JPH02244906A - Photocoupling type relay circuit - Google Patents

Abstract

PURPOSE:To attain rapid turning-off by photocoupling a photodiode array and a phototransistor with a light emitting diode and supplying a gate current from the load side to an output MOSFET to which the photoelectromotive force of the photodiode array is impressed between the gate and source through the phototransistor. CONSTITUTION:The light emitting diode 1 is connected between input terminals 9a, 9b and photocoupled with the photodiode array 2 and the phototransistor 6 and the positive and negative poles of the array 2 are respectively connected to the gate and source of the output MOSFET 3 through a bias resistor 5 for a control transistor 4. When an input signal is impressed to the diode 1, the phototransistor 6 is turned to a conductive state, a gate current is allowed to flow from the negative side to the gate of the MOSFET 3 and the gate capacity can be rapidly charged. Consequently, rapid switching can be attained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an optically coupled relay circuit that uses an optical coupling method to insulate input and output.

[Prior Art] FIG. 2 is a circuit diagram showing an optically coupled relay circuit prior to the present application. In this circuit, the phototransistor 6 which receives the optical signal generated by the light emitting diode 1 connected between the input terminals 9a and 9b becomes conductive, and the output M
Since the gate current flows from the i-thin side to the gate of OSFET3 and the gate capacitance is rapidly charged, the output MO
SFET3 turns on at high speed. On the other hand, the optical signal generated by the light emitting diode 1 is also applied to the photodiode array 2, and a photocurrent is generated in the photodiode array 2. This photocurrent flows between the drain and source of the debreflation type control transistor 4 and through the resistor 5, and the voltage generated across the resistor 5 biases the control transistor 4 into a high resistance state. Therefore,
The photovoltaic force of the photodiode array 2 is applied between the gate and source of the output MOSFET 3, and the output MOSFET 3
In order to keep the ET3 in an off state, the relay operation is made stable regardless of the voltage and current of the load power supply 11.

When the input signal to the light emitting diode 1 is cut off, the photovoltaic force of the photodiode array 2 disappears, and the heavy pressure across the resistor 5 disappears, so the depressing type control transistor 3 returns to the on state and the output The accumulated charge between the gate and source of MOSFET 3 is discharged. In addition, since the phototransistor 6 also returns to the off state, the output MO
SFET3 is turned off.

[Problem B 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 is a problem that the signal is distorted due to the influence of the offset.

Therefore, in applications where switching control is performed on minute signals, it is desirable to use a MOSFET 3 on the output side, as in the circuit shown in FIG. However, although the above-mentioned prior art combines the advantages of bipolar transistors and MOSFETs and is capable of high-speed turn-on and controllable switching of minute signals, it has the drawback of slow turn-off. This is because the circuit connected in series to the phototransistor 6 has a high resistance when turned off, which delays the recovery of the phototransistor 6 and makes it difficult for the gate charge of the MOSFET 3 to be discharged to the output side.

The present invention has been made in view of these points, and an object of the present invention is to provide an optically coupled relay circuit that is capable of high-speed switching and is also capable of controlling switching of minute signals.

[Means for Solving the Problems] In order to solve the above problems, the optically coupled relay circuit according to the present invention includes a light emitting diode 1 that generates an optical signal in response to an input signal, and a light emitting diode 1. a photodiode array 2 arranged to receive the optical signal;
The photovoltaic force of the photodiode array 2 is applied between the gate and source of the output MOSFET 3, which switches between a conducting state and a non-conducting state between the drain and source, and the accumulation between the gate and source of the output MOSFET 3. The photocurrent of the photodiode array 2 is passed through the normally-on type control transistor 4 that forms a charge discharge path and the control transistor 4 to generate a voltage that biases the control transistor 4 to a high resistance state. an impedance element 5 connected between the drain and gate of the output MOSFET 3 and a phototransistor 6 arranged to receive the optical signal of the light emitting diode 1; and a phototransistor 6 connected between the emitter of the phototransistor 6 and the gate of the output MOSFET 3. The device is characterized by comprising a connected diode 7 and a second impedance element 8 connected between the emitter of the phototransistor 6 and the source of the output MOSFET 3.

[Function] In the present invention, since the phototransistor 6 is connected between the drain and gate of the output MOS FET 3 and optically coupled to the light emitting diode 1, an input signal is not applied to the light emitting diode 1. Then, the phototransistor 6 becomes conductive, and a gate current flows from the load side to the gate of the output MOSFET 3, and the gate capacitance is rapidly charged, so the output MOSFET 3 turns on at high speed. , at turn-off, since the second impedance element 8 is connected to the phototransistor 6, the phototransistor 6 is turned off at high speed, the charging current from the load side is cut off, and the light of the photodiode array 2 is As the electromotive force disappears, the bias voltage across the impedance element 5 disappears, the normally-on control transistor 4 turns on, and the output MOSFET 3 turns off. moreover,
When the load becomes a minute voltage, the diode 7 prevents the photocurrent from flowing into the photodiode array 2, so the relay operates stably and switching control can be performed even with minute signals.

[Embodiment] 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 9a and 9b, and a light emitting diode 1 is optically coupled to a photodiode array 2 and a phototransistor 6. photodiode array 2
The positive terminal of the bias resistor 5 for the control transistor 4
The negative electrode is connected to the gate of the output MOSFET 3 through the gate, and the negative electrode is connected to the source of the output MOSFET 3.

The gate of the output MOSFET 3 is connected to the source of a normally-on control transistor 4 made of a depletion type P-channel MOSFET, and the drain of the control transistor 4 is connected to the source of the output MOSFET 3. The positive electrode of the photodiode array 2 is connected to the gate. The drain of the output MOSFET 3 is connected to one output terminal 10a, the source is connected to the other output terminal IQb, and a series circuit of a DC power supply 11 and a load 12 is connected between the output terminals 10a and 10b.

Furthermore, the collector of a phototransistor 6 is connected to the drain of the output MOSFET 3, a diode 7 is connected between the emitter of the phototransistor 6 and the gate of the output MOSFET 3, and a resistor 8 is connected between the source and the drain of the output MOSFET 3. are connected to each other.

Next, the operation of the above embodiment will be explained. First, input terminal 9
When an input signal is applied between a and 9b, 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 12. This current flows through the phototransistor 6 and the resistor 8. Also, this current flows through diode 7
The current is also shunted to the gate capacitance of output MOSFET 3 through
The gate voltage of FET3 rises rapidly.

Therefore, the output MOSFET 3 is quickly turned on.

On the other hand, when the phototransistor 6 is off, the relatively low resistance 8 is connected in series with the phototransistor 6, so the phototransistor 6 turns off quickly, cutting off the main charging flow from the load side. Due to the disappearance of the photovoltaic force, the bias voltage across the resistor 50 disappears, so
The depression type control transistor 4 is turned on, and the output MOSFET 3 is rapidly turned off.

Furthermore, when the load becomes a minute voltage, diode 7
Since this prevents photocurrent from flowing into the photodiode array 2, the relay operates stably and can control switching even with minute signals.

[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 gate current is supplied from the load side via the phototransistor to the output MOSFET applied between the gate and source, it has the effect of enabling high-speed turn-on. Since the impedance element is connected, it has the effect of significantly improving the turn-off compared to the previous example.Furthermore, since the diode is connected between the gate of the output MOSFET and the emitter of the phototransistor, the photodiode array This has the effect of preventing the inflow of photocurrent from the relay and allowing stable operation of the relay without depending on the signal applied to the load.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a circuit diagram showing a conventional example. l...Light emitting diode, 2...Photodiode array, 3...Output MOSFET, 4...Control transistor, 5...Impedance element, 6...Phototransistor, 7...Diode , 8...second
impedance element.

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 optical 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; a normally-on control transistor which forms a discharge path for accumulated charge between the gate and source of the output MOSFET; The impedance element is connected between the drain and gate of the output MOSFET and an impedance element that generates a voltage that biases the control transistor to a high resistance state when the photocurrent of the photodiode array is passed through the control transistor.
A phototransistor arranged to receive the light signal of the light emitting diode, a diode connected between the emitter of the phototransistor and the gate of the output MOSFET, and a diode connected between the emitter of the phototransistor and the source of the output MOSFET. An optically coupled relay circuit comprising a second impedance element.