JPH06103408B2 - High voltage power supply for image forming equipment - Google Patents

Description

Description: TECHNICAL FIELD The present invention switches a primary coil of a transformer to
The present invention relates to a multi-output high-voltage power supply that rectifies and smoothes the high voltage obtained in the next coil to obtain at least one high-voltage output, and lowers this high-voltage output to obtain a low low-voltage output, particularly in an image forming apparatus such as a copying machine. The present invention relates to a suitable high voltage power supply.

(Prior Art) As is well known in copying machines, application of a transfer charge (T) voltage and application of a developing bias (B) voltage are included in the copying process.

FIG. 4 shows the application timings of the transfer charge (T) and the bias (B) of the conventional machine, and the on and off timings of T and B are different. That is, since the bias B is inconvenient unless the bias voltage is applied to the photoconductor as long as the main motor M is driven and the developing unit is operating, the bias B is turned on almost in synchronization with the main motor. Since the transfer charge (T) needs to be turned on only at the timing when the transfer sheet reaches the transfer portion, it is turned on only at the timing shown in the figure, and it is originally turned on in this way. Of course, the off-timing is different.

However, in order to take out outputs having different on and off timings, the circuit is large and complicated as shown in FIGS. 5 and 6.

FIG. 5 shows a trigger signal generating circuit 1 for controlling the timings of T and B, which requires two dedicated ports P3 and P1 for T and B and two buffer ICs.

FIG. 6 shows a high-voltage power supply circuit for taking out the output. The transfer charge power supply and the bias power supply are independent switching control units A1 and A2, transformers T1 and T2, respectively.
Transistors Q1 and Q2 and their respective peripheral circuits are required.

For this reason, as mentioned above, it became a high-voltage power supply with a large number of parts and high cost and large size.

The on / off timing of B and T in FIG. 6 is obtained by inputting the trigger signals T and B on the input side to the switching control units A1 and A2.

In order to improve a high-voltage power source for a copying machine, which has a large number of parts and is inevitably increased in size, the characteristics of the photoconductor are improved in a copying machine with a small number of copies, and then, as shown in FIG. An output high voltage power supply was proposed.

That is, the transfer charge trigger has the same bias trigger, and (T / B) one set of switching control unit A3 and transformer T
3, Transfer charge output from transistor Q3 (T-OUT)
The bias power supply (B-OUT) is taken out from the resistor R13 and the zener diode Z, and the number of parts is smaller than that of the conventional example shown in FIG.
It is a low-cost and compact high-voltage power supply. As a matter of course, the transfer charge output and the bias output fall at the same time in this configuration.

By the way, even after the main motor signal is turned off, the developing sleeve rotates about 300 milliseconds by the inertia of the main motor. Therefore, during this period, unless a voltage of 50% or more of the rated value is applied as the bias output, the toner sticks to the sleeve. On the other hand, even if the characteristics of the photoconductor are improved, if a transfer charge is applied while the photoconductor is rotating at a low speed due to inertia, the photoconductor is charged more than the withstand voltage and dielectric breakdown occurs. Therefore, the drawback that either of the timings of the T / B trigger signal causes a defect is unavoidable.

(Purpose) The present invention has been made in view of the above-mentioned drawbacks of the conventional example, and is a highly reliable image forming apparatus that is free from troubles such as destruction of a photoconductor and sticking of toner to a developing sleeve in a multi-output high-voltage power supply. The purpose of the present invention is to provide a high-voltage power supply for use.

(Structure) To this end, the present invention provides a high-voltage power supply provided in an image forming apparatus in which a photosensitive member and a developing sleeve are driven by one main motor, and the photosensitive member and the developing sleeve are interlocked.
The present invention is characterized in that outputs having different falling timings are taken out from a multi-output high-voltage power supply composed of one control circuit and one transformer.

Therefore, a charging circuit for charging the high voltage obtained by the secondary coil between the low voltage output and the ground and a discharging circuit for discharging the electric charge charged in the charging circuit to the low voltage output with a time constant are provided, and the high voltage output is transferred. The low voltage output is connected to the developing means, and the control means for turning off the input to the transformer at the same time as the driving of the image carrier is turned off.

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 7 is a timing chart of the main part of the copying machine using the high voltage power source of the present embodiment. The main motor (M1) trigger signal and the transfer charge (T) and bias (B) trigger signals T /
B is the same.

FIG. 9 is a circuit diagram of the trigger signal generation circuit 2 showing the port allocation and buffer of the microcomputer at this time. The main motor trigger signal RA and the transfer charge and bias trigger signal T / B are one port and one. It consists of a buffer.

FIG. 1 is a circuit diagram of a high voltage power supply according to this embodiment. Switching the primary side of the transformer T3 with the transistor Q3, 2
A high voltage is obtained on the secondary side, and this is rectified and smoothed by a diode D5 and a capacitor C4 to obtain a DC high voltage. A high voltage output T-OUT is obtained via protection resistor R9, which is connected to the transfer charge. On the other hand, this DC high voltage is stepped down by a resistor R13 and is made a constant voltage by a zener diode Z, and a low voltage output B-OUT is obtained via a protection resistor R12. This is connected to the bias.

The current drawn by these outputs is the return resistor R1
It is detected by 4, is fed back to the switching control unit A3, and becomes a constant current. By the way, the bias current is several μA, which is 1 to 2% with respect to several hundred μA of the transfer charge current.
The change in bias current does not affect the constant current property of transfer charge. While the output of T-OUT is present, the capacitor C5 is charged by the resistor R16 connected to the Zener diode Z.
When the trigger signal T / B is turned off, the T-OUT output disappears and the charge stored in the capacitor C5 is discharged through the resistor R16 by the action of the diode D6, gradually lowering the B-OUT output. Now resistance R16 = 47MΩ Capacitor C5 = 0.02μF Diode D6 = TFR1 When the load resistance of B-OUT is 20MΩ at zener voltage of 200V, the rising / falling waveform of B-OUT output by turning on / off the trigger signal T / B is With the characteristics shown in Fig. 3 (a) and (b), the rise is 15 mS
The time to drop to 1/2 was 300 mS.

FIG. 2 is a block diagram showing the main part of the bias output. When the switch S is turned on, the power source voltage E appears at B-OUT and at the same time the capacitor C5 is charged through the resistor R16. Since this time constant R16 × C5 is sufficiently smaller than one copy time, it is completely charged by the time the switch S is turned off. Then when switch S turns off, capacitor C5 is discharged by load RB through diode D6. Where R16
Since one copy time is long, the value can be made larger than the load resistance, so that the capacitor C5 is discharged with a time constant of approximately RB × C5, and the bias voltage can be continuously applied for a desired time.

As described above, in the present invention, as is clear from the dimming chart of FIG. 7 and the above description, the fall of the transfer charge T is steep, but the time constant of the bias B is large and the fall is gentle. While the developing sleeve is rotating due to the inertia of the main motor, the bias B voltage is
Since 50% or more is applied, it is possible to prevent the toner from sticking to the sleeve, and since the transfer charge T does not apply a voltage to the photoconductor, it does not cause dielectric breakdown.

The output voltage of T-OUT is detected by the resistors R10 and R11, and the maximum voltage applied to the transfer charge is fed back to the switching control unit A3 to limit the maximum voltage applied to the transfer charge. A resistor R15 is connected to the output voltage detector so that a high voltage is not applied to the output voltage detector, and similarly limits the maximum voltage applied to the bias.

Although this embodiment is an example in which the transfer charge and the bias are integrated, the same effect can be obtained with the same configuration even in other combinations, for example, in which the charging charge and the bias or the transfer, the charge and the bias are integrated. .

Zener Z can be changed to resistance if the load range of T-OUT is narrow and the voltage change is small. If T-OUT is a constant voltage power source, it can be similarly replaced with a resistor.

(Effect) The present invention is as described above. According to the present invention, a transfer charge and a bias having different fall times can be obtained by a high voltage power supply composed of one control circuit, one transformer and one trigger signal. As a result, it is possible to provide a highly reliable high-voltage power supply for an image forming apparatus, which is free from the problems of dielectric breakdown of the photoconductor and toner sticking to the developing sleeve.

[Brief description of drawings]

FIG. 1 is a high voltage power supply circuit diagram according to one embodiment of the present invention, and FIG.
FIG. 3 is an equivalent circuit diagram of its main part, FIGS. 3 (a) and 3 (b) are the same as the output rising and falling characteristic diagrams, and FIG. 4 is an output timing chart of each part of a general copying machine. FIG. 5 is a trigger signal generating circuit diagram of the first conventional example, FIG. 6 is a high voltage power source circuit diagram of the first conventional example, FIG. 7 is an output timing chart of each part of the copying machine according to the present invention, and an eighth example. FIG. 9 is a high-voltage power supply circuit diagram according to the second conventional example, and FIG. 9 is a trigger signal generation circuit diagram thereof. T3 ... Transformer, D5, C4 ... Rectifying and smoothing circuit, T-OUT ... High-voltage output, B-OUT ... Low-voltage output, R16, C5, D6 ... Charge / discharge circuit.

Continuation of the front page (56) Reference JP-A-50-99743 (JP, A) JP-A-59-201066 (JP, A) JP-A-58-95769 (JP, A) JP-A-55-122379 (JP , A) JP 59-101668 (JP, A) JP 58-186763 (JP, A) JP 58-114051 (JP, A) JP 55-111954 (JP, A) JP 56-47064 (JP, A) JP 60-257772 (JP, A) JP 61-59463 (JP, A) JP 61-59460 (JP, A) JP 51-27441 (JP, A) JP-A-58-171064 (JP, A) JP-A-60-232576 (JP, A) Actually developed Shou-52-46839 (JP, U) JP-B-55-47393 (JP, B2)

Claims (1)

[Claims] 1. An image forming apparatus in which a photosensitive member and a developing sleeve are driven by one main motor, and the photosensitive member and the developing sleeve are interlocked with each other, and a primary coil of a transformer is switched to obtain a secondary coil. In a high-voltage power supply for an image forming apparatus, which rectifies and smoothes high voltage, takes out at least one high-voltage output, steps down this high-voltage output, and takes out low low-voltage output, a secondary coil between the low-voltage output and ground. A charging circuit for charging the obtained high voltage and a discharging circuit for discharging the charge charged in the charging circuit to a low voltage output with a time constant are provided, the high voltage output is connected to a transfer means, and the low voltage output is A control unit connected to the developing unit, further comprising a control unit for turning off the input to the transformer at the same time as the driving of the photoconductor is turned off. Power.