JPH0923643A - Power supply - Google Patents

Abstract

PURPOSE: To obtain a power supply in which an AC control signal is fed from an oscillation circuit to a control electrode and a DC power supply voltage is converted, depending on the AC control signal, into ant AC voltage which is then fed through a switching control element to a piezoelectric transformer and a high voltage is produced by inserting a flyback coil into the path for feeding a DC power supply voltage to the switching element. CONSTITUTION: A drive circuit 100 outputs an AC control signal of predetermined frequency from an oscillation IC1 and converts a DC power supply voltage VP, depending on the AC control signal being fed to control electrodes 6, 7, into an AC drive voltage VB which is then fed through a switching control element, i.e., an MOSFET 3, to a piezoelectric transformer 200 thus turning the piezoelectric transformer 200 on/off. A flyback coil 4 is inserted into the path for feeding a DC power supply voltage VP to the MISFIT 3 and a flyback voltage is outputted therefrom. Since a drive voltage having a large amplitude can be applied to the oscillatory section of piezoelectric transformer 200, a high voltage can be produced correspondingly therefrom.

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 in 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 downsizing of copying machines and the like,
Piezoelectric transformers are being used in place of winding transformers in high-voltage power supply devices. The piezoelectric transformer is subjected to polarization treatment in the thickness direction and the length direction of a ferroelectric material such as barium titanate or lead zirconate titanate (PZT), and is a vibration formed on one side in the length direction of the dielectric material. When an alternating voltage is applied to the part, it is known as a voltage converter that outputs a high voltage from a power generation part 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, through a pair of input electrodes provided so as to sandwich the thickness direction (or polarization direction) of the vibrating portion,
A drive circuit that applies an alternating voltage (or an alternating voltage) to the vibrating section is required.

On the other hand, in order to obtain a high voltage output from the power generation unit, in addition to setting the dimensional relationship between the vibration unit of the piezoelectric transformer and the power generation unit and an appropriate drive frequency, the input voltage to the vibration unit is made as high as possible. Therefore, a high voltage output type driving circuit is required. Japanese Unexamined Patent Publication (Kokai) No. 6-53569 discloses a method for raising the input electrode to the vibrating portion of the piezoelectric transformer 200.
There is one disclosed in the publication, which is shown in FIG. In the figure, in the conventional power supply device, the primary winding 400a is connected between the power supply and the ground GND, and the secondary winding 400b is connected between the first input electrode 6 of the piezoelectric transformer 200 and the ground GND. The boosting transformer 400 includes the primary winding 400a and the secondary winding 400b. The step-up transformer 400 steps up the alternating current voltage from the power source at a predetermined step-up ratio to apply a drive voltage between the first and second input electrodes 6 and 7 of the piezoelectric transformer 200.

[0004]

However, in the high voltage output type drive circuit, when the step-up transformer 400 formed of the winding transformer connected to the preceding stage of the piezoelectric transformer is used, the size of the device itself becomes large, and There is a problem that the circuit configuration becomes complicated. The present invention has been made to solve the above problems, and an object thereof is to provide a power supply device capable of generating a high voltage with a simple configuration.

[0005]

A power supply device according to the present invention comprises a drive unit formed by arranging a pair of input electrodes on a dielectric and a power generation unit formed by arranging an output electrode on the dielectric. And a drive circuit connected to a pair of input electrodes of a drive unit of the piezoelectric transformer to drive the piezoelectric transformer, the drive circuit outputs an alternating control signal of a predetermined frequency. Oscillator circuit,
An on / off controllable switching control element that converts a DC power supply voltage into an alternating voltage according to the alternating control signal given to a control electrode and supplies the piezoelectric transformer, and is inserted in a supply path of the DC power supply voltage of the switching element. And a flyback coil that has been made.

Further, the power supply device according to the present invention, if necessary, a detection circuit for detecting the voltage value output from the output electrode of the piezoelectric transformer, and the detected voltage value is input via a feedback circuit, A control circuit that drives and controls the drive circuit based on the voltage value, and a buffer circuit that prevents the detection circuit and the control circuit from interfering with each other in the feedback circuit are provided.

[0007]

According to the present invention, the oscillator circuit outputs a control signal having a predetermined frequency (resonance frequency of the piezoelectric element), and this control signal is input to the control electrode of the switching control element. The switching element is turned on / off according to the alternating control signal given to the control electrode, converts the DC power supply voltage into an alternating voltage, and supplies the alternating voltage to the piezoelectric transformer. When the switching control element is turned on, energy due to the back electromotive force is accumulated in the flyback coil, and this accumulated energy is superimposed on the DC power supply voltage when the switching control element is turned off, and becomes a high-voltage drive voltage to the piezoelectric transformer. Supplied. As a result, an input voltage having a large amplitude is applied to the vibration part of the piezoelectric transformer, and an output voltage having a large amplitude can be obtained from the power generation part of the piezoelectric transformer.

Further, in the present invention, by interposing a buffer circuit in the feedback circuit between the detection circuit and the control circuit, it is possible to prevent interference between the detection circuit and the control circuit whose voltage values greatly differ. Therefore, feedback control can be properly performed in the high-voltage output power supply device.

[0009]

【Example】

(First Embodiment of the Present Invention) A power supply device according to a first embodiment of the present invention will be described with reference to FIG. FIG. 1 shows a circuit configuration diagram of the power supply device according to the present embodiment. The power supply device according to the present embodiment is a piezoelectric transformer 20 formed of a ferroelectric material such as barium titanate or lead zirconate titanate (PZT).
0, a drive circuit 100 that supplies the drive voltage VB to the piezoelectric transformer 200, and an output circuit 300 that supplies the output voltage VC from the piezoelectric transformer 200 to the load 13.

The driving circuit 100 includes an N-channel MOSFET (Metal Oxide Si) which is a switching element.
licon FET) 3 and the oscillation IC 1 are basically used. The gate electrode of the MOSFET 3 is connected to the oscillation control signal output terminal of the oscillation IC 1 via the resistor R2, and the Zener diode 2 is connected to the ground GND. The drain electrode of the MOSFET 3 is connected to the power supply voltage VP via the flyback coil 4.
And the drain electrode is connected to the first input electrode 6 of the piezoelectric transformer 200 to supply the drive voltage VB. The source electrode of this MOSFET 3 is grounded. The oscillation IC 1
The variable resistor 5 is connected to the ground GND, and the variable resistor 5 arbitrarily changes its resistance value to set and adjust the oscillation frequency.

The piezoelectric transformer 200 includes a first and a second.
The vibrating portion formed between the input electrodes 6 and 7 and the power generating portion formed by disposing the output electrode 8 in a region other than the vibrating portion. This vibrating part is the symbol +,
The driving circuit 100 is connected between the first input electrode 6 on the positive side (+) of the polarization direction and the second input electrode 7 on the negative side (-) of the polarization direction. . In this state, the drive voltage VB is applied to the vibrating portion of the piezoelectric transformer 200 with a positive bias. The output circuit 300 is connected via the output electrode 8 arranged at the end of the power generation unit,
An output voltage is supplied to the load 13 via the output circuit 300.

The output circuit 300 includes a coupling capacitor 9 connected to the output electrode 8 and a rectifying diode 1.
A double-wave rectification circuit composed of 0 and 11 and a smoothing capacitor 12 are provided. The load 13 is connected to both ends of the smoothing capacitor 12. The rectifier circuit may be a bridge type.

Next, the operation of this embodiment based on the above configuration will be described. First, when a direct-current power supply voltage VP is applied to the input terminal of the drive circuit 100, the oscillation IC 1 causes the variable resistor 5
The control signal of the frequency f adjusted by is oscillated, and this control signal is output to the gate electrode of the MOSFET 3. When this control signal has a potential exceeding the threshold of MOSFET 3, M
OSFET3 turns on, power supply voltage VP, resistance R
1, a current flows through the flyback coil 4, the drain and source of the MOSFET 3, and the GND path. At this time,
Back electromotive force (flyback voltage) in the flyback coil 4
Occurs, and the energy is stored in the flyback coil 4. When the MOSFET 3 is turned on, the drive voltage VB becomes the GND potential, and the output electrode 8 of the piezoelectric transformer 200 outputs a negative (-) output voltage VC.

On the other hand, the control signal from the oscillation IC 1 is MO
When the potential is lower than the threshold of SFET3, the MOSFET
T3 is turned off, and the power supply voltage VP is the piezoelectric transformer 20.
0 to the first input electrode 6. At this time, the energy stored in the flyback coil 4 causes the first
A voltage having a value obtained by superimposing a flyback voltage on the power supply voltage VP is applied to the input electrode 6. As a result, the output voltage V output from the output electrode 8 of the piezoelectric transformer 200
C has a higher voltage than when the power supply voltage VP is simply supplied. The output voltage VC at this time is a positive (+) potential.

Output voltage V generated by the piezoelectric transformer 200
C is converted into direct current by a double-wave rectification circuit composed of a coupling capacitor 9, diodes 10 and 11, and is supplied to a load 13 via a smoothing capacitor 12. In addition,
In the above-described embodiment, the N-channel MOSFET 3 is used as the switching element, but a P-channel MOSFET may be used.
Further, it can be constituted by pnp type or npn type bipolar transistors. In these cases,
In both cases, the flyback voltage can be generated by the flyback coil 4 and a higher voltage superimposed on the power supply voltage Vp can be applied to the first input electrode 6 as in the above-described embodiments.

(Second Embodiment of the Present Invention) FIG. 2 is a circuit configuration diagram of a second embodiment of the present invention. The power supply device according to the second embodiment is provided with a drive circuit 100, a piezoelectric transformer 200, and an output circuit 300 in common, and the output voltage VC from the output circuit 300 is the same as in the embodiment shown in FIG.
The feedback voltage VFB based on the feedback voltage VFB is fed back to the oscillation IC 1 forming the drive circuit 100 by the feedback circuit 15,
The feedback control is performed by the separately excited oscillation so that the oscillation frequency of the oscillation IC 1 follows by the FB. This oscillating IC 1 includes an operational amplifier, and this operational amplifier forms a detection circuit with a voltage dividing resistance value R15 and the oscillating IC 1
It acts as a buffer circuit that prevents interference between the circuits due to the potential difference with the internal oscillation circuit.

Further, FIG. 3 shows a configuration in which the separately excited oscillation is performed similarly to the embodiment shown in FIG. 2, but the feedback current IFB is fed back to the oscillation IC 1 via the feedback circuit 15a.
When the feedback current IFB is input to the oscillation IC1, it is converted into a predetermined voltage by the resistance of the oscillation IC1, and the converted voltage is added to the voltage specified by the variable resistor VR5 or the like to generate the oscillation IC1. Control with the oscillation frequency of.
Also in the embodiment shown in FIG. 3, the output voltage VC is kept constant by using the feedback voltage VFB divided by the resistor R15 and the variable resistor VR15 as feedback control as in the embodiment shown in FIG. In addition to maintaining, the load 13 acts as a protection circuit when the load 13 is unloaded.

(Third Embodiment of the Present Invention) FIG. 4 is a circuit configuration diagram of a third embodiment of the present invention. The power supply device according to the third embodiment has a drive circuit 101 (corresponding to 100 in FIG. 1) similar to the embodiments described in FIG.
The piezoelectric transformer 200 and the output circuit 300 are provided in common,
This drive circuit 101 includes bipolar transistors 21 and 3
1. A voltage controlled oscillator circuit (hereinafter referred to as VCO) 1 including a push-pull type drive circuit and an operational amplifier 1
9 is formed by the oscillation circuit, and the feedback voltage VFB based on the output voltage VC from the output circuit 300 is supplied to the low-pass filter 17 and the buffer circuit 1 by the feedback circuit 15.
It is configured to perform feedback control by self-oscillation so that the frequency is followed by feedback to the VCO 19 via 8.

The feedback circuit 15 generates a feedback voltage VFB based on the output voltage VC from a connection midpoint of a monitor circuit composed of a resistor R15 and a variable resistor VR15 connected in parallel to the load 13 and feeds back the feedback voltage VFB. Composed. The low-pass filter 17 is connected to the feedback circuit 15, and the low-pass filter 17 is configured to remove the noise component superimposed on the feedback voltage VFB of the feedback circuit 15. In addition, since a phase delay occurs due to the inductance component of the line, the phase delay is advanced by the capacitor 17 and V
It is configured to improve the response by maintaining the frequency oscillated by the CO 19 at an appropriate value.

The buffer circuit 18 includes a detection circuit formed as a voltage dividing circuit of the resistor R15 and the variable resistor VR15,
It is configured so as to eliminate interference with each circuit after the VCO 19 connected to the subsequent stage. In the buffer circuit 18, the resistance R15 of the detection circuit is set in the order of mega ohm such as 15 MΩ, whereas the variable resistance VR of the VCO 19 is set.
Since 19 is set on the order of several kilo-ohms such as several tens KΩ and greatly differs, it is possible to prevent potential difference interference based on this difference.

The VCO 19 is constructed so that the output of the buffer circuit 18 is input via a resistor R19, and a control signal VA having a duty ratio determined by a variable resistor VR19 and a capacitor C19 is generated and output. Also, this VCO
The control operation of 19 is controlled so as to increase the oscillation frequency of the control signal VA to decrease the voltage value of the output voltage VC when the feedback voltage VFB which is the non-inverting input is high, and the feedback voltage VFB of the non-inverting input. Is low, the control signal VA is controlled to lower the oscillation frequency of the control signal VA and increase the voltage value of the output voltage VC.

A Zener diode ZD19 is connected between the resistor R19 of the non-inverting terminal of the VCO 19 and the power source VP, and this Zener diode ZD19 is used for starting up the present apparatus. That is, since the device of this embodiment is driven by self-oscillation, the starting voltage of the direct current from the power source VP is input to the non-inverting terminal only once at the beginning through the Zener diode ZD19.

This starting voltage is the Zener diode ZD19.
Is input to the non-inverting terminal of the VCO 19, a control signal VA of a predetermined cycle is generated, which is n of the drive circuit 101.
A switching operation for complementarily turning on or off the pn-type or pnp-type bipolar transistor 21 or 31 is performed.

Although the feedback voltage VFB is used as the non-inverting input of the VCO 19 in the above embodiment,
As shown in FIG. 5, the feedback current IFB may be used for the non-inverting input of the VCO 19. This feedback current IFB connects the resistor R15a to the ground GND side of the voltage doubler rectifier circuit forming the output circuit 300, and from the midpoint of this connection, the feedback circuit 15a and the buffer circuit 18 to the VCO1.
9. Also in the embodiment shown in FIG. 5, the output voltage VC is kept constant by using the feedback voltage VFB divided by the resistor R15 and the variable resistor VR15 as feedback control as in the embodiment shown in FIG. While maintaining the voltage of, the load 13 acts as a protection circuit when there is no load.

[0025]

As described above, according to the present invention, the flyback coil is inserted in the DC power supply voltage supply path of the switching element, and the energy due to the back electromotive force accumulated at the turn-on of the switching control element is applied to the switching control element. Since a high drive voltage is supplied to the piezoelectric transformer by superimposing it on the DC power supply voltage at the time of turn off, it is possible to apply a drive voltage with a large amplitude to the vibration part of the piezoelectric transformer. It is possible to obtain a high voltage with a large amplitude. Further, in the present invention, by interposing the buffer circuit in the feedback circuit between the detection circuit and the control circuit, it is possible to prevent the interference between the detection circuit and the control circuit, which greatly differ in voltage value. This has an effect that the feedback control in the voltage output power supply device can be appropriately performed.

[Brief description of drawings]

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

FIG. 2 is a circuit diagram of a power supply device according to a second embodiment of the present invention.

FIG. 3 is a circuit diagram of a power supply device according to another embodiment of the present invention.

FIG. 4 is a circuit diagram of a power supply device according to a third embodiment of the present invention.

FIG. 5 is a circuit diagram of a power supply device according to another embodiment of the present invention.

FIG. 6 is a circuit configuration diagram of a conventional power supply device.

[Explanation of symbols]

 1 Oscillation IC 2 Zener diode 3 MOSFET 4 Flyback coil 5 Variable resistance 6 1st input electrode 7 2nd input electrode 8 Output electrode 9 Coupling capacitor 10 Rectifying diode 11 Rectifying diode 12 Smoothing capacitor 13 Load 15, 15a Feedback circuit 17 Low pass filter 18 Buffer circuit 19 VCO 21, 31 Bipolar transistor 100 Driving circuit 200 Piezoelectric transformer 300 Output circuit VP DC power supply voltage VA Control signal VB Driving voltage VC Output voltage

Claims (2)

[Claims] 1. A piezoelectric transformer comprising a drive section formed by arranging a pair of input electrodes on a dielectric body and a power generation section formed by arranging output electrodes on a dielectric body, and a drive section for the piezoelectric transformer. A power supply device including a drive circuit connected to the pair of input electrodes for driving the piezoelectric transformer, the drive circuit outputting an alternating control signal of a predetermined frequency, and the alternating control applied to the control electrode. An ON / OFF controllable switching control element for converting a DC power supply voltage into an alternating voltage according to a signal and supplying the piezoelectric transformer, and a flyback coil inserted in the DC power supply voltage supply path of the switching element are provided. A power supply device characterized in that 2. The power supply device according to claim 1, wherein a detection circuit that detects a voltage value output from the output electrode of the piezoelectric transformer, and the detected voltage value are input via a feedback circuit, A power supply device comprising: a control circuit that drives and controls the drive circuit based on the voltage value; and a buffer circuit that prevents the feedback circuit from interfering with the detection circuit and the control circuit.