JP2723264B2 - Power supply - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply device, and more particularly, to a power supply device for outputting a high voltage in which an alternating current and a special current are superimposed.

[Related Art] Conventionally, various image forming apparatuses such as an electrophotographic printer and a copying machine have been known. In this type of apparatus, a DC, AC, or AC / DC superimposed high voltage is required for the charging step, the developing step, and the like. In particular, the developing bias applied to the developing device is a high voltage of AC / DC superposition. Conventionally, the power source for the developing bias is a step-up transformer for low-frequency AC output, and is coupled to the transformer to superimpose a DC voltage on the AC output. In many cases, DC / DC inverters were used.

[Problems to be Solved by the Invention] However, in the above-described conventional configuration, the low-frequency AC step-up transformer for generating the AC component of the developing bias becomes large, and the frequency of the AC component of the bias is in the audible band. For this reason, there is a problem that a considerable amount of noise is generated, and it is very difficult to reduce the noise. Further, there is a disadvantage that it is impossible to largely change the duty ratio from 50% because of the transformer's magnetization.

In view of the above problems, it is an object of the present invention to provide a power supply device that removes a low-frequency AC boost transformer and generates a power supply voltage of AC / DC superposition in which an AC component having a low frequency and a variable duty ratio is superimposed. It is in.

Means for Solving the Problems In order to solve the above problems, according to the present invention, in a power supply device for outputting a high voltage in which AC and DC are superimposed, a low frequency oscillator, a high frequency oscillator, An amplitude modulator that modulates the output of the high-frequency oscillator with the output of the oscillator, a transformer that controls the low-voltage DC input on the primary side according to the output of the amplitude modulator, and a rectifier that rectifies the output of the transformer. Switch means for intermittently turning on and off between the output point of the rectifier and the ground potential in synchronization with the output signal of the low-frequency oscillator; and an AC voltage generated at a connection point between the switch means and the rectifier is clamped to a predetermined DC level. A clamp circuit for supplying power to a post-load, and an amplitude value of an output AC component on a secondary side of the transformer is detected. Based on the detected value, an output of the high-frequency oscillator is transmitted to the transformer via the amplitude modulator. In this case, the amplitude of the output AC component is stabilized by controlling the length of the period transmitted to the power supply.

[Operation] According to the above configuration, the transformer is intermittently excited by the output of the high-frequency oscillator, so that there is no need to use a conventional low-frequency boosting transformer. Further, the amplitude of the output AC component is detected by detecting the amplitude value of the output AC component, and controlling the length of the period during which the output of the high-frequency oscillator is transmitted to the transformer via the amplitude modulator. Can be stabilized.

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

FIG. 1 shows an example of a circuit configuration of a power supply device employing the present invention, and FIG. 2 shows signal waveforms at various parts of the circuit of FIG.

In FIG. 1, reference numerals 1 and 2 denote oscillators for generating rectangular-wave low-voltage alternating current, respectively. The oscillator 1 is a rectangular wave having a frequency of 1800 Hz and a duty ratio of 20% (FIG. 2A). , And generates a signal of a rectangular wave (FIG. 2B) having a duty ratio of 50%.

The output of the oscillator 2 is input to the modulator 3, and the output signal of the oscillator 1 is amplitude-modulated by almost 100%. The modulator 3
The output signal controls the application of the low-voltage power supply voltage + Vcc to the primary winding of the step-up transformer T1 via the transistor Q1.

A rectifying diode D is connected to the secondary side of the step-up transformer T1.
1.Capacitor C1, diode D via discharge resistor R1
2. A DC power supply 5 is connected to a clamp circuit for DC component superposition. The clamp output is output from the terminal P1. The connection point between the resistor R1 and the clamping capacitor C1 is a switch 4 composed of a relay, an analog switch, and the like.
Can be grounded. The connection between the step-up transformer T1 and the rectifier diode D1 is a flyback method as shown in the figure.

As shown in FIG. 2 (c), the switch 4 is turned on in synchronization with the low level output of the oscillator 1, that is, the cutoff of the transistor Q1 and the step-up transformer T1.

During the period when the transistor Q1 is driven at 50 kHz, + V1 is obtained at the cathode of the clamping diode D1 and smoothed by the clamping capacitor C1, so that the output of the switch 4 is as shown in FIG. 2 (c). Become. The output obtained here is connected to the output terminal P1 by the capacitor C1, but the diode D2 conducts at the positive peak and is clamped by the clamping DC power supply 5 having an output voltage of -VE. An output having an output amplitude V1 and a positive peak value of −VE is obtained at P1.

This output is obtained by superimposing a negative DC voltage -VE and a rectangular wave AC of 1800 Hz and voltage V1 as shown in FIG. 2 (d), and is used as an electrophotographic developing bias.

According to the above configuration, since the converter transformer T1 is driven at a high frequency, it is not necessary to use a large transformer capable of driving at a low frequency as in the related art, and the power supply unit can be configured to be small and lightweight, and noise can be reduced. Countermeasures are easy.

FIGS. 1 and 2 show the most basic configuration, but various modifications as shown in FIG. 3 and thereafter are possible. In the following, the embodiments after FIG. 3 will be described. However, the same reference numerals are used for the same or corresponding components as those in the above embodiment, and the detailed description is omitted.

Although FIG. 1 does not show a configuration for stabilizing the output, FIG. 3 shows that the oscillator 2 applied to the base of the transistor Q1 is used to stabilize the amplitude of the output AC component to a predetermined value. A configuration for controlling the number of output pulses is provided.

That is, in FIG. 3, the output voltage (V1) of the switch 4
Is divided and rectified and smoothed by resistors R2 and R3 and diodes D3 and D2, and compared with a reference voltage value corresponding to a predetermined output amplitude externally input to a terminal P2 by an error amplifier 6 and the output of the comparator 10 Input to one of the input terminals.

The output of the oscillator 1 is input to the other input terminal of the comparator 10 via the integration circuit 9 using a CR filter circuit or an operational amplifier. The output of the oscillator 1 is connected to the inverter 20 for controlling the transistor Q2 forming the switch 4 and to the control input terminal of the modulator 3.

The switch 4 is composed of a high voltage transistor or FET, and its base is controlled by an inverter 20 via bias resistors R5 and R5 '. Transistor
Q2 is controlled to conduct by the low level output of the oscillator 1.

FIG. 4 shows a waveform diagram during operation in the configuration of FIG.

As shown in FIGS. 4 (a) and 4 (e), the oscillators 1 and 2 have a low frequency (1800 Hz) and a high frequency (50
KHz). Transistor Q constituting switch 4
4 is intermittently synchronized with the output pulse of the oscillator 1 as in the previous embodiment, as shown in FIG. 4 (b).

The error amplifier 6 compares a reference voltage corresponding to a predetermined AC component amplitude input from the terminal P2 with a voltage (symbol g in FIG. 4 (c)) corresponding to an actual amplitude value obtained from the resistor R3. The deviation is input to the comparator 10. On the other hand, the other input of the comparator 10 is supplied with the integrated waveform (reference f in FIG. 4 (c)) by the integrating circuit 9 of the oscillator 1. As a result, the comparator 10 outputs the waveform f of FIG. 4 (c). ,
A pulse having a timing as shown in FIG. 4 (d) is output during a period when g is f> g.

The output signal of the comparator 10 controls the modulation operation of the modulator 3 only during the low level period.

In this way, the number of high-frequency pulses input to the transistor Q1 is controlled according to the amplitude value of the AC component, so that the amplitude value of the AC component can be stabilized.

In FIG. 5, the AC amplitude is stabilized in the same manner as in the case of FIG. 3, but the DC power supply 5 for clamping is generated from the output point of the switch 4 here.

In FIG. 5, a part of the amplitude detection circuit, that is, the resistor R2,
The voltage at the connection point of the diode D3 is input to a voltage doubler rectifier circuit composed of diodes D4 and D5 and capacitors C3 and C4 to obtain a power supply voltage −VE for clamping. With such a configuration, the power supply unit can be simply and inexpensively configured without using a separate power supply.
Further, since the DC component is generated using the already stabilized AC component, the AC and DC components can be easily stabilized without using a separate stabilizing circuit.

In FIG. 6, the secondary-side output of the step-up transformer T1 is voltage-double rectified by the capacitor C5 and the diodes D1 and D6 to generate an AC component voltage V1. According to such a configuration, the withstand voltage of the step-up transformer T1 can be reduced, so that the configuration is simpler and less expensive. Other configurations are the same as those in FIG.

As the oscillator 1 for generating the low frequency, a known circuit configuration can be used. For example, a configuration as shown in FIG. 7 can be used. The oscillator shown in FIG. 7 has an operational amplifier 70 having a resistor R7 and a capacitor C6 as feedback time constants.
The waveform of the output terminal of the operational amplifier 70 is a rectangular wave as shown in FIG.
Is a triangular wave as shown.

By extracting the triangular wave signal and comparing the reference voltage (DC) input from the terminal P3 by the comparator 80, a rectangular wave having an arbitrary duty ratio according to the reference voltage can be output to the output of the comparator 80. . Therefore,
With such a configuration, it is possible to arbitrarily control the duty ratio of the AC component of the developing bias of the electrophotographic image forming apparatus, which has been impossible in the related art.

[Effects of the Invention] As is clear from the above, according to the present invention, in a power supply device for outputting a high voltage on which AC and DC are superimposed, a low frequency oscillator, a high frequency oscillator, and a high frequency An amplitude modulator that modulates the output of the oscillator, a transformer whose primary low-voltage DC input is controlled according to the output of the amplitude modulator, a rectifier that rectifies the output of the transformer, and an output point of the rectifier Switch means for turning on and off in synchronization with the output signal of the low-frequency oscillator between the switch and the ground potential. An AC voltage generated at a connection point between the switch means and the rectifier is clamped to a predetermined DC level, and then supplied to a load. A clamp circuit for detecting an amplitude value of an output AC component on the secondary side of the transformer, and based on the detected value, a length of time during which an output of the high-frequency oscillator is transmitted to the transformer via the amplitude modulator; The transformer is intermittently excited by the output of the high-frequency oscillator because it employs a configuration consisting of means for controlling the amplitude of the output AC component by controlling the output.
There is no need to use a low-frequency step-up transformer as in the past, and the power supply unit can be made simpler, cheaper, smaller, and lighter to improve reliability, and radiation noise countermeasures become easier. Period in which the duty ratio of the frequency AC output can be arbitrarily controlled, and the amplitude value of the output AC component is detected, and the output of the high-frequency oscillator is transmitted to the transformer via the amplitude modulator accordingly. There is an excellent advantage that the amplitude of the output AC component can be easily and inexpensively stabilized without using a complicated stabilizing circuit by controlling the length.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of a power supply device adopting the present invention, FIGS. 2 (a) to 2 (d) are waveform diagrams showing voltage waveforms of respective parts of the device of FIG. 1, and FIG. 1 is a circuit diagram showing a modification of the basic configuration of FIG. 1. FIG. 3 is a circuit diagram showing an example of stabilizing the output amplitude. FIGS. 4 (a) to 4 (e) show voltage waveforms at various parts in the configuration of FIG. FIG. 5 is a circuit diagram showing a specific example of a clamp power supply, FIG. 6 is a circuit diagram showing an example of a secondary-side output circuit of a converter transformer, and FIG. 7 is a low-frequency oscillator having a variable duty ratio. FIG. 3 is a circuit diagram showing a specific example of the embodiment. 1 ... oscillator 2 ... oscillator 3 ... modulator 4 ... switch 5 ... power supply 6 ... error amplifier 7 ... PWM circuit, 9 ... integration circuit 10, 80 ... comparator

Claims (1)

(57) [Claims] 1. A power supply device for outputting a high voltage on which AC and DC are superimposed, a low-frequency oscillator, a high-frequency oscillator, an amplitude modulator for modulating an output of the high-frequency oscillator by an output of the low-frequency oscillator, A transformer whose low-voltage DC input on the primary side is controlled according to the output of the modulator, a rectifier for rectifying the output of the transformer, and an output signal of the low-frequency oscillator between an output point of the rectifier and a ground potential. Switch means for switching on and off in synchronism with a switch circuit, a clamp circuit for clamping an AC voltage generated at a connection point between the switch means and the rectifier to a predetermined DC level, and thereafter feeding the load, and an output AC component on the secondary side of the transformer. The amplitude of the output AC component is controlled by controlling the length of the period during which the output of the high-frequency oscillator is transmitted to the transformer via the amplitude modulator based on the detected value. Power supply that comprises a means for Joka.