JP3008800B2 - DC-DC converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has an operation standby mode such as a video tape recorder or a facsimile,
The present invention relates to a DC-DC converter effective for use in a power supply device of a general home electric appliance which is always energized for 24 hours and most of which is used in an operation standby mode.

[0002]

2. Description of the Related Art In recent years, there have been many home appliances controlled by a microcomputer, and usage methods for operating the home appliance under certain conditions other than the original operation have become common. For this reason, it is necessary to always keep the power-on state in the operation standby mode, during which time constant power is consumed. Moreover, in reality, the operation standby mode makes up most of the use time of the device. This power must be kept as low as possible from the viewpoint of energy saving.

[0003] 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 denotes a switch element, and reference numeral 2 denotes a limiting resistor that limits a drive current for turning on the switch element 1. Reference numeral 3 denotes an output control circuit, 4 denotes a secondary-side rectifying / smoothing circuit, and 5 denotes a transformer, which insulates the primary and secondary sides and converts the primary-side input voltage into a required secondary-side voltage by electromagnetic coupling. . Reference numeral 6 denotes an output voltage detection circuit, and reference numerals 7 and 8 denote a light emitting portion and a light receiving portion of the photocoupler, which supply a control current to the primary side. 9 is a rectifying and smoothing circuit for supplying 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, a DC input voltage Vin supplied from the primary side is once converted into a high-frequency AC by a switch element 1, a control resistor 2, and a transformer. To 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, converts the output voltage, and transmits the current to the light-receiving section of the photocoupler 8 from the issuing section of the photocoupler 7. The output voltage is adjusted by adjusting the charging current.

[0006]

However, in the above-described conventional configuration, the output voltage set value cannot be changed in accordance with the output load condition. Even if this happens, the voltage must be supplied under the same conditions as in the normal operation, and there is a problem that the reactive power is very large.

SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problems. A DC-DC converter is disclosed in which a voltage output function of a power supply in an operation standby state is stopped by a control signal to enable energy saving in an operation standby state. 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. Rectifying / smoothing circuit connected to the primary auxiliary winding of the transformer, a second rectifying / smoothing circuit connected to the secondary winding of the transformer, Of 1
A first switch that switches on and off the current flowing through the next winding and switches to a conductive state when the control terminal voltage reaches a threshold voltage; and a drive current for switching the first switch to a conductive state. A limiting element for controlling
An output voltage detection circuit that sets an output voltage obtained from the second rectifying and smoothing circuit to a desired voltage, detects that the output voltage is a desired voltage value, and outputs a detected current, and an output voltage when the output voltage is short-circuited. An output short-circuit protection circuit that makes the drive current of the switch element zero by utilizing the fact that the detection current of the detection circuit becomes zero, and keeps the zero state as long as it is energized once the drive current is made 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 according to a control signal output from the control unit.

[0009]

According to this configuration, the power supply function operation in the operation standby state is stopped by using the control signal, and it is possible to realize significant power saving in the electric equipment operation standby state.

[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. 5 is 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 is a rectifying / smoothing circuit. An output voltage detecting circuit for setting an output voltage obtained from the circuit 4 to a desired voltage, detecting that the output voltage is a desired voltage value, and outputting a detected current, and 7 and 8 are a light emitting portion and a light receiving portion of a photocoupler. , A control current is supplied to the primary side. Reference numeral 9 denotes a rectifying / smoothing circuit connected to the primary auxiliary winding of the transformer 5, reference numeral 10 denotes an output load, and reference numeral 11 denotes a switch utilizing the fact that the detection current of the output voltage detection circuit 6 becomes zero when the output voltage is short-circuited. The output short circuit protection circuit 12 keeps the zero state as long as the drive current is set to zero and once the drive current is set to zero, and 12 is output from the control unit 14 and input via the photocoupler 13. This is 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 the voltage is converted by the transformer 5; To 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, converts the output voltage into a current, transmits the current from the light emitting unit of the photocoupler 7 to the light receiving unit of the photocoupler 8, and 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 section 7 to the light receiving section 8 of the photocoupler, and the capacitor C1 is short-circuited by Tr2. In addition, due to the control signal active high from the control unit 14, a current flows through the photodiode D1 of the light emitting unit of the photocoupler 13, turning on the phototransistor Tr4 of the light receiving unit and turning off Tr3 of the switch circuit 12.

Next, in the operation standby state, the phototransistor Tr4 of the light receiving section of the photocoupler 13 is turned off by a control signal active low from the control section 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 supply current from the resistor R1, and when the voltage across the capacitor C1 reaches the threshold voltage of Tr1, Tr1 turns on, short-circuits the control terminal of the switch element 1, and operates the oscillation circuit. The output voltage is set to zero by stopping.

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

[0017]

As described above, according to the present invention, a switch circuit which can be controlled by a control signal is provided, an output short-circuit protection circuit is operated, a power supply function operation is stopped, and an output voltage is reduced to zero, thereby consuming electric equipment. An excellent DC-DC conversion capable of realizing a reduction in electric energy can be realized.

[Brief description of the drawings]

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

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

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 switch element 2 control resistor 4 rectifying and smoothing circuit 5 transformer 6 output voltage detecting circuit 9 rectifying and smoothing circuit 11 output short-circuit protection circuit 12 switch circuit 14 control unit

Claims (1)

(57) [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. A first rectifying / smoothing circuit connected thereto, a second rectifying / smoothing circuit connected to a secondary winding of the transformer, and a current flowing to and from a primary winding of the transformer, and a control terminal voltage is reduced. 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;
An output voltage detection circuit that sets an output voltage obtained from the second rectifying / smoothing circuit to a desired voltage, detects that the output voltage is the desired voltage value, and outputs a detection current, and the output voltage is short-circuited. Sometimes the drive current of the switch element is made zero by utilizing the fact that the detection current of the output voltage detection circuit becomes zero, and once the drive current is made zero, the output short circuit keeps maintaining the zero state as long as it is energized. A control unit that outputs a control signal indicating a normal operation or an operation standby, and a second switch that controls the output short-circuit protection circuit by a control signal output from the control unit. Characteristic DC-DC converter.