JP2938241B2 - High voltage power circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-voltage power supply circuit having a function of switching a small current output between positive and negative outputs used in an electrophotographic printer or the like.

[0002]

2. Description of the Related Art Conventionally, in an electrophotographic printer such as an LED printer and a laser printer, a small current output (several μA) is used.
A high-voltage power supply (.about.100 μA) is used, and the polarity of the output voltage can be switched depending on the image forming process. FIG. 2 shows a conventional high-voltage power supply circuit.

In FIG. 1, reference numeral 11 denotes an output switching control circuit which receives a switching input signal and outputs an oscillation control signal;
Is an oscillation circuit that converts the voltage of the input power supply into an AC voltage,
Is a positive output rectifier circuit provided corresponding to the oscillation circuit 13,
Reference numeral 16 denotes a negative output rectifier circuit provided corresponding to the oscillator circuit 14, 17 denotes a transformer provided between the oscillator circuit 13 and the positive output rectifier circuit 15, and converts the AC voltage output from the oscillator circuit 13, and 18 denotes a transformer. A transformer, which is provided between the oscillation circuit 14 and the negative output rectification circuit 16 and converts the AC voltage output by the oscillation circuit 14, includes a positive DC current output from the positive output rectification circuit 15 and the negative output rectification circuit. A high-voltage relay 20 for selecting a negative DC current output from 16 is a relay drive circuit that receives a signal from the output switching control circuit 11 and outputs a signal for operating the high-voltage relay 19. .

[0004] In high-voltage power supply circuit having the above configuration, the input power is converted into alternating current of a few tens kH _Z by the oscillation circuit 13 and 14 is boosted to the required AC voltage by the transformer 17. The boosted AC voltage is applied to the positive output rectifier circuit 1
5 or the negative output rectifier circuit 16 converts the output into a positive or negative DC output. The high-voltage relay 19 selects one of the DC outputs, and outputs it as a high-voltage output. The voltage or current output from the positive output rectifier circuit 15 or the negative output rectifier circuit 16 is monitored.
The output is fed back to. Desired output characteristics such as constant voltage characteristics and constant current characteristics can be obtained by the output feedback.

The switching input signal is supplied to an output switching control circuit 11
, One of the DC outputs is selected. When the output switching control circuit 11 receives the switching input signal, the output switching control circuit 11 determines whether to output a positive or negative DC output, sends an oscillation control signal to one of the oscillation circuits 13 and 14 to operate it, and suspends the other. Let it. At this time, a signal is also sent to the relay drive circuit 20 to operate the high voltage relay 19 to select a DC output.

FIG. 3 is a diagram showing another conventional high-voltage power supply circuit. In the figure, reference numeral 21 denotes an output switching control circuit which receives a switching input signal and outputs an oscillation control signal; 13, 14 an oscillation circuit for converting a voltage of an input power supply into an AC voltage; The positive output rectifier circuit 16 is a negative output rectifier circuit provided corresponding to the oscillation circuit 14.
7 is provided between the oscillation circuit 13 and the positive output rectifier circuit 15,
A transformer for converting the AC voltage output by the oscillation circuit 13,
Reference numeral 18 denotes a transformer disposed between the oscillation circuit 14 and the negative output rectification circuit 16 for converting the AC voltage output from the oscillation circuit 14; 23, a resistor connected to the output side of the positive output rectification circuit 15; This is a resistor connected to the output side of the output rectifier circuit 16. The other ends of the resistors 23 and 24 are connected to an output.

In this case, the operation of the high-voltage power supply circuit is almost the same as that of FIG. 2, except that a resistor 23 is connected between the positive output rectifier circuit 15 and the output, and a resistor 24 is connected between the negative output rectifier circuit 16 and the output. The DC outputs of both rectifier circuits 15 and 16 are added by resistors 23 and 24. Therefore, the large-sized high-voltage relay 19 as shown in FIG. 2 becomes unnecessary.

[0008]

However, in the high-voltage power supply circuit having the above configuration, the oscillating circuits 13 and 14 and the transformers 17 and 18 are used to switch the DC output between positive and negative.
In addition, two systems of rectifier circuits 15 and 16 are required, which not only increases the size of the device but also increases the price.

Then, as shown in FIG.
In the case of a high-voltage power supply circuit provided with a high-voltage power supply circuit, not only the size and cost of the device are increased by the amount of the high-voltage relay 19, but also insulation and manufacturing become difficult. Further, as shown in FIG.
In the case of a high-voltage power supply circuit including
24 causes a voltage drop. For example, when the resistances of the resistors 23 and 24 are equal, the DC output becomes half of the DC output of the rectifier circuits 15 and 16 and the loss is large.

SUMMARY OF THE INVENTION An object of the present invention is to provide a high-voltage power supply circuit which is small, inexpensive, and easy to insulate and manufacture, by solving the above-mentioned problems of the conventional high-voltage power supply circuit.

[0011]

Therefore, in the high-voltage power supply circuit of the present invention, a positive output and a negative output can be switched, and a high-pressure output can be obtained with a small current. A first switching means which has a transformer on which at least two windings for a positive output and a negative output are arranged on a secondary side, and performs a switching operation corresponding to a required output polarity, It is connected to the positive output winding and the negative output winding on the primary side, respectively.

On the secondary side of the transformer, there are windings for positive output and negative output, and output means for positive output and negative output are respectively connected to the windings. The output means for the positive output and the output means for the negative output are connected to each other in series. The second switching means is connected to the first switching means, and the second switching means is connected to the second switching means while the first switching means is off.
Switching means supplies a regenerative current at the set voltage.

After the regenerative current becomes zero, a means for flowing a current to the first switching means is provided, and a current flows to the winding again. The rise time of the current when the first switching means is on is different from the rise time of the current when the first switching means is off, so that the voltage generated by on / off draws an asymmetrical AC waveform in the positive and negative directions. It is.

Further, in the apparatus wherein the resonance generating means for generating resonance while the first switching means is off is provided, the second switching means is connected to the resonance generating means, and the second switching means is connected to the resonance generating means. A regenerative current is supplied at a set voltage by a switching means, and the resonance is stopped.

[0015]

According to the present invention, the positive output and the negative output can be switched as described above, and a high pressure output can be obtained with a small current, and at least the positive output is provided on the primary side and the secondary side. And a transformer provided with two windings for negative output and negative output. A first switching means for performing a switching operation in accordance with a required output polarity is provided with a primary output positive output and a negative output. Each is connected to the output winding. On the secondary side of the transformer, there are windings for positive output and negative output,
Output means for positive output and negative output are connected to the windings, respectively. The output means for the positive output and the output means for the negative output are connected to each other in series. Therefore, by turning on / off the first switching means, an output voltage of a required polarity can be obtained.

A second switching means is connected to the first switching means, and while the first switching means is off, the second switching means flows a regenerative current at a set voltage, and the regenerative current becomes zero. After the first
Current flows through the switching means. The rise time of the current when the first switching means is on is different from the rise time of the current when the first switching means is off, and the voltage generated by on / off draws an asymmetrical AC waveform in the positive and negative directions. It is like that.

Therefore, the difference between the positive voltage and the negative voltage generated on the secondary side can be increased, and a large output voltage can be obtained. Further, in a configuration in which a resonance generating means for generating resonance while the first switching means is off is provided, a second switching means is connected to the resonance generating means, and the second switching means A regenerative current is supplied at a set voltage and the resonance is stopped.

In this case, a negative voltage can be generated while the resonance is occurring.

[0019]

Embodiments of the present invention will be described below in detail with reference to the drawings. 1 is a diagram showing a high-voltage power supply circuit of the present invention, FIG. 4 is a time chart of the high-voltage power supply circuit of the present invention, and FIG. 7 is a circuit diagram of a main part of the high-voltage power supply circuit showing a second embodiment of the present invention.

In FIG. 1, reference numeral 1 denotes a control circuit, to which an output switching signal is inputted, and which outputs an output signal to the transistors Tr1 and Tr2 from the control circuit 1 by the output switching signal. That is, at the time of positive output,
The transistor Tr1 switches (turns on), and the transistor Tr2 pauses (turns off). At the time of negative output, the transistor Tr1 is turned off, and the transistor T1 is turned off.
r2 turns on.

Next, the operation at the time of positive output will be described with reference to FIG.
Will be explained. The control circuit 1 first controls the transistor Tr1
Base voltage v_BETo turn on the transistor Tr1.
I do. At this time, the power supply voltage is_CC, The winding n of the transformer T1
Assuming that the inductance of L1 is L, the transistor Tr1
Collector current i_C1(= (V _CC/ L) · t) rises,
The energy stored in the winding n1 is (１ ／) · L · = i
_C1peak ^TwoBecomes

Therefore, when the transistor Tr1 is turned on only for a time during which energy corresponding to the required output is stored, and after turning on for a certain time, the base voltage v _BE is turned off and the transistor Tr1 is turned off, the winding n1 has: Due to the energy accumulated during that time, a voltage is generated in the direction in which the current continues to flow, and a regenerative current i _D1 flows through the Zener diode D1 and the diode D5. Diode D5 is for suppressing the direction of current in one direction, is used to clamp the voltage zener diode D1 generates a Zener voltage v _Z.

At this time, the regenerative current i _D1 flowing through the Zener diode _D1 becomes − (v _Z / L) with the release of energy.
Decrease as represented by t. Then, the current in1 flowing through the winding _n1 becomes [ _ic1 + _id1 ], and the voltage _{vn1 at} both ends becomes the value of the power supply voltage _vcc in the positive direction and the Zener voltage vcc in the negative direction.
It becomes an asymmetrical AC waveform that takes the value of _z . When this state has a transistor Tr1 is turned off, cause the inductance L is resonant within the distributed capacitance and winding n1 of the transformer T1, the voltage value of the positive direction substantially Zener voltage v _Z ends up occurring, the positive and negative Cannot be increased. Therefore, as soon as the regenerative current i _D1 becomes zero, the transistor Tr1 is turned on again.

This timing can be obtained by monitoring the voltage v _n3 generated in the winding _n3 by the control circuit 1. That is, the generation of the negative voltage stops at the voltage _vn3 , and the transistor Tr1 is turned on. On the secondary side, voltages v _O1 and v _O2 multiplied by the turns ratio of the transformer T1 are generated, and the capacitors C1 and
The DC voltage is smoothed by C2. The voltages at both ends of the capacitors C1 and C2 are referred to as v _C1 and v _C2 ,
Is given by r = n2 / n1 = n2 '/ n1, v _C1 = rv _Z V _C2 = rv _CC , and the output voltage v ₀ is [v _C1 −v _C2 ]. Accordingly, the Zener voltage v _Z if sufficiently larger than the power supply voltage v _CC, it is possible to increase the output voltage v _0. For example, if v _CC = 24 [V] v _Z = 240 [V] r = 20, v _C1 = 4.8 [kV] v _C2 = 0.48 [kV], which is approximately 4.3 [kV]. An output voltage v ₀ is generated.

Here, at the time of positive output, the resistors R2 and R3 are
At the time of a negative output, the resistor R1 outputs the output current i. ₀Voltage
Although the lower occurs, the output current i₀Is several tens of μA.
Loss is small. For example, R1 = R2 + R3 = 50 [MΩ] and the output current i₀Is 10 μA, the resistance R1
Loss is 4.8^Two/50≒0.46 [W], which is smaller than 1 [W]. In addition, resistance R2 and
Output current i flowing through the resistor R3_OIs 50 × 10 = 0.5 [kV], and the output voltage v₀As a result, 4.3−0.5 = 3.8 [kV] is obtained, and the voltage drop is far more than that of the high-voltage power supply circuit of FIG.
Become smaller.

Similarly, at the time of negative output, the output voltage v ₀ and the output current i ₀ can be generated by turning on / off the transistor Tr2. In the case of the above embodiment, the output feedback is applied so that a constant current is obtained at the time of positive output, and a substantially constant voltage is obtained at the time of negative output. At the time of positive output, a voltage given by i ₀ · R3 is generated by the output current i ₀ flowing through the resistor R3, so that the output current i ₀ can be monitored. At the time of negative output, the voltage v _C2 is divided by the resistors R2 and R3. The compressed voltage R3 / (R2 + R3) .v _C2 can be monitored.

The output feedback is input to the control circuit 1 and is used for setting the ON time of the transistors Tr1 and Tr2. When the output voltage v ₀ or the output current i _O is small, the on-time is long, and when the output voltage v ₀ or the output current i _O is large, the on-time is short. The emitter currents of the transistors Tr1 and Tr2 pass through the resistor R4.
The control circuit 1 monitors the voltage between the terminals of the resistor R4, and when the emitter current becomes too large, the transistor Tr1,
Tr2 is protected from being damaged.

The FETs are connected to the transistors Tr1, Tr
2 may be used, and the Zener diodes D1 and D2 and the diodes D5 and D6 may be shared as shown in FIG. The output feedback is also obtained by directly dividing the output voltage v ₀ , and the windings n3 and n
The voltage generated at 3 ', the current to ground, and the like may be monitored.

The distributed capacitance of the windings n1 and n1 'of the transformer T1 is large.
If the voltage generated when r1 and Tr2 are off is suppressed and the rating of transistors Tr1 and Tr2 is not exceeded, zener diodes D1 and D2 and diodes D5 and D6 can be omitted. Next, the transformer T
An embodiment in which a capacitor is provided on the primary side of the first embodiment will be described.

FIG. 5 is a diagram showing a high-voltage power supply circuit according to a third embodiment of the present invention, FIG. 6 is a time chart of the high-voltage power supply circuit according to the third embodiment of the present invention, and FIG. FIG. 9 is a circuit diagram of a main part of a high-voltage power supply circuit according to a fourth embodiment. In FIG. 5, 1 is a control circuit to which an output switching signal is input,
The output switching signal causes the control circuit 1 to output the transistor T
Output signals are sent to r1, Tr2, Tr3 and Tr4.

That is, at the time of the positive output, the transistor Tr1 turns on and the transistor Tr2 turns off.
At the time of negative output, the transistor Tr1 turns off and the transistor Tr2 turns on. Transistor Tr
Reference numeral 3 is for preventing the current from flowing through the diode D5 at the time of the negative output, and the transistor Tr4 is for preventing the current from flowing at the diode D6 at the time of the positive output.

The diodes D7 _and D8 are provided to prevent a reverse voltage from being applied to the transistors Tr1 _and Tr2. Next, the operation at the time of positive output will be described with reference to FIG. The control circuit 1 first applies the base voltage v _BE to the transistor Tr1, and turns on the transistor Tr1. At this time, the power supply voltage is set to v _CC and the winding n of the transformer T1 is set to n.
Assuming that the inductance of 1 is L, the collector current i _C1 (= (v _CC / L) · t) of the transistor Tr1 increases, and the energy stored in the winding n1 is (１ ／) · L · i _C1
It becomes _peak ² .

Therefore, when the transistor Tr1 is turned on for a time during which energy corresponding to the required output is accumulated, and after turning on for a certain time, the base voltage v _BE is turned off and the transistor Tr1 is turned off, the winding n1 has: Due to the energy accumulated during that time, a voltage is generated in the direction in which the current continues to flow, and the charging current _in1 flows in the direction in which the voltage _vn1 becomes negative in the resonance capacitor C3 connected in parallel with the winding n1.

Resonance is generated by the winding n1, the capacitor C3, other capacitances, the capacitor C4 coupled by the transformer T1, and the like, and the charging current _in1 has a substantially sinusoidal waveform. That is, when the voltage v _n1 becomes negative and the charging current i _n1 decreases and becomes zero, the voltage v _n1 becomes maximum in the negative direction due to the principle of the LC resonance circuit. At this time, assuming that the equivalent capacitance that is in parallel when viewed from the winding n1 is C, the value of the voltage v _n1 is approximately-(L / C) ^1/2 · i _C1peak .

Next, the charging current i _n1 is increased in the negative direction while decreasing the slope, and when the charging current i _{n1 reaches} the maximum value, the charging current i _n1 moves in the positive direction. Then, the voltage v _n1 approaches zero and is inverted to the positive side to become the value of the power supply voltage v _cc . At this time, the regenerative current i _D1 flows through the input power supply and the diode D5, the resonance between the capacitor C3 and the winding n1 stops, and the voltage between both terminals of the capacitor C3 becomes the value of the power supply voltage v _CC . Next, when the collector current i _C1 starts flowing, the charging current in ₁ does not flow through the capacitor C3.

The negative voltage generated during the resonance is caused by the winding n3
, And the control circuit 1 determines that the generation of the negative voltage ends and the base voltage v _n3 .
_BE is generated, and the transistor Tr1 is turned on. While regenerative current i _D5 to the diode D5 is flowing, the collector current i _C1 even if the transistor Tr1 is turned on does not flow as soon as the regenerative current i _D5 becomes zero, the flow collector current i _C1 again, It rises in the positive direction at the value of (v _CC / L) · t.

This operation is repeated, and the winding n1
Voltage v _n1 developed across the value of the positive direction to the supply voltage v _CC, it becomes an AC waveform asymmetric taking values of Zener voltage v _z in the negative direction. On the other hand, on the secondary side, the transformer T1
, The voltages V _O1 and V _O2 multiplied by the turns ratio of
1 and C2 to be a direct current. The voltages at both ends of the capacitors C1 and C2 are referred to as v _C1 and v _C2 ,
Assuming that the turns ratio of r is r, v _C1 = r · (L / C) ^1/2 · i _C1peak v _C2 = r · v _CC , and if (L / C) ^1/2 · i _C1peak is made sufficiently large, The output voltage [v _C1 -v _C2 ] can be increased.

For example, v _CC = 25 [V] L = 1.25 [mH] C = 5100 [pF] r = 20, and the time when the transistor Tr1 is on is 25 μm.
In the case of sec, i _C1peak = (25 / 1.25) × 25 = 0.5 [A], and v _C2 = 20 × 25 = 0.5 [kV] v _C1 = 20 × (1.25 / 5100) ^{1 / 2} × a 0.5 ≒ 4.9 [kV].

Further, the output voltage v ₀ becomes v _C1 -v _C2 = 4.9-0.5 = 4.4 [kV]. Since the resonance period is a half cycle, π · (L ·
C) ^1/2 , and in this case, π · (1.25 × 5100) ^1/2 ≒ 7.9 [μsec].

At the time of positive output, the resistors R2 and R3 are
At the time of a negative output, the resistor R1 outputs the output current i. ₀Voltage
Although the lower occurs, the output current i₀Is several tens of μA.
Loss is small. For example, R1 = R2 + R3 = 50 [MΩ] and the output current i₀Is 10 μA, the resistance R1
Loss is 4.9^Two/50≒0.48 [W], which is smaller than 1 [W]. In addition, resistance R2 and
Output current i flowing through the resistor R3₀Is 50 × 10 = 0.5 [kV], and the output voltage v₀As a result, 4.4-0.5 = 3.9 [kV] is obtained, and the voltage drop is far more than that of the high-voltage power supply circuit of FIG.
Become smaller.

Similarly, for the negative output, the transistors Tr1, Tr
3 is turned off, Tr4 is turned on, and the transistor Tr2 is turned on.
, An output voltage v ₀ and an output current i ₀ can be generated. The FET may be used in place of the transistors Tr1 and Tr2, and between the transistor Tr3 and the diode D5 coupled by the capacitors C3 and C4 and the transformer T1, the diode D8
The circuit between the transistor Tr2, the transistor Tr4 and the diode D6, and the circuit between the diode D7 and the transistor Tr1 can be shared as shown in FIG.

The distributed capacitance of the windings n1 and n2 of the transformer T1 is large, and this distributed capacitance causes the transistor Tr
1, the voltage generated when Tr2 is off is suppressed, and
If the rating of the transistors Tr1 and Tr2 is not exceeded, this distributed capacitance can be used as a substitute for the capacitors C3 and C4, and the capacitance of the capacitors C3 and C4 can be reduced or omitted.

The present invention is not limited to the above-described embodiment, but can be variously modified based on the gist of the present invention, and these are not excluded from the scope of the present invention.

[0044]

As described in detail above, according to the present invention, there is provided a transformer having at least two windings for the positive output and the negative output on the primary side and the secondary side, First switching means for performing a switching operation corresponding to the required output polarity is connected to the positive output winding and the negative output winding on the primary side, respectively, and on the secondary side of the transformer,
Output means for positive output and output means for negative output are respectively connected.
The output means for the positive output and the output means for the negative output are connected to each other in series. Therefore, a common transformer can be used, and a compact, low-cost, high-efficiency high-voltage power supply circuit can be provided.

The second switching means is connected to the first switching means, and while the first switching means is off, the second switching means flows a regenerative current at a set voltage, and the regenerative current is After the current becomes zero, a current flows through the first switching means.
The rise time of the current when the first switching means is on is different from the rise time of the current when the first switching means is off, and the voltage generated by on / off draws an asymmetrical AC waveform in the positive and negative directions. It is like that.

Further, in the apparatus having the resonance generating means for generating resonance while the first switching means is off, the second switching means is connected to the resonance generating means, and the second switching means is connected to the resonance generating means. A regenerative current is supplied at a set voltage by a switching means, and the resonance is stopped. Therefore, the difference between the positive and negative voltages generated on the secondary side can be increased, and a large output voltage can be obtained.

Further, by outputting an AC voltage without passing through a rectifier circuit, a positive / negative asymmetric AC bias voltage used in an electrophotographic process can be generated in a power supply circuit having one transformer.

[Brief description of the drawings]

FIG. 1 is a diagram showing a high-voltage power supply circuit of the present invention.

FIG. 2 is a diagram illustrating a conventional high-voltage power supply circuit.

FIG. 3 is a diagram showing another conventional high-voltage power supply circuit.

FIG. 4 is a time chart of the high-voltage power supply circuit of the present invention.

FIG. 5 is a diagram illustrating a high-voltage power supply circuit according to a third embodiment of the present invention.

FIG. 6 is a time chart of a high-voltage power supply circuit according to a third embodiment of the present invention.

FIG. 7 is a main part circuit diagram of a high-voltage power supply circuit showing a second embodiment of the present invention.

FIG. 8 is a main part circuit diagram of a high-voltage power supply circuit showing a fourth embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Control circuit n1 to n3 Winding T1 Transformer Tr1 to Tr4 Transistor i _D1 Regenerative current D1, D2 Zener diode D3 to D8 Diode R1 to R4 Resistance

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Akira Hagiwara 1-7-12 Toranomon, Minato-ku, Tokyo Oki Electric Industry Co., Ltd. (72) Inventor Naoji Akutsu 1-7-12 Toranomon, Minato-ku, Tokyo Oki Electric Industry Co., Ltd. (56) References JP-A-59-185120 (JP, A) JP-A-4-217866 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H02J 1/00 304 H02J 1/00 306 H02M 3/28

Claims (2)

(57) [Claims] 1. A high-voltage power supply circuit capable of switching between a positive output and a negative output and capable of obtaining a high-pressure output with a small current, comprising: (a) at least a positive output for a primary side and a secondary side; A transformer provided with two windings for negative output; and (b) connected to the windings for positive output and negative output on the primary side, respectively. (C) positive output and negative output means connected respectively to the positive output winding and the negative output winding on the secondary side, and connected in series with each other; (D) second switching means for supplying a regenerative current at a set voltage while the first switching means is off; and (e) supplying a current to the first switching means after the regenerative current becomes zero. And (f) the first switch. The rise time of the current when the switching means is on is different from the rise time of the current when the switching means is off, and the voltage generated by on / off draws an asymmetrical AC waveform in the positive and negative directions. And high voltage power circuit. 2. A high-voltage power supply circuit capable of switching between a positive output and a negative output and obtaining a high-pressure output with a small current, comprising: (a) at least a positive output for a primary side and a secondary side; A transformer provided with two windings for negative output; and (b) connected to the windings for positive output and negative output on the primary side, respectively. (C) positive output and negative output means connected respectively to the positive output winding and the negative output winding on the secondary side, and connected in series with each other; (D) resonance generating means for generating resonance while the first switching means is off; (e) second switching means for flowing a regenerative current at a set voltage and stopping the resonance; (f) After the regenerative current becomes zero, the first And (g) that the voltage generated by turning on / off the first switching means draws an asymmetrical AC waveform in the positive and negative directions. High voltage power supply circuit.