JPH0923644A - Switching power supply - Google Patents

Abstract

(57) [Abstract] [Purpose] The purpose is to change the operating point of the overcurrent protection circuit in the standby mode for the power supply unit of the equipment having the standby mode. [Structure] During operation standby, a control signal is transmitted from the secondary side to the transistor 111 of the overcurrent setting value adjustment circuit 11 through the photocoupler 12, and the transistor 111 is turned off. When the transistor 111 is turned off, the overcurrent detection resistance value becomes the value of only the current detection resistance 102, and the overcurrent protection circuit operates with lower power consumption than in the normal operation. In this state, when some electrical abnormality occurs on the load side and a current exceeding the maximum current value of the normal load flows, the control transistor 101 is turned on, and the base or gate voltage of the switch element 1 is lower than the threshold voltage. , Switch operation is stopped, output voltage is set to zero, and equipment failure is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally has an operation standby mode, such as a VTR and a facsimile, and is constantly energized for 24 hours a day, and the power consumption difference between the normal operation mode and the operation standby mode is large. The present invention relates to a power supply device for home appliances.

[0002]

2. Description of the Related Art In recent years, there are many home electric appliances which are controlled by a microcomputer, and in addition to the original operation, the usage for operating the operation under a certain condition has become common. Moreover, since the power consumption is kept as low as possible in the operation standby mode, the power consumption difference from the normal operation mode becomes large.

A conventional switching power supply device will be described below. FIG. 2 shows a circuit configuration of a conventional switching power supply device. In FIG. 2, 1 is a switch element, 2 is a switch element drive circuit for turning on / off the switch element 1, 3 is a control circuit, 4 is a secondary side rectifying / smoothing circuit, 5
Is a transformer that insulates the primary side from the secondary side and converts the primary side input voltage to the secondary side required voltage by electromagnetic coupling, and 6 is an overcurrent protection configured by a current detection resistor 102 and a control transistor 101. Circuit 7 is a detection circuit.

The operation of the switching power supply device configured as described above will be described below.

First, the value of the current detection resistor 102 is set so that the control transistor 101 is not turned on with the maximum current flowing through the switch element 1 during normal operation. And
When some abnormality occurs on the load side and a current exceeding the maximum current value of the normal load flows, the control transistor 101 is turned on, and the base or gate voltage of the switch element 1 is set below the threshold voltage to stop the switch operation. , Zero the output voltage and prevent equipment failure.

[0006]

However, in the conventional configuration described above, when a failure occurs during operation standby, that is, when the power consumption is low, and the power consumption at that time is less than the set value of the overcurrent protection circuit 6. Had a problem that failure detection could not be performed.

SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide a switching power supply device which can accurately detect a failure state at the time of operation standby as in normal operation.

[0008]

To achieve this object, a switching power supply device according to the present invention provides a primary winding, a primary auxiliary winding electromagnetically coupled to the primary winding, and an output voltage. A transformer having a secondary winding, a rectifying / smoothing circuit connected to the secondary winding of the transformer and composed of a diode and a capacitor, a detection circuit for detecting a secondary side output voltage obtained from the rectifying / smoothing circuit, and a transformer The switch element that turns on and off the current flowing in the primary winding of the switch and turns on when the control terminal voltage reaches the threshold voltage, the switch element drive circuit that turns the switch element on and off, and the detection circuit A control circuit that controls the ON time of the switch element by the feedback signal to stabilize the secondary output voltage, and a current that flows in the switch element is detected, and when the current reaches the set value, the switch element An overcurrent protection circuit for a switching function is stopped to zero the output voltage, in which a overcurrent setting value adjusting circuit for adjusting the control signal setting value of the overcurrent protection circuit.

[0009]

With this configuration, even when the device is in the normal operation mode,
Even in the operation standby mode, it is possible to always detect the failure mode under the same condition and to safely stop the device.

[0010]

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

In FIG. 1, 1 is a switch element, 2 is a switch element drive circuit that is turned on / off and turns on when a control terminal voltage reaches a threshold voltage, and 3 is a feedback signal from a detection circuit 7. The control circuit 4 for controlling the ON time of the switch element 1 to stabilize the secondary side output voltage by means of 4 is connected to the secondary winding of the transformer 5
Secondary rectifying and smoothing circuit composed of a capacitor and a capacitor, 5
Is a transformer that insulates the primary side from the secondary side and converts the primary side input voltage to the secondary side required voltage by electromagnetic coupling, and 6 is an overcurrent protection configured by a current detection resistor 102 and a control transistor 101. A circuit, 7 is a detection circuit for detecting the secondary side output voltage obtained from the secondary side rectifying / smoothing circuit 4, 11 is an overcurrent set value adjusting circuit including an adjusting resistor 112 and a transistor 111, and 12 is a control signal for the primary side. Is a photocoupler for transmitting.

The operation of the switching power supply device configured as described above will be described with reference to FIG.

First, during the normal operation, the control signal from the secondary side passes through the photocoupler 12 and the overcurrent set value adjusting circuit 11
Is transmitted to the transistor 111 of the
Is turned on. When the transistor 111 is turned on, the overcurrent detection resistance value becomes a value in which the current detection resistance 102 and the adjustment resistance 112 are connected in parallel. Then, when some electrical abnormality occurs on the load side and a current exceeding the maximum current value of the normal load flows, the control transistor 101 is turned on, and the base or gate voltage of the switch element 1 is set to a threshold voltage or less, Stop the switch operation, set the output voltage to zero, and prevent equipment failure.

On the other hand, in the standby mode, the control signal from the secondary side passes through the photocoupler 12 and the overcurrent setting value adjusting circuit 1
1 is transmitted to the transistor 111 and the transistor 11
1 is turned off. When the transistor 111 is turned off, the overcurrent detection resistance value becomes the value of only the current detection resistance 102, and the overcurrent protection circuit operates with lower power consumption than in the normal operation. In this state, when some electrical abnormality occurs on the load side and a current exceeding the maximum current value of the normal load flows, the control transistor 101 is turned on,
The base or gate voltage of the switch element 1 is set to the threshold voltage or less, the switch operation is stopped, the output voltage is set to zero, and the device failure is prevented.

As described above, according to this embodiment, the overcurrent set value adjusting circuit 11 is provided, and the operating point of the overcurrent protection circuit is changed by the control signal input from the secondary side, thereby waiting for operation. Even when the power consumption is less than the set value of the overcurrent protection circuit, such as when, the failure can be detected.

[0016]

As described above, according to the present invention, by providing the overcurrent set value adjusting circuit and changing the operating point of the overcurrent protection circuit by the control signal, the protection circuit which is equivalent to the normal operation even in the standby mode is provided. It is a switching power supply device that can realize the operation.

[Brief description of drawings]

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

FIG. 2 is a circuit diagram of a conventional switching power supply device.

[Explanation of symbols]

 1 switch element 2 switch element drive circuit 3 control circuit 4 secondary side rectifier circuit 5 transformer 6 overcurrent protection circuit 7 detection circuit 11 overcurrent set value adjustment circuit 12 photocoupler

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 connected to the secondary winding of the transformer. A rectifying / smoothing circuit for rectifying and smoothing a signal output from the transformer, a detection circuit for detecting a secondary side output voltage obtained from the rectifying / smoothing circuit, and turning on / off a current flowing through the primary winding of the transformer. A switch element that is turned on when the control terminal voltage reaches the threshold voltage, a switch element drive circuit that turns on and off the switch element, and an on time of the switch element by a feedback signal from the detection circuit. A control circuit that controls and stabilizes the secondary side output voltage, and detects the current flowing through the switch element, and when the current reaches a set value, the switch function of the switch element is stopped and output. A switching power supply comprising an overcurrent protection circuit for making the output voltage zero and an overcurrent set value adjustment circuit for adjusting the set value of the overcurrent protection circuit by a control signal input from the secondary side. apparatus.