JP2005217833A - Ac power supply and image-forming apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To allow the effective value of pseudo sinusoidal waves to be changed for reducing costs in an AC power supply used in the electrification bias generation circuit of an electronic photograph, a development bias generation circuit, and the like. <P>SOLUTION: Signals S1, S2 are created from a continuous rectangular wave pulse from a signal source, where the signals S1, S2 have the active period of 1/4 cycles in a logic circuit, have the non-active period of 1/4 cycle during the active period, and mutually deviate in the active period. The signals S1, S2 are given to the bases of transistors Q1, Q2 mutually connected in series between DC power supply lines each. The potential of a node when the transistors Q1, Q2 are off is determined by resistors R1, R2 mutually connected in series between the DC power supply lines. Therefore, step-wise pseudo sinusoidal waves are outputted from the node in a simple configuration. An effective value of the pseudo sinusoidal waves are changed by changing a balance between resistors R1, R2 and the duty of the rectangular pulse. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AC power source suitably implemented in a copying machine, a facsimile machine, a printer, and the like and an image forming apparatus using the AC power source. .

  In the electrophotographic image forming apparatus, a voltage obtained by superimposing an AC voltage on a DC voltage is used as a charging bias and a developing bias for toner activation and the like. As such an AC voltage, it is common to use a rectangular wave. This is because it can be generated with a relatively low cost configuration and it is relatively easy to change the effective value by changing the duty.

  However, when a high voltage of a rectangular wave is applied to the charging roller or the developing roller (magnet roller), discharge is likely to occur between the photoconductor adjacent to the roller due to steep voltage fluctuations, and printing occurs due to noise accompanying the discharge. There is a problem that malfunction occurs inside or the photoreceptor is damaged.

  Further, the charger is also subjected to contact charging by a sponge-like charging roller in order to suppress the generation of ozone, and the same problem occurs.

  Therefore, in order to solve such a problem, by using a sine wave instead of the rectangular wave, it is possible to reduce the resonance sound even if the AC frequency is the same. As an AC power source that can obtain the sine wave at a relatively low cost, a Wien bridge, an analog oscillation circuit such as a two-phase oscillation circuit as shown in FIG. 6, a digital / analog conversion circuit as shown in FIG. As shown in Patent Document 1, a filter that shapes the rectangular wave may be considered.

  FIG. 6 is a block diagram showing a configuration example of the two-phase oscillation circuit. In this two-phase oscillation circuit, two operational amplifiers a1 and a2 are connected in series, and a sine wave signal is created by applying positive feedback. The obtained sine wave signal is amplified by a power amplifying amplifier a3. The power is amplified and applied to the primary side coil of the high voltage transformer t so as to obtain a high voltage alternating current from the secondary side coil. The generated high-voltage alternating current is superimposed on a direct-current voltage from a direct-current power source (not shown) to become the charging bias or the developing bias. In this two-phase oscillation circuit, the oscillation frequency of the sine wave signal is determined by the values of C and R, and the amplitude fluctuation is suppressed by the Zener diode.

  FIG. 7 shows an oscillation circuit using the digital / analog conversion circuit. In this digital / analog conversion circuit 71, a clock and data are inputted to a decoder 72, and the switch circuit 73 corresponds to the data every clock cycle. Are sequentially switched, so that the reference voltage Vref is supplied to the power amplifying amplifier a3 through a resistor r having different resistance values and is supplied to the power amplification amplifier a3. output to t.

Furthermore, Patent Document 1 discloses that a rectangular wave clock signal is directly filtered into a sine wave, a trigger signal having an arbitrary divided frequency is created by a frequency divider and a PLL, and the sine wave signal is used as a trigger signal. A sine wave oscillation circuit is shown in which a sine wave signal having an arbitrary frequency that is the difference between a sine wave signal and a trigger signal is generated from a fixed frequency clock by sampling after sampling at the timing.
Japanese Patent No. 3217881

  Since the conventional technology shown in FIG. 6 is an analog oscillation circuit, in order to stabilize the oscillation frequency, a film capacitor having a small tolerance must be used as a circuit component, particularly a capacitor, and the oscillation amplitude also varies. Therefore, a means for making the amplitude constant, such as the Zener diode, is necessary, and there is a problem that the cost increases.

  Also in the prior art shown in FIG. 7, a circuit for high-speed digital / analog conversion is required, which increases the cost. Further, instead of using a dedicated conversion element, it is possible to perform digital / analog conversion simply by using a counter or a multiplexer as in the digital / analog conversion circuit 1, but the duty, that is, the effective value is set. It cannot change.

  Furthermore, the prior art disclosed in Patent Document 1 requires a frequency divider, PLL, and the like, which increases the cost.

  An object of the present invention is to provide an AC power source that can change the effective value of a pseudo sine wave and reduce the cost, and an image forming apparatus using the AC power source.

  The AC power supply according to the present invention includes a signal source that generates continuous rectangular wave pulses and a start of a cycle within a predetermined cycle period in which the active periods are shifted from each other and the rectangular wave pulses from the signal source are thinned out. Alternatively, a logic circuit that creates a plurality of frequency-divided signals having inactive periods at the end and the center, and a plurality of frequency-divided signals that are connected in series between the DC power supply lines and that are input to the control input terminals, respectively. The switching elements and the DC power supply lines are connected in series with each other, and their connection points are connected to intermediate connection points of the switching elements, and the intermediate connection points when the plurality of switching elements are off. And two sets of impedance elements that determine the potential of the current.

  According to the above configuration, when, for example, two switching elements are connected between the DC power supply lines, the high-side switching element and the low-side switching element have a mutual active period created by the logic circuit. They are driven by frequency-divided signals having inactive periods at the beginning or end of the period and at the center, within a predetermined period period.

  Therefore, the potential of the connection point is substantially equal to the high-side potential of the DC power source, for example, Vcc, during the on-period of the high-side switching element, and the DC power source during the on-period of the low-side switching element. Of the DC power source when the potentials defined by the two sets of impedance elements, for example, the impedances are equal to each other during the switching period in which both of the potentials are low, for example, GND. 2 potential, equal to Vcc / 2.

  Thereby, a step-like pseudo sine wave can be output from the intermediate connection point. The effective value of the pseudo sine wave can be changed by changing the impedance balance of the impedance element and the duty of the rectangular wave pulse. Further, such an AC power supply can be realized not by a complicated configuration such as an operational amplifier but by a simple configuration mainly of a logic circuit and a switching element such as a transistor.

  In the AC power supply according to the present invention, the switching elements are in two sets, and the frequency-divided signals input to the control input terminals have an active period of ¼ period and 1 between them. / 4 period of inactive period, and the impedance of the two sets of impedance elements is equal to each other.

  According to the above configuration, for example, when the high-side potential of the DC power supply is Vcc and the low-side potential is GND, the connection point includes approximately Vcc → Vcc / 2 → approximately GND → Vcc / 2 → approximately The potential of Vcc → Vcc / 2 →... Is sequentially generated every quarter cycle.

  Therefore, a pseudo sine wave closest to the sine wave can be generated.

  Furthermore, in the AC power supply of the present invention, the switching elements are in two sets, and the frequency-divided signals respectively input to the control input terminals have an active period of ¼ period, It has an inactive period of ¼ period, and the impedance of at least one of the two sets of impedance elements is variable.

  According to the above configuration, for example, when the high-side potential of the DC power supply is Vcc and the low-side potential is GND, the connection point includes approximately Vcc → intermediate potential → approximately GND → intermediate potential → approximately Vcc → An intermediate potential is sequentially generated every quarter cycle. The intermediate potential is Vcc / 2 when the impedances of the two sets of impedance elements are equal to each other, and becomes higher than Vcc / 2 when the low-side impedance increases due to at least one of the variable elements. If the impedance increases, it becomes lower than Vcc / 2.

  Therefore, the effective value of the pseudo sine wave can be arbitrarily changed.

  In the AC power supply of the present invention, the logic circuit includes a frequency divider that divides the rectangular wave pulse from the signal source by 1/2, a signal from the frequency divider, and a rectangular wave from the signal source. A logical product of a first AND gate that obtains a logical product with a pulse and provides an output to a control input terminal of one switching element, an inverted output from the frequency divider, and a rectangular wave pulse from the signal source And a second AND gate for providing an output to the control input terminal of the other switching element.

  According to the above configuration, a logic circuit that can generate two frequency-divided signals each having an active period of ¼ period and an inactive period of ¼ period between each other is simplified. This can be specifically realized with a simple configuration.

  Furthermore, the AC power supply according to the present invention has an operational amplifier to which an output from the connection point is given and negative feedback is performed by a parallel circuit of CR, and an output from the operational amplifier is given to a primary side coil. A high-voltage transformer that induces a high voltage in the coil is provided to generate a charging bias and / or a developing bias in the image forming apparatus.

  According to the above configuration, in the AC power source that generates a high-voltage AC that becomes a charging bias and / or a developing bias of the photosensitive member in the image forming apparatus, the above configuration is used, and an output from the connection point is further provided. By providing an operational amplifier in which negative feedback is performed by a parallel circuit, the stepped pseudo sine wave is shaped to be closer to a sine wave and power is amplified, and the output from the operational amplifier is given to the primary coil. By providing a high voltage transformer, a high voltage for the charging bias and / or developing bias is generated in the secondary coil. Thus, an AC power source that generates a high-voltage AC that becomes a charging bias and / or a developing bias in the image forming apparatus can be realized by the AC power source having a simple configuration as described above.

  In the image forming apparatus of the present invention, the AC power source is used as a power source for generating the charging bias and / or the developing bias.

  According to the above configuration, it is possible to realize an image forming apparatus that generates a high-voltage AC that becomes a charging bias and / or a developing bias with a simple configuration.

  As described above, the AC power supply according to the present invention has the active period deviated from each other by the logic circuit from the continuous rectangular wave pulse from the signal source, and the start or end of the cycle and the center within one predetermined cycle period. A plurality of divided signals having inactive periods are created, and the divided signals are respectively input to the control input terminals of a plurality of switching elements connected in series between the DC power supply lines, and connected in the middle. An output is derived from a point, and the intermediate connection point is connected to a DC power supply line by two sets of impedance elements, thereby determining the potential of the intermediate connection point when the plurality of switching elements are off.

  Therefore, the potential at the connection point is substantially equal to the high-side potential of the DC power source, for example, Vcc, during the ON period of the high-side switching element, and the DC power source during the ON period of the low-side switching element. Of the DC power source when the potentials defined by the two sets of impedance elements, for example, the impedances are equal to each other during the switching period in which both of the potentials are low, for example, GND. A potential of 2 is equal to Vcc / 2, and a stepped pseudo sine wave can be output from the intermediate connection point. The effective value of the pseudo sine wave can be changed by changing the impedance balance of the impedance element and the duty of the rectangular wave pulse. Further, such an AC power supply can be realized not by a complicated configuration such as an operational amplifier but by a simple configuration mainly of a logic circuit and a switching element such as a transistor.

[Embodiment 1]
FIG. 1 is a block diagram showing an electrical configuration of an AC power supply according to an embodiment of the present invention. This AC power supply generally has a signal source 1 that generates a clock signal CLK, which is a continuous rectangular wave pulse, and an active period that is shifted from the pulse of the clock signal CLK from the signal source 1, and Within one predetermined period, a logic circuit 2 for generating two frequency-divided signals S1 and S2 having inactive periods at the beginning or end and the center of the period and a DC power supply line of the power supply voltage Vcc are connected in series with each other. Are connected to each other in series between the DC power supply lines and the connection point between the transistors Q1, Q2 and the transistors Q1, Q2, respectively. Resistors R1 and R2 that are connected to a connection point P1 of Q2 and determine the potential of the connection point P1 when the two transistors Q1 and Q2 are turned off; An amplifier A1 to the waveform shaping as well as the connection point power amplifying stepped pseudo sine wave signal appearing at the P1 to so that, constituted by a high-voltage transformer T to boost the sinusoidal signal from the amplifier A1.

  The logic circuit 2 includes a D flip-flop F and two AND gates G1 and G2. The clock signal CLK from the signal source 1 is supplied to the clock input terminal of the edge trigger of the D flip-flop F and to one input terminal of the two AND gates G1 and G2. An output S3 from the normal output terminal Q of the D flip-flop F is given to the other input terminal of the AND gate G1, and an inverted output terminal / Q (/ of the D flip-flop F is supplied to the other input terminal of the AND gate G2. Represents the output S4). The inverted output S4 of the D flip-flop F is fed back to the data input terminal D of the D flip-flop F.

  Therefore, as shown in FIG. 2, from the clock signal CLK from the signal source 1, the D flip-flop F creates an output S3 divided by 1/2 and outputs it from the normal output terminal Q. An output S4 that is divided by two and inverted is generated and output from the inverted output terminal / Q. Accordingly, as shown in FIG. 2, the AND gates G1 and G2 each have two divided signals S1 having an active period of ¼ period and having an inactive period of ¼ period between each other. , S2 is created.

  On the other hand, in the two transistors Q1 and Q2 connected in series between the DC power supply lines, the high-side transistor Q1 is a PNP type, and the low-side transistor Q2 is an NPN type. For this reason, an NPN transistor Q3 and bias resistors R11 and R12 for inverting the polarity of the divided signal S1 are provided in association with the transistor Q1. The frequency-divided signal S1 is applied to the base of the transistor Q3 via a resistor R21, the emitter of the transistor Q3 is connected to GND, the collector is connected to the base of the transistor Q1 via a resistor R12, and the transistor The base of Q1 is pulled up to the power supply voltage Vcc by a resistor R11. On the other hand, the frequency-divided signal S2 is given to the base of the transistor Q2 via the resistors R22 and R23.

  The emitter of the transistor Q1 is connected to the high-side power supply line of the power supply voltage Vcc, the emitter of the transistor Q2 is connected to GND which is the low-side power supply line, and between the collector-emitter of these transistors Q1 and Q2. Are connected to the resistors R1 and R2, respectively, and the connection point P1 between the collectors serves as an output terminal. Accordingly, as shown in FIG. 2, the output S5 from the connection point P1 is generated in order of approximately Vcc → intermediate potential → approximately GND → intermediate potential → approximately Vcc → intermediate potential →. It becomes a stepped waveform. The intermediate potential is Vcc / 2 when the resistance values of the two resistors R1 and R2 are equal to each other. When the resistance value of the low-side resistor R2 is increased by at least one of the resistances, the intermediate potential is higher than Vcc / 2. As the resistance value of the high-side resistor R1 increases, the value becomes lower than Vcc / 2.

  The output S5 from the connection point P1 is given to the inverting input terminal of the amplifier A1 through a DC cut coupling capacitor C1 and a resistor R3. The amplifier A1 is driven by the power supply voltage Vcc, and the power supply voltage Vcc is divided and applied to non-inverting input terminals by resistors R6 and R5 connected in series between the DC power supply lines. , The operating point is set. The output of the amplifier A1 is negatively fed back through a parallel circuit of a capacitor C2 and a resistor R4. Therefore, the stepped output S5 from the connection point P1 is waveform-shaped as shown in FIG. 2 and the power amplified output S6 is output from the amplifier A1.

  The output S6 from the amplifier A1 is input to the primary winding of the high-voltage transformer T via a DC-cut coupling capacitor C3, and the secondary winding receives a high-voltage AC boosted by a turns ratio. Can be obtained. The generated high-voltage alternating current is superimposed on a direct-current voltage from a direct-current power source (not shown) to become the charging bias or the developing bias.

  Therefore, the charging bias and the developing bias swing in the positive direction and the negative direction around the DC bias voltage, and the peak value, area ratio, frequency, and the like greatly affect the image quality. Therefore, it is necessary to adjust them. First, the peak value can be adjusted by adjusting the amplification factor of the amplifier A1 according to the resistance ratio of the resistors R3 and R4. For example, the peak value is increased by decreasing the resistance R3 and increasing the resistance R4.

  Next, as described above, the ratio between the positive direction and the negative direction of the amplitude corresponding to the duty ratio of the rectangular wave can be adjusted by the resistance ratio of the resistors R1 and R2. If these resistors R1 and R2 have the same resistance value, the output S5 from the connection point P1 and the output S6 that has been waveform-shaped and amplified by the amplifier A1 are as shown in FIG. That is, a pseudo sine wave closest to the sine wave can be generated.

  On the other hand, if the resistance value of the resistor R2 is higher than that of the resistor R1, the voltage at the connection point P1 when the transistors Q1 and Q2 are turned off increases, and the outputs S5 and S6 are shown in FIG. As shown in On the other hand, if the resistance value of the resistor R1 is higher than that of the resistor R2, the voltage at the connection point P1 when the transistors Q1 and Q2 are off becomes lower, and the outputs S5 and S6 are as shown in FIG. become. In this way, a desired peak value or area ratio can be set.

  In this way, a pseudo sine wave is generated using the logic circuit 2 and the transistors Q1 to Q3 having a simple configuration, and the effective value is changed even though the DC power supply voltage is a single power supply with only Vcc. An AC power supply that can be made to be realized can be realized. In addition, an AC power source that generates a high-voltage AC that becomes a charging bias and / or a developing bias in the image forming apparatus can be realized by an AC power source having a simple configuration as described above.

[Embodiment 2]
FIG. 4 is a block diagram showing an electrical configuration of a developing bias generation circuit according to another embodiment of the present invention. The developing bias generation circuit is similar to the AC power source shown in FIG. 1 described above, and corresponding portions are denoted by the same reference numerals and description thereof is omitted. It should be noted that in this development bias generation circuit, a series circuit of a transistor Q4 and a resistor R2a is used instead of the resistor R2, and the AC / AC ratio is changed by an external control signal CTL to change the resistance ratio. This means that the peak value and area ratio of the waveform are variable. Thereby, for example, in the case of the developing bias, the print density can be changed.

  Specifically, the output S6 of the amplifier A1 is taken out via the coupling capacitor C4, rectified by the diodes D1 and D2, and smoothed by the capacitor C5. The capacitor C5 is provided with a discharging resistor R7 in parallel. The charging voltage of the capacitor C5 is taken out by the resistor R8 and applied to the inverting input terminal of the operational amplifier OP. The control signal CTL is supplied to the non-inverting input terminal of the operational amplifier OP via a resistor R31. The output of the operational amplifier OP is given to the base of the transistor Q4 through the resistors R32 and R33, and negatively fed back to the inverting input terminal by the series circuit of the resistor R34 and the capacitor C31.

  On the secondary side of the high-voltage transformer T, one terminal is connected to GND through a parallel circuit of a capacitor C41 and a resistor R41, and the other terminal is connected from a diode D41 having the other terminal side as a cathode to a capacitor C42 and The resistor R42 is connected to GND through a parallel circuit. The voltage at the other terminal is taken out via the resistor R43, and becomes the bias voltage VB used as the developing bias.

  Therefore, as shown in FIG. 5, the higher the control signal CTL, the higher the reference input of the operational amplifier OP, the higher the base voltage of the transistor Q4, and the voltage at the connection point P1 when the transistors Q1 and Q2 are off. Becomes lower. As a result, the duty of the current I41 flowing through the diode D41 decreases, and the charging voltage VC41 of the capacitor C41 obtained by smoothing the voltage generated by I41 × R41 by the capacitor C41 also decreases. The charging voltage VC41 of the capacitor C41 becomes a DC voltage superimposed on the AC voltage induced on the secondary side of the high voltage transformer T.

  Accordingly, the print density can be adjusted by activating the toner with the AC voltage and changing the DC voltage with the control signal CTL.

It is a block diagram which shows the electric constitution of the alternating current power supply of one Embodiment of this invention. It is a wave form diagram for demonstrating operation | movement of the alternating current power supply shown in FIG. It is a wave form diagram for demonstrating other operation | movement of the alternating current power supply shown in FIG. It is a block diagram which shows the electric constitution of the developing bias generation circuit of the other embodiment of this invention. FIG. 2 is a waveform diagram for explaining the operation of the development bias generation circuit shown in FIG. 1. It is a block diagram which shows one structural example of a two-phase oscillation circuit. It is a block diagram which shows one structural example of the oscillation circuit by a digital / analog converting circuit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Signal source 2 Logic circuit A1 Amplifier C1, C3, C4 Coupling capacitor C2, C5 Capacitor C31, C41 Capacitor D1, D2 Diode FD flip-flop G1, G2 AND gate Q1, Q2 Transistor (switching element)
Q3 Transistor Q4 Transistor (impedance element)
R1, R2, R2a Resistance (impedance element)
R3 to R8 Resistors R11 and R12 Bias resistors R22 and R23 Resistors R31 to R34, R41 to R43 Resistors T High voltage transformer

Claims (6)

A signal source for generating a continuous square wave pulse;
A plurality of frequency-divided signals having inactive periods at the beginning or end of the period and at the center are generated within one cycle period determined by deciphering rectangular wave pulses from the signal source. Logic circuit;
A plurality of switching elements connected in series with each other between the DC power supply lines, and the divided signals are respectively input to the control input terminals;
The DC power supply lines are connected in series with each other, and their connection points are connected to intermediate connection points of the switching elements, and determine the potential of the intermediate connection points when the plurality of switching elements are off. An AC power supply comprising two sets of impedance elements. There are two sets of the switching elements, and the frequency-divided signals respectively input to the control input terminals have an active period of ¼ period and an inactive period of ¼ period between them. Have
The AC power supply according to claim 1, wherein impedances of the two sets of impedance elements are equal to each other. There are two sets of the switching elements, and the frequency-divided signals respectively input to the control input terminals have an active period of ¼ period and an inactive period of ¼ period between them. Have
The AC power supply according to claim 1, wherein the impedance of at least one of the two sets of impedance elements is variable. The logic circuit is:
A frequency divider for dividing the rectangular wave pulse from the signal source by 1/2;
A first AND gate that obtains a logical product of a signal from the frequency divider and a rectangular wave pulse from the signal source and provides an output to a control input terminal of one switching element;
A second AND gate that obtains a logical product of the inverted output from the frequency divider and the rectangular wave pulse from the signal source and supplies the output to the control input terminal of the other switching element; The AC power supply according to claim 2 or 3, wherein An operational amplifier which is provided with an output from the connection point and performs negative feedback by a parallel circuit of CR;
An output from the operational amplifier is provided to the primary coil, and a high voltage transformer that induces a high voltage in the secondary coil,
5. The AC power supply according to claim 1, wherein a charging bias and / or a developing bias is generated in the image forming apparatus.   An image forming apparatus using the AC power source according to claim 5 as a power source for generating the charging bias and / or the developing bias.

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