JPH0746757A - Dc power supply protective circuit - Google Patents

Abstract

PURPOSE:To provide a DC power supply protective circuit which is connected between a DC power source and a load to protect the DC power supply by detecting short-circuit of the load and protecting the short-circuit of the DC power source for use under the condition that a positive and a negative power sources are used for a DC power supply. CONSTITUTION:A DC power supply protection circuit comprises a short-circuit detecting circuit 40 for outputting short-circuit signals 61, 63 by detecting a short-circuit of a load 20 when the load 20 is connected, a change-over circuit 30 for connecting the load 20 to the DC power supply 10 or to the short-circuit detecting circuit 40 and a control circuit 50 for outputting the short-circuit signals 61, 62 to external circuits and regulating operations of the change-over circuit 30 based on the short-circuit signals 61, 62 and an external control signal 63.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC power supply protection circuit, and more particularly to a function which is connected between a DC power supply and its load and which cannot detect power supply when the load is short-circuited. And a DC power protection circuit.

[0002]

2. Description of the Related Art A conventional DC power supply protection circuit 100 is shown in FIG.
As shown in, the short circuit detector 4 that detects a short circuit of the load 2 when the load 2 is connected and outputs the short circuit signal 61 and the load 2 are connected to the DC power source 1 or the short circuit detector 4. It includes a switching circuit section 3 for switching whether to perform or not, and a control section 5 for outputting the short circuit signal 61 to the outside and defining the operation of the switching circuit section 3 based on the short circuit signal 61 and the external control signal 63 ( For example, Japanese Patent Laid-Open No. 61-197
No. 123).

The short-circuit detector 4 operates when the load 2 is connected to the state detector 4. The variable resistor 41 is for short-circuit detection sensitivity adjustment, and since the positive input of the comparator 43 is divided by Vcc and GND by this, the positive input of the comparator 43 becomes lower than the negative input voltage when not short-circuited. At this time, the output of the comparator 43 becomes low (GND) level. On the contrary, when there is a short circuit, the voltage of the negative input of the comparator 43 falls close to the low level and becomes lower than the voltage of the positive input, so that the output of the comparator 43 becomes the high (Vcc) level.
Further, the inverter 47 receives the output of the comparator 43.
The output of goes to the low level when the short circuit is detected, and the short circuit signal 61
As a result, it is possible to monitor with an external device from the short circuit signal detection terminal 19.

The control unit 5 controls the relay coil 32 by a short circuit signal 61 and an external control signal 63. Since the relay coil 32 is not driven regardless of the input state of the external control signal 63 when the short circuit signal 61 is detected, the DC power source input terminals 11 and 12 and the DC power source output terminal 13,
14 is never connected. When there is no short circuit and the external control signal 63 is at a high level, the relay coil 32 is driven, the relay contact 31 is switched, the DC power input terminals 11 and 12 and the DC power output terminals 14 and 15 are connected, and power is supplied to the load. Is supplied.

[0005]

When the load 2 requires both positive and negative power supplies, two DC power supply protection circuits 100 are used, or one DC power supply protection circuit is used and the load 2 +
The DC power protection circuit 100 must be connected between the terminals and the-terminal to detect a short circuit between the terminals of the load 2.

As shown in FIG. 3, the DC power supply protection circuit 10
When using two 0s, it is possible to connect one between the + and G terminals of the load 2 and one between the G and -terminals, but there are two short-circuit detection power supplies (Vcc). When the DC power supply protection circuit 100 is common, the short circuit of the load 2 is not detected because the G terminal and the-terminal of the load 2 are short-circuited in the DC power supply protection circuit 100. Further, even when the two short-circuit detection power supplies (Vcc) of the DC power supply protection circuit 100 are separately provided, the number of wires is increased because two are required, which causes a problem in space saving.

Further, as shown in FIGS. 4A to 4C, D
When only one C power supply protection circuit 100 is used, there are three possible connection methods. Load 2 as shown in FIG.
In the case of connecting between the + terminal and the G terminal, the load between the + terminal and the G terminal is a load in which the load 71 and the load 73 + the load 72 are arranged in parallel when the load shown in FIG. 5 is considered. At this time, even if the load 73 is short-circuited, the short circuit may be overlooked when the load 72 has only a diode component. Further, when a circuit component having polarity such as an electrolytic capacitor of the load 72 is used, there is a possibility that the circuit component may be damaged due to the reverse voltage.

When the load 2 is connected between the positive terminal and the negative terminal as shown in FIG. 4C, the resistance of the load 72 is larger than that of the load 71 when the load shown in FIG. Sometimes, the short circuit of the load 71 may be overlooked.

As described above, the conventional DC power supply protection circuit is
There is a possibility that the load condition cannot be detected correctly or that the circuit components of the load 2 may be damaged. Further, when the DC power supply protection circuit 100 is unitized, two units are required, the number of wirings is increased, and there is a drawback that space saving is inferior.

[0010]

The DC power supply protection circuit of the present invention detects a short circuit of a load and outputs a short circuit signal when the load is connected, and a short circuit detector
A switching circuit section for switching between connecting to the C power supply or the short circuit detection section, a short circuit detection signal is generated from the short circuit signal and an external control signal, and the short circuit signal and the no-load detection signal are output to the outside. It includes a control unit that regulates the operation of the switching circuit unit based on the short circuit signal and the external control signal.

[0011]

Next, the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram showing an embodiment of the present invention. The DC power supply protection circuit 200 shown in FIG. 1 detects the short circuit and disconnection of the load 20 when the load 20 is connected, and outputs the short circuit signals 61 and 62 to the short circuit detection unit 40 and the load 20. Or short circuit detector 40
Switching circuit unit 30 and the short-circuit signal 6
1, 62 to the outside and short-circuit signals 61, 6
2 and the external control signal 63 based on the switching circuit unit 30.
And a control unit 50 that regulates the operation of.

Next, the operation will be described. When the load 20 is connected to the short-circuit detection unit 40, the variable resistors 41 and 42 for adjusting the short-circuit detection sensitivity are adjusted to appropriate values according to the load 20. As a result, the positive input of the comparator 43 is divided by V + and AG, and the negative input of the comparator 44 is divided by AG and V-.

With the above settings, when the load 20 is normal, the negative input voltage of the comparator 43 becomes higher than the positive input voltage, and the positive input voltage of the comparator 44 also becomes higher than the negative input voltage.
The outputs of 3, 44 are low (V-) level, and the outputs of the photocouplers 45, 46 are high (Vcc) level.

When the + terminal and the G terminal of the load 20 are short-circuited, the negative input voltage of the comparator 43 becomes higher than the positive input voltage, and the output of the comparator 43 becomes high (V +) level. G terminal of load 20 and V-
When the terminals are short-circuited, the positive input voltage of the comparator 44 becomes higher than the negative voltage, so that the output of the comparator 44 becomes the high (V +) level.

The load short-circuit signals 61 and 62 are the photo coupler 4
Since the outputs are 5, 46, when the + terminal and the G terminal of the load 20 are short-circuited, the load short-circuit signal 61 is low (GND).
When the G terminal and the-terminal of the load 20 are short-circuited, the load short-circuit signal 62 becomes low (GND) level.

The control unit 50 controls the relay coil 32 by the short circuit signals 61 and 62 and the external control signal 63.

When the external control signal 63 is low level, the relay coil 3 is irrespective of the input state of the short circuit signals 61 and 62.
2 is not driven, so DC power input terminals 11, 12,
The DC power supply output terminals 14, 15 and 16 are not connected to each other. Since the short circuit signals 61 and 62 can be monitored by the external device from the short circuit signal detection terminals 17 and 18, the state of the load 20 can be grasped.

As described above, in the DC power source protection circuit 200,
The voltage applied to the + terminal of the load 20 is higher than the voltage applied to the G terminal, and the voltage applied to the G terminal is higher than the voltage applied to the − terminal.
The load 2 does not apply reverse voltage to the loads 72 and 73.
It does not damage the polar circuit part inside 0.

If the load 20 may be a single power source, the power source input terminal 13 and the power source output terminal 16 need not be connected. At this time, the G terminal and the-terminal of the DC power source protection circuit 200 are not short-circuited. In order to
The switching circuit unit 3 operates only in the state between the terminals.

A DC power supply protection circuit 20 having a structure as shown in FIG.
0 is effective when the load condition changes frequently, and is applied to, for example, a functional inspection device for a printed circuit board. When inspecting a printed circuit board, the printed circuit board must be powered on.
When there is no 0, not only a short circuit cannot be detected, but also when the load 20 is short-circuited, an overcurrent may flow and the load 20 may be destroyed. Some DC power supplies have an overcurrent protection function that shuts off the power supply output.
It is also conceivable that the functional test is performed without the DC power supply being turned on to the printed circuit board.

If the printed circuit board is short-circuited by using the DC power supply protection circuit 200 of the present invention, the short circuit can be detected on the spot, and the next printed circuit board can be inspected without interrupting the output of the DC power supply 10. I can do it.

[0023]

As described above, the present invention can detect a short circuit of the load without damaging the circuit components of the load even when the load requires both positive and negative power supplies. In addition, whether the positive power supply side of the load is short-circuited or the negative power supply side is short-circuited can be grasped before the power is turned on.

If the load is a single power source, DC
It is sufficient to leave the negative terminal of the power protection circuit unconnected.
Even when the power protection circuit is unitized, the versatility is increased.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a conventional example.

FIG. 3 is a block diagram showing a conventional usage example.

4A to 4C are block diagrams showing conventional usage examples.

FIG. 5 is a block diagram showing an example of a load.

[Explanation of symbols]

 10 DC power supply 20 Load 30 Switching circuit part 40 Short circuit detection part 50 Control part 11-13 DC power supply input terminal 14-16 DC power supply output terminal 17, 18 Short circuit signal detection terminal 19 External control input terminal 31 Relay contact 32 Relay coil 41, 42 Variable resistor 43, 44 Comparator 45, 46 Photocoupler 47, 48 Short circuit prevention resistor 51 Gate 52 Buffer driver 61, 62 Short circuit signal 63 External control signal 71-73 Load

Claims (2)

[Claims] 1. A short circuit detection unit that detects a short circuit of the load and outputs a short circuit signal when the load is connected, and switches between connecting the load to a DC power source or connecting the short circuit detection unit. A switching circuit unit, which generates a short circuit detection signal from the short circuit signal and an external control signal, outputs the short circuit signal and a no-load detection signal to the outside, and operates the switching circuit unit based on the short circuit signal and the external control signal. A DC power supply protection circuit including a control unit that defines 2. The DC power supply protection circuit according to claim 1, wherein there is one dedicated power supply for operating the short-circuit detection unit.