JP4480682B2 - High voltage generation circuit - Google Patents

Description

  The present invention relates to a high voltage generating circuit that applies an oscillating voltage in which a DC voltage and an AC voltage are superimposed on a charging member arranged in contact with or close to an image carrier.

  In recent years, from the viewpoint of low pressure process, low ozone generation, low cost, etc., a charging member such as a roller type or a blade type is arranged in contact with or close to the surface of the image carrier, and a DC voltage and an AC voltage are applied to the charging member. Image forming apparatuses employing a contact charging method that uniformly charges the surface of an image carrier by applying a superposed vibration voltage are becoming mainstream. Here, the vibration voltage is not limited to a sine wave, but may be any vibration waveform that changes periodically, such as a rectangular wave, a triangular wave, and a pulse wave.

  When such a contact charging method is employed in a tandem color image forming apparatus provided with different image carriers corresponding to the four colors of YMCK, a high-voltage DC voltage and an AC voltage are generated on each charging member. Each of the transformers must be provided, which increases the number of parts, which increases the cost and reduces the mounting efficiency of the parts.

  Therefore, in Patent Document 1, in order to improve the mounting efficiency of components on a printed wiring board and realize an inexpensive power supply device, a single DC power supply circuit that outputs a high-voltage DC by a converter transformer, and the DC power supply The voltage value of the DC output from the circuit is converted using a separate high voltage transistor inserted in series between the DC power supply circuit and the corresponding load, and high voltage generation is provided with voltage conversion means for supplying to each load A circuit has been proposed.

JP 2002-162870 A

  However, in order to control the charging potential to each image carrier, it is necessary to measure the current between each charging member and the image carrier to control the DC output voltage. The technique described in Patent Document 1 described above is used. When used in a high voltage generation circuit applied to a charging member, a current detection circuit must be provided separately, and there is an inconvenience that the same problem of increased cost and reduced mounting efficiency due to an increase in the number of component circuits occurs. There was room for further improvement.

  In view of the above-described conventional problems, the object of the present invention is to improve the mounting efficiency of components on a printed wiring board while providing a common current detection circuit for appropriately controlling charging of a plurality of image carriers. And providing a high voltage generation circuit that can be realized at low cost.

In order to achieve the above-mentioned object, the first characteristic configuration of the high-voltage generating circuit according to the present invention is arranged in contact with or in close proximity to a plurality of image carriers, respectively , as described in claim 1 of the claims. a high voltage generation circuit to which a DC voltage and an AC voltage is applied an oscillating voltage which is superimposed on the charging member to each other with a plurality of linear DC regulator for generating a DC voltage applied to each charging member, the secondary-side terminal A single DC transformer in which each linear DC regulator is connected in parallel, one terminal on the secondary side is connected to each charging member, and the other terminal is connected to the output terminal of each linear DC regulator, to each charging member a plurality of AC transformer for generating an AC voltage applied to, and a single current detection circuit for detecting a DC current flowing through the direct current transformer, the other outputs except one of each linear DC regulators Adjusted to a lower pressure than the discharge starting voltage, an operation of detecting a DC current flowing through said image bearing member through a specific charging member from a linear DC regulator discharge starting voltage or higher is outputted by the current detecting circuit By repeating for each charging member, a direct current flowing from each charging member to the image carrier is individually detected.

  According to the above-described configuration, when detecting a direct current between a specific charging member and the image carrier, corresponding linear direct current regulators are prevented so that no direct current flows between the other charging member and the image carrier. Thus, the DC voltage is adjusted to be lower than the discharge start voltage, so that the specific DC current value can be detected by the current detection circuit. Therefore, it is not necessary to provide each of the current detection circuits corresponding to the number of the image carriers, so that an increase in cost can be suppressed and mounting efficiency can be increased.

In the second characteristic configuration, as described in claim 2, in addition to the first characteristic configuration described above, each linear DC regulator includes a pass transistor that controls the output voltage of the DC transformer, and a step-down voltage. A power supply circuit is provided that includes an operational amplifier that feedback-controls the base current of the pass transistor so as to achieve a target voltage, and that supplies a control power to each linear DC regulator from the secondary side output or the tertiary side output of the DC transformer. It is in the point.

  In general, a linear DC regulator is composed of an operational amplifier and a pass transistor driven by the output of the operational amplifier, and the output voltage to the load is controlled by controlling the base current of the pass transistor using the pseudo-short characteristic of the operational amplifier. In this case, when the driving power of the operational amplifier is supplied from the outside, the base current of the pass transistor is supplied from the external power, and the current value detected by the current detection circuit due to the influence is supplied. Will not be detected correctly. According to the above configuration, since the base current input to the pass transistor for adjusting the output voltage of the linear DC regulator is supplied from the secondary side output or the tertiary side output of the DC transformer, it is supplied from the external power source. The direct current between the charging member connected to the secondary side of the direct current transformer and the image carrier can be accurately detected without being affected by the base current generated when the image is carried.

In the third feature configuration, as described in claim 3, in addition to the first feature configuration described above, each linear DC regulator includes a pass transistor that controls the output voltage of the DC transformer, and a step-down voltage. It is constituted by an operational amplifier for feedback controlling the base current of the pass transistor so that the target voltage, the pass transistor is in that it is Darlington connected.

  By connecting the pass transistor of the linear DC regulator with a Darlington connection, a large current amplification factor can be secured as compared with a configuration including a single pass transistor, so even when the base current of the pass transistor is supplied from an external power source. The output voltage of the linear DC regulator can be adjusted with a small base current. Therefore, according to the above-described configuration, even if the driving power of the operational amplifier is supplied from the outside, the current detection circuit can detect the direct current almost accurately.

  As described above, according to the present invention, while providing a common current detection circuit used to appropriately charge-control a plurality of image carriers, the mounting efficiency of components on a printed wiring board is improved. In addition, it has become possible to provide a high voltage generating circuit that can be realized at low cost.

  Hereinafter, the high voltage generating circuit according to the present invention will be described. As shown in FIG. 1, the high voltage generating circuit 1 is a direct current applied to a charging member CH formed of a charging roller arranged in contact with or close to four image carriers PC that form four color toner images of YMCK. A single DC transformer for generating an oscillating voltage in which a voltage and an AC voltage are superimposed, wherein a shunt regulator 20 as a linear DC regulator corresponding to the number of image carriers PC is connected in parallel on the secondary side. 10, an AC transformer 30 corresponding to the number of the image carriers PC in which outputs of the shunt regulators 20 are separately connected to the secondary side, and a charging member CH connected to the secondary side of the DC transformer 10. It comprises a single current detection circuit 40 for detecting a direct current between the image carriers PC.

  As shown in FIG. 2, a pulse signal from a pulse signal generating means that outputs a pulse signal based on a remote drive signal input from the control unit CNT is input to the primary side of the DC transformer 10 and boosted to a predetermined voltage. The high-voltage AC voltage is output from the secondary side, and the high-voltage AC voltage is smoothed by the rectifier circuit including the diode D10 and the capacitor C10, and the high-voltage DC voltage is output from the output terminals t1 and t2. .

  Similar to the above, the pulse signal from the pulse signal generating means for outputting the pulse signal based on the remote drive signal input from the control unit CNT is input to the primary side of the AC transformer 10 and boosted to a predetermined voltage. An AC voltage is output from the secondary side. Here, the high-voltage AC voltage is variably controlled by a pulse signal voltage generated based on a variable analog input voltage input from the control unit CNT to the pulse signal generating means.

  The shunt regulator 20 is connected in four circuits in parallel to the terminals t1 and t2 of the DC transformer 10 so as to supply a DC voltage separately to the charging member CH corresponding to each image carrier PC of YMCK. As shown in FIG. 3, an operational amplifier OP20 as a differential amplifier, a pass transistor Q20 driven by an output current of the operational amplifier OP20, and a Zener diode ZD20 having a breakdown voltage of 250 V connected to the collector of the pass transistor Q20. Etc. are provided.

  A divided voltage obtained by dividing the output voltage of the shunt regulator 20 by resistors R21 and R20 is input to the non-inverting input terminal of the operational amplifier OP20, and a reference voltage is input to the inverting input terminal. Accordingly, a base current is supplied from the operational amplifier OP20 to the pass transistor Q20 so that the reference voltage and the divided voltage are equal. As a result, the output voltage Vdc is adjusted by the current flowing through the resistor R23 and the Zener diode ZD20.

  The reference voltage is variably adjusted by a fixed comparison voltage Vref and a control voltage Vcnt controlled by the control unit CNT, and a direct current applied to each charging member CH by individually adjusting the control voltage Vcnt. The voltage is variably and stably adjusted between 250V and 750V.

  As shown in FIG. 1, the output terminal of the shunt regulator 20 is connected to the secondary terminal of each AC transformer 30 via a bypass capacitor C that bypasses the AC voltage. And an oscillating voltage on which an AC voltage from the AC transformer 30 is superimposed is applied to each charging member CH.

  As shown in FIG. 4, the current detection circuit 40 includes a current / voltage conversion operational amplifier OP41 and an amplification operational amplifier OP40. The inverting input terminal of the operational amplifier OP41 is connected to the secondary low-voltage side terminal t2 of the DC transformer 10, and the non-inverting input terminal receives a voltage obtained by dividing the comparison voltage Vref by the resistors R43 and R44 as a reference voltage. The current value flowing through the feedback resistor R42 is converted into a voltage so that the voltage between the reference voltage and the secondary low-voltage side terminal t2 is equal, and further amplified by the operational amplifier OP40 and then input to the control unit CNT. .

  When the DC current between the specific charging member CH and the image carrier PC is measured by the current detection circuit 40, the outputs of the other shunt regulators 20 except for the shunt regulator 20 corresponding to the specific charging member CH The output of the AC transformer corresponding to the specific charging member CH is adjusted to be lower than the discharge start voltage.

  Specifically, after the control voltage Vcnt of the other three shunt regulators 20 is adjusted to about 250 V lower than the discharge stop level by the control unit CNT and turned off except for one of the AC transformers, The value of the current detection circuit 40 is read. In this way, when detecting a direct current between a specific charging member CH and the image carrier PC, each corresponding shunt regulator is arranged so that no current flows between the other charging member CH and the image carrier PC. Since the voltage is adjusted to be lower than the discharge start voltage by 20 and the AC transformer, the DC current value from the specific charging member CH can be detected by the single current detection circuit 40.

  Based on the DC current value Idc from each charging member CH thus detected, the output of each shunt regulator 20 or the output of each AC transformer 30 is adjusted to be maintained at a predetermined target value.

  In this embodiment, since the base current Ib of the pass transistor Q20 is supplied from an external power source that drives the operational amplifier OP20, the pass voltage is adjusted when the output voltage of the shunt regulator 20 is adjusted to be lower than the discharge start voltage. Due to the influence of the base current flowing into the secondary side of the DC transformer 10 via the transistor Q20, the influence of offset noise appears in the current value detected by the current detection circuit 40. Specifically, the current value detected by the current detection circuit 40 is obtained as Idc-ΣIb.

  The detection of the DC current Idc will be described in detail. In the operational amplifier OP41, each of the DC currents Idc out of the current Iac + Idc between the charging member and the image carrier that has flowed from each of the image carriers to the ground is The control voltage applied to the operational amplifier OP41 flows from the ground side terminal to the output terminal. The DC current ΣIdc, which is the sum of the DC currents Idc, flows to the low-voltage side of the DC transformer 10 via the resistor R42 and forms a DC current component loop of the high-voltage generating circuit 1.

  Of the DC currents ΣIb + ΣIc + ΣIr that is the sum of the DC currents Ib + Ic + Ir flowing from the shunt regulators 20 to the low-voltage side of the DC transformer 10, the drive current ΣIb flows to the ground because it is not output from the DC transformer 10. Further, all of the DC current ΣIdc does not flow from the current detection circuit 40 to the low voltage side of the DC transformer 10, and the DC current ΣIdc−ΣIb is transferred from the current detection circuit 40 to the DC transformer so as to cancel the drive current ΣIb. 10 flows to the low voltage side, and the same ΣIdc + ΣIc + ΣIr as the output current from the high voltage side flows to the secondary low voltage side of the DC transformer 10.

  Here, the high voltage generation circuit 1 is configured to detect the direct current separately by adjusting one of the shunt regulators 20 except for one of the shunt regulators 20 to a voltage lower than the discharge start voltage. Therefore, the DC current Idc flows only from one shunt regulator 20 when the current detection circuit 40 detects the current. That is, the current detection circuit 40 detects the direct current Idc−ΣIb, and cannot accurately detect the direct current Idc.

  If the value of the offset noise is always constant, there is no problem. However, since the current amplification factor of the pass transistor Q20 varies greatly due to the influence of temperature variation, the value of the base current Ib also varies greatly. Become. Due to such temperature characteristics, the current value detected by the current detection circuit 40 may be affected by errors.

  Therefore, as shown in FIG. 5, the pass transistor Q20 is Darlington-connected, and the pass transistor Q20 is driven with the drive current Ib having a small value, that is, the DC current Idc >> ΣIb is set. It becomes possible to reduce the influence of the fluctuation of the base current Ib due to the fluctuation.

  Further, by providing a power supply circuit that supplies control power to each shunt regulator 20 from the secondary side output or the tertiary side output of the DC transformer 10, the influence of the base current Ib can be avoided.

That is, as shown in FIG. 6, a rectifier circuit is provided at the secondary side output or the tertiary side output of the DC transformer 10 to generate a control voltage, and the control voltage is supplied to the operational amplifier OP20 provided in the shunt regulator 20. It is. With this configuration, the influence of offset noise can be eliminated.

  When the pass transistor Q20 of the shunt regulator 20 is Darlington-connected, the present inventors have the DC current Idc− that the drive current Ib of the pass transistor Q20 of one shunt regulator 20 is detected by the current detection circuit 40. It has been confirmed that if it is 5% or less of ΣIb, it can be regarded as within the measurement error range, and the drive current Ib is 5% or less of the DC current Idc−ΣIb, that is, the total ΣIb of all the drive currents is 20 When the drive current Ib can be adjusted to be equal to or less than%, the pass transistor Q20 may be constituted by one transistor.

  In the above-described embodiment, the shunt regulator is provided as the linear DC regulator. However, for example, a series regulator other than the shunt regulator may be provided.

  In the above-described embodiment, the number of image carriers, that is, one high-voltage generation circuit corresponding to four outputs has been described. However, the present invention is not limited to this, and any circuit corresponding to two or more outputs may be used.

  The above-described embodiments are merely examples of the present invention, and the scope of the present invention is not limited by the description, and the specific configuration of each part is appropriately changed within the scope of the effects of the present invention. It goes without saying that it can be done.

High voltage generation circuit configuration diagram DC transformer circuit diagram Shunt regulator circuit diagram Circuit diagram of shunt regulator pass transistor connected in Darlington connection Circuit diagram of current detection circuit Schematic diagram of a high-voltage generator with a power supply circuit that supplies the control voltage of the pass transistor of the shunt regulator from the tertiary side of the DC transformer

10: DC transformer 20: Linear DC regulator (shunt regulator)
30: AC transformer 40: Current detection circuit CH: Charging member PC: Image carrier

Claims (3)

A high-voltage generating circuit that applies an oscillating voltage in which a DC voltage and an AC voltage are individually superimposed on a charging member that is arranged in contact with or in proximity to each of a plurality of image carriers,
A plurality of linear DC regulators for generating a DC voltage to be applied to each charging member;
A single DC transformer with each linear DC regulator connected in parallel to the secondary terminal;
A plurality of AC transformers, one terminal on the secondary side is connected to each charging member, the other terminal is connected to the output terminal of each linear DC regulator, and generates an AC voltage applied to each charging member;
A single current detection circuit for detecting a direct current flowing in the direct current transformer,
Except for one of the linear DC regulators , the other output is adjusted to be lower than the discharge start voltage, and the image carrier is passed through a specific charging member from the linear DC regulator that outputs a voltage higher than the discharge start voltage. A high-voltage generating circuit configured to individually detect the DC current flowing from each charging member to the image carrier by repeating the operation of detecting the DC current flowing through the current detection circuit for each charging member. . Each linear DC regulator includes a pass transistor that step-down controls the output voltage of the DC transformer, and an operational amplifier that feedback-controls the base current of the pass transistor so that the step-down voltage becomes a target voltage . 2. The high voltage generation circuit according to claim 1, further comprising a power supply circuit for supplying control power from the secondary side output or the tertiary side output to each linear DC regulator. Each linear DC regulator includes a pass transistor that step-down controls the output voltage of the DC transformer, and an operational amplifier that feedback-controls the base current of the pass transistor so that the step-down voltage becomes a target voltage. 2. The high voltage generating circuit according to claim 1, wherein the high voltage generating circuit is Darlington connected.

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