JPH10215159A - Semiconductor relay - Google Patents

Abstract

PROBLEM TO BE SOLVED: To interrupt drain current for not less than prescribed current with high reliability by setting a thyristor in a state where drain current exceeds prescribed current and current flows from an anode to a cathode. SOLUTION: The optical trigger thyristor 4 is set in the state where drain current exceeds prescribed current, it flows and therefore current can flow from the anode to the cathode. A charge charged between the gate and the source of MOSFET 3 flows from the anode to the cathode and the drain and the source of MOSFET 3 become the interrupted state. Since current which once flows from the anode to the cathode continuously flows as long as photovoltaic power is applied between the anode and the cathode even if drain current of MOSFET 3 exceeds prescribed current and it does not flow, the gate and the source of MOSFET 3 are not charged. Thus, the interruption state and the conduction state of MOSFET 3 are prevented from repeating.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor relay for discharging a charge charged in a MOSFET when a current exceeding a predetermined current flows.

[0002]

2. Description of the Related Art Conventionally, there is a semiconductor relay of this type shown in FIG. The light-emitting element A emits light in response to an input signal, the light-receiving element B receives light from the light-emitting element A to generate a photoelectromotive force, and a photoelectromotive force is applied between the gate and the source. MOSFETM to be charged;
A resistor R connected to the source of MOSFETM and a resistor R
The base and the emitter are connected to both ends of the
A bipolar transistor T having a collector connected to the gate of SFETM.

Next, the operation will be described. When the light emitting element A emits light according to the input signal, the light receiving element B receives the light of the light emitting element A and generates a photovoltaic voltage. Then, MOSF
The ETM is charged by the application of photovoltaic voltage between its gate and source, and the ETM becomes conductive between the drain and source, causing a drain current to flow.

When this drain current flows beyond a predetermined current, the voltage across the resistor R connected to the source of the MOSFET M increases, and the base current of the bipolar transistor T whose base and emitter are connected to both ends of the resistor R flows. As a result, the collector current of the bipolar transistor T flows. In this way, when the collector current of the bipolar transistor T flows, the electric charge charged in the MOSFETM is discharged, and the connection between the drain and the source of the MOSFETM is cut off.

[0005]

In the above-described conventional semiconductor relay, when the drain current of the MOSFETM flows over a predetermined current, as described above, the MOSFETM
Is cut off between the drain and the source of the
It is possible to prevent a drain current exceeding a predetermined current from continuing to flow through the SFETM.

However, while the light emitting element A is emitting light, the MOSFET M is charged by the application of photovoltaic voltage between its gate and source, and the MOSFET M is in a conductive state between the drain and source. , Even if the connection between the drain and the source of MOSFETM is temporarily cut off,
When the MOSFET M is turned on and the drain current of the MOSFET M flows over a predetermined current, the drain current over the predetermined current may not be cut off with high reliability.

[0007] The present invention has been made in view of the above points, and its object is to achieve high reliability.
An object of the present invention is to provide a semiconductor relay capable of cutting off a drain current of a predetermined current or more.

[0008]

In order to solve the above-mentioned problems, the invention according to claim 1 comprises a light emitting element which emits light in response to an input signal, and a light electromotive force generated by receiving light from the light emitting element. The light-receiving element generated, the MOSFET charged by applying photovoltaic voltage between the gate and the source, and the MOSFET when the photovoltaic voltage is applied between the anode and the cathode.
A thyristor is connected to the MOSFET so that a current flows from the anode to the cathode when the drain current of the SFET exceeds a predetermined current.

According to a second aspect of the present invention, in the first aspect, a resistor connected to the source of the MOSFET and a second light emitting element connected in parallel with the resistor are provided.
The thyristor is a light-triggered thyristor that receives light from the second light-emitting element and allows current to flow from the anode to the cathode.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIG. The semiconductor relay includes a first light emitting diode (light emitting element) 1, a photovoltaic light emitting diode array (light receiving element) 2, a MOSFET 3, a light trigger thyristor 4, a second light emitting diode (second light receiving element) 5.
, Control transistor 6, first to third resistors 7, 8, 9
It is comprised including.

The first light emitting diode (light emitting element) 1
An optical signal is emitted according to an input signal input between the input terminals 10a and 10b. The photovoltaic light emitting diode array (light receiving element) 2 receives an optical signal from the first light emitting diode 1 and generates a photovoltaic power.

The MOSFET 3 has a gate connected to the anode of the photovoltaic light emitting diode array 2 and a source connected to the cathode of the photovoltaic light emitting diode array 2 via first and second resistors 7 and 8. I have.

The light trigger thyristor 4 has an anode connected to the gate of the MOSFET 3 and a cathode connected to the first.
Is connected to the drain of the MOSFET 3 via the resistor 7 of the MOSFET 3 and the gate is connected to the MOS through the first and second resistors 7 and 8.
Connected to the drain of FET3. The second light emitting diode (second light receiving element) 5 is connected in parallel to the first resistor 7.

The control transistor 6 has its gate connected to the cathode of the photovoltaic light emitting diode array 2,
The source is connected to the cathode of the photovoltaic light emitting diode array 2 via the second resistor 8, and the drain is connected to the anode of the photovoltaic light emitting diode array 2.

Next, the operation will be described. When the first light emitting diode 1 emits an optical signal according to the input signal, the photovoltaic light emitting diode array 2 receives the optical signal of the first light emitting diode 1 and generates photovoltaic power. Then, M
The OSFET 3 is charged by applying a photovoltaic force between its gate and source, and becomes conductive between the drain and source, causing a drain current to flow between the output terminals 11a and 11b.

On the other hand, when the photovoltaic light emitting diode array 2 generates photovoltaic voltage, the voltage across the second resistor 8 is applied between the gate and the source of the control transistor 6, so that the drain and the source Are in a conductive state.

When no input signal is input to the first light emitting diode 1 and light emission stops, the photovoltaic light emitting diode array 2 stops generating photovoltaic power. Then, the charge charged between the gate and the source of the MOSFET 3 is quickly discharged through the control transistor 6, so that the drain and the source of the MOSFET 3 are cut off, and the drain current stops flowing.

When the drain current of the MOSFET 3 flows over a predetermined current, the voltage across the first resistor 7 connected to the source of the MOSFET 3 increases, and the voltage across the second resistor connected in parallel to both ends of the first resistor 7 increases. Light-emitting diodes 5
Current flows through the second light-emitting diode 5, and the second light-emitting diode 5 emits light. Thus, when the second light emitting diode 5 emits light, the emitted light is received by the light trigger thyristor 4, and the anode and the cathode of the light trigger thyristor 4 become conductive, and the electric charge charged in the MOSFET 3 Is discharged, and the connection between the drain and the source of the MOSFET 3 is cut off.

In such a semiconductor relay, the light trigger thyristor 4 is in a state where a current can flow from the anode to the cathode when the drain current exceeds a predetermined current.
Charge charged between the gate and source of SFET3 flows, and the drain and source of MOSFET3 are cut off. Moreover, the light trigger thyristor 4 is an MO
Even if the drain current of SFET3 stops flowing beyond a predetermined current, as long as the photovoltaic voltage is applied between the anode and the cathode, the current once flowing from the anode to the cathode continues to flow. Is no longer charged between the gate and source of the MOSF
Since the drain current of ET3 stops flowing, MOSFE
The interruption state and the conduction state of T3 are not repeated, and the drain current exceeding a predetermined current can be interrupted with high reliability.

When the drain current of the MOSFET 3 exceeding the predetermined current flows through the resistor, the voltage across the first resistor 7 increases, and the second light emitting diode 5 connected in parallel to the first resistor 7 is activated. Since light is emitted and the emitted light serves as a trigger, a current flows from the anode to the cathode of the light-triggered thyristor 4.Thus, a current flows from the gate to the cathode, so that a current flows from the anode to the cathode. Insulation can be improved and noise is less likely to occur.

In this embodiment, the light trigger thyristor 4 is provided. For example, when the insulation property is sufficiently high, the thyristor in which the current flows from the anode to the cathode due to the current flowing from the gate to the cathode is provided. It may be provided.

[0022]

According to the first aspect of the present invention, the thyristor is
When the drain current exceeds the predetermined current, a current can flow from the anode to the cathode.
The charge charged between the gate and the source of the MOSFET flows from the anode to the cathode, so that the drain and the source of the MOSFET are cut off. In addition, even if the drain current of the MOSFET does not flow beyond a predetermined current, the thyristor can supply the current once flowing from the anode to the cathode as long as the photovoltaic voltage is applied between the anode and the cathode. Because it keeps flowing, M
Since it is not charged between the gate and the source of the OSFET and the drain current of the MOSFET does not flow,
The interruption state and the conduction state of the MOSFET are not repeated, and the drain current of a predetermined current or more can be interrupted with high reliability.

According to a second aspect of the present invention, in addition to the effect of the first aspect of the present invention, when a drain current of a MOSFET exceeding a predetermined current flows through the resistor, the voltage across the resistor increases, and the voltage across the resistor increases. The connected second light-emitting element emits light, and the emitted light serves as a trigger to cause current to flow from the anode to the cathode of the light-triggered thyristor. Than a thyristor where current flows to
Insulation can be improved and noise is less likely to occur.

[Brief description of the drawings]

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

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

[Explanation of symbols]

 1 light emitting element 2 light receiving element (photovoltaic light emitting diode array) 3 MOSFET 4 light trigger thyristor 5 light emitting diode (second light emitting element) 7 first resistor

Claims (2)

[Claims] A light emitting element that emits light in response to an input signal;
A light-receiving element that receives light from a light-emitting element to generate photovoltaic power, a MOSFET that is charged by applying photovoltaic power between a gate and a source, and a photovoltaic power is generated between an anode and a cathode. When the drain current of the MOSFET exceeds a predetermined current while being applied, the MOSF
And a thyristor connected to the ET and through which a current can flow from the anode to the cathode. 2. A resistor connected to a source of a MOSFET and a second light emitting element connected in parallel to the resistor, wherein the thyristor receives light from the second light emitting element and receives a light from an anode to a cathode. 2. The semiconductor relay according to claim 1, wherein the semiconductor relay is a light-triggered thyristor through which a current flows.