JPH1189226A - High voltage power source circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simplify a circuit constitution in a high voltage power source circuit of multi-output. SOLUTION: In a high voltage power source circuit, an oscillator OSC 21 is connected with the base of a transistor Q31 through a resistor R41. The collector of the transistor Q31 and a power source voltage Vcc1 are connected with a primary coil of a transformer 31. Voltage multiplier circuits 21, 22, 23... corresponding to the respective output terminals OUT1, OUT2, OUT3... are connected with a secondary coil of the transformer 31. The voltage multiplier circuit 21 is composed of a capacitor C31, diodes D31, D32, a capacitor C32 and a transistor Q32. The transistor Q32 acts as a control element.

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 circuit having a plurality of output terminals used in an electrophotographic recording apparatus or the like.

[0002]

2. Description of the Related Art Generally, a high-voltage power supply used in an electrophotographic printer is required to have multiple outputs, and a circuit as shown in FIG. 3 has been used as a conventional multi-output high-voltage power supply circuit. FIG. 3 is a circuit diagram showing a conventional multi-output high-voltage power supply circuit.

The high-voltage power supply circuit shown in FIG.
Each has a transformer and a control circuit corresponding to UT1, OUT2,. In the figure, a power supply voltage Vcc is switched by a transistor Q01, boosted by a transformer T01, and turned on by a diode D0.
1. Output terminal OUT rectified by capacitor C01
1 is output. The output voltage of the output terminal OUT1 is divided by the resistors R02 and R03, and the divided voltage is compared with the comparison voltage Vref.
1 is compared with the comparator CP01. The output of the comparator CP01 and the output of the oscillator OSC01 are input to the AND gate AND01, and the output is input to the base of the transistor Q01 via the resistor R01.

When the output voltage of the output terminal OUT1 is higher than a desired voltage value, the output of the comparator CP01 becomes Lo.
It becomes w level, and the output of the oscillator OSC01 is not input to the transistor Q01. When the output voltage of the output terminal OUT1 is lower than the desired voltage value, the comparator C
The output of P01 becomes High level and the oscillator OSC0
1 is input to the transistor Q01. Since the output voltage is generated when the output of the oscillator OSC01 is input to the transistor Q01, the output voltage of the output terminal OUT1 is maintained at a desired value. A similar operation is performed at the output terminal OUT.
2 is also performed.

[0005]

However, in the above-mentioned conventional high-voltage power supply circuit, a transformer, a switching transistor and a rectifier circuit are required for each output, so that the device becomes large and complicated, and the cost increases. was there.

[0006]

According to the present invention, there is provided a high-voltage power supply circuit comprising: an oscillating circuit; switching means connected to the oscillating circuit; boosting means controlled by the switching means; And a voltage doubler rectifier circuit independently arranged for each of a plurality of output terminals, and a control connected to the zero potential side of the voltage doubler rectifier circuit and controlling the voltage doubler rectifier circuit according to the output value of each output terminal And an element.

According to the present invention having the above configuration, the oscillation circuit, the switching means connected to the oscillation circuit, and the boosting means controlled by the switching means are provided in common for each output terminal. This simplifies the circuit configuration,
It can contribute to cost reduction.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. Elements common to the drawings are assigned the same reference numerals. FIG. 1 is a circuit diagram showing a high-voltage power supply circuit according to a first embodiment of the present invention.

In FIG. 1, an oscillator OSC21 has a resistor R
It is connected to the base of the transistor Q31 via 41. The collector of the transistor Q31 and the power supply voltage Vcc
1 is connected to the primary coil of the transformer T31. Each output terminal OUT is connected to the secondary coil of the transformer T31.
Double voltage rectifier circuit 2 corresponding to 1, OUT2, OUT3,.
1, 22, 23,... Are connected. Here, the output terminals OUT1 and OUT2 output a negative voltage, and the output terminal OU
T3 is a voltage doubler rectifier circuit 21 that outputs a positive voltage. The secondary coil of the transformer T31 has a diode D3 via a capacitor C31 and a resistor R42.
1, D32 are connected. The capacitor C32 is connected to the anode side of the diode D32. A transistor Q32 is inserted between the cathode side of the diode D31 and the ground side GND (zero potential side).
Thus, the voltage doubler rectifier circuit 21 is configured. The output terminal OUT1 is connected between the diode D32 and the capacitor C32.

The output terminal OUT1 has a voltage dividing resistor R44,
R45 is connected so that the voltage divided by the voltage dividing resistors R44 and R45 is input to the positive input terminal of the comparator CP41. Comparator C
A comparison voltage Vref11 that determines the output voltage of the output terminal OUT1 is connected to the negative input terminal of P41.
The output side of the comparator CP41 is connected to the base of the transistor Q32 via the resistor R43.

The voltage doubler rectifier circuit 22 corresponding to the output terminal OUT2 has the same configuration as the voltage doubler rectifier circuit 21 described above. The voltage dividing resistors R48 and R49 and the comparator CP42 have the same configuration as the voltage dividing resistors R44 and R45 and the comparator CP41.

The voltage doubler rectifier circuit 23 corresponding to the output terminal OUT3 for outputting a negative voltage includes a capacitor C35 and a capacitor C3 connected to the secondary coil of the transformer T31.
5, a diode D35 connected via a resistor R50,
D36, a capacitor C36 connected to the cathode side of the diode D36, and a transistor Q34 inserted between the anode side of the diode D35 and the ground side GND (zero potential side).

The transistor Q34 is a PNP transistor. The collector of the transistor Q34 is connected to the anode of the diode D35.
The emitter of 34 is connected to Vcc2 which is close to the GND potential with respect to the output voltage of the output terminal OUT3 and which is on the plus side of the GND potential. The output voltage of the output terminal OUT3 is connected so as to be divided by the resistors R53 and R54, and the divided voltage is connected so as to be input to the minus input terminal of the comparator CP43.
The comparison voltage Vref13 that determines the output voltage of the output terminal OUT3 is input to the positive input terminal of the comparator CP43. The output terminal of the comparator CP43 is connected to the base of the transistor Q35 via the resistor R52. The collector of the transistor Q35 is connected to the base of the transistor Q34 via the resistor R51.

Next, the operation of the high-voltage power supply circuit according to the first embodiment will be described. When the voltage at the output terminal OUT1 that is a negative voltage output is lower than the desired voltage (in the present embodiment, when the absolute value is small because it is a negative output), the output of the comparator CP41 becomes High level, and the transistor Q32 Turns on. When the transistor Q32 is turned on (conductive state), the capacitor C31, the diodes D31 and D32, and the capacitor C32 operate as the voltage doubler rectifier circuit 21, and an output voltage is generated at the output terminal OUT1.

When the absolute value of the output voltage of the output terminal OUT1 is higher than the desired voltage, the absolute value of the voltage divided by the resistors R44 and R45 exceeds the absolute value of the comparison voltage Vref11, and the output of the comparator CP41 is It becomes Low level, and the transistor Q32 is turned off. At this time, since the cathode side of the diode D31 becomes floating, the diodes D31 and D32 cannot perform the rectifying action, and the output of the transformer T31 is cut off by the capacitor C31 and does not appear in the output of the output terminal OUT1.

Since the above operation is performed at a voltage near a desired voltage determined by the comparison voltage Vref11, the output voltage of the output terminal OUT1 is kept constant at the desired voltage.

The same operation is performed in a circuit corresponding to the output terminal OUT3 which is a plus output. Comparison voltage Vre
The detection of the output voltage is performed in the same manner as described above, except that the polarity of f13 and the polarity of the input terminal of the comparator CP43 are opposite to those of the negative output circuit. When the output voltage of the output terminal OUT3 is higher than the desired voltage, the output of the comparator CP43 becomes Low level, and the transistors Q35 and Q3
4 are both turned off.

When the output voltage of the output terminal OUT3 is lower than the desired voltage, the output of the comparator CP43 is High.
When the transistor Q35 is turned on, the base voltage flows to the transistor Q35, the transistor Q35 is turned on, and the emitter of the transistor Q34 is at the potential of the power supply Vcc2. , The transistor Q34 is also turned on. Transistor Q3
When the switch 4 is turned on, the diodes D35 and D36 perform the voltage doubler rectification operation, so that an output voltage is generated at the output terminal OUT3. By repeating the above operation, the output terminal OUT3
Is kept constant.

When the transistor Q34 is on, the potential on the anode side of the diode D35 is not a perfect zero potential but the potential of the power supply Vcc2, but the output voltage of the output terminal OUT3 is a high voltage of several hundreds to several hundred volts. In comparison with this, the power supply Vcc2 of several to several tens of volts has a sufficiently small value and acts as almost zero potential. Transistor Q3
The reason why the emitter of No. 4 is connected to the power supply Vcc2 is to obtain a potential difference necessary for flowing the base current of the transistor Q34.

In the present embodiment, the voltage doubler rectifier circuit 21,
A control element (transistor Q3
2, Q33, Q34), one terminal (emitter) of these control elements can be connected to ground GND or a potential at a level close to ground, and each of the voltage doubler rectifier circuits has a high withstand voltage characteristic. Need only be provided with this one control element.

Further, since the voltage doubler operation is performed by the voltage doubler rectifier circuits 21, 22, 23, the output voltage on the secondary side of the transformer T31 may be about half, and as a result, the size of the transformer T31 can be reduced.

Further, a circuit block corresponding to each output terminal is connected by a capacitor like capacitors C31, C33 and C35. When each output terminal is off, the control element (Q32, Q33, Q34) on the zero potential side is connected. ) Is also off, so that there is no DC coupling between the outputs. Therefore, a wired OR connection between outputs (to connect the outputs to obtain both outputs) such as a plus output and a minus output is also possible.

Next, a second embodiment of the present invention will be described. FIG. 2 is a circuit diagram showing a high-voltage power supply circuit according to a second embodiment of the present invention. The high-voltage power supply circuit according to the second embodiment uses a thyristor and a triac as control elements.

In FIG. 2, output terminals OUT1, OUT1
Each of the circuit blocks corresponding to 2 and the output terminal OUT3 is provided with a voltage doubler rectifier circuit 31, 32, 33, respectively. Thyristors Q41 and Q42 are provided as control elements of the voltage doubler rectifier circuits 31 and 32, respectively. The output of the comparator CP41 is connected to the gate of the thyristor Q41 via a resistor R43, and the output of the comparator CP42 is connected to the gate of the thyristor Q42 via a resistor R47. A triac Q43 is provided as a control element of the voltage doubler rectifier circuit 33. One of the triacs Q43 is connected to the diode D35, and the other is connected to the ground. The gate of the triac Q43 is connected to the output of the comparator CP43 via the resistor R51. Other configurations are the same as those of the first embodiment.

Next, the operation of the second embodiment will be described.
When the voltage of the output terminal OUT1, which is a negative voltage output, is lower than the desired voltage, the output of the comparator CP41 becomes H
The thyristor Q41 is turned on.
When the thyristor Q41 is turned on, the capacitor C31,
The diodes D31 and D32 and the capacitor C32 operate as the voltage doubler rectifier circuit 31, and an output voltage is generated at the output terminal OUT1. The thyristor Q41 remains conductive once it is turned on. However, since the thyristor Q41 is connected to the zero potential side of the diode D31 of the voltage doubler rectifier circuit 31, the thyristor Q41 switches the polarity of the output of the transformer T31 by rectification. The voltage application direction is reversed, and the non-conductive state is restored.

When the absolute value of the output voltage of the output terminal OUT1 is higher than the desired voltage, the absolute value of the voltage divided by the resistors R44 and R45 exceeds the absolute value of the comparison voltage Vref11, and the output of the comparator CP41 is The thyristor Q41 is turned off and the thyristor Q41 is turned off. At this time, since the cathode side of the diode D31 becomes floating, the diodes D31 and D32 cannot perform the rectifying action, and the output of the transformer T31 is cut off by the capacitor C31 and does not appear in the output of the output terminal OUT1.

Since the above operation is performed at a voltage near a desired voltage determined by the comparison voltage Vref11, the output voltage of the output terminal OUT1 is kept constant at the desired voltage. A similar operation is performed in a circuit corresponding to the output voltage OUT2.

The same operation is performed in a circuit corresponding to the output terminal OUT3 which is a plus output. That is, the triac Q43 conducts the conduction and non-conduction (on and off) operations to keep the output voltage constant. Since the anode side of the diode D35 is connected to the triac Q43, and the other side of the triac Q43 is connected to the ground, a negative voltage is applied to the triac Q43. When the output of the comparator CP43 becomes High level, the triac Q43 is turned on (conducted). By repeating the above operation, the output voltage of the output terminal OUT3 is kept constant.

As described above, according to the second embodiment,
Since the thyristor and the triac are used as the control elements of the voltage doubler rectifier circuit, the control elements can be connected to the ground regardless of the plus output and the minus output, and the circuit configuration can be simplified. Further, since a thyristor or a triac can easily obtain a high withstand voltage product, the apparatus can be inexpensive.

The control element is driven at a logic level (several volts) and the withstand voltage of the drive source is low.
The control element can be driven by a general-purpose CPU or a logic circuit. For example, instead of the analog comparator, the comparator can be driven by an analog-to-digital converter and logic, or a comparator based on a comparison operation inside the CPU.
It is also possible to drive by the PWM (pulse width modulation signal) output of the PU.

[0031]

As described above in detail, according to the present invention, the oscillating circuit, the switching means connected to the oscillating circuit, and the boosting means controlled by the switching means are provided in common for each output terminal. . This simplifies the circuit configuration and contributes to cost reduction.

[Brief description of the drawings]

FIG. 1 is a circuit diagram illustrating a high-voltage power supply circuit according to a first embodiment.

FIG. 2 is a circuit diagram illustrating a high-voltage power supply circuit according to a second embodiment.

FIG. 3 is a circuit diagram showing a conventional multi-output high-voltage power supply circuit.

[Explanation of symbols]

 21, 22, 23 times voltage rectifier circuit OSC21 Oscillator Q21, Q32, Q33, Q34 Transistor T31 Transformer

Claims (3)

[Claims] 1. An oscillation circuit, switching means connected to the oscillation circuit, boosting means controlled by the switching means, and a voltage doubler rectifier circuit connected to the boosting means and arranged independently for each of a plurality of output terminals. And a control element connected to the zero potential side of the voltage doubler rectifier circuit and controlling the voltage doubler rectifier circuit according to the output value of each output terminal. 2. The high-voltage power supply circuit according to claim 1, wherein the control element controls the voltage doubler rectifier circuit based on a result of comparing an output value of each output terminal with a reference value. 3. The high-voltage power supply circuit according to claim 1, wherein the plurality of output terminals include an output terminal that outputs a positive voltage and an output terminal that outputs a negative voltage.