JPH071375B2 - Power supply circuit and image forming apparatus provided with this power supply circuit - Google Patents

Description

The present invention relates to a power supply circuit for energizing a load driven by a high frequency voltage such as a fluorescent lamp and an image forming apparatus provided with this power supply circuit.

Conventionally, an original is exposed by a fluorescent lamp, and its reflected light is guided onto a photoconductor through an optical system composed of a lens and a mirror,
An electrostatic copying apparatus has been proposed in which an electrostatic latent image is formed on a photoconductor, and then the latent image is developed and transferred to a transfer sheet to perform a process operation. Further, recently, a device has been proposed in which reflected light exposed by a fluorescent lamp is guided to an image sensor such as a CCD to electrically read an image.

These devices are provided with a plurality of load members for image formation that are operated by energization, in addition to the above-described fluorescent light for exposing the original. FIG. 1 shows a schematic structure of a conventional copying apparatus. In the figure, 7 is an original table on which an original to be copied is placed, 6 is a fluorescent lamp for exposing the original on the original table 7, 11 is a photosensitive drum, and 9 and 10 are exposed by the fluorescent lamp 6. It is a mirror for guiding the reflected light from the document to the photosensitive drum 11, and 8
Is a lens for forming an image of the light on the photosensitive drum 11. The photosensitive drum 11 rotates in the direction of the arrow, and the primary charger
The reflected light from the original after being uniformly charged by 14 forms an electrostatic latent image corresponding to the original image on the surface thereof. This latent image is developed by the developing device 12, and is transferred onto the transfer paper fed by a paper feeding mechanism (not shown) by the action of the transfer charger 15. Also, the drum surface after transfer is a cleaner
At 13, cleaning such as removal of the toner to be multiplied and removed is performed.

On the other hand, reference numeral 1 is a plug, which is inserted into an outlet of a commercial power source and supplies an alternating-current commercial power source to the apparatus. A switching regulator 2 generates a stable predetermined DC voltage based on the commercial AC power supply. A high-voltage transformer 3 converts a DC voltage from the switching regulator 2 into a high-voltage voltage for driving the primary charging device 14, the developing device 12, the transfer charging device 15, etc., and supplies it to each part. A sequence control unit 4 is composed of a well-known microcomputer or the like which operates by the DC voltage from the switching regulator 2 and controls the operation of each part of the copying machine. Reference numeral 5 denotes a fluorescent lamp ballast for achieving stable lighting of the fluorescent lamp 6, the detailed circuit configuration of which is shown in FIG. 2, and the timing chart of its operating state is shown in FIG.
Shown in the figure. In the figure, 21 is a fluorescent lamp, 22 is an oscillation transformer, and 23 is a switching transistor. A DC voltage from the above-mentioned switching regulator is applied to the terminal C.
An ON / OFF signal indicating the lighting period of the fluorescent lamp is input to the terminal A as shown in FIG. 3A, and when the signal is at a high level, the fluorescent lamp 21 can be energized. Further, a pulse signal as shown in FIG. 3 (2) is input to the terminal B, and a high frequency tube power source is applied to the fluorescent lamp from the transformer 22 as shown in FIG. 3 (3) during the high level period of this pulse signal. It Therefore, by controlling the duty ratio of this pulse signal, the amount of electricity to the fluorescent lamp 21 is controlled, and the fluorescent lamp 21 is controlled.
The light emission amount of is variable.

However, in the circuit configuration as shown in FIG. 1, not only the circuit configuration is complicated, but also the switching transistor, the oscillation transformer, etc. are relatively expensive, and the storage space for each component is large, so that the device is downsized. It was a hindrance to him.

The present invention has been made in view of the above points, and an object thereof is to provide an inexpensive and compact power supply circuit.

Another object of the present invention is to provide an image forming apparatus capable of driving a fluorescent lamp which is turned on at a high frequency for image formation with a simple structure.

That is, the present invention relates to a transformer, a first switching means connected to the primary side of the transformer and on / off controlled to operate the transformer, and a secondary side of the transformer to generate a DC voltage. A second secondary winding circuit for feeding back a part of the direct current voltage to the switching means, and a second secondary winding circuit connected to the secondary side of the transformer for generating a high frequency voltage and supplying it to an alternating current load. A second winding circuit, and second switching means for inputting a control pulse signal and controlling switching of the high frequency voltage supplied to the AC load through a rectifying element in response to the control pulse signal. And a power supply circuit having

The present invention also relates to a DC load for image formation, a fluorescent lamp used for image formation, a transformer, and a first side connected to the primary side of the transformer and controlled to turn on and off to operate the transformer. First switching means and a secondary side of the transformer for generating a direct current voltage, supplying the direct current voltage to the direct current load, and feeding back a part of the direct current voltage to the switching means. Secondary winding circuit connected to the secondary side of the transformer, generates a high frequency voltage, supplies the high frequency voltage to the fluorescent lamp, and turns on the fluorescent lamp at a high frequency, and a control pulse. A second switching means for inputting a signal and responding to the control pulse signal to control switching of the high frequency voltage supplied to the fluorescent lamp through a rectifying element. It is to provide.

Hereinafter, the present invention will be described in more detail.

FIG. 4 shows an example of the circuit configuration of a copying apparatus to which the present invention is applied. The configuration shown in FIG. 4 shares the resonance part of the switching regulator and the fluorescent lamp ballast in the electric unit in the conventional circuit configuration shown in FIG.

FIG. 4 will be described. In FIG. 4, a single ended method is used in the switching circuit section. A commercial AC power source input from a socket (not shown) is full-wave rectified and smoothed by a diode bridge D1 and a capacitor C1. This smoothed high-voltage DC voltage serves as a bias power supply for the converter circuit.

The DC energy is applied is converted to alternating current to the primary winding L ₂ by being switching-in period of 20KHz~40KHz by when to quenching transistor Q1 of the converter unit, via the inverter transformer (pulse transformer) T2 It is transmitted to the secondary side rectification unit by the secondary side winding L ₃ .

In the rectification unit, the high-frequency AC is rectified by rectification diodes D2 and D3 having a fast recovery time, and further, a predetermined DC voltage V ₀ with less ripple is supplied to the load by the filter unit including the chioke coil L1 and the capacitor C2.
The method of stabilizing the output V ₀ is to compare the output voltage taken in from the voltage dividing resistor R2 with the reference voltage E1 by the air amplifier Q3, detect the error, and amplify it. The amplified error signal is modulated by the next pulse width exchange circuit PWM and sent to the drive circuit DV. The drive circuit DV is a circuit for driving the switching transistor Q1 of the converter unit, and the transformer T1 serves to insulate the primary side and the secondary side of the inverter transformer T2. The switching transistor Q1 driven by the drive circuit DV has its on / off period controlled by its control signal to stabilize the switching transistor Q1. As described above, the control signal system of the switching power supply draws a closed loop, and power flows from the input to the output.

The explanation given above is for the control part of the DC stabilized power supply. Next, the lighting control circuit of the fluorescent lamp FL will be explained.

Stabilization on the secondary side of the inverter transformer T2 described above
In addition to winding L3 for DC power output, 2 for high frequency lighting of fluorescent lamps
The next winding L4 is also wound. By turning on / off the transistor Q2 by the lamp lighting control signal LS input to the terminal A, the filament preheating and the lamp current IL are controlled as shown in FIG. The signal LS is usually a PWM signal of about 1 KHz. Referring to FIG. 5, when the signal LS is at a high level, the transistor Q2 in FIG. 4 is turned on, and the high frequency current i generated in the secondary winding L4 of the inverter transformer T2 is generated by the high frequency response diode bridge D4 → resistor R1 → It flows through the route of transistor Q2 → diode bridge D4 and becomes the preheating current for the filament of the fluorescent lamp FL. When the signal LS is low level, the transistor Q2 is turned off, and the high frequency current i flows as the lamp current IL of the fluorescent lamp.

As described above, since the input side converter section of the line operation type switching current inverter transformer is also shared as the input side converter section of the inverter transformer for the high frequency lighting control of the fluorescent lamp, each of the conventional separate The switching power supply unit and the fluorescent lamp ballast unit, which are constituted by the control circuit, are integrated and made compact. Also, in terms of cost, two conventional converter units are combined into one, so that a significant cost reduction is achieved. Also functionally, the PW of the signal LS
Dimming of the fluorescent lamp is possible by changing the duty ratio of M, which does not impair the function of the conventional ballast.

The present invention is not limited to the circuit configuration shown in FIG. 4, but the converter system can also function similarly if it is a push-pull system, a flypack system, or the like, and the modulation unit or the like is not limited to the PWM system, and is not limited to the V / F. A conversion method or the like can also be used. In addition to the preheating circuit of the fluorescent lamp shown in FIG. 4, a method of independently relying on the filament heating coil from the secondary side of the inverter transformer T2 is also effective.

Further, the present invention can be applied to an apparatus other than a copying apparatus, for example, an image forming apparatus having a fluorescent lamp that is turned on at a high frequency, such as a device such as a facsimile machine that photoelectrically reads an original image with an image sensor.

As described above, according to the present invention, the stabilized DC current and the high frequency power source can be configured by using a common transformer.
The circuit scale can be reduced, and the cost is also effective. Therefore, the size of the device can be reduced by using this power supply circuit.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration example of a conventional copying apparatus, FIG. 2 is a circuit diagram of an example of the fluorescent lamp ballast shown in FIG. 1, and FIG. 3 is a timing chart diagram showing an operating state of the circuit shown in FIG. FIG. 4 is a diagram showing a circuit configuration example according to the present invention, and FIG. 5 is a timing chart showing an operating state of the circuit shown in FIG. 4, FL is a fluorescent lamp, Q1 is a switching transistor, T2 is an inverter transformer, and DV is The drive circuit and PWM are pulse width conversion circuits.

Claims (2)

[Claims] 1. A transformer, a first switching means which is connected to a primary side of the transformer and which is on / off controlled to operate the transformer, and a secondary side of the transformer, which generates a DC voltage. ,
A first secondary winding circuit for feeding back a part of the direct current voltage to the switching means, and a second secondary winding circuit connected to the secondary side of the transformer for generating a high frequency voltage and supplying the alternating current load. A second winding circuit, and a second switching means for inputting a control pulse signal and, in response to the control pulse signal, controlling switching of the high frequency voltage supplied to the AC load through a rectifying element. A power supply circuit having. 2. A DC load for image formation, a fluorescent lamp used for image formation, a transformer, and a first side which is connected to the primary side of the transformer and is on / off controlled to operate the transformer. Connected to the switching means and the secondary side of the transformer to generate a DC voltage,
The DC voltage is supplied to the DC load, and a first secondary winding circuit for feeding back a part of the DC voltage to the switching means and a secondary side of the transformer are connected to supply a high frequency voltage. A second secondary winding circuit that is generated and supplied to the fluorescent lamp and turns on the fluorescent lamp at a high frequency, and a control pulse signal is input, and is supplied to the fluorescent lamp in response to the control pulse signal. An image forming apparatus comprising: a second switching unit that controls switching of a high-frequency voltage through a rectifying element.