JPH10201250A - Load drive circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a drive circuit which does not emit sound when driving loads such as an electroluminescence(EL) panel with AC and which is of small size. SOLUTION: A chopper type boosting circuit A stores high electric potential in a ceramic capacitor C of low distortion factor using zirconium titanate as a dielectric. Using this high electric potential, a switching circuit B drives an electroluminescence(EL) panel with AC. Even if saw-tooth wave forms appear in the voltage of the capacitor C when charging and discharging are repeated in the capacitor C and when a luminous area becomes large for performing bright lighting, sound is not emitted because the vibration of the capacitor C is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive circuit for a load for driving a load such as an EL panel by AC.

[0002]

2. Description of the Related Art Conventionally, an EL panel is suitable as a flat light source for a backlight of an electronic device such as a portable computer or a cellular phone which is not susceptible to electromagnetic noise and voice noise, and drives an AC-driven load such as an EL panel. As a circuit, a DC power supply is boosted by a chopper type booster circuit to charge a capacitor, and a switching circuit is driven by applying an alternating voltage to a load. As a capacitor, a capacitor using a high-dielectric material such as barium titanate as a dielectric material is usually used because of the need for miniaturization.

[0003]

A small capacitor using a high dielectric material such as barium titanate as a dielectric material as in the prior art described above is used as a capacitor of a chopper type booster circuit, and a potential stored in the capacitor is used. When AC is driven to an EL panel or the like by a switching circuit, since the voltage of the capacitor has a saw-tooth waveform as shown in FIG. 2, there is a problem that sound is generated by the piezoelectric effect. An EL panel is often used as a backlight of a liquid crystal panel, a backlight of a key top, or the like, and has a large light-emitting area and needs to provide bright illumination. The sawtooth-shaped waveform is large, which causes troublesome noise. In addition, even if the sound is very weak, in a mobile phone or the like, since the sound is used close to the ear and is used in a state of being held by hand, the minute sound reaches the ear through the frame. The problem was that noise hindered conversation.

[0004]

In order to solve the above-mentioned problems, the present invention uses a low distortion ceramic capacitor as a capacitor used in a load driving circuit. In such a ceramic capacitor having a low distortion, downsizing can be achieved, and at the same time, even if a saw-tooth waveform appears, the capacitor is less deformed, vibration is suppressed, and generation of sound can be prevented.

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention relates to a drive circuit for driving a potential stored in a capacitor of a chopper type booster circuit to a load by an alternating current with a switching circuit, wherein a low distortion ceramic capacitor is used as the capacitor. Features. In the above ceramic capacitor, it is preferable to use lead titanate or zirconium titanate as its dielectric.

When a ceramic capacitor having a low distortion rate is used as described above, even if the charging by the chopper type boosting circuit and the discharging by the switching circuit are frequently repeated, a sawtooth waveform is generated, and the capacitor of the capacitor due to the piezoelectric effect is generated. Vibration is suppressed and no sound is generated. In addition, as in the case of a conventional capacitor using a high dielectric substance, this capacitor can achieve downsizing, and is suitable for use in electronic devices such as mobile phones, which are pursuing miniaturization to the utmost.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to the drawings. As shown in FIG. 1, a drive circuit of an EL panel as a load 1 is a chopper type booster for storing a high potential in a capacitor C. The circuit comprises a circuit A and a switching circuit B for AC-driving the load 1 with the potential stored in the capacitor C. The capacitor C is provided with a low distortion ceramic capacitor using zirconium titanate as a dielectric.

The chopper type booster circuit A has a ceramic capacitor C connected to a DC power supply E via a booster coil L and a diode D. The output of the pulse generating circuit 3 is controlled by the high frequency output signal P of the control circuit 2 of the EL panel 1, and the transistor Tr1 is turned on / off by the output of the pulse generating circuit 3, and the boosting coil L is chopped. At this time, a flyback voltage is generated, and this high current is stored in the ceramic capacitor C.

The switching circuit B includes a transistor Tr
2, the first and second switch circuits in which Tr3 and Tr4 and Tr5 are connected in series, respectively, and the first and second timings in which the resistor R1, the transistor Tr6 and the resistor R2 and the transistor Tr7 are connected in series, respectively. The circuit is connected in parallel to the ceramic capacitor C. Further, one terminal 1a of the EL panel 1 is connected to the first terminal 1a.
And the other terminal 1b of the EL panel 1 is connected to the connection point of the two transistors Tr2 and Tr3 of the switch circuit of FIG.
Two transistors Tr4, Tr of the second switch circuit
It is connected to connection point 5. Transistors Tr6, T
r3 and Tr5, Tr7 are turned on / off by the control circuit 2.
Output signals S1, S2 and S3, S4. The signals S1, S2 and S3, S4 correspond to the EL panel 1
Is a signal having the same driving frequency and having the opposite phase. Therefore, when the signals S1 and S2 are H, the transistor Tr3
Is turned on, and a ground potential is applied to the terminal 1a of the EL panel 1. At this time, since the transistor Tr6 is also on, the transistor Tr2 is off, and the potential of the ceramic capacitor C is not supplied to the terminal 1a. At the same time, since the signals S3 and S4 are L at this time, the transistor T
Since r7 is turned off and the transistor Tr4 is turned on, the potential of the ceramic capacitor C is supplied to the terminal 1b of the EL panel 1.

Next, when the phases of the signals S1, S2 and S3, S4 are inverted, the transistor Tr2 is turned on and the transistor Tr4 is turned off, so that the potential of the ceramic capacitor C is supplied to the terminal 1a of the EL panel 1 this time. Thus, a ground potential is applied to the terminal 1b. In this way, the EL panel 1 is AC-driven by the high potential stored in the ceramic capacitor C. As explained above,
Since a low potential ceramic capacitor using zirconium titanate is used, a high potential is stored in the capacitor C by the chopping circuit A, and the potential of the capacitor C is supplied to the EL panel 1 at a constant timing by the switching circuit B. Even if the sawtooth-shaped waveform as shown in FIG. 2 described with the conventional capacitor using a high dielectric substance appears, almost no vibration occurs in the capacitor, so that noise is suppressed.

The load 1 is not limited to the EL panel, but can be applied to any buzzer or any other AC-driven load. Where miniaturization is not required, a film capacitor having no piezoelectric effect may be used other than a low distortion ceramic capacitor.

[0012]

As described above, since a low distortion ceramic capacitor is used, charging of the chopper type boosting circuit and discharging of the switching circuit are frequently repeated, and even if a sawtooth waveform is generated, the vibration of the capacitor is suppressed. No sound is generated. As in the case of capacitors using high dielectrics, miniaturization can be achieved, so in fields where miniaturization is pursued to the utmost, such as mobile phones, load drive circuits using low distortion ceramic capacitors Has a special effect.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing one embodiment of the present invention.

FIG. 2 is a sawtooth waveform diagram generated in a capacitor.

[Explanation of symbols]

 A Chopper type booster circuit B Switching circuit C Ceramic capacitor 1 Load (EL panel)

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI H05B 33/08 H05B 33/08

Claims (2)

[Claims] 1. A drive circuit for driving a potential stored in a capacitor of a chopper type booster circuit to an AC load by a switching circuit with respect to a load, wherein a low distortion ceramic capacitor is used as the capacitor. circuit. 2. The load driving circuit according to claim 1, wherein said ceramic capacitor uses lead titanate or zirconium titanate as a dielectric.