JPH0572870A - High voltage ac power source circuit for image forming device - Google Patents

Abstract

PURPOSE:To provide a high voltage AC power source circuit for an image forming device which has a small power loss and can change the direct current component of the load current of an electrifier in a wide area from the positive polarity to the negative polarity, with simple structure. CONSTITUTION:This high voltage AC power source circuit for the image forming device is characterized as follows. A diode D1, a current control circuit 4 composed of the serial circuit of plural transistors TR4 and TR3, a diode D2 for flowing the current of the direction opposite to that of the current of the current control circuit, and resistance 12 higher than a difference between the positive/negative pseudo equivalent resistance values of the electrifier as a load, by a prescribed value, are connected between the secondary side winding of an AC high voltage transformer T1 and the ground, the detecting circuit 3 of the direct current of the load current is provided, and a control means controlling the base current of a current control circuit transistor TR3 with detection output, is provided as well.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an electrophotographic copying machine,
The present invention relates to a high voltage AC power supply circuit of an image forming apparatus such as a printer.

[0002]

2. Description of the Related Art In a conventional high-voltage AC power supply circuit for an image forming apparatus, a DC-DC converter circuit is used as a secondary winding of an AC high-voltage transformer in order to control a DC current flowing through an AC charging wire of a separation charger, which is a load. It was inserted between the low voltage side of the wire and the ground. In particular, when the control range of the DC current becomes wide so as to extend in the positive and negative directions, it is necessary to insert a DC-DC converter with a positive output and a DC-DC converter with a negative output.

FIG. 9 is an explanatory view showing the basic configuration of the above-mentioned conventional example, 21 is an AC high voltage power source equipped with an AC high voltage transformer, 22 is a DC-DC converter, P1 is an output terminal,
Reference numeral 23 indicates a separation charger which is a load, and idc indicates a direct current required for electrostatic separation. The direct current idc is DC-
It is necessary to flow in the opposite direction to the output of the DC converter 22.

FIG. 10 shows the DC-DC converter 2 described above.
In the circuit diagram of FIG. 2, the primary side DC input of the transformer T31 is turned on / off by the switching transistor TR31 controlled by the output control circuit 31, and the generated secondary side output is rectified and smoothed by the diode D31 and the capacitor C31. There is. R31 is a bleeder resistance of the secondary side rectifier circuit.

FIG. 11 is a characteristic diagram showing the voltage-current characteristic of the DC-DC converter 22, with the vertical axis representing the DC voltage vd.
DC current idc is shown on the horizontal axis of c. FIG. 12 is a characteristic diagram showing a voltage-current characteristic of the separation charger 23 to which the output of the high-voltage AC power supply circuit is supplied. The vertical axis represents current i and the horizontal axis represents voltage v. As shown in FIG. 12, the separation charger 23 has a positive and negative asymmetrical asymmetry, that is, a current on the negative side easily flows.

[0006]

With the above configuration and characteristics, when the DC current idc is approached to -400 μA, it is necessary to reduce the resistance value of the bleeder R31 as much as possible. For this reason, the DC-DC converter 22 needs a high power type, which causes heat generation and an increase in cost.

The range of the DC current idc is widened, and as shown in FIG.
When it becomes necessary to control from near zero to the positive current region shown in FIG. 13, a fixed output type DC-DC converter 25 having a polarity opposite to that of the variable output type DC-DC converter 22 is further connected in series as shown in FIG. You will need to insert it. Since the control range of the direct current idc on the load side is narrowed by the output voltage of the fixed output DC-DC converter 25, it becomes necessary to further widen the output control range of the variable DC-DC converter 22 and power loss occurs. Will grow more and more.

As described above, in the DC-DC converter 22, it is necessary to reduce the resistance value of the bleeder resistor R31 shown in FIG. 10, and the DC current idc necessary for electrostatic separation is required.
If the control width is increased, the power loss is remarkably increased. It also requires a complicated circuit configuration.

The present invention has been made in order to solve the above-mentioned problems of the prior art. It has a simple structure with little power loss, and the DC component of the load current of the charger changes widely from positive polarity to negative polarity. It is an object of the present invention to provide a high-voltage AC power supply circuit of an image forming apparatus capable of performing the above.

[0010]

Therefore, in the high voltage AC power supply circuit of the image forming apparatus according to the present invention, a current consisting of a series circuit of a diode and a plurality of transistors is provided between the secondary winding of the AC high voltage transformer and the ground. A control circuit, a diode for flowing a current in a direction opposite to that of the current control circuit, and a resistor larger than the difference between the positive and negative pseudo-equivalent resistance values of the charger as a load by a predetermined value are connected, and the load current DC The present invention is intended to achieve the above-mentioned object by a configuration characterized in that a minute detection circuit is provided and a control means for controlling the base current of the current control circuit transistor by the detection output is provided.

[0011]

With the above construction, the secondary side of the AC high-voltage transformer, the high-voltage current is divided into positive and negative DC currents by the diode, and the DC component of the load current can be controlled by the current control circuit inserted in one side of the divided current.

Further, since the resistance value of the resistance inserted in parallel to the current control circuit is larger than the difference between the positive and negative pseudo resistance values of the load charger, the direct current component of the load current can be controlled over both the positive and negative polarity ranges.

In order to control the DC component of the load current in a wide range, it is necessary that the output voltage of the series regulator of the current control circuit can be changed in a wide range. However, the series regulator divides the voltage as a series circuit of a plurality of transistors,
The circuit configuration is not limited by the withstand voltage limit of each transistor, and the base current of the transistor of the series regulator is controlled by the detection output of the detection circuit to make the load DC component of the charger of the positive polarity positive. It can be controlled in a wide range from to negative polarity.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A high voltage AC power supply circuit of an image forming apparatus according to the present invention will be described below with reference to embodiments. (First Embodiment) FIG. 1 is an AC high voltage output circuit diagram for electrostatic separation of an electrophotographic copying machine according to the first embodiment of the present invention. T1
Is an AC high voltage transformer, and TR1 and TR2 are switching transistors for driving the primary side, which are driven by the control circuit 1 to control the push-pull output. The output of the secondary side high voltage winding L2 of the AC high voltage transformer T1 has an output terminal P1.
Via a separate charger of the load.

At the other end of the high voltage secondary winding of the AC high voltage transformer T1, a current control circuit composed of a series circuit of a high voltage diode D1 and a series regulator 4 and a high voltage diode D2 are provided.
Is connected to the parallel circuit of the resistor R12.

The series regulator 4 is composed of a series circuit of high breakdown voltage transistors TR3 and TR4, and controls the load current, that is, the negative component of the separated corona current, by changing the base current of the transistor TR3 as described later. The diode D2 plays a role of bypassing the positive component which is the reverse current.

The resistor R12 determines the amount of the negative component of the load current when the series regulator 4 is cut off. Resistors R6, R
Reference numeral 7 is a resistance value that is substantially equal and is sufficiently larger than the resistance R12, and serves to divide the voltage of the entire series regulator 4 into the transistors TR3 and TR4 substantially equally.

Between the other end of the series regulator 4, the resistor R12 and the diode D2 and the ground, a detection circuit 3 for the direct current of the load current, which is a parallel circuit of the resistor R1 and the capacitor C1, is inserted.

The voltage detected by the detection circuit 3 is compared with the reference voltage (VR) applied to the terminal P2 by the differential amplifier 2. The output of the differential amplifier 2 is the transistor TR3 so that the output of the detection circuit 3 becomes equal to the reference voltage VR.
Control the base current of.

The power supply of the differential amplifier 2 is supplied by the floating power supply EF1. Since the other end of the floating power supply EF1 is connected to the emitter of the transistor TR3, the base current of the transistor TR3 is the current detection resistor R.
It doesn't flow to 1.

The value of the resistor R12 is roughly determined as follows. FIG. 2 is a schematic equivalent circuit diagram of the power supply circuit and the charger load of the first embodiment shown in FIG. 1, and FIG. 3 shows the voltage-current characteristic of the DC component of the charger.

The control range of the direct current component is from point A to point B in FIG.
It is assumed that the points are required. That is, the transistor TR
3 must be conductive at point A and cut off at point B. Then, with the transistor TR3 cut off, the positive current must be greater than the negative current by I ₃ .

V ₁ / R _LP −V ₁ / (R _LN + R ₁₂ ) = I ₃ (Equation 1) where V ₁ : 1/2 of AC high voltage output amplitude R _LP : Positive pseudo equivalent resistance of charger load the value R _LN: a negative pseudo equivalent resistance above formula 1 charger load as follows can be obtained R _12.

[0024]

[Equation 1]

The detection output of the DC component detection circuit 3 must be level-shifted by the resistors R3 and R4 so that it falls within the dynamic range of the input of the differential amplifier 2. Also,
Since the current flowing through the resistors R3, R4 flows through the DC component detecting resistor R1, the values of the resistors R3, R4 are set sufficiently large so as not to affect the detection accuracy.

As described above, the differential amplifier 2 constitutes a control means for controlling the base current of the transistor TR3 of the control circuit series regulator 4 by the detection output of the detection circuit 3 of the direct current component of the load current. Resistors R3, R4
For the same reason as above, a sufficiently large input impedance is selected.

With the above configuration, the AC high voltage transformer T1
The secondary side, high voltage current is divided into positive and negative DC currents by the diodes D1 and D2, and the DC component of the load current can be controlled by the series regulator 4 which constitutes a current control circuit inserted in one side divided.

Further, since the resistance value of the resistor R12 inserted in parallel to the current control circuit is larger than the difference between the positive and negative pseudo equivalent resistance values of the load charger, the direct current component of the load current can be controlled over both the positive and negative polarity ranges. it can.

In order to control the DC component of the load current over a wide range, it is necessary that the output voltage of the series regulator 4 of the current control circuit can be changed over a wide range, but the series regulator 4 is a series circuit of a plurality of transistors TR4, TR3. As a result, the circuit configuration is such that it is not limited by the withstand voltage limit of each transistor, and the detection output of the detection circuit 3 is compared with the reference voltage VR by the operational amplifier 2. By controlling the base current of, the load DC component of the load charger can be controlled in a wide range from positive polarity to negative polarity.

Further, the structure is simpler than that of the conventional example, and the power loss is small.

(Second Embodiment) FIG. 4 is a circuit diagram of a second embodiment of the present invention, in which the same or corresponding portions as those in the first embodiment are designated by the same reference numerals, and the duplicated description will be omitted.

In the present embodiment, the resistor R12 is eliminated by selecting the resistance values of the resistors R6 and R7 provided in parallel with the series regulator 4 so that the total sum thereof becomes the resistance value of the resistor R12 in the first embodiment. It is a thing.

The value of the resistance R8 between the base and the emitter of the transistor TR3 is selected to be sufficiently small with respect to the resistances R6 and R7 and can be ignored.

With the above structure, the same effect as that of the first embodiment can be obtained.

(Third Embodiment) FIG. 5 is a circuit diagram of a third embodiment of the present invention, in which the same or corresponding portions as those in the second embodiment are designated by the same reference numerals, and the duplicated description will be omitted.

In this embodiment, high breakdown voltage field effect transistors (FETs) Q3 and Q4 are used as the high breakdown voltage transistors TR3 and TR4 of the series regulator 4.

By the output of the differential amplifier 2, FET, Q
3 gate voltage is controlled. Gate G to source S,
Since there is no current leakage to the drain D, there is no need to float the power supply of the differential amplifier 2, the circuit configuration is simplified, and the same effects as the first embodiment are obtained.

(Fourth Embodiment) FIG. 6 is a circuit diagram of a fourth embodiment of the present invention, in which the same or corresponding portions as those of the third embodiment are designated by the same portions and their duplicated description will be omitted.

In the first and second embodiments, the voltage applied to the series regulator 4 decreases as the current flowing through the series regulator 4 increases.
The base current of the transistor TR4 decreases, the saturation voltage of the transistor TR4 reaches a considerable level, and the control range of the direct current component of the load current decreases.

Therefore, in this embodiment, the resistors R6 and R7 are used.
Is applied to the base of the transistor TR4 via the emitter follower TR5 at the base of the transistor TR4. The collector of the emitter follower TR5 is connected to the floating power supply EF2 whose reference is the emitter of the transistor TR4.

The base resistors R6 and R7 of the transistors TR3 and TR4 are selected to have a resistance value of several KΩ to several KΩ in order to increase their breakdown voltage.

FIG. 11 is a circuit diagram showing an example of the floating power supply (EF1, EF2) of the fourth embodiment.

A high frequency oscillator circuit 5 drives the pulse transformer T2. Then, the secondary side output of the pulse transformer T2 is rectified and the floating power supply EF of the differential amplifier 2 is rectified.
1 is an example of using a floating power source for the emitter 1 and the emitter floor TR5.

With the above configuration, the series regulator 4
The same effect as the first embodiment is obtained by eliminating the limitation of the load current variable range by the base currents of the high breakdown voltage transistors TR4 and TR3 forming the.

(Fifth Embodiment) FIG. 8 is a circuit diagram of the fifth embodiment, in which the same or corresponding portions as those in the above-mentioned embodiment are designated by the same reference numerals, and the duplicated description will be omitted.

In the fifth embodiment, the floating power supply EF1,
This is an example in which EF2 is obtained from a capacitively coupled rectifier circuit without using a pulse transformer.

The output frequency of the oscillation circuit 5 is set as high as possible so that the coupling capacitance between the rectifier circuit and the oscillation circuit can be minimized. That is, in this embodiment, the coupling capacitances C42, C43, C44, and C45 are set to 500 KH and set to 100.
It was PF.

With the above construction, the floating power supply can be constructed at a low cost, the attenuation of the AC high voltage output is minimized, and the same effect as the fourth embodiment can be obtained.

[0049]

As described above, according to the present invention, the secondary side of the AC high-voltage transformer, the high-voltage current is divided into positive and negative DC currents by the diode, and the load current is divided by the current control circuit inserted in one side. The DC component of can be controlled.

Further, since the resistance value of the resistance inserted in parallel to the current control circuit is larger than the difference between the positive and negative pseudo equivalent resistance values of the load charger, the direct current component of the load current can be controlled over both the positive and negative polarity ranges. ..

The series regulator has a circuit configuration that is not limited by the withstand voltage limit of each transistor as a series circuit of a plurality of transistors, and detects the base current of the transistor of the series regulator by the detection output of the detection circuit. By controlling, the DC component of the load current of the load charger can be controlled in a wide range from positive polarity to negative polarity. Further, the structure is simpler than that of the conventional example, and the power loss is small.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a first embodiment.

FIG. 2 is an equivalent circuit diagram of a power supply circuit and a charger load of the first embodiment.

FIG. 3 is a DC voltage-current characteristic diagram of the charger of the first embodiment.

FIG. 4 is a circuit diagram of a second embodiment.

FIG. 5 is a circuit diagram of a third embodiment.

FIG. 6 is a circuit diagram of a fourth embodiment.

FIG. 7 is a circuit diagram showing an example of a floating power supply of a fourth embodiment.

FIG. 8 is a circuit diagram of a fifth embodiment.

FIG. 9 is a diagram illustrating a basic configuration of a conventional example.

FIG. 10 is a conventional DC-DC converter circuit diagram.

FIG. 11 is a voltage-current characteristic diagram of the DC-DC converter.

FIG. 12 is a voltage-current characteristic diagram of the separation charger.

FIG. 13 is an explanatory diagram of a conventional example in which a fixed DC-DC converter is added.

[Explanation of symbols]

D1, D2 High voltage diode R12 Resistance T1 AC high voltage transformer TR3, TR4 High voltage transistor (series regulator) 1 AC drive circuit 2 Differential amplifier (control means) 3 Current detection circuit

Claims (7)

[Claims] 1. A current control circuit comprising a series circuit of a diode and a plurality of transistors between an AC high voltage transformer secondary winding and ground, and a diode for passing a current in a direction opposite to the current control circuit. Connect a resistor that is larger than the difference between the positive and negative pseudo equivalent resistance values of the charger, which is the load, by a specified value.
A high voltage AC power supply circuit for an image forming apparatus, further comprising a detection circuit for detecting a direct current component of a load current, and a control means for controlling the base current of the current control circuit transistor by the detection output. 2. The plurality of transistors of the current control circuit are:
The image forming method according to claim 1, wherein the base voltage of each transistor is connected by a resistor so that the collector-emitter voltage of each transistor becomes equal to divide the voltage applied to the entire transistor series connection circuit. High voltage AC power supply circuit of the device. 3. The high voltage AC power supply circuit for an image forming apparatus according to claim 1, wherein a plurality of transistors of the current control circuit use field effect transistors (FETs). 4. The control means compares a detection output of a detection circuit inserted between the current control circuit and the ground with a predetermined reference voltage, and selects a transistor located closest to the ground among a plurality of transistors of the current control circuit. Of a differential amplifier having a high input impedance for controlling the base current of the differential amplifier, the power source of the differential amplifier has a floating circuit configuration, and the operating current of the differential amplifier and the base current as its output do not flow to the detection resistor. The high-voltage AC power supply circuit of the image forming apparatus according to claim 1, wherein the high-voltage AC power supply circuit is connected as described above. 5. The bases of the transistors other than the transistor closest to the ground among the plurality of transistors of the current control circuit are connected to a voltage dividing resistor via an emitter follower having a current source by a floating power supply. The high voltage AC power supply circuit for an image forming apparatus according to claim 4, wherein 6. The high voltage AC power supply circuit for an image forming apparatus according to claim 4, wherein the floating power supply is configured by obtaining an AC output by an oscillation circuit and rectifying the AC output by voltage doubler. .. 7. The high voltage AC power supply circuit for an image forming apparatus according to claim 4, wherein the floating power supply is obtained by rectifying a tertiary winding of a high voltage AC transformer.