JPH0526432B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high voltage power supply device used in copying machines and the like.

Generally, in the process of a copying machine, copy content is transferred from a photoreceptor drum 1 to a copy paper 2 as shown in Fig. 1. During transfer, the photoreceptor drum 1 is charged with a direct current of 5 to 6 KV by a transfer charger 3. Therefore, the copy paper 2 is also charged with a considerably high voltage. Therefore, it is necessary to electrically neutralize (remove static electricity) the charged copy paper 2 and pull it out of the copying machine without any malfunctions such as paper jams. That is, removing static electricity facilitates the process of pulling out the copy paper 2 that is attracted to the photoreceptor drum 1 by electrostatic force, and also prevents an electric shock caused by static electricity when an operator touches the copy paper 2. . Therefore, this static elimination is extremely important in the copying process. However, although a high alternating current voltage is applied to eliminate static electricity, it is difficult to stably perform two operations: peeling the charged copy paper from the photoreceptor drum to which it is attracted, and performing electrical neutralization. is not an easy task in practice.

Therefore, due to this complicated process, in recent years, the AC voltage applied to the photoreceptor drum and charged copy paper has been changed to a DC bias as shown in Figure 2, in order to improve the performance and stability of the copy process. There is something I did. In other words, E′ _OP shown by the solid line in Fig. 2 is the peak voltage value of the positive/negative symmetrical waveform, whereas the waveform shown by the dotted line is the DC biased deviation waveform required for the process, and its deviation value. is E′ _OP1 −E′ _OP2 . In addition, in recent years, AC output voltage is also supplied by high-voltage power supplies such as semiconductor inverters. An example of this is shown in Figure 3, which consists of a DC power supply E', an oscillation transistor Q', and an inverter transformer. T', and a charger is connected as a load L'. And inverter transformer T
A diode D′ ₁ is connected to the ground potential of the secondary winding N′ ₂ ,
While D′ ₂ and the resistors R′ ₁ and R′ ₂ are connected in reverse, the resistors R′ ₁ ,
By creating a difference in the value of R′ ₂ , the voltage drop value is changed and a DC bias is applied to the AC output voltage waveform.

However, such a conventional method has the following drawbacks. In other words, the DC bias is usually several hundred V, but this is the difference in voltage drop between the resistors R' ₁ and R' _2. In order to obtain the DC bias shown by the dotted line in Figure 2, I' _OP ×R′ ₂ )−(I′ _OP ×
R′ ₁ )=(positive extreme value), and each voltage drop value exceeds 1000V. Then,
Diodes D' ₁ and D' ₂ and resistors R' ₁ and R' ₂ must also be able to withstand this value, and these become high-voltage components and become expensive. At the same time, the shape becomes larger and the set space becomes larger, which is disadvantageous. In addition, in the copying process, when varying this DC bias value, the resistor R′ ₁ or R′ ₂ must be made variable, but in the conventional method, high voltage polyurethane must be used. From this point of view as well, the size and cost increase, and there is no margin for structural design of the transformer device.

The present invention has been made in view of the above points, and an object of the present invention is to provide a high voltage power supply device that can easily and reliably apply a DC bias to an AC output voltage.

The present invention provides a variable impedance circuit on the base side of an oscillation transistor that changes the base current, thereby making it possible to apply a DC bias to an AC output voltage in a small, inexpensive, and simple manner that can withstand low voltage reliably. It is composed of

A first embodiment of the present invention will be described based on FIGS. 4 and 5. First of all, basically the DC power supply E
, an oscillation transistor Q, and an inverter transformer T. The inverter transformer T has a primary winding N ₁ , a base winding N _B , and a secondary winding N ₂ ,
A load L is connected to the secondary winding _N2 . Also,
The base of the oscillation transistor Q is a fixed bias resistor that flows a fixed bias base current.
ON/OFF together with R ₁ , R ₂ , R ₃ and capacitor C ₁
A base winding N _B through which a timing base current for timing flows is connected, and a variable resistor VR forming a variable impedance circuit 4 is connected to the base winding N _B via a capacitor C ₂ . Further, a protection resistor R _E is connected to the emitter of the oscillation transistor Q to prevent the bias current value from changing due to a change in V _BE caused by a temperature change in the oscillation transistor Q.

In such a configuration, the oscillation transistor Q
Resistors R ₁ , R ₂ , R ₃ are connected to the base of the DC power supply E.
A fixed bias base current is supplied through.
This base current value is determined by considering the load capacity, fluctuation characteristics, etc., but the primary voltage at the primary winding _N1 of the inverter transformer T during inverter oscillation operation is
V _N1 is set so that the center value of the amplitude has the same potential as the DC power source E, as shown in FIG. 5a. Further, the ON/OFF timing energy of the oscillation transistor Q is given by the base winding N _B , and this is supplied to the base of the oscillation transistor Q superimposed on the fixed bias base current. Therefore, the bias point of the oscillation transistor Q changes in accordance with the base current, resulting in a waveform as shown in FIG. 5a. FIG. 5b is a waveform diagram of the collector current I _C of the oscillation transistor Q corresponding to the base current I _B. As shown in FIG. 5b, during the ON period T _ON of the oscillation transistor Q, the waveform and height of the primary voltage V _N1 are determined by the collector current I _C supplied from the base circuit. and,
The magnetic energy supplied to the primary winding N ₁ during the ON period T _ON becomes an oscillating waveform in the OFF period T _OFF due to the distributed capacitance of the inverter transformer T, the inductance of the primary winding N ₁ , and the resistance component of the circuit. , the waveform and height of the primary voltage V _N1 when OFF is determined. Then, side waveforms are formed centering around the DC power supply E level. The secondary voltage V _N2 of the inverter transformer _{T is the induced voltage of the primary voltage V N1 .}
The waveform will be as shown in Figure c.

Therefore, the voltage generated in the base winding N _B is induced by the primary voltage V _N1 and applied to the oscillation transistor Q, but the resistance values of the resistors R ₂ , R ₃ , the variable resistor VR, and the base capacitors C ₁ , C ₂ The waveform has a value determined by the impedance of , and the base-emitter voltage V _BE of the oscillation transistor Q. This base current results in a waveform as shown in FIG. 5b and is applied to the oscillation transistor Q. Therefore, it can be seen that the collector-emitter voltage V _CE of the oscillation transistor Q changes according to this base current bias.As a result, in this example, by changing the impedance of the base bias circuit, The purpose is to change the waveform of the collector-emitter voltage V _CE of the oscillating transistor Q, that is, the primary voltage V _N1 , by changing the bias current value and especially its waveform. Now, Figure 5b
The waveform shown by the solid line in is the waveform of the base current I _B in normal conditions, and when applying a DC bias to the secondary voltage N _N2 waveform in Figure 5c, the primary voltage in Figure 5a is In the voltage _VN1 waveform, E _OP1 can be set as shown by the dotted line, but it can be seen that for this waveform, the base current bias value should be deepened (increased) as described above. Conversely, to add the side via to the secondary voltage V _N2 , the fifth
If _{the waveform} shown in FIG. In this case, the bias current value may be reduced as shown by the dashed line in the base current I _B waveform in FIG. 5b. As a result, the primary voltage V _N1 is shown by the dashed line.
E _OP2 waveform. By changing the base current value and its waveform in this way, the secondary voltage V _N2 ,
That is, a DC bias can be easily applied to an AC output voltage.

Here, in practical terms, the resistances R ₂ , R ₃ , the protective resistance R _E ,
Although this is possible by changing the resistance value of the variable resistor VR, it has been confirmed that changing the resistance value of the variable resistor VR is the most practical. That is, changing the resistors R ₂ and R ₃ changes the value of the fixed bias base current supplied through the resistor R ₁ to change the bias operating point of the oscillating transistor Q, the voltage E in FIG. 5a, and the overall amplitude of the primary voltage V _N1 . This is because it also changes the input voltage, which may become a factor that worsens the input voltage fluctuation characteristics. In this way, according to this embodiment, a variable resistor VR is used.
A single general-purpose small volume of about 4 W can extremely easily apply a DC bias of several hundred volts to a high-voltage AC output voltage. Furthermore, the small variable resistor VR with variable bias can be attached to the PC board for the low-voltage control circuit at the same time, and there is no need to worry about designing the mounting structure as in the past. It is also clear that costs can be significantly reduced compared to conventional high-voltage diode and resistance methods.

Next, a second embodiment of the present invention will be described based on FIG. 6. Components that are the same as those shown in the previous embodiment are designated by the same reference numerals, and explanations thereof will be omitted. In this embodiment, diodes D ₁ , D ₂ , _{capacitor C 3 ,}
A variable impedance circuit 5 mainly consisting of C ₄ , a differential amplifier A, a transistor Q ₁ , and a full-wave rectifier circuit REC is connected to the base winding _NB .

This reduces the AC output voltage to the low voltage feedback winding N _F
detects that side and side, and when it deviates from the specified bias voltage value due to load fluctuations, ambient temperature, humidity, atmospheric pressure, etc., this fluctuation value is detected, amplified by differential amplifier A, and the changed value is transmitted to transistor Q. In addition to the bias of ₁ , the base current of the oscillation transistor Q is corrected via the base winding N _B so that a constant DC bias can always be applied.

Further, a third embodiment of the present invention will be explained with reference to FIG. This embodiment includes low voltage components including diodes D ₃ and D ₄ connected to the ground side of the secondary winding N ₂ , resistors R ₁₀ and R ₁₁ , a differential amplifier A, a transistor Q ₁ ,
A variable impedance circuit 6 mainly consisting of a full-wave rectifier circuit REC is connected to the base winding N _B.

As a result, the DC bias voltage of the AC output voltage is detected by the low voltage components of the diodes D ₃ and D ₄ and the resistors R ₁₀ and R ₁₁ , and the component that changes with respect to the specified value is amplified and fed back by the differential amplifier A. As in the embodiment, a constant DC bias is always applied. Here, diodes D ₃ , D ₄ and resistance
Since R ₁₀ and R ₁₁ are for detecting the input signal of the differential amplifier A, they are approximately several volts, and it is clear that they are not high voltage components of the bias application circuit as shown in FIG.

As described above, the present invention provides a variable impedance circuit in which a base winding variable resistor is connected to the base circuit of an oscillation transistor, so that it is possible to easily apply a DC bias to an AC output voltage under low pressure in a small, inexpensive and simple manner. It is something that can be done.

[Brief explanation of the drawing]

FIG. 1 is a schematic side view of a copying machine, FIG. 2 is a waveform diagram showing a conventional example, FIG. 3 is a circuit diagram thereof, FIG. 4 is a circuit diagram showing a first embodiment of the present invention, and FIG. 5 a~c
6 is a circuit diagram showing a second embodiment of the present invention, and FIG. 7 is a circuit diagram showing a third embodiment of the present invention. 4 to 6... variable impedance circuit, E... DC power supply, Q... oscillation transistor, T... inverter transformer, N _B ... base winding, N _F ... low voltage feedback winding, VR... variable resistor.

Claims (1)

[Claims] 1. A DC power supply; an inverter transformer having a primary winding and a base winding connected to the DC power supply and having a secondary winding at an output end; and a DC power supply connected in series to the primary winding; an oscillating transistor whose collector and emitter are connected to the positive side of the DC power source between the primary winding and the negative side of the DC power source, and a fixed bias resistor connected between the positive side of the DC power source and the base of the transistor. and a variable impedance circuit in which the base winding and a variable resistor are connected between the base circuit and the negative side of the DC power supply.