JPH03289321A - High-voltage power source apparatus - Google Patents

Abstract

PURPOSE:To prevent a large abnormal current from continuously flowing by providing an abnormal current detecting means and output current controlling means so that an abnormal current can be detected immediately and a normal state can be restored by instantaneously lowering the output current in accordance with the detected value when the abnormal current flows to a load. CONSTITUTION:In a normal state, this high-voltage power source unit controls a PWM controller 11 at prescribed timing by using, for example, a control signal from a microcomputer (CPU) 10. In addition, this unit is equipped with an abnormal current detecting means 5 which detects an abnormal current when the current flows to a load, output current controlling means 13 which controls the output current by the time corresponding to the value of the abnormal current detected by the means 5, and means 14 and 16 which stop high- voltage outputting operations when the the control of the means 13 for lowering the output current repeatedly continues for a fixed period of time. Therefore, when an abnormal current flows to a high-voltage circuit, control can be made so as to avoid the abnormal current and, at the same time, such operations that stop a high-voltage output due to wrong detection can be prevented during normal operations.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a high-voltage power supply device that boosts an input voltage and supplies it to a load, and in particular, a high-voltage power supply device that boosts an input voltage and supplies it to a load, and in particular, a high-voltage power supply device that boosts an input voltage and supplies it to a load. The present invention relates to a high voltage power supply device suitable for applying high voltage to each charger such as a separate charger.

[Conventional technology]

Image forming apparatuses such as electrophotographic copying machines and laser printers perform a series of electrophotographic processes such as charging, exposure, development, and transfer and separation to form images.
In each process such as transfer and separation, a high voltage is applied to each charger from a high voltage power supply at a predetermined timing to cause corona discharge.

In such an image forming apparatus, if a short circuit or a drop in insulation occurs in any of the chargers that apply high voltage during image formation, such as the transfer charger or the transfer 2-separation charger, and an abnormal current flows, image formation may become impossible. Not only that, but there was also the risk that the recording paper inside the aircraft could emit smoke or catch fire.

To deal with this problem, high-voltage power supplies have traditionally been used that are equipped with a protection circuit that detects abnormal current flowing through each of the chargers (loads) mentioned above and shuts off the high-voltage output when an abnormality occurs. Ta.

FIG. 3 shows a conventional AC high voltage power supply device for applying AC high voltage to, for example, a separation charger, and FIG. 4 shows a conventional DC high voltage power supply device for applying DC high voltage to, for example, a charging charger, a transfer charger, etc. This is an example.

In any high-voltage power supply, normally the transistor Tr is controlled on and off at a predetermined timing by the control signal of the output control means 1, and the input voltage (DC24V) is controlled.
is supplied to the oscillation circuit 3 between the emitter and collector of this transistor Tr and through the ripple filter 2 to cause it to oscillate, and the oscillation output is applied to the primary side of the step-up transformer T to generate an AC high voltage on the secondary side. .

In the device shown in FIG. 3, the output voltage is directly supplied to the load, and in the device shown in FIG.
A DC high voltage is supplied to the load through a rectifying/smoothing circuit 4 including a capacitor 01 and the like.

In addition, the current flowing through the load is converted into voltage by the resistor R1, and the abnormal current detection circuit 5 monitors it, but corona discharge normally occurs in the charger, which is the load, and the current value is extremely low. small.

However, if a short circuit or poor insulation occurs between the charger and the photoreceptor or the charger case for some reason, an abnormally large current will flow, so the level is detected by the abnormal current detection circuit 5 and the detected value is When the comparison voltage (reference value) by the comparison voltage generation circuit 6 is exceeded, the output of the comparator 7 is inverted from low level to high level, and the hold circuit 8 holds it and continues to output high level tLH'', and the transistor Tr Turn off the oscillation circuit 3
oscillation and high voltage output operation.

[Problem to be solved by the invention]

However, in such a conventional high-voltage power supply device, abnormal current values are accumulated, and when the accumulated value exceeds a preset reference value, the output of the high-voltage power source is stopped.

For this reason, for example, if conductive recording paper is used and a paper jam occurs near the transfer charger, which is the load of the high-voltage power supply for transfer, even if an arc occurs between the recording paper and the transfer charger, abnormal current will not be generated. Because there was no instantaneous control over the output, smoke could be emitted or the recording paper could catch fire before high-voltage output was stopped.

As a countermeasure to this problem, it is conceivable to set the reference voltage low to speed up the detection time, but this poses a problem in that erroneous detection may occur during normal times and the high voltage output may be stopped.

This invention was made in view of these conventional problems, and it is possible to control the abnormal current to be immediately avoided when it flows in the high voltage load circuit, and to prevent the high voltage output from being caused by false detection during normal operation. The purpose is to prevent operations that would cause the system to stop.

[Means to solve the problem]

In order to achieve the above-mentioned object, the present invention provides a high-voltage power supply device that boosts an input voltage and supplies it to a load, including abnormal current detection means for detecting abnormal current flowing through the load.
An output current control means that controls the output current to be reduced for a period of time according to the detected value of abnormal current by the means, and a high voltage when the repetition of the control to reduce the output current by the means continues for a certain period of time. and means for stopping the output operation.

[For production]

The high-voltage power supply device according to the present invention has the above-described configuration, so that when an abnormal current flows through the load, it is immediately detected, and the output current is instantaneously reduced according to the detected value to restore the normal state. Furthermore, if such control is repeated continuously for a certain period of time, it will be treated as a completely abnormal state that cannot be recovered and the high voltage output will be stopped, thereby preventing smoke or ignition. can.

〔Example〕

Embodiments of the present invention will be specifically described below with reference to the drawings.

FIG. 1 shows an AC high voltage power supply device which is an embodiment of the present invention.
FIG. 2 is also a block circuit diagram of the DC high voltage power supply device, and parts corresponding to those in FIGS. 3 and 4 described as conventional examples are given the same reference numerals.

In any high-voltage power supply, normally a microcomputer (C
The PWM controller 11 is controlled at a predetermined timing by the control signal from the input voltage (DC
V) is pulse width modulated and supplied to an oscillation circuit 3 through a ripple filter 2 to oscillate it, and the oscillation output is applied to the primary side of the step-up transformer T to generate an AC high voltage on the secondary side.

In the device shown in Fig. 1, the output voltage is directly supplied to a load such as a separate charger, and in the device shown in Fig. 2, it is converted to a high DC voltage through a rectifier/smoothing circuit 4 including a diode D1 and a capacitor 01, and then charged. Supplied to loads such as chargers or transfer chargers.

Further, the current flowing through the load is converted into a voltage by the resistor R1, and the voltage is input to the abnormal current detection circuit 5 to detect the current level.

The abnormal level detection circuit 13 compares it with the comparison voltage (abnormal level) generated by the comparison voltage generation circuit 12, and when it exceeds the voltage, the magnitude is detected as an abnormal current, and the PWM controller is operated for a time corresponding to the detected value. Then, a control signal is output to the oscillation circuit 11 to reduce the duty of the pulse width modulation voltage input to the oscillation circuit 3, thereby temporarily lowering the oscillation output.

This allows the output current to be lowered and to restore normality when the abnormal current stops flowing thereafter.

If the abnormal current continues to flow even after performing control to reduce the output current for a period of time corresponding to the detected abnormal current value, such control is repeatedly executed, but the duration Current control time detection circuit (timer) 1
4, and outputs a voltage proportional to the duration to the comparator 16.

The comparator 16 compares the voltage with the voltage generating circuit 15.
The comparison voltage is compared with a comparison voltage corresponding to a preset period of time from Continue outputting.

When the signal is input to the PWM controller 11, the pulse width modulation output is set to zero, and the oscillation operation of the first oscillation circuit 3 is stopped, thereby stopping the high voltage output operation.

Also, at this time, the high level "H" from the hold circuit 17
It is preferable to input this signal to the CPUI○ as well, so that if it is a copying machine, the execution of the copying process is immediately interrupted, and the occurrence of an abnormality is displayed on the operation panel.

As described above, according to the high-voltage power supply device of this embodiment, when an abnormal current occurs in the load, control is performed to instantly reduce the output current, so that it is almost impossible for a large abnormal current to flow continuously. It is possible to prevent smoke or ignition by stopping the high voltage output only when abnormal current continues to flow for a certain period of time.

By doing so, the abnormal current detection time will not be shortened to an unnecessarily short time, and the possibility of stopping the high voltage output due to false detection is extremely reduced.

The high-voltage power supply according to the present invention is suitable for use as a high-voltage power supply for chargers in electrophotographic image forming devices such as copying machines and laser printers, but it can also be used as an AC or DC high-voltage power supply for other equipment. Of course it can be done.

〔Effect of the invention〕

As described above, in the high-voltage power supply device according to the present invention, when abnormal current occurs in the load, control is performed to instantly reduce the output current, so that there is almost no continuous flow of large abnormal current. Only in the case of a complete abnormality that cannot be recovered, can the high voltage output be stopped to prevent smoke or fire from occurring.

Therefore, the safety is extremely high, and since the abnormal current detection time is not shortened to an unnecessarily short time, there is no possibility that the high voltage output will be stopped due to false detection.

[Brief explanation of drawings]

FIG. 1 is a block circuit diagram of an AC high-voltage power supply device showing one embodiment of the invention, FIG. 2 is a block circuit diagram of a DC high-voltage power supply device showing another embodiment of the invention, and FIGS. They are block circuit diagrams showing examples of a conventional AC high-voltage power supply device and a conventional DC high-voltage power supply device, respectively. 3... Oscillation circuit 4... Rectifier/smoothing circuit 5
... Abnormal current detection circuit 10 ... Microcomputer (CPU) 11 ...
・PWM controller 13...Abnormal level detection circuit 14...Current control time detection circuit 16...Comparator F...Hold circuit Fig. 1 Fig. 2

Claims (1)

[Claims] 1. A high-voltage power supply device that boosts the input voltage and supplies it to a load, which includes an abnormal current detection means that detects when an abnormal current flows through the load, and an output current that outputs current for a period of time corresponding to the abnormal current detected by the means. A high voltage device comprising: output current control means for controlling the output current to decrease; and means for stopping the high voltage output operation when the repetition of control to decrease the output current by the means continues for a certain period of time. power supply.