JPH06335243A - Power supply device - Google Patents

Abstract

PURPOSE:To prevent a switching element from being turned off due to erroneous operation by stopping a protective function against overcurrent while surge noise is generated in the current of the switching element in synchronization with the ON/OFF signal of the switching element and generating a delay signal with an ON period which is shorter than the ON period of the ON/OFF signal. CONSTITUTION:A PWM output circuit 8 operates so that the flyback pulse width becomes constant during the OFF period of a transistor Tr1 and performs frequency control operation for making constant OFF period and varying the pulse width of ON period according to a feedback voltage. Then, the deviation width of timing is controlled by delay circuits 5 and 15 to prevent an overcurrent limiter function from functioning on turn-on/turn-off, thus preventing an overcurrent protection function from functioning by a logic circuit 4, namely an overcurrent protection function change-over means, while the surge noise is generated and preventing the transistor Tr1 from being turned off by an erroneous operation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply device. In particular, the present invention relates to a power supply device having a high voltage output suitable for an image forming apparatus such as a copying machine and a printer using an electrophotographic method.

[0002]

2. Description of the Related Art FIG. 14 is a circuit diagram showing an example of a conventional power supply device.

Conventionally, in a power supply device which generates a low voltage output and a high voltage output by one transformer, as shown in FIG. 14, a pulse signal from a control circuit 30 is supplied to a drive circuit 25 via a transformer 24. The switching transistor 27 is switched to supply the energy required by the output load through the transformer 26.

Low voltage output 52 by one transformer 26
In the power supply circuit that generates the high voltage output 53, the voltage of the low voltage output 52 is controlled by the control circuit 39 to be a constant voltage. Therefore, the voltage of the high-voltage output 53 is controlled by turning on and off the transistor 34 by the voltage comparator 43 and the like, irrespective of the switching operation of the switching transistor 27, so that the voltage becomes a constant voltage. .

Corona charging is used in the process of transferring the toner powder image on the photosensitive drum, which has been developed by a color copying machine or a color printer, to the transfer paper, and the corona wire is generally 6-9 KV, 0.1-0.1. It was powered by a 1 mA constant current power supply.

As the output voltage generating means for both positive and negative polarities, positive and negative power supplies are connected in series, the polarity side having a small output range is a fixed output, and the reverse polarity side is variable to cover the required positive and negative output ranges. It was normal to do so.

In the conventional power supply device, the method of detecting the overcurrent of the switching element is such that the current flowing through the collector (drain) is detected, and when the current exceeds a certain value, the drive is stopped or intermittent oscillation is performed. ing.

That is, regardless of whether the signal applied to the gate (base) of the switching element is on or off, the switching element is immediately turned off as soon as it exceeds a certain value. There is.

[0009]

However, in the above-described switching element overcurrent detection method, for example, when the current is detected by the resistor, the inductance component of the resistor causes
Surge noise occurs at turn-on and turn-off. This surge has a drawback that the overcurrent protection circuit malfunctions.

Particularly, when the oscillation frequency becomes high, there is a problem that this defect becomes remarkable other than the resistance detection.

In the conventional example shown in FIG. 14, the high voltage output voltage is controlled by turning on and off the high voltage control transistor 34 regardless of the switching operation of the switching transistor 27. Therefore, when the high voltage control transistor 34 is turned on and off, a considerable switching loss of the high voltage control transistor 34 occurs. As a result, the efficiency of the power supply device is reduced and heat is generated, and there is a problem that the reliability of the power supply device as a whole is reduced and the power supply device is enlarged.

The present invention has been made to solve the above-mentioned problems of the prior art. The high voltage control transistor for controlling the high voltage output voltage is turned on and off independently of the control of the switching transistor. The purpose of the present invention is to eliminate the efficiency reduction and heat generation of the power supply device due to the loss of the high-voltage control transistor, which is caused by the loss of power, thereby realizing a highly reliable, highly efficient and miniaturized power supply device.

In recent years, the transfer process has been reviewed to improve color image quality, and corona charging has been switched to contact charging.

In order to attract the toner on the photosensitive drum to the transfer paper, a transfer brush is brought into contact with the back side of the transfer paper via a mylar film, and a high voltage having a polarity opposite to that of the toner is applied to the transfer brush. . Yellow on the same transfer paper,
In order to transfer the four color toners of magenta, cyan, and black, the applied voltage increases stepwise as the number of times of transfer increases.

Since the fourth color exceeds 10 kV, adverse effects such as leakage will occur. In order to prevent this, the applied voltage has both positive and negative polarities so that the maximum absolute value of the applied voltage is halved.

That is, a negative high voltage is applied to the transfer paper before the transfer of the first color, and a positive high voltage of the same level as the negative high voltage at the start is applied to the fourth color. To do so.

One of the objects of the present invention is to provide a positive and negative bipolar high voltage power supply required for such a transfer process. Particularly, in the conventional positive / negative bipolar voltage generating means, the output range of the power source on the variable output side is significantly widened, which prevents cost increase, size increase, and reliability decrease.

The present invention has been made to solve the above-mentioned problems of the prior art, and the output can be controlled more reliably.
An object of the present invention is to provide a power supply device suitable for an image forming apparatus such as a copying machine and a printer.

[0019]

For this reason, the power supply device according to the present invention corresponds to the secondary side output voltage of the transformer.
A power supply device for controlling at least one of a plurality of secondary outputs to a predetermined voltage, comprising control means for calculating an on / off time of a secondary switching element and controlling an excitation period of a primary side of a converter transformer. There, current detection means for detecting the current of the switching element, comparison means for comparing the value detected by the current detection means with a designated value, and in synchronization with the ON / OFF signal of the switching element from the control means, And a delay signal generating means for generating a delay signal having an ON period shorter than the ON period of the same signal, an AND circuit for inputting the output of the comparing means and the delayed signal, and an output of the AND circuit The present invention is intended to achieve the above object by a configuration including an overcurrent protection means for turning off the switching element.

[0020]

With the above structure, during the period when surge noise is generated in the current of the switching element, the AND circuit for inputting the delay signal from the delay signal generation means controls the overcurrent protection means so that it does not function. It is possible to prevent the switching element from being turned off due to a malfunction. That is, it also functions as a switching means for the overcurrent protection function.

Since the control means itself generates and controls the timing of the drive signal for turning on / off the switching element, the overcurrent protection function can be switched easily and reliably.

[0022]

EXAMPLES A power supply device according to the present invention will be described by way of examples.

(First Embodiment) FIG. 1 is a block diagram of the first embodiment, and the configuration of the first embodiment will be described with reference to FIG. The + output obtained by rectifying and smoothing the AC line input voltage 1 is connected to one end of the N1 winding of the transformer T1. The other end of the N1 winding is a switching transistor (in this embodiment, F
ET) Tr1 is connected to the drain, and the source of the switching transistor Tr1 (hereinafter referred to as transistor Tr1) is connected to the rectified / smoothed-output. Further, a resonance capacitor C2 is inserted between the drain and the source of the transistor Tr1. This is to resonate with the inductance of the N1 winding and efficiently transmit the power to the secondary side of the transformer T1. A pulse signal for driving the transistor Tr1 is generated by a pulse width modulation (hereinafter referred to as PWM) output circuit 8 and drives the gate of the transistor Tr1 via the drive circuit 3. In this embodiment, since the PWM output circuit 8 is placed on the secondary side, the drive circuit 3 includes an insulating means.

The output of the secondary winding N2 of the transformer T1 is rectified and smoothed by the diodes D1 and D2, the inductance L1 and the capacitor C2, and output as output 2.
The output of the secondary winding N3 of the transformer T1 is rectified and smoothed by the diode D3 and the capacitor C3 and output as output 1. Then, this output 1 is fed back to the control system, and PWM control is performed. In this embodiment, the secondary side control circuit is supplied with power from another auxiliary power supply (not shown).

Reference numeral 7 denotes an A / D conversion circuit for taking the value of the output 1 into a central processing unit (hereinafter referred to as CPU) 14, 6
Are oscillation circuits of the CPU 14, and 10 and 11 are memory RAM and ROM for the CPU 14. Reference numeral 12 is a down counter for determining the on / off time when performing PWM control, and controls the time and the time ratio by changing this initial value.

Reference numeral 13 denotes a pulse width modulation (PWM) control calculation circuit, which outputs the output voltage taken in by the A / D conversion circuit 7, and other factors such as input voltage and output timing control, for example, in the case of a copying machine, during copying. Based on parameters such as sequence control, turn on / off transistor Tr1.
Calculate the off time.

Reference numeral 8 denotes a PWM output circuit, which is based on the value calculated by the PWM control calculation circuit 13
Drive 1 Reference numerals 5 and 15 are delay circuits, which generate signals whose timings are slightly different from the drive signal of the transistor Tr1. This signal shift prevents malfunction of the overcurrent protection circuit.

Reference numeral 4 denotes an AND circuit (hereinafter referred to as an AND circuit), which outputs a signal whose timing is slightly different from the drive signal when the output of the comparator Q1 is high, that is, when an overcurrent flows. This is an AND circuit whose output becomes high (High: hereinafter, referred to as H) only when the state, that is, the state in which a timing signal that does not pick up a current surge comes, occurs at the same time.

Reference numeral 9 indicates P when the output of the AND circuit 4 is high.
This is a latch-type output stop circuit for stopping the output of the WM circuit 8. R2 and R3 are resistors for determining the reference voltage of the comparator Q1, and R1 is a resistor for detecting overcurrent.

Next, the operation of this embodiment will be described.

FIG. 2 is a timing chart of the first embodiment, in which points (a) to (g) are associated with the points in FIG. However, (a) to (e) are the present embodiment, and (f) and (g) are the conventional examples.

FIG. 2A shows the gate voltage of the transistor Tr1 from the output of the PWM output circuit 8. When the N3 winding output 1 is lower than a predetermined value, the transistor Tr1 is turned on.
The period (H period in this figure) is lengthened, and when it is higher than a predetermined value, the ON period of the transistor Tr1 is shortened.

While the transistor Tr1 is ON, a negative voltage is generated in the N3 winding, the diode D3 is non-conducting, no energy is released through the N3 winding, and electromagnetic energy is stored in the primary inductance. To do. Then, when the transistor Tr1 is turned off, a flyback pulse is generated in the N1 winding, the voltage waveform of the N3 winding is inverted at the same time, and the diode D3 is turned on to release the energy stored in the primary inductance to the secondary side. To do. The flyback pulse has a pulse width determined by the primary inductance, the resonance capacitor C2, and the winding capacitance.

The PWM output circuit 8 includes a transistor Tr1.
During the OFF period of, the flyback pulse width is kept constant. This is to eliminate switching loss by zero potential switching that turns on the transistor Tr1 when the voltage waveform is at the zero level. That is, the OFF period is constant, and the frequency control operation of varying the pulse width of the ON period is performed.

FIG. 2B shows a drain current waveform of the transistor Tr1 (without a limiter). In (b), the first ON and the second ON are current waveforms in a state in which the overcurrent limiter does not need to be applied, and the third ON is some overcurrent flows to the load and the overcurrent limiter is applied. The current waveforms in the states that must be shown are shown respectively.

FIG. 2C shows the input 2 of the AND circuit 4,
The timing of this signal is t1 at the time of turn-on and t at the time of turn-off than the timing of the signal in (a).
It is off by 2. Due to this shift, even if the comparator Q1 is turned on, that is, the input 1 of the AND circuit 4 becomes H, the output is not turned on because the input 2 is low (LOW: hereinafter referred to as L).

That is, the limiter function acts so that it does not function only during turn-on / turn-off. This allows
It is possible to prevent the overcurrent limiter from malfunctioning due to the surge of drain current at turn-on / turn-off. However, if the deviation width becomes too large, it will not be necessary to apply the overcurrent limiter originally, so it is necessary to be careful in setting the deviation width.

The control of the above-mentioned timing deviation width is performed by
The delay circuits 1 and 2 shown in FIG. The deviation width control and the deviation width calculation can be easily performed because the CPU 14 owns the timing data necessary for the calculation.

FIG. 2 (d) shows a state in which the output of the AND circuit 4 becomes H due to the overcurrent when the third transistor is turned on. Since the surge is not picked up by the first ON current and the second ON current, the output of the AND circuit 4 does not become H.

FIG. 2E shows how the drain current is limited by the signal from the AND circuit output (d).

Here, the operation of the conventional example is shown in FIG.
This will be described with reference to (g). In the conventional example, the AND circuit 4
There is no. Therefore, when the comparator Q1 is turned on, the overcurrent limiter is immediately applied and the output is stopped. In (f) and (g), when the first switch is turned on, the surge of the drain current causes the overcurrent limiter function to malfunction and the latch-type output stop circuit 9 to operate.

With the above configuration and control, during the period when surge noise is generated, the AND circuit 4, that is, the overcurrent protection function switching means, prevents the overcurrent protection function from functioning. It is possible to prevent the transistor Tr1 from turning off.

Since the CPU 14 itself knows the timing of the ON / OFF drive signal, the switching of the overcurrent protection function can be easily and surely performed. That is, since it is not necessary to provide another circuit for picking up the timing of the on / off drive signal, it can be realized with a simple circuit configuration.

(Second Embodiment) FIG. 3 is a block diagram of the second embodiment. The same or corresponding parts as those in the first embodiment are designated by the same reference numerals, and the duplicated description will be omitted.

The first embodiment has one PWM output circuit, whereas the second embodiment has two PWM output circuits 8 and 16. In the first embodiment, the AND circuit 4 is provided. The same signal from the PWM output circuit 8 is input to the delay circuit 1 (15) and the delay circuit 2 (5) as the deviation between the timing of the input 2 and the timing of the driver 3, and However, in the second embodiment, the two PWM output circuits (8, 16) are configured to perform each independently.

Compared to the first embodiment, the second embodiment has the advantage that the delay circuit is not necessary, but the load on the PWM control calculation circuit 13 is heavy.

(Third Embodiment) FIG. 9 is a block diagram of a third embodiment, in which the same or corresponding parts as in the first embodiment are designated by the same reference numerals, and the duplicated description will be omitted.

In the first embodiment, the resistor R1 is used for current detection, whereas in the third embodiment, the current transformer 17 is used. There is an advantage that insulation in the driver circuit 3 is unnecessary. Then, as compared with the resistance detection of the first embodiment, the components become slightly larger, but when the switching frequency of the transistor Tr1 becomes higher, there is a problem that the influence of the surge due to the inductance component cannot be ignored in the resistance detection. However, the structure of the third embodiment does not cause such a problem.

(Fourth Embodiment) FIG. 5 is a block diagram of the fourth embodiment. The same or corresponding parts as those in the above-mentioned embodiment are designated by the same reference numerals, and the duplicated description will be omitted.

In the fourth embodiment, the CPU and R of the above embodiment are used.
Digital circuits such as OM, RAM, counter, A / D
An analog circuit such as a conversion circuit and the above-described overcurrent limiter function circuit are integrated on one chip.

Reference numeral 18 in FIG. 5 is a portion formed by the same chip. By doing so, for example, while the sequence control of the copying machine, printer, etc. is performed by the copying machine control microcomputer 19, it is most adapted to the state. Power control can be performed.

For example, if the delay circuits 5 and 15 are composed of programmable counters, the PW will depend on the load state.
Even when the optimum value to be output by the M output circuit 8 changes, the CPU 14 keeps track of the load state, so that the optimum value can be set in the programmable counter. Further, by switching the comparison voltage of the comparator Q1 between the steady state and the stationary state, low power consumption becomes possible.

By integrating them on the same chip as described above, versatility is high and more intelligent power supply control is possible.

(Fifth Embodiment) FIG. 6 is a circuit diagram of the fifth embodiment.

21 is an AC power source, 22 is a rectifying diode,
Reference numeral 23 is a smoothing capacitor, 24 is a drive transformer for the switching transistor 27, 25 is a drive circuit for the switching transistor 27, 26 is a transformer for transmitting energy to the loads 52 and 53, 27 is a switching transistor, 28 is a rectifying diode, and 29 is a smoothing capacitor. Three
0 is a control circuit, 31, 35 and 38 are high voltage capacitors, 32, 36 and 37 are high voltage diodes, 33 is a current limiting resistor, 34 is a high voltage control transistor, 39 and 40
Is a high voltage output voltage detecting resistor, 41, 42, 50 and 51 are reference voltage generating resistors, 43 and 49 are voltage comparators, 44 is a flip-flop, 45 and 54 are resistors, 46 is a capacitor,
47 is a diode, 48 is a current transformer, 52, 5
3 is a load.

When an AC voltage is applied, a pulse voltage is supplied from the control circuit 30 to the drive circuit 25 of the switching transistor 27 via the transformer 24, the switching transistor 27 performs a switching operation, and the loads 52 and 53 are required. Energy is supplied to the loads 52 and 53 via the transformer 26.

The voltage supplied to the load 52 is controlled by the control circuit 30 to a voltage required by the load 52. In addition, the voltage supplied to the load 53 is the voltage comparator 4
3, 49, flip-flop 44, current transformer 4
8, diode 47, capacitor 46, resistors 39, 4
It is controlled by 0, 41, 42, 45, 50, 51, 54 and the high voltage control transistor 34.

The feature of this embodiment resides in the control circuit for controlling the high voltage output voltage of the load 53.

In order to synchronize ON / OFF of the high voltage control transistor 34 for controlling the high voltage output voltage of the load 53 with the switching operation of the switching transistor 27, a current between the collector and emitter currents of the switching transistor 27 is provided by the current transformer 48. Is detected, the signal is converted into a voltage by the diode 47 and the capacitor 46, the value is given to the voltage comparator 49, and the voltage comparator 49
Is used as the clock signal of the flip-flop 44, and the detection output of the high voltage output voltage of the voltage comparator 43 is used as the D terminal signal of the flip-flop 44.
The Q terminal signal of 4 turns on the high voltage control transistor 34,
An off signal is used to control the high voltage output voltage.

By controlling the high-voltage output voltage with the above configuration, it is possible to synchronize the switching transistor 27 with ON and OFF, so that the high-voltage control transistor 3 is controlled.
Since the high-voltage control transistor 34 can be turned on and off while the collector-emitter voltage of 4 is zero, the switching loss due to the on-off of the high-voltage control transistor 34 can be eliminated as before, and the power supply can be eliminated. It is possible to eliminate a decrease in efficiency of the device and heat generation.

As described above, with the configuration of this embodiment, it is possible to realize high efficiency, high reliability, and miniaturization of the power supply device. For example, in the conventional system, the high voltage control transistor 34 has a T
Although the O-3 package was used, the control circuit of the present invention almost eliminated heat generation even in the TO-220 package. Further, the high voltage control transistor 34 is turned on,
The loss due to off is zero.

That is, it becomes possible to turn on and off the high voltage control transistor for controlling the high voltage output voltage at a point where the voltage between the collector and emitter of the high voltage control transistor is zero. It is possible to realize high reliability, high efficiency and miniaturization.

(Sixth Embodiment) FIG. 7 is a circuit diagram of the sixth embodiment, in which the same or corresponding parts as in the fifth embodiment are designated by the same reference numerals.

That is, 21 is an AC power supply, 22 is a rectifying diode, 23 is a smoothing capacitor, 24 is a drive transformer for the switching transistor 27, 25 is a drive circuit for the switching transistor 27, and 26 is a transformer for transmitting energy to the loads 52 and 53. , 27 is a switching transistor, 28 is a rectifying diode, 29 is a smoothing capacitor, 30 is a control circuit, 31, 35 and 38 are high voltage capacitors, 32, 36 and 37 are high voltage diodes, 33
Is a current limiting resistor, 34 is a high voltage control transistor, 3
Reference numerals 9 and 40 are high-voltage output voltage detecting resistors, 41 and 42 are reference voltage generating resistors, 43 is a voltage comparator, 44 is a flip-flop, 54 is a resistor, 46 is a capacitor, 47 is a diode, and 52 and 53 are loads.

When an AC voltage is applied, a pulse voltage is supplied from the control circuit 30 to the drive circuit 25 of the switching transistor 27 via the transformer 24, the switching transistor 27 performs a switching operation, and the loads 52 and 53 are required. Energy is supplied to the loads 52 and 53 via the transformer 26.

The voltage supplied to the load 52 is controlled by the control circuit 30 to the voltage required by the load 52. In addition, the voltage supplied to the load 53 is the voltage comparator 4
3, the flip-flop 44, the diode 47, the capacitor 46, the resistors 39, 40, 41, 42, 54, and the high voltage control transistor 34.

The feature of this embodiment resides in the control circuit for controlling the high voltage output voltage of the load 53.

That is, in order to synchronize ON / OFF of the high voltage control transistor 34 for controlling the high voltage output voltage of the load 53 with the switching operation of the switching transistor 27, the winding voltage from the low voltage output voltage winding is used. Is detected by the diode 47 and the capacitor 46, the signal is converted into a direct current voltage, the value is used as the clock signal of the flip-flop 44, and the detection output of the high voltage output voltage of the voltage comparator 43 is used as the D terminal signal of the flip-flop 44. Q terminal signal of the high voltage control transistor 34 for high voltage control
The high voltage output voltage is controlled by the ON and OFF signals of.

With the above configuration, by controlling the high voltage output voltage, it is possible to synchronize the switching transistor 27 with ON and OFF, so that the high voltage control transistor 3 is controlled.
Since the high-voltage control transistor 34 can be turned on and off while the collector-emitter voltage of 4 is zero, the switching loss due to the on-off of the high-voltage control transistor 34 can be eliminated as before, and the power supply can be eliminated. It is possible to eliminate a decrease in efficiency of the device and heat generation. As a result, it is possible to realize high efficiency, high reliability, and downsizing of the power supply device.

(Seventh Embodiment) FIG. 8 is a circuit diagram of the seventh embodiment, in which the same or corresponding parts as in the fifth embodiment are designated by the same reference numerals.

That is, 21 is an AC power supply, 22 is a rectifying diode, 23 is a smoothing capacitor, 24 is a drive transformer for the switching transistor 27, 25 is a drive circuit for the switching transistor 27, and 26 is a transformer for transmitting energy to the loads 52 and 53. , 27 is a switching transistor, 28 is a rectifying diode, 29 is a smoothing capacitor, 30 is a control circuit, 31, 35 and 38 are high voltage capacitors, 32, 36 and 37 are high voltage diodes, 33
Is a current limiting resistor, 34 is a high voltage control transistor, 3
Reference numerals 9 and 40 are high-voltage output voltage detection resistors, and 53 and 53 are loads.

When an AC voltage is applied, a pulse voltage is supplied from the control circuit 30 to the drive circuit 25 of the switching transistor 27 via the transformer 24, the switching transistor 27 performs a switching operation, and the loads 52 and 53 are required. Energy is supplied to the loads 52 and 53 via the transformer 26.

The voltage supplied to the load 52 is controlled by the control circuit 30 to a voltage required by the load 52. Similarly, the voltage supplied to the load 53 is also controlled by the control circuit 30 by transmitting ON / OFF signals to the high voltage control transistor 34.

The feature of this embodiment resides in the control circuit for controlling the high voltage output voltage of the load 53.

In order to synchronize ON / OFF of the high voltage control transistor 34 for controlling the high voltage output voltage of the load 53 with the switching operation of the switching transistor 27, a microprocessor is used for the control circuit 30 and the high voltage output voltage is controlled. The value of the detection port and the timing of the switching pulse are compared inside the microprocessor, and in synchronization with the switching pulse, the high voltage output transistor 3 is adjusted to match the high voltage output voltage detection port value.
An ON / OFF signal is supplied to 4 to control the high voltage output voltage.

By controlling the high-voltage output voltage with the above configuration, it is possible to synchronize the switching transistor 27 with ON and OFF, so that the high-voltage control transistor 3 is controlled.
Since the high-voltage control transistor 34 can be turned on and off while the collector-emitter voltage of 4 is zero, the switching loss due to the on-off of the high-voltage control transistor 34 can be eliminated as before, and the power supply can be eliminated. It is possible to eliminate a decrease in efficiency of the device and heat generation. As a result, high efficiency, high reliability, and downsizing of the power supply device can be realized.

(Eighth Embodiment) FIG. 9 is a block diagram of an eighth embodiment, and FIG. 10 is a schematic view of the peripheral structure of a transfer brush and an attraction brush to which the output of this embodiment is fed.

In FIG. 10, 1 is placed on the photosensitive drum 310.
The powder image formed by the secondary charging 311, the image exposure by the laser light 312, and the developing process by the developing device 313 is transferred to the transfer paper 320 adsorbed on the transfer drum 314.

The transfer drum 314 is formed by winding a thin Mylar film around a cylindrical frame.
The image forming portion that contacts 10 is composed of a single film.

The suction brush 318 uses the electrostatic force to transfer the transfer paper 320 that has passed through the transfer guide to the transfer drum 314.
It serves to adsorb to. The transfer brush 317 serves to transfer the toner on the photosensitive drum 310 onto the transfer paper by electrostatic force.

The outer charge eliminating charger 316 is used to reduce the absolute value of the voltage applied to the transfer brush 317, which will be described later. Reference numeral 315 denotes an inner charge eliminating charger.

The separation charger 319 charges the transfer paper 320 and the transfer drum 3 by performing AC + DC corona charging.
It serves to completely eliminate the electrostatic adsorption force between the fourteen.

The high-voltage power supply of this embodiment shown in FIG. 9 is for supplying power to the transfer brush 317 and the suction brush 318.

FIG. 11 is a timing chart showing the operation sequence of the charger and the charging brush around the transfer drum.

The transfer drum 314 has a circumference enough to stick one A3 transfer sheet in the vertical direction. FIG. 11 shows the case of copying one sheet of A4 transfer paper.

When the transfer paper 320 is sent from the paper carrying system, +15 μA is applied to the suction brush 318 in the constant current control mode.
It is made to flow and the transfer paper is adsorbed to the transfer drum.

A high negative voltage is applied to the inner charge eliminating charger 315 to charge the inside of the transfer drum 314 to −6 kV. At the same time, a positive high voltage is applied to the outer charge eliminating charger 316 to prevent the transfer paper from peeling off.

When the transfer paper 320 is attracted to the transfer drum 314 and the inside of the transfer drum is further charged to −6 kV, +10 μA is flown to the transfer brush 317 in the constant current control mode, and the toner image from the photosensitive drum to the transfer paper is transferred. Is transcribed.

It goes without saying that the transfer process is repeated for each of the four colors of magenta, cyan, yellow and black. The transfer brush power supply voltage at this time stays at about −6 kV between the sheets as shown in FIG. 10B, but since the previous charge is retained at the transfer timing to the transfer sheet, it is about 2 kV for each color. Ascend in steps.

When the transfer of the fourth color is completed, a high voltage of AC + DC is applied to the separation charger 319 (not shown),
By corona charging, the charges on the transfer paper and the transfer drum are removed to separate the transfer paper 320 from the transfer drum 314.

As is clear from the above description, the power supply for supplying power to the transfer brush 317 and the suction brush 318 must be a power supply of both positive and negative polarities.

In the eighth embodiment shown in FIG. 9, 320 is an oscillator, T2 is a step-up transformer, and its secondary winding NS.
A positive output forward converter is formed by diode D3, D4 and inductance L6 at
A diode D5 forms a negative output flyback converter at 2. Both converter outputs are connected in series.

The primary winding Np is connected to a transistor (FET) Q
7, and ON / OFF and DUTY are PWM-controlled by a pulse width (PWM) controller 321.
Here, assuming that PWM and DUTY are D, a voltage of Vin * (NS1 / NP) * D on the forward side and a voltage of −Vin * (NS2 / NP) * {D / (1-D)} on the flyback side are obtained. Occurrence occurs, and in the series connection, Vo = Vin * D / (1-D) * {(AB) -AD} where A = NS1 / NP B = NS2 / NP where A> B As described above, if A and B are selected, the positive and negative voltages can be continuously controlled by obviously controlling the value of D.

(Ninth Embodiment) FIG. 12 is a block diagram of the ninth embodiment, in which the same or corresponding parts as those of the eighth embodiment are designated by the same reference numerals and their duplicate description is omitted.

In this embodiment, the DUTY of the oscillator 320 is operated with two specific values. That is, one is the output Vo
Is a positive voltage and the other is a value that the output Vo is a negative voltage. The control circuit 322 controls the input voltage of the step-up transformer T2. Both positive and negative power supplies are realized by the combination of both.

(Tenth Embodiment) FIG. 13 is a block diagram of the tenth embodiment, in which the same or corresponding parts as those of the eighth and ninth embodiments are designated by the same reference numerals and their duplicate description will be omitted.

In this embodiment, the inductance L6 of the secondary side NS1 circuit is cut off and the forward side has a peak rectification structure, which is suitable for high voltage and low current.

With the configurations and controls of the above twelfth, thirteenth and fourteenth embodiments, the number of transformers can be increased as compared with the conventional bipolar high voltage generating system in which a fixed output DC-DC converter and a variable output DC-DC converter are connected in series. Can be reduced from 2 to 1. Moreover, only one PWM controller can be realized.

Further, a constant current can be automatically and stably supplied to any variation of the resistance component and the voltage source component included on the load side.

Since the positive and negative DC-DC converters are switched by one PWM controller and one transformer, the operation of positive and negative outputs can be smoothly switched, and abnormal output may occur. Absent.

As described above, since the transformer and the PWM controller are each configured by one, the cost can be significantly reduced and the reliability can be improved.

[0102]

As described above in detail in each embodiment,
According to the present invention, it is possible to provide a power supply device that can reliably control output and is suitable for an image forming apparatus such as a copying machine or a printer.

That is, by using the drive signal sent from the control means CPU to the switching element, it is possible to realize a composite power supply without a malfunction of the overcurrent limiter with a simple circuit configuration.

In the ON / OFF operation of the high-voltage control transistor for controlling the high-voltage output voltage, the current between the collector and emitter of the switching transistor is detected by the current transformer in order to synchronize with the switching transistor, and the current is synchronized with the detection signal. By turning on and off the high-voltage control transistor, the switching loss of the high-voltage control transistor can be eliminated.
Further, by detecting and synchronizing the winding voltage from the winding for low voltage output voltage and turning on and off the high voltage controlling transistor, the switching loss of the high voltage controlling transistor can be eliminated. Further, by using a microprocessor for the control circuit, the ON / OFF signals synchronized with the switching pulse are supplied to the high voltage control transistor, whereby the switching loss of the high voltage control transistor can be eliminated. This allows
High efficiency, high reliability, and miniaturization of the power supply device can be realized.

Further, the number of transformers can be reduced from two to one as compared with the conventional bipolar high-voltage generating system in which a fixed output DC-DC converter and a variable output DC-DC converter are connected in series. Moreover, only one PWM controller can be realized. And the resistance component included on the load side,
A constant current can be automatically and stably supplied to any fluctuation of the voltage source component.

By switching the positive and negative DC-DC converters by one PWM controller and one transformer, the operation of the positive and negative outputs can be smoothly switched, and no abnormality occurs in the output. Transformer, PW
By configuring one M controller, it is possible to significantly reduce costs and improve reliability.

[Brief description of drawings]

FIG. 1 is a block diagram of a first embodiment.

FIG. 2 is a timing chart of the first embodiment.

FIG. 3 is a block diagram of a second embodiment.

FIG. 4 is a block diagram of a third embodiment.

FIG. 5 is a block diagram of a fourth embodiment.

FIG. 6 is a circuit diagram of a fifth embodiment.

FIG. 7 is a circuit diagram of a sixth embodiment.

FIG. 8 is a circuit diagram of a seventh embodiment.

FIG. 9 is a block diagram of an eighth embodiment.

FIG. 10 is a schematic diagram of a configuration around a transfer drum of a copying machine.

FIG. 11 is a timing chart of the eighth embodiment.

FIG. 12 is a block diagram of a ninth embodiment.

FIG. 13 is a block diagram of a tenth embodiment.

FIG. 14 is a circuit diagram of a conventional power supply device.

[Explanation of symbols]

 1 AC input voltage 4 AND circuit (AND circuit) 5,15 Delay circuit 6 Oscillation circuit 9 Latch type output stop circuit 14 Central processing unit (CPU) C Delay signal Q1 Comparator R1 Overcurrent detection resistor T1 Converter transformer Tr1 Switching transistor

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Satoshi Saito 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (13)

[Claims] 1. A value corresponding to the secondary output voltage of the transformer is 1
A power supply device for controlling at least one of a plurality of secondary outputs to a predetermined voltage, comprising control means for calculating an on / off time of a secondary switching element and controlling an excitation period of a primary side of a converter transformer. There, current detection means for detecting the current of the switching element, comparison means for comparing the value detected by the current detection means with a designated value, and in synchronization with the ON / OFF signal of the switching element from the control means, And a delay signal generating means for generating a delay signal having an ON period shorter than the ON period of the same signal, an AND circuit for inputting the output of the comparing means and the delayed signal, and an output of the AND circuit A power supply device comprising: an overcurrent protection unit that turns off the switching element. 2. The power supply device according to claim 1, wherein the current detecting means for detecting the current of the switching element is constituted by a resistor. 3. The power supply device according to claim 1, wherein the current detecting means for detecting the current of the switching element is constituted by a current transformer. 4. The power supply device according to claim 1, further comprising a delay signal generation unit that generates a delay signal by delaying the on / off timing signal to the switching element. 5. The power supply device according to claim 1, further comprising delay signal generation means for calculating turn-on / turn-off timing by a pulse width modulation control calculation circuit provided in the control means. 6. An arithmetic processing unit which is a digital circuit and a memory and peripheral analog circuits provided in the control means,
The power supply device according to any one of claims 1 to 5, wherein the comparison means, the delay signal generation means, the AND circuit, and the overcurrent protection means are formed on the same chip. 7. The delay signal generating means changes the degree of delay of the delay signal in response to variations in switch characteristics of the switching element.
The power supply device according to any one of 1. 8. A power supply device for generating a high voltage output and a low voltage output by the same transformer, and a primary side current detecting means for detecting a collector-emitter current of a primary side switching transistor, comprising a current transformer. A power supply device comprising a high voltage control means for controlling on / off of a high voltage control transistor provided on the secondary side in synchronization with a detection signal from the primary side current detection means. 9. A power supply device for generating a high voltage output and a low voltage output by the same transformer, wherein a voltage is input from a low voltage output winding to generate a synchronization signal, and the high voltage provided on the secondary side by the synchronization signal. A power supply device comprising high-voltage control means for performing on / off control by synchronizing a control transistor with a switching transistor on a primary side. 10. A power supply device for generating a high-voltage output and a low-voltage output by a single transformer, wherein an ON / OFF timing signal of a switching transistor on the primary side and a high-voltage control signal synchronized with the ON / OFF timing signal are provided. A power supply device comprising a high-voltage control means for outputting and outputting a high-voltage control transistor provided on the secondary side to perform on / off control in synchronization with a switching transistor on the primary side. 11. A switching means for turning on / off the primary side input of the transformer, a pulse width modulation control means for controlling the switching means, and a first high voltage output and a second high voltage output on the secondary side. A power supply device having the first high-voltage output winding forms a forward converter, and the second high-voltage output winding forms a flyback converter;
A high-voltage output and a second high-voltage output are connected in series. 12. A secondary side output is rectified so that a positive voltage is output from a forward converter formed of a first high voltage output winding and a negative voltage is output from a flyback converter formed of a second high voltage output winding. 12. The power supply device according to claim 11, wherein the pulse width modulation control means controls so that the positive and negative voltages are continuously output. 13. The secondary side output is rectified so that a negative voltage is output from a forward converter formed of the first high voltage output winding and a positive voltage is output from a flyback converter formed of a second high voltage output winding. 12. The power supply device according to claim 11, wherein the pulse width modulation control means controls so that the positive and negative voltages are continuously output.