JPH08214542A - Dc-dc converter - Google Patents

Abstract

PURPOSE: To reduce the dissipation power at the time of waiting an operation by using a control signal in a power source having an operation waiting mode and used for various elecric devices. CONSTITUTION: At the time of waiting an operation, the photo-transistor Tr 4 of the photoreceiver of a photocoupler 12 is turned OFF according to a control signal active low from a controller 14, and the Tr 3 of a switch circuit 12 is turned ON according to the supply current from a resistor R3. The control current transmitted from a photocoupler 7 to a photocoupler 8 turns OFF the Tr 2 of an output short-circuit protective circuit 11 by the ON of the Tr 3 of the circuit 12. A change current continuously flows to a capacitor Cl by the supply current from a resistor R1. When the voltage across the capacitor C1 reaches the threshold voltage of the Tr 1, the Tr 1 is turned ON to short- circuit the control terminal of a switch element 1 to thereby stop the operation of an oscillator, thereby setting the output voltage to zero.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention has an operation standby mode such as a video tape recorder and a facsimile.
The present invention relates to a DC-DC converter which is effectively used for a power supply device of a general household electric appliance which is always energized for 24 hours and most of the time is used as an operation standby mode.

[0002]

2. Description of the Related Art In recent years, there are many home electric appliances which are controlled by a microcomputer, and a usage method for operating the electric appliances under a condition other than the original operation has become common. Therefore, it is necessary to keep the power supply in the operation standby mode at all times, and constant power is consumed during that time. Moreover, in actuality, this operation standby mode occupies most of the usage time of the device. This power must be kept as low as possible from the viewpoint of energy saving.

A conventional DC-DC converter will be described below. FIG. 2 shows a circuit configuration of a conventional DC-DC converter. In FIG. 2, reference numeral 1 is a switch element, and 2 is a limiting resistor, which limits a drive current for turning on the switch element 1. 3 is an output control circuit, 4 is a secondary side rectifying / smoothing circuit, and 5 is a transformer that insulates the primary side from the secondary side and converts the primary side input voltage into a required secondary side voltage by electromagnetic coupling. . Reference numeral 6 is an output voltage detection circuit, and 7 and 8 are a light emitting portion and a light receiving portion of the photocoupler, which supply a control current to the primary side. Reference numeral 9 is a rectifying / smoothing circuit that supplies current to the photocouplers 7 and 8, 10 is an output load, and 11 is an output short-circuit protection circuit.

The operation of the DC / DC converter configured as described above will be described below.

First, the DC input voltage Vin supplied from the primary side is once converted into a high frequency AC by the switch element 1, the control resistor 2 and the transformer, and after the voltage is converted by the transformer 5, the secondary side rectifying / smoothing circuit 4 is converted. Is converted into a DC output, and a DC output voltage Vout is obtained. The photocoupler 7 detects a change in the output voltage obtained from the output voltage detection circuit 6 and converts the current into a current, which is transmitted from the issuing unit of the photocoupler 7 to the light receiving unit of the photocoupler 8 and the capacitor of the output limiting circuit 3 The output voltage is adjusted by adjusting the charging current.

[0006]

However, in the conventional configuration described above, it is impossible to change the output voltage setting value according to the output load condition. Even if this happens, the voltage must be supplied under the same conditions as in normal operation, and the reactive power is very large.

The present invention solves the above-mentioned conventional problems and provides a DC-DC converter in which the voltage output function of the power supply during operation standby is stopped by a control signal to enable energy saving during operation standby. The purpose is to provide.

[0008]

In order to achieve this object, a DC-DC converter of the present invention obtains a primary winding, a primary auxiliary winding electromagnetically coupled to the primary winding, and an output voltage. A secondary rectifying and smoothing circuit connected to the primary auxiliary winding of the transformer, a second rectifying and smoothing circuit connected to the secondary winding of the transformer, Of 1
A first switch that conducts and blocks a current flowing through the next winding and switches to a conducting state when the control terminal voltage reaches a threshold voltage, and a drive current for making the first switch conductive. A limiting element for controlling
An output voltage detection circuit that sets the output voltage obtained from the second rectifying and smoothing circuit to a desired voltage, detects that the output voltage has a desired voltage value, and outputs the detected current, and an output voltage when the output voltage is short-circuited. Equipped with an output short-circuit protection circuit that keeps the zero state as long as it is energized when the drive current of the switch element is set to zero by utilizing the fact that the detection current of the detection circuit becomes zero. A control unit that outputs a control signal indicating normal operation or operation standby and a second switch that controls the output short-circuit protection circuit by the control signal output from the control unit.

[0009]

With this configuration, it is possible to use the control signal to stop the operation of the power supply function in the standby state for the operation, and to realize a large power saving in the standby state for the operation of the electric device.

[0010]

An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, 1 is a first switch, 2 is a limiting element for controlling a drive current for making the switch 1 conductive, 3 is an output control circuit, and 4 is connected to a secondary winding of a transformer 5. A second rectifying and smoothing circuit, a transformer having a primary winding, a primary auxiliary winding electromagnetically coupled to the primary winding, and a secondary winding for obtaining an output voltage, and 6 a rectifying and smoothing An output voltage detection circuit that sets the output voltage obtained from the circuit 4 to a desired voltage, detects that the output voltage has a desired voltage value, and outputs the detected current, and 7 and 8 are a light emitting portion and a light receiving portion of the photocoupler. A control current is supplied to the primary side. 9 is a rectifying / smoothing circuit connected to the primary auxiliary winding of the transformer 5, 10 is an output load, and 11 is a switch utilizing that the detection current of the output voltage detection circuit 6 becomes zero when the output voltage is short-circuited. When the drive current of 1 is set to zero and once the drive current is set to zero, the output short circuit protection circuit keeps the zero state as long as the current is supplied. 12 is output from the control unit 14 and input via the photocoupler 13. A switch circuit controlled by a control signal.

The operation of the DC / DC converter configured as described above will be described with reference to FIG.

First, the DC input voltage Vin supplied from the primary side is once converted into a high frequency AC by the switch element 1, the control resistor 2 and the transformer, and after the voltage is converted by the transformer 5, the secondary side rectifying / smoothing circuit 4 is converted. Is converted into a DC output, and a DC output voltage Vout is obtained. The photocoupler 7 detects a change in the output voltage obtained from the output voltage detection circuit 6 and converts the current into a current, which is transmitted from the light emitting portion of the photocoupler 7 to the light receiving portion of the photocoupler 8 and is output from the capacitor of the output limiting circuit 3. The output voltage is adjusted by adjusting the charging current.

During normal operation, the transistor Tr2 of the output short-circuit protection circuit 11 is turned on by the control current transmitted from the light emitting portion 7 of the photocoupler to the light receiving portion 8, and the capacitor C1 is short-circuited by Tr2. In addition, the control signal active high from the control section 14 causes a current to flow in the photodiode D1 of the light emitting section of the photocoupler 13, turning on the phototransistor Tr4 of the light receiving section and turning off Tr3 of the switch circuit 12.

Next, during operation standby, the phototransistor Tr4 of the light receiving portion of the photocoupler 13 is turned off by the control signal active low from the control portion 14, and the transistor Tr3 of the switch circuit 12 is turned on by the supply current from the resistor R3. Become. The control current transmitted to the photocouplers 7 to 8 turns off Tr2 of the output short circuit protection circuit 11 by turning on Tr3 of the switch circuit 12. The charging current continues to flow to the capacitor C1 by the current supplied from the resistor R1, and when the voltage across the capacitor C1 reaches the threshold voltage of Tr1, Tr1 turns on, the control terminal of the switch element 1 is short-circuited, and the operation of the oscillation circuit is started. The output voltage is made zero by stopping.

As described above, according to this embodiment, the switch circuit 12 short-circuits the control terminal of the switch element 1 by the control signal output from the control section 14 during the operation standby state, and the operation of the oscillation circuit is stopped. Therefore, the power consumption during the operation standby can be reduced.

[0017]

As described above, according to the present invention, the switch circuit which can be controlled by the control signal is provided, the output short-circuit protection circuit is operated, the power supply function operation is stopped, and the output voltage is made zero, thereby consuming electric equipment. It is possible to realize excellent DC-DC conversion capable of realizing reduction of electric power amount.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a DC / DC converter of the present invention.

FIG. 2 is a circuit diagram of a conventional DC-DC converter.

[Explanation of symbols]

 1 Switch Element 2 Control Resistor 4 Rectifier Smoothing Circuit 5 Transformer 6 Output Voltage Detection Circuit 9 Rectifier Smoothing Circuit 11 Output Short Circuit Protection Circuit 12 Switch Circuit 14 Control Section

Claims (1)

[Claims] 1. A transformer having a primary winding, a primary auxiliary winding electromagnetically coupled to the primary winding, and a secondary winding for obtaining an output voltage, and a primary auxiliary winding of the transformer. The first rectifying / smoothing circuit connected, the second rectifying / smoothing circuit connected to the secondary winding of the transformer, and the current flowing in the primary winding of the transformer are conducted and cut off, and the control terminal voltage is A first switch that switches to a conductive state when a threshold voltage is reached, and a limiting element that controls a drive current for bringing the first switch into a conductive state,
The output voltage obtained by setting the output voltage obtained from the second rectifying / smoothing circuit to a desired voltage, detecting that the output voltage has the desired voltage value, and outputting the detected current, and the output voltage are short-circuited. Sometimes the output current of the output voltage detection circuit becomes zero and the drive current of the switch element is set to zero, and when the drive current is once set to zero, the output current short circuit keeps the zero state as long as it is energized. And a second switch for controlling the output short-circuit protection circuit according to a control signal output from the control unit, the control unit including a protection circuit and outputting a control signal indicating normal operation or standby for operation. Characteristic DC-DC converter.