JPH03111867A - Developing bias circuit - Google Patents

Abstract

PURPOSE:To supply stable output voltage even when developing bias is changed by comparing and amplifying the output voltage and the control input voltage of a developing bias circuit and generating an optional output voltage in accordance with a control input voltage. CONSTITUTION:In the case that a potential gap must be changed, the different control input voltage Vref is impressed on the noninversion terminal of an operational amplifier A from a microcomputer, and error amplification is performed with the reference voltage impressed on an inversion terminal so as to impress the output voltage to the primary winding of a transformer T form the emitter terminal of a transistor (Tr) Q1. A clock signal is impressed on the base terminal of a Tr Q2 to control the on/off of the current of the primary winding. Then, AC voltage induced in the secondary winding of the transformer T is rectified to be in a negative polarity so as to charge capacitors C3 and C4, and the DC voltage is impressed on a developing sleeve. Thus, the output voltage is stably supplied even when the developing bias is changed.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a developing bias circuit, and particularly to a developing bias circuit in an electrophotographic image forming apparatus such as a copying machine or a laser beam printer.

[Conventional technology]

In a conventional image forming apparatus, an original on a platen glass is optically scanned by an optical system to form a latent image on a photoreceptor, and a photoreceptor and a developer are supported to develop the latent image formed on the photoreceptor. By applying a developing bias to the developing sleeve and forming a developing potential gap between the surface of the photoreceptor and the developing sleeve, the toner in the developer carried on the developing sleeve is attracted to the latent image formed on the surface of the photoreceptor. It has become clear. A developing bias circuit for generating the aforementioned developing potential gap will be explained. FIG. 2 is a block diagram showing the configuration of a conventional developing bias circuit. The developing bias circuit 100 includes an error amplifier circuit 60, a switching circuit 70, a transformer T1 voltage doubler circuit 801 and a feedback circuit 9.
0, and a control input voltage Vref obtained by A/D converting a DC input voltage from a microcomputer or the like is fed back and amplified, and a DC voltage is applied to the developing sleeve. The error amplification circuit 60 applies a control input voltage V ref from a microcomputer or the like to the non-inverting terminal of the operational amplifier A1, amplifies it and outputs it, and the transformer T transforms the output voltage of the error amplification circuit 60. The switching circuit 70 conducts current to the primary winding Tl of the transformer T by switching based on a clock signal input from the outside, and the voltage doubler circuit 80 conducts current to the primary winding Tl of the transformer T. It rectifies and doubles the secondary voltage caused by the current excited in the line T2, and the feedback circuit 90 feeds back the output voltage from the voltage doubler circuit 80 to the error amplification circuit 90.

[Problems to be solved by the invention]

However, in the developing bias circuit 100,
The feedback circuit 90 connects the resistive element R2 to the output terminal of the voltage doubler circuit 80.
6 and R27 are connected in series, and a series circuit consisting of a variable resistor R28 and a resistance element R29 is provided in parallel with the resistance element R27. The variable resistance R
The voltage detected by the series circuit of 28 and resistance element 29 is stepped down by resistance element R30 and fed back to error amplification circuit 60. On the other hand, the operational amplifier AI constituting the error amplification circuit 60 is configured to input the feedback voltage from the feedback circuit 90 to its inverting terminal. Therefore, the feedback voltage applied to the operational amplifier AI constituting the error amplification circuit 60 fluctuates following the output voltage of the voltage doubler circuit 80. This has the problem that it is difficult to adopt it if it becomes necessary to change the developing bias. SUMMARY OF THE INVENTION In view of the above-mentioned problems, it is an object of the present invention to provide a developing bias circuit whose purpose is to supply a stable output voltage even when the developing bias is changed.

[Means to solve the problem]

The present invention achieves the above object by applying a control input voltage to a non-inverting terminal of an operational amplifier, and using an output voltage from the operational amplifier to turn on/off the primary winding of a transformer using a switching circuit.
an error amplifier that compares and amplifies its output voltage with the control input voltage in a developing bias circuit that is turned off and applies a negative polarity DC voltage obtained by rectifying the AC voltage induced in the secondary winding of the transformer to the developing sleeve; , and is characterized in that it generates an arbitrary output voltage according to the control input voltage.

【Example】

Next, embodiments of the present invention will be described based on the accompanying drawings. FIG. 1 is a block diagram showing one embodiment of the developing bias circuit of the present invention. In the figure, the developing bias circuit 50 is an error amplifier circuit lO
, a transformer T, a switching circuit 20, a voltage doubler circuit 30, and a feedback circuit 40, and amplifies the control input voltage V ref of multiple stages from a microcomputer etc. to apply a negative polarity DC voltage to the developing sleeve. be. The error amplification circuit 10 amplifies and outputs the control input voltage V ref of multiple stages from a microcomputer, etc., the transformer T transforms the output voltage of the error amplification circuit IO, and the switching circuit 20 The voltage doubler circuit 30 conducts current to the primary winding T1 of the transformer T by switching based on a clock signal inputted from the outside, and the voltage doubler circuit 30 conducts current to the primary winding T2 of the transformer T by switching based on a clock signal input from the outside. The feedback circuit 40 rectifies the secondary voltage to negative polarity and charges the capacitor.
The output voltage from 0 is fed back to the error amplifier circuit IO. The circuit configuration of the developing bias circuit 50 of this embodiment will be described below. The error amplification circuit lO includes an operational amplifier A and a transistor Ql.
The control input voltage V ref is amplified by an error, and includes a transistor Ql, an operational amplifier A1, a Zener diode ZD, capacitors CI and C6, and a resistor R1-.
It consists of R3, R5-R7, and variable resistance element R4. The transistor Ql has a collector terminal connected to a 24V DC power supply, a pace terminal connected to an output terminal of an operational amplifier A through a resistive element R6, and an operational amplifier A connected to its non-inverting input terminal through a resistive element R1. An input voltage V ref is applied, and a variable power supply circuit 15 that supplies a variable reference voltage is connected to the inverting terminal. The input voltage V ref applied to the non-inverting input terminal of operational amplifier A is
The error is amplified using the reference voltage applied to the inverting input terminal of the transistor Ql, and the emitter output of the transistor Ql is negatively fed back to the inverting terminal of the operational amplifier A through a parallel circuit of a resistor R7 and a capacitor C1. In addition, the variable power supply circuit 15 has a resistance element R1, a variable resistance R4, and a resistance element R3 connected in series to a 10V DC power supply, one end of the resistance element R3 is grounded, and a resistance is connected to the connection point between the resistance element R1 and the variable resistance element R4. The other end of the resistor R2 is connected to the inverting input terminal of the operational amplifier A, and the reference voltage of the operational amplifier A is changed by changing the resistance value of the variable resistor R4. It is a protective resistance. The transformer T induces a voltage transformed according to the turns ratio between the primary winding Tl and the secondary winding T2.The emitter terminal of the transistor Ql is connected to one end of the primary winding TI, and the By connecting the other end of the next winding Tl to the collector terminal of the transistor Q2, the output voltage of the transistor Ql is applied. The switching circuit 20 is made up of a transistor Q2, resistive elements R8 and R9, and a diode DI, and is connected to the base terminal of the transistor Q2 through a parallel circuit of a resistive element R8 and a capacitor C2, and switches the transistor Q2 on based on an external clock signal. By switching and conducting current to the primary winding T1 of the transformer T, a secondary voltage is induced in the secondary winding T2 of the transformer T. The voltage doubler circuit 30 consists of diodes D2 and D3 and capacitors C2 and C3. The output voltage charged to The output voltage from the series-connected capacitors C3 and C4 is twice the AC voltage induced in the secondary winding T2 of the transformer T. The feedback circuit 40 is composed of resistors R1O, 11 and a capacitor C5, and one end of a parallel circuit composed of a resistor RIO and a capacitor C5 is connected to the output terminal of the voltage doubler 30, and the resistor is connected to the other end of the parallel circuit. By connecting resistive element R11 in series and connecting the other end of resistive element R11 to the non-inverting terminal of operational amplifier A, the output voltage of voltage doubler circuit 30 is fed back to voltage stabilizing circuit IO. Note that since the output voltage of the voltage doubler circuit 30 has negative polarity, negative feedback occurs. The operation of the developing bias circuit 50 of this embodiment will be explained below. For example, when it becomes necessary to change the developing potential gap according to changes in the density of the original image, the developing bias circuit 50 receives a different control input voltage Vref from a microcomputer (not shown) through a buffer circuit or the like. The voltage is applied to the non-inverting terminal of the operational amplifier A, and the error is amplified using the reference voltage applied to the inverting terminal of the operational amplifier A, and an output voltage is applied from the emitter terminal of the transistor Ql to the primary winding Tl of the transformer T. The transistor Q2 is turned on/off by applying a clock signal to its base terminal via a parallel circuit consisting of a resistor R8 and a capacitor C2, thereby conducting current to the primary winding Tl of the transformer T. The AC voltage induced in the secondary winding T2 is rectified to negative polarity and charged to the capacitors C3 and C4 connected in series.
A DC voltage charged to 1 is applied to a developing sleeve (not shown). Furthermore, by feeding back the output voltage from the series-connected capacitors C3 and C4 to the non-inverting terminal of the operational amplifier A through the feedback circuit 40, it is possible to stably amplify the control input voltage that changes in multiple stages. , a stable output voltage can be supplied even if the developing bias is changed. The DC variable power supply 15 is characterized in that it can be used to adjust the parameters of the developing bias circuit 50. As described above, the developing bias circuit 50 of this embodiment can supply a stable output voltage when it becomes necessary to change the developing potential gap in accordance with changes in the density of the original image.

【Effect of the invention】

As explained above, the control input voltage is input to the non-inverting terminal of the operational amplifier, the output voltage from the operational amplifier is used to turn on/off the primary winding of the transformer using a switching circuit, and the voltage is induced in the secondary winding of the transformer. In the development bias circuit that applies a DC voltage that is rectified from the AC voltage that is applied to the developing sleeve, the DC voltage that has been rectified to negative polarity is charged when it becomes necessary to change the development potential gap depending on changes in the density of the original image, etc. and a feedback circuit that feeds back the output voltage from the circuit to the non-inverting terminal of the operational amplifier, the output voltage can be negatively fed back, and - a variable direct current that applies a reference voltage to the inverting terminal of the operational amplifier. By being equipped with a power supply, it is possible to stably amplify the control input voltage that changes in multiple stages, so it is possible to provide a developing bias circuit that can supply a stable output voltage even if the developing bias is changed. did it.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the developing bias circuit of the present invention, and FIG. 2 is a block diagram showing the configuration of a conventional developing bias circuit. 10.60... Voltage stabilization circuit 15... Variable power supply circuit 20.70... Switching circuit 30.80... Voltage doubler circuit 40.90... Feedback circuit 50.100... Development bias circuit

Claims (1)

[Claims] A control input voltage is applied to the non-inverting terminal of the operational amplifier, the output voltage from the operational amplifier is used to turn on/off the primary winding of the transformer using a switching circuit, and the alternating current voltage induced in the secondary winding of the transformer is rectified. A developing bias circuit that applies negative polarity DC voltage to the developing sleeve includes an error amplifier that compares and amplifies its output voltage with the control input voltage, and generates an arbitrary output voltage according to the control input voltage. A developing bias circuit featuring: