JP2945710B2 - High voltage power supply - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-voltage power supply for boosting an input voltage and supplying the load to a load. The present invention relates to a high-voltage power supply device suitable for applying a high voltage to each charger such as a separator.

[Conventional technology]

2. Description of the Related Art In an image forming apparatus such as an electrophotographic copying machine or a laser printer, a series of electrophotographic processes such as charging, exposure, development, transfer, and separation are performed to form an image. Then, a high voltage is applied to each of these chargers at a predetermined timing from a high-voltage power supply device to cause corona discharge.

In such an image forming apparatus, if an abnormal current flows due to a short circuit, a decrease in insulation, or the like in any of the chargers for applying a high voltage during image formation, such as charging, transferring, and separating, the image forming cannot be performed. In addition, there was a risk that the recording paper in the aircraft would smoke or ignite.

Therefore, in order to cope with such a problem, an abnormal current flowing through each of the above-described chargers (loads) has been conventionally detected,
A high-voltage power supply device provided with a protection circuit that shuts off a high-voltage output when an abnormality occurs has been used.

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

In any of the high-voltage power supply devices, the transistor Tr is normally turned on / off at a predetermined timing by a control signal of the output control means 1 so that the input voltage (24 V DC) is applied between the emitter and collector of the transistor Tr and The oscillation circuit 3 is supplied to the oscillation circuit 3 through the ripple filter 2 and oscillates.

In the device shown in FIG. 3, it is supplied as it is from the output terminal to the load, and in the device shown in FIG.
And a DC high voltage through a rectifier / smoothing circuit 4 including a capacitor C1 and the like, and supplies it to a load.

Also, the current flowing through the load is converted into a voltage by the resistor R1, and the abnormal current detection circuit 5 monitors the voltage. Normally, a corona discharge occurs in the charge, which is a load, and the current value Is extremely small.

However, if a short circuit or insulation failure occurs between the charger and the photoconductor or the charger case for some reason, an abnormally large current flows. Exceeds the comparison voltage (reference value) from the comparison voltage generating circuit 6, the output of the comparator 7 is inverted from the low level to the high level, and the hold circuit 8 holds the same and keeps outputting the high level "H". The transistor Tr is turned off to stop the oscillation of the oscillation circuit 3 and stop the high voltage output operation.

[Problems to be solved by the invention]

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

Therefore, for example, when a paper jam occurs near the transfer charger, which is a load of the transfer high-voltage power supply, using conductive recording paper, even if an arc is generated between the recording paper and the transfer charger, an abnormal current is generated. Because of the lack of instantaneous control of the, there were cases where smoke or recording paper ignited before the high-pressure output was stopped.

As a countermeasure, it is conceivable to shorten the detection time by setting the reference voltage low. However, in such a case, there is a problem that a high voltage output is stopped due to erroneous detection in normal times.

The present invention has been made in view of such a conventional problem, and when an abnormal current flows in a high-voltage load circuit, it can be controlled so as to immediately avoid the abnormal current. An object of the present invention is to prevent an operation that stops high voltage output.

[Means for solving the problem]

In order to achieve the above object, the present invention provides a high-voltage power supply that boosts an input voltage and supplies the load to a load. Output current control means for controlling the output current to decrease by a time corresponding to the detected value; and means for stopping the high voltage output operation when the control for reducing the output current by the means is continuously performed for a predetermined time. It is provided with.

(Operation)

With the above configuration, the high-voltage power supply device according to the present invention performs control such that when an abnormal current flows through the load, the abnormal current is immediately detected, and the output current is instantaneously reduced according to the detected value to restore a normal state. Because of this, large abnormal currents rarely flow continuously, and the output current is not reduced unnecessarily or the output is temporarily stopped. You can continue to do. Furthermore, if such control is repeated continuously for a certain period of time, the high-pressure output is stopped assuming that it is an unrecoverable complete abnormal state, so that it is possible to prevent smoke or ignition from occurring. .

〔Example〕

Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings.

FIG. 1 is a block diagram of an AC high-voltage power supply according to an embodiment of the present invention, and FIG. 2 is a block circuit diagram of a DC high-voltage power supply according to the present invention.
Parts corresponding to those in the figures are denoted by the same reference numerals.

In any high-voltage power supply device, the input voltage (24 VDC) is normally controlled by controlling the PWM controller 11 at a predetermined timing according to a control signal from a micro computer (CPU) 10 which controls the sequence control of a copying machine. The pulse width is modulated, supplied to the oscillation circuit 3 through the ripple filter 2 and oscillated, 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 apparatus shown in FIG. 1, it is supplied as it is from the output terminal to a load such as a separation charger. In the apparatus shown in FIG. 2, it is charged to a high DC voltage through a rectifying / smoothing circuit 4 including a diode D1 and a capacitor C1. Supply to a load such as a charger or a transfer charger.

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.

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

As a result, the output current is reduced, and when the abnormal current stops flowing thereafter, it can be restored to the normal state.

If the abnormal current continues to flow even after the control for reducing the output current for the time corresponding to the detected value of the abnormal current as described above, such control is repeatedly performed. The current control time detection circuit (timer)
14 and outputs a voltage proportional to the duration to the comparator 16.

The comparator 16 compares the voltage with a comparison voltage corresponding to a predetermined period of time from the comparison voltage generation circuit 15, and when the voltage exceeds the voltage, inverts the output from a low level to a high level. And keep outputting the high level “H” signal.

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

At this time, a high-level "H" signal from the hold circuit 17 is also input to the CPU 10, so that the copying machine immediately terminates the execution of the copying process and displays the occurrence of an abnormality on the operation panel. It is good to

As described above, according to the high-voltage power supply device of the present embodiment, when an abnormal current is generated in the load, the control for instantaneously reducing the output current is performed, so that a large abnormal current rarely continuously flows. The high-voltage output is stopped only when the abnormal current flows continuously for a certain period of time, thereby preventing generation of smoke or ignition.

By doing so, the detection time of the abnormal current is not shortened to a necessary abnormal level, and the possibility of stopping the high-voltage output due to erroneous detection is extremely reduced.

Although the high-voltage power supply according to the present invention is suitable for a high-voltage power supply for each charger of an electrophotographic image forming apparatus such as a copying machine or a laser printer, it is also used as an AC or DC high-voltage power supply for other equipment. Of course, you can.

〔The invention's effect〕

As described above, in the high-voltage power supply device according to the present invention, with the above-described configuration, when an abnormal current is generated in the load, control is performed to reduce the output current for a time corresponding to the magnitude of the abnormal current. A large abnormal current hardly flows, and a substantially sufficient high voltage can be continuously supplied when the abnormality is mild without lowering the output current more than necessary or temporarily stopping the output.

Accordingly, the safety is extremely high, and the detection time of the abnormal current is not shortened to a necessary abnormal level, so that the high voltage output is not stopped due to erroneous detection.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram of an AC high-voltage power supply showing one embodiment of the present invention, FIG. 2 is a block circuit diagram of a DC high-voltage power supply showing another embodiment of the present invention, and FIGS. 1 is a block circuit diagram showing an example of a conventional AC high voltage power supply and a conventional DC high voltage power supply, respectively. 3 Oscillation circuit 4 Rectifying / 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, 17 Hold circuit

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-61-4469 (JP, A) JP-A-61-185757 (JP, A) JP-A-1-166432 (JP, U) (58) Survey Field (Int.Cl. ⁶ , DB name) H02H 9/02 H02M 3/00 H02M 7/42 H02J 1/00

Claims (1)

(57) [Claims] 1. A high-voltage power supply for boosting an input voltage and supplying the load to a load, comprising: an abnormal current detecting means for detecting when an abnormal current flows in the load; and a time corresponding to a detected value of the abnormal current by the means. Output current control means for controlling only the output current to decrease, and means for stopping the high voltage output operation when the control for reducing the output current by the means is continuously performed for a predetermined period of time. High-voltage power supply characterized.