JPH0568942B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a high-voltage power supply, and more particularly to a high-voltage power supply used in copying machines, printers, television sets, and the like.

[Prior art] As one of the above-mentioned high-voltage power supplies, the first
A circuit like the one shown in the figure is often used to control chargers in copying machines.

The circuit shown in FIG. 1 is a circuit that generates a high-voltage current by superimposing a desired alternating current on a high-voltage direct current. Rectangular wave (or sine wave) pulses are input to the step-up transformer 6 from terminals 3 and 4 in the same figure, and an alternating current that is boosted according to the winding ratio is generated on the secondary side of the transformer. A high DC voltage V1 is generated by a rectifying and smoothing circuit consisting of a load resistor 10 and a load resistor 10.
get.

On the other hand, from terminals 1 and 2, alternating current at a frequency determined according to the desired control characteristics of the load is applied to the transformer 5. The high-voltage DC output of the transformer 6 is connected to one end of the secondary side of the transformer 5. Therefore, the secondary side of the transformer 5 has the aforementioned DC voltage V1 and the terminal 1, as shown in FIG. A voltage V1+V2 is generated by superimposing AC V2 obtained by boosting the AC input from the output terminal 7, and is supplied to the load from the output terminal 7.

As shown in FIG. 2, the output voltage is obtained by superimposing the AC potential boosted by the transformer 5 around the voltage V1 boosted by the transformer 6.

The conventional configuration that generates high voltage by superimposing alternating current as described above requires two transformers, one for the direct current system and the other for the alternating current system, which results in high costs.Also, since the transformer is a relatively large component, it is necessary to downsize the entire device. There are drawbacks that hinder this. In addition, the high value current voltage V1 shown in Fig. 2 is often as high as several KV,
There is a disadvantage that the insulation between the first and second orders of the transformer 5 and the insulation between the high voltage output part and other low voltage parts requires a considerable amount of cost. Furthermore, when it is desired to make the superimposed alternating current have a low frequency in order to obtain desired load control characteristics, there is a drawback that the transformer 5 becomes large in order to avoid magnetic saturation of the transformer 5.

[Objective] The present invention has been made in view of the above points, and provides a high-voltage power supply device that can prevent uneven charging in copying machines and the like and obtain good images by superimposing alternating current on direct current. The purpose is to

[Example] Hereinafter, the present invention will be described in detail based on an example shown in the drawings.

FIG. 3 shows an example of the circuit configuration of the power supply device according to the present invention. In FIG. 3, the reference numeral 12 is a step-up transformer, and this step-up transformer 12
A switching transistor 2 is connected to one end of the primary side of the
1 of the step-up transformer 12 is connected to the collector of step-up transformer 12 by this switching transistor 20.
The power supply to the next side is interrupted. That is, the base of switching transistor 20 is controlled by the output of oscillator 21.

On the other hand, the other end of the primary side of the step-up transformer 12 is connected to a known chopper type switching regulator composed of a transistor 26, resistors 22, 27 to 29, a diode 25, a choke coil 24, and a smoothing capacitor 23. There is. This switching regulator is used for control purposes as detailed later.
Controlled by IC30.

A diode 1 is connected to the secondary side of the step-up transformer 12.
3. A rectifier and smoothing circuit consisting of a capacitor 14 and a discharge resistor 15 is connected to the step-up transformer 1.
The voltage boosted by 2 is converted into direct current and is supplied to the load 18. The load current flowing through the load 18 is detected as a voltage via the detection resistor 16. The detected voltage is integrated (smoothed) by a capacitor 17, and further fed back to pins 1 and 16 of the control IC 30 via a resistor 19 for overcurrent protection.

The control IC 30 has 16 pins as shown in the figure, and controls the switching operation of the switching regulator in accordance with the control input. A switching regulator is connected to pins 10 to 12 as shown. A resistor 31 and a capacitor 32 connected to pins 5 and 6 are time constants that determine the switching frequency. Also, 2
A resistor 34 and a capacitor 33 connected to pin No. 3 and pin No. 3 form a feedback circuit of an error amplifier within the IC 30. Furthermore, resistance 36, 37
is the resistor for dead time control of IC30,
The capacitor 35 is for ripple removal.

Further, the output of the oscillator 38 is connected to the second pin of the IC 30, that is, one input of the error amplifier. The configuration of this oscillator will be described in detail. The output voltage of oscillator 38 is determined by resistors 39 and 40. Capacitor 41 is for ripple removal.

FIG. 4 shows the internal structure of the switching regulator control IC 30 of FIG. 3 in detail.

In FIG. 4, block 42 connected to pins 7 and 12 is a reference regulator that generates a 5V reference voltage, block 43 is a low voltage stop, and block 44 is an oscillator. code 4
5 is a 0.1V power supply, 46 is a dead time comparator, 47 is an AND gate,
48 is a PWM (pulse width modulation) comparator, 4
9 and 50 are both error amplifiers. Also, 51
is an inverter, 52 is a T flip-flop, 5
3 and 54 are NAND gates, and 57 and 58 are transistors for current amplification.

5A to 5C show waveforms at various parts of the IC 30 shown in FIG. 4.

FIG. 5A shows the output waveform of the 11th pin, and FIG. Figure C shows the waveform of pin 3, that is, the input waveform of the PWM comparator.

FIG. 6 shows the configuration of the oscillator 38 of FIG. 3.

The potential formed by the resistors 39 and 40 is input to a comparator circuit constituted by an operational amplifier 68 and resistors 77 and 78. This comparator circuit generates a square wave at its output by comparing the output voltage 66 with the input voltage. The gain of the square wave is adjusted to a predetermined level by variable resistor 75 and resistor 76, and resistors 70, 71, 73 and capacitor 6.
9, 72, 74 and an operational amplifier 67 to generate a sine wave superimposed on an input 65.

FIG. 7 shows an example of the circuit of the oscillator 21. Here, an oscillator using an operational amplifier 86 is shown. Resistors 85 and 90 are connected to the + input of the operational amplifier 86.
The threshold value formed by the resistor 83 is input, and its own output is fed back via the resistor 83. Further, a time constant circuit consisting of a resistor 87 and a capacitor 91 that regulates the oscillation frequency is connected between the output terminal and one input. The generated triangular wave has its gain adjusted by resistors 81 and 82, and is input to the base of a switching transistor 80 that performs power amplification. The collector of the transistor 80 is connected to the power supply voltage Vcc via a current limiting resistor 79, and the collector of the switching transistor 28
connected to the base of

As is well known, in such an oscillation circuit, a square wave pulse is formed by the operational amplifier 122 repeating high-level and low-level outputs based on a threshold value. Figure 8 shows the operational amplifier 86 in Figure 7.
The waveform of one input terminal of is shown. code 92,9
4 is the input threshold level of the +input terminal of the operational amplifier 86, which is switched depending on whether the output is high or low. Since the capacitor 87 is charged in the high level section P, the voltage at the - input terminal rises according to a time constant, and when this reaches level 92, the amplifier switches to low level. In the low level section Q, the capacitor 87 is discharged, and the voltage at the - input terminal decreases according to the time constant. In this section, the threshold voltage of the + input terminal is set to level 94 by the feedback resistor 83, and when the - input voltage reaches this level, the operational amplifier 122 is inverted again. By repeating such operations, the transistor 80 is turned on and off, and the switching transistor 20 shown in FIG. 3 is driven by its current amplified output.

Next, the operation of the above configuration will be explained.

In FIG. 3, all high voltage current flowing through load 18 returns to the transformer via resistor 16. This current is detected by a detection resistor 16 and integrated by a capacitor 17. The voltage corresponding to the load current is controlled by the control IC30.
The voltage is compared with a reference voltage by an error amplifier comprised of operational amplifiers 49 and 50 within. The operational amplifier 49 works for constant current control, and the operational amplifier 50 works for overcurrent protection.

As shown in FIG. 9, the potential at the negative input terminal of the operational amplifier 49 has a voltage waveform in which the sine wave 66 obtained by the oscillator 38 as described above is superimposed on the divided potential 97 of the resistors 39 and 40. .

The control IC 30 controls the output of the switching regulator to keep the load current (or voltage) constant by applying a detection voltage according to the load current (or voltage) to an internal error amplifier. Therefore, as mentioned above, by giving a signal obtained by superimposing a sine wave on the detection voltage as the reference voltage of the error amplifier inside the control IC, the power generated by the switching regulator is changed, and the secondary side The high voltage output voltage can be oscillated.

Here, FIG. 10 shows the input/output relationship in this embodiment.

Here, the horizontal axis represents the voltage at pin 2 of the control IC 30, and the vertical axis represents the high voltage output voltage. Here, the broken line indicated by reference numeral 97 is the reference voltage of the resistors 39 and 40, and the control voltage input to the control IC is oscillated above and below this voltage 97 by the oscillator 38 as described above. Control IC 30, transistor 26
The amplification factor of the switching regulator is linear as shown by the straight line 61, and by inputting the above sine wave to the control IC 30, a high voltage waveform in which the sine wave is superimposed on the anode of the diode 13 in Fig. 3 is generated. 59 can be obtained.

As described above, in a high-voltage power supply with a constant current output such that the integral value of the high-voltage output current is constant, an output equivalent to the high-voltage output obtained by superimposing alternating current obtained by the conventional alternating current superimposing method can be obtained. I can do it. According to the above configuration, the output waveform equivalent to the conventional one is obtained by changing the intensity of the high voltage output at a predetermined frequency, so the conventional AC transformer can be omitted, and the power supply section can be significantly downsized. can be formed into Naturally, since there is no alternating current transformer, even when setting the superimposed alternating current to a low frequency, there are no restrictions caused by increasing the size of the transformer, making the design work easier. Furthermore, since there are fewer connection points that handle high voltage, insulation from other low voltage parts becomes easier and costs can be reduced.

The embodiments described above are for high-voltage power supplies that perform constant current control to keep the load current constant; however, it goes without saying that the present invention can also be implemented in high-voltage power supplies that control the load voltage to be constant. . When performing constant voltage control, a voltage dividing resistor is inserted in parallel with the load 18 to form a detection voltage according to the load voltage, and this detection voltage is used for control in the same way as above.
It can be used as an IC control input.

In the embodiments described above, the AC waveform output from the oscillator 38 is shown as a sine wave, but any desired waveform such as a rectangular wave, sawtooth wave, triangular wave, etc. can be used. This allows the output intensity to be varied in a desired variation pattern depending on the nature of the load.
From the perspective of conventional technical thinking, this corresponds to an operation in which alternating current of a desired waveform is superimposed on high voltage direct current output. Further, although the waveform of the oscillator 26 is set to have a constant frequency, it is also possible to change it depending on the desired load characteristics.

[Effect] Good images can be obtained by superimposing alternating current on high voltage DC output.

As is clear from the above description, according to the present invention, in a high-voltage power supply device that obtains a high-voltage output on the secondary side by intermittent operation of the primary side of the boosting means, it is possible to compare the load current or load voltage with a reference value. Since the configuration includes a means for controlling the primary side disconnecting means and a means for changing the reference value according to a predetermined frequency, the high voltage output with superimposed alternating current is achieved with a low cost and compact configuration. It is possible to provide an excellent high-voltage power supply device that can obtain

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing the configuration of a conventional high-voltage power supply, FIG. 2 is a waveform diagram showing the output of the circuit in FIG. 1, and FIG. Figure 3 is a circuit diagram showing the configuration of the high voltage power supply circuit according to the present invention, Figure 4 is a circuit diagram showing the detailed configuration of the control IC in Figure 3, and Figure 5A.
-C are waveform diagrams showing voltage waveforms of various parts of the control IC, FIG. 6 is a circuit diagram explaining in detail the configuration of the oscillator 38 in FIG. 3, and FIG. 7 is a diagram showing the configuration of the oscillator 21 in FIG. 3. Figure 8 is a waveform diagram showing the output of the circuit in Figure 7, Figure 9 is a waveform diagram showing the control input signal input to the control IC, and Figure 10 is the circuit diagram shown.
The figure is a diagram showing the input/output relationship in the device of the present invention. 12... Step-up transformer, 21, 30... Oscillator, 30... Control IC, 20, 26... Switching transistor.

Claims (1)

[Claims] 1. In a high voltage power supply device which obtains a high voltage output on the secondary side by intermitting the primary side of the boosting means, means for controlling the primary side intermittent means by comparing the load current or load voltage with a reference value; A high-voltage power supply device comprising means for changing the value according to a predetermined frequency.