JPH01297916A - Optical coupling type relay circuit - Google Patents

Abstract

PURPOSE:To obtain the linearity of output by fast switching by connecting a series circuit of a control transistor(TR) and a phototransistor between the drain and gate of an output MOSFET and coupling the phototransistor and a light emitting diode optically with each other. CONSTITUTION:When an input signal is applied between input terminals 8a and 8b, the light emitting diode 1 generates a light signal to turn on the phototransistor(PT) 6 and a load current flows to a load 10. This current flows from a 2nd control TR 4 through the PT 6, a 1st control TR 3, and a resistance 5 and is also shunt to the capacity between the gate and source of an output MOSFET 7, which is charged fast, so the gate-source voltage rises abruptly. The FET 7 is turned on speedily. A photodiode PD array 2, on the other hand, generates a photoelectromotive force to turn off the TRs 3 and 4 and the current from a DC power source 9 to the load 10 does not flow through the PT 6 any more, but the photoelectromotive force of the PD array 2 is applied between the gate and source of the FET 7, which is held on, so that the linearity of the output is held.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an optically coupled relay circuit in which input and output are insulated using an optical coupling method.

[Conventional technology] FIG. 2 is a circuit diagram of a conventional optically coupled relay circuit.

In this circuit, a photodiode array 2 receives an optical signal generated by a light emitting diode 1 connected between input terminals, generates a photovoltaic force, and transfers this photovoltaic force to a resistor 5.
The voltage is applied between the gate and source of the output MO3FET 7 via. The gate and source of the output MO3FET 7 are connected to the drain and source of a control transistor 3, which is a depletion type JFET, respectively, and the gate and source of this transistor 3 are connected to both ends of a resistor 5.

When an input signal is applied to the light emitting diode 1 and a photovoltaic force is generated in the photodiode array 2, a photocurrent flows between the drain and source of the depletion type control transistor 3 and through the resistor 5, and the photocurrent flows across the resistors. A voltage is generated. Since the control transistor 3 is biased to a high resistance state by this voltage, the photoelectromotive force of the photodiode array 2 is applied between the gate and source of the output MO3FET 7, and the output MOSFET 7 is turned on.

When the input signal to the light emitting diode 1 is cut off, the photovoltaic force of the photodiode array 2 disappears, and the voltage across the resistor 5 disappears, so the depression type control transistor 3 returns to the on state and the output Since the accumulated charge between the gate and source of MOSFET7 is discharged, the output M
O3FET7 is turned off.

[Problems to be Solved by the Invention] Generally, semiconductor relays are required to have high switching speed. Conventionally, photocouplers, in which a light emitting diode and a phototransistor are optically coupled, have been widely used as optically coupled relays capable of high-speed switching, but since this uses a bipolar transistor on the output side, When controlling signal switching,
There was a problem that the signal was distorted due to the influence of the offset.

For applications in which switching control is performed on minute signals, it is desirable to use a MOSFET 7 on the output side, as in the conventional circuit shown in FIG. However, in the conventional example mentioned above,
Since the gate capacitance of MO9FET7 is charged with the photocurrent of the photodiode array 2 and the output MO9FET7 is turned on, there is a problem that high-speed switching cannot be expected because the photocurrent is small relative to this gate capacitance. Ta.

The present invention has been made in view of these points, and its object is to provide an optically coupled relay circuit that is capable of high-speed switching and has good output linearity.

[Means for Solving the Problems] In order to solve the above problems, the optically coupled relay circuit according to the present invention transmits an optical signal in response to an input signal, as shown in FIG. The generated light emitting diode 1, the photodiode array 2 arranged to receive the optical signal of the light emitting diode 1, and the photoelectromotive force of the photodiode array 2 are applied between the gate and the source to establish conduction between the drain and source. MO for output that switches between state and non-conducting state
The photodiode array 2 is connected to the SFET 7 and the normally-on first control transistor 3 that forms a discharge path for the accumulated charge between the gate and source of the output MOSFET 7. An impedance element (resistance 5) that generates a voltage that biases the first control transistor 3 to a high resistance state when a photocurrent is applied thereto is connected between the train gate of the output MOSFET 7 and the optical signal of the light emitting diode 1. a normally-on type second control transistor 4 connected in series with the phototransistor 6 and biased to a high resistance state by the photovoltaic force of the photodiode array 2. It is characterized by consisting of.

[Function] In the present invention, as described above, the output MO9FET7
Since the phototransistor 6 is connected between the drain and gate of the phototransistor 6 and optically coupled to the light emitting diode 1, when an input signal is applied to the light emitting diode 1, the phototransistor 6
becomes conductive, a gate current flows from the load side to the gate of output MOSFET 7, and the gate-source capacitance is rapidly charged.
performs high-speed switching. Also, output M
When the gate-source voltage of the OSFET 7 rises sufficiently, this voltage blocks the second control transistor 4 connected in series with the phototransistor 6.
The load current passes only through the output MO3FET 7, ensuring output linearity.

[Embodiment] FIG. 1 is a circuit diagram of an embodiment of the present invention. A light emitting diode 1 is connected between input terminals 8a and 8b. The light emitting diode 1 is optically coupled to a photodiode array 2 and a phototransistor 6 . The positive electrode of the photodiode array 2 is connected to the gate of the output MO3FET 7, and the negative electrode is connected to the source of the output MO3FET 7.

The drain of a normally-on type first control transistor 3 made of a depletion type JFET is connected to the gates of the output MO8 and FET7, and the source of this control transistor 3 is connected to the output MOSFET through a resistor 5.
Connected to the source of T7. MO3FET7 for output
The train is connected to the output terminal 11a, and the source is connected to the output terminal 11.
connected to b. Between the output terminals 11a and llb,
A series circuit of a DC power source and a load 10 is connected. The drain of the output MO3FET 7 is connected to a train of a normally-on second control transistor 4 made of a depletion type JPET. The source of the control transistor 4 is connected to the gate of the output MOSFET 7 via the collector and emitter of the phototransistor 6. The gates of the control transistors 3 and 4 are both connected to the negative electrode of the photodiode array 2.

The operation of this embodiment will be explained below. Input terminal 8a
, 8b, when an input signal is applied between the light emitting diode 1
generates an optical signal, and upon receiving this optical signal, the phototransistor 6 becomes conductive, so that a load current flows through the load 10. This current flows from the second control transistor 4 to the phototransistor 6 to the first control transistor 3.
, flows through resistor 5. Also, this current is the output M
Since the current is also shunted to the gate-source capacitance of the O3FET 7 and this capacitance is charged at high speed, the gate-source voltage of the output MO9FET 7 rises rapidly.

Therefore, the output MOSFET 7 is quickly turned on. On the other hand, in the photodiode array 2, a photovoltaic force is generated by receiving an optical signal.

Due to this photovoltaic force, the first and second control transistors 3 and 4 are cut off, and the DC power source 9 is connected to the load 10.
The current flowing through the phototransistor 6 stops flowing through the phototransistor 6, but since the photovoltaic force of the photodiode array 2 is applied between the gate and source of the output MO3FET 7, the output MO3FET 7 remains on and the output Linearity is maintained.

[Effects of the Invention] As described above, in the present invention, a photodiode array and a phototransistor are optically coupled to a light emitting diode that generates an optical signal in response to an input signal, and the photovoltaic force of the photodiode array is Since the output MOS FET, which is applied between the gate and source, is supplied with the gate I current from the load side via the phototransistor,
This has the effect of enabling high-speed switching, and since the control transistor connected in series with the phototransistor is turned off by the photovoltaic force of the photodiode array, the current flowing through the phototransistor in a steady state is reduced. is shut off, and the output MO3F
Since the load current flows only through the ET, the offset is small even when a weak signal is controlled by switching, so that the signal linearity is less likely to be impaired.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an embodiment of the present invention, and FIG. 2 is a circuit diagram of a conventional example. 1 is a light emitting diode, 2 is a photodiode array, 3
．． 4 is a control transistor, 5 is a resistor, 6 is a phototransistor, and 7 is an output MO3FET.

Claims (1)

[Claims] (1) A light emitting diode that generates an optical signal in response to an input signal, a photodiode array arranged to receive the light signal from the light emitting diode, and a photovoltaic force of the photodiode array applied between the gate and source. an output MOSFET whose drain and source are switched between conducting and non-conducting states, and a normally-on first control device which forms a discharge path for accumulated charge between the gate and source of the output MOSFET. a transistor, an impedance element that generates a voltage that biases the first control transistor to a high resistance state when the photocurrent of the photodiode array is energized through the first control transistor, and an output M
A phototransistor that is connected between the drain and gate of the OSFET and arranged to receive the optical signal from the light emitting diode, and a normal transistor that is connected in series with the phototransistor and biased to a high resistance state by the photovoltaic force of the photodiode array. - An optically coupled relay circuit characterized by comprising an on-type second control transistor.