JP3378599B2 - EL drive circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used, for example, as a backlight for displaying a message on a pager or a pocket computer, or as a backlight for displaying a liquid crystal display on a sewing machine. EL (Electrolum
inescence) driving circuit. 2. Description of the Related Art As an EL drive circuit of this type, a conventionally known EL drive circuit supplies electric power by using a step-up transformer or a resonance inductance. is there. These are adapted to resonate by adjusting the secondary side inductance and resonance inductance of the step-up transformer to the capacitance of EL. [0003] By the way, EL is about 700 to 1000H.
driving at a low frequency and high voltage of about 140 V
L is the most efficient in terms of life and luminance balance. However, in the conventional EL drive circuit using the boosting transformer and the resonance inductance, in order to perform the above-described efficient resonance, a large inductance value is required because of a low frequency, and as a result, There is a disadvantage that the transformer and the inductance become large. [0004] The frequency range of about 700 to 1000 Hz is an audible range, and has an unpleasant vibration sound. Further, in the case of use in DC superposition, it is generally preferable to use a transformer or an inductance having a core with a gap.
When resonance is performed at a low frequency of 0 Hz, the vibration sound from the gap increases. SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and eliminates the need for using a transformer or a resonance inductance, thereby enabling downsizing and reducing the generation of noise such as vibration noise. It is intended to provide. [0006] 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 includes a first and a second half. Operate in each first half of the cycle to turn the switching element on and off intermittently
The pulse signal has a longer period on the rear side than on the front side in the first half.
In addition, a boost chopper circuit for inducing a high voltage is provided. Further, operating in the first half of the first half cycle, E
A first power supply circuit for applying a high voltage induced by the boost chopper circuit with a first polarity to an output terminal connected to L, and a booster that operates in the first half of a second half cycle and applies the boost voltage to the output terminal. A second power supply circuit for applying the high voltage induced by the chopper circuit with a second polarity, and operating in the second half of the first half cycle to charge the charged E.
A first discharge circuit for discharging L and a second discharge circuit that operates in the latter half of the second half cycle and discharges the charged EL are provided. 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, during which the high voltage is applied to the first voltage. The first polarity is applied to the output terminal connected to the EL via the power supply circuit. Next, in the second half of the first half cycle, the EL charged in the first half is discharged via the first discharging circuit. In the first half of the next second half cycle, a high voltage is similarly induced in the boost chopper circuit, and during this time the high voltage is applied to the output terminal with the second polarity via the second power supply circuit. Is done. Next, in the second half of the second half cycle, the EL charged in the first half is discharged via the second discharging circuit. By repeating this operation, an AC output having a constant frequency is output from the output terminal. An embodiment 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 according to the present invention. In FIG.
ELs 3a and 3b serving as loads of the drive circuit are output terminals connected to the EL2. The DC power supply 1 is connected to a boost chopper circuit 14. The step-up chopper circuit 14 has an inductance 4 to which a DC voltage is supplied from the DC power supply 1 and a first switching element 5 for interrupting the supply of the DC voltage, and supplies an AC output VO to be applied to the output terminals 3a and 3b. It operates during 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 an output unit including a diode 6 and a capacitor 7. A second switching element 8 is provided between the boost chopper circuit 14 and the output terminals 3a and 3b.
And a first power supply circuit 15 having a third switching element 9, a first discharging circuit 16 having a fourth switching element 10, and a second discharging circuit 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. The first power supply circuit 15 turns on the switching elements 8 and 9 in the first half of the first half cycle, and converts the high voltage induced by the boost chopper circuit 14 to the first polarity with the first polarity. This is applied to the output terminals 3a and 3b. The first discharging circuit 16 turns on the switching element 10 intermittently in the second half of the first half cycle to discharge the EL2 charged in the first half of the same first half cycle. The second power supply circuit 17 turns on the switching elements 11 and 12 in the first half of the second half cycle to change the high voltage induced by the boost chopper circuit 14 to a second polarity with the second polarity. This is applied to the output terminals 3a and 3b. The second discharge circuit 18 turns on the switching element 13 intermittently in the second half of the second half cycle to discharge the EL2 charged in the first half of the same second half cycle. The first, second and fifth switching elements 5, 8 and 11 are constituted by FETs, and third, fourth, sixth and seventh switching elements 9, 10, 12 and 13 are provided.
Is composed of a transistor, but is not limited to this, and various switching means can be appropriately selected and used. The EL drive circuit controls the on / off of each of the switching elements 5, 8, 9, 10, 11, 12, and 13 so that a constant frequency AC output is output to output terminals 3a and 3b. Frequency control circuit 1 for extracting VO
9, an input power detection circuit 20 for detecting input power to the boost chopper circuit 14, and an input power detection circuit 20
And a power control circuit 21 for controlling a power supply time from the DC power supply 1 to the step-up chopper circuit 14 so as to maintain the input power detected by the DC power supply 1 at a constant value. Are built in the CPU 22. FIG. 2 shows details of the EL drive circuit of FIG.
In FIG. 1, a DC power supply 1 has an inductance 4 and a first
Are connected in series. A diode 6 is connected between both terminals of the first switching element 5.
And the capacitor 7 are connected in series and the boost chopper circuit 14
Is configured. A second point is provided between a connection point P between the diode 6 and the capacitor 7 and the output terminal 3a.
Is connected, and a fifth switching element 11 is connected between the connection point P and the output terminal 3b. Further, a fourth switching element 10 and a sixth switching element 12 are connected between the output terminal 3a and the negative pole of the DC power supply 1, and a fourth switching element 10 and a sixth switching element 12 are connected between the output terminal 3b and the negative pole of the DC power supply 1. The third switching element 9 and the seventh switching element 13 are connected. The frequency control circuit 19 shown in FIG. 2 is controlled by a CPU 22 which operates in response to a clock pulse generated by a clock generator 23 using a crystal oscillator or the like, and controls the switching elements 5, 8, 9, 10 ,
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. In a 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
Due to α, the second switching element 8 and the third switching element 9 constituting the first power supply circuit 15 are kept on. As a result, the first switching element 5
Is turned 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 taken out to the output terminals 3a and 3b via the first power supply circuit 15. As a result, the first output terminal 3a becomes positive.
A high voltage having a 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 is obtained. Are adjusted so that the output waveform applied to the output terminals 3a and 3b becomes a sine waveform. Further, in the latter half H1b of the same half cycle H1,
The first switching element 5 is kept off. At this time, the pulse signal S output from the frequency control circuit 19
1 controls the fourth switching element 10 of the first discharging circuit 16 to be turned on and off. Thereby, the discharge of EL2 charged in the first half H1a of the half cycle H1 is performed by the fourth switching element 10 and the diode 26.
Done through. The pulse signal S1 is not set to have a constant cycle, but is set so that the cycle is gradually shortened 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 is set. The output waveform applied to the output terminals 3a and 3b at H1b is a sine waveform. Next, in the first half H2a of the second half cycle H2, the first half H2a is similar to the first half H1a of the first half cycle H1.
Of the switching element 5 is controlled to be turned on and 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 constituting the second power supply circuit 17 are kept on by the control signal Sβ separately output from the frequency control circuit 19. As a result, the first switching element 5
Is turned 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 taken out through the second power supply circuit 17 to the output terminals 3a and 3b. , Whereby one output terminal 3b becomes positive.
A high voltage having a 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. Same as in the case. Further, in the latter half H2b of the same half cycle H2, the first switching element 5 is kept off. At this time, the pulse signal S2 output from the frequency control circuit 19
Accordingly, the seventh switching element 13 included in the second discharge circuit 18 is turned on and off. 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 whose cycle gradually decreases from the first half to the second half, similarly to the previous pulse signal S1. As described above, the boost chopper circuit 14 having one inductance 4 is connected to one switching element 5 without using a boost transformer or resonance inductance.
To turn on and off to induce a high voltage. The high voltage is taken out to the output terminals 3a and 3b while switching the polarity by the first and second power supply circuits 15 and 17, while the charged EL2 is taken out by the first and second power supply circuits 15 and 17. Since the second discharge circuits 16 and 18 discharge the AC output VO with a constant period to the EL2, the EL output can be driven by the 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
KHz or higher. Therefore, the size of the inductance 4 can be reduced. Further, since the high frequency of 500 KHz is out of the audible range, there is almost no generation of noise such as vibration noise during the operation of the EL drive circuit, and it is possible to eliminate harshness accompanying use. Output terminals 3a, 3b
Can be increased or decreased by changing the frequency of the pulse signal Sa. Since the impedance of EL2, which is the load of the EL drive circuit, tends to increase with time, the luminance of EL2 also increases with time when the voltage applied to the output terminals 3a and 3b is constant. This causes a problem that the temperature decreases. 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,
It is possible to prevent the luminance of L2 from lowering, and EL2 can be used for a long time. As described above, according to the present invention, the high voltage induced by the step-up chopper circuit having the inductance supplied from the DC power supply can be reduced without using the transformer or the resonance inductance. The polarity is switched between the first and second power supply circuits in the first half of the first and second half cycles and taken out to the output terminal, thereby charging the charged EL.
Is discharged by the first and second discharge circuits in the second half of each of the first and second half cycles, so that an AC output for EL driving is taken out, so that a high frequency can flow through the inductance. Therefore, the size of the inductance can be reduced accordingly. Moreover, since there is one boost chopper circuit, only one inductance is included in this boost chopper circuit. Therefore, downsizing of the entire EL driving circuit can be realized. Further, since a pulse signal for chopper control can use a high frequency outside the audible range, EL
Generation of noise such as vibration noise during operation can be significantly reduced.

BRIEF DESCRIPTION OF THE 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. [Description of Signs] 1 ... DC power supply, 2 ... EL, 3a, 3b ... output terminals, 4 ...
Inductance: 5: first switching element, 8: second switching element, 9: third switching element,
Reference numeral 10: fourth switching element, 11: fifth switching element, 12: sixth switching element, 13: seventh
Switching elements, 14 ... step-up chopper circuits, 15 ...
1st power supply circuit, 16 ... 1st discharge circuit, 17 ... 2nd power supply circuit, 18 ... 2nd discharge circuit, 19 ... frequency control circuit, 20 ... input power detection circuit, 21 ... input power control circuit.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H05B 33/08 H05B 41/24 G09G 3/12 H02M 7/42-7/98

Claims (1)

(57) Claims 1. A DC power supply 1, output terminals 3a and 3b connected to EL2, an inductance 4 and a switching element 5 connected in series to the DC power supply 1, 1 and the second half period H1, operating in each of the first half of the H2, the Sui
Before the pulse signal for turning on and off the switching element 5 intermittently.
The step-up chopper circuit 14 for inducing a high voltage by increasing the period of the rear side from the front side of the first half and the output terminal 3 which operates in the first half of the first half period H1
a first power supply circuit 15 for applying a high voltage induced by the step-up chopper circuit 14 with a first polarity to a and 3b, and operating in the latter half of the first half cycle H1 to discharge the charged EL2. A first discharging circuit 16 which operates in the first half of the second half cycle H2 and operates at the output terminal 3;
a second power supply circuit 17 for applying the high voltage induced by the boost chopper circuit 14 with a second polarity to a and 3b, operating in the second half of the second half cycle H2, and discharging the charged EL2. An EL driving circuit comprising: a second discharging circuit 18 for causing the EL driving circuit 18 to operate.