JPH0543623U - Optically coupled relay circuit - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide an optical coupling type relay circuit having excellent controllability. A light emitting diode 1, a photodiode array 2, an output MOSFET 7 that switches between a drain-source conductive state and a non-conductive state, and the MOSFET.
7, a normally-on type control transistor 3 forming a discharge path for accumulated charge between the gate and source, and two series resistors 5 and 12 generating a voltage for biasing the control transistor 3 in a high resistance state. , A bipolar transistor 4 connected between the drain and gate of the output MOSFET and switched between a conductive state and a non-conductive state by the resistor 5, and a diode 6 connected between the drain side of the output MOSFET 7 and the bipolar transistor 4. .

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to an optical coupling type relay circuit in which an input / output circuit is insulated by using an optical coupling method.

[0002]

[Prior Art]

 FIG. 2 is a circuit diagram showing a conventional optical coupling type relay circuit. In this circuit, the photodiode array 2 receives an optical signal generated by the light emitting diode 1 connected between the input terminals 10a and 10b to generate a photoelectromotive force. Is applied between the gate and the source of the output MOSFET 7 via the bipolar transistor 4 which is rendered conductive by the voltage generated by the resistor 5, and the load current is transmitted through the bipolar transistor 4 at the high speed of the gate-source capacitance of the output MOSFET 7. It will be charged properly. The source and drain of the control transistor 3 composed of a depletion type JFET are connected to the gate and source of the output MOSFET 7, and the gate and source of this transistor 3 are connected to both ends of the resistor 5. There is.

When an input signal is applied to the light emitting diode 1 and a photovoltaic power is generated in the photodiode array 2, a photocurrent flows through between the source and drain of the depletion type control transistor 3 and both ends of the resistor 5 are connected. Voltage is generated. This voltage biases the control transistor 3 into a high resistance state, so that the photovoltaic power of the photodiode array 2 is applied between the gate and source of the output MOSFET 7. At the same time, the bipolar transistor 4 becomes conductive due to the voltage across the resistor 5, the load current rapidly charges the gate-source capacitance of the output MOSFET 7, and the output MOS FET 7 is rapidly turned on.

When the input signal to the light emitting diode 1 is cut off, the photovoltaic power of the photodiode array 2 disappears, so that the control transistor 3 becomes conductive and the bipolar transistor 4 becomes non-conductive, so that the output MOSFET 7 is turned off. Since the stored charge between the gate and the source is discharged, the output MOSFET 7 is turned off.

[0005]

[Problems to be solved by the device]

 In the above-mentioned conventional circuit, the control transistor 3 is controlled by the terminal voltage of the resistor 5. However, since the control transistor 3 is also connected between the base and emitter of the bipolar transistor 4, the terminal voltage of the resistor 5 is bipolar. It is regulated by the base-emitter voltage of the transistor 4. Therefore, when the threshold voltage of the control transistor 3 becomes higher than the threshold voltage due to variations or the like, the control transistor 3 does not operate and the relay also stops operating.

The present invention has been made in view of the above drawbacks, and an object thereof is to provide an optically coupled relay circuit having excellent controllability.

[0007]

[Means for Solving the Problems]

 In order to solve the above-mentioned problems, in the optical coupling type relay circuit according to the present invention, as shown in FIG. 1, two resistors 5 and 12 for controlling the control transistor 3 and the bipolar transistor 4 are connected in series. The control transistor 3 is controlled by two resistors 5 and 12 connected, and the bipolar transistor 4 is controlled by the resistor 5 from the gate of the output MOSFET 7.

[0008]

【Example】

 FIG. 1 is a circuit diagram showing an embodiment of the present invention, in which a light emitting diode 1 is connected between input terminals 10a and 10b and is optically coupled to a photodiode array 2. The positive electrode of the photodiode array 2 is connected to the gate of the output MOSFET 7 through the two resistors 5 and 12, and the negative electrode is connected to the source of the MOSFET 7. The gate of the output MOSFET 7 is connected to the source of a normally-on type control transistor 3 composed of a depletion type JFET. The drain of the control transistor 3 is the source of the output MOSFET 7 and the gate thereof is a photodiode array. 2 is connected to the positive electrode.

The drain of the output MOSFET 7 is connected to the anode of the diode 6, and the cathode of the diode 6 is connected to the collector of the bipolar transistor 4. The emitter of the bipolar transistor 4 is connected to the gate of the output MOSFET 7, and the base is connected to the connection point of the two resistors 5 and 12.

Further, the drain of the output MOSFET 7 is connected to one output terminal 11a, the source is connected to the other output terminal 11b, and the series circuit of the DC power supply 9 and the load 8 is connected between the output terminals 11a and 11b. There is.

Next, the operation of the above embodiment will be described. First, when an input signal is applied between the input terminals 10a and 10b, the light emitting diode 1 generates an optical signal, and the photodiode array 2 receives the optical signal to generate a photoelectromotive force. Due to this photovoltaic force, a photocurrent flows through the two resistors 5 and 12 and between the source and drain of the depletion type control transistor 3, and a voltage is generated across the two series resistors 5 and 12.

Since the control transistor 3 is biased in a high resistance state by the voltage generated across the series resistors 5 and 12, the photovoltaic power of the photodiode array 2 is generated between the gate and the source of the output MOSFET 7. Is applied. At the same time, the bipolar transistor 4 becomes conductive due to the voltage generated across the resistor 5 from the gate of the output MOSFET 7, and the load current from the drain side of the output MOSFET 7 rapidly charges the gate-source capacitance of the output MOS FET 7. To do. As a result, the output MOS FET 7 is rapidly turned on.

When the input signal between the input terminals 10a and 10b is cut off, the photoelectromotive force between the terminals of the photodiode array 2 disappears, the control transistor 3 is turned on, and the bipolar transistor 4 is turned off. It becomes conductive. Therefore, the gate-source capacitance of the output MOSFET 7 is discharged through the control transistor 3, and the output MOSFET 7 is turned off.

[0014]

[Effect of the device]

 In the present invention, as described above, the bipolar transistor is controlled by dividing the resistor into only one resistor and controlling the bipolar transistor and the controlling transistor separately. The disadvantage that the gate-source voltage of the transistor is regulated is eliminated, and the relay can be operated with good control.

[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.

[Explanation of symbols]

 1 Light-Emitting Diode 2 Photodiode Array 3 Control Transistor 4 Bipolar Transistor 5 Resistor 6 Diode 7 Output MOSFET 12 Resistor

Claims (1)

[Scope of utility model registration request] 1. A light emitting diode that generates an optical signal in response to an input signal, a photodiode array arranged to receive the optical signal of the light emitting diode, and a photovoltaic voltage of the photodiode array between a gate and a source. And a normally-on type control transistor that forms a discharge path for accumulated charge between the gate and source of the output MOSFET by applying the , Two series resistors for generating a voltage for biasing the control transistor to a high resistance state when a photocurrent of the photodiode array is passed through the control transistor, and an output MOSFET
A bipolar transistor connected between the drain and gate of the output MOSFET and switching between a conductive state and a non-conductive state by the resistance from the gate of the output MOSFET, of the two resistors, and connected between the drain side of the output MOSFET and the bipolar transistor. An optical coupling type relay circuit characterized by comprising a diode.