JPH08182315A - Switching power source - Google Patents

Abstract

PURPOSE: To protect a switching regulator by stopping the operation of the regulator without melting a fuse at the time of inputting an overvoltage. CONSTITUTION: A switching power source 1 comprises a rectifying and smoothing circuit 2 for converting AC to DC and a switching regulator 3 having a switching controller 10 to convert the DC of the circuit 2 to an AC, and outputs a switching control signal of OFF operation to the controller 10 if the output voltage of the circuit 2 is below a lower limit control value and above an upper limit control value. An input voltage monitor control circuit 20 for outputting a switching control signal of on-operation to the switching controller if the output voltage of the circuit 2 falls within the range of the lower limit control value and the upper limit control value is provided.

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 device having a switching regulator circuit, and more particularly to a device for protecting a switching regulator circuit when an input voltage becomes an overvoltage.

[0002]

2. Description of the Related Art FIG. 3 is a circuit diagram showing a configuration of a conventional switching power supply device. In the figure, reference numeral 1 denotes a switching power supply device, which includes a rectifying / smoothing circuit 2 and a switching regulator circuit 3. 4 is a rectifying / smoothing circuit 2
Is an input terminal, 5 is a fuse, 6 is a rectifying diode bridge, and 7 is a smoothing capacitor. Reference numeral 8 is a transformer of the flyback type switching regulator circuit 3, and the primary side is a smoothing capacitor 7 which is an output side of the rectifying / smoothing circuit 2.
Connected with. Reference numeral 9 is a switching transistor provided on the primary side of the transformer 8, 10 is a switching control circuit for on / off controlling the switching transistor 9, 11 is a rectifying diode provided on the primary side of the transformer 8, 12 is a smoothing capacitor, and 13 is The output terminal of the switching regulator circuit 3 is connected to the smoothing capacitor 12. Reference numeral 14 is a load connected to the output terminal 13.

The conventional switching power supply circuit is constructed as described above, and the AC voltage input from the input terminal 4 of the rectifying / smoothing circuit 2 is converted into a DC voltage by the rectifying diode bridge 6 via the fuse 3 and smoothed. Smoothing is performed by the capacitor 7, and power is supplied to the switching regulator circuit 3. When there is an abnormality in the switching regulator circuit 3 or the like, an excessive current flows, and the fuse 5 is blown to disconnect the switching power supply device 1 and the AC power supply to protect the switching regulator circuit 3 and the like. Further, the fuse 5 is included in the switching power supply device 1, and in most cases, the fuse 5 is mounted on the substrate forming the circuit.

[0004]

However, the conventional switching power supply device having the above-mentioned structure has the following problems. 1) The fuse 5 is blown even when an excessive voltage is input due to a mistake in the connection of the AC power source connected to the input terminal 4 of the rectifying / smoothing circuit 2 to protect the switching power supply device 1, but the fuse replacement is easy. I can't. 2) The switching regulator circuit 3 is prone to failure,
It takes a lot of repair man-hours for the switching regulator circuit 3. In order to eliminate the above problems, an object of the present invention is to protect the switching regulator circuit and the like by stopping the operation of the switching regulator circuit rather than cutting the fuse when an excessive voltage is input. To do.

[0005]

A switching power supply device according to the present invention outputs a switching control signal of operation OFF to a switching control circuit when the output voltage of a rectifying / smoothing circuit is below a lower limit specified value and above an upper limit specified value. However, when the output voltage of the rectifying / smoothing circuit is within the range between the lower limit specified value and the upper limit specified value, the switching control circuit is provided with an input voltage monitoring control circuit that outputs an operation-on switching control signal.

[0006]

In the present invention, when the input voltage monitoring control circuit outputs the rectification / smoothing circuit with the output voltage of the rectification / smoothing circuit being below the lower limit specified value and above the upper limit specified value, it outputs a switching control signal of operation OFF to the switching control circuit. When the output voltage of the smoothing circuit is within the range of the lower limit value and the upper limit value, the operation control signal is output to the switching control circuit, so the input voltage input to the rectifying / smoothing circuit is outside the specified range. In this case, the input voltage monitoring control circuit outputs a switching control signal of operation OFF to the switching control circuit to stop the operation of the switching regulator circuit, so that the fuses of the switching regulator circuit and the rectifying / smoothing circuit can be protected.

[0007]

【Example】

(Structure) FIG. 1 is a circuit diagram showing the structure of a switching power supply device according to an embodiment of the present invention, and FIG. 2 is a graph showing the relationship between the output voltage of the present invention and the operation of a switching regulator circuit. In the figure, the same configurations as those of the conventional example are denoted by the same reference numerals as those of the conventional example, and duplicate description of the configurations is omitted. Two
Reference numeral 0 is an input voltage monitoring control circuit that controls the on / off operation of the switching control circuit 10 according to the input voltage input to the rectifying / smoothing circuit. Reference numerals 21 and 22 denote series-connected high-voltage determination resistors provided between terminals of the smoothing capacitor 7 of the rectification / smoothing circuit 2, and reference numeral 23 denotes high-voltage determination resistors 21 and 22.
Is a Zener diode for high voltage determination having a cathode connected to a connection point of.

Reference numeral 24 is a low voltage determination resistor having one end connected to the positive terminal of the smoothing capacitor 7, 25 is a low voltage determination zener diode having a cathode connected to the other end of the low voltage determination resistor 24, and 26 is a control. Transistor, the base of which is connected to the anode of the high-voltage determination Zener diode 23, the collector of which is connected to the other end of the low-voltage determination resistor 24, and the emitter of which is connected to the negative terminal of the smoothing capacitor 7. ing. Reference numeral 27 is a control photocoupler for outputting a switching control signal for turning on / off the operation to the switching control circuit 10.
a is provided between the low-voltage determination Zener diode 25 and the negative terminal of the smoothing capacitor 7, and its phototransistor 27b is provided on the control input side of the switching control circuit 10. Input voltage monitoring control circuit 20
Is composed of a high voltage determination resistor 21 to a control photocoupler 27. The input voltage monitoring control circuit 20 monitors the output voltage of the rectifying / smoothing circuit 2, but since the output voltage fluctuates in accordance with the input voltage, it substantially monitors the input voltage.

(Operation) The operation of the switching power supply device of the present invention will be described below with reference to the graphs of FIGS. First, before explaining the operation of the switching power supply device of the present invention, the voltage equations of the output voltage and the voltage at each part of the switching power supply device are shown below. 1) In the low voltage range Vin <Vz1 + VD 2) In the power supply operating range Vz1 + VD <Vin, and VinR <Vzu +
VBE 3) High voltage range Vzu + VBE <VinR where Vin = output voltage of rectifying / smoothing circuit VinR = (resistor 22 / resistor 21 + resistor 22) x Vin VD = operating voltage of photocoupler 27 for control Vz1 = for low voltage judgment Breakdown voltage of Zener diode 25 Vzu = Breakdown voltage of Zener diode 23 for high voltage judgment VBE = Base-emitter voltage of control transistor 26

Next, the operation of the switching power supply device of the present invention will be described. The AC voltage input from the input terminal 4 of the rectifying / smoothing circuit 2 of the switching power supply device 1 is converted into a DC voltage by the rectifying diode bridge 6 via the fuse 5, smoothed by the smoothing capacitor 5, and then supplied to the switching regulator circuit 3. While supplying electric power, the input voltage monitoring control circuit 20 monitors the output voltage of the rectification / smoothing circuit 2. When the output voltage Vin of the rectifying / smoothing circuit 2 is equal to or lower than the lower limit specified value, the lower limit specified value is set to a voltage obtained by adding the breakdown voltage Vz1 of the low voltage determination Zener diode 24 and the operating voltage VD of the control photocoupler 27. Because
The output voltage Vin of the rectifying / smoothing circuit 2 is a voltage obtained by adding the breakdown voltage Vz1 of the low-voltage determination Zener diode 24 and the operating voltage VD of the control photocoupler 27 (this voltage is substantially the voltage of the low-voltage determination Zener diode 24). It does not reach the breakdown voltage).

Therefore, the low-voltage determination Zener diode 24 is non-conductive, and the photodiode 27a of the control photocoupler 26 is also turned off and the phototransistor 27b.
Is also turned off, and the phototransistor 27b inputs a switching control signal for turning off the operation to the control input side of the switching control circuit 10 to turn off the switching control circuit 10. When the output voltage Vin of the rectifying / smoothing circuit 2 is equal to the lower limit specified value, the low voltage determination Zener diode 24 is considered to be conductive, but the low voltage determination Zener diode 24 is unstable because the operation is unstable. The condition was set to be non-conductive.

When the output voltage Vin of the rectifying / smoothing circuit 2 is equal to or higher than the upper limit specified value, the high voltage determination Zener diode 23 receives a voltage VinR which is a voltage division ratio of the high voltage determination resistors 21 and 22, and the upper limit thereof is applied. The specified value is the voltage V of the voltage division ratio
Since the breakdown voltage Vzu of the high-voltage determination Zener diode 23 at inR is added to the base-emitter voltage of the control transistor 26, the output voltage Vin of the rectifying / smoothing circuit 2 is for high-voltage determination. Resistance 2
When the voltage becomes equal to or higher than the voltage VinR of the voltage division ratio of 1 and 22, the voltage obtained by adding the breakdown voltage Vzu of the high-voltage determination Zener diode 23 and the base-emitter voltage of the control transistor 26 (this voltage is a substantial high-voltage determination Voltage becomes the breakdown voltage of the Zener diode 23).

Therefore, the high-voltage determination zener diode 23 becomes conductive, the control transistor 26 is turned on accordingly, and the base-emitter voltage of the control transistor 26 becomes smaller than that of the low-voltage determination zener diode 24. The low voltage determination Zener diode 24 becomes non-conductive, the photodiode 27a of the control photocoupler 26 also turns off, the phototransistor 27b also turns off, and the phototransistor 27b is turned off at the control input side of the switching control circuit 10. The switching control circuit 10 is turned off by inputting a signal. When the output voltage Vin of the rectification / smoothing circuit 2 is equal to the upper limit specified value, the high-voltage determination Zener diode 23 is considered to be conductive, but the high-voltage determination Zener diode 23 is unstable because the operation is unstable. The condition was set to be non-conductive.

Further, the output voltage Vin of the rectifying / smoothing circuit 2
Is within the range between the lower limit specified value and the upper limit specified value, the output voltage Vin of the rectifying / smoothing circuit 2 exceeds the breakdown voltage Vz1 of the low voltage determination zener diode 24, and the low voltage determination zener diode 24 becomes conductive. . Further, since the breakdown voltage Vzu of the high voltage determination Zener diode 23 is not reached, the high voltage determination Zener diode 23 is non-conductive. Therefore, the photodiode 27a of the control photocoupler 26 is turned on, the phototransistor 27b is also turned on, and the phototransistor 27b inputs the switching control signal of the operation on to the control input side of the switching control circuit 10 to operate the switching control circuit 10. It turns on.

(Effect) As described above, according to the above embodiment, when the output voltage of the rectifying / smoothing circuit 2 is out of the predetermined range, the input voltage monitoring control circuit 20 turns off the operation of the switching control circuit 10. Since the switching control signal is output and the switching regulator circuit 3 stops operating, the switching regulator circuit 3 and the fuse 5 of the rectifying / smoothing circuit 2 can be protected. Further, the trouble of the switching regulator circuit 3 due to the input outside the input voltage range is eliminated, and the man-hours for repairing the switching regulator circuit 3 are eliminated. When the switching regulator circuit 3 is abnormal, an excessive input current flows as usual, and the fuse 5 is blown to protect the switching power supply device 1.

(Usage mode) In the above embodiment, an example in which the present invention is applied to a switching power supply device having a flyback type switching regulator circuit has been described, but it is also applicable to a switching power supply device having a forward type switching regulator circuit.

[0017]

As described above, according to the present invention, the input voltage monitoring control circuit provided in the rectifying / smoothing circuit performs switching control when the output voltage of the rectifying / smoothing circuit is lower than the lower limit specified value or higher than the upper limit specified value. When the rectification / smoothing circuit outputs a switching control signal that is operation-off and the output voltage of the rectifying / smoothing circuit is within the specified lower and upper limits, the switching control circuit outputs an operation-on switching control signal. When the input voltage input to the smoothing circuit is outside the specified range, the input voltage monitoring control circuit outputs an operation-off switching control signal to the switching control circuit and the switching regulator circuit stops operating. And a rectification / smoothing circuit fuse protection, and a switching regulator with an input outside the input voltage range It has the effect that repair man-hours of the switching regulator circuit is eliminated gone failure of the road.

[Brief description of drawings]

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

FIG. 2 is a graph showing the relationship between the output voltage of the present invention and the operation of the switching regulator circuit.

FIG. 3 is a circuit diagram showing a configuration of a conventional switching power supply device.

[Explanation of symbols]

 1 Switching Power Supply Device 2 Rectification / Smoothing Circuit 3 Switching Regulator Circuit 10 Switching Control Circuit 20 Input Voltage Monitoring and Control Circuit

Claims (2)

[Claims] 1. A switching power supply device comprising a rectifying / smoothing circuit for converting alternating current to direct current, and a switching regulator circuit having a switching control circuit for converting direct current of the rectifying / smoothing circuit to alternating current. When the output voltage of the smoothing circuit is below the lower limit specified value and above the upper limit specified value, a switching control signal of operation OFF is output to the switching control circuit, and the output voltage of the rectifying / smoothing circuit is below the lower limit specified value and the upper limit specified value. A switching power supply device comprising an input voltage monitoring control circuit for outputting an operation-on switching control signal to the switching control circuit when within the range. 2. The input voltage monitoring control circuit includes a control photocoupler for outputting a switching control signal of operation OFF or operation ON to the switching control circuit, and an output side of the rectifying / smoothing circuit and the control photocoupler. If the output voltage of the rectifying / smoothing circuit is less than or equal to the lower limit specified value, the output voltage of the rectifying / smoothing circuit becomes the lower limit when the output voltage of the rectifying / smoothing circuit is in a non-conducting state so that no current flows through the diode of the control photocoupler. In the case of a specified value or more, a zener diode for low voltage determination that becomes conductive so that a current flows through the diode of the control photocoupler, and is provided between the output side of the rectifying / smoothing circuit and the control photocoupler, When the output voltage of the rectifying / smoothing circuit is below the upper limit specified value, it becomes non-conductive, and when the output voltage is above the upper limit specified value, it becomes conductive. High-voltage determination Zener diode which is in a state, and is provided between the output side of the rectifying / smoothing circuit and the control photocoupler, and the output voltage of the rectifying / smoothing circuit is in a conductive state at an upper limit value or more. A control transistor that is turned on by a high-voltage determination zener diode and that controls the low-voltage determination zener diode to be in a non-conducting state so that current does not flow to the diode of the control photocoupler. The switching power supply device according to claim 1, which is characterized in that.