JP3396017B2 - Piezoelectric transformer DC 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 DC power source using a piezoelectric transformer for limiting or controlling an output current,
For example, it is used for high-voltage DC power supplies such as electrophotographic devices, air cleaning devices, and sterilization devices.

[0002]

2. Description of the Related Art Conventionally, a DC power supply for boosting and rectifying and smoothing a primary voltage by using a winding transformer has been used as a high voltage power supply. However, a DC power supply using a winding transformer has problems that electromagnetic noise is generated from the transformer, the transformer is large and heavy, the cost is high, and the power conversion efficiency of the transformer is poor. Recently, piezoelectric transformers are often used instead of winding transformers.

In a piezoelectric transformer used for a high voltage power supply, when an oscillating voltage is applied to the piezoelectric element in the thickness direction, that is, on the primary side,
Mechanical vibration is generated in the length direction, and this mechanical vibration is converted into voltage vibration and taken out in the length direction, that is, the secondary side. At this time, the primary side voltage is boosted corresponding to the ratio of the dimension in the length direction and the dimension in the thickness direction.

[0004] DC power supply using such a piezoelectric transformer, small size, light weight, no electromagnetic noise, the power conversion efficiency is good, there are advantages such, the inexpensive piezoelectric transformer used for general purpose, conventional Unlike the winding transformer, the input (primary side) and the output (secondary side) have a non-insulated structure. Along with this, there is a problem that it is difficult to detect the magnitude of the current flowing through the load (one end grounded) connected to the output of the DC power supply inside the DC power supply. Therefore, a method of separating the load from grounding without grounding the power supply connected to the input side of the DC power supply,
Alternatively, the present inventor has developed a circuit in which an insulating transformer is added to the input of the piezoelectric transformer and the output current is detected in the same manner as the conventional winding transformer (Japanese Patent Application No. 8-16416).
No. 4).

In Japanese Patent Publication No. 59-33991, an insulation transformer is not added, and a resistor is inserted between the diode of the multiple voltage rectifier circuit and the ground to detect an abnormal current of the output and to detect a short-circuited load. It shows how to protect.

[0006]

However, if the ground of the load and the ground of the power supply input to the DC power supply are separated,
There arises a problem that the electromagnetic noise generated from the device becomes large or weak to the electromagnetic noise from the outside.
Therefore, if a method of adding an auxiliary insulating transformer is adopted, there arises a problem that it is impossible to achieve a sufficiently small size, light weight, and low cost. In the multiple voltage rectifier circuit disclosed in Japanese Patent Publication No. 59-33991, a first diode is connected between the secondary side of the piezoelectric transformer and the output terminal, and a second diode is connected between the secondary side of the piezoelectric transformer and ground. In the rectifier circuit connecting the two, the load current is detected by the current flowing in the second diode. In this case, although the current flowing in the load and the detected current are almost proportional, there is a problem that the error is large.

A first object of the present invention is to provide a DC power supply which is simple and has no problem of electromagnetic noise without separating the ground of the power supply supplied to the DC power supply from the ground of the load.
A second object is to detect the output current inexpensively, compactly and lightly without adding an auxiliary insulating transformer, and a third object is to make the current detection highly accurate.

[0008]

[Means for Solving the Problems] (1) A piezoelectric transformer DC power supply of the present invention includes a piezoelectric transformer (10) whose primary side and secondary side are not insulated; and a primary side (11, 12) of the piezoelectric transformer. Switch voltage generating means (50 to 64) for giving a switch voltage; a first diode () connected in the direction of the polarity of the output voltage between the output end (13) of the piezoelectric transformer and the DC power supply output end (4). 20), this
Smoothing code, one end of which is connected to the output side end of the first diode of
Capacitor (21) and a second diode in which one end is connected to the output end of the piezoelectric transformer in the opposite polarity to the first diode and the other end (Cc) is connected to the other end of the smoothing capacitor (21). (twenty two),
Rectifying and smoothing means (20 to 22) for converting the switch voltage generated on the secondary side of the piezoelectric transformer into a direct current;
End is connected to the other end (Cc) and the other end is the ground end (3, 5)
Output detection means including a resistor (23) for current detection connected to
(23,24); and the smoothing capacitor (21) is charged.
In the period when the current is discharged (bc in FIG. 4),
Based on the voltage value (VR23) of the resistor (23) for current detection
A control means (50) for controlling the switch voltage applied to the primary side of the piezoelectric transformer so as to make the flow constant is provided.

For ease of understanding, reference numerals are given in parentheses for reference to corresponding elements or corresponding portions in embodiments described later with reference to the drawings.

According to this, the switch voltage generating means (50
~ 64) switch voltage generated by the piezoelectric transformer (10)
Piezoelectric transformer (10) by applying to the secondary side (11, 12)
A high voltage AC voltage is generated on the secondary side (13, 12) of the. The high-voltage AC voltage is rectified and smoothed by the rectifying / smoothing means (20-22), whereby a high-voltage DC voltage is generated at the DC power output terminal (4).

The load current supplied from the DC power supply output terminal (4) to the load (CH / OPC) flows through the current detection resistor (23), which causes a voltage proportional to the load current (load current detection voltage). It appears at the other end (Cc) of the second diode (22). Control means
(50) controls the switch voltage applied to the primary side (11, 12) of the piezoelectric transformer according to this load current detection voltage. For example, when the control means (50) controls the switch voltage so that the load current detection voltage matches the set value, the load current is controlled to the set value.

Due to the combination of the rectifying / smoothing means (20-22) and the output detecting means (23, 24), the AC voltage generated by the piezoelectric transformer (10) is forwarded to the first diode (20). The flow of charge flowing into the smoothing capacitor (21) at the time of the direction, the load current flowing out from the smoothing capacitor (21) to the load, and the reverse current flowing into the second diode (22) are the resistance for current detection.
Run through (23) to the grounding end (3, 5). Smoothing capacitor
The absolute value of the reverse current flowing through the second diode (22) and that of the charging current flowing into (21) are approximately the same value, but they cancel because they are in opposite directions, and the smoothing capacitor (21) Since only the load current flowing out from the load to the load remains, the output amount (output current value) can be obtained from this. For example, if a capacitor (24) is connected in parallel with the current detection resistor (23), the voltage appearing on this capacitor (24) will change to the smoothing capacitor (2).
Indicates the load current flowing from 1) to the load.

The piezoelectric transformer DC power supply of the present invention uses the piezoelectric transformer (10) having a non-insulated structure on the primary side and the secondary side,
Since it is not necessary to separate the load ground (5) from the power supply ground (3) input to the DC power supply, and the output current can be accurately detected with a simple circuit, highly accurate output current control is possible. Therefore, the piezoelectric transformer (10) to be used may have a simple structure and a low cost, and since the detection circuit is simple and inexpensive, a simple, inexpensive, small and lightweight DC power source that can perform output current control with high accuracy. Can be provided.

[0014]

DETAILED DESCRIPTION OF THE INVENTION

(2) The control means (50) is the other end of the second diode (22).
The switch voltage applied to the piezoelectric transformer (10) is controlled so that the load current detection voltage of (Cc) becomes a set value. According to this, the load current becomes a constant current determined by the set value.

(3) Damping in parallel with the smoothing capacitor (21)
Resistors (25,26) are connected. According to this, the piezoelectric characteristics of the piezoelectric transformer (10) are not deteriorated by the no-load driving.

(4) The control means (50) controls the switch voltage applied to the piezoelectric transformer (10) in accordance with the divided voltage of the dummy resistor. According to this, the piezoelectric characteristic of the piezoelectric transformer (10) is not deteriorated by no-load driving, and the output voltage of the piezoelectric transformer (10) can be limited within a required range. The voltage is automatically suppressed within the required range.

(5) The first diode (20) has a negative polarity that energizes in the direction from the DC power output terminal (4) to the output terminal (13) of the piezoelectric transformer (10) and shuts off in the opposite direction. Yes; the control means (50) controls the switch voltage of the piezoelectric transformer so that the voltage of the other end (Cc) of the second diode (22) matches the set value (Rv), and the dummy resistor ( Since the divided voltage of (25, 26) has a negative polarity, it is converted to a positive polarity and this is converted into an abnormal load reference voltage.
Compared with (Rv), the switch voltage of the piezoelectric transformer is limited when the absolute value of the divided voltage of the dummy resistor becomes large.
According to this, in the mode in which a negative voltage is applied to the load with respect to the ground, the output voltage is abnormal due to load abnormality, etc.
When it goes higher than v), the output voltage rise is suppressed. This mode is a constant current output power source that outputs a negative voltage, and the output voltage is limited to a predetermined voltage even when the load becomes abnormal, so that safety can be ensured.

(6) The first diode (20) has a positive polarity that energizes in the direction from the output end of the piezoelectric transformer (10) to the DC power supply output end (4) and shuts off in the opposite direction; control Means (5
0) controls the switch voltage of the piezoelectric transformer so that the voltage obtained by converting the voltage at the other end (Cc) of the second diode (22) to the positive polarity matches the set value, and the dummy resistor (25 When the divided voltage of (26) becomes larger than the abnormal load reference voltage (Rv), the switch voltage of the piezoelectric transformer is limited. According to this, in a mode in which a positive voltage is applied to the load with respect to the ground, when the output voltage rises above the abnormal load reference voltage (Rv) due to a load abnormality or the like, the rise of the output voltage is suppressed. This mode is a constant current output power supply that outputs a positive voltage, and limits the output voltage to a predetermined voltage even when the load becomes abnormal, so that safety can be ensured.

Other objects and features of the present invention will become apparent from the following description of embodiments with reference to the drawings.

[0020]

【Example】

First Embodiment FIG. 1 shows a mode in which the piezoelectric transformer DC high voltage power supply HVU of the first embodiment of the present invention is connected to an electrophotographic apparatus. The power supply terminals PSU of the DC high-voltage power supply HVU are connected to power supply terminals (1) and (2) to supply DC 24V. The DC high-voltage power supply HVU boosts the DC voltage (DC 24V) of the power supply PSU to a high-voltage DC voltage (DC 4KV to 8KV), and gives an oscillating voltage to the primary side (11) of the piezoelectric transformer 10. Switch voltage generator circuit (50c, 6
3, 64) are connected to the secondary side 13 of the piezoelectric transformer 10.
The rectifying and smoothing circuit (20-22) and the current detection circuit (2
3, 24) are connected.

Switch voltage generation circuit (50c, 63, 6)
4) is composed of a control circuit 50c, a transistor 63 for exciting and driving the primary side (11) of the piezoelectric transformer 10, and a choke coil 64. The configuration of the control circuit 50c is the same as that shown in FIG. 2, and the control IC 50 (FIG. 2) in the control circuit 50c incorporates a pulse oscillator and its control circuit to drive the transistor 63 on / off. Therefore, one of the piezoelectric transformer 10 is connected via the choke coil 64.
DC 2 from the power supply PSU supplied to the secondary side (11)
4V is turned on / off by the transistor 63 and applied to the primary side (11) of the piezoelectric transformer 10. This is the oscillating voltage.

When an oscillating voltage (primary voltage) is applied to the piezoelectric transformer 10 used for the DC high-voltage power supply HVU in the thickness direction, that is, on the primary side (terminals 11 and 12), the piezoelectric transformer 10 mechanically vibrates in the longitudinal direction. This mechanical vibration causes a high-voltage vibration voltage (secondary voltage), and this high-voltage vibration voltage is taken out as an electrical output from the longitudinal direction, that is, from the secondary side (terminals 13 and 12). At this time, the voltage is boosted corresponding to the ratio of the dimension in the length direction and the dimension in the thickness direction. Further, the level of the output (secondary voltage) changes in proportion to the pulse width of the oscillating voltage applied to the primary side.

A charger CH for charging the photoconductor OPC of the electrophotographic apparatus ECU is connected to the output terminal 4 of the DC high-voltage power supply HVU. DC high voltage power supply H to charger CH
When a high-voltage DC voltage generated by VU is applied, corona discharge occurs and the surface of the photoconductor OPC is charged. Although the charger CH shown in the drawing has a structure in which a wire is stretched, the surface of the photoconductor OPC can be charged in the same manner with a contact type charger using a conductive roller.

The photoconductor OPC of the electrophotographic apparatus ECU is fixed to a metallic structure which is a framework of the electrophotographic apparatus ECU, and the DC high-voltage power supply HVU and the power supply PSU are also fixed to the metallic structure. Therefore, they are electrically grounded (GND) in common. Therefore, the output current from the output terminal (4) of the DC high voltage power supply HVU is
It is returned to the ground terminal (5) of the DC high voltage power supply HVU via H, the photoconductor OPC and the metallic structure. The ground terminal (5) has the same potential as the ground terminal (3) of the power supply PSU.

Image light 71 is projected on the surface of the charged photoconductor (photosensitive drum) OPC, and an electrostatic latent image is formed on the surface of the OPC. This is the developing roller 7 of the developing unit.
2 develops. At this time, a DC voltage supplied from the developing bias power supply circuit 73 is applied to the developing roller 72 in order to obtain a toner image having an optimum density. The developed toner image is brought into close contact with the photoconductor OPC by a transfer sheet, and a transfer charger 75 connected to the output of the transfer high-voltage power supply circuit 74 applies a potential from the rear side of the transfer paper to give a potential on the photoconductor OPC. Transfer the development onto a transfer paper. The transfer paper is sent to a fixing device (not shown), where the toner image is heated and pressed and fixed to the transfer paper. The surface of the photoconductor OPC which has been transferred is discharged by the charge eliminator 76, and the process proceeds to the next step.

In the electrophotographic apparatus ECU, the charger C
The stability of the charging current flowing through the photoreceptor OPC via H affects the image quality. Therefore, it is necessary to control the output current of the DC high-voltage power supply HVU, which is the current supply source, to be constant.

Therefore, the DC high-voltage power supply HVU performs so-called pulse width control so that a predetermined output is obtained. The pulse width control can be easily configured with a general-purpose IC. The control IC 50 (FIG. 2) in the control circuit 50 of the present embodiment determines the voltage generated by the current detection resistor 23 (proportional to the current value flowing through the resistor 23), that is, the difference between the voltage at the connection point Cc and the set voltage Rv. Accordingly, the width of the drive pulse of the transistor 63 is changed,
The output current is controlled to be constant.

The negative half wave of the high voltage AC voltage obtained from the output terminal (13) of the piezoelectric transformer 10 is rectified and smoothed by the first diode 20 and the smoothing capacitor 21 to obtain high voltage DC. The second diode 22 connected to the output terminal (13) of the piezoelectric transformer 10 causes a positive half wave of the high voltage AC voltage generated by the piezoelectric transformer 10 to flow through the current detection resistor 23.

FIG. 4 shows a voltage waveform VR23 between terminals of the current detecting resistor 23 and a voltage waveform V11 of the primary side of the piezoelectric transformer 10.
And the relationship of the secondary side voltage waveform V13 of the piezoelectric transformer. The horizontal axis represents time (scale interval is 2 μsec), and the vertical axis is voltage value (scale interval is 100 V or 1 KV). Between point a and point b shown in FIG. 4, voltage V1 is applied to the primary side of the piezoelectric transformer.
When 1 is applied, a voltage V13 is generated on the secondary side of the piezoelectric transformer, and this voltage causes a current to flow in the circuit of the current detection resistor 23, the smoothing capacitor 21 and the first diode 20, and charges the smoothing capacitor 21. During this period, a negative voltage indicated by VR23 is generated in the current detection resistor 23.

Next, from the point b to the point c, the charged current of the smoothing capacitor 21 is discharged through the current detection resistor 23 and the load (CH / OPC), and during this period, the current detection resistor 23 is discharged. Generates a positive voltage indicated by VR23.

Next, between the points c and d, the output of the piezoelectric transformer is about to have the opposite polarity, and the second rectifying diode 2
2. A current flows in the circuit of the current detection resistor 23, and a large positive voltage is generated in the current detection resistor 23 as indicated by VR23. Here, the voltage between the voltage and cd between ab the current sensing resistor 23 is offset because the polarity substantially equal in magnitude is reversed, remains as the voltage the voltage between bc is proportional to the load current. That is, the voltage VR23 between the terminals of the current detection resistor 23.
The voltage averaged (smoothed) by the capacitor 24 is proportional to the current flowing through the load. That is, the current detection resistor 23
And the voltage between the terminals of the capacitor 24 (potential at the connection point Cc)
Is a voltage representing the output amount (load current), and is fed back to the control circuit 50c to output the output current (photoconductor O).
The charging current flowing through the PC is controlled to be constant.

The structure of the control circuit 50c of the first embodiment (FIG. 1) is the same as that of FIG. 2 (second embodiment).
The feedback control (constant current control) of the output current of c is
Since it is similar to the second embodiment, the control circuit 5 of the first embodiment is
The detailed description of the configuration and function of 0c is omitted here,
The second embodiment (Fig. 2) will be described in detail below.

-Second Embodiment- FIG. 2 shows the configuration of a DC high voltage power supply HVU according to a second embodiment. The DC high voltage power supply HVU of the second embodiment has a function of limiting the output voltage in addition to the constant current control function. The control circuit 50c includes a control IC 50 and peripheral circuits. In this example, a general-purpose IC TL494 manufactured by TI (Texas Instruments) or an equivalent product was used. Control IC5
0 includes two operational amplifiers, a pulse oscillator, an amplifier, a constant voltage circuit, and the like.

The power source of the control IC 50 is the transistor 32.
It is supplied from the power supply power supply PSU connected to the power supply power supply terminal 1 via. The transistor 32 has a trigger terminal (2)
It is turned on / off by setting the signal of the high level H / low level L. Bias resistors 30 and 31 are connected to the base of the transistor 32. When the signal of the trigger terminal (2) is set to H, the transistor 32 is turned off (non-conducting) and the power supply to the control IC 50 is stopped, so that the output of the piezoelectric transformer 10 is stopped and the signal of the trigger terminal (2) is set to L. Then, the transistor 32 is turned on (conducted) and power is supplied to the control IC 50.
The piezoelectric transformer 10 operates to generate high voltage. In this embodiment, a trigger signal is supplied to the trigger terminal (2) from a controller (not shown) of the electrophotographic apparatus ECU.

The pulse generated by the pulse oscillator incorporated in the control IC 50 is connected to the gate of the external switching transistor 63. The resistors 61 and 62 are the transistor 6
3 and a bias resistor.

Primary side terminal (11) of the piezoelectric transformer 10
Is connected to the power supply terminal (1) and the source of the transistor 63 via the choke 64, and is connected to the other primary side terminal (1).
2) is connected to the ground terminals (3) and (5). Therefore, the transistor 63 is provided on the primary side of the piezoelectric transformer 10.
A pulse voltage generated by turning on / off of is applied.

As a result, an AC high voltage is obtained from the secondary side terminal (13) of the piezoelectric transformer 10, so that the rectifying and smoothing circuit formed by the first diode 20, the second diode 22 and the smoothing capacitor 21 produces a high voltage DC voltage. The voltage.

The second diode 22, one end of which is connected to the secondary side terminal (13) of the piezoelectric transformer 10, is the piezoelectric transformer 1.
It acts to pass the current flowing into 0. That is, the negative half-wave of the alternating current generated on the secondary side of the piezoelectric transformer 10 charges the capacitor 21, but the positive half-wave is applied to the current detection resistor 23 through the second diode 22 (discharges through the resistor 23).

A current detection resistor 23 is connected between the other end of the second diode 22 and the connection point (Cc) of the smoothing capacitor 21 and the ground (5). And a noise absorbing capacitor 24 are connected.

Dummy resistors 25 and 26 are connected in series at both ends of the smoothing capacitor 21 of the rectifying / smoothing circuit in order to stabilize the control and ensure safety under no load. One of the dummy resistors 26 is used for detecting the output voltage, and a capacitor 27 is connected in parallel with the resistor 26. Since the current flowing in the series circuit of the dummy resistors 25 and 26 flows only between the dummy resistors 25 and 26, the current does not pass through the current detecting resistor 23, and the output current detection error does not occur.

Output voltage of DC high-voltage power supply HVU (negative polarity)
Voltage divided by dummy resistors 25 and 26, that is, resistor 2
The voltage (Vc) of 6 is fed back to the control IC 50 for the output voltage limit control. The capacitor 27 connected in parallel with the resistor 26 is for noise absorption. The voltage (potential) at this point viewed from the ground (GND) changes depending on the potential of the current detection resistor 23. However, when the output is subjected to constant current control, the current detection voltage generated by the current detection resistor 23 is constant, so the relationship between the output voltage and the voltage detection voltage is fixed, and the voltage (Vc) of the resistor 26 is fixed. From this, the output voltage can be uniquely obtained.

The 5V output voltage of the constant voltage circuit built in the control IC 50 is divided by the resistors 42 and 43, and the divided voltage Rv (hereinafter referred to as the reference voltage Rv) is the current for performing the constant current control. Use as the reference voltage (set value). At the same time, this voltage is also used as a voltage reference voltage (abnormal load reference voltage) for limiting the maximum output voltage.

Of the control IC 50 used for controlling the output current,
The reference voltage Rv is applied to the inverting input terminal of the first operational amplifier via the resistor 44, and the current detection voltage of the current detection resistor 23 is applied to the non-inverting input terminal. The capacitor 46 is connected between the input and output of the first operational amplifier and stabilizes the control.
The voltage V of the output voltage detecting resistor 26 which is also a dummy resistor
Since c has a negative polarity, it is converted to a positive polarity by adding it to the 5V power source built in the control IC 50 via the resistors 40 and 45. The polarity-converted voltage is applied to the inverting input terminal of the second operational amplifier used for voltage control of the control IC 50, and the reference voltage Rv is applied to the non-inverting input terminal via the resistor 41.

The switching frequency of the pulse oscillator incorporated in the control IC 50 is determined by the capacitor 48 and the resistor 49. Since the control IC 50 has a terminal that determines the maximum value of the pulse width to be output by the voltage given from the outside, the reference voltage Rv is also used for this purpose and is applied to this terminal via the resistor 47.

The first operational amplifier of the control IC 50 compares the reference voltage Rv with the current detection voltage of the current detection resistor 23, and changes the pulse width of the pulse oscillator incorporated in the control IC 50 according to the difference between them. The operational amplifier has a reference voltage Rv.
And a voltage obtained by converting the voltage Vc of the resistor 26 into a positive polarity are compared with each other, and when the voltage converted into a positive polarity becomes lower than the reference voltage Rv (the absolute value of the voltage Vc of the resistor 26 becomes large), a difference between them is found. Accordingly, the pulse width of the pulse oscillator having the control IC 50 is changed to be narrower. The pulse drives a transistor of an amplifier incorporated in the control IC 50. The collector of this transistor is connected to the power supply terminal (1) via the resistor 60, and the emitter thereof is connected to the gate of the external switching transistor 63 via the resistor 61.

By the way, when an abnormality occurs in the load and the output voltage becomes high, the control circuit 50c works so as to suppress it to a predetermined output voltage or less. When the output is unloaded (when the load is normally off or when the load is broken), the output current does not flow, so the current detection voltage (voltage of the resistor 23) is 0.
Is. Therefore, the potential at the connection point between the dummy resistors 25 and 26 (voltage of the resistor 26) is not affected by the current detection voltage (potential bias). That is, the voltage of the resistor 26 directly represents a value obtained by dividing the output voltage by the resistors 25 and 26.
In this state, the voltage of the resistor 26 is limited to the output voltage (maximum allowable voltage) corresponding to the reference voltage Rv by the voltage limiting control of the control IC 50. In particular, when the output current is used by being varied over a wide range, this limitation of the no-load voltage is effective.

Third Embodiment FIG. 3 shows a third embodiment in which the DC high voltage power supply HVU shown in FIG. 2 has a positive output. 2 shows the case where the output of the DC high voltage power supply HVU has a negative polarity, but in FIG. 3, the output has a positive polarity. Therefore, in the third embodiment, the polarities of the first and second diodes 20 and 22 are opposite to those in the first and second embodiments. In addition, since the voltage of the resistor 23, that is, the current detection voltage, has a negative polarity, it is converted to a positive polarity by adding it to the 5V power supply built in the control IC 50 via the resistors 40 and 45 and the inverted input terminal of the first operational amplifier. The reference voltage Rv is applied to the non-inverting input terminal through the resistor 41. Further, since the voltage of the dummy resistor 26 for detecting the output voltage has a positive polarity, this is applied to the non-inverting input terminal of the second operational amplifier without polarity conversion,
The reference voltage Rv is applied to the inverting input terminal via the resistor 44. Other configurations and functions are the same as those of the second embodiment described above, and the control IC 50 performs constant current control and output voltage control as in the second embodiment.

In each of the above-mentioned first to third embodiments, the control circuit 50c of the DC power source is of the separately excited oscillation type pulse width control, but a pulse frequency control method or a self excited oscillation type control circuit is used. May be adopted. Further, the DC high-voltage power supply HVU of the present invention can be used in the same configuration for a high-voltage power supply such as an air cleaning device and a sterilizer that uses high voltage. Furthermore, it can be used as a DC power source for devices for other purposes.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a high voltage DC power supply HVU according to a first embodiment of the present invention.

FIG. 2 is an electric circuit diagram showing a configuration of a high voltage DC power supply HVU according to a second embodiment of the present invention.

FIG. 3 is an electric circuit diagram showing a configuration of a high voltage DC HVU according to a third embodiment of the present invention.

FIG. 4 is a piezoelectric transformer 1 shown in FIGS. 1, 2 and 3.
7 is a graph showing voltage waveforms of the primary side, the secondary side of 0 and the current detection resistor 23.

[Explanation of symbols]

1: Power supply power supply terminal 2: Control terminal 3, 5: Ground terminal (GND) 4: Output terminal 10: Piezoelectric transformer 11: Piezoelectric transformer primary terminal (input terminal) 12: Piezoelectric transformer grounding terminal 13: Piezoelectric transformer secondary terminal (Output terminal) 2
0: 1st diode 21: Smoothing capacitor 22: 2nd diode 23: Current detection resistor 24: Bypass capacitor 25: Dummy resistor 26: Dummy resistor (voltage detection resistor) 27: Bypass capacitors 30, 31: Resistor 32: Transistors 40 to 45, 47, 49: Resistor 46, 48: Capacitor 50: Control IC 60 to 62: Resistor 63: Transistor 64: Choke coil 71: Image light 72: Developing device 73: Developing bias power supply circuit 74 : Transfer power supply circuit 75: Transfer charger 76: Static eliminator Cc: Connection point CH: Charger ECU: Electrophotographic device HVU: DC high-voltage power supply OPC: Photoconductor PSU: Power supply Rv: Reference voltage Vc: Resistor 26
Voltage

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-9-74744 (JP, A) JP-A-9-23643 (JP, A) JP-A-9-84335 (JP, A) JP-A-10- 12356 (JP, A) JP-A-8-237943 (JP, A) JP-A 61-220386 (JP, A) JP-A 5-64437 (JP, A) JP-A 5-110368 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H02M 3/24

Claims (6)

(57) [Claims] 1. A piezoelectric transformer whose primary side and secondary side are non-insulated; Switch voltage generating means for applying a switch voltage to the primary side of the piezoelectric transformer; Output voltage between the output end of the piezoelectric transformer and the DC power supply output end. The first diode connected in the direction of the
A smoothing capacitor with one end connected to the output end of one diode
And a second diode whose one end is connected to the output end of the piezoelectric transformer in a polarity opposite to that of the first diode and the other end is connected to the other end of the smoothing capacitor. Rectifying / smoothing means for converting a switch voltage generated on the side into a direct current; an output detecting means including a current detecting resistor having one end connected to the other end of the second diode and the other end connected to a ground end;
And the current charged in the smoothing capacitor is discharged
In the period, based on the voltage value of the current detection resistor
A piezoelectric transformer DC power supply, comprising: a control unit that controls a switch voltage applied to the primary side of the piezoelectric transformer so as to keep the output current constant . 2. The piezoelectric transformer DC power supply according to claim 1, wherein the control means controls the switch voltage applied to the piezoelectric transformer so that the voltage at the other end of the second diode becomes a set value. 3. The piezoelectric transformer DC power source according to claim 1, wherein a dummy resistor is connected in parallel with the smoothing capacitor. 4. The control means controls the switch voltage applied to the piezoelectric transformer in response to the divided voltage of the dummy resistor.
The piezoelectric transformer DC power supply according to claim 3. 5. The first diode has a negative polarity that energizes in the direction from the output end of the DC power source to the output end of the piezoelectric transformer and shuts off in the opposite direction; the control means is the second diode. The switch voltage of the piezoelectric transformer is controlled so that the voltage at the other end matches the set value, the divided voltage of the dummy resistor is converted to positive polarity, and this is compared with the abnormal load reference voltage to determine the amount of the dummy resistor. The piezoelectric transformer DC power supply according to claim 4, wherein the switch voltage of the piezoelectric transformer is limited when the absolute value of the piezoelectric voltage becomes large. 6. The first diode has a positive polarity that energizes in the direction from the output end of the piezoelectric transformer to the output end of the DC power supply and shuts off in the opposite direction; the control means is the second diode. The switch voltage of the piezoelectric transformer is controlled so that the voltage obtained by converting the voltage at the other end to positive polarity matches the set value, and when the divided voltage of the dummy resistor becomes larger than the abnormal load reference voltage, the switch voltage of the piezoelectric transformer. The piezoelectric transformer DC power supply according to claim 4.