JPH09186573A - Semiconductor relay circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a relay circuit in which continuous flowing of an overcurrent to a load is prevented. SOLUTION: In the case of limiting a load current, since MOSFETs 3a, 3b reach a high impedance state, a voltage generated between output terminals O1, O2 is increased. A current is supplied to Zener diodes 8a, 8b by the voltage generated between the output terminals O1 and O2, either of over-current display LEDs 10a, 10b is lighted to indicate the overcurrent flowing. In this case, since photo transistors(TRs) 9a, 9b receive an optical signal from a light emitting element 1, the current flowing is made available. On the other hand, when no input signal is given to the light emitting element 1 and the photo TRs 9a, 9b receive no optical signal from the light emitting element 1, no current flowing is made and it is a shut-off state for the relay circuit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor relay circuit in which an input and an output are insulated by using an optical coupling method.

[0002]

2. Description of the Related Art FIG. 2 is a circuit diagram showing an overall configuration of a semiconductor relay circuit according to a conventional example. In this semiconductor relay circuit, the LED connected between the input terminals I1 and I2
And the like, the photodiode array 2 receives an optical signal generated by the light emitting element 1 to generate a photoelectromotive force, and the photoelectromotive force generated at both ends of the photodiode array 2 is used as an output MOS.
It is applied between the gate (G) and the source (S) of the FETs 3a and 3b. An example of the MOSFETs 3a and 3b is an N-channel enhancement type MOSFE.
T, and the sources (S) of the MOSFETs 3a and 3b are connected to each other via resistors 7a and 7b.
The drains (D) of T3a and 3b are connected to the output terminals O1 and O2, respectively. In this way, two MOSF
By connecting the ETs 3a and 3b in inverse series between the output terminals O1 and O2, it is possible to realize a semiconductor relay circuit that also serves as AC / DC.

Photovoltaic power generated at both ends of the photodiode array 2 is applied between the gate (G) and the source (S) of the MOSFET 3a via the resistor 5 and the resistor 7a as an impedance element, and the resistor 5 and the resistor 7b. Is applied between the gate (G) and the source (S) of the MOSFET 3b via. The gates (G) of the MOSFETs 3a and 3b have depletion type MOSFETs (or JFEs).
The drain (D) of the control transistor 4 composed of T or SIT) is connected to the source (S) of the MOSFET 3a.
Is connected to the source (S) of the control transistor 4 via the resistor 7a, and the source (S) of the MOSFET 3b is connected to the source (S) of the control transistor 4 via the resistor 7b. The gate (G) and the source (S) of the control transistor 4 are connected to both ends of the bias resistor 5 as shown in FIG.

When an input signal is applied to the light emitting element 1 and a photoelectromotive force is generated at both ends of the photodiode array 2,
A photocurrent flows between the drain (D) and the source (S) of the control transistor 4 and through the resistor 5, and a voltage is generated across the resistor 5. This voltage biases the control transistor 4 into a high impedance state, so that the MOSFE
Photovoltaic force is applied between the gate (G) and the source (S) of T3a and 3b, and the MOSFETs 3a and 3b are turned on.

The number of photodiode arrays 2 connected in series is selected to be sufficient to generate a voltage exceeding the threshold voltage of MOSFETs 3a and 3b.

When the input signal to the light emitting element 1 is cut off,
Since the photoelectromotive force at both ends of the photodiode array 2 disappears and the voltage at both ends of the resistor 5 disappears, the depletion type control transistor 4 returns to the low impedance state, and the gate (G) -source (of the MOSFETs 3a and 3b (source)). By discharging the accumulated charge between S),
The ETs 3a and 3b are turned off.

A constant voltage element is connected in parallel with the bias resistor 5 so that the potential difference across the resistor 5 does not rise above a predetermined voltage. Here, an enhancement type MOSFET 6 in which a gate (G) and a drain (D) are commonly connected is used as a constant voltage element,
The potential difference across the resistor 5 does not rise above the threshold voltage of the MOSFET 6.

When the MOSFETs 3a and 3b are in the ON state, a load current flowing between the output terminals O1 and O2 generates a voltage across the resistors 7a and 7b. When the voltage exceeds a certain value, the NPN transistor 11a, A current flows through the base (B) of 11b, and the NPN transistor 11
a, 11b operate to discharge the accumulated charge between the gate (G) and the source (S) of the MOSFETs 3a, 3b, and
The FETs 3a and 3b are set to a high impedance state to limit the load current flowing between the output terminals O1 and O2.

[0009]

However, in the semiconductor relay circuit having the above-described structure, the upper limit value of the load current is determined by the values of the resistors 7a and 7b, and the instantaneous overcurrent such as surge is prevented. Although effective, there is a problem that the upper limit current continues to flow with respect to the overcurrent of the load current due to a wiring mistake or the like, and the circuit on the load side is destroyed.

The present invention has been made in view of the above points, and an object thereof is to provide a semiconductor relay circuit which prevents an overcurrent from continuing to flow to the load side.

[0011]

According to the first aspect of the present invention,
A light-emitting element that generates an optical signal in response to an input signal; a photodiode array that receives the optical signal and generates a photoelectromotive force; an impedance element that is connected in series with the photodiode array; Electromotive force is applied between the gate and the source through the impedance element to change two output impedances from the first impedance state to the second impedance state, and two output MOSFETs.
A current-carrying electrode is connected between the gate and the source of the OSFET, and a control electrode is connected to a connection point between the impedance element and the photodiode array so that both ends of the impedance element are generated when a photovoltaic force is generated by the photodiode array. A depletion type control transistor biased to a high impedance state by a voltage generated in the MOSFET, a resistor for detecting a load current inserted in series between the sources of the two MOSFETs, and a voltage generated across both ends of the resistor are predetermined. And a transistor which is turned on when the value is equal to or more than a value, and when the transistor is turned on, the charge accumulated between the gate and the source of the two MOSFETs is discharged to limit the load current. In a semiconductor relay circuit, a Zener is connected in parallel with the MOSFET. Phototransistor and LED overcurrent indication for receiving diode and the optical signal from the light emitting element
And are provided in series.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing the overall configuration of a semiconductor relay circuit according to an embodiment of the present invention. The semiconductor relay circuit according to the present embodiment is the same as the semiconductor relay circuit shown in FIG.
Zener diode 8 is connected in parallel to OSFETs 3a and 3b.
a, 8b, phototransistors 9a, 9b for receiving an optical signal from the light emitting element 1, and LEDs 10a, 10b for anti-current display connected in antiparallel are provided in series.

The operation of this embodiment will be described below. First, when the load current is small, the NPN transistors 11a and 11b are in the cut-off state as shown in the conventional example. Therefore, the output terminals O1 and O2 are electrically connected, and when the load current is large, the load current detection resistor is used. The voltage generated at both ends of 7a and 7b increases, and the NPN transistor 11
A current flows through the bases (B) of a and 11b, and the NPN transistors 11a and 11b operate to output MOSFETs.
The accumulated charges in the gates (G) of 3a and 3b are discharged, and MO
The SFETs 3a and 3b are set in a high impedance state to limit the load current flowing between the output terminals O1 and O2.

When the load current is limited,
Since the MOSFETs 3a and 3b are in a high impedance state, the voltage generated between the output terminals O1 and O2 rises. By the voltage generated between the output terminals O1 and O2,
A current flows through the Zener diodes 8a and 8b, and one of the LEDs 10a and 10b for indicating the overcurrent is illuminated to indicate that the overcurrent is flowing.

At this time, the phototransistors 9a and 9b
Since an optical signal is received from the light emitting element 1, it is possible to pass a current. On the other hand, when there is no input signal to the light emitting element 1 and the phototransistors 9a and 9b do not receive the optical signal from the light emitting element 1, the current cannot flow and the relay circuit is in the cutoff state.

Therefore, in the present embodiment, the user can easily know when an overcurrent flows by the LED, and by doing this, the load side circuit can be prevented from being broken by cutting off the load current. .

In the present embodiment, the NPN transistors 11a and 11b are provided in order to prevent the load side circuit from being destroyed when an instantaneous overcurrent flows, but the present invention is not limited to this. Alternatively, a PNP transistor may be used.

[0018]

According to the first aspect of the present invention, a light emitting element that generates an optical signal in response to an input signal, a photodiode array that receives the optical signal and generates a photoelectromotive force, and a series of the photodiode array are provided. Gate connected to the impedance element and the photovoltaic element through the impedance element.
Two output MOs that are applied between the sources and change from the first impedance state to the second impedance state
Current-carrying electrodes are respectively connected between the SFET and the gates and sources of the two MOSFETs, and control electrodes are connected to a connection point between the impedance element and the photodiode array, so that when the photovoltaic array generates a photoelectromotive force, A depletion type control transistor that is biased to a high impedance state by the voltage generated at both ends, a load current detection resistor inserted in series between the sources of two MOSFETs, and a voltage generated at both ends of the resistor has a predetermined value. A semiconductor relay circuit configured to have a transistor that is turned on when the above condition occurs, and discharge a stored charge between the gate and source of two MOSFETs to limit a load current when the transistor is turned on. In parallel with the MOSFET, the Zener diode and Since the phototransistor for receiving the optical signal from the element and the LED for displaying the overcurrent are provided in series, the user is notified by the LED when the overcurrent flows, whereby the load current can be cut off. It has been possible to provide a semiconductor relay circuit that prevents an overcurrent from continuing to flow to the load side.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an overall configuration of a semiconductor relay circuit according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing an overall configuration of a semiconductor relay circuit according to a conventional example.

[Description of Reference Signs] 1 light emitting element 2 photodiode array 3a, 3b, 6 MOSFET 4 control transistor 5, 7a, 7b resistor 8a, 8b Zener diode 9a, 9b phototransistor 10a, 10b LED 11a, 11b NPN transistor I1, I2 input Terminals O1, O2 output terminals

Claims (1)

[Claims] 1. A light emitting element that generates an optical signal in response to an input signal, a photodiode array that receives the optical signal and generates a photoelectromotive force, and an impedance that is connected in series with the photodiode array. Element and two MOSFETs for output that apply the photovoltaic force between the gate and the source through the impedance element to change from the first impedance state to the second impedance state
A current-carrying electrode is connected between the gate and the source of each of the two MOSFETs, and a control electrode is connected to a connection point between the impedance element and the photodiode array, and when a photoelectromotive force is generated by the photodiode array, A depletion type control transistor biased to a high impedance state by a voltage generated across the impedance element, and a load current detection resistor inserted in series between the sources of the two MOSFETs,
A MOSFET that is turned on when a voltage generated across the resistor exceeds a predetermined value, and the two MOSFETs are turned on when the transistor is turned on.
In the semiconductor relay circuit configured to discharge the accumulated charge between the gate and the source of the device to limit the load current,
A semiconductor relay circuit comprising a Zener diode, a phototransistor for receiving an optical signal from the light emitting element, and an LED for overcurrent display, which are provided in series in parallel with the OSFET.