JPH0916274A - Power source input protecting circuit and switching power source - Google Patents

Abstract

PURPOSE: To prevent malfunction, etc., by the application of an abnormal input voltage to an internal circuit. CONSTITUTION: The protecting circuit and switching power source are provided with a cutoff circuit 15f which is connected to the input voltage line of the switching power source and electrically connects or disconnects the input voltage line, a rectifying and smoothing circuit 15a which rectifies and smoothes the input voltage, detecting circuits 15b and 15c which detect the level of the input voltage from the output of the rectifying and smoothing circuit 15a, and drive circuits 15d and 15e which disconnect the input voltage line 2 by placing the cutoff circuit 15f in operation when the level of the input voltage drops below a specific low voltage or rises above a specific high voltage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply input protection circuit and a switching power supply.

[0002]

2. Description of the Related Art A conventional switching power supply will be described with reference to FIG. 6. In this switching power supply, an AC input voltage input to an input terminal 1 is a fuse 3 in an input voltage line 2, a noise filter 4, and an inrush. Rectification and smoothing is performed by the rectification and smoothing circuit 6 through the current prevention thermistor 5.
The rectified and smoothed input voltage is converted into alternating current by the switching operation of the switching transistor 8 connected to the primary winding 7a of the converter transformer 7. The alternating current induced in the secondary winding 7b of the converter transformer 7 is rectified and smoothed by the rectifying and smoothing circuit 9 and output from the output terminal 10 as an output voltage. The output voltage is detected by the output voltage detection circuit 11 and given to the control circuit 12. The control circuit 12 operates by being supplied with power from the winding 7c of the transformer 7,
The switching operation of the switching transistor 8 is controlled according to the detected output of the output voltage to stabilize the output voltage.

In the above switching power supply,
An overcurrent protection circuit 13 connected to the emitter of the switching transistor 8 is provided. Overcurrent protection circuit 13
When the current from the emitter of the switching transistor 8 is an overcurrent, the control circuit 12 outputs an overcurrent detection output.
Output to The control circuit 12 stops the switching operation of the switching transistor 8 in response to the input of this overcurrent detection output. Further, in this switching power supply, the overvoltage protection circuit 1 connected to the output terminal 10 side
4 is provided. The overvoltage protection circuit 14 outputs an overvoltage detection output to the control circuit 12 when the output voltage is an overvoltage. The control circuit 12 stops the switching operation of the switching transistor 8 in response to the input of this overvoltage detection output.

[0004]

In the conventional switching power supply described above, since the overcurrent and overvoltage protection circuit described above is provided, it is possible to prevent the load connected to the output terminal side from burning, but the internal circuit. Is operating in the high voltage mode, if the input voltage is abnormal, even if the load burnout can be prevented by stopping the switching operation of the switching transistor with the overcurrent protection circuit and the overvoltage protection circuit, Since the abnormal input voltage is applied to the internal circuit, it is not preferable for the circuit components that form the internal circuit.

Further, a fuse is provided on the input side in order to prevent the load from being burned. However, if the fuse is blown out when the input voltage is abnormal, the fuse cannot be restarted unless it is replaced. Therefore, for example, when such a switching power supply is provided as the power supply of the plant equipment operating for 24 hours, such fuse replacement work is not preferable.

Furthermore, when the input voltage drops, the output voltage naturally becomes unstable, but not only that, but there is a possibility that a device using the switching power supply will malfunction.

Therefore, in view of the above-mentioned problems, it is an object of the present invention to prevent an abnormal input voltage from being applied to the internal circuit.

[0008]

In order to achieve such an object, in the power input protection circuit of the first invention,
A cutoff circuit connected within the input voltage line of the power supply to electrically cut off the input voltage line in response to a drive input, a detection circuit for detecting the level of the input voltage, and a predetermined level of the input voltage. And a drive circuit that outputs the drive input to the cutoff circuit in response to the output of the detection circuit that is lowered to a low voltage or less.

In the power supply input protection circuit of the second invention, a cutoff circuit connected within the input voltage line of the power supply to electrically cut off the input voltage line in response to a drive input, and the level of the input voltage. And a drive circuit that outputs the drive input to the cutoff circuit in response to the output of the detection circuit that the level of the input voltage rises above a predetermined high voltage. I am trying.

In the power supply input protection circuit of the third invention, a cutoff circuit connected within the input voltage line of the power supply to electrically cut off the input voltage line in response to a drive input, and the level of the input voltage. A first drive circuit that outputs a drive input to the cutoff circuit in response to an output of the detection circuit that the level of the input voltage has dropped to a predetermined low voltage or less; A second drive circuit that outputs a drive input to the cutoff circuit in response to the output of the detection circuit that the level has risen above a predetermined high voltage.

In the second drive circuit of the third invention, preferably, the first drive circuit is responsive to the detection circuit output that the level of the input voltage has risen above a predetermined high voltage. The drive input may be forcibly output to the cutoff circuit via.

In the third invention, preferably, the detection circuit outputs a first detection output when the level of the input voltage drops below the predetermined low voltage.
And a second detection circuit that outputs a second detection output when the level of the input voltage rises above the predetermined high voltage.
And a detection circuit of the first drive circuit,
A first transistor responsive to a base input of the detection output of the second drive circuit, the second drive circuit responsive to a base input of the second detection output, and a base-emitter of the first transistor. A second transistor connected in parallel to the collector-emitter of
It may be composed of a thyristor which operates in response to the output of the first transistor to the control terminal.

The switching power supply of the fourth invention is characterized by including the power supply input protection circuit.

In the switching power supply of the fifth invention, the power supply input protection circuit is provided, and a display operation is performed in response to the output of the first detection circuit that the input voltage is lower than the predetermined low voltage. A low-voltage input status indicator, a high-voltage input status indicator that performs a display operation in response to the second detection circuit output that the input voltage rises above the predetermined high voltage, and an output voltage is normal. The power supply panel is provided with an output voltage indicator for performing a certain display operation and stopping the display operation when any one of the two indicators is performing the display operation.

[0015]

According to the power supply input protection circuit of the first aspect of the invention, the drive circuit inputs the drive signal to the cutoff circuit in response to the detection output that the voltage of the input voltage line has dropped below a predetermined low voltage from the detection circuit. When the voltage is applied, the cutoff circuit electrically cuts off the input voltage line in response to the drive input, so that an abnormally low input voltage is not input to the internal circuit of the power supply, and malfunction can be prevented.

According to the power input protection circuit of the second invention,
When the drive circuit provides a drive input to the cutoff circuit in response to the detection output that the voltage of the input voltage line has risen above a predetermined high voltage from the detection circuit, the cutoff circuit responds to the drive input and the input voltage is input. Since the line is electrically cut off, an abnormally high input voltage will not be input to the internal circuit of the power supply, which is preferable for parts of the internal circuit.

According to the power input protection circuit of the third invention,
Each drive circuit provides a drive input to the cutoff circuit in response to a detection output that the voltage of the input voltage line drops below a predetermined low voltage or a detection output that rises above a predetermined high voltage from the detection circuit. Then, the cutoff circuit electrically cuts off the input voltage line in response to the drive input, so that an abnormally low or high input voltage is not inputted to the internal circuit of the power supply, so that malfunction can be prevented.

According to the switching power supply of the fourth invention,
Since the power supply input protection circuit is provided, it is possible to prevent the internal circuit components constituting the power supply protection circuit from malfunctioning due to an abnormally low input voltage or a high input voltage.

According to the switching power supply of the fifth invention,
When the input voltage drops below the specified low voltage, the low-voltage input status indicator, when the input voltage rises above the specified high voltage, the high-voltage input status indicator, when the output voltage is normal Since the output voltage indicators each perform a display operation, the user can easily monitor the input voltage and the output voltage.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is an overall circuit block diagram of a switching power supply equipped with a switching power supply input protection circuit according to an embodiment of the present invention. Parts corresponding to those in FIG. Detailed description of the parts related to the reference numerals will be omitted.

Referring to FIG. 1, 1 is an input terminal, 2 is an input voltage line, 3 is a fuse, 4 is a noise filter, 5 is a thermistor, 6 is a rectifying / smoothing circuit, 7 is a converter transformer, 8 is a switching transistor, Reference numeral 9 is a rectifying / smoothing circuit, 10 is an output terminal, 11 is an output voltage detection circuit, 12 is a control circuit, 13 is an overcurrent protection circuit, and 14 is an overvoltage protection circuit.

Since the above-mentioned structure is the same as the conventional one, the description of its operation will be omitted.

In this embodiment, the power input protection circuit 1
It is characterized by having 5. The power supply input protection circuit 15 includes a rectifying / smoothing circuit 15a and a low voltage detecting circuit 15
b, high voltage detection circuit 15c, low voltage side drive circuit 15d,
It has a high voltage side drive circuit 15e and a cutoff circuit 15f.

The input part of the rectifying / smoothing circuit 15a is connected to the input voltage line 2, and the input voltage of the input voltage line 2 is rectified and smoothed and the rectified and smoothed output is output from the output part.

The input portion of the low voltage detection circuit 15b is connected to the output portion of the rectifying / smoothing circuit 15a and the rectifying / smoothing circuit 15a is connected to the output portion.
When the output a falls below a predetermined low voltage, a low voltage detection output is output from the output section to the input section of the low voltage side drive circuit 15d.

The high voltage detection circuit 15c has an input part connected to the output part of the rectifying / smoothing circuit 15a, and the rectifying / smoothing circuit 15c is connected to the output part.
When the output a rises above a predetermined high voltage, a high voltage detection output is output from the output section to the input section of the high voltage side drive circuit 15e.

The low-voltage side drive circuit 15d outputs a low-voltage drive signal from the output section in response to the input of the detection output from the output section of the low-voltage detection circuit 15b.

The high voltage side drive circuit 15e outputs a high voltage side drive signal from the output section to the input section of the low voltage side drive circuit 15d in response to the input of the detection output from the output section of the high voltage detection circuit 15c.

The cutoff circuit 15f is, for example, the noise filter 4.
Two thyristors connected in anti-parallel to the input voltage line 2 between the thermistor 5 and the thermistor 5, or a three-terminal bidirectional thyristor (having almost the same function as the two thyristors connected in anti-parallel and It has a control terminal and two input / output terminals, and is composed of a product name of TRIAC), and the input / output terminals a and b are also controlled in the input voltage line 2 on the front side of the rectifying and smoothing circuit 6. The terminal c is connected to the output section of the low-voltage side drive circuit 15d, and the turn-on operation is performed when the drive signal from the output section of the low-voltage side drive circuit 15d to the control terminal c has a voltage higher than a predetermined value. The input voltage line 2 between the noise filter 4 and the thermistor 5 is electrically connected to each other. However, when the input voltage line 2 is below a predetermined value, a turn-off operation is performed to electrically cut off the power voltage line 2. Eteiru.

In the input protection circuit 15 of the embodiment having such a configuration, when the input voltage of the input voltage line 2 drops below a predetermined low voltage, it responds to the drive input from the low voltage side drive circuit 15d. Since the cutoff circuit 15f composed of a thyristor cuts off the input voltage line 2, it is prevented that an abnormally low input voltage is applied to the internal circuit of the switching power supply, and as a result, malfunction of the power supply is prevented. . When the input voltage of the input voltage line 2 rises above a predetermined high voltage, the low-voltage side drive circuit 15d responds by the output of the high-voltage side drive circuit 15e, whereby the cutoff circuit 15f performs the cutoff operation. Since the input voltage line 2 is cut off, it is possible to prevent an abnormally high input voltage from being applied to the internal circuit of the switching power supply.

FIG. 2 is a detailed circuit diagram of the embodiment shown in FIG. 1, and the portions corresponding to those in FIG. 1 are designated by the same reference numerals. In FIG. 2, the power supply input protection circuit 15 according to this embodiment will be described in detail. The rectifying / smoothing circuit 15a is a rectifying diode D1 and a smoothing capacitor C1, and the low voltage detecting circuit 15b is a dividing resistor R1 and R2, and a high voltage detecting circuit. The circuit 15c includes a Zener diode D2 and a resistor R.
3, the low-voltage side drive circuit 15d has a current limiting resistor R5,
The transistor TR1 and the current limiting resistor R6, the high-voltage side drive circuit 15e is a current limiting resistor R4 and the transistor TR2, and the cutoff circuit 15f is a three-terminal bidirectional thyristor (trade name: TRIAC).

The operation of the power input protection circuit 15 composed of such concrete circuit elements will be described below.
The input voltage of the input voltage line 2 is rectified by the rectifying diode D1 in the rectifying / smoothing circuit 15a, smoothed by the smoothing capacitor C1, and input to the low voltage detecting circuit 15b and the high voltage detecting circuit 15c, respectively.

In the low voltage detection circuit 15b, the output of the rectifying / smoothing circuit 15a, that is, the output of the smoothing capacitor C1 is divided by the dividing resistors R1 and R2. The resistance value of each of the dividing resistors R1 and R2 is set so that the dividing voltage appearing at the connection point d between them becomes the voltage when the input voltage is a predetermined low voltage. Therefore, the transistor TR1 which is the low voltage side drive circuit 15d is turned off by the voltage of the connection point d when the input voltage drops below a predetermined low voltage, that is, the detection output of the low voltage detection circuit 15b, and the thyristor 15f which is the cutoff circuit. Is turned off by its off output, that is, the drive input provided to its control terminal c, whereby the input voltage line 2 is electrically cut off, and as a result, the input voltage is applied to the switching power supply internal circuit such as the rectifying and smoothing circuit 6. The internal circuit of the switching power supply is prevented from malfunctioning due to an abnormally low input voltage below a predetermined low voltage.

In the high voltage detection circuit 15c,
When the input voltage in the input voltage line 2 rises above a predetermined high voltage, the Zener diode D2 to which the output of the rectifying / smoothing circuit 15a is applied becomes conductive, resulting in the voltage at the connection point e between the Zener diode D2 and the resistor R3. That is, the detection output of the high-voltage detection circuit 15c turns on the transistor TR2 which is the high-voltage side drive circuit 15d, and the transistor TR1 is turned off by this, so that the thyristor 15f turns off its output, that is, the drive input. In response to the turn-off operation, the input voltage line 2 is electrically cut off, the input voltage is not applied to the switching power supply internal circuit such as the rectifying / smoothing circuit 6, and the switching power supply internal circuit has a predetermined high voltage. Prevents abnormally high input voltage above the applied voltage It is.

In the switching power supply shown in FIG. 2, the overcurrent protection circuit 13 and the overvoltage protection circuit 14 are provided.
(In the figure, 14a and 14b form a photocoupler), and the circuit element groups respectively constituting them are surrounded by blocks. Although the output voltage detection circuit 11 is not shown surrounded by blocks, the three-terminal regulator 11a, which is a circuit element forming the output voltage detection circuit 11, conducts in accordance with the magnitude of the output voltage, whereby the photocouplers 11b and 11c are connected. Is supposed to work. The control circuit 12 is also not shown surrounded by blocks, but the overcurrent protection circuit 1
It operates in response to the three outputs, the output of the overvoltage protection circuit 14, and the output of the output voltage detection circuit 11. Since the overcurrent protection operation of the overcurrent protection circuit 13, the overvoltage protection operation of the overvoltage protection circuit 14, and the output voltage stabilization operation of the control circuit 12 shown in FIG. 2 are well known, the description thereof will be omitted. To do.

FIG. 3 is a detailed circuit diagram of a switching power supply having a power supply input protection circuit according to another embodiment of the present invention. Parts corresponding to those in FIG. Detailed description of the part related to is omitted.

Referring to FIG. 3, in this embodiment,
A resistor R7 and a transistor T are provided in the power input protection circuit 15.
The series circuit of the collector and the emitter of R3 and the series circuit of the resistors R8 and R9 are both connected in parallel to the smoothing capacitor C1 of the rectifying and smoothing circuit 15a, and the base of the transistor TR3 is connected to the connection point f of the resistors R7 and R8. And a circuit constituted by connecting a light emitting diode D3 (input voltage abnormal drop display element) to the collector of the transistor TR3, and further, a high voltage detection circuit 15c.
A light-emitting diode D4 (input voltage abnormal rise display element) is connected between the Zener diode D2 and the resistor R3 constituting the.

In addition, the switching power supply having the above-mentioned configuration further includes a light emitting diode D5 (output voltage normal display element) on the output terminal 10 side, which operates to emit light when the output voltage is normal.

The light emitting operation of these light emitting diodes D3, D4 and D5 will be described with reference to FIG. Here, (a) of FIG. 4 shows a change of the input voltage, HI is a line of a predetermined high voltage, and when the input voltage rises beyond this, it means that the input voltage has risen abnormally. . LO is a predetermined low voltage line, and when the input voltage drops below this line, it means that the input voltage has dropped abnormally. Therefore, when there is an input voltage between both lines of this HI LO, the thyristor 15f is turned on, the input voltage line 2 is connected and the output voltage appears normally at the output terminal 10, and the line between both lines of this HI and LO is When there is no input voltage, the thyristor 15f is turned off, the input voltage line 2 is cut off, and the output voltage does not normally appear at the output terminal 10. FIG. 4B shows a state in which the thyristor 15f is turned on and off corresponding to FIG. 4A. In FIG. 4C, the light emitting diode D5 is lit, the light emitting diode D4 is lit,
Indicates the lighting of the light emitting diode D3.

Referring to FIG. 4, when the input voltage is normal, thyristor 15f is turned on, so that the output voltage normally appears at output terminal 10, and
The light emitting diode D5 is in a lighting operation (period in FIG. 4). When the output voltage is not normal, the light emitting diode D5
Is extinguished (period in FIG. 4). When the output voltage is not normal, there are cases where the input voltage drops below a predetermined low voltage and cases where it rises above a predetermined high voltage. First, when the input voltage drops below a predetermined low voltage, the voltage at the connection point between the resistors R8 and R9 drops and the transistor TR3 is turned on. As a result, a current flows through the light emitting diode D3 and the light emitting diode D3 operates. It emits light (period of FIG. 4). When the input voltage rises above a predetermined high voltage, the Zener diode D2
As a result, the current flows through the light emitting diode D4, and the light emitting diode D4 operates to emit light (period in FIG. 4). In this way, the light emitting diode D5 operates to emit light when the output voltage is normal to notify the user of this switching power supply of that fact, but the light emitting diode D3 detects that the input voltage is abnormally lowered. When the power supply to the device equipped with this switching power supply is too low to cause the malfunction, the light emitting operation is performed, and by stopping the light emitting operation of the light emitting diode D5, the alarm is issued, and the light emitting diode D4 is input. When the voltage rises abnormally and may affect the components of the internal circuit of this switching power supply, the light emitting operation is performed and the light emitting diode D5
It can be warned by stopping the light emitting operation of.

FIG. 5 is a diagram showing the configuration of the power supply panel on the back side of the switching power supply. From the upper side of the power supply panel 16, the light emitting diode D5 that lights up when the output voltage is normal, and the input voltage abnormally dropped. A light emitting diode D3 that lights up when the input voltage abnormally rises, and a light emitting diode D4 that lights up when the input voltage rises abnormally are provided. In the figure, (a) shows a state where the light emitting diode D5 is lit, (b) shows a state where the input voltage abnormally rises and the light emitting diode D4 is lit, and (c) shows an abnormal input voltage. The state is shown in which the light emitting diode D3 is lowered and is turned on.

[0043]

As described above, according to the present invention, the input voltage line is cut off when the level of the input voltage drops below a predetermined low voltage or rises above a predetermined high voltage. The internal circuit does not malfunction due to abnormal input voltage.

[Brief description of the drawings]

FIG. 1 is an overall circuit block diagram of a switching power supply including a power input protection circuit according to an embodiment of the present invention.

FIG. 2 is a specific circuit diagram of FIG.

FIG. 3 is a specific circuit diagram of a switching power supply including a power supply input protection circuit according to another embodiment of the present invention.

FIG. 4 is a diagram for explaining the operation of the light emitting diode that displays the state of the input voltage and the output voltage of the embodiment of FIG. 3 by emitting light.

5 is a diagram showing a configuration of a power supply panel on the back surface of the switching power supply of FIG.

FIG. 6 is a circuit block diagram of a conventional switching power supply.

[Explanation of symbols]

 1 Input Terminal 2 Input Voltage Line 3 Fuse 4 Noise Filter 5 Thermistor 6 Rectification Smoothing Circuit 15 Input Protection Circuit 15a Rectification Smoothing Circuit 15b Low Voltage Detection Circuit 15c High Voltage Detection Circuit 15d Low Voltage Side Driving Circuit 15d High Voltage Side Driving Circuit 15e Interruption circuit

Claims (7)

[Claims] 1. A cutoff circuit connected to an input voltage line of a power supply to electrically cut off the input voltage line in response to a drive input, a detection circuit for detecting a level of the input voltage, and the input voltage. And a drive circuit that outputs the drive input to the cutoff circuit in response to the detection circuit output that the level has fallen below a predetermined low voltage. 2. A cutoff circuit connected to an input voltage line of a power supply to electrically cut off the input voltage line in response to a drive input, a detection circuit for detecting a level of the input voltage, and the input voltage. And a drive circuit that outputs the drive input to the cutoff circuit in response to the output of the detection circuit that the level has risen above a predetermined high voltage. 3. A cutoff circuit connected to an input voltage line of a power supply to electrically cut off the input voltage line in response to a drive input, a detection circuit for detecting a level of the input voltage, and the input voltage. A first drive circuit that outputs a drive input to the cutoff circuit in response to the detection circuit output that the level of the input voltage has dropped below a predetermined low voltage; and the level of the input voltage rises above a predetermined high voltage. And a second drive circuit that outputs a drive input to the cutoff circuit in response to the output of the detection circuit. 4. The second drive circuit is forcibly forced through the first drive circuit in response to the detection circuit output that the level of the input voltage rises above a predetermined high voltage. The power supply input protection circuit according to claim 3, wherein the drive input is output to the cutoff circuit. 5. A first detection circuit that outputs a first detection output when the level of the input voltage drops below the predetermined low voltage, and the level of the input voltage is the predetermined level. A second detection circuit that outputs a second detection output when the voltage rises above the high voltage of the first detection circuit, wherein the first drive circuit responds to a base input of the first detection output. A second drive circuit having a transistor, wherein the second drive circuit is responsive to the base input of the second detection output, and the base-emitter of which is connected in parallel to the collector-emitter of the first transistor; 5. The power supply input protection circuit according to claim 4, wherein the cutoff circuit comprises a thyristor which operates in response to an output of the first transistor to a control terminal. 6. A switching power supply comprising the power input protection circuit according to claim 1. Description: 7. A display operation comprising the power supply input protection circuit according to claim 3, wherein the display operation is responsive to the output of the first detection circuit that the input voltage is lower than the predetermined low voltage. A low voltage input status indicator, a high voltage input status indicator that performs a display operation in response to the second detection circuit output that the input voltage rises above the predetermined high voltage, and an output voltage A switching power supply, comprising: a power supply panel; and an output voltage indicator for performing a normal display operation and stopping the display operation when any one of the two displays is in the display operation.