JPH06151056A - El driving circuit - Google Patents

Abstract

PURPOSE:To miniaturize the whole body without using a resonating inductance in an EL driving circuit and suppress the generation of vibrating sound at EL operation. CONSTITUTION:An EL driving circuit is provided with a booster chopper circuit 14 having an inductance 4 to which a current is fed from a DC power source 1 and a switching element 5 for interrupting the feed. The polarity of the high voltage induced in the booster chopper circuit 14 is switched every first half of first and second half periods by first and second feed circuits 15, 17 to take out the voltage to output terminals 3a, 3b connected to an EL 2. The EL 2 charged in each period is discharged in each second half of the first and second half periods by first and second discharge circuits 16, 17. This operation is repeated, whereby an AC output VO for EL drive is taken out to the output terminals 3a, 3b. The ON/OFF of the booster chopper circuit 14 is controlled by a high frequency pulse signal Sa outside an audible range to eliminate rasping vibrating sound, and the miniaturization of the inductance 4 is also attained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an EL (Electrolum) used as, for example, a backlight for displaying a message on a pager or a pocket computer, or a display for a liquid crystal display in a sewing machine.
inescence) drive circuit.

[0002]

2. Description of the Related Art As an EL drive circuit of this kind, there is a conventionally known one which supplies electric power by using a step-up transformer or a resonance inductance. These are adapted to resonate by matching the secondary side inductance of the step-up transformer and the resonance inductance to the capacitance of the EL.

By the way, EL is about 700 to 1000H.
z, driving at a low frequency high voltage of about 140V
It is most efficient in terms of L life and brightness balance. However, in the conventional EL drive circuit that uses the above step-up transformer and the inductance for resonance, a large inductance value is required because of the low frequency in order to perform the above-mentioned efficient resonance, and as a result, It has the drawback of increasing the size of the transformer and inductance.

Further, about 700 to 1000 Hz is in the audible range, which is accompanied by an offensive vibration sound. Further, when using in DC superposition, it is generally preferable to use a transformer having a core with a gap or an inductance.
When the low frequency resonance of 0 Hz is performed, the vibration sound from the gap becomes loud.

The present invention has been made in view of the above circumstances, and an EL drive circuit which can be downsized without using a transformer or an inductance for resonance and which can reduce the generation of noise such as vibration noise. It is intended to be provided.

[0006]

In order to achieve the above object, an EL drive circuit according to the present invention includes an inductance and a switching element connected in series to a DC power supply, and each of the first and second half cycles. A boost chopper circuit that operates in the first half of the above to induce a high voltage is provided. Furthermore, a first power feeding circuit that operates in the first half of the first half cycle to apply the high voltage induced by the boost chopper circuit with the first polarity to the output terminal connected to the EL; It operates in the first half of the half cycle and the high voltage induced in the boost chopper circuit is applied to the output terminal by the second voltage.
And a second power supply circuit for applying the polarity of the second half cycle, and a second discharge circuit that operates in the latter half of the first half cycle to discharge the charged EL and the second half cycle of the second half cycle. And a second discharge circuit which operates in the step of discharging the charged EL.

[0007]

According to the EL drive circuit of the present invention, in the first half of the first half cycle, a high voltage is induced by the on / off control of the boost chopper circuit, and during that time, the high voltage causes the first power feeding circuit to operate. The first polarity is applied to the output terminal connected to the EL via. Next, in the latter half of the first half cycle, the EL charged in the first half is discharged through the first discharging circuit. Also in the first half of the next second half cycle, a high voltage is similarly induced in the boost chopper circuit, and during this period, the high voltage is applied to the output terminal through the second power feeding circuit with the second polarity. To be done. Next, in the latter half of the second half cycle, the EL charged in the first half is discharged through the second discharging circuit. By repeating this operation, an AC output having a constant frequency is taken out to the output terminal.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram of an EL drive circuit of the present invention, in which 1 is a DC power supply and 2 is this EL.
EL, 3a and 3b, which are loads of the drive circuit, are output terminals connected to the EL2. A boost chopper circuit 14 is connected to the DC power supply 1. The step-up chopper circuit 14 has an inductance 4 to which a DC voltage is fed from a DC power source 1 and a first switching element 5 which connects and disconnects the feeding, and the AC output VO to be applied to the output terminals 3a and 3b. It operates in a period corresponding to the first half of each of the first and second half cycles to induce a high voltage, and the high voltage is output from the output section including the diode 6 and the capacitor 7.

Further, a second switching element 8 is provided between the boost chopper circuit 14 and the output terminals 3a and 3b.
And a first feeding circuit 15 having a third switching element 9, a first discharging circuit 16 having a fourth switching element 10, a second discharging circuit 11 having a fifth switching element 11 and a sixth switching element 12. Power supply circuit 17
And a second discharge circuit 18 having a seventh switching element 13 are connected.

The first power supply circuit 15 turns on the switching elements 8 and 9 in the first half of the first half cycle, so that the high voltage induced in the boost chopper circuit 14 has the first polarity. It is applied to the output terminals 3a and 3b. The first discharge circuit 16 intermittently turns on the switching element 10 in the latter half of the first half cycle to discharge EL2 charged in the first half of the same first half cycle.

The second power feeding circuit 17 turns on the switching elements 11 and 12 in the first half of the second half cycle, so that the high voltage induced in the boost chopper circuit 14 has the second polarity. It is applied to the output terminals 3a and 3b. The second discharge circuit 18 intermittently turns on the switching element 13 in the latter half of the second half cycle to discharge EL2 charged in the first half of the same second half cycle.

The first, second and fifth switching elements 5, 8 and 11 are composed of FETs, and the third, fourth, sixth and seventh switching elements 9, 10, 12, 13 are provided.
Is composed of a transistor, but is not limited to this, and various switching means can be appropriately selected and used.

Further, the EL drive circuit controls the switching elements 5, 8, 9, 10, 11, 12, and 13 to be turned on and off so that an AC output having a constant frequency is output to the output terminals 3a and 3b. Frequency control circuit 1 for extracting VO
9, an input power detection circuit 20 for detecting the input power to the boost chopper circuit 14, and the input power detection circuit 20.
A power control circuit 21 that controls the power supply time from the DC power supply 1 to the step-up chopper circuit 14 is provided so as to keep the input power detected by the constant value, and the frequency control circuit 19 and the power control circuit 21 are provided. Are built in the CPU 22.

Details of the EL drive circuit of FIG. 1 are shown in FIG.
In the figure, the DC power supply 1 has an inductance 4 and a first
Switching elements 5 are connected in series. A diode 6 is placed between both terminals of the first switching element 5.
And the capacitor 7 are connected in series to connect the boost chopper circuit 14
The output part of is configured. In addition, a second point is provided between the connection point P of the diode 6 and the capacitor 7 and the output terminal 3a.
Switching element 8 is connected, and the fifth switching element 11 is connected between the connection point P and the output terminal 3b. Further, the fourth switching element 10 and the sixth switching element 12 are connected between the output terminal 3a and the negative pole of the DC power source 1, and the fourth switching element 10 and the sixth switching element 12 are connected between the output terminal 3b and the negative pole of the DC power source 1. The third switching element 9 and the seventh switching element 13 are connected.

The frequency control circuit 19 of FIG. 2 is controlled by a CPU 22 which operates by receiving a clock pulse generated by a clock generator 23 using a crystal oscillator or the like, and each of the switching elements 5, 8, 9, 10 described above. ，
Signal Sa for controlling on / off of 11, 12, and 13 , S
α, Sβ, S1 , S2 Generate.

Next, the operation of the EL drive circuit configured as described above will be described with reference to the signal waveform diagrams of FIGS. 3 and 4. During the period corresponding to the first half H1a of the first half cycle H1 of the AC output VO to be applied to the output terminals 3a and 3b, the first switching element 5 constituting the boost chopper circuit 14 is built in the CPU 22. The pulse signal S output from the frequency control circuit 19
ON / OFF control is performed at a constant cycle by a. At this time, the control signal S separately output from the frequency control circuit 19
The second switching element 8 and the third switching element 9 forming the first feeding circuit 15 are kept in the ON state by α.

As a result, the first switching element 5 is
When the switch is on, the energy stored in the inductance 4 is released to the capacitor 7 via the diode 6 when the switching element 5 is turned off, and the released energy is extracted to the output terminals 3a and 3b via the first power supply circuit 15. This causes the first output terminal 3a to become positive.
A high voltage with the polarity of is induced. At this time, the pulse signal Sa is set so that the period on the rear side H1ab is slightly longer than the period on the front side H1aa as shown in FIG. 4A, whereby the first half H1a of this half period H1. In, the output waveform applied to the output terminals 3a and 3b is adjusted to be a sine waveform.

Further, in the latter half H1b of the same half cycle H1,
The first switching element 5 is kept in the off state. At this time, the pulse signal S output from the frequency control circuit 19
1 controls ON / OFF of the fourth switching element 10 that constitutes the first discharge circuit 16. Accordingly, the discharge of EL2 charged in the first half H1a of the half cycle H1 is caused by the fourth switching element 10 and the diode 26.
Done through. The pulse signal S1 is set not to have a constant cycle but to have a cycle that gradually becomes shorter from the first half to the second half as shown in FIG. 4B, whereby the discharge waveform, that is, the second half of the first half cycle H1. In H1b, the output waveform applied to the output terminals 3a and 3b is a sine waveform.

Then, in the first half H2a of the second half cycle H2, as in the first half H1a of the first half cycle H1, the first half H2a
The switching element 5 is controlled to be turned on / off at a constant cycle by the pulse signal Sa output from the frequency control circuit 19. At this time, the fifth switching element 11 and the sixth switching element 12 forming the second power feeding circuit 17 are kept in the ON state by the control signal Sβ separately output from the frequency control circuit 19.

As a result, the first switching element 5
The energy stored in the inductance 4 is released to the capacitor 7 through the diode 6 when the switching element 5 is turned off, and the released energy is taken out through the second power supply circuit 17 and the output terminals 3a and 3b. , So that one of the output terminals 3b becomes positive
A high voltage with the polarity of is induced. In the pulse signal Sa at this time, the period of the rear side H2ab is set to be slightly longer than the period of the front side H2aa as shown in FIG. It is similar to the case.

Further, in the second half H2b of the same half cycle H2, the first switching element 5 is kept in the off state. At this time, the pulse signal S2 output from the frequency control circuit 19
Thus, the seventh switching element 13 forming the second discharge circuit 18 is on / off controlled. This allows
The discharge of EL2 charged in the first half H2a of the half cycle H2 is
This is performed via the seventh switching element 13 and the diode 27. The pulse signal S2 in this case also has a pulse waveform in which the cycle is gradually shortened from the first half to the second half similarly to the previous pulse signal S1.

As described above, the step-up chopper circuit 14 having one inductance 4 is used as one switching element 5 without using the step-up transformer and the resonance inductance.
To turn on and off to induce a high voltage, and the high voltage is taken out to the output terminals 3a and 3b while switching the polarities by the first and second power feeding circuits 15 and 17, while the charged EL2 is discharged to the first and second terminals. By discharging in the second discharge circuits 16 and 18, the AC output VO having a constant cycle is taken out to the EL2, it is possible to drive the EL2 with this AC output VO.

Here, the frequency of the pulse signal Sa, that is, the high frequency flowing through the inductance 4 is, for example, 500.
It can be KHz or higher. Therefore, the size of the inductance 4 can be reduced. Further, since a high frequency of 500 KHz is out of the audible range, almost no noise such as vibration noise is generated during the operation of the EL drive circuit, and the annoyance associated with use can be eliminated. Output terminals 3a, 3b
The voltage value of the AC output VO taken out can be increased or decreased by changing the frequency of the pulse signal Sa.

By the way, since the impedance of EL2 which is the load of the EL drive circuit tends to increase with time, if the voltage applied to the output terminals 3a and 3b is constant, the brightness of EL2 also changes with time. Inconveniently, it will decrease. On the other hand, in the EL drive circuit, the input power is detected by the input power detection circuit 20, and the power control circuit 21 of the CPU 22 keeps the input power constant based on the detected value. The voltage of the applied AC output VO becomes high, which causes E
It becomes possible to prevent the luminance of L2 from decreasing, and EL2 can be used for a long period of time.

[0025]

As described above, according to the present invention, the high voltage induced by the step-up chopper circuit having the inductance fed from the DC power supply is eliminated without using the transformer or the resonance inductance. In the power feeding circuit of No. 2, the polarity is switched every first half of the first and second half cycles and is taken out to the output terminal, and the EL charged by this is charged.
Is discharged by the first and second discharge circuits in the latter half of each of the first and second half cycles, so that an AC output for EL drive is taken out, so that a high frequency wave can flow in the inductance. Therefore, the size of the inductance can be reduced accordingly. Moreover, since there is only one boost chopper circuit, only one inductance is required in this boost chopper circuit. Therefore, miniaturization of the entire EL drive circuit can be realized. In addition, since the chopper control pulse signal can use high frequencies outside the audible range,
It is possible to significantly reduce the generation of noise such as vibration noise during operation.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an EL drive circuit according to the present invention.

FIG. 2 is a specific configuration diagram of FIG.

FIG. 3 is a signal waveform diagram for explaining the operation of the present invention.

4A is a waveform diagram of a pulse signal Sa, and FIG. 4B is a waveform diagram of pulse signals S1 and S2.

[Explanation of symbols]

1 ... DC power supply, 2 ... EL, 3a, 3b ... Output terminal, 4 ...
Inductance, 5 ... First switching element, 8 ... Second switching element, 9 ... Third switching element,
10 ... 4th switching element, 11 ... 5th switching element, 12 ... 6th switching element, 13 ... 7th
Switching elements, 14 ... Step-up chopper circuit, 15 ...
1st electric power feeding circuit, 16 ... 1st discharge circuit, 17 ... 2nd electric power feeding circuit, 18 ... 2nd discharge circuit, 19 ... Frequency control circuit, 20 ... Input power detection circuit, 21 ... Input power control circuit.

Claims (1)

[Claims] 1. A direct current power supply 1, output terminals 3a and 3b connected to EL2, an inductance 4 and a switching element 5 serially connected to the direct current power supply 1, and a first and a second half cycle H1. The step-up chopper circuit 14 that operates in the first half of each H2 and induces a high voltage, and the output terminal 3 that operates in the first half of the first half cycle H1.
The first feeding circuit 15 for applying the high voltage induced by the step-up chopper circuit 14 to the a and 3b with the first polarity, and the second feeding circuit 15 which operates in the latter half of the first half cycle H1 to discharge the charged EL2. The first discharge circuit 16 operates in the first half of the second half cycle H2 and operates at the output terminal 3
The second feeding circuit 17 for applying the high voltage induced by the step-up chopper circuit 14 with the second polarity to a and 3b, and the second feeding circuit 17 which operates in the latter half of the second half cycle H2 to discharge the charged EL2. An EL drive circuit including a second discharge circuit 18 for causing the discharge.