JPH03152574A - 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 the switch 40a 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 operates similarly to the 1st high-voltage circuit. Then a constant-voltage control circuit 60 controls the high voltages of the high voltage circuits to constant voltages. 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
The present invention relates to a high-voltage power supply circuit used as a power supply for a corona discharger of a Laser Beam Printer.

, [Prior Art] Of the high-voltage power supplies used in PPC and LBP, the developing bias of the developing device and the corona discharge voltage of the charger are obtained from a medium-voltage circuit and a high-voltage circuit connected to the secondary winding of one output transformer. Examples of high-voltage power supply circuits include Utility Model Application No. 62-195378 and Utility Model Application No. 62-195379.
It is disclosed in the publication no.

[Problem 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. In order to obtain the corona discharge voltage of this transfer discharge device, similar to the charging discharge device,
Requires high voltage circuit. Therefore, it is conceivable to use a common high voltage circuit for the two dischargers. However, the third
As shown in Figure A and Figure 3B, 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] A second invention provides an output transformer having first and second secondary windings commonly coupled to one primary winding, connected to the first secondary winding. a first high voltage circuit connected to the second secondary winding; a first high voltage circuit having a discharge electrode connected to the output of the first high voltage circuit and a first grid electrode; a discharger, a first regulator circuit connected to a first grid electrode of the first discharger for controlling its grid voltage, a first switch for turning on/off the first regulator circuit; a second high voltage circuit having a discharge 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 voltage control circuit that controls one primary winding based on the output voltage from the second 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 (#OV). Therefore, even if a voltage is applied to the discharge electrode of the first discharger, since there is no grid voltage (ζOV), the corona discharge of the first discharger will occur between 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 not applied to the discharge electrode of the second discharge device, corona discharge of the transfer device occurs only between the discharge electrode and the second grid electrode because there is no grid voltage (:OV). , no corona discharge occurs between the drum and the drum, and as a result, no drum current flows, so 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 voltage control circuit so as to constant voltage control the high voltage of the second high voltage circuit based on the output voltage of the second secondary winding. On the other hand, regarding the first discharger, since the drum is cleaned, its impedance is stable, so this constant voltage control equivalently controls the first high voltage circuit with constant current. becomes.

[Effects of the Invention] According to the present invention, voltage can be supplied to each of the first and second high-voltage circuits using one output transformer, so there is no need to prepare a separate power supply for each high-voltage circuit. , it is possible to reduce the size and cost of the high-voltage power supply circuit.

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 also does not fluctuate, so the output of the medium 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.

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

One end of the secondary winding 16a is grounded, and the other end is connected to the cathode of the 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 grounded.

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 is connected to the cathode of 8b, and the other terminal of the capacitor 20b is grounded.

Furthermore, the discharge electrode 54 of the transfer device 52 is connected to the cathode of the diode 18b. The transfer device 52 is the 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 56 of the transfer device 52 is grounded or connected to a grid electrode 58, and the grid electrode 58 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 voltage to the discharge electrode 54 constant, a constant voltage circuit 60 that performs feedback control is provided.

Constant voltage control circuit 60 includes an operational amplifier 62. and,
The output voltage to discharge electrode 54 is divided by resistors 64 and 66 and supplied to the negative (-) input terminal of operational amplifier 62 . And the plus (+) of operational amplifier 62
A reference voltage from reference voltage 'a68 is supplied to the input terminal. The output of this operational amplifier 62 is the driver circuit 70
The output of driver circuit 70 is applied to the base of transistor 72. And transistor 72
The collector 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 output voltage to the discharge electrode 54 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 52 .

In operation, when a voltage is generated in the chemistries 12, 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 52 connected to the transfer device 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. Furthermore, when the grid voltage Vg is applied to the grid electrode 32, 1 g of grid current 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 Id, 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 there is no change in the voltage of the discharge electrode 24, grid current Ig flows between the discharge electrode 24 and the grid electrode 32 due to the disappearance of the grid voltage g. During this period, no current flows, that is, corona discharge with the surface of the photoreceptor drum 28 is stopped, and the drum current Td is cut off. That is, when the regulator circuit 34a is turned off by turning on the switch 40a, the 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 voltage of the developing device 46 is kept constant, there is no fluctuation in the voltage supplied to the medium voltage circuit 44 (therefore, the voltage supplied to the developing device 46
The developing bias is also kept constant.

On the other hand, when a voltage is applied to the discharge electrode 54 of the transfer device 52, the transfer device 52 operates in the same manner as the corona charger 22, so a description thereof will be omitted here.

Here, the output voltage to the discharge electrode 54 is determined by the constant voltage control circuit 6.
Constant voltage control is performed by 0. That is, the discharge electrode 54
The operational amplifier 62 compares the voltage obtained by dividing the output voltage to the reference voltage with the reference voltage by the resistors 64 and 66, and when the divided voltage is smaller, the operational amplifier 62 outputs "H".
is output. Then, this "°H°" is input to the driver circuit 70, turning on the emitter-collector of the transistor 72 and turning on the primary winding 14 of the output transformer 12. Ba,
"L11" is output from the operational amplifier 62, 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, and the voltage is applied to the discharge electrode 54. The output voltage 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, output transformer 1
When the primary winding 14 of 2 is turned on/off as described above,
The first secondary winding 16a, that is, the first high voltage circuit, is equivalently controlled to have a constant current even though it has a constant voltage.

As mentioned above, in the high voltage power supply circuit 10 of this embodiment, 1
Corona charging 2522.
Each of the developing device 46 and the transfer device 52 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.

Further, even when corona discharge is stopped, the corona charger 22 is simply turned off without changing the voltage 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, the two first and second secondary windings 16a and 16b are configured as one and the same secondary winding.

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

The regulator circuit 78 consists of two PNPs connected in series.
) transistors 80 and 82 and Zener diode 84. 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 (:OV)
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, 24.54 is a discharge electrode, 28 is a photosensitive drum, 30 .56 is a shield electrode, 32.58 is a grid electrode, 34a, 34b, 78 is a regulator circuit, 4
0a and 40b are switches, 44 is a medium voltage circuit, 46 is a developing device, 52 is a transfer device, and 60 is a constant voltage control circuit. Figure 2 Figure 3A Charging image L IL

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, a second switch for turning on/off the second regulator circuit, and controlling the one primary winding based on the output voltage from the second secondary winding. A high voltage power supply circuit equipped with a constant voltage control circuit.