JPH03152575A - High-voltage power circuit - Google Patents

Abstract

PURPOSE:To eliminate the need to prepare a power source individually for each high-voltage circuit and to reduce the size and cost of the high-voltage power circuit by supplying voltages to a 1st and a 2nd high-voltage circuit by one output transformer. CONSTITUTION:The 1st high-voltage circuit is supplied with the voltage from secondary winding 16a of the output transformer 12 and the 2nd high-voltage circuit is supplied with the voltage from secondary winding 16b. Then when a switch 40a turns off a regulator circuit 34a, a discharger 22 starts corona discharge between a discharging electrode 24 and a grid electrode 32, and the grid electrode 32 and a drum 28 and when a switch 40 is turned on, the grid voltage drops to cause corona discharge only between the discharging electrode 24 and grid electrode 32, so that no drum current flows. The 2nd high voltage circuit operated similarly to the 1st high-voltage circuit. Then a constant-voltage control circuit 60 controls the currents of the high voltage circuits to constant currents. Consequently, a dual high-voltage power source system is replaceable with a single high-voltage power source system and the size and cost are reducible.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a high voltage power supply circuit, and in particular, for example, P P
C (Plain Paper Copy) and L
B P (Laser Beam Print
r) A high-voltage power supply circuit used as a power supply for the corona discharger.

[Prior art]

Among high-voltage power supplies used in PPC and LBP, this is an example of a high-voltage power supply circuit that obtains the developing bias of the developing device and the corona discharge voltage of the charger from a medium-voltage circuit and a high-voltage circuit connected to the secondary winding of one output transformer. However, for example, Utility Model Application No. 62-195378 and Utility Model Application No. 62-195379
It is disclosed in the publication no.

(Problems to be Solved by the Invention) These PPCs and LBPs include not only a charging discharge device and a developing device, but also a transfer discharge device. Similar to the discharger,
Requires high voltage circuit. Therefore, it is conceivable to use a common high voltage circuit for the two dischargers. However, the second
As shown in Figure A and Figure 2B, charging and transfer are turned on/off.
Separate power supplies were necessary because of the difference in off-time. Therefore, there are problems in that the shape of the high-voltage power supply circuit itself becomes large and the cost becomes high.

Therefore, the main object of the present invention is to provide a high-voltage power supply circuit that is more compact, simple, and inexpensive and can supply voltage to a plurality of high-voltage circuits.

(Means for Solving the Problems) The present invention provides an output transformer having first and second secondary windings commonly coupled to one primary winding; a first high voltage circuit connected to the second secondary winding; a first high voltage circuit connected to the discharge electrode of the first high voltage circuit and having a first grid electrode; an electric appliance, a first regulator circuit connected to the first grid electrode of the first discharger for controlling its grid voltage, a first switch for turning on/off the first regulator circuit, its discharge; a second electrode connected to the output of the second high voltage circuit and having a second grid electrode;
a second regulator circuit connected to a second grid electrode of the second discharger for controlling its grid voltage, a second switch for turning on/off the second regulator circuit; and a constant current control circuit that controls one primary winding based on the current of the first secondary winding.

[Operation] The first high voltage circuit is supplied with voltage from the first secondary winding of the output transformer, and the second high voltage circuit is supplied with voltage from the second secondary winding. .

When the first regulator circuit is turned off by the first switch, the grid voltage is applied to the first grid electrode of the first discharger, and the first discharger connects the discharge electrode and the first grid electrode. corona discharge is started between the first grid electrode and the drum. Then, when the first switch is turned on, the grid voltage of the first grid electrode decreases (', O■). Therefore, even if a voltage is applied to the discharge electrode of the first discharger, since there is no grid voltage ('=:OV), the corona discharge of the first discharger is caused by the discharge electrode and the first grid electrode. No corona discharge occurs between the drum and the drum. As a result, since no drum current flows, the first high voltage circuit is equivalently turned off (as viewed from the drum side).

Note that since the first high-voltage circuit is only equivalently turned off, that is, there is no change in the output voltage of the first secondary winding, even if the medium-voltage circuit is connected to it, the voltage does not change.

Further, the second high voltage circuit to which the voltage from the second secondary winding is supplied also operates in the same manner as the first high voltage circuit.

That is, when voltage is supplied to the second high voltage circuit, the second
A voltage is applied to the discharge electrode of the second discharger connected to the output terminal of the high voltage circuit. Therefore, when the second regulator circuit is turned off by the second switch, the grid voltage is applied to the second grid electrode of the second discharger, and the first discharger is connected to the discharge electrode and the second grid. A corona discharge is started between the electrode and the second grid electrode and the drum. When the second switch is turned on, the grid voltage of the second grid electrode decreases (', OV).

Therefore, even if voltage is applied to the discharge electrode of the second discharge device, since there is no grid voltage (-, 0■), the corona discharge of the transfer device will occur between the discharge electrode and the second grid electrode. No corona discharge occurs between the drum and the drum. As a result, since no drum current flows, the second high voltage circuit is equivalently turned off (as viewed from the drum side).

Then, the primary winding is turned on/off by the constant current control circuit so as to perform constant current control of the current in the first high voltage circuit based on the current in the first secondary winding. Further, regarding the first discharger, since the drum is cleaned, its impedance is stabilized, so the output voltage of the first high voltage circuit is stabilized. Therefore, equivalently, the high voltage of the second high voltage circuit is controlled at a constant voltage. [Effect of the Invention] According to the present invention, one output transformer supplies voltage to each of the first and second high voltage circuits. Therefore, there is no need to prepare a separate power supply for each high voltage circuit, and the high voltage power supply circuit can be made smaller and lower in cost.

In addition, since it is equipped with first and second regulator circuits for controlling the grid voltage and first and second switches for turning them on and off, the voltage is constantly applied to the first and second dischargers. The first and second high-voltage circuits can be equivalently turned on and off while the voltage is applied. Therefore, even if the first high voltage circuit is equivalently turned off, no fluctuation in high voltage occurs due to the equivalent turning off, so even if the medium voltage circuit is connected to the first secondary winding, the The voltage doesn't change either. Therefore, the output of the intermediate voltage circuit, such as the developing bias, is always a constant and stable output, and the image quality is extremely stable.

The above objects, other objects, features and advantages of the present invention will become more apparent from the following detailed description of embodiments with reference to the drawings.

〔Example〕

Referring to FIG. 1, the high voltage power supply circuit IO of this embodiment includes an output transformer 12. The output transformer 12 has one primary winding 14 and two secondary windings 16a and 16b that are magnetically coupled in common to the primary winding 14.

One end of the secondary winding 16a is connected to the cathode of a diode 18a. One terminal of a smoothing capacitor 20a is connected to the anode of the diode 18a, and the other terminal of the capacitor 20a is connected to the other end of the secondary winding 16a.

Further, a discharge electrode 24 of a corona charger 22 is connected to the anode of the diode 18a. Corona charger 22 is arranged near the outer surface of photoreceptor drum 28, which rotates in the direction of arrow 26. The surface of the photosensitive drum 28 is uniformly charged by the corona charger 22. Although not shown, the shield electrode 30 of the corona charger 22 is grounded or connected to a grid electrode 32, and the grid electrode 32 is connected to the output terminal of the regulator circuit 34a. This is a circuit for applying a grid voltage Vg to the electrode 32, and includes a varistor 36a and a resistor 38a connected in series with the varistor 36a, and a switch 40a is connected in parallel to this series connection. In this embodiment, the output voltage of the regulator circuit 34a, that is, the grid voltage Vg, is determined by the varistor 36a.
It is determined by the voltage across the resistor 38a.

Furthermore, a medium voltage circuit 44 is connected to the anode of the diode 18a through a high resistor 42. Medium voltage circuit 44
outputs a developing bias voltage to the developing device 46. Developing device 46 has a magnetic brush 50 that rotates in the direction of arrow 48.

On the other hand, one end of the secondary winding 16b is grounded, and the other end is connected to the anode of the diode 18b. diode 1
One terminal of a smoothing capacitor 20b and a resistor 52 are connected to the cathode of the capacitor 8b, and the other terminal of the capacitor 20b and the resistor 52 is grounded.

Furthermore, a discharge electrode 56 of the transfer device 54 is connected to the cathode of the diode 18b. The transfer device 54 is a developing device 46
It is arranged on the downstream side in the rotational direction 26 of the photoreceptor drum 28 when viewed from above. Although not shown, the shield electrode 58 of the transfer device 54 is grounded or connected to a grid electrode 60, and the grid electrode 60 is connected to the output terminal of the regulator circuit 34b. This regulator circuit 34b includes a varistor 36b and a resistor 38, similar to the regulator circuit 34a described above.
b and switch 40b, and function in the same manner.

In order to make the current to the discharge electrode 24 a constant current, a constant current circuit 62 that performs feedback control is provided.

Constant current control circuit 62 includes an operational amplifier 64. here,
Secondary winding 16a, capacitor 20a and medium voltage circuit 44
is grounded through a resistor 66, and the voltage generated by the current flowing through this resistor 66 is connected to the negative (-) of the operational amplifier 64.
) is supplied to the input terminal. A reference voltage from a reference voltage source 68 is supplied to the plus (+) input terminal of the operational amplifier 64. The output of this operational amplifier 64 is supplied to a driver circuit 70, and the output of the driver circuit 70 is supplied to the base of a transistor 72. The collector of the transistor 72 is connected to one end of the primary winding 14 of the transformer 12, and the emitter is grounded. By controlling the oscillation of this transistor 72, the discharge electrode 5
The output voltage to 4 is stabilized.

Further, a fixing roller 76 for fixing toner on the copy paper 74 is disposed on the downstream side in the rotation direction 26 of the photosensitive drum 28 when viewed from the transfer device 54 .

In operation, when the output transformer 12 generates a voltage, the voltage is applied to the corona charger 22 and the medium voltage circuit 44 connected to the secondary winding 16a. Also, the secondary winding 1
A voltage is also applied to the transfer device 54 connected to 6b.

When a voltage is applied to the discharge electrode 24 of the corona charger 22, a shield current Is flows into the discharge electrode 24 via the shield electrode 30. Here, if the regulator circuit 34a is not driven and the grid voltage Vg is not applied, the drum current 1d does not flow into the discharge electrode 24, and only the grid current 1g remains. Therefore, in this state, the corona charger 22 is equivalently in an off state.

Therefore, when the switch 40a of the regulator circuit 34a is turned off, the grid voltage Vg is applied to the grid electrode 32. By this grid voltage g, the discharge electrode 2
4 and the grid electrode 32 and between the grid electrode 32 and the photoreceptor drum 28, and a drum current 1d flows from the photoreceptor drum 28 to the discharge electrode 24. Further, when the grid voltage Vg is applied to the grid electrode 32, the grid current rg also flows into the discharge electrode 24. Therefore, in the operating state where the corona charger 22 is performing corona discharge, the operating current of the corona charger 22 is 1 h.
is the sum of shield current Is, drum current 1d, and grid current 1g.

Note that, as described above, when voltage is applied to the intermediate voltage circuit 44, a developing bias is applied to the developing device 46.

When the switch 40a of the regulator circuit 34a is turned on while the corona charger 22 is performing corona discharge,
The grid voltage Vg of the grid electrode 32 decreases (ζOV)
do. Then, even if the voltage of the discharge electrode 24 does not change (even if the grid voltage g disappears, a grid current of 1 g flows between the discharge electrode 24 and the grid electrode 32, but the voltage between the grid electrode 32 and the photoreceptor drum 2 In other words, the corona discharge with the surface of the photoreceptor drum 28 is stopped, and the drum current 1d is cut off.That is, when the regulator circuit 34a is turned off by turning on the switch 40a, , corona charger 22
Even if there is no change in the voltage of the discharge electrode 24 of the photosensitive drum 2
8 stops, and equivalently, the corona charger 22 is turned off in terms of high voltage.

Even if the corona charger 22 is equivalently turned off, the discharge electrode 2
Since the discharge current of 4 is kept constant, there is no fluctuation in the voltage supplied to the medium voltage circuit 44, and therefore the developing device 46
The developing bias is also kept constant.

On the other hand, when a voltage is applied to the discharge electrode 56 of the transfer device 54, the transfer device 54 operates in the same manner as the corona charger 22, so a description thereof will be omitted here.

Here, the current of the discharge electrode 24 is controlled by a constant current control circuit 62. That is, the current from the discharge electrode 24 flows through the resistor 66, the voltage generated across the resistor 66 is compared with the reference voltage in the operational amplifier 64, and when the voltage applied to the resistor 66 is smaller, the operational amplifier 64 outputs 'H''. be done. Then, this "l H)" is input to the driver circuit 70, turns on the emitter-collector of the transistor 72, and turns on the primary winding 14 of the output transformer 12. Also, the current flowing through the resistor 66 increases,
When the voltage across the resistor 66 becomes higher than the reference voltage, the operational amplifier 64 outputs "L", turning off the transistor 72 and turning off the primary winding 14 of the output transformer 12.

In this way, the oscillation voltage of the primary winding 14 is controlled,
The output current of the discharge electrode 24 is controlled to be constant.

Note that since the photosensitive drum 28 is moved to the position of the corona charger 22 in a cleaned state, its impedance is stable.

Therefore, when the primary winding 14 of the output transformer 12 is turned on/off as described above, the first secondary winding 16a, that is, the first high voltage circuit, is equivalently controlled at a constant voltage despite the constant current. Therefore, the second high voltage circuit is also equivalently subjected to constant voltage control.

As mentioned above, in the high voltage power supply circuit 10 of this embodiment, 1
Corona charger 22. Each of the developing device 46 and the transfer device 54 can be operated. That is, the conventional two high voltage power supply system can be changed to a single high voltage power supply system. Therefore, the high voltage power supply circuit 10 can be made smaller and lower in cost.

Furthermore, even when corona discharge is stopped, the corona charger 22 is simply turned off without changing the current of the discharge electrode 24, so no fluctuation occurs in the voltage supplied to the medium voltage circuit 44. Therefore, the developing bias of the developing device 46 can always be kept constant.

In the above-described embodiments, negative high voltage output is described, but it goes without saying that positive output can also be controlled using the same principle.

Furthermore, if the output voltages of the charger and the transfer device are equal, each output voltage may be taken out from one high voltage winding. In this case, two secondary windings, the first and second secondary windings 16a and 16b. are configured as the same single secondary winding.

Further, in place of the above-mentioned regulator circuits 34a and 34b, regulator circuits 78 shown in FIG. 2 may be used.

Regulator circuit 78 includes two series-connected PnP transistors 80 and 82 and Zener diode 8.
Contains 4. Three fixed resistors are connected in series between the cathode of the Zener diode 84 and the collector of the transistor 80.

A variable resistor 86 and a pnp) transistor 88 are connected in parallel. Further, connection points of fixed resistors are connected to the bases of transistors 80 and 82, respectively.

Regulator circuit 78 is controlled by turning transistor 88 on or off. That is, transistor 8
8 performs a switch function similar to the switch 40a or 40b described above. Variable resistor 86 changes the base voltage of transistor 82 to determine the magnitude of grid voltage Vg and grid current 1g.

When a low level pulse is applied to the base of the transistor 88, the transistor 88 is turned on, and the transistor 88 is turned on.
When turned on, transistors 80 and 82 are also turned on, and grid voltage Vg is applied to grid electrode 32. Also, when transistor 88 is turned off,
The grid voltage Vg of the grid electrode 32 decreases (ζOV)
do.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing one embodiment of the present invention. FIG. 2 is a circuit diagram showing a regulator circuit that can replace the regulator circuit of the embodiment shown in FIG. FIGS. 3A and 3B are process charts illustrating the time lag between charging and transfer. In the figure, 10 is a high voltage power supply circuit, 12 is an output transformer, 14 is a primary winding, 16a, 16b are secondary windings, 22 is a corona charger, 24.56 is a discharge electrode, 28 is a photosensitive drum, 30 .58 is a shield electrode, 32.60 is a grid electrode, 34a, 34b, 7B is a regulator circuit, 4
0a and 40b are switches, 44 is a medium voltage circuit, 46 is a developing device, 54 is a transfer device, and 62 is a constant current control circuit.

Claims (1)

Claims: an output transformer having first and second secondary windings commonly coupled to one primary winding; a first high voltage circuit connected to the first secondary winding; , a second high-voltage circuit connected to the second secondary winding, a first discharger having a first grid electrode and a discharge electrode of which the output of the first high-voltage circuit is connected; a first regulator circuit connected to the first grid electrode of the first discharger to control its grid voltage; a first switch to turn on/off the first regulator circuit; a second discharger to which the output of the second high voltage circuit is connected and having a second grid electrode; connected to the second grid electrode of the second discharger for controlling the grid voltage thereof; a second regulator circuit for controlling the one primary winding based on the current in the first secondary winding; a second switch for turning on/off the second regulator circuit; High-voltage power supply circuit equipped with a current control circuit.