JP2000102261A - Power circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the stray capacitance of wiring and thus the capactance of a transformer for outputting AC voltage in a power circuit, which superposes AC voltage and DC voltage and supplies a load with it. SOLUTION: A DC output section for producing a direct-current voltage and an AC output section for producing alternating-current voltage are mounted on separate boards, and the AC power supply board mounted with the AC output section is placed close to a load, so that the stray capacitance of wiring for connection between the output of the AC output section and the load is smaller than the stray capacitance of wiring for connection between the output of the DC output section and the load. The output of the DC output section is connected with the output of the AC output section to obtain a power circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a DC (direct current)
The present invention relates to a power supply circuit for supplying a high voltage superimposed with C (alternating current) to a load. For example, the present invention relates to a power supply circuit for supplying power to a developing device of an electrophotographic image forming apparatus.

[0002]

2. Description of the Related Art FIG. 2 shows a conventional power supply circuit for supplying power to a developing device of an electrophotographic image forming apparatus. The high voltage power supply board is provided with an AC output unit and a DC output unit.
The AC output, high-voltage power supply control circuit CC1 is switched transistor Q _1. As a result, the input voltage of 24 V is amplified by the transformer T ₁ to generate the AC output voltage V _{1, which} is output via the capacitors C ₁ and C ₂ . The DC output section, the high-voltage power supply control circuit CC2 to switch the transistor Q _2. Thus the input voltage of 24V is voltage amplified by the transformer T _2. This half-wave rectified by the diode D _1, further is smoothed by the capacitor C _0, a negative DC output voltage V ₂ is generated.

The above DC output voltage V_Two Is the resistance R₁ And (R
_Two + R_Three ) And a resistor R_Four Through the capacitor C
₁ Is applied to the output side. As a result, AC and DC are overlapped.
Output voltage V folded_Three Is generated and connected via the wiring a.
The bias 1 is supplied to the developed developing device. Also on
DC output voltage V_Two Is the resistance (R₁ + R_Two ) And R_Three In minutes
Pressed, resistance R _Five Through the capacitor C_Two Mark on the output side of
Be added. As a result, the output voltage obtained by superimposing AC and DC
V_Four Is generated, and the developing device connected via the wiring b is
Supplied as bias 2.

[0004]

[SUMMARY OF THE INVENTION] In the wiring a connects the output voltage V ₃ to the bias 1, due to its stray capacitance C ₁₁ -C _1n, flows reactive current i _11C ~i _1nC. Similarly, the wiring b for connecting the output voltage V ₄ to the bias 2, due to its stray capacitance C ₂₁ -C _2n, flows reactive current i _21C ~i _{2n C.}

The value of the reactive current i _1nC flowing through the stray capacitance C _1n is:

I _1nC = 2πfC _1n V (1) Here, f is the output frequency of the AC voltage, and V is AC
Output voltage.

The total value i of the load current viewed from the transformer T ₁ that generates the AC output voltage is:

[Number 2] _{i = i 01 + i R1 +} i 02 + i R2 = i 11C + ·· + i 1nC + i L1 + i R1 + i 21C + ·· + i 2nC + i L2 + i R2 = i 11C + ·· + i 1nC + i 21C + ·· _{+ i 2nC + i L1 + i} L2 + i R1 + i R2 ≒ 2πfV {Σ (C 1k + C 2k)} + (1 / R L1 + 1 / R L2) V + V / (R 4 + R 2 + R 3) + V / (R 5 + R 3 ) (2) However, the capacity of C ₁ and C ₂ is sufficiently large and AC
Output voltages V ₁ is substantially equal to the output voltage V ₃ and V ₄ of the high-voltage power supply board. The total range of Σ is from k = 1 to k
= N.

The frequency used for the developing bias voltage is as large as about several KHz. For this reason, the reactive current flowing through the floating capacitance of the wiring becomes larger than the load current, and a large-capacity transformer is required as the AC voltage output transformer.
In order to reduce the stray capacitance, the length of the wiring may be shortened. However, since the high-voltage power supply substrate is large in size, it has been difficult to arrange the high-voltage power supply substrate near a developing device where space is limited.

The present invention has been made in view of the above circumstances, and in a power supply circuit for superimposing an AC voltage and a DC voltage to supply a load, a stray capacitance of a wiring is reduced to reduce a reactive current. Accordingly, an object of the present invention is to reduce the capacity of the AC voltage output transformer.

[0009]

According to the first aspect of the present invention, there is provided a power supply circuit for superposing a DC voltage and an AC voltage and supplying the superposed DC voltage to a load, wherein the DC output section generates a DC voltage and the AC output section generates an AC voltage. The output unit is mounted on a separate board, and the AC output unit is connected so that the stray capacitance of the wiring connecting the output of the AC output unit and the load is smaller than the stray capacitance of the wiring connecting the output of the DC output unit and the load. The mounted substrate is provided near the load, and D
A power supply circuit wherein an output of a C output unit is connected to an output of an AC output unit. The invention of Claim 2 is Claim 1
Wherein the output of the DC output section is connected to the output of the AC output section via a resistor.

[0010]

FIG. 1 shows a power supply circuit according to an embodiment. The circuit shown is also a high-frequency power supply in which an AC voltage and a DC voltage are superimposed on a developing device (toner developing device) of an electrophotographic image forming apparatus (copier / printer / facsimile, etc.), similarly to the circuit of FIG. (Frequency: about 1 KHz or more, voltage: about 1 KV or more).

The components and operation of the circuit shown in FIG.
This is substantially the same as each component and operation of the circuit of FIG. The difference between the circuit of FIG. 1 and the circuit of FIG. 2 is that in the circuit of FIG. 2, the AC output unit and the DC output unit are provided on the same substrate, and the substrate is installed at a position distant from the developing device as a load. On the other hand, in the circuit of FIG. 1, the AC output unit and the DC output unit are provided on separate substrates, and the substrate on which the AC output unit is mounted is installed near the developing device which is a load, and The point that the substrate on which the output unit is mounted is installed at a position distant from the developing device as a load.

[0012] In AC output unit mounted on the AC power supply board, high-voltage power supply control circuit CC1 is switched transistor Q _1. Thus the input voltage of 24V is voltage amplified AC output voltage V ₁ is generated in the transformer T _1,
They are respectively output via a capacitor C ₁ and C _2. The DC outputs that are mounted on the DC power supply board, high-voltage power supply control circuit CC2 to switch the transistor Q _2. Thus the input voltage of 24V is voltage amplified by the transformer T _2. This half-wave rectified by the diode D _1, further
Smoothing is performed by the capacitor C ₀ to generate a negative DC output voltage V ₂ .

The DC output voltage V ₂ is determined by the resistances R ₁ and (R
₂ + R ₃₎ in divided by the output voltage V _5. This output voltage V _5, the capacitor C via the wiring A resistor R _4
1 is applied to the output side. Thus superimposed output voltage V ₃ of the AC and DC are generated, the output voltage V _3,
It is supplied as a bias 1 to the developing device. In addition, the DC
The output voltage V ₂ is divided by the resistor (R ₁ + R ₂ ) and R ₃ to obtain an output voltage V ₆ . This voltage V ₆ is applied to the output side of the capacitor C ₂ via the wiring 20 and the resistor R ₅ . As a result, the output voltage V ₄ where AC and DC are superimposed is obtained.
Is generated, and this output voltage V ₄ is applied to the developing device with bias 2.
Supplied as

That is, in the circuit shown in FIG. 1, since the AC power supply substrate is provided near the developing device and the length of the connection wiring is short, the stray capacitance thereof can be ignored. Therefore, as described above, as a bias 1 output voltage V _3, the output voltage V ₄ is as a bias 2, is supplied to each developing unit.

On the other hand, the DC power supply board is
Provided at a position distant from the imager, relatively long wiring
Connected to the output side of the AC power supply board via A and wiring B
The stray capacitance C₁₁~ C_1nAnd C_{twenty one}~ C_2nfor
The reactive current i_C11 ~ I_C1n And i _C21 ~ I_C2n Flows.
This effect is estimated as follows.

The total value i of the load current as viewed from the transformer T ₁ that generates the AC output voltage is:

## _EQU3 ## i = i ₀₁ + i ₀₂ = i ₂₁ + i _L1 + i ₂₂ + i _L2 = i _C11 +... + I _C1n + i _R1 + i _L1 + i _C21 +... + I _C2n + i _R2 + i _L2 ≒ V / ｛(R ₂ + R _{3) / (1 + 2πf (R 2} + R 3) ΣC 1k) + R 4} + V / R L1 + V / {R 3 / (1 + 2πfR 3 ΣC 1k) + R 5} + V / R L2 ·· (3). However, it is assumed that the capacities of C ₁ and C ₂ are sufficiently large. The total range of Σ is from k = 1 to k = n.

[0017] That is, provided the AC power board in the vicinity of a is developing unit load, in the configuration provided away DC power board, because the output current flows limit the resistor R ₄ by a resistor R _5,
Influence of the stray capacitance is reduced, thereby reducing the output capacitance of the AC transformer T _1. In the case of FIG. 2, it is difficult to provide a relatively large-sized high-voltage power supply board (a board on which an AC power supply and a DC power supply are mounted) near the developing device, which is a load, but as shown in FIG. It is possible to provide only the AC power supply board for the power supply.

[0018]

According to the present invention, in the power supply circuit for supplying the AC and DC voltages in a superimposed manner, the AC power supply board is provided near the load, and the DC power supply board is provided away from the load. The reactive current of the stray capacitance due to the routing of the wiring can be reduced, so that the AC voltage output transformer can have a small capacitance.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a power supply circuit of an embodiment.

FIG. 2 is a configuration diagram of a conventional power supply circuit.

[Explanation of symbols]

CC1 high-voltage power supply control circuit CC2 high-voltage power supply control circuit R _L1 load R _L2 load

Claims (2)

[Claims] 1. A power supply circuit for superimposing a DC voltage and an AC voltage and supplying the load to a load, wherein a DC output section for generating a DC voltage and an AC output section for generating an AC voltage are mounted on separate substrates.
The stray capacitance of the wiring connecting the output of the AC output unit and the load is
A board on which the AC output unit is mounted is provided near the load so that the output of the DC output unit is smaller than the stray capacitance of the wiring connecting the load, and the output of the DC output unit is connected to the output of the AC output unit. A power supply circuit characterized by the following. 2. The power supply circuit according to claim 1, wherein an output of the DC output section is connected to an output of the AC output section via a resistor.