JP2014068448A - Input overvoltage prevention circuit and power supply unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a circuit capable of protecting elements in a circuit and a power supply unit during application of an input overvoltage without generating unnecessary power loss.SOLUTION: The input overvoltage prevention circuit is connected in parallel to an input side of a power supply section and includes at least a capacitor and a switching element, and further includes a bypass section that comes into continuity when a switching element is under an on state and a detection section that is connected in parallel between the power supply section and a DC power supply, detects an increase in an input voltage from the DC power supply, and sets the switching element of the bypass section to be ON and, at a normal operation, sets the switching element to be OFF.

Description

  The present invention relates to a circuit for protecting elements in a circuit and a power supply unit when an input voltage is an overvoltage, and a power supply device.

  2. Description of the Related Art A circuit that prevents input overvoltage in a DC input switching power supply apparatus is known. On the other hand, when the power supply in the switching power supply is shut off, a high-voltage counter electromotive force is generated by a self-induction action from an inductance component caused in the input source, such as a circuit of the input source of the power supply apparatus or a cable. When this back electromotive force is input from the input source to the main body power circuit of the switching power supply device, the input voltage rises and an input overvoltage state is entered. As a result, a failure occurs in an element in the main body power supply circuit. The input overvoltage prevention circuit protects elements in the circuit and the power supply device (main body power supply circuit) from the input overvoltage.

  An example of a circuit for preventing input overvoltage is described in Patent Document 1. The circuit described in Patent Document 1 activates the constant voltage setting circuit when the input voltage rises above a predetermined voltage, and the voltage above the predetermined voltage is not applied to the primary input side of the DC / DC converter. Like that.

  The circuit described in Patent Document 2 compares a reference voltage created by a constant current source and a reference voltage generation circuit and a feedback voltage obtained by dividing the input voltage with each other by a comparator. By supplying an error signal corresponding to the difference to the base of the output transistor inserted in series with the power supply through the control transistor, the base current of the output transistor is adjusted and constant voltage operation is performed.

  As another example of a circuit for preventing an input overvoltage, it is conceivable to connect a varistor to an input source of a power supply device in parallel with the power supply device to protect elements and the power supply device in the circuit from the input overvoltage.

JP 2001-095240 A JP 2001-109531 A

  However, in the technique described in Patent Document 1 described above, a current limiting resistor is inserted in series with the DC power source, and a current flows through the current limiting resistor until a steady state is reached. Further, a capacitor is inserted in parallel with the DC / DC converter, and a current always flows through the capacitor side circuit. In the technique described in Patent Document 2, an output transistor is inserted in series with a DC power supply, and a current always flows through the output transistor. Similarly to Patent Document 1, an output capacitor is inserted in parallel with the load, and a current always flows through the output capacitor side circuit. Therefore, the techniques described in Patent Documents 1 and 2 have a problem that unnecessary power loss occurs.

  Further, when a varistor is used as an input source, there are the following problems. That is, the varistor has a characteristic that the varistor voltage increases according to the amount of current, and therefore there is a problem that the input voltage cannot be suppressed with high accuracy.

  An object of the present invention is to provide an input overvoltage prevention circuit and a power supply device that can solve the above-described problems.

  An input overvoltage prevention circuit according to an aspect of the present invention includes a bypass unit that is connected in parallel to the input side of a power supply unit, includes at least a capacitor and a switch element, and conducts when the switch element is in an ON state, the power supply unit, and the input A detection unit that is connected in parallel with a power supply, detects an increase in input voltage from the input power supply, turns on the switch element of the bypass unit, and turns off the switch element during normal operation.

  A power supply device according to an aspect of the present invention includes the above-described input overvoltage prevention circuit and a power supply unit connected in parallel thereto.

  According to the present invention, it is possible to protect the elements and the power supply device in the circuit at the time of input overvoltage without causing unnecessary power loss.

FIG. 1 is a circuit diagram showing the configuration of the first embodiment of the present invention. FIG. 2 is a circuit diagram showing the configuration of the second embodiment of the present invention.

  Next, embodiments of the present invention will be described in detail with reference to the drawings.

[First embodiment]
FIG. 1 is a circuit diagram of a power supply device according to the first embodiment of the present invention. Referring to FIG. 1, a DC power source 1 as an input power source is connected to the input side of a power source device 2, and a load 3 is connected to the output side of the power source device 2. The input voltage from the DC power source 1 is Vin1. In addition, an inductance component 4 caused by an input source of the power supply device 2 such as a DC power supply or a cable is generated.

  The power supply device 2 includes a power supply unit 13, a detection unit 11, and a bypass unit 12. The power supply unit 13 converts the DC voltage from the DC power supply 1 into a DC voltage corresponding to the load 3. The detection unit 11 and the bypass unit 12 constitute an input overvoltage prevention circuit. In the power supply device 2, the input voltage of the power supply unit 13 is Vin2.

  The detection unit 11 of the input overvoltage prevention circuit is connected in parallel between the DC power supply 1 and the bypass unit 12. The detection unit 11 includes a series circuit of a resistor 22 and a resistor 23 in parallel with the DC power source 1 and a comparator 25 in which one input is connected to a connection point of each resistor. The bypass portion 12 of the input overvoltage prevention circuit is configured by a series circuit of a capacitor 26, a resistor 27, and a semiconductor switch 28 as a switch element. The bypass unit 12 is connected in parallel to the input side of the power supply unit 13. Here, the semiconductor switch is a transistor, and uses a switching action to control conduction (hereinafter referred to as an ON state) and cutoff (hereinafter referred to as an OFF state) between the emitter and the collector by a base current.

  The base of the semiconductor switch 28 is connected to the output of the comparator 25. The input of the comparator 25 is a voltage (also referred to as input voltage) V11 applied to the resistor 23 and a reference voltage Vref. Here, the input voltage V11 is a voltage applied to both ends of the resistor 23 when the input voltage Vin1 input from the DC power supply 1 to the power supply device 2 is divided by the resistors 22 and 23. The reference voltage Vref is a voltage generated by the constant voltage source 24. Further, a portion configured by the resistors 22 and 23, the constant voltage source 24, and the comparator 25 to detect a rise in voltage and output it to the base of the semiconductor switch 28 is defined as a detection unit.

  Next, the operation of the power supply device in the first embodiment will be described.

  During normal operation of the power supply apparatus, that is, when the influence of the inductance component 4 can be ignored, the resistance value ratio of the resistors 22 and 23 is adjusted so that the input voltage V11 of the comparator 25 is set to be lower than the reference voltage Vref. At this time, the output of the comparator 25 is turned off, and the base current is not supplied from the comparator 25 to the base of the semiconductor switch 28. Therefore, the semiconductor switch 28 is turned off. That is, no current flows through the bypass portion.

  In the input overvoltage state, for example, when the power supply 2 is turned off, the input current of the power supply 2 decreases sharply, and the inductance component 4 in which energy is stored generates a counter electromotive voltage that cannot be ignored due to the self-induction action. Let As a result, the input voltage Vin2 of the power supply unit 13 increases, and the input voltage V11 exceeds the reference voltage Vref. At this time, the output of the comparator 25 is turned on, and the base current is supplied from the comparator 25 to the base of the semiconductor switch 28. Accordingly, the semiconductor switch 28 is turned on, and a current flows through the bypass unit 12. In this way, the energy stored in the inductance component 4 is absorbed by the capacitor 26 of the bypass unit 12 that has been conducted. For this reason, voltage increase of Vin2 is suppressed.

[Second Embodiment]
Next, a second embodiment of the present invention will be described in detail with reference to the drawings. Hereinafter, the description overlapping with the above description is omitted as long as the description of the present embodiment is not obscured.

FIG. 2 is a circuit diagram according to the second embodiment of the present invention.
The power supply device 20 includes a power supply unit 13, a detection unit 21, and a bypass unit 12. The detection unit 21 and the bypass unit 12 constitute an input overvoltage prevention circuit. In the power supply device 20, the input voltage of the power supply unit 13 is Vin2.

  Referring to FIG. 2, the detection unit 21 in this embodiment is different from the detection unit 11 in the first embodiment in that a Zener diode 29 and a resistance 23 are used instead of the resistors 22 and 23, the constant voltage source 24, and the comparator 25. The detection unit is configured by a series circuit. The base of the semiconductor switch 28 of the bypass unit 12 is connected to the anode side of the Zener diode 29.

  Next, the operation of this circuit in the second embodiment will be described.

  During normal operation of the circuit, that is, when the influence of the inductance component 4 can be ignored, the Zener diode 29 is selected so that the Zener voltage Vz is higher than the input voltage Vin2 of the power supply unit. At this time, since the Zener diode 29 does not generate the Zener effect, the Zener diode 29 does not conduct, and the base current is not supplied from the Zener diode 29 to the base of the semiconductor switch 28. Therefore, the semiconductor switch 28 is turned off. That is, no current flows through the bypass portion.

  In the input overvoltage state, for example, when the power supply device 2 is turned off, the input current of the power supply device decreases sharply, and the inductance component 4 in which energy is stored generates a counter electromotive voltage that cannot be ignored due to the self-induction action. . As a result, the input voltage Vin2 of the power supply unit 13 increases, and Vin2 exceeds the Zener voltage Vz. Since the Zener diode 29 generates a Zener effect, the Zener diode 29 becomes conductive, and a base current is supplied from the Zener diode 29 to the base of the semiconductor switch 28. Accordingly, the semiconductor switch 28 is turned on, and a current flows through the bypass unit 12. In this way, the energy stored in the inductance component 4 is absorbed by the capacitor 26 of the bypass unit 12 that has been conducted. For this reason, voltage increase of Vin2 is suppressed.

  Next, effects of the first embodiment and the second embodiment of the present invention will be described.

  The power supply apparatus and the input overvoltage prevention circuit in the first embodiment and the second embodiment described above can protect the elements and the power supply apparatus in the power supply apparatus at the time of input overvoltage without causing unnecessary power loss.

  This is because the following configuration is included. That is, first, the bypass unit is connected in parallel to the input side of the power supply unit, includes at least a capacitor and a switch element, and conducts when the switch element is in the ON state. Second, the detection unit is connected in parallel between the power supply unit and the input power supply, detects an increase in the input voltage from the input power supply, turns on the switch element of the bypass unit, and operates normally. Sometimes the switch element is turned off. In this way, the bypass portion does not flow current when the switch element is turned off during normal operation of the power supply device. In addition, during normal operation, elements that cause loss are not connected in series between the DC power supply and the power supply unit. Therefore, since the loss due to the input overvoltage prevention circuit can be suppressed during normal operation of the power supply device, it is possible to protect the elements and the power supply device in the circuit during the input overvoltage without causing unnecessary power loss. .

DESCRIPTION OF SYMBOLS 1 DC power supply 2, 20 Power supply device 3 Load 4 Inductance component 11, 21 Detection part 12 Bypass part 13 Power supply part 22, 23, 27 Resistance 24 Constant voltage source 25 Comparator 26 Capacitor 28 Semiconductor switch 29 Zener diode

Claims (5)

A bypass unit connected in parallel to the input side of the power supply unit, including at least a capacitor and a switch element, and conducting when the switch element is in an ON state;
Detection in which the switch element of the bypass unit is turned on and the switch element is turned off during normal operation by detecting an increase in input voltage from the input power supply in parallel between the power supply unit and the input power supply. Input overvoltage protection circuit. The detection unit includes a comparator,
The comparator compares the input voltage with a reference voltage;
2. The input overvoltage prevention circuit according to claim 1, wherein, when the input voltage exceeds the reference voltage, the comparator turns on the switch element of the bypass unit. 3. A zener diode is included in the configuration of the detection unit,
The zener diode conducts when the input voltage exceeds the zener voltage,
The input overvoltage prevention circuit according to claim 1, wherein the switch element of the bypass unit is turned on.   The input overvoltage prevention circuit according to any one of claims 1 to 3, wherein the capacitor of the bypass unit accumulates a back electromotive force generated when the power is shut off. An input overvoltage prevention circuit according to any one of claims 1 to 4,
A power supply device including the input overvoltage prevention circuit and a power supply unit connected in parallel.

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