JPH03276168A - High voltage power source device - Google Patents

Abstract

PURPOSE:To use a small-sized high frequency transformer in order to obtain a low frequency output and to miniaturize a device by comparing a load voltage detection output with a reference signal and controlling a charge period or a discharge period based on the compared result. CONSTITUTION:A microcomputer (control circuit) 10 turns on/off a switching transistor Tr1 to generate a high frequency alternating current in the secondary winding 1b of a converter transformer 1. The output from the transformer 1 is rectified by a diode D1 and used for the charge and discharge of a charge circuit 2 and a discharge circuit 4. A direct current from a DC power source 5 is superposed on a low frequency output obtained by the above charge and discharge, and a high voltage output is generated in an output terminal 6. In such a case, the computer 10 compares the reference signal which is a specified function obtained by an inner timer and inner programming with the output from an A-D converter 9 and controls charging and discharging timing in accordance with the compared result. In the concrete, the digital signal of the load voltage detection output is compared with the reference signal, the charge period and the discharge period are decided and furthermore the amplitude of the specified function is controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a high-voltage power supply device used in electrophotographic copying machines, developing bias circuits of printers, and the like.

[Conventional technology]

Conventionally, a high-voltage power supply device used in a developing bias circuit of a jump-pin developing method in a copying machine, for example, is composed of a step-up transformer that steps up alternating current and a DC-DC converter.
A DC voltage is superimposed on the high frequency AC output from the step-up transformer. For example, the frequency output from a step-up transformer is 200Hz to 2KHz, and the amplitude is 500Vp-p to 2
KVp-p (7) A DC voltage of 0 to 600 V is superimposed on AC, and this high voltage is used in the bias circuit of the developing machine.

[Problem 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 low-frequency output, which causes the 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 becomes complicated and expensive, and the power loss of the drive circuit increases, resulting in a large temperature rise. was there.

The present invention was made in view of these problems, and it is possible to downsize the device and obtain a sine wave output and any other arbitrary waveform output with an inexpensive and simple circuit configuration. The objective is to obtain a high-voltage power supply device with improved reliability.

[Means to solve the problem]

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

an output transformer, a charging circuit for charging a capacitive load with a rectified output from a secondary winding of the output transformer, a discharging circuit for discharging the charged charge, and a voltage detection circuit for detecting the voltage of the load; an A-D converter that converts the detected output of the load voltage into a digital signal, and a charging period of the charging circuit and a discharging period of the discharging circuit based on the result of comparing the output of the A-D converter with a predetermined reference signal. Equipped with a control circuit to control the period.

■An output transformer, a charging circuit that charges a capacitive load using the rectified output from the secondary winding of this output transformer, a voltage detection circuit that detects the voltage of the capacitive load, and a digital signal that outputs the detected load voltage. and a control circuit that controls the charging period of the charging circuit based on the result of comparing the output of the AD converter with a predetermined reference signal.

(2) In the above-mentioned device or (2), there is provided a current detection circuit that detects the current flowing through the load, an A-D converter that converts the detected output of the load current into a digital signal, and an A-D converter that converts the output of the A-D converter into a digital signal. A control circuit is provided for controlling the amplitude of the predetermined reference signal based on the result of comparison with the reference signal.

[Effect]

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 A-D converter, and the
The output of the -D converter is compared with a reference signal by a control circuit. Then, based on the comparison result, the charging period or discharging period of the load on the secondary side of the output transformer is controlled.

〔Example〕

FIG. 1 is a circuit 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 (Vcc) and a smoothing capacitor C1 are connected to one end of the -order winding 1a, and the other end of the -order winding 1a is connected to a DC power supply (Vcc) and a smoothing capacitor C1. is connected to a driving switching transistor T,1. Further, a rectifying tie is connected to the secondary winding 1b of the converter transformer 1. 2 is a charging circuit that charges the capacitive load 3 by the rectified output from the secondary winding 1b, and the capacitor C2
It is made up of. Reference numeral 4 denotes a discharging circuit for discharging the charged charge, and is constituted by transistors T and 2.

5 is a DC power supply that superimposes DC on the AC output of the converter transformer 1, and is connected in series with a resistor R4. 6 is an output terminal, 7 is a current detection circuit for detecting the current flowing through the load 3, and the terminal voltage of the resistor R1 connected in series with the transistors T and 2 is inputted thereto. Reference numeral 8 denotes a voltage detection circuit for detecting the voltage of the load 3, into which a voltage obtained by dividing the rectified output of the converter transformer I by resistors R2 and R3 is input. 9
10 is an A-D converter that converts the load current and load voltage detection outputs from these detection circuits 7 and 8 into digital signals, and 10 is an A-D converter that compares the output of this A-D converter 9 with a reference signal of a predetermined function. A microcomputer constitutes a control circuit that controls the charging period of the charging circuit 2 and the discharging period of the discharging circuit 4 based on the results of the above-mentioned transistors T, 1. The driving of T, 2 is controlled by this microcomputer 10. The capacitive load 3 corresponds to a developing roller in an electrophotographic copying machine or printer, and its resistance is so large that it can be completely ignored compared to other circuit impedances.

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

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

FIG. 2 is a flowchart showing details of the control operation of the microcomputer 1o. Also, Figures 3 and 4
The figure is a signal waveform diagram of each part in FIG. 1.

The microcomputer 10 first sets the internal clock to the fourth clock.
As shown in Figure (a), the frequency is divided into frequency f1 (period T) (step Sl). Next, an interrupt is generated at time t (step S2), and the digital output (AC load current) ia from the current detection circuit 7 is read (step 33).

Then, the read output i,... and the target value I8 of the load current
The instantaneous value of the sine wave of amplitude vPt1 is calculated using the following equation (step S4).

vp t+ ”α+ (Ia la )st
n t+ (1) α1: Predetermined coefficient Next, the digital output from the voltage detection circuit 8 (AC amplitude)
vpt+ is read (step S5).

Then, the read output vpt is compared with the amplitude V,t obtained by equation (i), and the charge/discharge amount Xt is calculated by the following equation (step S6).

X j+ = CL2 (Vp j+ VP j+
) (100)α2: Predetermined coefficientNext, if the charge/discharge amount xt obtained by equation (i) is positive (x
In step S7), it is determined whether t + > 0), and if it is positive, the on-time of the charging switching transistor Tr1 that drives the primary side of the converter transformer 1 is determined for a time proportional to the charging/discharging amount xt. The ratio is increased and the charging switch is turned on (step S8). At that time, the driving frequency f of the switching transistor T,1
2 is set to a high frequency that allows the converter transformer 1 to be sufficiently miniaturized. Further, at this time, the discharge transistors T and 2 are kept in an off state.

In addition, when the charge/discharge amount Xtl determined by the above formula (ii) is negative, the switching transistor T,1 is turned off, and at the same time, the transistor T, - for discharging for a time proportional to the charge/discharge amount xt, is 2, and the discharge switch is turned on (step S9). At this time, the drive frequency of the transistors T, 2 is set to the same frequency as the drive frequency f2 of the switching transistors T, 1, and the on time of the charging switch and the on time of the discharging switch are both jc = α3Xj + (α3 is a coefficient ).

Hereinafter, as shown in FIG. 4(a), time t2 for each period T
The same operation as above is repeated at ~t4. (b), (c), and (d) of FIG. 4 show the output waveform taken out from the output terminal 6 of FIG. 1 and the timing of the charging and discharging described above.

In this way, a low frequency output can be obtained from the output terminal 6 using the small converter transformer 1 for high frequency, and therefore the device can be made smaller and less expensive. In addition, since digital signal processing is performed,
A sine wave output and any other waveform output can be easily obtained with a simple circuit configuration, and reliability is improved. In other words, a large number of oscillation circuits, sine wave generation circuits, surf circuits, PWM circuits, etc. can be implemented in one microcomputer 10, which greatly simplifies the circuit, reduces costs, and increases reliability. Any other waveform can be obtained by simply changing the block programming of the microcomputer 10.

Here, in the waveform diagram of each part shown in Fig. 3, (a)
The waveform shown by the solid line indicates the sine wave output vP (t) waveform that is ultimately desired to be extracted as an output, and this output V
The frequency f3 of p (t) is, for example, an electrophotographic copying machine,
This value is determined by the developing conditions of the printer. that time,
The above-mentioned frequency division frequency f is selected to be an integral multiple of this frequency f3. At this time, in order to increase the control product and control response, it is desirable to make the dividing frequency f1 sufficiently large to make the sampling link interval dense. However, depending on the processing speed of the A-D converter 9 and the microcomputer 1o, The upper limit of f1 is limited. The waveform shown by the broken line in FIG. 3(a) is the output vp based on the signal from the actual voltage detection circuit 8.
(t) Shows the waveform. In addition, (b) in Fig. 3 shows the difference output when the aforementioned charge/discharge amount x(t) is positive (X (t)>O), and this output is actually stored in the microcomputer lo as a digital value. The result is calculated by . (C) in FIG. 3 is a base drive signal of the switching transistor T, -1, which becomes a charging pulse of frequency f2. Third
In (d) of the figure, the charge/discharge amount X(1) is negative (x (t)<
The difference output in case O) is actually the result calculated in the microcomputer 10 as a digital value in the same way as above. Further, (e) in FIG. 3 is a pulse drive signal for the transistors T and 2, which serves as a discharge pulse.

5(a) and 5(b) show an example of the current detection circuit 7 and voltage detection circuit 8 of FIG. 1.

The load current (18) is detected by a resistor R inserted between the emitter ground of the discharge transistor Tr2 in FIG.
1 and the current detection circuit 7 shown in FIG. 5(a). That is, the alternating current is smoothed by the transistors T, 2, and the resistor R51 in FIG. 5(a)
It is smoothed by an integrating circuit including capacitor C51 and capacitor C51. At this time, the time constants of the resistor R51 and the capacitor C51 are selected to such an extent that the alternating current component can be completely removed (for example, 1 second to 60 seconds). The rectified and smoothed direct current is then input to the A/D converter 9 in FIG. 1 via the operational amplifier Q51. R52, R53° and R54 are resistors. In addition, A
-D converter 90 When the impedance of the resistor R51 is sufficiently large, the operational amplifier Q51 can be omitted.

To detect the load voltage (output voltage), the rectified output from the secondary winding lb of the converter transformer 1 in FIG. 1 is connected to the resistor R2.
After dividing the voltage at a predetermined ratio by R3 and R3, the voltage follower Q52 shown in FIG. 5(b) lowers the impedance.

At this time, the value of the resistor R2 is selected to be large enough to be sufficiently smaller than the current flowing through the resistor R2 or the load current. R55 and R56 are resistors. Note that, similar to the above-described current detection circuit 7, when the input impedance of the AD converter 9 is sufficiently large with respect to the resistor R2, the voltage follower Q52 can be omitted.

FIG. 6 is a circuit diagram showing another example of the voltage detection circuit 8. In FIG. This detection circuit 8 is designed to prevent switching noise of the converter transformer 1 from being superimposed on the output of the circuit 8, and includes two operational amplifiers Q61. I am using Q62. The operational amplifier Q61 at the front stage constitutes a low-pass filter with a cutoff frequency f2, and removes the above-mentioned switching noise. R61 to R67 are resistors,
C61 is a capacitor.

Further, FIG. 7 is a circuit configuration diagram showing another embodiment of the present invention. In this embodiment, the discharge circuit is omitted, and a resistor R is connected between the tie motor D1 connected to one end of the secondary winding 1b of the converter transformer 1 and the other end of the secondary winding lb.
7 is interposed, and the charged charges are constantly discharged through the resistor R7 and the resistor R1. This configuration is effective when the output frequency is low and the load capacity is small. That is, in this case, the power loss of the resistor R7 is small, so the above configuration is established. Note that the load current (i,) is detected through a resistor R1 inserted between the secondary winding 1b of the converter transformer 1 and the ground.

(Effects of the Invention) As described above, according to the present invention, a small high-frequency transformer can be used to obtain a low-frequency output, and therefore the device can be made smaller and less expensive. Furthermore, since digital signal processing is performed, it is possible to easily obtain a sine wave output and any other waveform output with a simple circuit configuration, and the reliability is improved.

[Brief explanation of drawings]

FIG. 1 is a circuit configuration diagram showing an embodiment of the present invention, FIG. 2 is a flowchart showing the control operation of the microcomputer shown in FIG. 1, and FIGS. 3 and 4 are signal waveform diagrams of each part of FIG. 1. , FIG. 5 is a circuit diagram showing an example of each detection circuit in FIG. 1,
FIG. 6 is a circuit diagram showing another example of the voltage detection circuit, and FIG. 7 is a circuit configuration diagram showing another embodiment of the present invention. 1...Converter transformer (output transformer) 1
a...--Secondary 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 ... -A -D converter

Claims (3)

[Claims] (1) An output transformer, a charging circuit that charges a capacitive load with the rectified output from the secondary winding of the output transformer, a discharge circuit that discharges the charged charge, and a voltage detection circuit that detects the voltage of the load. , an A-D converter that converts the load voltage detection output into a digital signal, and a charging period of the charging circuit and a discharge circuit based on the result of comparing the output of this A-D converter with a predetermined reference signal. A high-voltage power supply device comprising a control circuit that controls a discharge period. (2) An output transformer, a charging circuit that charges a capacitive load using the rectified output from the secondary winding of this output transformer, a voltage detection circuit that detects the voltage of the capacitive load, and a digital detection output of the load voltage. It is characterized by comprising an A-D converter that converts the output into a signal, and a control circuit that controls the charging period of the charging circuit based on the result of comparing the output of the A-D converter with a predetermined reference signal. High voltage power supply. (3) A current detection circuit that detects the current flowing through the load, and A that converts the detected output of the load current into a digital signal.
-D converter; and a control circuit that controls the amplitude of the predetermined reference signal based on the result of comparing the output of the A-D converter with a reference signal. high voltage power supply.