JP2728902B2 - Power cut-off device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power cutoff device, and more particularly to a power supply cutoff device that supplies a relatively large power to a load when a semiconductor switch element that is turned on and off is short-circuited. The present invention relates to a power cutoff device that forcibly cuts off power supplied to a load.

[Prior Art] FIGS. 3 and 4 show circuit examples of a conventionally proposed fail-safe power supply cutoff device.

In the power supply shut-off device shown in FIG. 3, a contactless solid state constituted by a load 32 such as a motor and a semiconductor switch element such as a transistor, a thyristor, and a triac is provided for an AC power supply 31 capable of supplying a relatively large power.・
A relay (hereinafter referred to as SSR) 33 is connected in series in a loop, and a normally closed (closed during normal operation) relay contact 34 is interposed between the load 31 and the SSR 33.
The opening / closing operation of the relay contact 34 is controlled by the relay 35. Then, the voltage between the terminals of the SSR 33 is input to the voltage sensor 36, the output of the voltage sensor 36 is supplied to one input terminal of the two-input OR circuit 37, and the SSR 33 is turned on and off to control the SSR 33 on and off.
The control signal I supplied to the SR 33 is also supplied to the other input terminal of the OR circuit 37, and the relay 35 is operated by the output of the OR circuit 37 obtained by such a configuration.

In the above conventional device, the relay 35 is in the OFF state at the beginning of use, and therefore, the contact 34 is open. In this state, when the control signal I becomes a high potential level (hereinafter, referred to as H level), the SSR 33 is turned on, but no current flows to the load 32 due to the opening of the contact 34. However, since the OR circuit 37 outputs the signal according to the H level of the control signal I, the relay 35 operates, and the contact 34 comes into contact, so that the current flows to the load 32 and the load 32 operates.

In addition, when the control signal I becomes a low potential level (hereinafter, referred to as L level), as long as the SSR 33 is normal, the SSR
Is turned off, so that no current flows through the load 32. Also, the voltage between the SSR terminals becomes H level, and the voltage sensor 36
Is output and the OR circuit outputs, so that the relay 35 maintains the operating state, and the contact 34 maintains the contact state.

When the short-circuit fault occurs in the SSR 33, when the control signal I is at the H level, the operation of the relay 35 and the contact state of the contact 34 are not different from the case where no short-circuit fault occurs, so that the load is not affected. Absent.

On the other hand, if a short-circuit fault occurs in the SSR 33 when the control signal I is at the L level, the potential between the SSR terminals becomes the L level, so that the voltage sensor 36 does not output and the OR circuit is turned off. The relay 35 is de-energized and the contact 34
To release. That is, the load power supply is forcibly shut off.
Thus, in this conventional circuit example, although the control signal I is at the L level, a failure occurs in the SSR 33 and the SSR 33 is short-circuited.
Even if 33 is eventually turned on, relay contacts 34
Since the power supply is in the OFF state, power is not supplied to the load 32, thereby avoiding the danger of operating the load 32 and increasing control safety.

Further, by using another contact of the relay 35, it is possible to detect a short-circuit failure of the SSR.

Next, in the power cutoff device shown in FIG.
32, SSR 33, and relay 35 are the same as those described above. In this circuit example, a power supply sensor 41 is arranged on a line between the SSR 33 and the power supply 31, and the presence or absence of a current flowing in the line is converted into a logic signal by voltage, and one of the coincidence detection circuits 42 having two inputs is converted. Input to the input terminal. The control signal I is supplied to the other input terminal of the coincidence detection circuit 42,
The output of the coincidence detection circuit 42 is provided to the relay 35.

In the above configuration, when the control signal I is at the L level, the SSR 33 is in the off state.
The inputs are both at L level to keep the relay 35 energized, so that the relay contact 34 is normally kept on, as shown in FIG. Next, when the control signal I becomes H level, the SSR 33 turns on, and the power is supplied from the power supply 31 to the load 32. Therefore, the current sensor 41 detects the power supply, and as a result, the two inputs of the coincidence detecting circuit 42 become H level, so that the relay 35 is kept in the excited state and the relay contact 34 is kept in the on state. When the short-circuit fault occurs in the SSR 33 and the SSR 33 is turned on even though the control signal I is at the L level, the two inputs of the match detection circuit 42 do not match, and the relay 35 is de-energized. Relay contact 34
Operates off to prevent power from being supplied to the load 32.

[Problem to be Solved by the Invention] In the power cutoff device shown in FIG.
Since the relay 35 is in the non-excited state, when using this device from the state where the control signal I is at the L level, the SSR3
3 cannot know whether a short-circuit fault has occurred,
To make this possible, the OR circuit 37 or relay 35
There is a problem that another operation signal must be given at the beginning of use.

In the power shut-off device shown in FIG. 4, when the control signal I is at the L level and the SSR 33 is short-circuited, the coincidence detecting circuit 42 and the relay contact 35 are turned off via the relay 35, and the coincidence detecting circuit 42 is turned off. Both inputs become L level, the relay contact 34 is turned on again via the relay 35 to return to the initial state, and then the above operation is repeated, which causes a problem in circuit design. Further, when the relay contact 34 is repeatedly turned on and off in this way, since the relay contact 34 is formed with a mechanical structure, a problem such as welding occurs at the contact portion.

Thus, an object of the present invention is to solve the above-described problems of the conventional device by adding a simple circuit to the conventional device, and to provide a power supply shut-off device with less damage to the mechanical movable part and high operation reliability. To provide.

[Means for Solving the Problems] A power supply shut-off device according to the present invention provides a semiconductor switch element that controls power supply from a load power supply to a load based on a control signal to change the operation state of the semiconductor switch element for fail-safe purposes. A sensor (voltage sensor or current sensor) for detecting, and when the semiconductor switch element is short-circuited, a contact on a power supply line is turned off via the sensor and a relay circuit to forcibly cut off power supply to a load. In the power cutoff device, a second power supply unit different from the power supply to the load is provided, and a voltage from the second power supply unit is always applied to the semiconductor switch element and the sensor.

[Operation] In the device of the present invention, by the operation of the second power supply means different from the power supply to the load, in the power supply cutoff device using the voltage sensor and the OR circuit, the relay is excited even when the control signal is at the L level. And the contact is kept on. Therefore, even when the control signal is started to be used in the L level state, it functions normally. If the SSR is short-circuited when the control signal is at the L level, the relay is de-energized, the relay contact is opened, and power supply to the load is forcibly shut off.

Further, in the power cutoff device using the current sensor and the coincidence detection circuit, even after the two inputs of the coincidence detection circuit become inconsistent due to the short-circuit failure of the SSR while the control signal is at the L level, the contact is turned off. Since the current from the second power supply continues to flow through the current sensor, the input states of the two inputs of the match detection circuit do not match again, and the non-excited state of the relay is maintained.

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2.

FIG. 1 shows a first embodiment of a power cutoff device according to the present invention. This embodiment is an improvement on the conventional circuit described with reference to FIG.

In FIG. 1, reference numeral 31 denotes an AC power supply for supplying power to a load, 32 denotes a load, 33 denotes an SSR, 34 denotes a relay contact, 35 denotes a relay, 36 denotes a voltage sensor, and 37 denotes an OR circuit. Since they are the same as those described in the drawings, the same reference numerals are given in the following description, and detailed description is omitted.

The power supply 31, the load 32, the relay contact 34, and the SSR 33 are connected in series in this order, and the SSR 33 is supplied with a control signal I for load power supply control.

According to this circuit configuration, power is supplied from the power supply 31 to the load 32 when both the relay contact 34 and the SSR 33 are on. Since the load 32 is, for example, a motor, the power supply 31 is for supplying relatively high power.

The above circuit is further provided with a second AC power supply 11, a transformer 12, and a resistor 13 having a predetermined high impedance as new circuit elements. The resistor 13 and the secondary coil 12b of the transformer 12 are connected in series and are connected between both terminals of the SSR 33. In this case, the resistor 13 side terminal is connected to the relay contact 34 and SS
Connected on line between R33. In addition, the second power supply 11
Is connected to the primary coil 12a of the transformer 12. Voltage sensor 3
The input of 6 is the voltage between the terminals of SSR33, in other words, the resistor 13
, And a voltage between terminals of a series circuit portion of the secondary coil 12b. The output of the voltage sensor 36 and the control signal I input to each of the two inputs of the OR circuit 37 and the control of the on / off operation of the relay contact 34 by the output of the relay 35 have been described with reference to FIG. The configuration is the same.

The operation of the above circuit will be described. When the control signal I is at the L level, the output voltage of the power supply 11 is converted to a predetermined voltage by the transformer 12 and further reduced by a voltage drop by the resistor 13 and input to the voltage sensor 36 when the SSR 33 is in the OFF state. Therefore, the relay 35 is excited through the OR circuit 37, and the relay contact
34 is kept on.

The supply voltage of the power supply 11 is also given to the load 32 because the relay contact 34 is in the on state, but the supply voltage is low because the resistance 13 is set to a high impedance, and the load 32 is driven by this voltage. Never. Further, when the relay contact 34 is in the ON state, an energizing path is also formed for the power supply 31 via the resistor 13 and the secondary coil 12b, but the supply current is limited to a low value by the high impedance of the resistor 13. In this state, the load 32 is not driven. In other words, the impedance of the resistor 13 is set to a predetermined high value so that the above-described circuit state is formed.

In this circuit state, when the control signal I becomes H level, the SSR 33 is turned on, a large power is supplied from the power supply 31 to the load 32, and the load 32 is driven.

At this time, the voltage input to the voltage sensor 36 is SSR33
Since the voltage between the terminals is input, it becomes L level,
Since the control signal I is also supplied to the OR circuit 37, this keeps the relay 35 energized and the relay contact 34 remains on. Thus, as long as the control signal I is at the H level, the power supply from the load power supply 31 to the load 32 is continued.

Next, when the control signal I is at the L level,
Is turned on due to a short circuit fault, the voltage sensor
The output of the OR circuit 37 goes low because the output of the OR 36 goes low and the control signal I is also low.
35 is de-energized. As a result, the relay contact 34 is turned off to prevent the drive power from being supplied to the load 32.

According to the configuration of this embodiment, in a normal state, the relay 35 is excited by the operation of the circuit such as the second power supply 11 and the like, and the relay contact 34 is kept in the ON state. Since the excitation state is established, a short-circuit fault in the SSR 33 can be determined, which is also preferable in circuit design.

FIG. 2 shows a second embodiment of the present invention. This example is
This is an improvement on the conventional circuit shown in FIG.

The power supply 31, the load 32, the SSR 33, the relay contact 34, and the relay 35 are the same as those described in FIG. 1, and the current sensor 41 and the coincidence detection circuit 42 are the same as those described in FIG.
Since the second power supply 11, the transformer 12, and the resistor 13 are the same as those described with reference to FIG. 1, they are denoted by the same reference numerals. Since the above circuit elements have already been described according to the corresponding drawings, detailed description thereof will be omitted here.

Power supply 31, load 32, SSR33, relay contact 34, relay 35,
The connection configuration of the current sensor 41 and the coincidence detection circuit 42 is the same as the configuration in FIG. In such a circuit configuration, a series circuit portion of the resistor 13 and the secondary coil 12b of the transformer 12 is connected to the intermediate line of the relay contact 34 and the SSR 33, the current sensor 41 and the power supply 3
Connected to one intermediate line. The relationship between the transformer 12 and the second power supply 11 is as described in FIG.

According to the above configuration, since the voltage is always applied to the SSR 33 by the power supply 11, when the control signal I is at the L level,
Even if the SSR 33 is short-circuited and the relay contact 34 is turned off as described above, the current continues to flow to the current sensor 41 by the second power supply 11 and the mismatch state at the input of the match detection circuit 42 is maintained. Thus, when a short-circuit fault occurs in the SSR 33, the relay contact 34 is kept in the off state, and the on / off operation is not repeated.

Note that a relay contact that performs an operation opposite to that of the relay contact 34 (a back contact of the relay contact 34) may be disposed at a position A between the resistor 13 and the secondary coil 12b. According to this configuration, power can be supplied from the second power supply 11 only when the relay 35 is not excited, that is, only when the relay contact 34 is turned off. Thus, power consumption of the second power supply 11 can be reduced.

Further, in each of the above embodiments, it is also possible to generate a voltage corresponding to the second power supply by using the power supply 31 without separately preparing the second power supply 11.

[Effects of the Invention] As is apparent from the above description, according to the present invention, only a small circuit, that is, a second power supply circuit different from the power supply to the load is added to the circuit of the conventional power cutoff device. so,
The problem of the conventional device can be solved, the circuit performance can be improved, and the operation reliability of the power cutoff device required in an emergency can be improved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a first embodiment of a power cutoff device according to the present invention, FIG. 2 is a circuit diagram showing a second embodiment of the power cutoff device according to the present invention, and FIG. FIG. 4 is a circuit diagram showing the configuration of the device, and FIG. 4 is a circuit diagram showing the configuration of another conventional power cutoff device. 11 ... second AC power supply, 12 ... transformer, 13 ... resistor, 31 ... load AC power supply, 32 ... load, 33 ... SSR (Solid State Relay), 34 ... relay contact , 35 ... relay, 36 ... voltage sensor, 37 ... OR circuit, 41 ... current sensor, 42 ... match detection circuit.

Claims (2)

(57) [Claims] A semiconductor switch element for controlling power supply to a load, a sensor for detecting an operation state of the semiconductor switch element, and when the semiconductor switch element has a short-circuit fault, the fault is detected by the sensor; In a power cutoff device for turning off a relay contact of a power supply line via a relay circuit to cut off power supply to a load, a second power supply unit different from power supply to the load is provided,
A power supply shut-off device, wherein a voltage of the second power supply means is always supplied to the semiconductor switch element and the sensor. 2. The semiconductor switching device is turned off between a second power supply means and the semiconductor switching device and the sensor.
The power supply cut-off device according to claim 1, wherein a resistor having a predetermined high impedance for preventing the load from being operated by the load power supply or the second power supply is connected in the state.