JPH11341801A - High-voltage power unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the accuracy of the high-voltage output for a high-voltage transformer by changing the electric current flowing to the base of a switching element connected to the primary winding of the transformer from the base winding of the transformer with the converted DC voltage of the pulse width-modulated output of the transformer, and feeding back the voltage detected from the output winding of the transformer to a microcomputer. SOLUTION: One end of a base winding 20 of a high-voltage transformer 17 is connected to the base of a switching element 19, and the other end is connected to the microcomputer 24 of an electrophotographic device via an integrator 23. A load 29 is connected to the output winding 25 of the transformer 17 via a rectifying and smoothing circuit 28 composed of a diode 26 and a capacitor 27, and a detector 30 connected to the output winding 25 is connected to the microcomputer 24. The electric current flowing to the base of the element 19 varies depending upon the value obtained by integrating pulse width modulation(PWM), and with a collector current saturated, the switching element 19 is abruptly turned off. The electric current flowing to the base of the element 19 is controlled to a specific value, by means of a CPU 32 through an A/D converter 31 through feeding back the voltage generated across the output winding 25 to the microcomputer 24, and setting the winding 25 is set to a self-excited state with the PWM output from the microcomputer 24.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high voltage power supply for supplying a potential to a photosensitive member of an electrophotographic apparatus.

[0002]

2. Description of the Related Art A conventional high-voltage power supply of this type is configured as shown in FIG. That is, in FIG. 6, reference numeral 1 denotes a low-voltage DC power supply, and a series circuit of a primary winding 3 of a high-voltage transformer 2 and a switching transistor 4 is connected to the low-voltage power supply 1.

The base of the switching transistor 4 is connected to a base winding 5 of the high-voltage transformer 2. One end of the base winding 5 is connected to the collector of a transistor 6, and the emitter of the transistor 6 is connected via a base resistor 7. Connected to the low-voltage power supply 1. Further, the base of the transistor 6 is connected to the output terminal of the operational amplifier 8, and one of the input terminals of the operational amplifier 8 is connected to the reference power supply 9.

The secondary winding 10 of the high-voltage transformer 2 has a rectifying and smoothing circuit 1 comprising a diode 11 and a capacitor 12.
3 and a detection resistor 14 are connected. The detection resistor 14 is connected to the operational amplifier 8, detects the current flowing through the load 15 with the detection resistor 14, and detects the voltage with the voltage of the reference power supply 9 by the operational amplifier. It is configured to be controlled to be equal.

[0005]

However, such a conventional high-voltage power supply requires an operational amplifier 8 and its peripheral circuits for control, which is disadvantageous in terms of size and cost. .

An object of the present invention is to eliminate the above-mentioned disadvantages of the prior art and to provide a small, low-cost, high-precision high-voltage power supply.

[0007]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, a high-voltage power supply according to the present invention comprises a high-voltage transformer having a primary winding to which a DC power is input and an output winding for extracting an output; A switching element is connected to the primary winding in series, and the DC input is turned on and off by the switching element, and the voltage generated at the output winding of the high-voltage transformer is output via a rectifying and smoothing circuit connected to the output winding. In the high-voltage power supply device, a base winding is provided on the high-voltage transformer, and a current flowing from the base winding to the base of the switching element is converted to a direct current through an integrator for converting a PWM output of a microcomputer of the electrophotographic apparatus into a direct current. A means for changing the voltage is provided, and a detector for detecting the voltage or current of the output winding is provided. The pressure is obtained then, it is fed back to the microcomputer.

With this configuration, a microcomputer of the electrophotographic apparatus can be used, so that a high-precision high-voltage output can be obtained, and the size and cost can be reduced.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention is directed to a high-voltage transformer having a primary winding to which a DC power supply is input and an output winding for extracting an output, and switching to the primary winding of the high-voltage transformer. A high-voltage power supply device in which elements are connected in series and a DC input is turned on and off by the switching element to obtain a high-voltage output through a rectifying and smoothing circuit in which a voltage generated in an output winding of the high-voltage transformer is connected to the output winding. A means for providing a base winding to the high-voltage transformer and changing a current flowing from the base winding to the base of the switching element by a DC voltage via an integrator for converting a PWM output of a microcomputer of the electrophotographic apparatus into a DC. And a detector for detecting the voltage or current of the output winding is provided, and the DC voltage detected by the detector is fed to the microcomputer. Is configured to be Dobakku, it can be made inexpensive compact with obtaining a high pressure output accuracy.

According to a second aspect of the present invention, the DC voltage is applied to the base of a transistor via an integrator for converting the PWM output of the microcomputer according to the first aspect to a direct current, and the emitter of the transistor is grounded. The collector is connected to the base of the switching element, one end of the base winding is connected to the ground, and the other end is connected to the base of the switching element via a resistor. With this configuration, the base current of the switching element can be controlled. it can.

According to a third aspect of the present invention, the DC voltage is applied to the base of a transistor via an integrator for converting the PWM output of the microcomputer according to the first aspect to a direct current, and the emitter of the transistor has a resistance. Through the DC power supply,
The collector is connected to one end of the base winding, and the other end of the base winding is connected to the base of the switching element.
With this configuration, the base current of the switching element can be controlled.

According to a fourth aspect of the present invention, the relationship between the PWM duty and the output is changed by switching the voltage of the DC power supply applied to the emitter of the transistor, and flows to the base of the switching element. The current can be switched to achieve higher output accuracy.

An embodiment of the present invention will be described below with reference to the drawings. (Embodiment 1) Embodiment 1 of the high-voltage power supply device of the present invention
Will be described with reference to FIG. FIG. 1 is a circuit diagram showing a high-voltage power supply according to Embodiment 1 of the present invention.

In FIG. 1, reference numeral 16 denotes a low-voltage DC power supply.
The DC power supply 16 has a primary winding 18 of a high voltage transformer 17.
And a series circuit of a switching element 19 composed of a transistor. The high-voltage transformer 17 is provided with a base winding 20. One end of the base winding 20 is connected to the base of the switching element 19, and the other end is connected via an integrator 23 composed of a resistor 21 and a capacitor 22. Connected to the microcomputer 24 of the electrophotographic apparatus.

The output winding 25 of the high-voltage transformer 17 has a diode 26 and a rectifying / smoothing circuit 28 of a capacitor 27.
The load 29 is connected via the. This output winding 25
Is connected to the output terminal of the microcomputer 30. The detector 30 is connected to the microcomputer 24. The microcomputer 24 includes an A / D converter 31, a CPU 32, and a PWM.
It is constituted by a converter 33.

In the above configuration, a certain value of PWM is output from the microcomputer 24 in order to obtain an output, and the integrator 2
3 and is supplied to the base of the switching element 19 via the base winding 20. A collector current flows from the DC power supply 16 via the primary winding 18 and the switching element 19. When a voltage is generated in the switching element 20, a large collector current flows through the switching element 19.

However, since the current flowing to the base of the switching element 19 is determined by a value obtained by integrating the PWM, the current does not become larger than the value determined by the PWM, and the collector current flowing to the switching element 19 is saturated. As a result, no voltage is generated in the base winding 20 and the switching element 19 is rapidly turned off.

Next, since the PWM is output from the microcomputer 24, the above operation is repeated and the self-oscillation state is repeated, a voltage is generated in the output winding 25, and the voltage rectified by the rectifying and smoothing circuit 28 is output. become. This output voltage is the load 2
9 and a voltage is generated in the detector 30 when the output current flows. This voltage is fed back to the microcomputer 24, converted into a digital signal by the A / D converter 31, and controlled by the CPU 32 to a specified current value.
The PWM signal is converted by the converter 33 into a PWM signal having a duty such that the output current from the microcomputer 24 becomes a specified value.

(Embodiment 2) Next, Embodiment 2 of the present invention will be described with reference to FIG. In FIG. 2, the basic configuration is the same as that shown in FIG. 1, except that a transistor 34 for amplifying the signal of the integrator 23 is provided between the base winding 20 and the integrator 23. To the integrator 23 and the collector to the base winding 2
The emitter is connected to the DC power supply 16 via the base current limiting resistor 35 at the other end of the output winding 0, and detectors 30 and 36 each composed of two resistors are provided at the output end of the output winding 25 to divide the output voltage. In such a way as to feed back to the microcomputer 24.

In such a configuration, the operation of the microcomputer 24 is such that a certain value of PWM is output from the microcomputer 24, converted into DC by the integrator 23, applied to the base of the transistor 34, and supplied to the DC power supply via the base current limiting resistor 35. A voltage is applied from 16 to the base of the switching element 19, and a collector current flows from the DC power supply 16 via the primary winding 18 and the switching element 19.

Thereafter, the output voltage is output in the self-excited oscillation state of the same operation as in the first embodiment. In this configuration, the detection voltage divided by the two detectors 30 and 36 is supplied to the microcomputer 24. The feedback output voltage becomes a voltage specified by the microcomputer 24. Further, a transistor 34 is connected between the integrator 23 and the base winding 20 to amplify the base current, so that an output larger than that of the first embodiment can be obtained.

Third Embodiment Next, a third embodiment of the present invention will be described with reference to FIG. The basic configuration is the same as that of the first and second embodiments. Only different points will be described. A base current limiting resistor 35 is connected to one end of the base winding 20, and the switching element 1 is connected to the base current limiting resistor 35.
The DC power supply 16 is connected via the base 9, the collector of the transistor 34, and the starting resistor 37, and the output terminal is provided with only one detector 30.

In the above configuration, the operation is performed by the DC power supply 1
6 is applied to the base of the switching element 19 via the starting resistor 37, and a collector current flows through the switching element 19 via the primary winding 18.
Due to this collector current, a voltage is generated in the base winding 20 and the base current increases via the base current limiting resistor 35, so that a larger collector current flows.

However, a DC voltage obtained by integrating the PWM signal output from the microcomputer 24 by the integrator 23 is applied to the base of the transistor 34.
It does not become larger than the value determined by the duty of WM, and the collector current flowing through the switching element 19 is saturated, so that no voltage is generated in the base winding 20 and the switching element 19 is rapidly turned off, and self-excited. Oscillation occurs.

The other operations are the same as those of the above-described embodiment, and the description is omitted here. (Embodiment 4) Next, Embodiment 4 of the present invention will be described with reference to FIG. This configuration is almost the same as that of the second embodiment, except that the microcomputer 24 is provided with a terminal having an ON / OFF function for switching the voltage, a voltage switching resistor 38 is connected to this terminal, and the transistor 34 and the base current This is configured to be connected to the limiting resistor 35.

The operation is similar to the operation of the second embodiment.
When the duty and the output are shown, the characteristics are as shown in FIG. At this time, in a place where the output is small, that is, in a place close to 0% of the duty, a slight change in the duty causes a large output change. In particular, since the PWM output from the microcomputer 24 changes digitally, the output is controlled with high precision. Is difficult to do.

Therefore, in a place where the output is small as in the fourth embodiment, the voltage switching resistor 38
Is turned on, and the voltage applied to the emitter of the transistor 34 is reduced, so that the duty and output of the PWM become as shown in FIG. 5B, and high-precision control is possible even in a place where the output is small.

[0028]

As described above, since the high-voltage power supply of the present invention is constructed, an operational amplifier and peripheral circuits are not required, so that the apparatus can be made small and inexpensive, and the output is controlled by the microcomputer of the electrophotographic apparatus. Therefore, a highly accurate output can be obtained, which is of great industrial value.

[Brief description of the drawings]

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

FIG. 2 is a circuit diagram in Embodiment 2;

FIG. 3 is a circuit diagram in Embodiment 3;

FIG. 4 is a circuit diagram in Embodiment 4;

FIG. 5 is an output characteristic diagram of the second and fourth embodiments.

FIG. 6 is a circuit diagram of a conventional high-voltage power supply device.

[Explanation of symbols]

 Reference Signs List 16 DC power supply 17 High-voltage transformer 18 Primary winding 19 Switching element 20 Base winding 23 Integrator 24 Microcomputer 25 Output winding 28 Rectifying and smoothing circuit 30 Detector 34 Transistor 35 Base current limiting resistor 36 Detector 37 Starting resistor 38 Voltage switching resistor

Claims (4)

[Claims] A high-voltage transformer having a primary winding to which a DC power is input and an output winding for extracting an output; a switching element connected in series to the primary winding of the high-voltage transformer;
In the high voltage power supply device which obtains a high voltage output through a rectifying and smoothing circuit connected to the output winding by turning on / off a DC input by the switching element and applying a voltage generated in an output winding of the high voltage transformer to the high voltage transformer, Means for changing the current flowing from the base winding to the base of the switching element by means of a DC voltage via an integrator for converting the PWM output of the microcomputer of the electrophotographic apparatus into DC; A high-voltage power supply device comprising a detector for detecting a line voltage or a current, and feeding back a DC voltage detected by the detector to the microcomputer. 2. A DC voltage is applied to a base of a transistor via an integrator for converting a PWM output of the microcomputer into a direct current. An emitter of the transistor is connected to the ground, a collector is connected to a base of the switching element, and a base winding is connected. 2. The high-voltage power supply according to claim 1, wherein one end of the wire is connected to the ground and the other end is connected to the base of the switching element via a resistor. 3. A DC voltage is applied to the base of a transistor via an integrator for converting the PWM output of the microcomputer into DC, the emitter of the transistor is connected to a DC power supply via a resistor, and the collector is connected to one end of a base winding. The high-voltage power supply device according to claim 1, wherein the other end of the base winding is connected to a base of the switching element. 4. The high-voltage power supply device according to claim 3, wherein the relationship between the PWM duty and the output is changed by switching the voltage of the DC power supply applied to the emitter of the transistor.