JPS61236363A - High voltage power source for copying machine - Google Patents

Abstract

PURPOSE:To reduce the size and cost of a high voltage power source by providing output voltage detecting means and output current detecting means, and providing externally operable switch means in the current detecting means. CONSTITUTION:A transistor (Tr) Q3 connected with the input winding of a transformer TR is switched, a high voltage pulse from the output winding is rectified by a rectifier D4, and smoothed by a capacitor C6 to obtain a transfer charge DC high voltage T. This is stabilized by constant-voltage means 4 to obtain a developing bias output B. Output voltage detecting means 1 and output current detecting means 2 are provided, and input through selecting means 5 to a pulse width controller P. In this case, a switch 3 which can be externally operated is connected with the means 2. When the transfer output trigger TT of the external operation is turned OFF, Tr Q4 is conducted to short-circuit a current detecting resistor R19. Thus, the controller P is controlled to set the output to completely constant voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a high voltage power supply for a transfer charger and a developing bias of a copying machine (Prior Art) The transfer charger and the developing bias of a copying machine have different application timings. If this is controlled at one timing to cover both on-times, the on-state will occur even when the transfer charger is off, which will cause problems such as accelerated deterioration of the photoreceptor and generation of a large amount of ozone. In the past, even if they were stored in the same unit, all (
It was configured as two independent power supplies.

Therefore, a large space is required and the cost is high, so that it cannot be used as a high-voltage power supply for a small, low-cost copying machine.

In order to solve this problem, the present applicant has already filed an application for a method in which two reference voltages are provided to be compared with the current detection signal, and the output current is switched in two stages by switching between them using an external signal. However, even in this method, if the load is removed, no current flows to the current detection section, so the control section issues a signal to increase the output, resulting in an abnormally high voltage output.

(Purpose) The present invention was made based on this background,
A small, low-cost, high-voltage power supply that provides the appropriate output to each load by switching between constant current and constant voltage according to the output timing in a power supply that obtains multiple outputs with different output timings from one power supply. The purpose is to provide.

(Structure) For this purpose, the present invention includes an output voltage detection means and an output current detection means, and the output current detection means is provided with a switch means that can be operated from the outside, and the switch means is operated.
This is characterized in that an output voltage lower than usual can be obtained.

Embodiments of the present invention will be described below based on the drawings.

FIG. 1 shows an embodiment of a high-voltage power supply that integrates a transfer charge (■) and a development bias (◎) output for an electrophotographic apparatus.

The toner image formed on the photoreceptor is transferred to the transfer charge at a rate of 20
A constant current output of 0 to 600 μA is applied and the image is transferred to the copy paper by corona discharge.

To prevent deterioration of the photoreceptor when no transfer is performed:! A constant voltage output of -2 to -3 KV below the Rona discharge starting voltage is used, and a constant voltage element is used to constantly obtain a developing bias output from the transfer output.

The circuit configuration and operation will be specifically explained below.

Transistor Q3 connected to the input winding of transformer TR
The high voltage pulse obtained in the output winding by switching is rectified and smoothed by diode D4 and capacitor C6 to produce DC high voltage T for transfer charging, and this is stepped down by resistor R16 and stabilized by constant voltage element Z, which is the output for developing bias. get B.

The output current is detected by resistor R19 and input to the non-inverting input of comparator i1.

In addition, a reference voltage obtained by dividing the reference power supply S by resistors R4 and R5 is connected to the inverting input, and when the detection voltage Y becomes smaller than the reference voltage, the output of the comparator becomes low level and the pulse width controller P widens the pulse width. Increase output current.

Conversely, when the output current is large and the detection voltage Y becomes larger than the reference voltage, the output of the comparator i1 becomes high level, and the pulse width controller P narrows the pulse width to reduce the output current, so that the detection voltage Y and the reference voltage are equal. controlled so that

The output voltage detection means 1 is provided closer to the output winding of the transformer TR than the output current detection means 2 so as not to impair the constant current property, and the voltage is divided by resistors R14 and R15. Since this is a negative voltage, it is input as a difference from the reference voltage S to the inverting input of comparator "2. Also, a reference voltage obtained by dividing the reference power supply S by resistors R2 and R3 is connected to the non-inverting input. When the voltage X fed back to the inverting input becomes smaller than the reference voltage, the output of the comparator becomes high level and acts on the pulse width control section P to narrow the pulse width and lower the output voltage.

For example, when the transfer output load LT becomes lighter and the output voltage increases and the feedback voltage X decreases, it functions to suppress the output voltage. Normally, since the electromotive voltage Y generated by the current detection resistor FL19 is added, the feedback voltage X becomes larger than the reference voltage, and the pulse width control section PK does not act and constant current control is performed.

The above description has been made regarding the case where the switch 3 connected to the output current detection means 2 is open, that is, the transfer output trigger TT is on, but when the transfer output trigger TT is turned off, the bias current flows from the resistor R1 to the transistor Q4. When turned on, the current detection resistor R19 is short-circuited, the electromotive force Y there disappears, and the voltage X fed back to the inverting input of the comparator 102 becomes smaller than this reference voltage, and the voltage
The output becomes high level, the pulse width is narrowed, the output voltage is lowered, and the feedback voltage X is controlled to be equal to the reference voltage, so the output becomes a completely constant voltage.

The transfer output voltage at this time is about -3 KV, which does not cause corona discharge, and the developing bias output is extracted from this by the resistor R16 and the constant voltage element Z. Furthermore, the developing bias output trigger B'r
When turned off, the transistor Q1 is turned off and the power to the hybrid IC HIC is cut off, so switching stops and the output stops.

As explained above, with the configuration including one switching transistor Q3 and one transformer TR, the developing bias output B can be obtained even when the transfer output trigger TT is off, and the transfer output 'r at this time is the corona discharge voltage. Since the output voltage does not change even if the transfer or development bias load changes, a highly reliable power source that does not cause arcing due to abnormally high voltage can be provided at a small size and low cost.

FIG. 2 shows another embodiment of the output current detection means 2, in which the current is detected by a resistor R20 even when the switch means 3 is on, and the abnormal current is limited to 51 CI. Furthermore, R
20 is a small value that does not affect constant voltage properties.

Next, the constant voltage and constant current selection means 5 will be explained. Here, the outputs of comparisons 501 and 02 are combined by diodes DI and D2, respectively, and the signal with a higher quantity ratio level enters the next stage pulse width control unit PIC, which acts to narrow the switching pulse width and reduce the output. Ru.

First, the case when the transfer output trigger TT is off will be explained.

At this time, the transistor Q4 is on and the resistor R19 is short-circuited, resulting in the circuit shown in FIG. 3, and the voltage X fed back to the comparator 2 is expressed by equation 1. FIG. 4 shows the relationship with the output voltage V using specific circuit constants. Since the feedback voltage X when the output voltage V=-3KV is 2.06V, if the reference voltage of the non-inverting input of the comparator i2 is set to this value,
When the feedback voltage is lower than this, that is, when the output voltage becomes high, the output of comparator 2 becomes high level, lowering the output, and becoming a constant voltage output. At this time, the detection voltage Y of the output current is Ov and the comparator i
The output of 1 is at a low level and does not affect the pulse width control section P.

Next, when the transfer output trigger TT is turned on, an electromotive voltage is generated in the resistor R19, and the feedback voltage X is increased, so that the output voltage is controlled to be increased. When the output current detection voltage Y becomes equal to the reference voltage Z determined by Equation 2, it becomes stable and becomes a constant output current. FIG. 5 shows the circuit at this time, and the feedback voltage X is determined by Equation 3, and FIG. 6 shows the relationship between the output voltage V and the feedback voltage X by entering specific circuit constants.

The operating range of the load LT when the transfer output is on is 14KV to 17KV, and when the transfer output is on, the voltage is 233V. Since this value is larger than the above-mentioned X = 2D6"l/, the output of comparator 2 is at a low level and does not affect the pulse width control section P. In the event of an abnormality such as a breakage of the charge wire, the output voltage will further increase to approximately -9KV. When this happens, the feedback voltage X becomes 24)6 V or less and shifts to constant voltage control.

In this way, when the transfer output trigger TT is off, it is a constant voltage of -3KV, and when the TT is on, it is a constant current output that can output a voltage higher than this voltage, and the maximum pressure is a constant voltage of -9KV, which is highly accurate and safe. It is possible to provide a high-voltage power supply with high performance.

Complete set 1 %formula% Then! The characteristics shown in Figure 4 are obtained.

complete set 3 %formula% Then, the characteristics shown in FIG. 6 are obtained.

(Effects) The present invention is as described above, and the high-voltage power supply for copying machines according to the present invention can provide an appropriate output to each load by switching between constant current and constant voltage.
Since the maximum voltage is limited even when the current is constant, there is no damage to the photoreceptor due to abnormally high voltage, making it safe. Further, for this purpose, no special voltage detection means is required, and the voltage detection means for constant voltage can be used as is, resulting in miniaturization and cost reduction.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a high-voltage power supply according to an embodiment of the present invention, FIG. 2 is a circuit diagram showing another embodiment of the output current detection means, and FIG. 3 is a reference power supply circuit when the transfer output trigger is set to 7. Figure 4 is a characteristic diagram showing the relationship between feedback voltage and output voltage, Figure 5 is a characteristic diagram showing the relationship between feedback voltage and output voltage.
The figure is a reference voltage circuit diagram when the transfer output trigger is on, and FIG. 6 is a diagram showing the relationship between the feedback voltage and the output voltage at that time. DESCRIPTION OF SYMBOLS 1... Output voltage detection means, 2... Output current detection means, 3... Switch means, 4...
... Constant voltage means, 5... Selection means. Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 V (KV)

Claims (3)

[Claims] (1) Equipped with an output voltage detection means and an output current detection means,
A high-voltage power supply for a copying machine, characterized in that the output current detection means is provided with a switch means that can be operated from the outside, and by operating the switch means, an output voltage lower than usual is obtained. (2) A high-voltage power supply for a copying machine as set forth in claim (1), characterized in that output current detection means is provided between the output voltage detection means and the load. (3) Normally, a selection means is provided that gives priority to the signal from the output current detection means, and when the switch means is operated, the signal from the output voltage detection means is given priority, and the constant current output is changed to the constant voltage output. A high-voltage power supply for a copying machine according to claim (2), characterized in that the high-voltage power supply for a copying machine is configured to be replaceable.