is large at the time of turning on, it is conceivable to use one of the transistors with low driving ability.

JP 2001-282371 A (published on October 12, 2001)

  However, when an LED is used for illumination, it is necessary to pass a high voltage and a large current through the LED, and the driving transistor 96 must be a transistor created by a high withstand voltage process. However, the LED driving circuit 97 that controls the large current can operate at a low voltage. For this reason, if the drive transistor 96 is built in the LED drive circuit 97, the entire LED drive circuit 97 needs to be formed by a high withstand voltage process, resulting in an increase in cost. Therefore, the LED drive circuit 97 and the drive transistor 96 need to be separate parts. If the LED driving circuit 97 and the driving transistor 96 are separate parts, wiring is required between them. Since the generation status of EMI noise varies depending on the wiring status, it is necessary to change the driving capability in accordance with this status, and it is necessary to select a transistor for each LED lighting product having a different wiring status. Occurs.

  Also, as in Patent Document 1, when using transistors with different driving capabilities to prevent the generation of EMI noise, a plurality of transistors are prepared separately from the LED driving circuit 97 in order to use transistors with different driving capabilities. It is necessary to increase the number of parts and the cost.

  An object of the present invention is to provide a light emitting diode lighting circuit capable of reducing the generation of EMI noise at low cost.

  A light-emitting diode lighting circuit according to the present invention includes a drive transistor that controls a drive current of a light-emitting diode and an integrated circuit that controls the drive transistor, and the integrated circuit is a drive that can control a rise time and a fall time. A signal is supplied to the driving transistor.

  Due to this feature, the rise time and the fall time of the drive signal are controlled. Therefore, the differential speed (dv / dt) of the drive signal can be reduced by increasing the rise time and the fall time of the drive signal. can do. Since the EMI noise of the circuit depends on the dv / dt of the drive signal, the EMI noise of the light emitting diode lighting circuit can be reduced at a low cost by increasing the rise time and the fall time of the drive signal.

  In the light emitting diode lighting circuit according to the present invention, the integrated circuit includes a comparison amplification circuit that supplies the drive signal for controlling the drive transistor based on a voltage value based on the drive current and a reference voltage, and the comparison amplification. It is preferable to have an output control circuit that is disposed between the circuit and the driving transistor and controls the driving signal.

With the above configuration, dv / dt of the drive signal supplied by the comparison amplifier circuit can be reduced with a simple configuration, and EMI noise of the light emitting diode lighting circuit can be reduced at low cost.
In the light emitting diode lighting circuit according to the present invention, the integrated circuit includes a circuit that performs on / off control of the light emitting diode based on a PWM signal for adjusting luminance of the light emitting diode, and the circuit that performs the on / off control includes: A switch circuit group connected in series with one end connected to the comparison amplifier circuit, and a control circuit provided for turning on and off the switch circuit group based on the PWM signal, The output control circuit includes at least a first switch circuit and a second switch circuit, wherein the output control circuit includes a third switch disposed between the drive transistor and one end of the first switch circuit, the drive transistor, and the first switch circuit. A fourth switch disposed between one end of the two-switch circuit and the on / off of the third and fourth switches based on the control signal. By controlling the changes the connection between the driving transistor and the switch group, and the drive transistor preferably includes a switch control circuit for changing a resistance value between the comparison amplifier.

  With the above configuration, the dv / dt of the drive signal from the comparison amplifier circuit can be reduced by using the luminance adjustment switch circuit, and the EMI noise of the light emitting diode lighting circuit can be reduced at low cost. Further, the control of the rise / fall time of the drive signal and the pulse control by the PWM control circuit can be performed simultaneously.

  In the light-emitting diode lighting circuit according to the present invention, the output control circuit is provided between a plurality of resistors having different resistance values connected in parallel and between the comparison amplifier circuit and the resistor corresponding to each resistor. It is preferable to include a plurality of switches and a switch control circuit that changes a resistance value between the drive transistor and the comparison amplifier circuit by controlling on / off of each switch based on a control signal.

  With the above configuration, it is possible to reduce the dv / dt of the drive signal from the comparison amplifier circuit by providing a resistor at the output of the comparison amplifier circuit, and to reduce the EMI noise of the light emitting diode lighting circuit at low cost.

  In the light emitting diode lighting circuit according to the present invention, the integrated circuit includes a comparison amplification circuit that supplies a drive signal for controlling the drive transistor based on a voltage value based on the drive current and a reference voltage, and the comparison amplification circuit. It is preferable to include an operating current control circuit provided for controlling the driving signal by controlling the operating current.

  With the above configuration, the operating current of the comparison amplifier circuit is controlled, the driving capability of the comparison amplifier circuit is adjusted, and the dv / dt of the drive signal supplied by the comparison amplifier circuit can be reduced. EMI noise can be reduced at low cost.

  In the light emitting diode lighting circuit according to the present invention, the operating current control circuit includes a plurality of current sources, a switch for adjusting the number of current sources to be supplied, and a control for supplying a constant current to the comparison amplifier circuit. The operating current is preferably controlled by a switch control circuit that controls the switch based on a signal.

  With the above configuration, the number of transistors of the constant current source is changed, that is, the constant current value is changed by changing the size of the transistor, thereby changing the driving capability of the comparison amplifier circuit and the drive signal dv / Dt can be reduced, and the EMI noise of the light emitting diode lighting circuit can be reduced at low cost.

  In the light emitting diode lighting circuit according to the present invention, the operating current control circuit includes a transistor for supplying a constant current to the comparison amplifier circuit, and adjusts a constant current by adjusting a gate voltage of the transistor. Is preferred.

  With the above configuration, the constant current value of the comparison amplifier circuit can be changed based on a logic signal input from the outside, and the dv / dt of the control pulse supplied by the comparison amplifier circuit can be reduced. EMI noise can be reduced at low cost.

  In the light-emitting diode lighting circuit according to the present invention, it is preferable that the gate voltage of the transistor is generated by a resistance dividing circuit.

  With the above configuration, the gate voltage can be created with a simple configuration.

  In the light emitting diode lighting circuit according to the present invention, the integrated circuit includes a comparison amplification circuit that supplies the drive signal for controlling the drive transistor based on a voltage value based on the drive current and a reference voltage, and the comparison amplification. It is preferable to include an output current control circuit provided for controlling the drive signal by controlling the output current of the circuit.

  With the above configuration, the output current of the comparison amplifier circuit can be controlled to increase the rise time and fall time of the drive signal.

  In the light emitting diode lighting circuit according to the present invention, the output current control circuit includes a switch that adjusts the number of output buffers connected to the drive transistor to control the output current from the comparison amplifier circuit, and a control signal. And a switch control circuit for controlling on / off of the switch.

  With the above configuration, the output current of the comparison amplifier circuit can be controlled with a simple configuration.

  In the light-emitting diode lighting circuit according to the present invention, it is preferable that the control signal is input from a control terminal provided in the integrated circuit, and the control signal is a signal indicating a control value of the drive signal.

  With the above configuration, the rise time and fall time of the drive signal can be controlled from the outside of the integrated circuit.

  A light-emitting diode lighting circuit according to the present invention includes a drive transistor that controls a drive current of the light-emitting diode and an integrated circuit that controls the drive transistor. The integrated circuit uses a voltage based on the drive current and a reference voltage. A comparison amplifier circuit for supplying a drive signal for controlling the drive transistor, and a rise time of the drive signal provided between the comparison amplifier circuit and the drive transistor and supplied by the comparison amplifier circuit; And a filter circuit for adjusting the fall time.

  With this feature, the rise time and fall time of the control signal supplied by the comparison amplifier circuit are adjusted, and the control signal dv / dt is adjusted by adjusting the rise time and fall time of the control signal to be longer. Can be small. Since the EMI noise of the circuit depends on the dv / dt of the control signal, the EMI noise of the light emitting diode lighting circuit can be reduced at a low cost by increasing the rise time and the fall time of the drive signal.

  In the light emitting diode lighting circuit according to the present invention, it is preferable that the filter circuit includes at least one of a variable resistor and a variable capacitor.

  With the above feature, it is possible to adjust dv / dt of the control pulse supplied by the comparison amplifier circuit by adjusting at least one of the variable resistor and the variable capacitor, and to reduce the EMI noise of the light emitting diode lighting circuit at low cost. can do.

  In the light emitting diode lighting circuit according to the present invention, a switch control circuit for controlling on / off of a switch provided between the drive transistor and the comparison amplifier circuit based on a PWM signal for adjusting the luminance of the light emitting diode. It is preferable that these are further included.

  Since the light-emitting diode lighting circuit according to the present invention is provided with the control means for controlling the rise time and the fall time of the control pulse supplied by the comparison amplifier circuit, the differential speed (dv / dt) of the control pulse is reduced. Can do. Since the EMI noise of the circuit depends on the dv / dt of the control pulse, the EMI noise of the light emitting diode lighting circuit can be reduced at a low cost by increasing the rise time and the fall time of the control pulse.

It is a circuit diagram which shows the basic principle of the light emitting diode lighting circuit which concerns on embodiment. 1 is a circuit diagram illustrating a basic concept of a light-emitting diode lighting circuit according to Embodiment 1. FIG. 3 is a circuit diagram showing a configuration of a light-emitting diode lighting circuit according to Embodiment 1. FIG. It is a figure which shows the truth table used for operation | movement of the said light emitting diode lighting circuit. FIG. 6 is a circuit diagram showing a configuration of another light-emitting diode lighting circuit according to Embodiment 1. 6 is a circuit diagram showing a configuration of a light-emitting diode lighting circuit according to Embodiment 2. FIG. 6 is a circuit diagram showing a configuration of a light-emitting diode lighting circuit according to Embodiment 3. FIG. FIG. 10 is a circuit diagram showing a configuration of another light-emitting diode lighting circuit according to Embodiment 3. FIG. 10 is a circuit diagram showing a configuration of still another light-emitting diode lighting circuit according to Embodiment 3. FIG. 10 is a circuit diagram showing a configuration of still another light-emitting diode lighting circuit according to Embodiment 3. FIG. 6 is a circuit diagram showing a configuration of a light emitting diode lighting circuit according to a fourth embodiment. FIG. 10 is a circuit diagram showing a configuration of another light-emitting diode lighting circuit according to Embodiment 4. It is a circuit diagram which shows the structure of the conventional light emitting diode lighting circuit.

  An embodiment of the light-emitting diode lighting circuit according to the present invention will be described below with reference to FIGS.

(Basic principle of the present invention)
FIG. 1 is a circuit diagram showing the basic principle of a light-emitting diode lighting circuit according to an embodiment. The light emitting diode lighting circuit is connected to the LED array 5 in which six LEDs are connected in series, the power supply Vdd1 connected to one end of the LED array 5 for lighting the LED array 5, and the other end of the LED array 5. A constant current circuit 1 is provided.

  The constant current circuit 1 is composed of a power MOS transistor connected to the other end of the LED array 5, and a driving transistor 6 that controls the driving current of the LED array 5, and the opposite side of the LED array 5 with respect to the driving transistor 6. And an LED driving circuit 7 that is configured by an integrated circuit and controls the driving transistor 6.

  The LED drive circuit 7 has various functions such as LED brightness control, driving of a plurality of LED arrays, LED open detection, and short detection. However, FIG. 1 shows only the operational amplifier 8 that controls the constant current value flowing in the LED array 5 and the PWM control circuit 28 for brightness control.

  The LED drive circuit 7 has an operational amplifier 8. The operational amplifier 8 sends a control pulse for controlling the drive transistor 6 to the drive transistor 6 via the switch circuit 27 based on the voltage V0 based on the drive current supplied to the LED array 5 by the drive transistor 6 and the reference voltage Vref. Supply.

  As shown in FIG. 1, the operational amplifier 8, the drive transistor 6, and the resistor 26 in the LED drive circuit 7 constitute a constant current circuit. The LEDs of the LED array 5 are turned on by a current determined by the reference voltage Vref input to the Vref terminal and the resistance value of the resistor 26.

  Further, the LED drive circuit 7 has a function of adjusting the brightness of the LED by the PWM waveform input from the terminal PWM_IN. The LED drive circuit 7 includes a PWM control circuit 28 and a pull-down transistor 29. The PWM control circuit 28 controls the switch circuit 27 and the pull-down transistor 29 based on the PWM waveform input to the terminal PWM_IN.

  Specifically, the PWM control circuit 28 turns on the switch circuit 27 and turns off the pull-down transistor 29 when the PWM waveform input from the terminal PWM_IN is “H”. At this time, the constant current flows through the driving transistor 6 to light the LED. When the PWM waveform is “L”, the switch circuit 27 is turned off and the pull-down transistor 29 is turned on. At this time, the driving transistor 6 is turned off and the LED is turned off. As described above, the brightness of the LED can be adjusted by repeatedly turning the LED on and off.

  The constant current circuit 1 shown in FIG. 1 is different from the conventional constant current circuit 91 shown in FIG. 13 in the LED driving circuit. A control terminal 12 is added to the LED drive circuit 7. By controlling the control signal input to the control terminal 12, the rise (fall) time (dv / dt) of the control pulse Vop for driving the transistor 6 for controlling the LED lighting current can be controlled.

  When the control pulse Vop for driving the LED array 5 suddenly rises, EMI (Electro Magnetic Interference) noise is generated. Since EMI noise depends on dv / dt, by slowing the rise (fall) of the control pulse, the rise time and fall time of the control pulse become longer, and the generation of EMI noise can be prevented.

  In the circuit shown in FIG. 1, the power supply Vdd1 and the constant current circuit 1 are connected to the LED array 5 in order to light the LED array 5 in which six LEDs are connected in series. For example, if the LED is a light emitting diode that emits white light with a forward voltage drop Vf of 3.6 V (typ.), The voltage drop in the LED array 5 is the sum of the LED forward voltage drop Vf. 21.6V. When the voltage value of the power supply Vdd1 is 30V, the voltage on the LED array 5 side of the drive transistor 6 is 8.4V.

  When the LED is a light emitting diode that emits orange light with a forward voltage drop Vf of 2.1 V (typ.), The voltage drop in the LED array 5 is 12.6 V, which is the sum of the LED forward voltage drop Vf. is there. Similarly, when the voltage value of the power supply Vdd1 is set to 30V, the voltage on the LED array 5 side of the driving transistor 6 is 17.4V.

  As described above, even when the LEDs are lit using the same power supply Vdd1, the voltage applied to the drive transistor 6 varies depending on the number of LEDs to be lit and the number of connected LEDs. In addition, when a product is produced as a lighting device, different lengths of wiring or the like are arranged between the LED array 5 and the drive transistor 6 for each product, so that parasitic elements that differ depending on the product affect the drive transistor 6. It will be a thing. For this reason, a difference occurs in the way the current flows when the drive transistor 6 is turned on due to various changes in the situation as described above.

  In order to cope with such a situation, the LED drive circuit 7 shown in FIG. 1 controls the control signal input to the control terminal 12 to rise (fall) the control pulse Vop for driving the drive transistor 6. (Dv / dt) is controlled. As a result, the lighting device including the LED drive circuit 7 can be adjusted for each product so as to prevent generation of EMI noise.

  Hereinafter, a specific circuit example for controlling the dv / dt of the control pulse Vop for driving the LED array 5 will be described.

(Embodiment 1)
(Basic concept)
FIG. 2 is a circuit diagram showing a basic concept of the light-emitting diode lighting circuit according to the first embodiment. The same components as those described above are denoted by the same reference numerals, and detailed description thereof will not be repeated.

  The light emitting diode lighting circuit includes a constant current circuit 1A, and the constant current circuit 1A includes an LED drive circuit 7A. The operational amplifier 8A of the LED drive circuit 7A includes an operating current control circuit 2A. The operating current control circuit 2A is schematically illustrated by extracting a constant current source that supplies a constant current to the differential unit 138 of the operational amplifier 8A, and is arranged in parallel with each other to supply a constant current. Transistors 9a, 9b, 9c, and 9d are provided. The gate of each transistor 9a, 9b, 9c, 9d is coupled to the control terminal 12.

  FIG. 2 shows a concept of changing the driving capability by controlling the operating current of the operational amplifier 8A. The operational amplifier 8A has a constant current function in which a current that can flow through the entire circuit is determined by the operating current control circuit 2A. When the constant current is small, charging to the capacitive load connected to the output of the operational amplifier 8A is also slowed, so that the driving ability of the operational amplifier 8A is lowered. On the other hand, when the constant current is large, the charging to the capacitive load is accelerated and the driving capability is increased.

  The LED drive circuit 7A shown in FIG. 2 changes the constant current supplied to the differential unit 138 of the operational amplifier 8A by changing the number of transistors. The number of transistors of the constant current source is changed according to the value of the control voltage input to the control terminal 12 for changing the driving capability. That is, the constant current value supplied to the differential unit 138 of the operational amplifier 8A is changed by changing the size of the transistor. As a result, the driving capability of the operational amplifier 8A can be changed.

  As described above, the change in the driving capability of the operational amplifier 8A and the charging speed to the capacitive load have the relationship as described above. That is, when the driving ability is lowered, the charging speed is slowed down, the output change is slowed down, and the rise time and fall time are slowed down. Conversely, if the driving capability is increased, the charging speed is increased, and the rise time and fall time are increased. In this way, the rise (fall) time (dv / dt) of the control pulse Vop that drives the transistor 6 that controls the LED lighting current can be controlled by changing the drive capability of the operational amplifier 8A.

(Light Emitting Diode Lighting Circuit According to Embodiment 1)
FIG. 3 is a circuit diagram showing a configuration of the light-emitting diode lighting circuit according to the first embodiment. The same components as those described above are denoted by the same reference numerals, and detailed description thereof will not be repeated. FIG. 3 shows an example provided with a circuit for changing the constant current by a general differential amplifier circuit.

  The light emitting diode lighting circuit includes a constant current circuit 1B, and the constant current circuit 1B includes an LED drive circuit 7B. The LED drive circuit 7B includes an operational amplifier 8B, and the differential section 138 of the operational amplifier 8B is provided with four transistors 9a, 9b, 9c, and 9d arranged in parallel with each other in FIG. It has been. The gate of each transistor 9a, 9b, 9c, 9d is coupled to a bias circuit 34.

  A switch 10a is provided between the transistor 9a and the differential portion 138. A transistor 10b is provided between the transistor 9b and the differential portion 138. A transistor 10c is provided between the transistor 9c and the differential portion 138.

  A transistor 35 is provided between the differential unit 138 and the driving transistor 6. The gate of the transistor 35 is connected to the differential unit 138. The drain of the transistor 35 is connected to the gate of the driving transistor 6.

  The gate of the driving transistor 6 is provided with four transistors 30a, 30b, 30c, and 30d arranged in parallel with each other. The gate of each transistor 30a, 30b, 30c, 30d is coupled to a bias circuit 34.

  A transistor 31 a is provided between the transistor 30 a and the gate of the driving transistor 6. A transistor 31 b is provided between the transistor 30 b and the gate of the driving transistor 6. A transistor 31 c is provided between the transistor 30 c and the gate of the driving transistor 6.

  The LED drive circuit 7B is provided with a switch control circuit 11 that controls on / off of the transistors 10a, 10b, and 10c and the transistors 31a, 31b, and 31c based on the control signals input to the control terminals 12A and 12B. The switch control circuit 11 includes a selector 32 and logic elements 33a and 33b.

  FIG. 4 is a diagram showing a truth table used for the operation of the light emitting diode lighting circuit. The selector 32 receives inputs A and B from the control terminals 12A and 12B, and supplies outputs Q1, Q2, Q3, and Q4 according to the truth table shown in FIG. Based on the outputs Q1 and Q2, the logic element 33a supplies a control signal Q6 to the transistors 10b and 31b according to the truth table shown in FIG. The output Q1 is supplied as it is to the transistors 10a and 31a as the control signal Q5 to control on / off. Based on the output Q4, the logic element 33b supplies the control signal Q7 to the transistors 10c and 31c according to the truth table shown in FIG.

  The constant current generated by the bias circuit 34 is transmitted to the transistors 9a to 9d and 30a to 30d. The same constant current as the constant current created by the bias circuit 34 flows through the transistors 9a to 9d and 30a to 30d.

  A constant current is applied to the differential stage (the operational amplifier 8) by the transistors 9a to 9d. The constant current flowing through the transistors 9a to 9d is selectively given to the differential stage using the transistors 10a to 10c.

  That is, when all the transistors 10a to 10c are on, the constant current given to the differential stage is the sum of the currents flowing through the transistors 9a to 9d. If this case is 1, a constant current of 3/4 is applied to the differential stage when the transistor 10a is turned off, and a constant current of 2/4 (1/2) is applied when the transistors 10a and 10b are turned off. When the transistors 10a, 10b, and 10c are turned off, 1/4 constant current is applied to the differential stage.

  Transistors 30a-30d provide a constant current to the output stage. Similarly to the above, the magnitude of the current can be changed by turning on and off the transistors 31a to 31c.

  At this time, ON / OFF of the transistors 10a to 10c and 31a to 31c is controlled by the selector 32 and the logic circuits 33a and 33b.

  The transistors 10a to 10c and 31a to 31c are switches that are turned on when the control signal is “1”, and are configured by Nch transistors, for example. FIG. 4 shows a truth table at this time. The LED drive circuit 7B is provided with control terminals 12A and 12B, and inputs A and B are supplied thereto.

  One of the outputs Q1 to Q4 of the selector 32 becomes “1” by the combination of binary values (0, 1) of the input A and the input B. The states of the control signals Q5 to Q7 for controlling the transistors 10a to 10c and 31a to 31c are determined by logic to values in the truth table shown in FIG.

  Thus, the magnitude of the constant current flowing through the operational amplifier 8 can be changed by the input A and the input B. Specifically, when (A, B) = (0, 0), all of the created constant currents are used in the circuit of the operational amplifier 8. If the value of the constant current in this case is 1, when (A, B) = (0, 1), the transistors 10a and 31a are turned off, so the constant current becomes 3/4. When (A, B) = (1, 0), the transistors 10a and 31a and the transistors 10b and 31b are turned off, so that the constant current becomes 2/4 (1/2). When (A, B) = (1, 1), the transistors 10a to 10c and the transistors 31a to 31c are turned off, so that the constant current becomes 1/4.

  As described above, the driving capability can be adjusted by changing the magnitude of the constant current of the operational amplifier 8B according to the value input to the control terminals 12A and 12B.

(Other light emitting diode lighting circuit according to Embodiment 1)
FIG. 5 is a circuit diagram showing a configuration of another light emitting diode lighting circuit according to the first embodiment. The same components as those described above are denoted by the same reference numerals, and detailed description thereof will not be repeated. FIG. 5 shows another circuit example for changing the magnitude of the constant current of the operational amplifier 8.

  The light emitting diode lighting circuit includes a constant current circuit 1C, and the constant current circuit 1C includes an LED drive circuit 7C. The LED drive circuit 7C includes an operational amplifier 8C, and the operational amplifier 8C includes a transistor 36a for supplying a constant current to the differential unit 138 and a transistor 36b connected to the gate of the drive transistor 6. The LED drive circuit 7C is provided with a voltage follower operational amplifier 37 that applies the control voltage adjusted by the resistance dividing circuit 13 and input to the control terminal 12 to the gates of the transistors 36a and 36b. The transistor 36 a supplies a constant current to the differential section 138 based on the control voltage adjusted by the resistance dividing circuit 13 and input to the control terminal 12.

  In the example shown in FIG. 5, the resistance dividing circuit 13 is configured by a fixed resistor and a variable resistor, and the voltage value input to the input terminal 12 is adjusted.

  As described above, the constant current is controlled by the voltage value applied to the control terminal 12, and the driving capability of the operational amplifier 8C can be changed.

(Embodiment 2)
(Light Emitting Diode Lighting Circuit According to Embodiment 2)
FIG. 6 is a circuit diagram showing a configuration of the light-emitting diode lighting circuit according to the second embodiment. The same components as those described above are denoted by the same reference numerals, and detailed description thereof will not be repeated. FIG. 6 shows a circuit example for changing the current of the output stage of the operational amplifier 8.

  The light emitting diode lighting circuit includes a constant current circuit 1D, and the constant current circuit 1D includes an LED drive circuit 7D. The LED drive circuit 7D includes an operational amplifier 8D and an output current control circuit 3D that controls an output current output from the operational amplifier 8D. The output current control circuit 3D can change the number of transistors in the output stage of the operational amplifier 8D. In FIG. 6, the four transistors 14a, 14b, 14c, and 14d arranged in parallel to the drive transistor 6 in FIG. have. The gate of each transistor 14a, 14b, 14c, 14d is coupled to a bias circuit 34. A transistor 10 a is provided between the transistor 14 a and the gate of the driving transistor 6. A transistor 10b is provided between the transistor 14b and the gate of the driving transistor 6. A transistor 10 c is provided between the transistor 14 c and the gate of the driving transistor 6.

  The output current control circuit 3D includes a switch control circuit 11 that controls on / off of the transistors 10a, 10b, and 10c based on a control signal input to the control terminals 12A and 12B. The output current control circuit 3D is provided with transistors (output buffers) 38a, 38b, 38c, and 38d. Transistor 38a is connected to transistor 14a and coupled to the gate of drive transistor 6 through transistor 10a. The gate of transistor 38a is coupled to the output of differential portion 138. Transistor 38b is connected to transistor 14b and coupled to the gate of drive transistor 6 via transistor 10b. The gate of transistor 38b is coupled to the output of differential portion 138. Transistor 38c is connected to transistor 14c and coupled to the gate of drive transistor 6 via transistor 10c, and the gate of transistor 38c is coupled to the output of differential portion 138. Transistor 38d is connected to transistor 14d and coupled to the gate of drive transistor 6, and the gate of transistor 38d is coupled to the output of differential portion 138.

  The LED drive circuit 7D is the same as that shown in FIG. 3 for controlling on / off of the transistors 10a, 10b, and 10c and the transistors 31a, 31b, and 31c based on the control signals input to the control terminals 12A and 12B. A switch control circuit 11 is provided.

The switch control circuit 11 supplies a control signal Q6 to the transistor 10b according to the truth table shown in FIG. The output Q1 is supplied as it is to the transistor 10a as the control signal Q5 to control on / off. Based on the output Q4, the logic element 33b supplies the control signal Q7 to the transistor 10c according to the truth table shown in FIG.
The constant current created by the bias circuit 34 is transmitted to the transistors 14a to 14d. Then, the same constant current as the constant current created by the bias circuit 34 flows through the transistors 14a to 14d.

  A constant current is applied to the output stage (driving transistor 6) by the transistors 14a to 14d. The constant current flowing through the transistors 14a to 14d is selectively given to the output stage using the transistors 10a to 10c.

  As shown in FIG. 6, four output stage transistors 14a, 14b, 14c, and 14d are provided, and the output transistors 14a, 14b, 14c, and 14d are connected to the gate of the drive transistor 6 by the same selector 32 as in FIG. Is changed from 4 stages to 1 stage. As a result, the same effect as changing the transistor size of the output stage from 1 to 1/4 occurs, and the driving capability of the operational amplifier 8 can be changed.

  1 to 3, 5, and 6 described above show the case where the PWM control circuit 28 is provided, the present invention is not limited to this. Since the operational amplifier is controlled in the above embodiment, the present invention can be implemented even when there is no PWM control circuit.

(Embodiment 3)
(Light Emitting Diode Lighting Circuit According to Embodiment 3)
FIG. 7 is a circuit diagram showing a configuration of the light-emitting diode lighting circuit according to the third embodiment. The same components as those described above are denoted by the same reference numerals, and detailed description thereof will not be repeated.

  The light emitting diode lighting circuit includes a constant current circuit 1E, and the constant current circuit 1E includes an LED drive circuit 7E. The LED drive circuit 7E is provided between the operational amplifier 98 and the drive transistor 6 and includes a filter circuit 4E for adjusting the rise time and fall time of the control pulse supplied by the operational amplifier 98. The filter circuit 4E has one end connected to the gate of the drive transistor 6, the other end connected to the ground, the one end connected to the gate and the capacitor 39 of the drive transistor 6, and the other end connected to the transistor 35. And a variable resistor 24 externally attached to the control terminals 12A and 12B.

  The operational amplifier 98 is the same as the operational amplifier 98 of the conventional circuit shown in FIG. 13, and FIG. 7 shows an example of an internal circuit. FIG. 7 does not show the switch circuit 77, the PWM control circuit 78, and the pull-down transistor 79 shown in FIG. 13, but the embodiment of FIG. 7 only shows that the embodiment can be implemented without the PWM control circuit. Yes, a PWM control circuit or the like may be provided. The same applies to the examples shown in FIGS.

  As described above, the filter circuit 4E including the external variable resistor 24 and the built-in capacitor 39 is provided, and the resistance value of the external variable resistor 24 is changed and adjusted, thereby changing the characteristics of the filter and changing the output of the operational amplifier 8. dv / dt can be adjusted.

(Other light emitting diode lighting circuit according to Embodiment 3)
FIG. 8 is a circuit diagram showing a configuration of another light emitting diode lighting circuit according to the third embodiment. The same components as those described above are denoted by the same reference numerals, and detailed description thereof will not be repeated.

  The light emitting diode lighting circuit includes a constant current circuit 1F, and the constant current circuit 1F includes an LED drive circuit 7F. The LED drive circuit 7F includes a filter circuit 4F that is arranged between the operational amplifier 98 and the drive transistor 6 and adjusts the rise time and fall time of the control pulse supplied by the operational amplifier 8. The filter circuit 4F has one end connected to the gate of the drive transistor 6 and the other end grounded, the one end connected to the gate and the capacitor 39 of the drive transistor 6, and the other end connected to the transistor 35. The variable resistor 24 is externally attached to the control terminals 12A and 12B, and a capacitor 39B having one end connected to the other end of the variable resistor 24 and the other end grounded.

  Thus, by providing the filter circuit 4F with the external variable resistor 24 and the two built-in capacitors 39A and 39B, by changing and adjusting the resistance value of the external variable resistor 24, the characteristics of the filter are changed, The dv / dt of the output of the operational amplifier 8 can be adjusted.

(Still another light emitting diode lighting circuit according to Embodiment 3)
FIG. 9 is a circuit diagram showing a configuration of still another light-emitting diode lighting circuit according to the third embodiment. The light emitting diode lighting circuit includes a constant current circuit 1G, and the constant current circuit 1G includes an LED drive circuit 7G. The LED drive circuit 7G is disposed between the operational amplifier 8 and the drive transistor 6 and includes a filter circuit 4G for adjusting the rise time and fall time of the control pulse supplied by the operational amplifier 98. The filter circuit 4G has one end connected to the gate of the drive transistor 6 and the other end grounded, the one end connected to the gate of the drive transistor 6 and the resistor 40A, and the other end connected to the transistor 35. A variable capacitor 25 externally attached to the control terminals 12A and 12B, and a resistor 40B having one end connected to the other end of the variable capacitor 25 and the other end grounded.

  Thus, by providing the filter circuit 4G with the external variable capacitor 25 and the two built-in resistors 40A and 40B, by changing and adjusting the capacitance value of the external variable capacitor 25, the characteristics of the filter are changed, The dv / dt of the output of the operational amplifier 8 can be adjusted.

  FIG. 10 is a circuit diagram showing a configuration of still another light-emitting diode lighting circuit according to the third embodiment. The light emitting diode lighting circuit includes a constant current circuit 1H, and the constant current circuit 1H includes an LED drive circuit 7H. The LED drive circuit 7H includes a filter circuit 4H for adjusting the rise time and fall time of the control pulse supplied by the operational amplifier 98. The filter circuit 4H includes an external variable capacitor 25 having one end connected to the control terminal 12 and the other end grounded. Control terminal 12 is coupled to the gate of drive transistor 6 and transistor 35.

  Thus, by providing the filter circuit 4H with the external variable capacitor 25 and changing and adjusting the capacitance value of the external variable capacitor 25, the characteristics of the filter are changed, and the dv / dt of the output of the operational amplifier 98 is adjusted. can do.

(Embodiment 4)
(Light Emitting Diode Lighting Circuit According to Embodiment 4)
FIG. 11 is a circuit diagram showing a configuration of a light-emitting diode lighting circuit according to the fourth embodiment. The same reference numerals are given to the same components as those described above. Detailed description of these components will not be repeated.
In the above-described third embodiment, an example in which the filter characteristic is changed by adjusting the value of the external electronic component to adjust the dv / dt of the output of the operational amplifier 98 has been described. It is not limited. As described above with reference to FIGS. 3 and 6, the electronic components constituting the filter are provided in parallel, the binary data is input to the control terminal, and the number of components is changed by the selector, thereby changing the filter characteristics and the operational amplifier. The output dv / dt of 8 may be adjusted. An example is shown in FIG.
FIG. 11 shows an example in which a resistor is provided at the output of the operational amplifier 98 to change the output dv / dt.

  The light emitting diode lighting circuit includes a constant current circuit 1I, and the constant current circuit 1I includes an LED drive circuit 7I. The LED drive circuit 7I is provided with an output control circuit 3I that is disposed between the operational amplifier 98 and the drive transistor 6 and controls a control pulse output from the operational amplifier 98.

  The output control circuit 3I is connected to the gate of the driving transistor 6 and is arranged in parallel with each other, so that four resistance units 17a, 17b, 17c, and 17d having different resistance values and the respective resistance units 17a, 17b, 17c, and 17d are connected. Corresponding to the four transistors 18a, 18b, 18c, and 18d provided between the respective resistance units and the operational amplifier 98, and based on the control signal input to the control terminals 12A and 12B, And a selector 32 for controlling on / off of 18b, 18c and 18d.

  The resistance unit 17a is configured by a resistor R1. The resistance unit 17b has resistors R2 and R3. The resistance unit 17c has resistors R4, R5, and R6. The resistance unit 17d has resistors R7, R8, R9, and R10. A capacitor C1 is connected between the gate of the driving transistor 6 and the ground.

  The dv / dt of the output from the operational amplifier 98 changes with a time constant determined by the resistance and the capacitance. As shown in FIG. 12, the dv / dt of the output is changed by changing the resistance to 1 to 4 times to increase the time constant to 1 to 4 times.

  Similarly to the selectors shown in FIGS. 3 and 6, the selector 32 has only the output Q1 when the input A and the input B = 0 and 0, and only the output Q2 when the input A and the input B = 0 and 1. When “1”, input A, input B = 1, 0, only the output Q3 is “1”, and when input A, input B = 1, 1, only the output Q4 is “1”. When the output Q1 changes from the output Q1 to "1", the transistors 18a to 18d are turned on. When the transistor 18a is turned on, the output waveform is determined by the resistor R1 and the capacitor C1. When the transistor 18b is turned on, the output waveform is determined by the resistor R2 + the resistor R3 and the capacitor C1. When the transistor 18c is turned on, the output waveform is determined by the resistor R4 + the resistor R5 + the resistor R6 and the capacitor C1. When the transistor 18d is turned on, the output waveform is determined by the resistor R7 + the resistor 85 + the resistor R9 + R10 and the capacitor C1.

  When the resistors R1 to R10 have the same value, the time constant changes from 1 to 4 times, and the dv / dt of the output from the operational amplifier 8 can be changed.

  In the above description, the PWM control circuit 28 for adjusting the luminance based on the PWM waveform shown in FIG. 1 is omitted. However, as will be described below, the resistors shown in FIG. 11 can also be used as the switch circuits 27a to 27d.

(Other light emitting diode lighting circuit according to Embodiment 4)
FIG. 12 is a circuit diagram showing a configuration of another light emitting diode lighting circuit according to the fourth embodiment. The same reference numerals are given to the same components as those described above. Detailed description of these components will not be repeated. FIG. 12 shows an example in which the resistor units 17a to 17d shown in FIG. 11 are also used as the luminance adjustment switch circuits 27a to 27d.

  The light emitting diode lighting circuit includes a constant current circuit 1J, and the constant current circuit 1J includes an LED drive circuit 7J. The LED drive circuit 7J is provided with an output control circuit 3J that is disposed between the operational amplifier 8 and the drive transistor 6 and controls the output current output from the operational amplifier 98.

  The output control circuit 3J has four switch circuits 27a, 27b, 27c, and 27d coupled in series. One end of the switch circuit 27 a is connected to the transistor 35. The other end of the switch circuit 27a is coupled to one end of the switch circuit 27b. The other end of the switch circuit 27b is coupled to one end of the switch circuit 27c, and the other end of the switch circuit 27c is coupled to one end of the switch circuit 27d.

  A transistor 18 a is provided between the other end of the switch circuit 27 a and the gate of the driving transistor 6. A transistor 18b is provided between the other end of the switch circuit 27b and the gate of the driving transistor 6. A transistor 18 c is provided between the other end of the switch circuit 27 c and the gate of the driving transistor 6. A transistor 18d is provided between the other end of the switch circuit 27d and the gate of the driving transistor 6.

  The output control circuit 3J has a selector 32. The selector 32 controls on / off of the transistors 18a, 18b, 18c, and 18d based on the control signal input to the control terminals 12A and 12B.

  The transistors 18a to 18d are switches that are turned on when the control signal is "1", and are configured by analog switches that connect Nch transistors and Pch transistors in parallel, for example.

  The PWM control circuit 28 switches the switch circuits 27a to 27d, but the selector 32 outputs the signal output from the switch circuit 27a, the signal output through the switch circuit 27a and the switch circuit 27b, and the switch circuits 27a to 27c. A signal output through the switch circuits 27a to 27d is selected. As a result, the same effects as those of the resistance units 17a to 17d shown in FIG. 11 can be generated by the switch circuits 27a to 27d.

  As described above, according to the first to fourth embodiments, since the dv / dt of the output pulse of the operational amplifier 8 is configured to be adjustable from the outside via the control terminal 12, it is created overseas or by a user with different EMI regulations. On-chip adjustment is possible for each lighting module.

  Further, in order to suppress the generation of EMI noise, a snubber circuit is provided as an exterior component. However, if the light emitting diode lighting circuit (countermeasure circuit) according to the present embodiment is incorporated, the exterior component can be reduced.

  By the way, in the integrated circuit for LED driving, a plurality of driving circuits for lighting a plurality of colors of LEDs are provided. These multi-color LEDs are used for applications such as driving by switching between daylight white and light bulb color, or performing color illumination by turning on the three primary colors of RGB. “CH” means an output of each driving circuit (an output for controlling the gate of the driving transistor). As described in the section of the problem to be solved by the invention, the LED drive circuit 97 and the drive transistor 96 are separate parts, and a wiring exists between the LED drive circuit 97 and the drive transistor 96. For example, in a light bulb for color illumination, it is necessary to mount a driving transistor for an R LED and a driving transistor for a G, B LED separately on a substrate, and between the driving integrated circuit and the driving transistor. It is assumed that the wiring length R is long and G and B are short. In this case, the R CH (drive output) of the driving integrated circuit reduces the delay amount of the output waveform performed by the light emitting diode lighting circuit (countermeasure circuit) according to the present embodiment, and the R and B CHs emit light. Adjustment to increase the delay amount of the output waveform performed by the diode lighting circuit (countermeasure circuit) can be performed. Thereby, the drive timing in each LED can be adjusted.

  The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Is also included in the technical scope of the present invention.

  INDUSTRIAL APPLICABILITY The present invention can be applied to a light emitting diode lighting circuit in which a plurality of light emitting elements such as LEDs are assembled to constitute one light source, and the light source can be controlled to be controlled to an arbitrary brightness as an illumination lamp. .

1 Constant current circuit (light emitting diode lighting circuit)
2A Operating current control circuit 3D Output current control circuit 4E Filter circuit 5 LED array (light emitting diode)
6 Drive transistor 7 LED drive circuit (drive transistor)
8 Operational amplifier (comparison amplification circuit)
9a to 9d Transistors 10a to 10d Switch 11 Switch control circuit 12 Control terminal 13 Resistance dividing circuits 14a to 14d Transistors 17a to 17d Resistance units 18a to 18d Transistors (switches)
24 Variable resistor 25 Variable capacitor 27 Switch circuit 138 Differential section

Claims (14)

A drive transistor for controlling the drive current of the light emitting diode;
An integrated circuit for controlling the driving transistor,
The integrated circuit supplies a driving signal whose rise time and fall time can be controlled to the drive transistor. The integrated circuit includes a comparison amplifier circuit that supplies the drive signal for controlling the drive transistor based on a voltage value based on the drive current and a reference voltage;
The light-emitting diode lighting circuit according to claim 1, further comprising an output control circuit that is disposed between the comparison amplifier circuit and the driving transistor and controls the driving signal. The integrated circuit includes a circuit that performs on / off control of the light emitting diode based on a PWM signal for adjusting the luminance of the light emitting diode,
The circuit that performs the on / off control includes:
A group of switch circuits connected in series with one end connected to the comparison amplifier circuit;
A control circuit provided for turning on and off the switch circuit group based on the PWM signal,
The switch circuit group includes at least a first switch circuit and a second switch circuit,
The output control circuit includes:
A third switch disposed between the drive transistor and one end of the first switch circuit;
A fourth switch disposed between the drive transistor and one end of the second switch circuit;
Based on the control signal, by controlling on / off of the third and fourth switches, the connection between the switch group and the driving transistor is changed, and the resistance value between the driving transistor and the comparison amplifier circuit is changed. The light emitting diode lighting circuit according to claim 2, further comprising a switch control circuit. The output control circuit includes a plurality of resistors having different resistance values connected in parallel.
A plurality of switches respectively provided between the comparison amplifier circuit and the resistor corresponding to each resistor;
3. The light-emitting diode lighting circuit according to claim 2, further comprising: a switch control circuit that changes a resistance value between the drive transistor and the comparison amplifier circuit by controlling on / off of each switch based on a control signal. The integrated circuit includes a comparison amplifier circuit that supplies a drive signal for controlling the drive transistor based on a voltage value based on the drive current and a reference voltage;
2. The light emitting diode lighting circuit according to claim 1, further comprising an operating current control circuit provided for controlling the driving signal by controlling an operating current of the comparison amplifier circuit.   The operating current control circuit includes a plurality of current sources, a switch for adjusting the number of supplied current sources, and a switch for controlling the switch based on a control signal in order to supply a constant current to the comparison amplifier circuit. 6. The light emitting diode lighting circuit according to claim 5, wherein the operating current is controlled by the control circuit. The operating current control circuit includes a transistor for supplying a constant current to the comparison amplifier circuit,
6. The light emitting diode lighting circuit according to claim 5, wherein the constant current is adjusted by adjusting a gate voltage of the transistor.   The light emitting diode lighting circuit according to claim 7, wherein the gate voltage of the transistor is created by a resistance dividing circuit. The integrated circuit includes a comparison amplifier circuit that supplies the drive signal for controlling the drive transistor based on a voltage value based on the drive current and a reference voltage;
2. The light emitting diode lighting circuit according to claim 1, further comprising an output current control circuit provided for controlling the drive signal by controlling an output current of the comparison amplifier circuit. The output current control circuit adjusts the number of output buffers connected to the drive transistor in order to control the output current from the comparison amplifier circuit;
The light emitting diode lighting circuit according to claim 9, further comprising: a switch control circuit that controls on / off of the switch based on a control signal. The control signal is input from a control terminal provided in the integrated circuit,
The light emitting diode lighting circuit according to claim 3, wherein the control signal is a signal indicating a control value of the drive signal. A drive transistor for controlling the drive current of the light emitting diode;
An integrated circuit for controlling the driving transistor,
The integrated circuit comprises:
A comparison amplification circuit for supplying a drive signal for controlling the drive transistor based on a voltage based on the drive current and a reference voltage;
A light emitting circuit including a filter circuit disposed between the comparison amplifier circuit and the drive transistor and configured to adjust a rise time and a fall time of the drive signal supplied by the comparison amplifier circuit; Diode lighting circuit.   The light emitting diode lighting circuit according to claim 12, wherein the filter circuit includes at least one of a variable resistor and a variable capacitor.   3. A switch control circuit for controlling on / off of a switch provided between the drive transistor and the comparison amplifier circuit based on a PWM signal for adjusting the luminance of the light emitting diode. The light-emitting diode lighting circuit according to claim 4.

Images