JP2012063416A - High-voltage power unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-voltage power unit that stably supplies electric power by reducing an influence of noise.SOLUTION: The high-voltage power unit includes, for each of a plurality of chargers, a high-voltage power supply part 1100 including a transformer 1209, a switching element 1207 switching a voltage applied to a primary winding of the transformer 1209, a high-frequency modulation circuit 1205 which generates a control signal for controlling switching operation of the switching element 1207, an FET driving circuit 1206 which turns on and off the switching element 1207 according to the control signal supplied from the high-frequency modulation circuit 1205, and a saw-tooth wave generation circuit 1204 which receives a resonance-frequency signal determining the frequency of the control signal from an MCU 1000, and converts the resonance-frequency signal into a saw-tooth wave signal. The high-frequency modulation circuit 1205 is arranged nearby the FET driving circuit 1206 to shorten the wiring length of a wiring line for transmitting the saw-tooth wave signal supplied from the saw-tooth wave generation circuit 1204 to the high-frequency modulation circuit 1205.

Description

  The present invention relates to a high-voltage power supply device.

  High frequency modulation AC high voltage power supply devices have come to be used as power supply devices that supply power to charging devices provided in image forming apparatuses. The harmonic modulation type AC high-voltage power supply device is particularly effective for energy saving in a multicolor image forming apparatus such as a color printer.

  In Patent Document 1, a charging high-voltage power source and a development high-voltage power source generate a charging AC voltage and a developing AC voltage based on one basic clock, and an AC frequency of the charging AC voltage and an AC frequency of the developing AC voltage are integers. The image forming apparatus is characterized in that the phase relationship between the charging AC voltage and the developing AC voltage is fixed.

  Patent Document 2 discloses a photosensitive member, a charging member, a developing member, a first supply unit that supplies an output obtained by superimposing a first AC voltage on a first DC voltage to the charging member, and a second DC voltage. An electrophotography comprising a second supply means for supplying an output on which the alternating voltage is superimposed to the developing member, and a changing means for changing the frequency ratio between the first alternating voltage and the second alternating voltage to an integer corresponding to the print density. Inventive image forming apparatus.

JP 2004-109711 A Japanese Patent No. 3359111

  An object of this invention is to provide the high voltage power supply device which can reduce the influence of a noise and can supply the power stably.

  In order to achieve this object, a high-voltage power supply apparatus according to the present invention is a high-voltage power supply apparatus that supplies power to a plurality of loads included in an image forming apparatus, and a voltage applied to a transformer and a primary winding of the transformer. A switching element that switches, a high-frequency modulation circuit that generates a control signal that controls a switching operation of the switching element, a drive circuit that switches on and off the switching element in accordance with a control signal supplied from the high-frequency modulation circuit, A plurality of high-voltage power supply units each including a first conversion circuit that inputs a resonance frequency signal that determines the frequency of the control signal from control means of the high-voltage power supply device and converts the resonance frequency signal into a sawtooth wave signal. A plurality of loads are provided for each load, the first conversion circuit is disposed in the vicinity of the high-frequency modulation circuit, and the front of the first conversion circuit It is characterized in that shortening the wiring length of the wiring for transmitting the sawtooth signal supplied to the high frequency modulation circuit.

  In the high-voltage power supply device, an output frequency signal for controlling the frequency of the AC output output from the secondary winding of the transformer, the resonance frequency signal, and an output variable signal for controlling the current value of the AC output. The control means for controlling the AC output by transmitting to the plurality of high-voltage power supplies, and the high-voltage power supply is detected by a current detection means for detecting a current value of the AC output, and the current detection means. An error amplifier that obtains and amplifies an error between the voltage value obtained by converting the current value of the AC output into a voltage and the output variable signal, an error signal output from the error amplifier, and the output frequency signal are input. A second conversion circuit for converting the output frequency signal into a sine wave signal having a frequency matching the frequency of the output frequency signal and an amplitude having an amplitude set based on the error signal; The high frequency modulation circuit compares the signal level of the sine wave signal supplied from the second conversion circuit and the sawtooth wave signal, and the frequency matches the frequency of the sawtooth wave signal, The on-duty control signal corresponding to the amplitude of the sine wave signal is generated and supplied to the drive circuit, and the frequency of the output variable signal and the resonance frequency signal is an integral multiple of the frequency of the output frequency signal. It is characterized by that.

  In the above high-voltage power supply device, the plurality of loads are charging devices provided for each color of a multicolor image formed by the image forming apparatus.

  According to the first aspect of the present invention, it is possible to provide a high voltage power supply device that can reduce the influence of noise and can stably supply power.

  According to the second aspect of the present invention, stable power supply can be performed.

  According to the third aspect of the present invention, it is possible to stably supply power to a plurality of charging devices provided in the image forming apparatus.

It is a block diagram which shows the structure of a high voltage power supply device. It is a circuit diagram which shows the structure of a sawtooth wave generation circuit. It is a figure for demonstrating the modulation method of a high frequency modulation circuit. It is a circuit diagram which shows the circuit structure of a high voltage power supply part.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 shows a configuration of an embodiment in which the present invention is applied to a high voltage power supply device mounted on an image forming apparatus. A high-voltage power supply device 1 shown in FIG. 1 is a high-voltage power supply device used in an image forming apparatus that forms a multicolor image of Y (yellow), M (magenta), C (cyan), and K (black). As shown in FIG. 1, the high-voltage power supply device 1 includes a high-voltage power supply unit 1100 and an MCU (machine control unit) 1000 that controls the high-voltage power supply unit 1100 to control the output voltage of the high-voltage power supply unit 1100. One high-voltage power supply unit 1100 is provided for each of Y, M, C, and K colors. In the following description, the high-voltage power supply units for Y, M, C, and K colors are referred to as high-voltage power supply units 1100Y, 1100M, 1100C, and 1100K, respectively. If not, it is represented as a high voltage power supply unit 1100. FIG. 1 shows a detailed configuration of the high-voltage power supply unit 1100Y, and the other high-voltage power supply units 1100M, 1100C, and 1100K are the same as those of the high-voltage power supply unit 1100Y, and are omitted.

The high voltage power supply unit 1100Y includes an AC voltage output unit 1200 and a DC voltage output unit 1250. The AC voltage output unit 1200 includes an analog voltage conversion circuit 1201, an error amplification amplifier (simply abbreviated as “amplifier” in FIG. 1) 1202, a first low-pass filter 1203, a sawtooth wave generation circuit 1204, and high-frequency modulation. A circuit 1205, a field effect transistor (FET) drive circuit 1206, a switch circuit (hereinafter abbreviated as SW) 1207, a second low-pass filter 1208, a transformer 1209, and an output current detection circuit 1210. Yes.
Note that the configuration of the DC voltage output unit 1250 is omitted in FIG.

The analog voltage conversion circuit 1201 receives an AC output variable signal sent from the MCU 1000. In FIG. 1, a wiring for transmitting an AC output variable signal from the MCU 1000 to the analog voltage conversion circuit 1201 is indicated by a wiring A (the same applies to the analog voltage conversion circuit 1201 of other colors (M, C, K)). ). This AC output varying signal is a PWM (Pulse Width Modulation) signal. The AC output varying signal is a signal that determines the current value of the AC output (sine wave) that is the output of the transformer 1209, and is a signal whose on-duty changes between 3% and 100%, for example.
The analog voltage conversion circuit 1201 receives an AC output variable signal, and receives an analog voltage signal (hereinafter referred to as an analog voltage) corresponding to the duty ratio of the input AC output variable signal (duty ratio between on-duty and off-duty). Signal). For example, when the reference voltage used for voltage conversion by the analog voltage conversion circuit 1201 is 5 [V], if the on-duty of the AC output variable signal is 25%, 5 [V] × (25/100) = 1. If the on-duty is 50%, the analog voltage signal is 5 [V] × (50/100) = 2.5 [V]. The analog voltage conversion circuit 1201 sends the generated analog voltage signal to the error amplification amplifier 1202.

The error amplification amplifier 1202 inputs an analog voltage signal output from the analog voltage conversion circuit 1201. Further, the error amplification amplifier 1202 receives the voltage signal output from the output current detection circuit 1210. The output current detection circuit 1210 receives the AC output (sine wave) output from the transformer 1209, detects the input AC output current, and generates a voltage signal obtained by converting the detected current into a voltage value.
The error amplification amplifier 1202 calculates an error between the analog voltage signal input from the analog voltage conversion circuit 1201 and the voltage signal input from the output current detection circuit 1210, and generates an error amplification signal obtained by amplifying the calculated error. Output to the first low-pass filter 1203.

The first low-pass filter 1203 receives an output frequency signal supplied from the MCU 1000. In FIG. 1, a wiring for transmitting an output frequency signal from the MCU 1000 to the first low-pass filter 1203 is indicated by a wiring B (the same applies to the first low-pass filter 1203 of other colors (M, C, K)). The first low-pass filter 1203 receives the error amplification signal supplied from the error amplification amplifier 1202. The output frequency signal is a rectangular waveform and is a signal that determines the frequency of the AC output output from the transformer 1209. The frequency of the output frequency signal matches the frequency of the AC output output from the transformer 1209. The duty of the output frequency signal is fixed at 50%.
The first low-pass filter 1203 includes a coupling capacitor, inputs a rectangular waveform output frequency signal, and extracts an AC component of the output frequency signal by capacitor coupling. The first low-pass filter 103 filters the output frequency signal, outputs the low-frequency component of the output frequency signal that has become an AC component to the output side of the first low-pass filter 103, and the high-frequency component of the output frequency signal. Is generated to generate a sine wave signal that matches the frequency of the output frequency signal. The error amplification signal supplied from the error amplification amplifier 1202 is used to determine the potential difference (Vp-p) between the peaks (pp) of the sine wave signal. The first low pass filter 103 outputs the generated sine wave signal to the high frequency modulation circuit 1205.

The sawtooth wave generation circuit 1204 receives a resonance frequency signal from the MCU 1000 and converts the resonance frequency signal into a sawtooth wave signal. In FIG. 1, a wiring for transmitting a resonance frequency signal from the MCU 1000 to the sawtooth wave generation circuit 1204 is indicated by a wiring C (the same applies to the sawtooth wave generation circuit 1204 of other colors (M, C, K)). ). The resonance frequency signal is a signal that determines the frequency of the modulated wave signal (control signal) generated by the high frequency modulation circuit 1205 modulating the resonance frequency signal. Note that the sawtooth wave generation circuit 1204 that generates the sawtooth wave signal is not particularly limited, and a generally known sawtooth wave generation circuit can be used.
FIG. 2 shows an example of the sawtooth wave generation circuit 1204. A sawtooth wave generation circuit 1204 shown in FIG. 2 includes a transistor Tr1 and a resistor R1 connected in series to a wiring 100 connected to a reference voltage (in this embodiment, 5 V, and expressed as Vref in FIG. 2). The transistor Tr2, the transistor Tr3, and the capacitor C connected in series are connected to each other. The emitter of the transistor Tr1 is connected to the wiring 100, and the collector is connected to the resistor R1. Further, the other end of the resistor R1 having one end connected to the transistor Tr1 is grounded. The emitter of the transistor Tr2 is connected to the wiring 100, and the collector is connected to the emitter of the transistor Tr3. The collector of the transistor Tr3 is connected to the capacitor C. The other end of the capacitor C that connects one end to the collector of the transistor Tr3 is grounded. Further, the bases of the transistor Tr1 and the transistor Tr2 are connected by a wiring 101, and the collector of the transistor Tr2 and the wiring 101 are connected by a wiring 102. The base of the transistor Tr3 is connected to the connection point between the transistor Tr1 and the resistor R1. Further, the connection point between the transistor Tr3 and the capacitor C and the collector of the transistor Tr4 are connected by the wiring 104, and the output terminal of the sawtooth wave generation circuit 1204 is connected to the wiring 104. Further, a resonance frequency signal sent from the MCU 1000 is applied to the base of the transistor Tr4.

  The sawtooth wave generation circuit 1204 shown in FIG. 2 constitutes a constant current circuit by transistors Tr1, Tr2, Tr3. The rise timing of the sawtooth wave signal is determined by the time constant of the resistor R1 connected in series to the transistor Tr1 and the capacitor C connected in series to the transistor Tr3, and the rise of the resonance frequency signal applied to the base of the transistor Tr4. When the transistor Tr4 is turned on by the falling edge, the falling timing of the sawtooth signal is determined.

The high frequency modulation circuit 1205 receives the sine wave signal output from the first low-pass filter 1203 and the sawtooth wave signal output from the sawtooth wave generation circuit 1204. FIG. 3 shows signal waveforms of a sine wave signal and a sawtooth wave signal input to the high frequency modulation circuit 1205 and a signal waveform of the modulation wave signal generated by the high frequency modulation circuit 1205. A signal indicated by a dotted line in FIG. 3 is a sawtooth signal. Moreover, the sine wave signal has shown the signal waveform for the half period of a sine wave signal.
The frequency of the modulated wave signal generated by the high frequency modulation circuit 1205 matches the frequency of the sawtooth wave signal. The on-duty of the modulated wave signal is minimized when the amplitude of the sine wave signal is maximized on the plus side, and is maximized when the amplitude of the sine wave signal is maximized on the minus side. The high frequency modulation circuit 1205 outputs the generated modulated wave signal to the SW circuit 1207.

  The FET drive circuit 1206 inputs the modulation wave signal generated by the high frequency modulation circuit 1205. The FET drive circuit 1206 turns on the switch of the SW circuit 1207 in synchronization with the rising edge of the input modulation wave signal, and turns off the switch of the SW circuit 1207 in synchronization with the falling edge of the modulation wave signal.

  The SW circuit 1207 is a switching element composed of an FET. The SW drive 1207 is intermittently switched by the FET drive circuit 1206, thereby switching the voltage applied to the primary winding of the transformer 1209. The 24V voltage switched by the SW circuit 1207 is increased by the transformer 1209 and output to the secondary winding of the transformer 1209.

  The second low-pass filter 1208 blocks the high frequency component of the 24V voltage switched by the SW circuit 1207 and supplies the low frequency component to the primary winding of the transformer 1209.

  FIG. 4 shows an example of a detailed circuit configuration of the high-voltage power supply unit 1100Y shown in FIG. The description of the configuration of the high-voltage power supply unit 1100Y is omitted because it is a generally known configuration. 4 also shows the configuration of the DC voltage output unit 1250 that is not shown in FIG. The DC voltage output unit 1250 shown in FIG. 4 includes a DA (digital-analog) conversion circuit 1251, an error amplification amplifier 1252, a drive circuit 1253, and a transformer 1254. In FIG. 1, a wiring for transmitting a DC output variable signal input from the MCU 1000 by the DC voltage output unit 1250 to the DC voltage output unit 1250 is indicated by a wiring D (other colors (M, C, K)). The same applies to the DC voltage output unit 1250). The DC output variable signal is a signal that determines the voltage value of the DC output that is the output of the transformer 1254.

An output frequency signal, a resonance frequency signal, an AC output variable signal, and a DC output variable signal are supplied from the MCU 1000 to the high-voltage power supply units 1100Y, 1100M, 1100C, and 1100K. Note that the output frequency signal, the resonance frequency signal, and the AC output variable signal supplied from the MCU 1000 to each of the high voltage power supply units 1100Y, 1100M, 1100C, and 1100K have the same frequency.
The output frequency signal supplied from the MCU 1000 to the high-voltage power supply units 1100Y, 1100M, 1100C, and 1100K, the resonance frequency signal, and the AC output variable signal are set to synchronized frequencies. That is, the frequency of the resonant frequency signal and the AC output variable signal is set to an integral multiple of the output frequency signal having the smallest frequency. When the output frequency signal, the resonance frequency signal, and the AC output variable signal are not synchronized, a plurality of frequencies cause interference, and the AC output waveform output from the transformer 1209 has a low frequency fluctuation. End up. Therefore, in this embodiment, the frequencies of the resonance frequency signal and the AC output variable signal are set to integer multiples of the output frequency signal having the smallest frequency so that each signal does not cause interference.
When the image forming apparatus can change the process speed (the rotational speed of the photosensitive member, that is, the image forming speed), the frequency of the AC output that is the output of the high-voltage power supply unit 1100 according to the change in the process speed, It is also necessary to change the amplitude. The MCU 1000 synchronizes the resonance frequency signal, the AC output variable signal, and the output frequency signal when changing the output frequency signal, the resonance frequency signal, and the AC output variable signal with the change of the process speed. Change the frequency of each signal.
The frequency of the resonance frequency signal is preferably about 50 times the frequency of the output frequency signal. For example, when the frequency of the output frequency signal is 2 [kHz], the frequency of the resonant frequency signal is preferably 100 [kHz].

Further, the high voltage power supply unit 1100 of this embodiment is provided with a sawtooth wave generation circuit 1204 in each of the high voltage power supply units 1100Y, 1100M, 1100C, and 1100K, and generates a sawtooth wave signal in each high voltage power supply unit.
One sawtooth wave generation circuit 1204 is provided for the four high-voltage power supply units 1100Y, 1100M, 1100C, and 1100K, and the sawtooth wave signal generated by the sawtooth wave generation circuit 1204 is converted into Y, M, C, and K. When the power is supplied to the high voltage power supply unit 1100 for each color, the signal line distance for transmitting the sawtooth wave signal becomes long, and the signal line is routed on the circuit board of the high voltage power supply unit 1100. Then, the routed signal line may be close to the 24V power supply line (wiring E shown in FIG. 1) or the ground (GND) line.
In the high frequency modulation circuit 1205 that performs high frequency modulation, an image formed by the image forming apparatus may be deteriorated by noise incident from the outside. For example, when noise such as RFI (Radio Frequency Interference) noise enters the apparatus from outside, there is a possibility that this noise will enter the high-voltage power supply unit 1100 through the 24V power supply line or the ground line. There is. When noise is connected to a sawtooth wave signal line arranged close to a 24V power supply line or a ground line, and noise is superimposed on the sawtooth wave signal, the high voltage power supply unit 1100 of the present embodiment particularly performs high frequency modulation. Since the circuit 1205 performs modulation while comparing the sawtooth signal and the sine wave signal, an abnormality occurs in the modulation of the high frequency modulation circuit 1205, and the waveform of the sine wave signal output from the second low-pass filter 1208 is distorted. Arise. For this reason, the charging device cannot be charged normally, and image quality may be deteriorated.
Therefore, in this embodiment, each of the high-voltage power supply units 1100Y, 1100M, 1100C, and 1100K is provided with a sawtooth wave generation circuit 1204, and the sawtooth wave generation circuit 1204 is connected to the high frequency modulation circuit 1205 as shown in FIG. By arranging it in the vicinity, the line length of the signal line for transmitting the sawtooth wave signal from the sawtooth wave generation circuit 1204 to the high frequency modulation circuit 1205 is made as short as possible so that the high frequency modulation circuit 1205 is not affected by noise. Yes.

  The embodiment described above is a preferred embodiment of the present invention. However, the present invention is not limited to this, and various modifications can be made without departing from the scope of the present invention.

1000 MCU
DESCRIPTION OF SYMBOLS 1100 High voltage power supply part 1200 AC voltage output part 1201 Analog voltage conversion circuit 1202 Error amplification amplifier 1203 1st low pass filter 1204 Sawtooth wave generation circuit 1205 High frequency modulation circuit 1206 FET drive circuit 1207 Switch circuit 1208 2nd low pass filter 1209 Transformer 1210 Output Current detection circuit 1250 DC voltage output section

Claims (3)

A high-voltage power supply device that supplies power to a plurality of loads included in the image forming apparatus,
A transformer, a switching element that switches a voltage applied to a primary winding of the transformer, a high-frequency modulation circuit that generates a control signal that controls a switching operation of the switching element, and a control signal supplied from the high-frequency modulation circuit In accordance with the drive circuit for switching on and off the switching element and a resonance frequency signal for determining the frequency of the control signal are input from the control means of the high-voltage power supply device, and the resonance frequency signal is converted into a sawtooth signal A plurality of high-voltage power supply units each including a first conversion circuit that performs the plurality of loads,
The first conversion circuit is disposed in the vicinity of the high-frequency modulation circuit, and the wiring length of the wiring for transmitting the sawtooth signal supplied from the first conversion circuit to the high-frequency modulation circuit is shortened. High voltage power supply. An output frequency signal for controlling the frequency of the AC output output from the secondary winding of the transformer, the resonance frequency signal, and an output variable signal for controlling the current value of the AC output are the plurality of high-voltage power supply units. And the control means for controlling the AC output,
The high-voltage power supply unit includes: current detection means for detecting a current value of the AC output; a voltage value obtained by converting the current value of the AC output detected by the current detection means into a voltage; and the output variable signal. An error amplifier that obtains and amplifies an error, an error signal output from the error amplifier, and the output frequency signal are input, and the output frequency signal has a frequency that matches the frequency of the output frequency signal, and the amplitude is the error. A second conversion circuit for converting into a sine wave signal having an amplitude set based on the signal,
The high frequency modulation circuit compares the signal level of the sine wave signal supplied from the second conversion circuit and the sawtooth wave signal, the frequency matches the frequency of the sawtooth wave signal, and the sine wave Generating the on-duty control signal according to the amplitude of the signal and supplying it to the drive circuit;
2. The high-voltage power supply apparatus according to claim 1, wherein the frequency of the output variable signal and the resonance frequency signal is an integral multiple of the frequency of the output frequency signal.   The high-voltage power supply device according to claim 1, wherein the plurality of loads are charging devices provided for each color of a multicolor image formed by the image forming apparatus.

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