JP2002165449A - Switching power supply unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce power consumption in a power supply unit. SOLUTION: This power supply unit includes a control circuit 13 of a power factor converter 5, having an output circuit 14, a compensation circuit 15, an error amplification circuit 16, and an overvoltage detection circuit 17 and is also structured so that the grounds of first to third detection circuits 20, 23, 26 are integrated, and a switch 36 is positioned between the integration point and the ground to be opened, when output current from an output terminal 2 decreases.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching power supply used for a copy printing apparatus, a facsimile, a data projector, and the like.

[0002]

2. Description of the Related Art In recent years, there has been a demand for a switching power supply for improving a power factor. Therefore, the configuration is such that a rectifier circuit, a power factor improving converter, and a DC-DC converter are provided in order from the input terminal to the output terminal, from the input terminal side to the output terminal.

That is, as described above, the rectifier circuit and the DC-
The power factor of the power supply device is improved by interposing a power factor improving converter between the DC converters.

[0004]

The control circuit of the power factor correction converter includes an output circuit to the power factor correction converter, a correction circuit connected to the output circuit, an error amplifier circuit,
An overvoltage detection circuit, a first detection circuit for detecting a voltage between the rectifier circuit and the power factor correction converter is connected to the correction circuit, and the power factor correction converter and DC-DC are connected to the error amplifier circuit. A second detection circuit for detecting a voltage between the converters is connected, and a third detection circuit for detecting a voltage between the power factor correction converter and the DC-DC converter is connected to the overvoltage detection circuit. In the above configuration, when the output current from the output terminal decreases, an attempt has been made to stop the power factor correction converter to suppress the power consumption in that portion.

Specifically, at this time, an operation is performed to stop the output circuit in the control circuit of the power factor correction converter. However, even if the output circuit of the control circuit is stopped, the other correction circuits, error amplifier circuits, and overvoltage detection circuits of the control circuit have first to first circuits, respectively.
The third detection circuit is connected, and even when the operation of the power factor correction converter is stopped, a current continues to flow through these first to third detection circuits. Power consumption is being performed.

Accordingly, an object of the present invention is to prevent the power consumption of the first to third detection circuits from being wasted when the operation of the power factor correction converter is stopped.

[0007]

In order to achieve this object, the present invention combines the first to third detection circuits and the ground side of an output circuit, a correction circuit, an error amplifier circuit, and an overvoltage detection circuit. A switch is interposed between the junction and the ground, and the switch opens when the output current from the output terminal decreases. That is, with the above configuration, the output current from the output terminal decreases, and when the operation of the power factor correction converter is stopped, opening the switch enables not only the control circuit but also the first to third detection circuits. No current flows, which can reduce wasteful power consumption.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the accompanying drawings. In FIG. 1, reference numeral 1 denotes an input terminal, and a filter 3, a rectifier circuit 4, a power factor improving converter 5, and a DC-DC converter 6 are connected between the input terminal 1 and the output terminal 2 in this order from the input terminal 1. . The filter 3 includes four capacitors 7 and a line filter 8. The rectifier circuit 4 is of a type that performs full-wave rectification.

The power factor improving converter 5 is composed of a choke coil 9, a diode 10, a capacitor 11, and a switching element 12. The control circuit 13 for controlling the power factor correction converter 5 includes an output circuit 14 for the switching element 12, a correction circuit 15 for sending a control signal to the output circuit 14, an error amplifier circuit 16, and an overvoltage detection circuit 17, respectively. ing.
The correction circuit 15 includes a rectifier circuit 4 and a power factor correction converter 5.
A first detection circuit 20 composed of a series body of two resistors 18 and 19 is provided for detecting the voltage between the two resistors. The error amplification circuit 16 includes the power factor improving converter 5 and the DC-DC
The second detection circuit 23 is provided so as to detect a voltage between the converters 6 and includes a series body of two resistors 21 and 22. Further, the overvoltage detection circuit 17 also includes the power factor correction converter 5 and the DC-DC
Two resistors 2 for detecting voltage between converters 6
There is provided a third detection circuit 26 composed of 4, 25 series bodies. Next, the DC-DC converter 6 includes a transformer 27, and a switching element 28
Are connected, and the switching circuit 28 is controlled to be opened and closed by a control circuit 29. Transformer 2
7 is provided with a smoothing circuit comprising a diode 30 and a capacitor 31, and a control circuit 32 is connected to the output terminal 2 side of the smoothing circuit.

The simple operation of this power supply device with the above configuration will be described. The commercial power supply 33 at the input terminal 1 is connected to the rectifier circuit 4.
After being subjected to full-wave rectification and waveform shaping by the power factor improving converter 5, the DC power is supplied to the output terminal 2 via the DC-DC converter 6. As the supplied load, for example, a copy printing device, a facsimile,
Such as a data projector. When the load supplied to the output terminal 2 is in a standby state, the output current flowing from the output terminal 2 to the load decreases. At this time, in this embodiment, a signal from the load side is transmitted to the photocoupler 35 via the terminal 34, and the switch 36 is opened by the photocoupler 35.

The switch 36 is connected to the first switch as shown in FIG.
-The third detection circuits 20, 23, 26, the output circuit 14, the correction circuit 15, the error amplifier circuit 16, and the ground side of the overvoltage detection circuit 17 are all gathered and interposed between this junction point and the earth. . Therefore, when the switch 36 is opened, current does not flow not only to the control circuit 13 but also to the first to third detection circuits 20, 23, 26. That is, when the operation of the power factor improving converter 5 is stopped, no current flows to the detection circuit portion, which leads to a significant reduction in power consumption in this portion.

[0012]

As described above, according to the present invention, not only the output circuit, the correction circuit, the error amplification circuit, and the overvoltage detection circuit provided in the control circuit of the power factor correction converter but also the first circuit connected to them are provided.
The third detection circuit is connected to the ground side, and a switch is interposed between the connection point and the ground. The switch is configured to open when the output current decreases from the output terminal. For example, when the load connected to the power supply becomes a standby state, not only the power factor improving converter but also the power consumption flowing to the detection circuit thereof can be reduced, and the power consumption can be greatly reduced.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 input terminal 2 output terminal 3 filter 4 rectifier circuit 5 power factor improving converter 6 DC-DC converter 7 capacitor 8 line filter 9 choke coil 10 diode 11 capacitor 12 switching element 13 control circuit 14 output circuit 15 correction circuit 16 error amplifier circuit 17 Overvoltage detection circuit 18 Resistance 19 Resistance 20 First detection circuit 21 Resistance 22 Resistance 23 Second detection circuit 24 Resistance 25 Resistance 26 Third detection circuit 27 Transformer 28 Switching element 29 Control circuit 30 Diode 31 Capacitor 32 Control circuit 33 Commercial Power supply 34 Terminal 35 Photocoupler 36 Switch

Claims (1)

[Claims] 1. A rectifier circuit, a power factor improving converter, and a DC-DC converter are provided between an input terminal and an output terminal in order from the input terminal side to the output terminal, and the control circuit of the power factor improving converter comprises: An output circuit to the rate improvement converter, a correction circuit connected to the output circuit, an error amplifier circuit, and an overvoltage detection circuit, wherein the correction circuit detects a voltage between the rectifier circuit and the power factor improvement converter. And a second detection circuit for detecting a voltage between the power factor correction converter and the DC-DC converter is connected to the error amplification circuit, and the power factor correction circuit is connected to the overvoltage detection circuit. A third detection circuit for detecting a voltage between the converter and the DC-DC converter is connected, and the first to third detection circuits are connected to an output circuit, a correction circuit, an error amplification circuit, and an earth side of an overvoltage detection circuit. A switching power supply unit that gathers, and a switch is interposed between the gathering point and the ground, and the switch is opened when the output current from the output terminal decreases.