JPH0626466B2 - High voltage power supply - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a high-voltage power supply device that supplies a high-voltage current in which a direct current is superimposed on an alternating current.

[Prior Art] As one of the high-voltage power supply devices as described above, a circuit as shown in FIG. 1 is often used for controlling a charger of a copying machine.

The circuit shown in FIG. 1 is a circuit for generating a high voltage current by superimposing a desired alternating current on a high voltage DC. A rectangular wave (or sine wave) pulse is input from terminals 3 and 4 of the same figure to a step-up transformer 6, and an alternating current boosted according to the winding ratio is generated on the secondary side thereof. A high-voltage DC voltage V1 is obtained by a rectifying and smoothing circuit composed of a load resistor 10.

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

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

The conventional configuration for generating a high voltage by superimposing alternating current as described above requires a transformer of two systems of a direct current system and an alternating current system. Therefore, the cost is high, and since the transformer is a relatively large component, the overall size of the device can be reduced. There is a drawback that prevents Also, the second
In many cases, the high-voltage DC voltage V1 shown in the figure is as high as several KV, and there is a drawback in that insulation between the primary and secondary sides of the transformer 5 and insulation of the high-voltage output part and other low-voltage parts requires a considerable cost. is there. Further, when it is desired to make the superposed alternating current have a low frequency in order to obtain a desired load control characteristic, there is a drawback that the transformer 5 becomes large in size in order to avoid magnetic saturation of the transformer 5.

[Objective] The present invention has been made in view of the above problems, and an object of the present invention is to provide a high-voltage power supply device that supplies a high-voltage current in which an alternating current is superimposed on a direct current at a small size and at low cost.

[Examples] Hereinafter, the present invention will be described in detail based on examples shown in the drawings.

FIG. 3 shows an example of the circuit configuration of the power supply device according to the present invention. A reference numeral 14 in FIG. 3 denotes a step-up transformer, and a low-voltage DC voltage Vcc is applied to one end of the step-up transformer 14 on the primary side through a filter including a resistor 12 and an electrolytic capacitor 13. . The collector of a switching transistor 28 is connected to the other end of the primary side, and the switching transistor 28 controls power supply to the primary side of the step-up transformer 14.

A rectifying / smoothing circuit including a diode 15, a capacitor 16 and a discharging resistor 17 is connected to the secondary side of the step-up transformer 14, and the voltage boosted by the step-up transformer 14 is converted into direct current and supplied to the load 18. It The load current flowing through the load 18 is detected as a voltage via the detection resistor 19. The detection voltage is integrated (smoothed) by the capacitor 20.
Further, it is led to a + input of an error amplifier 25 composed of an operational amplifier or the like via a bias circuit composed of resistors 21 and 22. The resistors 19 to 22 and the capacitor 20 form a high voltage current detection circuit 29.

The-input of the error amplifier 25 is supplied with a reference voltage obtained by dividing the low-voltage power supply voltage Vcc by the resistors 23 and 24 which form the reference voltage generator 30. The output 31 of the error amplifier 25 is input to the AC oscillator 26 and controls the AC oscillator 26.

FIG. 4 shows a detailed configuration of the AC oscillator 26 shown in FIG.

The output 31 of the error amplifier 25 is an operational amplifier 57, a resistor 5
It is input to the comparator circuit composed of 4, 55. This comparator circuit generates a rectangular wave at its output by comparing the output voltage 32 of the AC oscillator 26 with the input voltage. The rectangular wave gain is variable resistor 52, resistor 53
Adjusted to a predetermined level by resistors 47, 48, 5
0, capacitors 46, 49, 51, and operational amplifier 5
A sine wave that is input to the filter circuit composed of 6 and is superimposed on the input 31 is generated.

This is shown in FIG. In FIG. 5, reference numeral 31 is an error voltage output of the error amplifier 25, and an amplitude 3 is added to this voltage 31.
The sine wave with 6 is superimposed to produce the output 32.

The sine wave 32 generated by the AC oscillator 26 is PWM
(Pulse width modulator) 27 is input. The rectangular wave 33 output from the PWM 27 is input to the base of the switching transistor 28, and the PWM 27 controls the switching pulse width of the switching transistor 28 according to the load current.

FIG. 6 shows the structure of the PWM 27 in detail.

The output of the AC oscillator 26 is led to the + input of the comparator functioning as a triangular wave generator via the series connection of the resistor 64, the diode 63 and the resistor 62. The voltage at the voltage dividing point 89 of the resistors 58 and 59 of the power supply voltage Vcc is connected to the connection point 85, that is, the + input of the operational amplifier 68 via the diode 60 and the resistor 61. The-input of the comparator 68 is grounded by the capacitor 69.

The output terminal of the comparator 68 is pulled up to the power supply voltage via the resistor 65, and is further fed back to the + input via the feedback resistor 66.

The output of the comparator 68 is connected to the + input of the operational amplifier 73 via the resistors 67 and 70. Resistance 67, 70
Is connected to the-input of the comparator 68.

The negative input of the comparator 73 has a resistor 7 of the power supply voltage Vcc.
The voltage at the voltage dividing point 87 of 1, 72 is given. The comparator 73 has a feedback resistor 74, the output of which is a resistor 75.
Is pulled up to the power supply voltage. The output of the comparator 73 is connected to the base of the transistor 77 via the resistor 76.

The emitter of the transistor 77 is grounded, and the collector is connected to the power supply voltage Vcc via the resistor 78. The collector of the transistor 77 has resistors 79 and 80.
A transistor 81 connected in series via
It is connected to the base of 82. The emitter of the transistor 81 is connected to the power supply voltage via the resistor 83, and the emitter of the transistor 82 is grounded. The voltage at the connection point between the collector and the emitter of the transistors 81 and 82 is given to the base of the switching transistor 28 via the resistor 84.

FIG. 7 shows the voltage at each connection point in FIG.

In FIG. 7, reference numerals 86A and 86B indicate different potential changes at the connection point 86, respectively. When the output of the comparator 68 is low level, the electric potential 92 at the lower end of the triangular wave is Is uniquely determined by Here, the resistance value is indicated by R, the voltage value is indicated by V, and each resistance or connection point is indicated by a subscript (the same applies in the following formulas). Vf represents the forward potential of the diode.

Further, the potentials 93 and 94 at the upper end of the triangular wave are the comparator 68.
Is a high level potential and is controlled by the level of the output voltage 32 of the AC oscillator 26 input. At this time, the potential 92 is And changes depending on the potential V ₃₂ to reach a potential of 93 or a potential of 94. The inclination of the triangular wave at the connection point 68 is determined by the time constants of the resistor 67 and the capacitor 69.

Further, the potential 87 is the potential of the connection point 87, Is uniquely determined by this potential 87 and the potential 86
By comparing the potentials of the above with the comparator 87, rectangular wave pulses as indicated by reference numerals 88A and 88B are formed.

When the voltage waveform of the connection point 86 is the waveform 86A, the output waveform of the comparator 73 becomes like the waveform 88A, and when the waveform of the connection point 86 is the waveform 86B, the output waveform of the comparator 73 becomes like the waveform 88B. .

As described above, since the time constant determined by the potential 92 at the lower end of the triangular wave, the potential at the connection point 87, the resistor 67, and the capacitor 69 is constant, the output of the comparator 73 does not depend on the change of the output 32 of the AC oscillator 26. The off time is 9 in FIG.
8, 101 are always equal, and the on-time is adjusted according to the output of the AC oscillator 26 as shown by 99, 100.

The rectangular wave pulse thus obtained is generated by the transistor 7
The current amplifying circuit composed of 7, 81, 82 and resistors 76, 78-80, 83, 84 drives the switching transistor 28 which is amplified by a predetermined gain and has a large current.

The output waveform of the PWM 27 is briefly shown in FIG. PWM2
In the output waveform 33 of FIG. 7, the off time 45 is always constant, and the on period 44 is adjusted by the output 32 of the AC oscillator 26.

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

In FIG. 3, all the high-voltage current flowing through the load 18 returns to the transformer via the resistor 19. This current is detected by the detection resistor 19
Detected by and integrated by the capacitor. Since this potential becomes a negative potential and falls outside the operating range of the error amplifier 25, the resistance 2
A bias is applied at 1 and 22, and the potential moved to the operation range of the error amplifier 25 is input to the error amplifier 25.

In the error amplifier 25, the reference potential formed by the resistors 22 and 23 is compared with the applied + side input. That is, if the + input is higher, the high level is output, and if the + input is higher, the low level is output, and both are kept at the same potential and stable.

As shown in FIG. 5, the sine wave generated by the AC oscillator 26 is superimposed on the output 31 of the error amplifier 25 to obtain a waveform 32. The relationship between the waveform 32 and the high voltage output at the connection point 34 in FIG. 3 is shown in FIG. Here, the horizontal axis is the AC oscillator 26
Of the output 32, the vertical axis represents the voltage of the high voltage output 34. The amplification factors of the PWM 27 and the step-up transformer 14 are linear as indicated by a straight line 43, and by inputting a sine wave to the PWM 27, a sine wave whose level is shifted to a high voltage can be generated at the connection point 34.

As described above, in a high-voltage power supply having a constant current output such that the integrated value of the high-voltage output current is constant, an output equivalent to the high-voltage output obtained by superimposing AC obtained by the conventional AC superposition method is obtained. You can 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 that the conventional AC transformer can be omitted and the power supply unit can be remarkably compact. Can be formed into As a matter of course, since there is no AC system transformer, the design work becomes easy even when the superposed AC is set to a low frequency. In addition, since the number of connection points handling high voltage is reduced, insulation processing from other low voltage parts is facilitated and the cost can be reduced.

In the above, an example of the high-voltage power supply device which performs constant current control so as to keep the load current constant has been shown, but the present invention can of course be implemented in a high-voltage power supply device where the load voltage is kept constant. .

FIG. 10 corresponds to FIG. 3 described above and shows an embodiment in which constant voltage control is performed. Here, the same or corresponding members as those described above are designated by the same reference numerals, and detailed description thereof will be omitted.

In the embodiment of FIG. 10, the voltage input to the error amplifier 25 is a voltage corresponding to the load voltage. That is, the negative input of the error amplifier 25 is input with a potential obtained by dividing the voltage applied to the load 18 by the resistors 17 and 19 and integrating it by the capacitor 20. The negative input of the error amplifier 25 is pulled up by the Zener diode 25A.
This Zener diode 25A is the resistor 21, 2 of FIG.
In the circuit corresponding to 2, the zener voltage serves to keep the input voltage within the operating range of the error amplifier 25. The power supply voltage Vcc is applied to the + input terminal of the error amplifier 25 through the resistor 2
A reference voltage divided by 3, 24 is applied. Therefore, in the case of the present embodiment, the error amplifier 25 includes the resistor 2
An error signal between a predetermined reference voltage determined corresponding to the divided voltages of 3 and 24 and the load voltage is output.

The operations of the AC oscillator 26 and the PWM 27 at the subsequent stage of the error amplifier 25 are the same as those described above. Therefore, according to the present embodiment, in the high voltage power source having a constant voltage output such that the integrated value of the high voltage output voltage becomes constant, The same effect as can be obtained.

In the above embodiments, the high voltage output is controlled by controlling the switching transistor that connects and disconnects the primary side low voltage power source of the step-up transformer. A configuration for controlling the electric power of is also conceivable.

FIG. 11 shows an example of such a configuration. 11th
In the figure, the switching transistor 98 is excited by a fixed frequency oscillator 110, and the power supply voltage Vcc to the other end of the step-up transformer 14 is applied to the series regulator 1.
It is controlled by 17. Series regulator 117
The operation of the error amplifier 25 having the same configuration as that of FIG.
It is controlled by the AC oscillator 26.

FIG. 12 shows an example of the circuit of the oscillator 110. Here, a transmitter using the operational amplifier 122 is shown. The threshold value formed by the resistors 120 to 123 is input to the + input of the operational amplifier 122, and its output is fed back via the resistor 126. Also, the output terminal,
Resistor 124 and capacitor 1 that regulate the frequency between the inputs
A time constant circuit consisting of 25 is connected. The generated pulse wave is input to the base of the switching transistor 129 which performs current amplification via the resistor 127. The collector of the transistor 129 is connected to the power supply voltage Vcc via the current limiting resistor 130 and is also connected to the base of the switching transistor 28.

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. Thirteenth
The figure shows the waveform at the-input terminal of the operational amplifier 122 in FIG. Reference numerals 72A and 72B are input threshold levels of the + input terminal of the operational amplifier 122, and the output is switched to either high or low. Since the capacitor 125 is charged in the high level section P, the voltage at the-input terminal rises according to the time constant, and when this reaches the level 72A, the amplifier switches to the low level. Low level section Q
Then, the capacitor 125 is discharged, and the voltage at the-input terminal decreases according to the time constant. Feedback resistor 126
Thus, the threshold voltage of the + input terminal is at level 72B, and when the − input voltage reaches this level, the operational amplifier 122 is inverted again. By repeating this operation, the transistor 129 is turned on and off, and the current-amplified output thereof causes the switching transistor 2 of FIG.
8 is driven.

On the other hand, one end of the primary winding of the step-up transformer 14 on the side opposite to the transistor 28 has transistors 114 and 115 and a resistor 1
It is connected to a series regulator 117 composed of 11 to 113 and 115. This series regulator 1
An AC oscillator 26 similar to the above is connected to the input of 17, and a sine wave controlled to keep the load voltage constant is input. The series regulator 117 changes the power supplied from the power supply to the step-up transformer 14 according to the input sine wave. It is to be noted that reference numeral 13 in FIG. 11 denotes a smoothing capacitor.

Even with such a configuration, high pressure can be generated on the secondary side, and in this case, the same effect as described above can be obtained.

In the embodiment described above, the AC waveform output from the AC oscillator 26 is shown as a sine wave, but a desired waveform such as a rectangular wave, a sawtooth wave, or a triangular wave can be used. This makes it possible to change the output intensity in a desired variation pattern according to the nature of the load. Viewed from the conventional technical idea, this corresponds to the operation of superimposing an alternating current of a desired waveform on the high voltage direct current output. Although the waveform of the AC oscillator 26 has a constant frequency, it may be changed according to desired load characteristics.

[Effects] As described above, the present invention rectifies the alternating current output from the secondary side of the transformer, and the means for intermittently supplying electric power to the primary side of the transformer with the first cycle. And a means for increasing / decreasing the amount of electric power supplied by the means for supplying electric power in the second cycle, thereby reducing the size and cost of the high-voltage power supply device for supplying high-voltage current in which alternating current is superimposed on direct current. Can be provided.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing the configuration of a conventional high-voltage power supply device, FIG. 2 is a waveform diagram showing the output in the circuit of FIG. 1, and FIG.
FIG. 3 is a circuit diagram showing the configuration of a high-voltage power supply circuit according to the present invention, and FIG.
FIG. 6 is a circuit diagram showing in detail the configuration of the AC oscillator in FIG. 3, FIG. 5 is a waveform diagram showing the output of the AC oscillator, and FIG.
FIG. 7 is a circuit diagram showing in detail the PWM configuration in FIG. 3, and FIG. 7 is a waveform diagram showing the waveform of each connection point in FIG.
FIG. 8 is a waveform diagram showing the output of PWM, FIG. 9 is a diagram showing the input / output relationship in the device of the present invention, FIG. 10 is a circuit diagram showing a different embodiment of the present invention, and FIG. Is the tenth
12 is a circuit diagram showing a configuration obtained by further modifying the embodiment shown in FIG.
FIG. 13 is a circuit diagram showing the configuration of the oscillator shown in FIG.
The figure is a diagram showing the voltage waveform at the negative input terminal of the operational amplifier of FIG. 14 ... Step-up transformer, 15 ... Diode 16, 20 ... Capacitor 19-24 ... Resistor, 25 ... Error amplifier 26 ... AC oscillator, 27 ... PWM 28 ... Switching transistor 110 ... Oscillator 117 ... Series regulator

Claims (1)

[Claims] 1. A transformer for outputting electric power input from the primary side as high-voltage electric power from the secondary side, and power supply for intermittently supplying electric power to the primary side of the transformer in a first cycle. Means, rectifying means for rectifying the alternating current output from the secondary side of the transforming means, and control means for increasing or decreasing the amount of power supplied by the power supply means in a second cycle. High-voltage power supply device.