JP2816719B2 - Power supply for developing bias - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing bias power supply device for an electrophotographic printer, a copying machine or the like.

[Conventional technology]

Conventionally, this type of developing bias power source uses a low-frequency AC output step-up transformer, and a DC-DC converter is coupled to the transformer to superimpose a DC voltage on the AC output of the transformer. Is common.

[Problems to be Solved by the Invention] However, in the conventional power supply device for developing bias as described above, audible band noise is generated,
There was a problem that even if an attempt was made to change the duty ratio significantly from 50%, it was not possible because of the transformer's magnetization.
Further, since the load is a capacitive load and rapid charging is difficult, there is a problem that the rising speed of the output pulse cannot be increased.

The present invention has been made in view of such problems, and eliminates the need for a low-frequency AC step-up transformer, is compact, does not generate audible band noise, and can freely set the output duty ratio. It is another object of the present invention to provide a developing bias power supply capable of increasing the rising speed of an output pulse.

[Means for solving the problem]

The developing bias power supply device of the present invention is configured as follows.

a. a first oscillation circuit that outputs a low-frequency signal, a second oscillation circuit that outputs a high-frequency signal, a converter transformer whose primary side is driven by the high-frequency signal gated by the low-frequency signal, and the converter Switching for supplying a rectified output via a rectifying element on the secondary side of a transformer as a developing bias, and short-circuiting the rectified output to ground at a phase where the rectifying element on the secondary side of the converter transformer for the low frequency signal is cut off Circuit.

b. In the power supply device described in a above, an amplitude control circuit is provided to prevent the primary side of the converter transformer from being energized when the rectified output reaches a predetermined level.

c. In the power supply device of a or b, the amplitude control circuit includes a voltage dividing circuit that divides the rectified output at a predetermined ratio, a comparator that compares an output of the voltage dividing circuit with a predetermined reference value,
And a switch circuit for shutting off the switching element on the primary side of the converter transformer by the output of the comparator.

[Action]

In the power supply device for developing bias of the present invention, the drive signal on the primary side of the high-frequency inverter transformer is modulated at a low frequency, and the rectified output on the secondary side of the transformer is short-circuited to the ground at the low frequency. The high-voltage output of the specified frequency is supplied by a switching circuit for developing bias. Therefore, a low frequency AC step-up transformer is not required. Further, in order to make the rising of the output pulse faster and stabilize the amplitude, the charging voltage of the load capacitance is increased, and the charging is stopped when the output reaches a predetermined level.

〔Example〕

FIG. 1 is a basic configuration diagram of a developing bias power supply device according to the present invention. FIG. 2 shows the voltage waveform of each part. The output signal of the low frequency f ₁ of the oscillation circuit 1 of FIG. 1 is a rectangular wave of duty 20% in the range of up to a few 10KHz from repetition frequency number 100 Hz, the second output of the high frequency f ₂ of the oscillator circuit 2 The signal is a rectangular wave having a repetition frequency of 10 kHz or more and a duty of 50%. Then, the switching transistor Q1 of the primary-side converter transformer T ₁ by a high-frequency signal f ₂ which is gated by the frequency signal f ₁ is driven via a modulation circuit 3. Here, the converter transformer T1 connected to the + V _CC power supply can be made sufficiently small because of high-frequency driving.

The switch 4 is closed at a low level timing of the output of the oscillation circuit 1. At the same time, the switching transistor Q1 on the primary side of the converter transformer T1 is kept in the cutoff state at this timing. That is, the rectified output of the converter transformer T1 via the rectifying diode D1 and the resistor R1 is short-circuited to the ground at a phase at which the rectifying diode of the low-frequency signal is cut off.

The switching transistor Q1 is, for example, 50KH
While driving at the frequency of z, the rectifier diode D1
The cathode of the obtained voltage V ₁ shown in FIG. 2 is, since the voltage is smoothed by a clamp capacitor C _1, the output of the switching circuit 4 is as shown in Figure 2. The output obtained here is output to the output terminal through the clamping capacitor C1.
Although delivered to P _1, the clamp diode D2 becomes conductive when positive peak, because it is clamped to the clamp power source 5 serving as -V, V ₁ is output amplitude at the output terminal P _1, forward the peak value of the output of -V _E is obtained, this output is supplied as a developing bias.

Here, the circuit shown in FIG. 1 has the following problem. That is, the developing roller which is connected via the output terminal P ₁ is, for the capacitance between the opposing drum surface is a capacitive load that most, 3 (a), as shown in (b) The output pulse rises slowly. Therefore, in the present invention, in order to overcome this problem, the charge voltage of the load capacitor that is, increasing the charging time constant by increasing the rectified output V _0,
The rise of the output is made faster, and the power supply to the primary side of the converter transformer T1 is cut off when the output reaches a predetermined level. FIG. 4 shows a circuit diagram of the first embodiment of the present invention controlled as described above. FIG. 5 shows the voltage waveform of each part. Rectified output V of converter transformer T1
₀ is divided at a predetermined ratio by the voltage circuit A for the resistors R41 and R42, and compared with a predetermined reference voltage input to the input terminal P2 by the comparator 6 as a detected voltage level value. When the rectified output V ₀ reaches a predetermined value V _1, the comparator 6
Is inverted from L (low) level to H (high) level, and the inverted output turns on the diode D41 and turns on the transistor Q3. As a result, the base of the transistor Q1 becomes zero potential, and the transistor Q1 is cut off. That is, the above-described voltage dividing circuit A, the comparator 6, and the transistor Q3 constitute an output amplitude control circuit B.

At that time, the rise of the output V ₀ as shown in Fig. 5 has to have been significantly improved.

V _m shown in FIG. 5 is a saturation value of the rectified output V _0. The capacitor C41 is a load capacity, that is, a capacity of the developing roller.

Here, in order to reduce the overshoot and ripple of the rectified output V _0, comparator 6 must be fast enough.

FIG. 6 is a circuit diagram showing a second embodiment of the present invention. In this embodiment, the resistors R41 and R42 of the voltage dividing circuit A are connected to the capacitors C41 and C42.
42, a delay time in the voltage dividing circuit A is reduced to reduce overshoot and ripple.

FIG. 7 is a circuit diagram showing a third embodiment of the present invention. This embodiment, transistor when the rectified output V ₀ compared to the levels set higher than the predetermined value V ₁ at a comparator 7 provided separately from the comparator 6, which reached the set level
This is an example in which a protection circuit is provided for turning on Q2 to prevent overvoltage destruction of the transistor Q2 or prevention of leakage between drums due to application of overvoltage to the developing roller.

FIG. 8 is a circuit diagram showing a fourth embodiment of the present invention. According to the present invention, a DC high voltage is superimposed on an AC high voltage of the comparator T1.

That is, the output of the secondary winding of the converter transformer T1 is rectified by the high-voltage diode D81 to obtain a superimposed DC. Then, the resistor R84, the high voltage transistor Q81 and the error amplifier 81
Constitute a parallel type voltage regulator. Capacitor C81
Is a smoothing capacitor. The potential at the connection point between this capacitor C81 and the collector of the transistor Q81 is
And R82 are divided by a predetermined ratio and compared with the reference voltage applied to the input terminal P4 by the error amplifier 81. As a result, the collector current of the transistor Q81 is controlled, and the collector voltage of the transistor Q81 is kept constant. The output voltage of this circuit is combined with the AC output by a resistor R83 and applied to the developing roller.

Although the embodiments of the present invention have been described above, the present invention has the following advantages by adopting the above circuit configuration.

I. Because the low-frequency transformer can be eliminated, significant downsizing and cost reduction are achieved, and reliability is improved.

II. For the same reason as in I above, noise in the audible band can be completely eliminated.

III. The duty ratio of the AC output other than 50%, which was impossible in the past, can be freely set and changed easily.

IV. Stabilization of AC amplitude can be obtained very easily.

V. When a part of the amplitude-stabilized output is double-voltage rectified to obtain a clamp power supply, the clamp power supply itself is also stabilized. Therefore, a stable output is easily obtained for both the amplitude and the DC level.

VI. The rise of the AC output is remarkably improved, the development efficiency is increased, and the density is increased and the density is stabilized.

VII. It is possible to protect a high breakdown voltage transistor, apply an overvoltage to the developing roller, etc. with a high-precision voltage limiter.

VIII. Amplitude can be stabilized with high accuracy.

〔The invention's effect〕

As described above, according to the present invention, the step-up transformer for low-frequency AC is not required, the size is small, no noise in the audible band is generated, the output duty ratio can be freely set, and the rising of the output pulse is achieved. The effect is that the speed can be increased.

[Brief description of the drawings]

FIG. 1 is a basic configuration diagram of the power supply device according to the present invention, FIG. 2 is a voltage waveform diagram of each part of FIG. 1, FIG. 3 is an output waveform diagram of the circuit of FIG. 1, and FIG. 1 is a circuit diagram showing a first embodiment,
5 is a voltage waveform diagram of each part in FIG. 4, FIG. 6 is a circuit diagram showing a second embodiment of the present invention, FIG. 7 is a circuit diagram showing a third embodiment of the present invention, FIG. FIG. 9 is a circuit diagram showing a fourth embodiment of the present invention. DESCRIPTION OF SYMBOLS 1 ... 1st oscillation circuit 2 ... 2nd oscillation circuit 3 ... Modulation circuit 4 ... Switch circuit 6 ... Comparator T1 ... Converter transformer Q1 ... Switching transistor D1 ... Rectifier diode A ... Minute Voltage circuit B: Amplitude control circuit

Claims (3)

(57) [Claims] A first oscillation circuit for outputting a low-frequency signal;
A second oscillation circuit that outputs a high-frequency signal, a converter transformer whose primary side is driven by the high-frequency signal gated by the low-frequency signal, and a rectified output via a rectifying element on the secondary side of the converter transformer. A switching circuit for supplying power for biasing and for short-circuiting the grounded rectified output to the ground at a phase where the rectifying element on the secondary side of the converter transformer for the low-frequency signal is cut off. . 2. When the rectified output reaches a predetermined level,
2. The developing bias power supply device according to claim 1, further comprising an amplitude control circuit for preventing power supply to the primary side of the converter transformer. 3. An amplitude control circuit comprising: a voltage divider for dividing a rectified output at a predetermined ratio; a comparator for comparing an output of the voltage divider with a predetermined reference value; 3. The developing bias power supply device according to claim 1, further comprising a switch circuit for shutting off a primary-side switching element.