JPH03143229A - Power supply device - Google Patents

Abstract

PURPOSE:To supply a high-voltage power supply having desired waveforms in response to the characteristics of load by filtering the output of an amplitude detecting signal by a low-pass filter when conduction on the primary side is interrupted in response to the output amplitude of a rectifier performing conduction/interruption at a flyback mode. CONSTITUTION:The rectifying output V0 of a transformer T1 is voltage-divided at a specified ratio, and compared with reference voltage. When output voltage V0 reaches a specified value V1, a comparator 6 is inverted at a high level, and a transistor (TR) Q1 is interrupted. On the other hand, one part of an output from the comparator 6 is input to a delay circuit 41, is delayed only by a fixed value, and short-circuits a TRQ41. An output at a time when the TRQ41 is interrupted is input to a PWM circuit 43, and TRs Q3, Q1 are driven. A spike component in an output from an attenuation circuit 44 is removed completely by a low-pass filter 45, and the output is input to the comparator 6.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a power supply device, and particularly to a power supply device that outputs a high voltage in which alternating current and direct current are superimposed.

[Prior Art] Conventionally, various electrophotographic image forming apparatuses have been used as image forming mechanisms of printers or copying machines. An electrophotographic image forming apparatus uses loads that require a high voltage power supply, such as a charger and a developer. Since the voltage required for each high-voltage load and the control method depending on the progress of the image forming sequence are different for each load, these power supply devices are controlled by different independent control structures.

In particular, the power supply for developing bias of the developing device is often composed of a step-up transformer for low-frequency AC output, and a DC-DC inverter coupled to the transformer for superimposing a DC voltage on the AC output.

[Problems to be Solved by the Invention] In the conventional structure of the developing bias power supply described above, the step-up transformer for low frequency AC is large, and noise is generated because it is in the audible band, and it is difficult to reduce this. It is very difficult to do so, and it is difficult to change the duty ratio by more than 50%, which is impossible due to the biased magnetization of the transformer. In addition, since the load is a capacitive load and rapid charging is difficult, there are problems such as the inability to increase the pulse rise speed.

In view of the above problems, conventional configurations as shown in FIGS. 7 and 8 are known. FIG. 8 shows signal waveforms at various parts of the circuit shown in FIG. In FIG. 7, numerals 1 and 2 are oscillators that generate constant pressure alternating current of rectangular waves, and oscillator 1.
is a square wave with a frequency of 1, 800 Hz and a duty ratio of 20% (Fig. 8 (A)), and the oscillator 2 has a frequency of 50 k
H2, a rectangular wave signal (waveform portion in FIG. 8(B)) with a duty ratio of 50% is generated.

The output of the oscillator 2 is input to the modulator 3, and is almost 100% modulated by the output signal of the oscillator 1 to obtain the waveform shown in FIG. 8(B). The modulation circuit 3 connects the constant voltage power supply voltage Vc to the primary winding of the step-up transformer TI via the transistor Q1.
Control the application of c.

On the secondary side of the transformer TI, a rectifying diode D1,
A clamp circuit for superimposing a DC component, which includes a large-capacity capacitor CI, a diode D2, and a DC power source 5 (output -VE), is connected via a discharge resistor R1. The clamp output is output from the terminal P1 to the developing device as a developing bias. Further, the connection point between the resistor R1 and the clamp capacitor C1 can be grounded by a switch 4 consisting of a relay, an analog switch, or the like.

The connection method of the transformer T1 and the diode DI is a flyback method as shown in FIG. As shown in FIG. 8(C), the switch circuit 4 becomes conductive in synchronization with the low level output of the oscillator 1, that is, the cutoff of the transistor Ql and the transformer TI. Transistor Q1 is 50kHz
During the period when it is driven by z, the clamping diode D
Since the voltage +Vl is obtained at the cathode of the switching circuit 1 and smoothed by the clamping capacitor C1, the output of the switch circuit 4 becomes as shown in FIG. 8(C). The power supply output obtained in this way is connected to the output terminal P1 via the clamping capacitor C2, but the clamping diode D2 conducts at the peak timing in the positive direction and is connected to the DC power supply 5 having an output of -VE. Since the output is clamped, an output whose peak value in the positive direction is -VE is obtained as shown in FIG. 8(D). As is clear from FIG. 8(D), this output is a superposition of the negative DC voltage -VE and the rectangular wave AC of 1800 Hz voltage vi.

According to the above configuration, since the transformer T1 itself is driven at a high frequency, there is no need to use a large transformer that can be driven at a low frequency as in the past, and the power supply section can be configured to be small and lightweight, and noise countermeasures can be easily implemented. There is an advantage.

However, in the conventional configuration described above, the load is the developing roller of the developing device, and this developing roller is a capacitive load whose majority is the capacitance between it and the opposing photosensitive drum surface. As shown, there is a problem in that the rise is considerably slower than that of the output waveform (FIG. 9(A)) when forward resistance is used as the load.

An object of the present invention is to solve the above problems and provide a power supply device that can supply high-voltage power with a desired waveform depending on the characteristics of the load.

[Means for Solving the Problems] In order to solve the problems described above, in the present invention, in a power supply device that outputs high voltage in which alternating current and direct current are superimposed, a low frequency oscillator, a high frequency oscillator, and an output a transformer whose low-voltage direct current input is controlled according to the output of one of these oscillators depending on the voltage; a rectifier which rectifies the output of this transformer in flyback mode; and an output point of this rectifier. switch means for switching on and off between ground potentials in synchronization with the output signal of the low frequency oscillator; and a frequency higher than the frequency of the low frequency oscillator for filtering an output amplitude detection signal obtained by attenuating the output voltage of the rectifier with a resistor circuit. A low-pass filter has a cutoff frequency lower than the frequency of the high-frequency oscillator, and the output of this low-pass filter is compared with a predetermined reference value, and if the output of the low-pass filter exceeds the reference value, the primary side of the transformer is The present invention employs a configuration consisting of means for blocking energization, and a clamp circuit that clamps the AC voltage generated at the connection point between the switch means and the rectifier to a predetermined DC level and then supplies power to the load.

[Function] According to the above configuration, when the primary side current is cut off according to the output amplitude of the rectifier that conducts/cuts off in the flyback mode, by filtering the output of the amplitude detection signal with a robust filter, It is possible to prevent output amplitude overshoot and amplitude fluctuation.

[Example] Hereinafter, the present invention will be described in detail based on the example shown in the drawings.

FIG. 1 shows the configuration of a power supply device employing the present invention. In FIG. 1, the same reference numerals are used for the same members as in the conventional example shown in FIG.

The major difference from the conventional example shown in FIG. 7 is that the high frequency oscillation circuit 2 in FIG. A comparator 6.47 and a delay circuit 17 are used to control the operation of the driving transistor Q1.
．． The point is that a plurality of control systems consisting of 41 units have been added. In addition, the switch circuit 4 is a high voltage transistor Q in FIG.
It is composed of 2.

The embodiment shown in FIG. 1 has a drawback in the conventional configuration shown in FIG. 7, that is, the capacitive load is mostly the capacitance between the developing roller and the opposing photosensitive drum surface, so the embodiment shown in FIG. This is to overcome the problem of slow rise, and increases the charging voltage of the load capacitor, that is, the rectified output vO, and speeds up the charging time constant to speed up the output rise and rise to a specified level. When this occurs, the power supply to the primary side of the transformer T1 is cut off.

The configuration shown in FIG. 1 will be described in detail below.

The base of transistor Q1, which drives the primary side of transformer T1, is controlled by transistor Q3. The base of transistor Q3 is diode D41, D42, D43.
It is controlled by the level of the higher voltage among the outputs of the comparator 6, the oscillator 1, or the PWM circuit 43 via the output voltage.

The half-wave rectified output by the capacitor C5 and diode D6 of the secondary side output of the transformer TI is output by the diode D1. Resistance R1
It is connected to the collector of the transistor Q2 constituting the switch circuit 4 (the collector potential is 0) via the transistor Q2. Transistor Q2 is driven by the output of oscillator 1.

The collector potential vO1 of the transistor Q2, ie, the voltage value corresponding to the output voltage, is divided by resistors R41 and R42 (attenuation circuit 44), and input to the comparator 6 via the low-pass filter 45.

The low-pass filter 45 can be constructed, for example, from the circuit shown in FIG. The circuit shown in FIG. 5 is a secondary active low-pass filter in which an active filter consisting of an operational amplifier 50, resistors R53, R54, R52, and a capacitor C52 is connected after a passive filter consisting of a resistor R51 and a capacitor C51. The cutoff frequency f3 of the low-pass filter 45 is set sufficiently higher than the frequency f1 of the oscillator l and lower than the frequency f2 of the PWM circuit 43 by two time constants.

The comparator 6 compares this input voltage with a control voltage input from a control system (not shown) via the terminal P2, and outputs a difference voltage.

The output of the comparator 6 is input to the transistor Q3 via the diode D41, and after being delayed by the delay circuit 41, controls the base of the transistor QO41.

The delay circuit 41 turns on or off the transistor Q41, so that the collector of the transistor Q4I controls the input terminal of the voltage follower 42 to one of two voltages described below.

The voltage follower 42 outputs these voltage values as they are.
The signal is transmitted to the WM circuit 43 and input to the PWM circuit 43. The delay circuit 41 and voltage follower 42 have the same functions as the modulation circuit shown in FIG.

The PWM circuit 43 controls the output pulse width according to the input voltage.

Note that C41 in FIG. 1 indicates the load capacity of the developing roller in the case of an image forming apparatus. In addition, in Fig. 1 (or Figs. 3, 4, and 6 described later), the capacitor C
The illustration of the clamp circuit (see FIG. 7) connected after I is omitted.

FIGS. 2A to 2E show the operation of the circuit shown in FIG. 1.

When the power supply voltage Vcc is applied to each application point in FIG. 1, and a control voltage corresponding to a predetermined output voltage is input to the terminal P2, the circuit in FIG. 1 starts supplying power to the load.

The rectified output VO of the transformer TI is divided into voltages at a predetermined ratio by resistors R4N and R42, and input terminal P2 at the comparator 6.
is compared with the reference voltage input to the

When the output voltage vO reaches the predetermined value ■1, the comparator 6
is reversed from low level to high level. This output causes the diode D41 to conduct, making the transistor Q3 conductive and bringing the base of the transistor Q1 to zero potential, cutting off the transistor Q1.

That is, as shown in FIG. 2(C), each time the output 0 divides the control voltage of the comparator 6, the transistor Q1 is turned on (FIG. 2(B)), and the output voltage Vt is maintained at Vt. , ), the rise of the output vO is significantly improved. vO shown in FIG. 2(A) is the saturation value of the rectified output. Note that the comparator 6 must be sufficiently fast in order to reduce overshoot and ripple in the output vO.

On the other hand, a part of the output of the comparator 6 is input to the delay circuit 4I and delayed by a predetermined value T1 which is larger than the period 1/f2 and sufficiently smaller than 1/f1, and short-circuits the transistor Q41 only during TI. When the transistor Q41 of the voltage follower 42 is cut off, the output is 44 Vcc.
・(1) R44+R43.

This output is input to the PWM circuit 43 of frequency f2,
Transistor Q3 with a pulse width according to the voltage in equation (1),
Drive Ql. When the output vO reaches Vl, the comparator 6 and the delay circuit 41 operate to turn on the transistor Q41 by TI, and the output of the voltage follower 42 becomes 44.

Therefore, the pulse width of the output of the PWM circuit 43 becomes shorter,
Even if the comparator 6 is turned off again, the charging speed of the load capacitor C41 becomes slow.

(2) The output of 0 has a particularly large spike component of frequency f2 at the rising edge (see FIG. 2(A)). This is due to discharge by the attenuation circuit 44 (resistors R, 41, R42).

Since the resistor R41 constituting the attenuation circuit 44 has a high resistance, the ratio of the distributed capacitance of the resistor itself increases, and the output of the attenuation circuit 44 has an even larger spike component as shown in FIG. 2(D). It will appear. For this reason, the detection level becomes unstable, and if this is input to the comparator 6 as it is, the amplitude level will increase.

Therefore, the output of the attenuation circuit 44 is filtered through a low-pass filter 45.
By completely removing the spike component and inputting it to the comparator 6 as shown in FIG. 2(E), more accurate amplitude control becomes possible.

4. The configuration of FIG. 1 can be modified as shown in FIG. 3, FIG. 4, or FIG. 6.

In Figure 3, instead of providing a delay circuit, the output
This slows down the charging speed of C41.

The comparator 6 is exactly the same as the embodiment shown in FIG.
The final level V1 is detected and the primary side energization is completely cut off. On the other hand, the added comparator 61 operates at a level 2 set slightly lower than Vl, and the transistor Q
41 and reduce the amount of current on the primary side to increase the load capacity C41.
Slow down the charging speed.

FIG. 4 shows an example in which the configuration shown in FIG. 3 is further modified and the output VO is supplied to the developing sleeve via a DC superimposition circuit and a high-frequency cut filter 72.

The DC superimposition circuit includes a rectifier diode D71. Smoothing capacitor C71, operational amplifier 71, high voltage transistor Q7
1.

A part of the secondary output of the transformer TI is supplied to the DC superimposition circuit through a resistor R745. The rectified output of the diode D71 is input to the comparator 71 through a voltage dividing circuit of resistors R71 and R72, and is compared with the reference voltage input to the terminal P4, and the collector current of the transistor Q71 is controlled to stabilize it at a predetermined times the reference voltage. be done. Thereby, the direct current component can also be controlled at a constant voltage.

A rectified output from a diode D71 is superimposed on the AC output vO by a capacitor C1 and a resistor R73. This output is synthesized by an LC filter using an impedance element and a load capacitance C4].

The ripple component of the high frequency f2 is removed. As the high-frequency cut filter 72, a choke coil or a resistor can be used.

Note that in the configurations shown in FIGS. 3 and 4, the low-pass filter 4
5 is omitted from the drawing, it goes without saying that low-pass filters can be connected to appropriate locations in the input circuits of converters 6 to 61, respectively.

FIG. 6 shows a low-pass filter 46 having the same configuration as the low-pass filter 45 in the circuit of FIG.
This is an example in which the filter characteristics are improved by connecting the filters in series.

According to each of the above embodiments, the following effects can be obtained.

[1] There is no need to use a low-frequency transformer, resulting in significant downsizing, lower costs, and improved reliability.

(2) For the same reason as (1), audible noise can be completely eliminated.

(3) It is possible to freely set the duty ratio of AC output other than 50%, which was previously impossible, and it is also possible to use a desired duty ratio.

(4) AC amplitude can be stabilized very easily.

(5) According to the configuration shown in Fig. 4, a part of the amplitude-stabilized output is voltage-doubled and rectified to obtain the clamping power source.
The clamp power supply itself is also stabilized. Therefore, stable outputs in both amplitude and DC level can be easily obtained.

7 (6) The power cutoff on the primary side is controlled according to the switch current of the switch circuit on the secondary side of the transformer, and the rise speed of the AC output is significantly improved, so the load is reduced to less than the developing speed of the image forming apparatus. In the case of containers, it can be expected to increase development efficiency, improve recording density, and stabilize density.

(7) Output amplitude can be stabilized with high precision.

(8) By using a high-speed element for the comparator 6, overshoot and high frequency ripple can be eliminated.

(9) Also, the high voltage transistor Q
2 collector voltage can be lowered, and cheaper elements can be used.

(10) By feeding back the output of the amplitude detection circuit (attenuation circuit 44) to the primary side of the transformer via the low-pass filter 45 (~46), overshoot of the output amplitude and amplitude fluctuation can be reduced. More accurate output amplitude control is possible.

8. In the above description, the developing device of the image forming apparatus is considered as a load, but a similar configuration can be implemented for AC/DC superimposed output to other loads, especially capacitive loads.

[Effects of the Invention] As is clear from the above, according to the present invention, in a power supply device that outputs high voltage in which alternating current and direct current are superimposed, a low frequency oscillator, a high frequency oscillator, and these oscillators can a transformer whose primary side low-voltage DC input is controlled in accordance with one of the outputs of the transformer, a rectifier which rectifies the output of this transformer in flyback mode, and a connection between the output point of this rectifier and ground potential with said low frequency DC input. a switch means that is switched on and off in synchronization with the output signal of the oscillator; and a cut that is higher than the frequency of the low frequency oscillator and lower than the frequency of the high frequency oscillator, which filters the output amplitude detection signal obtained by attenuating the output voltage of the rectifier with a resistor circuit. a low-pass filter having an off frequency; means for comparing the output of the low-pass filter with a predetermined reference value and blocking energization of the primary side of the transformer when the output of the low-pass filter exceeds the reference value; 9 Since the configuration includes a clamp circuit that clamps the AC voltage generated at the connection point between the switch means and the rectifier to a predetermined DC level and then supplies power to the load, the rectifier that conducts/cuts off in flyback mode is used. 1 depending on the output amplitude
When cutting off power to the next side, filtering the output of the amplitude detection signal with a low-pass filter prevents output amplitude overshoot and amplitude fluctuation, enables highly accurate output amplitude control, and enables power supply to capacitive loads. Also, the rise speed of AC output is significantly improved, and, for example, when connecting a developing unit of an image forming apparatus, there are excellent advantages such as improvement and stabilization of recording density.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of a power supply device adopting the present invention, FIGS. 2(A) to (E) are power waveform diagrams showing the operation of the device in FIG. 1, and FIGS. The figures are circuit diagrams showing other embodiments of the present invention, FIG. 5 is a circuit diagram of the low-pass filter of FIG. 1, FIG. 6 is a circuit diagram of another embodiment of the power supply device, and FIG. 7 is a circuit diagram of the low-pass filter of FIG. Circuit diagram showing the configuration of the device, Figures 8 (A) to (D)
9 is a power waveform diagram of each part of FIG. 7, and FIGS. 9(A) and 9(B) are enlarged views of the output waveform of FIG. 7. 1.2--Oscillator 3--Modulation circuit 4--Switch circuit 6.61
... Comparator 41 ... Delay circuit 42 ... Voltage follower 43 ... PWM circuit 45.46 ... Low pass filter 72 ... High frequency cut filter Tl - ... Transformer silencer 7. Showing the name of the work, f < 5, difference in balance Figure 9

Claims (1)

[Claims] 1) A power supply device that outputs a high voltage in which alternating current and direct current are superimposed, including a low frequency oscillator, a high frequency oscillator, and a primary-side power source according to the output of one of these oscillators depending on the output voltage. a transformer that controls low-voltage DC input; a rectifier that rectifies the output of the transformer in flyback mode; and a connection between the output point of the rectifier and ground potential in synchronization with the output signal of the low-frequency oscillator. a low-pass filter having a cutoff frequency higher than the frequency of the low-frequency oscillator and lower than the frequency of the high-frequency oscillator, which filters an output amplitude detection signal obtained by attenuating the output voltage of the rectifier by a resistor circuit; Compare the output of the filter with a predetermined reference value,
means for blocking energization of the primary side of the transformer when the output of the low-pass filter exceeds the reference value; and after clamping the AC voltage generated at the connection point between the switch means and the rectifier to a predetermined DC level. A power supply device comprising a clamp circuit that supplies power to a load.