JP3150287B2 - Power supply - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply device used for electronic equipment such as a copying machine and a display device, and more particularly to a power supply device using a piezoelectric transformer.

[0002]

2. Description of the Related Art In recent years, with the demand for miniaturization of copying machines and the like,
Piezoelectric transformers are being used in power supply devices for generating high voltage instead of winding transformers. The piezoelectric transformer is subjected to polarization processing in a thickness direction and a length direction of a ferroelectric material such as barium titanate or lead zirconate titanate (PZT), and a vibration formed on one side in the length direction of the dielectric material. When an alternating voltage is applied to the portion, a voltage converter is known in which a high voltage is output from a power generation portion formed on the other side in the length direction of the dielectric due to an electrostrictive effect and a piezoelectric effect (for example, See JP-A-61-54686).

In order to drive this piezoelectric transformer, an alternating voltage (or an AC voltage) is applied to the vibrating section via a pair of input electrodes provided so as to sandwich the thickness direction (or polarization direction) of the vibrating section. A drive circuit for applying the input voltage of Furthermore, in order to obtain a high voltage output from the power generation unit, in addition to setting the dimensional relationship between the vibration unit and the power generation unit of the piezoelectric transformer and an appropriate drive frequency, it is necessary to increase the input voltage to the vibration unit as much as possible. Yes, a high voltage output type driving circuit is required.

As a conventional example of increasing the input voltage to the piezoelectric transformer, a power supply device using a step-up transformer in an input stage of the piezoelectric transformer is known (Japanese Patent Laid-Open No. 6-535).
No. 69). As shown in FIG. 9, the power supply device includes a step-up transformer 40 connected to a first input electrode 6 of a piezoelectric transformer 200.
0, and the primary winding 400a of the step-up transformer 200 is excited by a transistor switched by a phase shifter of a predetermined frequency, so that the power supply voltage is boosted at a predetermined step-up ratio, and the piezoelectric transformer 200 A drive voltage is applied between the first and second input electrodes 6 and 7.

[0005]

However, the configuration in which the step-up transformer 400 is connected to the front stage of the piezoelectric transformer 200 as in the above-described example causes an increase in the size of the power supply device or a complicated circuit configuration. It is an object of the present invention to provide a power supply device capable of stably generating a high voltage with a simple configuration.

[0006]

A power supply device according to the present invention comprises a vibrating portion formed by arranging a pair of input electrodes on a dielectric and a power generator formed by arranging an output electrode on the dielectric. In a power supply device using a piezoelectric transformer comprising a piezoelectric transformer, an oscillation circuit capable of variably controlling an oscillation frequency and a driving circuit for performing a switching operation by a control voltage output from the oscillation circuit to output a driving voltage to an input electrode of the piezoelectric transformer Connected to the input electrode of the piezoelectric transformer,
A resonance circuit including a capacitance between a pair of input electrodes of the piezoelectric transformer;
A detection circuit that outputs a first detection voltage and a second detection voltage, and a first circuit that feeds back the first detection voltage to the oscillation circuit.
And a second feedback circuit for feeding back the second detection voltage to the oscillation circuit, wherein the first feedback circuit prevents interference between the output circuit and the oscillation circuit. A circuit and an operational amplifier circuit that operates only when the power supply device is started and supplies a starting voltage to the oscillation circuit are inserted, and the output circuit and the oscillation circuit that operate during normal operation are inserted in the second feedback circuit. And a buffer circuit for preventing interference between them is inserted. According to the present invention, the feedback circuit has two stages, the feedback control of the oscillation operation at the time of startup is performed through the first feedback circuit, and the feedback control of the oscillation operation during the normal operation is performed through the second feedback circuit. Therefore, stable and smooth control becomes possible, and the output voltage of the piezoelectric transformer can be controlled to be constant.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, preferred embodiments of the present invention will be described with reference to the drawings. (One Embodiment of the Present Invention) FIG. 1 shows a circuit configuration diagram of a power supply device according to one embodiment of the present invention. In FIG. 1, a power supply device includes a piezoelectric transformer 200 formed of a ferroelectric material such as barium titanate or lead zirconate titanate (PZT), and a drive circuit 102 for outputting a drive voltage VB for driving the piezoelectric transformer 200. , Which supplies a control voltage VA having a predetermined frequency to the drive circuit 102.
CO 190, an output circuit 300 for rectifying the output voltage VC of the piezoelectric transformer 200, a detection circuit 141 for detecting the output voltage VC and outputting two types of feedback voltages VFB1 and VFB2, and a voltage difference between the detection circuit 141 and the VCO 190. The two feedback circuits 150, 1
50, an operational amplifier circuit 170 for stabilizing the feedback of the feedback voltage VFB1 to the VCO 190 and expanding the control range of the feedback control, and a constant voltage power supply for supplying the power supply voltage VP. And a circuit 160.

[0008] The constant voltage power supply circuit 160 is constructed using a three-terminal regulator RGE, and supplies a DC power supply voltage VP to each unit in response to a supply power supply VSUP. The transistor Q2 is
A switching element that is turned on by the operation signal VSW and supplies the power supply voltage VCC to each operational amplifier in the circuit. The piezoelectric transformer 200 has a vibrating portion formed between the first and second input electrodes 6 and 7, and a power generating portion formed by disposing the output electrode 8 in a region other than the vibrating portion. The vibrating part is polarized in the directions of + and-shown in the figure.
The drive circuit 100 is connected between the first input electrode 6 on the positive side (+) in the polarization direction and the second input electrode 7 on the negative side (-) in the polarization direction. In this state, the driving voltage VB is applied to the vibrating portion of the piezoelectric transformer 200 with a positive bias. An output circuit 300 is connected to the output electrode 8 formed at the end of the power generation unit, and supplies an output voltage to the load 13 via the output circuit 300.

The output circuit 300 is a double-wave rectifier circuit (or bridge circuit) comprising a coupling capacitor 9 connected to the output electrode 8 and rectifier diodes 10 and 11.
And a smoothing capacitor 12. In some piezoelectric transformers 200, the resonance mode is set to λ (wavelength of the resonance frequency of the piezoelectric transformer) mode,
Since there is a possibility that the mode is set to the / 2λ mode, it may be appropriately adapted to the specification of the piezoelectric transformer 200. The output voltage VC generated by the piezoelectric transformer 200 is converted to a direct current by a double-wave rectifier circuit including the coupling capacitor 9 and the diodes 110 and 11, and the smoothing capacitor 1
2 to the load 13.

The buffer circuit 180 (or 181) includes a detection circuit 141 formed by a voltage dividing circuit of the resistors RD1, RD2, and RD3 (or the resistors RD1, RD2, and RD3), and each circuit after the VCO 190. This is a circuit for eliminating interference with the feedback circuits 150 and 151. That is, the resistance RD1 of the detection circuit 141 is set on the order of megaohms (15 MΩ or the like), while the variable resistance VR19 of the VCO 190 is set on the order of kiloohms (several tens of KΩ or the like). This is because it is necessary to prevent potential difference interference. Outputs of the buffer circuits 180 and 181 are input to the VCO 190 via the input resistor R19.

The VCO 190 has a feedback resistor VR.
A control voltage VA that oscillates with a duty ratio determined by the capacitor 19 and the capacitor C19 is generated and output. V
CO 190 is a feedback voltage V which is a non-inverting input.
When the FB1 and VFB2 are high, the oscillation frequency of the control voltage VA is increased to reduce the voltage value of the output voltage VC. When the feedback voltages VFB1 and VFB2 of the non-inverting input are low, the oscillation frequency of the control voltage VA is decreased and output. This is a configuration that operates to increase the voltage value of the voltage VC.

The feedback circuits 150 and 151 in which the buffer circuits 180 and 181 are interposed are connected in parallel in a two-stage configuration. This two-stage feedback circuit 15 connected in parallel
0, 151, the detection circuit 141 for detecting the output voltage VC of the piezoelectric transformer 200 has a two-stage configuration.
Generates different kinds of feedback voltages VFB1 and VFB2. That is, the detection circuit 141 includes three voltage dividing resistors RD.
1, RD2, and RD3 are connected in series. A feedback voltage VFB1 is extracted from a connection point between the resistors RD2 and RD3, and a feedback voltage VFB2 is extracted from a connection point between the resistors RD1 and RD2. . Resonance circuit 41
Is designed to adjust the resonance frequency and the selectivity (so-called Q), and is adapted to this embodiment. The resonance circuit 41 includes a parallel circuit including an inductance L40 and a capacitor C40, and an inductance L41 and a capacitor C41 in series with the parallel circuit.

The feedback circuit 150 includes a buffer circuit 180 and an operational amplifier circuit 170.
A buffer circuit 181 is provided in the feedback circuit 151 parallel to 0. The feedback circuit 150 is a circuit that operates only when the power supply device starts up or when an abnormality occurs.
Reference numeral 1 denotes a circuit that operates during normal operation. Next, the operation of the present embodiment will be described. When the DC power supply voltage VP is initially turned on (at startup), the output voltage VC is applied to the piezoelectric transformer 200.
Does not occur, and the feedback voltage VFB1 to the operational amplifier circuit 170 via the feedback circuit 150 is zero.
The operational amplifier circuit 170, which is an inverting amplifier circuit, outputs a high voltage. On the other hand, at this time, the feedback voltage VFB2 passing through the feedback circuit 151 is also zero, and the feedback voltage VFB2 to the VCO 190 passing through the feedback circuit 151 is zero. This is the output voltage of the operational amplifier circuit 170.

The output voltage of the operational amplifier circuit 170 activates the VCO 190 to start oscillating. By this oscillating operation, the VCO 190 generates a control voltage VA that oscillates at a duty ratio determined by the feedback resistor VR19 and the capacitor C19, and the control voltage VA
Represents a driving transistor (N-channel type M
OSFET) applied to the gate of Q1. The drive transistor Q1 is turned on / off in synchronization with the frequency of the control voltage VA.
Repeat the FF operation. Then, the DC power supply voltage VP is applied to the piezoelectric transformer 2 through the resonance circuit 41 in which the inductance L41 and the capacitor C41 are connected in series to the parallel circuit of the inductance L40 and the capacitor C40.
It is applied between the input terminal 6 and the input terminal 7 of 00, and vibrates the vibrating part of the piezoelectric transformer 200. Due to this vibration, an output voltage VC is generated from the piezoelectric transformer 200, and the output circuit 3
Sent to 00. The output circuit 300 rectifies the output voltage VC and converts it to DC, and supplies the DC to the load 13.

On the other hand, when the output voltage VC is generated, the output voltage VC is detected by the detection circuit 141, and two feedback voltages VFB1 and VFB2 are output. Of these two feedback voltages, VFB1 is sent to the operational amplifier circuit 170 through the feedback circuit 150, the low-pass filter (the capacitor CF1 and the inductance LF1) and the buffer circuit 180. At the same time, the feedback voltage VFB2 is fed back to the buffer circuit 181 through a feedback circuit 151 and a low-pass filter (a capacitor CF2 and an inductance LF2). When the feedback voltage VFB1 is applied, the feedback voltage VFB1 becomes relatively higher than VFB2, and the output voltage of the operational amplifier circuit 170 is inverted to a lower voltage, which does not contribute to the operation of the VCO 190.

Therefore, in a normal state after the output voltage VC is generated, the feedback voltage VFB2 becomes effective. In this manner, the feedback voltage is switched from VFB1 to VFB2 at the time of startup and during normal operation. In the subsequent operation, when the output voltage VC of the piezoelectric transformer 200 changes, the oscillation frequency of the VCO 190 is controlled by the feedback voltage VFB2 passing through the feedback circuit 151, and the fluctuation of the output voltage VC is corrected, and the stable output voltage VC is obtained. VC is supplied to the load 13.

[0017]

As described above, according to the present invention, the stability and the control width of the feedback control of the drive circuit based on the detection voltage of the output voltage of the piezoelectric transformer can be increased, and the output voltage of the piezoelectric transformer can be kept constant. Can be held.

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram of a power supply device according to an embodiment of the present invention.

FIG. 2 is a circuit configuration diagram of a conventional power supply device.

[Explanation of symbols]

 6 First input electrode 7 Second input electrode 8 Output electrode 9 Coupling capacitor 10 Rectifier diode 11 Rectifier diode 12 Smoothing capacitor 13 Load 102 Drive circuit 141 Output voltage detection circuit 150, 151 Feedback circuit 160 Constant voltage power supply circuit 170 Operational amplifier circuit 180, 181 Buffer circuit 190 VCO (voltage controlled oscillator) 200 Piezoelectric transformer 300 Output circuit 400 Boost transformer VP DC power supply voltage VA Control voltage VB drive voltage VC Output voltage Q1 Drive transistor

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H02M 3/24 H01L 41/107 H02M 7/48

Claims (1)

(57) [Claims] 1. A power supply device using a piezoelectric transformer comprising a vibrating portion formed by disposing a pair of input electrodes on a dielectric and a power generating portion formed by disposing an output electrode on the dielectric. An oscillation circuit capable of variably controlling the oscillation frequency and a drive circuit that performs a switching operation by a control voltage output from the oscillation circuit to output a drive voltage to an input electrode of the piezoelectric transformer, and is connected to an input electrode of the piezoelectric transformer; A resonance circuit including a capacitance between a pair of input electrodes of the piezoelectric transformer, a detection circuit that detects an output voltage of the piezoelectric transformer and outputs a first detection voltage and a second detection voltage, A first feedback circuit that feeds back a detection voltage to the oscillation circuit; and a second feedback circuit that feeds back the second detection voltage to the oscillation circuit. A buffer circuit that prevents interference between the circuit and the oscillation circuit, and an operational amplifier circuit that operates only at the time of activation of the power supply device and supplies a startup voltage to the oscillation circuit, and is inserted into the second feedback circuit. A power supply device, wherein a buffer circuit which operates during normal operation and prevents interference between the detection circuit and the oscillation circuit is inserted.