JP3450324B2 - High voltage AC power supply - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a high-voltage power supply device used in a developing bias circuit of an electrophotographic copying machine or printer.

[Conventional technology]

Conventionally, for example, a high-voltage power supply device used in a developing bias circuit of a jumping development system of a copying machine is composed of a step-up transformer for stepping up an alternating current and a DC-DC converter, and superimposes a direct current voltage on a high frequency alternating current output from the step-up transformer. I am letting you. For example, 0 to 600V for alternating current of frequency 200Hz to 2KHz and amplitude 500V _{PP to} 2KV _PP output from the step-up transformer.
DC voltage is superposed and this high voltage is used for the bias circuit of the developing machine.

[Problems to be Solved by the Invention]

However, in the conventional high-voltage power supply device as described above, a large transformer is required to obtain a low-frequency output, and there is a problem that the device becomes large and expensive. In addition, when a sine wave output is required, the circuit configuration of the sine wave generation circuit and the like becomes complicated, which is also expensive, and the power loss of the drive circuit is large and the temperature rise is large. was there.

The present invention has been made in view of such a problem, and it is possible to reduce the size of the device and obtain a sine wave output and an arbitrary waveform output other than this with a simple circuit configuration. The purpose of the present invention is to obtain a high-voltage power supply device capable of achieving high reliability.

[Means for Solving the Problems]

The high voltage power supply device of the present invention is configured as follows.

(1) Step-up transformer, charging switching means connected to the primary side thereof, rectifying diode connected to the secondary side, discharging switching means connected to the output side of the diode and ground, diode A high-voltage AC power supply device comprising a coupling capacitor connected to the output side of and a control means for controlling both switching means, the output for outputting a detection signal to the control means at the output end of the power supply device. The voltage detection means is provided, and the control means compares the low-frequency AC reference signal obtained as the output waveform with the detection voltage signal at a cycle sufficiently shorter than the reference signal, and when the detection signal is lower than the reference signal, the control means responds to the difference. PWM signal with ON time width is supplied to the switching device for charging on the primary side, and when detection signal is higher than the reference signal, PWM signal with ON time width according to the difference By supplying the secondary side discharge switching unit, high voltage AC power supply, characterized in that those allowed to generate an AC waveform at the output terminal of the coupling capacitor.

(2) A detection resistor for detecting a discharge current and outputting it to the control means is inserted between the discharge switching element and the ground of the high-voltage AC power supply device according to claim 1, and the control means outputs the discharge current. A sine wave signal having an amplitude that is a predetermined multiple of the difference between the required load current target value and the detected discharge current signal is created, and this is used as a low frequency AC reference signal, and the reference signal and the detected voltage signal are used as the reference signal. Compare in a sufficiently shorter cycle, when the detection signal is lower than the reference signal, the PWM signal having the ON time width corresponding to the difference is supplied to the primary side charging switching means, and when the detection signal is higher than the reference signal By supplying a PWM signal having an ON time width corresponding to the difference to the secondary side discharge switching means, an AC waveform is generated at the output end of the coupling capacitor. Power supply.

(3) A high-voltage AC power supply device, characterized in that a direct current from a direct current power supply is superimposed on the output of the coupling capacitor according to claim 1 or 2.

[Action]

In the high-voltage power supply device of the present invention, the detection output of the load voltage is converted into a digital signal by the AD converter, and the operation amount of the charging circuit or the charging circuit and the discharging circuit is determined based on the output of the AD converter. It is controlled and an AC high voltage output is applied to the capacitive load.

〔Example〕

FIG. 1 is a circuit configuration diagram of a high voltage power supply device according to an embodiment of the present invention. In the figure, 1 is a high-frequency converter transformer (output transformer), a DC power supply (V _CC ) and a smoothing capacitor C1 are connected to one end of the primary winding 1a, and the other end of the primary winding 1a is connected. The driving switching transistor T _r 1 is connected. In addition, converter transformer 1
A rectifying diode is connected to the secondary winding 1b. Reference numeral 2 is a charging circuit for charging the capacitive load 3 by the rectified output from the secondary winding 1b, which is composed of a capacitor C2. Reference numeral 4 denotes a discharge circuit for discharging the charge, which is composed of a transistor _Tr 2. Reference numeral 5 is a DC power supply for superimposing DC on the AC output of the converter transformer 1, and a resistor R4 is connected in series. Reference numeral 6 is an output terminal, and 7 is a current detection circuit for detecting a current flowing through the load 3. The terminal voltage of the resistor R1 connected in series with the transistor _Tr2 is input. Reference numeral 8 is a voltage detection circuit for detecting the voltage of the load 3, to which the voltage obtained by dividing the rectified output of the converter transformer 1 by resistors R2 and R3 is input. Reference numeral 9 is an AD converter for converting the detection outputs of the load current and the load voltage from the detection circuits 7 and 8 into digital signals, and 10 is the AD converter 9
A microcomputer based output of a result of comparison with a reference signal of a predetermined function constitute a control circuit for controlling the charge period and discharge period of the discharge circuit 4 of the charging circuit 2, the transistors of the above T _r 1 The driving of T _r 2 is controlled by this microcomputer 10. In the electrophotographic copying machine and printer with the capacitive load 3, it corresponds to a developing roller, and its resistance is large enough to be ignored as compared with other circuit impedances.

  Next, the operation of the power supply device having the above configuration will be described.

When the switching transistor _Tr 1 is driven (turned on and off) by the microcomputer 10, a high frequency alternating current is generated in the secondary winding 1b of the converter transformer 1. The high frequency output of the secondary winding 1b is rectified by the diode D1 and used for charging and discharging in the charging circuit 2 and the discharging circuit 4.
Then, a low-frequency output is obtained by this charging / discharging, the direct current from the DC power supply 5 is superimposed on this low-frequency output, and a high voltage output is generated at the output terminal 6. At that time, the microcomputer 10 compares the reference signal of the predetermined function obtained by the internal timer and the internal programming with the output of the A / D converter 9, and determines the charging / discharging timing according to the comparison result. Have control. Specifically, the charge period and the discharge period are determined by comparing the digital signal of the detection output of the load voltage and the reference signal of the predetermined function, and the digital signal of the detection output of the load current and the reference signal are compared. By comparison, the amplitude of the predetermined function is controlled.

FIG. 2 is a flow chart showing details of the control operation of the microcomputer 10. Also, FIGS. 3 and 4
The figure is a signal waveform diagram of each part of FIG.

The microcomputer 10 first sets the internal clock to the fourth
As shown in FIG. _6A , the frequency is divided into frequencies f ₁ (period T) (step S1). Next, at time t _l , an interrupt is made (step S2), and the digital output (AC load current) i _a from the current detection circuit 7 is read (step S3). Then, the read output i _a is compared with the target value I _{a of the} load current, and the amplitude V _p t _l
The instantaneous value of the sine wave of is calculated by the following formula (step S
Four).

V _p t _l = α _l (I _a −i _a ) sin t _l (i) α _l : predetermined coefficient Next, the digital output (AC amplitude) from the voltage detection circuit 8
Read V _p t _l (step S5). Then, the read output V _p t _l is compared with the amplitude V _p t _l obtained by the equation (i), and the charge / discharge amount xt _l is calculated by the following equation (step S6).

xt _l = α ₂ (V _p t _l −v _p t _l ) (ii) α ₂ : predetermined coefficient Next, the charge / discharge amount xt _l obtained by the equation (ii) is positive (xt _l > 0).
Is determined (step S7), and if positive, the on-time ratio of the charging switching transistor T _r 1 that drives the primary side of the converter transformer 1 for a time proportional to the charge / discharge amount xt _l is determined. Increase and turn on the charging switch (step S8). At that time, the drive frequency f ₂ of the switching transistor _Tr 1 is set to a high frequency so that the converter transformer 1 can be sufficiently miniaturized. At this time, the discharging transistor _Tr 2 is held in the off state.

Further, the case (ii) charge-discharge amount xt _l determined by the formula is negative, the switching transistor T and at the same time the _r 1 to the OFF state, the transistor T _r for discharge by a time proportional to the charge and discharge amount xt _l The ratio of the on time of 2 is increased and the discharge switch is turned on (step S9). At this time, the drive frequency of the transistor T _r 2 is
_It is set to the same frequency as the drive frequency f _{2 of r} 1, and both the on time of the charge switch and the on time of the discharge switch are t _c = α ₃ x
t _l (α ₃ is a coefficient).

Hereinafter, as shown in FIG. 4 (a), time t _{2 in} each cycle T
The operation similar to the above is repeated at ~ t ₄ . 4 (b), (c), and (d) show output waveforms taken out from the output terminal 6 of FIG. 1 and the timing of the charge / discharge.

Thus, a compact converter transformer 1 for high frequencies
Can be used to obtain a low frequency output from the output terminal 6,
Therefore, the size of the device can be reduced, and the device can be made inexpensive. In addition, since the digital signal processing is performed, a sine wave output and an arbitrary waveform output other than this can be easily obtained with a simple circuit configuration, and the reliability is improved. That is, a large number of oscillator circuits, sine wave generation circuits, servo circuits, PWM circuits, etc. can be realized with one microcomputer 10, and the circuits can be greatly simplified, cost reduced, and reliability improved. Any waveform other than can be obtained only by changing the programming of the microcomputer 10.

Here, in the waveform diagram of each part shown in FIG.
The waveform shown by the solid line in (a) shows the output V _p (t) waveform of the sine wave that is desired to be finally output.
The frequency f ₃ of V _p (t) is a value determined by the developing conditions of an electrophotographic copying machine or printer, for example. At this time, the above-mentioned frequency division frequency f ₁ is selected to be an integral multiple of this frequency f ₃ . At this time, it is desirable to increase the frequency division frequency f ₁ sufficiently to make the sampling interval dense in order to improve the control accuracy and control responsiveness, but the frequency f depends on the processing speed of the AD converter 9 and the microcomputer 10. The upper limit of ₁ is limited. The waveform shown by the broken line in (a) of FIG. 3 represents the output v _p (t) waveform based on the actual signal from the voltage detection circuit 8. Further, FIG. 3B shows the above-mentioned charge / discharge amount x
The difference output when (t) is positive (x (t)> 0) is shown, and this output is actually a result calculated as a digital value in the microcomputer 10. FIG. 3 (c) shows the base drive signal of the switching transistor T _r 1, which has a frequency f
₂ charge pulses. FIG. 3 (d) shows the difference output when the charge / discharge amount x (t) is negative (x (t) <0).
The result is calculated within 10. Further, FIG. 3 (e) shows a base drive signal of the transistor _Tr 2 which is a discharge pulse.

5 (a) and 5 (b) show an example of the current detection circuit 7 and the voltage detection circuit 8 of FIG.

Detection of the load current (i _a), the emitter of the transistor T _r 2 for discharge of the Figure 1 - made by the current detection circuit 7 shown in FIG. 5 of the inserted resistor R1 Toko between ground (a). That is, the AC current is smoothed by the transistor _Tr 2 and further smoothed by the integrating circuit of the resistor R51 and the capacitor C51 shown in FIG. 5 (a). At this time, the resistance R51
The time constants of the capacitor C51 and the capacitor C51 are selected so that the AC component can be completely removed (for example, 1 second to 60 seconds). Then, the rectified and smoothed direct current is input to the AD converter 9 of FIG. 1 through the operational amplifier Q51. R52, R53 and R54 are resistors. When the input impedance of the AD converter 9 is sufficiently larger than the resistance R51, the operational amplifier Q51 can be omitted.

The load voltage (output voltage) is detected by using the resistor R2 as the rectified output from the secondary winding 1b of the converter transformer 1 shown in FIG.
After the voltage is divided by R3 at a predetermined ratio, the voltage follower Q52 shown in FIG. 5 (b) reduces the impedance. At this time, the value of the resistor R2 is selected to be large so that the current flowing through the resistor R2 becomes sufficiently smaller than the load current. R55 and R56 are resistors. Like the current detection circuit 7 described above, when the input impedance of the AD converter 9 is sufficiently higher than the resistance R2, the voltage follower Q52 can be omitted.

FIG. 6 is a circuit diagram showing another example of the voltage detection circuit 8. The detection circuit 8 is provided with a measure against the case where the switching noise of the converter transformer 1 is superimposed on the output of the detection circuit 8 and uses two operational amplifiers Q61 and Q62. The operational amplifier Q61 in the previous stage has a cutoff frequency f
_It composes a low pass filter of ₂ and removes the above switching noise. R61 to R67 are resistors, and C61 is a capacitor.

FIG. 7 is a circuit configuration diagram showing another embodiment of the present invention. In this embodiment, the discharge circuit is omitted,
A resistor R7 is provided between the diode D1 connected to one end side of the secondary winding 1b of the converter transformer 1 and the other end side of the secondary winding 1b, and the charge is constantly discharged through the resistor R7 and the resistor R1. I am letting you. This configuration is effective when the output frequency is low and the load capacitance is small. Ie in this case the resistance
Since the power loss of R7 is small, the above configuration is established. The detection of the load current (i _a) is carried out through the converter transformer secondary winding 1b and the inserted resistor between ground R1.

〔The invention's effect〕

As described above, according to the present invention, a small high-frequency transformer can be used to obtain a low-frequency output, so that the device can be downsized, the cost is low, and the digital signal processing is performed. Therefore, it is possible to easily obtain a sine wave output and an arbitrary waveform output other than this with a simple circuit configuration, and there is an effect that reliability is improved.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing an embodiment of the present invention, FIG. 2 is a flow chart showing a control operation of the microcomputer of FIG. 1, and FIGS. 3 and 4 are signal waveform diagrams of respective parts of FIG. 5, FIG. 5 is a circuit diagram showing an example of each detection circuit of FIG. 1, FIG. 6 is a circuit diagram showing another example of the voltage detection circuit,
FIG. 7 is a circuit configuration diagram showing another embodiment of the present invention. 1 ... Converter transformer (output transformer) 1a ... Primary winding 1b ... Secondary winding 2 ... Charging circuit 3 ... Capacitive load 4 ... Discharging circuit 5 ... DC power supply 7 ... Current detection circuit 8 ... … Voltage detection circuit 9… AD converter 10… Microcomputer (control circuit)

Claims (3)

(57) [Claims] 1. A step-up transformer, a charging switching means connected to the primary side of the step-up transformer, a rectifying diode connected to the secondary side, and a discharging switching means connected between the output side of the diode and ground. A high-voltage AC power supply device comprising: a coupling capacitor connected to the output side of the diode; and control means for controlling both switching means, wherein a detection signal is output to the control means at the output end of the power supply device. The control means compares the low-frequency AC reference signal obtained as the output waveform with the detection voltage signal at a cycle sufficiently shorter than the reference signal, and when the detection signal is lower than the reference signal, the difference between them is provided. The PWM signal with the ON time width corresponding to the PW is supplied to the primary side charging switching means, and when the detection signal is higher than the reference signal, the PW with the ON time width corresponding to the difference A high-voltage AC power supply device for generating an AC waveform at the output end of a coupling capacitor by supplying the M signal to the secondary side discharge switching means. 2. A detection resistor for detecting a discharge current and outputting it to the control means is inserted between the discharge switching element and the ground of the high-voltage AC power supply device according to claim 1, and the control means is a discharge device. A sine wave signal having an amplitude that is a predetermined multiple of the difference between the load current target value obtained as the current and the detected discharge current signal is created, and this is used as a low-frequency AC reference signal, and the reference signal and the detected voltage signal are Compare the reference signal at a sufficiently shorter cycle, and if the detection signal is lower than the reference signal, supply a PWM signal with an ON time width corresponding to the difference to the primary side charging switching means, and the detection signal is higher than the reference signal. At this time, the high-voltage AC power supply device is configured to generate an AC waveform at the output end of the coupling capacitor by supplying a PWM signal having an ON time width corresponding to the difference to the secondary side discharge switching means. 3. A high-voltage AC power supply device in which a DC from a DC power supply is superimposed on the output of the coupling capacitor according to claim 1.