JPH09121547A - Power supply unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to obtain a high power factor and a high VA efficiency regardless of a small load or a large load. SOLUTION: By a control signal from an external control circuit 12, an SW switching circuit 11 selects either choke input rectifying circuit or active filter circuit as an operation circuit. In a state of applying a power supply circuit 1 having this configuration to a image forming equipment, a choke input, rectifying circuit is selected by a control circuit 12 when the picture forming equipment, is in waiting state. When the choke input rectifying circuit is selected, a charging current is smoothened by the choke coil L1, the peak value of current is lowered, and components of higher harmonics are reduced. Also in this state of selection, noise can be reduced and power supply efficiency can be improved compared to the power supply efficiency.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a power supply device,
In particular, the present invention relates to a DC-DC voltage control type power supply device applied to a copying machine, a printer and the like.

[0002]

2. Description of the Related Art A circuit example of a conventional general power supply device is shown in FIG.
6 to FIG. These power supply devices are applied to office automation equipment such as copying machines and printers. In the application of the power supply device to OA equipment, recent multifunctionalization and high functionality of OA equipment,
Due to the tendency toward miniaturization and the like, functionalization similar to that of equipment applied to a power supply device is required. However, when generating various required power sources in the equipment to which it is applied,
The power supply is also generally a noise source.

Conventional example 1 shown in FIG. 3 is a power supply device for a capacitor input rectification circuit, which is composed of a rectification circuit for converting an AC voltage into a DC voltage and a smoothing capacitor. The output voltage waveform of the power supply device having this configuration becomes the charging voltage of the capacitor as shown in FIG. 2 and has a ripple. As a result, the input current flows only when it is lower than the capacitor terminal voltage, and becomes a pulse-like one as shown in FIG. Therefore, a harmonic component is generated in addition to the fundamental waveform component (50, 60 Hz).

The noise generated by such a power supply device is
This may hinder the stable operation of the applied device itself or peripheral devices. Therefore, these power supply devices are required to have high efficiency and low noise generation. As power supply circuits with improved power factor, there are a choke input type circuit (FIG. 5) to which a commercial reactor is added and an active filter circuit (FIG. 6).

The choke input type is a method of inserting a choke coil L1 between a rectifying diode and a smoothing capacitor C1. The peak value of the charging current is low due to the impedance component of the choke coil L1, the conduction angle through which the current is flowing is widened, and harmonics are suppressed.

Further, the choke input type requires a reactance capable of obtaining a sufficient reactance at a commercial frequency and becomes large in size, so that there is a limit in power supply output. When the choke input type is used beyond the limit value, an active filter circuit is used. Are using.

This active filter circuit is composed of a choke coil L2 as a current limiting element, a harmonic switch Tr, an active filter control circuit, a flywheel diode D2 and a smoothing capacitor C1. The active filter circuit detects the instantaneous values of the line voltage and line current, and controls so that the actual value is constant within one cycle of switching due to the choke coil and the transistor inserted in series in the line. Is improved and harmonics are suppressed.

On the other hand, the active filter circuit has a drawback that unnecessary noise increases and power supply efficiency deteriorates due to the switching operation. The circuit operation will be briefly described as follows. When the switch is turned on, a current flows through the choke coil L2. When the switch is turned off, the choke coil L2
The energy stored during the ON period is
2 is emitted and output. The switch Tr is turned on / off so that the average current flowing through the choke coil L2 is proportional to the AC voltage.

As described above, the choke input type and the active filter type have their respective advantages and disadvantages. Therefore, one method of improving the power factor of a DC-DC voltage control type power supply is to provide both a capacitor input type and a choke input type, and perform circuit switching for each. The circuit switching at this time is controlled by the value of the output current value of the secondary circuit.

[0010]

However, current general copying machines include motors, solenoids, clutches, and
A number of electrical components such as heaters, lamps, high voltage power supplies, and control boards are used. Therefore, the power consumption of the machine during copying becomes considerably large. Moreover, there is a considerable difference in power consumption between copying and standby. Further, the fixing of the copied image onto the transfer paper is carried out by being conveyed between a fixing roller heated by an AC heater and a pressure roller.

In the ON / OFF control of the fixing heater control in which the input voltage is controlled in half cycle units, the power factor when the heater is ON is approximately 1. Therefore, the power factor of the system is better when the fixing heater is on than when it is off.

An object of the present invention is to provide a power supply device which can obtain a high power factor and a high VA efficiency regardless of whether the load is light or heavy.

[0013]

In order to achieve the above object, the power supply device of the present invention has a choke input rectifier circuit, an active filter circuit, and either the choke input rectifier circuit or the active filter circuit as an operating circuit. It is characterized in that it has a switching means to be selected and a control input terminal for controlling the switching operation of the switching means, and that the switching operation can be controlled based on a control signal inputted to this control input terminal.

Further, the above power supply device is applied to a predetermined device, and the control signal input to the control input terminal is a signal based on the power supply amount from the power supply device to the predetermined device, and the predetermined device is image-formed. It is preferable that the device is a device and the control signal for the amount of power supply is different at least during image formation and during non-image formation.

Further, discrimination between image formation and non-image formation is performed by turning on / off the fixing heater, and the switching operation is performed by turning on the active filter circuit, turning off the fixing heater, and turning on the fixing heater. Therefore, the active filter circuit should be turned off.

[0016]

Therefore, according to the power supply device of the present invention, the choke input rectifier circuit and the active filter circuit are provided, and either the choke input rectifier circuit or the active filter circuit is selected as the operating circuit. The control of this switching operation is performed based on the control signal input to the control input terminal. Therefore, the switching between the choke input rectifier circuit and the active filter circuit by this control signal can be finely executed.

[0017]

Embodiments of the power supply device according to the present invention will now be described in detail with reference to the accompanying drawings. 1 and 2, an embodiment of the power supply device of the present invention is shown. FIG. 1 is a circuit diagram showing a configuration example of the power supply device of the embodiment, and FIG. 2 is a timing chart for explaining the operation when the power supply device of FIG. 1 is applied to an image forming apparatus.

The power supply circuit 1 of this embodiment shown in FIG. 1 includes a rectifying diode 10, a SW switching circuit 11 and a choke coil L.
1, L2, diodes D1 and D2, a switch Tr, an AF control circuit 13, a capacitor C1 and a PWM control circuit 14. The control circuit 12 is a circuit equipped in a device to which the power supply device 1 is applied, and the power supply device 1 has a control input terminal (not shown).

The power supply circuit 1 composed of the above-mentioned parts has both a choke input rectifier circuit and an active filter circuit, and these circuits are connected to the SW switching circuit 1
It is configured to be switched by 1. SW switching circuit 1
As the first component, a relay, a FET or the like can be considered. Further, the control circuit 12 controls the switching operation of the SW switching circuit 11, and the AF (active filter) control circuit 13
Controls the operation of the semiconductor switch Tr, and the PWM control circuit 14 controls the output operation of the FET at the output stage.

When the power supply circuit 1 is applied to the image forming apparatus, the choke input rectifying circuit is selected by the control circuit 12 because the output is small when the image forming apparatus is in the standby state. In the selected state of the choke input rectifier circuit, the connection of the SW switching circuit 11 brings the choke input circuit passing through the choke coil L1 and the diode D1 into the connected state with the rectifier diode 10.

When the choke input rectifier circuit is selected, the choke coil L1 smoothes the charging current, lowers the peak value of the current, and reduces harmonic components. When the choke input rectifier circuit is selected, noise can be reduced and power supply efficiency can be improved as compared with the active filter circuit.

Next, since a large output is required during the copy operation of the image forming apparatus, the switch circuit 11 is connected to the control circuit 1.
By inputting the control signal from 2, the SW is switched from the choke input rectifier circuit to the active filter circuit side.

In the active filter circuit, the AF (active filter) control circuit 13 turns on / off the switch Tr so that the average current flowing through the choke coil L2 is proportional to the AC voltage, thereby improving the power factor. .

Next, when the fixing heater is controlled to be turned off, the control signal from the control circuit 12 is input to the SW switching circuit 11 before the heater is turned off (FIG. 2).
Switch from the choke input rectifier circuit to the active filter circuit first. After switching to the active filter circuit, the fixing heater is turned off.

In the active filter circuit state, the AF control circuit 13 turns on / off the switch Tr so that the average current flowing through the choke coil L2 is proportional to the AC voltage.
By turning off, the power factor can be improved.

When the fixing heater is turned on again, a control signal is generated from the control circuit 12 so that the power supply circuit 1 is switched to the choke input rectifying circuit after the fixing heater is turned on (FIG. 2). By this switching control, after the fixing heater is turned on, the circuit configuration of the power supply circuit 1 is switched from the active filter circuit to the choke input circuit.

According to the above embodiment, either the choke input rectifier circuit or the active filter circuit can be switched to the drive circuit and selected based on the control signal from the device to which the power supply device of the embodiment is applied. . According to this selection, the timing of switching the control signal based on the amount of power supply from the power supply device to the applied device can be freely set on the applied device side. Therefore, reduction of unnecessary noise generated by the power supply device and improvement of power supply efficiency can be achieved more reliably.

In the above embodiment, the fluctuation of the power supply load is turned on / off of the fixing heater, but the load fluctuation is not limited to this.

[0029]

As is apparent from the above description, the power supply device of the present invention selects either the choke input rectifier circuit or the active filter circuit as the operating circuit by switching. The control of the switching operation is performed based on the control signal input to the control input terminal, and the switching between the choke input rectifier circuit and the active filter circuit by this control signal can be finely executed. For example, it becomes possible to positively perform optimal control by knowing the operating state of the applied device, the required power source capacity, and the like.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of a power supply device of the present invention.

FIG. 2 is a timing chart for explaining an operation when the power supply device of FIG. 1 is applied to an image forming apparatus.

FIG. 3 is a circuit diagram of a power supply device of Conventional Example 1.

FIG. 4 shows an example of waveform diagrams of an output voltage and an output current of Conventional Example 1.

FIG. 5 is a circuit diagram of a power supply device of Conventional Example 2.

FIG. 6 is a circuit diagram of a power supply device of Conventional Example 3.

[Explanation of symbols]

 1 power supply device 10 rectifier diode 11 SW switching circuit 12 control circuit 13 AF control circuit 14 PWM control circuit L1, L2 choke coil D1, D2 diode C1 capacitor Tr switch

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location H03H 7/09 H03H 7/09 A 11/04 8731-5J 11/04 L

Claims (5)

[Claims] 1. A choke input rectifier circuit, an active filter circuit, switching means for selecting one of the choke input rectifier circuit and the active filter circuit as an operating circuit, and control for controlling the switching operation of the switching means. A power supply device comprising an input terminal, wherein the switching operation can be controlled based on a control signal input to the control input terminal. 2. The power supply device is applied to a predetermined device,
The power supply device according to claim 1, wherein the control signal input to the control input terminal is a signal based on an amount of power supply from the power supply device to the predetermined device. 3. The predetermined device is an image forming device,
3. The power supply device according to claim 2, wherein the power supply amount is such that the control signal is different at least during image formation and during non-image formation. 4. The power supply device according to claim 3, wherein the determination of the image formation and the non-image formation is performed by turning on / off a fixing heater. 5. The switching operation according to claim 4, wherein the fixing heater is turned off after turning on the active filter circuit, and the active filter circuit is turned off after turning on the fixing heater. Power supply.