JP2738836B2 - Power supply - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a power supply device, in particular, a DC superimposed AC to a plurality of loads using an AC output obtained from a secondary side of a transformer.
The present invention also relates to a power supply apparatus having means for supplying DC power and independently controlling the potential of a DC component supplied to a load or the power supply timing for each load.

[Prior art] Conventionally, in direct charging and direct transfer type copying machines,
In order to control image forming conditions as desired, a technique is known in which a DC superimposed AC output is generated as a charging high voltage output, and a DC component is controlled to a constant voltage and an AC component is controlled to a constant current.
In such a system, it is common to use one transformer and one drive circuit which constitute a switching power supply for one AC / DC superimposed output.

[Problem to be Solved by the Invention] The above conventional structure has the following problems.

1) There is a problem that the circuit becomes large-scale and complicated to control each of the multiple outputs with a constant current and a constant voltage, and the cost and the size of the high-voltage power supply are increased.

2) Although a technique for extracting multiple outputs from the same transformer has been proposed, since a load such as a charger is connected to a common casing potential, an alternating current flowing to one load among currents flowing to a plurality of loads is proposed. It was not possible to detect only minutes.

3) Since the charging DC potential and the developing bias DC potential are controlled in an interlocked manner, two independently controllable variable resistors and two control output generation circuits are required, which causes an increase in cost.

An object of the present invention is to solve the above problems and to provide a simple, inexpensive, small, and lightweight power supply device that can be used for electronic devices that require various types of power supplies.

[Means for Solving the Problems] In order to solve the above problems, in the present invention, a transformer is connected to one secondary winding of the transformer, and an alternating current generated in the secondary winding is converted to a direct current. First rectifying means for converting the alternating current generated in the secondary winding and the direct current changed by the first rectifying means, and supplying the resulting direct current to a first load; The rectifier circuit is connected to the secondary winding in parallel with the first rectifier circuit, converts AC generated in the secondary winding into DC,
A second rectifier for supplying a current to the first load, a detector for detecting a current of the AC component supplied to the first load, and a first rectifier for the transformer based on the current of the AC component detected by the detector. And a driving circuit for controlling the driving of the next side, and stabilizing the current of the AC component to stabilize the superimposed output supplied to the first load and the DC output supplied to the second load. The structure which makes it change is adopted.

[Operation] According to the above configuration, the superimposed output of the alternating current generated in the secondary winding via the superimposing means and the direct current changed by the first rectifying means is supplied to the first load. DC current is supplied from the second rectifier to the second load. At this time, the current of the AC component supplied to the first load is detected by the detector, and the primary drive of the transformer is driven based on the detected output. To stabilize the AC component current, thereby stabilizing the AC / DC superimposed output to the first load and the DC output to the second load.

EXAMPLES Hereinafter, the present invention will be described in detail based on examples shown in the drawings.

FIG. 1 shows the structure of an electrophotographic image forming apparatus using a power supply device employing the present invention.

In FIG. 1, reference numeral 1 denotes a photosensitive drum which is driven to rotate in the direction of the arrow in the figure, and passes through an image forming process by a charger 2, a developing unit 3 and a transfer unit 4. After being uniformly charged by the charger 2, a laser beam or reflected light of a document is irradiated between the charger 2 and the developing device 3 to form an electrostatic latent image on the photoconductor 1. Next, the latent image is visualized by the developing device 3 and then transferred to a medium such as paper by the transfer device 4.

The charger 2, the developing device 3, and the transfer device 4 are typical high-pressure loads required in this type of apparatus. These high-voltage loads are supplied from a switching power supply using the transformer 6 and the transformer 49.

The transformer drive circuit 5 is a circuit for driving the primary winding of the transformer 6, and is composed of a PWM (pulse width modulation) circuit switching circuit and the like as in the related art. The drive efficiency of the transformer drive circuit 5 with respect to the transformer 6 is determined by an AC current detection circuit.
Closed loop control is possible via 20. The configuration and operation of the AC current detection circuit 20 will be described later.

The output AC of the transformer 6 is directly output to the charger 2 through a protection circuit 7 such as a current limiting resistor. However, as shown in the figure, the output winding of the transformer 6 is not directly grounded, and the output of the voltage doubler rectifier circuit composed of diodes 9, 10 and capacitors 8, 9 is connected to the high voltage transistor 23 via resistors R12, R13. The DC level is shifted by grounding to generate a superimposed DC component. Resistor 13 is a capacitor
11 is a current limiting resistor that prevents the charge charged in 11 from suddenly flowing into the transistor 23.

The degree of conduction of the transistor 23 is controlled via an error amplifier 21 connected to the base of the transistor 23. The error amplifier 21 compares the reference voltage V1 with the voltage V2 corresponding to the DC shift level detected via the resistors 16 and 18, and applies a bias corresponding to the potential difference to the transistor 23.

 Here, the operation of this circuit will be briefly described.

The output of the smoothing rectification circuit including the elements denoted by reference numerals 8 to 14 flows through the high breakdown voltage Tr 23 and the resistors 18 and 16. Here, the transistor 23 is controlled by the error amplifier 21, and V1 = V2
Becomes stable. Therefore, assuming that the value of each resistor n is represented by Rn, the DC shift potential V0 of the output winding of the transformer 6 is Vo = (R / R17-R ') Vcc-RV1 / R17 where R = (R16 + R18) (R18 + R17 ) / R18−R18 R ′ = (R18 + R16) / R18

V1 is a resistor 44 for dividing the power supply voltage (low voltage) Vcc.
By ~ 46 and variable resistor 47 It is variable up to.

Accordingly, as shown in FIG. 2, the waveform applied to the charging member 2 is shifted from the ground potential to the negative side by V0 (the DC potential −V0 is superimposed) (in the case of sine wave driving).
The resistor 14 prevents the peak of the AC output from being cut by the rectifier circuit.

Similarly, the output of the transformer 6 is composed of two systems composed of capacitors 24 and 28, a diode 25, resistors 27 to 29, and capacitors 30, 35, diodes 31, 33, resistors 32, 34, 36, 37 and a varistor 39. The rectification and smoothing are input to the rectification and smoothing circuit, and the superimposed output thereof is supplied to the transfer device 4.

The outputs of the two rectifying / smoothing circuits are connected in series, and the output terminal of the lower rectifying / smoothing circuit is connected to a resistor 40 and a transistor 41. By controlling the continuity of these transistors, the transfer device is controlled. 4 can be controlled.

Here, the capacitor 38 is a bias capacitor, and the resistors 37 and 40 are elements for protecting the transistor 41 when the transistor 41 is turned on to lower the output potential of the lower rectifier circuit. Resistors 27, R32, and R34 are resistors 14
Is inserted for the same purpose as. A varistor 39 fixes the potential applied to the transfer member 4.

 The operation of the power supply circuit to the transfer device 4 is as follows.

Here, + VT is applied to the transfer device 4 when the transistor 41 is off and -VT when the transistor 41 is on.

Here, of the currents flowing into the transfer voltage generating circuits 24 to 39, components other than the DC component flowing into the transfer device 4, which is a load, return to the transformer 6 via the bypass capacitor 15.
It does not flow into the resistor 19 for detecting the DC output voltage.

Here, since the current when the transistor 41 is on is generated only at the timing when the non-image portion of the photoconductor 1 passes,
It doesn't matter.

In addition, the current ip flowing into the charger 2 is an alternating current ip (ac).
And the DC component ip (dc), and the current flowing into the transfer device 4 is DC it. These currents are expressed as ip (ac)
9, through the capacitor 15, also ip (dc), it is the resistance 18, 1
Return to the transformer via 6. Therefore, only the alternating current flowing into the charger 2 is uniquely detected by the resistor 19.

The power supply to the developing device 3 is substantially the same as the power supply circuit to the charger 2.

That is, it is composed of a transformer 49 and a level shift circuit connected to the secondary side of the transformer 49.

One of the output terminals of the transformer 49 is connected to the developing device 3 and is input to a rectifying and smoothing circuit including a diode 50, resistors 51 and 52, and a capacitor 53. The output of the rectifying and smoothing circuit is connected to a ground potential via a resistor 54 and a transistor 56. The degree of conduction of the transistor 56 is controlled by the error amplifier 62. The reference voltage of the error amplifier 62 is V1 as described above, and the detection voltage is a divided value of the resistances 58 and 59 of the DC level shift voltage Vdc.

 Here, the DC component Vdc is determined by the following equation.

Here, RO = (R58 + R59) (R59 + 57) / R59−R59 Ro ′ (R59 + R58) / R59 Therefore, by selecting the resistors 16 to R18 and R57 to R59, the charger 2, the developing device for the same control input V1 Arbitrary DC component outputs V0 and Vdc for supplying power to the unit 3 can be obtained. Reference numeral 55 denotes a protection circuit for protecting the developing device 3, which is configured in the same manner as the protection circuit 7.

FIG. 3 shows the configuration of the internal circuit of the current detection circuit 20 and the overvoltage protection circuit.

The resistor 19 is inserted between one end of the output winding of the transformer 6 and the ground together with the capacitor 15 as shown in FIG.
A voltage corresponding to the current of the AC component is generated at both ends. This alternating current is converted into a direct current by a rectifying and smoothing circuit including diodes 72 and 73, capacitors 71 and 74, and resistors 75 and 77 of the alternating current detection circuit 20.

Here, the resistances 76 and 77 are for treating the effective value as a DC output charged in the capacitor 74 as an effective value, and when these are omitted, the peak value is detected.

In this way, the current of the AC component flowing on the secondary side of the transformer 6 is fed back to the transformer drive circuit 5,
The transformer drive circuit 5 controls the drive of the transformer 6 so as to stabilize this.

Although not shown in FIG. 1, overvoltage protection circuits such as those indicated by reference numerals 78 to 88 in FIG. 3 can also be provided. Reference numeral 78 denotes a voltage detection winding provided on the transformer 6, and its output is a diode 79, a capacitor 80, and a resistor 81.
The DC level is input via a current control resistor 82 to the base of a transistor 83 whose emitter is grounded by a Zener diode. The connection point between the transistor 83 and the Zener diode 85 is connected to the power supply voltage Vc via the resistor 84.
It has been pulled up to c.

The collector potential of the transistor 83 controls the base of another transistor 88 via a bias circuit composed of resistors 86 and 87. Transistor (PNP) 8
The emitter 8 is connected to the power supply voltage Vcc, and the collector is connected to the output point of the AC current detection circuit 20.

In the above configuration, the winding 78 generated at both ends of the resistor 81
When the rectified output of the transistor 83 becomes larger than the sum of the Zener voltage VZ of the Zener diode 85 and the base-emitter voltage VBE of the transistor 83, both the transistor 83 and the transistor 88 are turned on and current flows into the resistor 75, and the current of the transformer 6 Control so that the output does not rise.

According to the above embodiment, from the same step-up transformer 6,
A plurality of DC or high-voltage outputs of AC / DC superposition can be taken out, so that the power supply unit can be reduced in size and weight or cost can be reduced. In addition, since a plurality of output systems are separated in an AC manner, load current detection can be performed with high accuracy.

FIG. 4 shows another embodiment. The difference from the embodiment of FIG. 1 is that the separation output generation circuits 65 to 70 and the separation neutralizing needle 71 are added, and the AC of the output winding of the transformer 6 is directly cut off by the separating neutralizing needle 71. The other configuration is the same as that of FIG. 1 in that a direct current rectified and smoothed by a diode 66, a capacitor 68, and resistors 67 and 69 is supplied by a diode 65, a capacitor 68, and resistors 67 and 69. Also here, the common potential side of the power supply circuit of the separation needle 71 is connected to the terminal of the resistor 19 so that the AC output does not flow through the resistor 19 as in the transfer output generation circuit.

With such a configuration, power can be supplied to more loads without increasing the main parts (such as transformers) of the power supply circuit.

FIG. 5 shows a current detection circuit using a so-called drum ground DG.
This is an embodiment provided between the signal ground SG and the signal ground SG. Normally, the drum ground DG is a signal ground inside the high voltage power supply.
In the case of FIG. 5, a resistor 93 for measuring the drum current is connected between the ground side terminal of the photosensitive member 1 and the ground potential, and this voltage is configured in the same manner as in FIG. The current is fed back to the transformer drive circuit 5 via the AC current detection circuit 20 thus obtained. Other configurations are the same as those in FIG.

In such a configuration, the ground potential DG of the photoconductor 1 is
It floats above SG by the terminal voltage of 83 (several volts), but does not significantly affect image quality. According to the configuration as shown in FIG. 5, there is an advantage that the pattern layout on the printed board becomes easier than in FIG.

FIG. 6 shows an embodiment in which outputs necessary for the charging, developing and transferring steps are obtained from the same transformer 6. That is, the configuration is such that one secondary winding of the transformer 6 of FIG. 4 is added, and a power supply circuit for the developing device 3 same as that of FIG. 4 is connected to this.

In the case of FIG. 6, there is a restriction that the AC component of the developing bias of the developing device 3 has the same frequency and the same timing as the AC component of the charging device 2 as compared with FIG. This is very advantageous in terms of conversion.

Further, when the developing device 3 is not a jumping developing device but a brush developing device, and only the DC component needs to be supplied,
A simpler configuration can be used as shown in FIG.

FIG. 7 shows a transformer 6 added in the configuration of FIG.
The output of the rectifier circuit, instead of the output AC component of the secondary winding, is supplied to the developing device 3 as it is. The output DC level is controlled by the error amplifier 62 and the transistor 56.

With such a configuration, the power supply circuit can be further simplified.

[Effects of the Invention] As is clear from the above, according to the present invention, the superimposed output of the alternating current generated in the secondary winding via the superimposing means and the direct current changed by the first rectifying means is converted to the first output. Supply to the load,
Also, a direct current is supplied from the second rectifier to the second load,
At this time, the current of the AC component supplied to the first load is detected by the detection means, and the primary-side drive of the transformer is controlled based on the detection output to stabilize the current of the AC component. It employs a configuration for stabilizing the AC / DC superimposed output to the first load and the DC output to the second load, and outputs the AC / DC superimposed output from the same transformer to the first load.
A power supply circuit that supplies a DC output to the second load, stabilizes the AC / DC superimposed output to the first load, and the DC output to the second load, and supplies a high voltage to a plurality of loads. In addition, there is an excellent effect that the configuration can be made easily and inexpensively.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing the structure of an image forming apparatus using the power supply device according to the present invention, FIG. 2 is a waveform diagram showing the operation of the circuit of FIG. 1, and FIG. FIGS. 4 to 7 are circuit diagrams showing configurations of the detection circuit, and FIGS. 4 to 7 are circuit diagrams showing different embodiments of the power supply device. DESCRIPTION OF SYMBOLS 1 ... Photoreceptor 2 ... Charging device 3 ... Developer 4 ... Transfer device 5 ... Transformer drive circuit 6 ... Transformer 7 ... Protection circuit 20 ... AC current detection circuit 21, 62 ... Error amplifiers 23, 41, 56, 83, 88 Transistor 71 Static electricity removal needle

Claims (1)

(57) [Claims] A transformer connected to one secondary winding of the transformer, a first rectifier for converting an alternating current generated in the secondary winding into a direct current, and a first rectifier generated in the secondary winding. Superimposing means for superimposing the alternating current and the direct current changed by the first rectifying means and supplying the alternating current to the first load, and connected to the secondary winding in parallel with the first rectifying circuit;
A second rectifier that converts an alternating current generated in the secondary winding into a direct current and supplies the direct current to a second load; a detector that detects a current of an alternating current component supplied to the first load; A drive circuit for controlling the driving of the primary side of the transformer based on the current of the AC component detected by the detection means, and supplying the current to the first load by stabilizing the current of the AC component A power supply device for stabilizing a superimposed output and a DC output supplied to a second load.