JPH0389850A - Power source - Google Patents

Abstract

PURPOSE:To obtain a small size power source in which the rising speed of a pulse is large with a small overshoot and ripple by driving a converter transformer in high frequency of large amplitude, and so controlling as to increase the rise driving amount of a high voltage output larger than a driving amount at a high voltage level of the high voltage output. CONSTITUTION:When a rectified output V0 reaches a predetermined value V1, the output of a comparator 6 is inverted from a low level to a high level. A transistor Q1 is cut OFF by this output to stop driving of following converter transformer T1. If the output V0 becomes a predetermined value or less, the output of the comparator 6 is inverted from a high level to a low level, and driving of a converter transformer T1 by a PWM circuit 43 is started. Then, the output V0 is raised, the output of the comparator 6 is inverted, and the driving of the transformer T1 is stopped.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a power supply device suitable for use as a power supply for a developing bias of an electrophotographic printer, a copying machine, and the like.

[Conventional technology]

Conventionally, a power source for developing bias has often been constructed 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.

[Problem to be solved by the invention]

However, in the conventional example, the step-up transformer for low-frequency AC is large, it generates noise because it is in the audible range, and it is very difficult to reduce this noise, and the output duty ratio has to be changed significantly beyond 50%. However, there were problems such as it being impossible due to the biased magnetization of the transformer.

Furthermore, since the load is a capacitive load and rapid charging is difficult, it is not possible to increase the pulse rise speed.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a power supply device that is small in size and has a high pulse rise speed, but has low overshoot and ripple.

[Means for Solving the Three Problems] In order to achieve the above object, the present invention configures a high voltage rectangular wave power supply device as shown in (1) to (4) below.

(1) A power supply device that drives the primary side of a converter transformer with a large-amplitude high-frequency wave amplitude-modulated with a low-frequency signal, and rectifies the secondary side output of the converter transformer with a rectifier diode to obtain a high-voltage output. detecting the voltage level of the high-voltage output and comparing it with a predetermined value, and when the voltage level becomes higher than the predetermined value, stopping the subsequent driving of the primary side of the converter transformer by the high frequency; When the voltage level becomes lower than the predetermined value, the primary side of the converter transformer is started to be driven by the high frequency thereafter, and a predetermined voltage level larger than the period of the high frequency and sufficiently smaller than the period of the low frequency is started. A power supply device equipped with a control means that increases its drive amount with a time delay.

(2) A power supply device that drives the primary side of a converter transformer with a large-amplitude high-frequency wave amplitude-modulated with a low-frequency signal, and rectifies the secondary side output of the converter transformer with a rectifier diode to obtain a high-voltage output. detecting the voltage level of the high voltage output and comparing it with a second predetermined value and a first predetermined value that is a little higher level than the second predetermined value; If the voltage level is between the first and second predetermined values, the driving amount when the converter transformer primary side is driven by the high frequency is reduced from the driving amount when the voltage level does not reach the second predetermined value,
A power supply device comprising a control means for stopping the subsequent driving of the primary side of the converter transformer by the high frequency when the voltage becomes higher than a predetermined value.

(3) In the power supply device described in (1) or (2) above,
A power supply device for developing bias, which is provided with grounding means for grounding the output side during a low level period of a low-frequency signal on the output side of a rectifier diode, and is also provided with a DC bias weight circuit and a low-pass filter.

(4) In the above (3), the low-pass filter is a power supply device for a developing bias configured integrally with the developing sleeve and the space capacitance between the photoreceptor.

(Function) According to the configurations (1) to (4) above, the converter transformer is driven at a high frequency with a large amplitude, and the amount of drive at the rise of the high voltage output is larger than the amount of drive at the high voltage level of the high voltage output. controlled.

〔Example〕

The present invention will be explained in detail below based on examples.

(Circuit diagram that is the basis of the present invention) ′! Figure J5 is a circuit diagram that is the basis of the present invention, and Figure 6 shows voltage waveforms at various parts thereof. As shown in FIG. 6(a), the output of the oscillation circuit 1 has a repetition frequency of 1800 Hz,
It is a low frequency rectangular wave with a duty of 20%. Oscillation circuit 2
The output has a repetition frequency of 50 Hz and a duty of 50
% high frequency rectangular wave. The modulation circuit 3 is shown in FIG.
), the output of the oscillation circuit 2 is subjected to 100% amplitude modulation with the output of the oscillation circuit 1. The converter transformer T can be made sufficiently small because it is driven at a high frequency.

The switch circuit (grounding means) 4 is closed at the timing when the output of the oscillation circuit 1 is at a low level. At the same time, the switching transistor Q1 for driving the converter transformer T is kept in a cut-off state. With the switching transistor Q1 being driven at 50 Hz,
+vI is obtained at the cathode of the rectifier diode D1,
Since it is smoothed by the clamping capacitor C1, the output of the switch circuit 4 becomes as shown in FIG. 6(c).

The output obtained here is connected to the output terminal P1 by the clamping capacitor C1, but since the Kumbh diode D2 conducts at the peak in the positive direction and is clamped to the clamp power supply 5 which becomes -vE, the output is connected to the output terminal P1. is shown in Figure 6(d).
The output amplitude v1. An output of the positive direction peak value -v8 is obtained.

However, the power supply shown in FIG. 5 has the following problem. Since the developing roller connected via the output terminal P1 is a capacitive load whose main part is the capacitance between the developing roller and the opposing drum surface, the output waveform has a slow rise as shown in FIG.

In order to overcome this problem, the present invention increases the charging voltage of the load capacitor, that is, the saturation value of the rectified output, to make the output rise faster, and when the output reaches a predetermined level, the primary Cut off the power supply to the side.

(First Embodiment) FIG. 1 is a circuit diagram of a "high voltage rectangular wave power supply device" which is a first embodiment of the present invention, and FIG. 2 is a voltage waveform diagram of each part thereof.

The basic configuration of this embodiment is the same as that shown in FIG. 5, but the drive source of the converter transformer T is PWM (pulse
(width n+odulation) circuit 43, and this circuit is feedback-controlled by the output of the comparator 6. The output of the PWM circuit 43 is a high frequency of +lz with a repetition frequency f2:50, and its output amplitude is selected to be "large amplitude" so that the saturation value v0 of the rectified output Vo is sufficiently larger than the predetermined value V (this In invention “
"large amplitude" is used in this sense).

The oscillation circuit 1 is similar to that shown in FIG. 5, and has a repetition frequency f: 1
Outputs a low frequency rectangular wave of B00Hz and a duty of 20%. The large-amplitude high frequency from the PWM circuit 43 is 100% amplitude-modulated by turning on and off the transistor Q3 with the rectangular wave from the oscillation circuit 1, and is then transmitted to the transistor Q1.
is supplied to the base of converter transformer T, and drives the primary side of converter transformer T. The reference voltage of the comparator 6 is selected so that the rectification vo becomes a predetermined value V1, and the delay circuit 41
A predetermined time that is larger than the high frequency period of the WM circuit 43 and sufficiently smaller than the low frequency period of the oscillation circuit 1.1. is selected to delay the output of comparator 6 by .

Rectified output V. is voltage-divided to a predetermined ratio by resistors R41 and R42, input to the comparator 6, and compared with the reference voltage input to the input terminal P2. The rectified output v0 is a predetermined value V,
(see FIG. 2), the output of the comparator 6 is inverted from low level to high level. The output causes diode D41 to conduct, causing transistor Q3 to conduct;
The base of the transistor Q1 is brought to zero potential, the transistor Q1 is cut off, and the subsequent driving of the converter transformer T is stopped. When the rectified output vo becomes less than the predetermined value v1, the output of the comparator 6 is inverted from high level to low level, and the converter transformer T by the PMW circuit 43 is inverted.
1 drive is started, the rectified output v0 rises, the output of the comparator 6 is inverted, and the drive of the converter transformer T1 is stopped.

By repeating this, the rectified output V. is controlled to a predetermined value V. Since the saturation value v0 of the rectified output is selected to be sufficiently larger than the predetermined value vI as described above, the rise of the rectified output vo is significantly improved as shown in FIG. 2(a). The comparator 6 must be fast enough to reduce overshoot and ripple on the rectified output Vo. C41 in FIG. 1 is the load capacity, that is, the capacity of the developing roller.

A part of the output of the comparator 6 is supplied to the transistor Q41 via the delay circuit 41, and is supplied to the transistor Q41 for a predetermined period of time 1.
The transistor Q41 is made conductive after a delay of .times. 42 is a voltage follower using an operational amplifier, and the output when transistor Q41 is cut off is as follows. The output is input to the PWM circuit 43, and the voltage (
1) with a pulse width corresponding to transistor Q3. Drive Ql. When transistor Q41 becomes conductive, the output of voltage follower 42 becomes. For this reason, the PWM circuit 43
The pulse width of the output becomes smaller, and comparator 6
Even if the output of the PWM circuit 43 is inverted, during the delay time t,
Since the pulse width of the output remains small, the charging speed of the load capacitor C41 becomes slow and the output ripple is small (see FIG. 2). When the output falls, the delay time 1. Later, the pulse width of the output of the PWM circuit 43 becomes larger, so when the next output rises, the amount of drive (amount of current) on the primary side of the converter transformer increases.
increases and rises quickly.

(Second Embodiment) In FIG. 3, instead of providing the delay circuit 31, a rectified output v0
reaches the level V2 (second predetermined value) immediately before reaching the final level V+ (first predetermined value), the driving amount (all) on the primary side of the converter transformer is reduced to increase the charging speed of C41. A second embodiment of the invention is shown in which the comparator 6 slows down the final level v, just as in the first embodiment.
1 is detected and the primary side energization of the converter transformer T is completely cut off. Comparator 61 operates at a level v2 set slightly lower than vl, and transistor Q4
1 is made conductive, and the converter transformer primary side driving amount (energization amount) is reduced to slow down the charging speed of C41.

Therefore, after the rectified output v0 reaches the second predetermined value v2, the charging speed is slow and the overshoot of the output rise is small. While the comparator 6 is fluctuating near the final level vI, the charging speed is slow and the ripple is small (second
See figure (a).

(Third Embodiment) FIG. 4 shows a third embodiment of the present invention in which the rectified output V0 of the second embodiment is supplied to the developing sleeve via a DC superimposition circuit and a low-pass filter 72. Rectifier diode D71.
Smoothing capacitor C71, operational amplifier 71. A DC bias circuit is configured by the high voltage transistor Q71 and the like. A part of the secondary output of the converter transformer T is connected to a resistor R74.
Power is supplied to the DC bias circuit via. The rectified output of the diode D71 is input to the operational amplifier 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 high voltage transistor Q71 is controlled, and the voltage of the DC bias circuit is The voltage is stabilized at a predetermined times the reference voltage.

The AC output v0 is superimposed on the rectified output of the diode D71, that is, the DC bias, by the capacitor C1 and the resistor R73. The superimposed output consists of 72 impedance elements and load capacity j
The high frequency ripple of the PWM circuit 43 is removed by the low pass filter configured by the lc 41. As the element 72, a choke coil or a resistor with a predetermined value is used. In this embodiment, since a part of the amplitude-stabilized output is rectified to obtain the clamp power supply, the clamp power supply itself is also stabilized. Therefore, an output with stable amplitude and DC level can be easily obtained. As explained in the second embodiment, since the overshoot and ripple of the rectified output v0 are small, a transistor with a low collector voltage standard can be selected as the high voltage transistor Q71.

〔Effect of the invention〕

As explained above, according to the present invention, the following (ri~(
6) effect can be obtained.

(1) Significant miniaturization as no low frequency transformer is used;
Costs are reduced and reliability is increased.

(2) Since no low frequency transformer is used, audible noise can be completely eliminated.

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

(4) A remarkable improvement in the rise speed of AC output is obtained, which increases the efficiency of development, leading to increased density and stabilization of density.

(5) The output amplitude can be stabilized with high precision.

(6) Overshoot and high frequency ripple can be reduced.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of a first embodiment of the present invention, Fig. 2 is a voltage waveform diagram of each part of the same embodiment, Fig. 3 is a circuit diagram of a second embodiment of the present invention, and Fig. 4 is a circuit diagram of the present invention. FIG. 5 is a circuit diagram of the third embodiment of the invention, FIG. 6 is a voltage waveform diagram of each part of the circuit diagram of FIG. 5, and FIG. 7 is an output of the circuit of FIG. 5. FIG. 1--Oscillation circuit 6.61--Comparator 41--Delay circuit 43--PWM circuit

Claims (4)

[Claims] (1) A power supply device that drives the primary side of a converter transformer with a large-amplitude high-frequency wave amplitude-modulated with a low-frequency signal, and rectifies the secondary side output of the converter transformer with a rectifier diode to obtain a high-voltage output. detecting the voltage level of the high-voltage output and comparing it with a predetermined value, and when the voltage level becomes higher than the predetermined value, stopping the subsequent driving of the primary side of the converter transformer by the high frequency; When the voltage level becomes lower than the predetermined value, the primary side of the converter transformer is started to be driven by the high frequency thereafter, and a predetermined voltage level larger than the period of the high frequency and sufficiently smaller than the period of the low frequency is started. A power supply device comprising a control means for increasing its driving amount with a time delay. (2) A power supply device that drives the primary side of a converter transformer with a large-amplitude high-frequency wave amplitude-modulated with a low-frequency signal, and rectifies the secondary side output of the converter transformer with a rectifier diode to obtain a high-voltage output. detecting the voltage level of the high voltage output and comparing it with a second predetermined value and a first predetermined value that is a little higher level than the second predetermined value; If the voltage level is between the first and second predetermined values, the driving amount when the converter transformer primary side is driven by the high frequency is reduced from the driving amount when the voltage level does not reach the second predetermined value,
1. A power supply device comprising: control means for stopping the subsequent driving of the primary side of the converter transformer by the high frequency when the voltage becomes higher than a predetermined value. (3) In the power supply device according to claim 1 or claim 2,
A power supply device for developing bias, characterized in that a grounding means is provided on the output side of a rectifier diode to ground the output side during a low level period of a low frequency signal, and a DC bias weight circuit and a low pass filter are provided. . (4) The power supply device for developing bias according to claim 3, wherein the low-pass filter is configured integrally with the developing sleeve and the space capacitance between the photoreceptor.