JP4626809B2 - Overvoltage protection circuit - Google Patents

Description

  The present invention relates to an overvoltage protection circuit for a power supply device, and more particularly to an overvoltage protection circuit for a power supply device in which a surge countermeasure is applied to an input unit.

  In the overvoltage protection circuit of the conventional power supply device, when an overvoltage exceeding the rated voltage occurs in the output, the output is stopped by short-circuiting between the input lines and blowing the fuse connected to the input terminal There is.

FIG. 6 is a diagram illustrating a configuration example of a conventional overvoltage protection circuit.
In the DC / DC converter circuit 1, a fuse F1 connected to the input terminal IN +, a surge protection element 2 connected between the input lines and clamping the surge voltage below a certain voltage, and an output voltage of the DC / DC converter circuit 1 , And an overvoltage detection circuit 3 that detects the occurrence of an overvoltage and outputs an overvoltage detection signal, and a switch element SW1 that turns on / off the switch according to the overvoltage detection signal output from the overvoltage detection circuit 3.

When the DC / DC converter circuit 1 fails and an overvoltage exceeding the rated voltage is generated in the output, the overvoltage detection circuit 3 detects this and sends an overvoltage detection signal to the switch element SW1. When the switch element SW1 receives this signal, the switch is turned on to short-circuit between the input lines. As a result, when a large short-circuit current flows from the IN + terminal through the path of the fuse F1, the switch element SW1, and the IN− terminal, the fuse F1 is blown, and the output of the DC / DC converter circuit 1 is stopped. Protected from.
Here, when a surge voltage exceeding the withstand capability of the element is applied to the surge protection element 2, the surge protection element 2 may be short-circuited, so the fuse F1 is provided on the upstream side of the surge protection element 2. Yes.

JP 2005-102348 A

When a surge voltage is applied between the input lines, the surge current flows through the path from the input terminal IN + to the fuse F1, the surge protection element 2, and the input terminal IN−. At this time, if the fuse F1 is blown out, the power supply device is not subjected to surge countermeasures. Therefore, when a surge voltage lower than the surge voltage defined in the specifications of the power supply device is applied, the fuse F1 is blown out. Do not. The surge resistance of the fuse F1 is evaluated by the Joule integral value I ² t. Therefore, I ² t of the fuse F1 must be larger than I ² t of the surge current that flows when a surge voltage is applied.

On the other hand, when an overvoltage is detected in the output, the switch of the switch element SW1 is turned on to short-circuit the input line, so that a large short-circuit current flows. At this time, in order to blow the fuse F1 reliably. The switch element SW1 must not be broken before the fuse F1 is blown.
Accordingly, the following relationship needs to be established in all time regions with respect to I ² t.
[Surge current ^I 2 t] <[fuse F1 of the ^{I 2 t] <[I 2} t of the switch element SW1]

In general, since the surge current I ² t is a considerably large value, the switch element SW1 that satisfies this relationship becomes large, which hinders downsizing of the power supply device and increases the cost. It was.
Further, a large fuse F1 of surge resistance satisfying the relationship [surge current I ^{2 t]} <[fuse F1 of the I ^{2 t],} since the greater the rated current, fault excessively large input current flows such input shorted For example, the fuse blows, but for example, even if a failure occurs in which an input current about 2 to 3 times the rated current flows, the fuse does not blow and the protection does not work. The smaller the power supply with a smaller rated input current, the more prominent the problem.

  The present invention has been made to solve the above-described problems, and in an overvoltage protection circuit of a power supply apparatus in which a surge countermeasure is applied to an input portion, an appropriate switching element is not affected by the magnitude of a surge current. And an overvoltage protection circuit using a fuse.

In order to solve such a problem, the present invention has the following configuration.
(1) In the overvoltage protection circuit of the power supply device,
A first overcurrent interrupting means provided on the input line and configured to interrupt the input line when a predetermined current flows;
Overvoltage limiting means connected between the input lines of the subsequent stage of the first overcurrent interrupting means , and for limiting the current to a constant voltage by flowing a conduction current when the voltage exceeds a predetermined limit voltage;
A second overcurrent interrupting means provided on an input line subsequent to the first overcurrent interrupting means and the overvoltage limiting means, which interrupts the input line when a predetermined current flows;
Overvoltage detecting means for detecting an overvoltage with respect to a predetermined output voltage determined in advance;
Open / close means connected between the input lines in the subsequent stage of the second overcurrent interrupting means, and for opening and closing the input lines according to the detection voltage of the overvoltage detection means;
An overvoltage protection circuit comprising:

(2) The overvoltage protection unit according to (1), wherein the overvoltage detection unit detects whether or not the detection voltage has reached a threshold value, and the opening / closing unit is closed when the detection voltage exceeds a threshold value. circuit.

(3) The overvoltage protection circuit according to (1) or (2), wherein a Zener diode is used for the overvoltage detection means, and a Zener voltage is used as a threshold value of the detection voltage.

(4) A thyristor is used for the opening / closing means, and when the overvoltage detection means detects an overvoltage with respect to a predetermined output voltage , a gate current is applied to the gate of the thyristor (1) to (3) The overvoltage protection circuit according to any one of the above.

(5) When the opening / closing means is in a closed state, the second overcurrent cutoff means is in a cutoff state, and the first overcurrent cutoff means is not in a cutoff state (1) to (4) An overvoltage protection circuit according to any one of the above.

(6) The first and second overcurrent interruption means are fuses, and the second overcurrent interruption means has a smaller capacity than the first overcurrent interruption means. 5) The overvoltage protection circuit according to any one of the above.

(7) The overvoltage protection circuit according to any one of (1) to (6), wherein the overvoltage limiting means is a varistor.

The present invention has the following effects.
Since a small switch element can be used without being affected by the magnitude of the surge current, the mounting area and the component cost can be reduced.
In addition, since the fuse can be optimized, the circuit can be safely stopped by appropriately fusing the fuse not only at the time of overvoltage but also at the time of overcurrent.

Hereinafter, the present invention will be described in detail with reference to the drawings.
FIG. 1 is a block diagram showing an embodiment of the present invention. The same parts as those in the previous figure are given the same reference numerals.
In the DC / DC converter circuit 1, a varistor serving as a first overcurrent blocking means connected to the input terminal IN + and a fuse F1 connected between the input lines and an overvoltage limiting means for clamping the surge voltage to a certain voltage or less. D1, a fuse F2 that is a second overcurrent interrupting means connected to the subsequent stage of the fuse F1 and the varistor D1, and an overvoltage detection means that inputs the output voltage of the DC / DC converter circuit 1 and detects the occurrence of the overvoltage. It comprises a Zener diode D2 and a resistor R1, and a thyristor D3 which is an opening / closing means for short-circuiting the input lines when the output voltage is an overvoltage.
The resistor R1 is a bleeder resistor for preventing the thyristor D3 from malfunctioning due to the leakage current of the Zener diode D2.
Further, smoothing capacitors C1 and C2 for smoothing the input / output voltage are provided at the input / output of the DC / DC converter circuit 1, respectively.

  For example, as a specification of the power supply device, when normal operation is performed, 24 VDC is applied between the input terminals IN + and IN−, 5 VDC is output between Vcc and GND, and an overvoltage is generated between Vcc and GND. The DC / DC converter circuit 1 is stopped so as not to exceed 7 VDC. For this reason, 6.8V is selected as the Zener voltage of the Zener diode D2.

  When the output voltage rises due to failure of the DC / DC converter circuit 1 and reaches 6.8 V, the Zener diode D2 becomes conductive, a gate current flows to the gate of the thyristor D3, and the anode and cathode of the thyristor D3 become conductive. And the input lines are short-circuited. As a result, a large short-circuit current flows from the IN + terminal through the fuse F1, fuse F2, thyristor D3, and IN− terminal, so that the fuse F2 is blown and the DC / DC converter circuit 1 is stopped. Protected from.

On the other hand, when a surge voltage is applied between the input lines, the surge current flows from the input terminal IN + to the fuse F1, the varistor D1, and the input terminal IN-, and does not flow to the fuse F2.
Therefore, the fuse F1 uses a large surge withstand that does not melt even when a surge voltage less than the surge voltage defined in the specifications of the power supply device is applied. The fuse F2 and the thyristor D3 are affected by the surge withstand. Without fail, it is possible to use an appropriate fuse F2 and thyristor D3 that blow when the output voltage is overvoltage. As a result, the power supply device can be reduced in size and cost.

Further, a large fuse F1 of surge resistance satisfying the relationship [surge current I ^{2 t]} <[fuse F1 of the I ^{2 t],} since the greater the rated current, fault excessively large input current flows such input shorted In contrast, the fuse F1 is blown, but even if a failure occurs in which an input current about 2 to 3 times the rated current flows, the fuse F1 is not blown and the protection may not work. Since the fuse F2 is melted, the DC / DC converter circuit 1 can be safely stopped.

FIG. 2 is a diagram showing another configuration example of the present invention. An example in which the fuse F2 having higher sensitivity is used by eliminating the influence of the inrush current will be described.
Since an inrush current flows to the input smoothing capacitor C1 when the power is turned on, in the case of FIG. 1, the fuse F2 must be able to withstand this inrush current.
In FIG. 2, by connecting the input smoothing capacitor C1 to the input terminal side from the fuse F2, no inrush current flows through the fuse F2. Therefore, the rated current of the fuse F2 is up to the maximum input current of the DC / DC converter circuit 1. Can be lowered, and fast-acting fuses can also be used.

FIG. 3 is a diagram showing another configuration example of the present invention. An example of application to an insulating DC / DC converter will be described.
An overvoltage of the output voltage is detected by the secondary Zener diode D2 of the DC / DC converter circuit 1, and a detection signal is transmitted to the primary side by the photocoupler PC1.

FIG. 4 is a diagram showing another configuration example of the present invention. An example of application to an insulating DC / DC converter will be described.
The rectifier bridge D4 is added to the input stage of the isolated DC / DC converter of FIG.

FIG. 5 is a diagram showing another configuration example of the present invention. An example of adding input overvoltage protection is shown.
A Zener diode D4 is added between the anode and the gate of the thyristor D3. For example, when the rated input voltage of the power supply device is 12 VDC, if the Zener voltage of the Zener diode D4 is set to about 20 V, it is mistakenly 24 VDC. Is input, the gate current flows through the thyristor D3, the thyristor D3 is turned on, the fuse F2 is blown, and the DC / DC converter circuit 1 is stopped to provide protection.

It is a block diagram which shows one Example of this invention. It is the figure which showed the other structural example of this invention. It is the figure which showed the other structural example of this invention. It is the figure which showed the other structural example of this invention. It is the figure which showed the other structural example of this invention. It is a figure which shows the structural example of the conventional overvoltage protection circuit.

Explanation of symbols

F1 First overcurrent cutoff means F2 Second overcurrent cutoff means D1 Overvoltage limiting means D2 Overvoltage detection means D3 Opening / closing means

Claims (7)

In the overvoltage protection circuit of the power supply unit,
A first overcurrent interrupting means provided on the input line and configured to interrupt the input line when a predetermined current flows;
Overvoltage limiting means connected between the input lines of the subsequent stage of the first overcurrent interrupting means , and for limiting the current to a constant voltage by flowing a conduction current when the voltage exceeds a predetermined limit voltage;
A second overcurrent interrupting means provided on an input line subsequent to the first overcurrent interrupting means and the overvoltage limiting means, which interrupts the input line when a predetermined current flows;
Overvoltage detecting means for detecting an overvoltage with respect to a predetermined output voltage determined in advance;
Open / close means connected between the input lines in the subsequent stage of the second overcurrent interrupting means, and for opening and closing the input lines according to the detection voltage of the overvoltage detection means;
An overvoltage protection circuit comprising:   2. The overvoltage protection circuit according to claim 1, wherein the overvoltage detection means detects whether or not the detection voltage has reached a threshold value, and the opening / closing means is closed when the detection voltage becomes equal to or greater than the threshold value.   3. The overvoltage protection circuit according to claim 1, wherein a Zener diode is used for the overvoltage detection means, and a Zener voltage is used as a threshold value of the detection voltage. 4. A thyristor is used as the opening / closing means, and a gate current is applied to the gate of the thyristor when the overvoltage detecting means detects an overvoltage with respect to a predetermined output voltage that is determined in advance. The overvoltage protection circuit described.   The said 2nd overcurrent interruption | blocking means will be in a interruption | blocking state, and the said 1st overcurrent interruption | blocking means will not be in a interruption | blocking state, when the said opening / closing means is a closed state. Overvoltage protection circuit.   7. The first and second overcurrent interrupting means are fuses, and the second overcurrent interrupting means is a child capacity rather than the first overcurrent interrupting means. The overvoltage protection circuit described.   The overvoltage protection circuit according to claim 1, wherein the overvoltage limiting means is a varistor.

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