JPH10214123A - Circuit for detecting abnormality and power source unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To exactly detect an abnormal state including short circuit even when the excess current protection characteristics of a constant voltage element have fold-back characteristics. SOLUTION: A constant voltage element 1 turns a voltage inputted from a DC power source 3 into a contact voltage, and outputs it to an output terminal 4. An abnormality detecting circuit 2 monitors the voltage at the input side and the voltage at the output side of the constant voltage element 1, and when the relation of the both voltages is within a prescribed range, the abnormality detecting circuit 2 judges that a normal operation is executed, and does not operate abnormality detection. In this case, when a load connected with the output terminal 4 side is short-circuited, the constant voltage element 1 performs a protecting operation having fold-back characteristics for pressing both the output voltage and the output currents. Therefore, the voltage at the output side is made lower than the voltage at the input side of the constant voltage element 1, and the relation of the both voltages is beyond the prescribed range. Then, The abnormality detecting circuit 2 detects this, and outputs an abnormality signal 100.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply device using a constant voltage element for stabilizing an output voltage, and more particularly to an abnormality detection circuit for detecting an abnormality such as a load short circuit.

[0002]

2. Description of the Related Art A constant voltage element generally called a three-terminal / four-terminal regulator has a protection function of detecting an overcurrent by itself and lowering an output voltage. These functions are those of the element itself, and are not intended to protect the entire device that supplies power to the constant voltage element. However, when there is an abnormality in the output of the constant voltage element,
By transmitting an abnormality to a device that supplies power to the constant voltage element, the entire device can be protected, safety can be improved, and a disaster or the like can be minimized. Such a conventional technique can be easily performed by a method as disclosed in Japanese Patent Application No. 2-409531.

FIG. 12 is a block diagram showing an example of a conventional DC power supply device having a function of easily protecting the entire device when an abnormality occurs when the above-described constant voltage element is used. The DC output supplied from the DC power supply 3 is supplied to the constant voltage element 1 through the overcurrent detector 16. The constant voltage element 1 converts the input DC voltage into a constant voltage and outputs the voltage to the output terminal 4 side. Here, when a load (not shown) on the output terminal 4 side causes a short circuit or the like, the constant voltage element 1 protects the circuit by reducing both the voltage and the current as shown in FIG. However, at this time, since the constant-voltage element 1 has a so-called square-shaped characteristic, the current on the input side also becomes small, the overcurrent detection unit 16 cannot detect the overcurrent, and the protection function for the entire device works. There was a problem that there was no.

[0004]

In a conventional power supply device for stabilizing an output voltage through a constant voltage element, when the overcurrent protection characteristic of the constant voltage element has a characteristic of "f", when a load short circuit occurs, There was a problem that the abnormality of the device could not be detected and the protection function for the entire device did not work.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problem, and reliably detects an abnormal state including a short circuit even when the overcurrent protection characteristic of the constant voltage element has a characteristic. It is an object of the present invention to provide an abnormality detection circuit capable of detecting an abnormal state including a short circuit and reliably protecting the entire apparatus by mounting the abnormality detection circuit.

[0006]

According to a first aspect of the present invention, there is provided a first input circuit for inputting the input voltage of a constant voltage element for outputting an input voltage at a constant voltage; and an output voltage of the constant voltage element. And a comparison circuit that compares the two voltages input by the first and second input circuits and outputs an abnormal signal when an abnormality is detected.

With such a configuration, the first and second input circuits are constituted by, for example, resistance voltage dividing circuits, and input from the first and second input circuits by appropriately setting a resistance value. If the difference between the input voltage and the output voltage of the constant voltage element in the normal state and the difference between the input voltage and the output voltage of the constant voltage element when an abnormality such as a short circuit occurs on the output side, it is possible to make a difference. The comparison circuit constituted by the arithmetic circuit and the like detects the difference between the differences and detects an abnormality. Therefore, if the constant-voltage element has an overcurrent characteristic in the shape of a square, if an abnormality such as a short circuit occurs on the output side, the voltage on the output side decreases. The comparison circuit detects an abnormality.

According to a second aspect of the present invention, there is provided a configuration in which a time constant circuit is provided on the output side of the comparison circuit, and the abnormal signal is extracted through the time constant circuit.

With this configuration, when the power supply is turned on and the voltage on the output side is lower than the voltage on the input side of the constant voltage element, the comparison circuit outputs an abnormal signal. It is absorbed by the constant circuit until the circuit reaches a steady state. For this reason, the comparison circuit does not output an abnormal signal during an excessive period such as when the power is turned on.

According to a third aspect of the present invention, when an output voltage of a DC power supply for supplying a voltage to the constant voltage element becomes a predetermined value or more,
A power supply control circuit is provided for supplying the output voltage of the DC power supply to the comparison circuit and operating the comparison circuit.

With this configuration, when the power is turned on, the power supply control circuit supplies the output voltage of the DC power supply to the comparison circuit until the output voltage of the DC power supply that supplies the voltage to the constant voltage element reaches a predetermined value. Therefore, immediately after the power supply is turned on, the comparison circuit does not operate, and even when the voltage on the output side is lower than the voltage on the input side of the constant voltage element when the power supply is turned on, the comparison circuit does not output an abnormal signal. . Thereafter, when the output voltage of the DC power supply becomes equal to or higher than a predetermined value, the power supply control circuit supplies the output voltage of the DC power supply to the comparison circuit to operate the comparison circuit. At this time, the circuit is in a steady state, and the comparison circuit is not in a state of erroneously detecting an abnormal signal.

A fourth aspect of the present invention is a voltage detecting circuit for detecting that the output voltage of the constant voltage element becomes equal to or higher than a threshold value;
A power switch circuit for supplying an operating current to the comparison circuit to operate the comparison circuit when the voltage detection circuit detects that the output voltage has become equal to or higher than a threshold value.

With this configuration, when the power is turned on, the voltage on the output side is lower than the voltage on the input side of the constant voltage element. Therefore, when the power is turned on, the output voltage detected by the voltage detection circuit is detected. Is less than or equal to the threshold, the power supply control circuit does not supply an operating current to the comparison circuit. Therefore, when the power is turned on, the comparison circuit does not output an abnormal signal even if the voltage on the output side is lower than the voltage on the input side of the constant voltage element. Thereafter, when the voltage detection circuit detects that the output voltage has become equal to or higher than the threshold value, the power switch circuit supplies an operation current to the comparison circuit to operate the comparison circuit. At this time, the circuit is in a steady state,
The comparison circuit is not in a state where the abnormal signal is erroneously detected.

According to a fifth aspect of the present invention, there is provided an abnormality notification circuit which, when an abnormality detection signal output from the comparison circuit is input, informs the abnormality by appealing to human vision or hearing.

With this configuration, when the abnormality notification circuit receives the abnormality detection signal output from the comparison circuit,
Turn on the lamp or sound a buzzer to notify maintenance personnel of the abnormality detection.

The invention according to claim 6 is a first input circuit for inputting the input voltage of a constant voltage element for outputting an input voltage at a constant voltage; and a second input circuit for inputting the output voltage of the constant voltage element. An input circuit; a first comparison circuit that outputs an abnormal signal by comparing the two voltages input by the first and second input circuits; and the constant voltage that is inserted at an input side of the constant voltage element. A resistor for passing a current input to the element; a third input circuit for inputting a voltage on a current input side of the resistor; a fourth input circuit for inputting a voltage on a current output side of the resistor; A second comparison circuit that compares the two voltages input by the fourth input circuit and outputs an abnormality signal when an abnormality is detected; and a logical sum of the abnormality signals output from the first and second comparison circuits And a logic circuit for taking the output.

With such a configuration, the first and second input circuits are constituted by, for example, resistance voltage dividing circuits, and input from the first and second input circuits by appropriately setting a resistance value. If the difference between the input voltage and the output voltage of the constant voltage element in the normal state and the difference between the input voltage and the output voltage of the constant voltage element when an abnormality such as a short circuit occurs on the output side, it is possible to make a difference. The first comparison circuit detects the difference between the differences,
Detect abnormalities. Therefore, if the constant voltage element has the overcurrent characteristic in the shape of a square, the voltage on the output side drops when an abnormality such as a short circuit occurs on the output side. The first comparison circuit detects an abnormality. Also,
The third and fourth input circuits are also constituted by, for example, resistance voltage dividing circuits, and by appropriately setting the resistance value, the second comparison circuit allows the current input to the constant voltage element in a normal state to pass. An overcurrent abnormality is detected by detecting a difference between an input voltage and an output voltage of the resistor and a difference between the input voltage and the output voltage when an overcurrent flows through the resistor. On the other hand, the logic circuit outputs an abnormal signal output from one or both of the first and second comparison circuits to detect an abnormality when the overcurrent protection of the square-shaped constant voltage element is activated and An abnormal signal indicating an overcurrent abnormality when the constant voltage element is operating in a steady state is output.

A voltage output circuit for outputting a DC voltage; a constant voltage element for making the output voltage of the voltage output circuit constant; a voltage on the input side and a voltage on the output side of the constant voltage element 7. The method according to claim 1, further comprising detecting an abnormality.
And the abnormality detection circuit described above.

With this configuration, the abnormality detection circuit detects abnormality when a short circuit or the like occurs on the output side of the constant voltage element and the voltage on the output side of the constant voltage element drops.
Outputs an abnormal signal. This abnormal signal protects the entire power supply device including the voltage output circuit.

The invention according to claim 8 is provided with a feedback circuit for reducing or cutting off the DC voltage from the voltage output circuit when the abnormality detection circuit detects an abnormality.

With this configuration, when a short circuit or the like occurs on the output side of the constant voltage element and the voltage on the output side of the constant voltage element drops, the abnormality detection circuit outputs an abnormality signal to the feedback circuit. . The feedback circuit reduces or cuts off the DC voltage from the voltage output circuit according to the input of the abnormal signal.

[0022]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a first embodiment of a power supply device provided with an abnormality detection circuit according to the present invention. 1 is a constant voltage element having a characteristic called a three-terminal / four-terminal regulator, 2 is an abnormality detection circuit for detecting an abnormality on the load side such as a load short circuit, 3 is a DC power supply, 4 is an output to which a load is connected. Terminal. Note that a five-terminal regulator may be used as the constant voltage element 1.

FIG. 2 is a circuit diagram showing a first embodiment of the abnormality detection circuit of the present invention shown in FIG. 21 is a divided voltage V1 of the input voltage to the constant voltage element 1 and the constant voltage element 1
A comparison circuit that compares the output voltage from the divided voltage V2 with the divided voltage V2 and outputs an abnormal signal based on the comparison result;
1, R1 and R2 are resistors for dividing the input voltage to the constant voltage element 1, and R3 and R4 are resistors for dividing the output voltage from the constant voltage element 1.

Next, the operation of this embodiment will be described. The DC output supplied from the DC power supply 3 is a constant voltage element 1
Supplied to The constant voltage element 1 converts the input DC voltage into a constant voltage and outputs the voltage to the output terminal 4 side. At this time, the input voltage of the constant voltage element 1 is divided by the resistors R1 and R2, and the obtained divided voltage V1 is input to the inverting input terminal of the comparison circuit 21. Further, the output voltage of the constant voltage element 1 is divided by resistors R3 and R4, and the obtained divided voltage V2 is
Is input to the non-inverting input terminal. As a result, the comparison circuit 21 compares the input voltage of the constant voltage element 1 with the output voltage.
In a normal state, V1 <V2, the output voltage of the comparison circuit 21 is at a low level, and the abnormality signal 100 indicates that there is no abnormality.

Here, when a short circuit or the like occurs on the load side, the protection function of the constant voltage element 1 operates, and the output voltage and current are reduced, so that the divided voltage by the resistors R3 and R4 decreases. > V2. Thereby, the comparison circuit 21
Output signal is inverted to output a high-level abnormality signal 100, indicating that abnormality has been detected. However, the resistance R1,
It is assumed that the respective values of R2, R3, and R4 are set such that V1 <V2 in a normal state and V1> V2 in an abnormal state.

According to the present embodiment, since an abnormality such as a load short circuit is detected based on the difference between the input voltage and the output voltage of the constant voltage element 1, the constant voltage element 1 has a square character. In this case, when an abnormality such as a load short-circuit occurs, the output voltage of the constant voltage element 1 always drops, so that the abnormality can be reliably detected.

FIG. 3 is a circuit diagram showing a second embodiment of the abnormality detection circuit of the present invention. A time constant circuit including resistors R5, R6, and a capacitor C1 is provided on the output side of the comparison circuit 21 of the present embodiment, and an abnormal signal 100 of the comparison circuit 21 is extracted through the time constant circuit. Other configurations are the same as those of the first embodiment shown in FIG.

In the transient period when the input voltage of the constant voltage element 1 rises and reaches a steady value, such as when the power is turned on, the output voltage becomes lower than the input voltage of the constant voltage element 1 regardless of whether there is any abnormality. In some cases, the abnormal signal 10 of the comparison circuit 21
In some cases, 0 becomes a high level and an abnormality is erroneously detected.

However, if the time constant of the time constant circuit is set to such an extent that the above-mentioned transient period ends as in the present embodiment, for example, the input voltage of the constant voltage element 1 during the above-mentioned transient period is reduced. Therefore, even if the output voltage of the comparison circuit 21 is about to go to a high level, the terminal voltage of the capacitor C1 does not go to a high level so as to indicate an abnormality during the transient period, thereby preventing erroneous detection. be able to. When an abnormality occurs due to a short circuit on the load side or the like in a steady state, the output signal 100 becomes high level although the time is delayed by the time constant of the time constant circuit, and the same effect as the embodiment shown in FIG. There is.

FIG. 4 is a circuit diagram showing a third embodiment of the abnormality detection circuit according to the present invention. Power is supplied from the DC power supply 3, which is the same as the input power supply of the constant voltage element 1, to the comparison circuit 21 of this example through the transistor 23. The base of the transistor 23 is connected to the low side through a Zener diode 24. A resistor R7 for base bias is connected between the collector and the emitter of the transistor 23.

While the output voltage of the DC power supply 3 when the power is turned on is low, the voltage applied to the terminal of the Zener diode 24 is low, and thus, the Zener diode 24 is off and the transistor 23 is off. No power is supplied to the comparator 21 and the comparison circuit 21 does not operate. Therefore, during the transient period when the input voltage of the constant voltage element 1 rises and reaches a steady value as in the case of power-on as described above, the constant voltage element 1
Even if the output voltage becomes lower than the input voltage, the comparison circuit 21 does not operate, so that the high-level abnormality signal 100 is not output, and erroneous detection can be prevented.

Thereafter, when the output voltage of the DC power supply 3 rises and approaches a steady state, the voltage applied to the terminal of the Zener diode 24 also increases, and this Zener diode 24
Is turned on and the transistor 23 is turned on,
Power is supplied to the comparison circuit 21, and the comparison circuit 21 enters an operating state. When an abnormality occurs due to a short circuit on the load side or the like in a steady state, the comparison circuit 21 outputs an abnormality signal 100
However, as in the second embodiment shown in FIG. 3, there is no delay in the output of a high-level abnormal signal, and good responsiveness can be maintained.

FIG. 5 is a circuit diagram showing a fourth embodiment of the abnormality detection circuit according to the present invention. 21b is a comparison circuit for detecting an abnormality by comparing the divided voltage on the current input side of the resistor R8 with the divided voltage on the current output side.
For detecting an overcurrent of the current flowing to the load side through R9, R9 and R10 are voltage dividing resistors for dividing the voltage on the input side of the resistor R8 to obtain a divided voltage V3, and R11 and R12 are for the output side of the resistor R8. Is a voltage dividing resistor that divides the voltage V.sub.1 to obtain a divided voltage V4. Reference numeral 21a denotes a comparison circuit that compares the divided voltage on the current input side of the constant voltage element 1 with the divided voltage on the current output side to detect an abnormality. The output sides of the comparison circuits 21a and 21b are commonly connected through diodes Da and Db so that the logical sum of the output signals of the comparison circuits 21a and 21b is obtained.

In the steady state, the output voltage of the constant voltage element 1 is in the region indicated by A in FIG. 6 and is constant. In such a region, V3 <V4, and the output of the comparison circuit 21b is at a low level. At this time, for the same reason as described in the first embodiment, since the output of the comparison circuit 21a is at a low level, the abnormality signal 100 output from the diodes Da and Db indicates an abnormality at a low level. Absent. Here, if an overcurrent occurs in the region A as described above for some reason, the voltage on the current output side of the resistor R8 decreases, so that V3> V4, and the comparison circuit 21
The output of b becomes high level. As a result, a high-level abnormality signal 100 is output from the diode Db, and an overcurrent abnormality is detected. However, resistors R9, R10, R1
1, the values of R12 are normal, V3 <V4, and abnormal,
It is assumed that V3> V4 is set.

In the area B shown in FIG. 6 where the voltage and current on the output side of the constant voltage element 1 are reduced due to a short circuit on the load side, for the same reason as in the first embodiment, the comparison is made. The output of the circuit 21a becomes high level and the diode D
a outputs a high-level abnormality signal 100, and an overcurrent abnormality is detected.

According to the present embodiment, by monitoring the voltage drop of the resistor R8 inserted in the preceding stage of the constant voltage element 1 by the comparison circuit 21b, it is possible to detect an overcurrent abnormality in the A region in the steady state. . Other operations are the same as those in the first embodiment, and have the same effects.

FIG. 7 is a circuit diagram showing a fifth embodiment of the abnormality detection circuit of the present invention. In this example, the comparison circuit 21
The alarm circuit 25 is connected to the output side. Other configurations are the same as those of the first embodiment in FIG. Therefore, when the comparison circuit 21 detects an abnormality, the high-level abnormality signal 10
0 is input to the alarm circuit 25. When the high-level abnormality signal 100 is input, the alarm circuit 25 turns on the lamp 26 to notify that abnormality has been detected. Thus, the abnormality can be visually notified to a maintenance person or the like. The same effect can be obtained even if the alarm circuit 25 is connected to the output side of the comparison circuit 21 of the other embodiment shown in FIGS. 3 and 4 or the output side of the diodes Da and Db shown in FIG. is there.

When the power supply from the DC power supply 3 is frequently turned on and off, the balance between the voltage on the input side and the output side of the constant voltage element 1 is different from that in the steady state during the transient state when the power supply is turned on and off. Therefore, in each of the above-described embodiments, the comparison circuit 21 may erroneously detect an abnormality, and the second and third embodiments shown in FIGS. There is.

FIG. 8 is a circuit diagram showing a sixth embodiment of the abnormality detection circuit of the present invention. In this example, the comparison circuit 21
The power supply 22 is connected to the comparison circuit 2 via the switch circuit 6.
1 is supplied. Further, a voltage detection circuit 5 is provided which monitors whether or not the voltage on the output side of the constant voltage element 1 exceeds a threshold value and controls the switch circuit 6. Other configurations are the same as those of the first embodiment.

When the power supply voltage supplied from the DC power supply 3 to the constant voltage element 1 is turned on, the voltage on the output side of the constant voltage element 1 is initially low, and thereafter, the output voltage of the constant voltage element 1 starts to rise. . At this time, until the output voltage of the constant voltage element 1 exceeds the threshold value, the voltage detection circuit 5 turns off the switch circuit 6 and stops the power supply to the comparison circuit 23 to keep the operation stopped. I do.

Thereafter, when the output voltage of the constant voltage element 1 rises and exceeds the threshold value, the voltage detection circuit 5 turns on the switch circuit 6 and supplies power to the comparison circuit 23 to operate it. . Thereafter, if there is no abnormality, since the voltage on the input side and the output side of the constant voltage element 1 is stable, the comparison circuit 23 does not erroneously detect the abnormality.
The voltage detection circuit 5 does not turn off the switch circuit 6 once the switch circuit 6 is turned on even if the voltage on the output side of the constant voltage element 1 falls below the threshold value.
In the steady state, the comparison circuit 23 can detect an abnormality on the load side when the voltage on the output side of the constant voltage element 1 decreases.

In this embodiment, the comparator 23 does not operate unless the voltage on the output side of the constant voltage element 1 is equal to or higher than the threshold value. Detection can be prevented.

FIG. 9 is a circuit diagram showing a seventh embodiment of the abnormality detection circuit of the present invention. The comparison circuit 21 of the present embodiment includes a DC power supply 3 having the same power supply as the input power supply of the constant voltage element 1.
Through the transistor 23. The base of this transistor 23 is a thyristor 28
Through to the low side. The control terminal of the thyristor 28 is connected to the anode side of the Zener diode 29, and the cathode side of the Zener diode 29 is connected to the output side of the constant voltage element 1 via the resistor R15. Further, the control terminal of the thyristor 28 is connected to the low side through the resistor R16.

When the power is turned on, the voltage on the output side of the constant voltage element 1 rises. When the voltage exceeds the Zener voltage, the Zener diode 29 turns on and the thyristor 2
A current flows through the control terminal 8 and the thyristor 28 is turned on. As a result, the transistor 23 is turned on, and power is supplied from the DC power supply 3 to the comparison circuit 21 so that the comparison circuit 2
1 becomes active. Once turned on, the thyristor 28 maintains this state. For this reason, even in the steady state, even if the voltage on the output side of the constant voltage element 1 falls below the Zener voltage and the Zener diode 29 is turned off, the comparison circuit 21 maintains the operating state and can perform abnormality detection. Can,
There is an effect similar to that of the sixth embodiment shown in FIG.

FIG. 10 is a circuit diagram showing an eighth embodiment of the abnormality detection circuit according to the present invention. The constant voltage element 1 of this example has an on / off terminal, and this terminal is a thyristor 2
8 is connected to the cathode side. Thyristor 2
The cathode side of 8 is connected to the low side via an on / off switch 7. The other configuration is the same as that of the seventh embodiment shown in FIG.

When the on / off switch 7 of the constant voltage element 1 is turned on and its on / off terminal is connected to the low side,
It turns on and turns off when the on / off switch 7 is turned off and the on / off terminal is opened. Now, when the on / off switch 7 is turned on and the constant voltage element 1 is turned on, the voltage on the output side of the constant voltage element 1 increases. When the voltage exceeds the Zener voltage, the Zener diode 29 is turned on and the thyristor is turned on. A current flows through the control terminal 28, and the thyristor 28 is turned on.

As a result, the transistor 23 is turned on, and power is supplied from the DC power supply 3 to the comparison circuit 21.
The comparison circuit 21 enters an operation state. Once turned on, the thyristor 28 maintains this state. For this reason, even in the steady state, even if the voltage on the output side of the constant voltage element 1 falls below the Zener voltage and the Zener diode 29 is turned off, the comparison circuit 21 maintains the operating state and can perform abnormality detection. This has the same effect as that of the seventh embodiment shown in FIG.

FIG. 11 is a circuit diagram showing a second embodiment of the power supply device provided with the abnormality detection circuit of the present invention. The power supply of this example is an AC-DC converter,
The abnormality detection circuit 2 of the first embodiment shown in FIG. 1 is used on the secondary side of the converter. 1 is a constant voltage element, 2 is an abnormality detection circuit, and its configuration is the same as that of the first embodiment shown in FIG. Reference numeral 8 denotes an AC power supply such as a commercial power supply, 9 denotes a rectifier circuit including a diode bridge for converting AC to DC, 10 denotes a shunt regulator that is turned on / off by a voltage of a control terminal, 11 denotes a control unit that performs PWM control of switching of the FET 12, C3 C6 is a smoothing capacitor, 12 is an FET (field effect transistor) for passing a switching current to the primary side of the transformer T, D1, D
2, D3 is a rectifying diode, PC1T and PC2T are light emitting elements of a photocoupler, PC1R and PC2R are light receiving elements of a photocoupler, R18 and R19 are voltage dividing resistors, and T is a transformer.

Next, the operation of this embodiment will be described. Normally, when the power is turned on, the AC output from the AC power supply 8 is rectified by the rectifier circuit 9 and then smoothed by the capacitor C3 to become DC, and this DC is passed through the primary winding N1 of the transformer T. Applied to the FET 12.
Accordingly, the control unit 11 starts switching of the FET 12, and a switching current flows through the primary winding N1 of the transformer T. Therefore, the secondary windings N2 to N4 of the transformer T
Voltage is generated. The switching voltage generated in the secondary winding N2 of the transformer T is rectified by the diode D1, and then smoothed by the capacitor C4.
Is output to the load side (not shown). The control unit 11
Is supplied with a DC power obtained by rectifying and smoothing the switching voltage generated in the secondary winding N4 of the transformer T by the diode D3 and the capacitor C6.

The voltage at the output terminal 14 is divided by a voltage dividing resistor R18,
The voltage is divided by R19 and applied to the control terminal of the shunt regulator 10. Therefore, for example, when the output voltage decreases, the divided voltage decreases, and the shunt regulator 10
Turns on. Thus, a current flows through the photocoupler PC1T to emit light. This light emission is transmitted to
Is received and turned on. The control unit 11 is a photocoupler PC
When the ON signal of 1 is input, the ON duty of the FET 12 is lengthened to increase the output. As a result, the voltage generated in the secondary winding N2 of the transformer T increases, and the output voltage of the output terminal 14 is maintained at a predetermined value.

On the other hand, the switching voltage generated in the secondary winding N3 of the transformer T is rectified by a diode D2, and then smoothed by a capacitor C5.
Through the output terminal 15 to the load side. If a short circuit or the like occurs on the load side of the output terminal 15, the voltage on the output side of the constant voltage element 1 is lower than that on the input side due to the transient current protection characteristic of the fold-back characteristic. Then, by setting the output to a high level, the photocoupler PC2T emits light. This light is emitted by a photocoupler PC
2R receives light and turns on. When the photocoupler PC2R is turned on, the control unit 11 stops the switching of the FET 12. Thereby, the secondary windings N2, N of the transformer T
3. The switching voltage generated at N4 becomes zero, and the entire device is protected.

According to the present embodiment, a power supply device having an output circuit using a constant voltage element 1 having a square-shaped characteristic is provided with an abnormality detection circuit 2 having the same performance as the embodiment shown in FIG.
By using this, it is possible to reliably detect an abnormality due to a short circuit in the load of the output circuit and to automatically stop the switching operation on the primary side, thereby protecting the entire power supply device.

By the way, if a failure occurs in the secondary system N2 of the transformer T and the feedback system of the control unit 11 and the feedback becomes ineffective, the secondary systems N2 and N3 of the transformer T are used.
Voltage rises. As a result, the voltage on the input side of the constant voltage element 1 increases, so that V1> V2, and the comparison circuit 2
In the case of 1, the output becomes high level to detect an abnormality. As a result, the photocoupler PC2T emits light, and this light emission is received by the photocoupler PC2R and turned on. When the photocoupler PC2R is turned on, the control unit 11 stops the switching of the FET 12. Thereby, the switching voltage generated in the secondary windings N2, N3, N4 of the transformer T becomes zero, and there is also an effect of protecting the entire device.

According to the above-described embodiment, when an abnormality is detected by the abnormality detection circuit 13, the control for stopping the primary side switching is performed. The on-duty of the
The output voltage on the secondary side may be reduced.

[0055]

As described above, according to the first aspect of the present invention, by comparing the voltage on the input side and the voltage on the output side of the constant voltage element, the overcurrent protection characteristic of the constant voltage element has the characteristic Even in this case, an abnormal state including a short circuit on the load side can be reliably detected.

According to the second aspect of the present invention, by providing the time constant circuit on the output side of the comparison circuit, it is possible to prevent erroneous detection of an abnormality during an excessive period when the power is turned on.

According to the third aspect of the present invention, the operation of the comparison circuit is stopped while the output voltage of the DC power supply at the time of turning on the power is low. Can be prevented.

According to the fourth aspect of the present invention, the operation of the comparison circuit is stopped while the output voltage of the constant voltage element at the time of turning on the power is lower than the threshold value. Detection can be prevented.

According to the fifth aspect of the present invention, when an abnormality detection signal is output, the abnormality is notified by appealing to human vision or hearing, so that the abnormality can be reliably notified to maintenance personnel and the like.

According to the invention of claim 6, in addition to the comparison circuit for comparing the voltage on the input side and the voltage on the output side of the constant voltage element, the comparison circuit for comparing the voltage across the resistor for supplying a current to the constant voltage element The provision of the circuit makes it possible to detect not only the protection operation of the constant voltage element but also the abnormality when the constant voltage element operates normally.

According to the seventh aspect of the present invention, since an abnormality detecting circuit is provided which can detect an abnormality on the load side even when a constant voltage element having a fold-over current characteristic is used, protection of the constant voltage element is provided. An abnormality can be reliably detected even during operation, and the entire apparatus can be protected.

According to the eighth aspect of the present invention, the power supply apparatus feeds back an abnormality signal output from an abnormality detection circuit capable of detecting an abnormality on the load side even when a constant voltage element having a fold-over current characteristic is used. Is stopped, the entire device can be automatically protected during the protection operation of the constant voltage element.

[Brief description of the drawings]

FIG. 1 shows a first example of a power supply device provided with an abnormality detection circuit according to the present invention.
FIG. 2 is a block diagram showing an embodiment.

FIG. 2 is a circuit diagram showing a first embodiment of the abnormality detection circuit of the present invention shown in FIG. 1;

FIG. 3 is a circuit diagram showing a second embodiment of the abnormality detection circuit of the present invention.

FIG. 4 is a circuit diagram showing a third embodiment of the abnormality detection circuit of the present invention.

FIG. 5 is a circuit diagram showing a fourth embodiment of the abnormality detection circuit of the present invention.

FIG. 6 is a characteristic diagram showing output voltage and current characteristics of the constant voltage device shown in FIG.

FIG. 7 is a circuit diagram showing a fifth embodiment of the abnormality detection circuit according to the present invention.

FIG. 8 is a circuit diagram showing a sixth embodiment of the abnormality detection circuit according to the present invention.

FIG. 9 is a circuit diagram showing a seventh embodiment of the abnormality detection circuit of the present invention.

FIG. 10 is a circuit diagram showing an abnormality detection circuit according to an eighth embodiment of the present invention.

FIG. 11 is a circuit diagram showing a second embodiment of the power supply device provided with the abnormality detection circuit of the present invention.

FIG. 12 is a block diagram showing an example of a conventional power supply device.

FIG. 13 is a characteristic diagram showing output voltage and current characteristics of the constant voltage element shown in FIG.

[Explanation of symbols]

 Reference Signs List 1 constant voltage element 2 abnormality detection circuit 3 DC power supply 4, 14, 15 output terminal 5 voltage detection circuit 6 switch circuit 7 on / off switch 8 AC power supply 9 rectifier circuit 10 shunt regulator 11 control unit 12 FET 21, 21a, 21b comparison circuit 22 Power supply 23 Transistor 24, 29 Zener diode 25 Alarm circuit 26 Lamp 28 Thyristor C3 to C6 Capacitor D1 to D3, Da, Db Diode PC1T, PC2T Photocoupler light emitting element PC1R, PC2R Photocoupler light receiving element R1 to R19 Resistor T Transformer

Claims (8)

[Claims] A first input circuit for inputting the input voltage of a constant voltage element for outputting an input voltage at a constant voltage;
A second input circuit for inputting an output voltage of the constant voltage element; and a comparing circuit for comparing the two voltages input by the first and second input circuits and outputting an abnormal signal when an abnormality is detected. An abnormality detection circuit, comprising: 2. The abnormality detection circuit according to claim 1, wherein a time constant circuit is provided on an output side of the comparison circuit, and the abnormality signal is extracted through the time constant circuit. 3. A power supply control circuit that supplies an output voltage of the DC power supply to the comparison circuit and operates the comparison circuit when an output voltage of the DC power supply that supplies a voltage to the constant voltage element becomes a predetermined value or more. 2. The method according to claim 1, further comprising:
Abnormality detection circuit as described. 4. A voltage detection circuit for detecting that an output voltage of the constant voltage element is equal to or higher than a threshold value; and when the voltage detection circuit detects that the output voltage is equal to or higher than a threshold value,
The abnormality detection circuit according to claim 1, further comprising: a power supply switch circuit that supplies an operation current to the comparison circuit to operate the comparison circuit. 5. An alarm circuit according to claim 1, further comprising an alarm circuit which, upon input of an abnormality detection signal output from said comparison circuit, informs the abnormality by appealing to human vision or hearing. Abnormality detection circuit as described. 6. A first input circuit for inputting the input voltage of a constant voltage element for outputting an input voltage at a constant voltage;
A second input circuit for inputting an output voltage of the constant voltage element; a first comparing circuit for outputting an abnormal signal by comparing the two voltages input by the first and second input circuits; A resistor inserted on the input side of the constant-voltage element for passing a current input to the constant-voltage element; a third input circuit for inputting a voltage on the current input side of the resistor; and a voltage on a current output side of the resistor A second input circuit for comparing the two voltages input by the third and fourth input circuits and outputting an abnormal signal when an abnormality is detected; and the first and second input circuits. A logic circuit for calculating the logical sum of the abnormal signals output from the comparison circuit and outputting the logical sum. 7. A voltage output circuit for outputting a DC voltage; a constant voltage element for making the output voltage of the voltage output circuit constant;
A power supply device comprising: an abnormality detection circuit according to any one of claims 1 to 6, wherein an abnormality is detected from a voltage on an input side and a voltage on an output side of the constant voltage element. 8. When the abnormality detection circuit detects an abnormality,
The power supply device according to claim 7, further comprising a feedback circuit that reduces or cuts off a DC voltage from the voltage output circuit.