JP2805974B2 - Optically coupled relay circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optically coupled relay circuit in which an input / output circuit is insulated by using an optical coupling method.

[Prior Art] FIG. 2 is a circuit diagram showing a conventional optically coupled relay circuit. In this circuit, an optical signal generated by the light emitting diode 1 connected between the input terminals 10a and 10b is received by the photodiode array 2 to generate a photovoltaic power. This is applied between the gate and the source of the output MOSFET 3 through the gate. The gate and source of the output MOSFET 3 are connected between the drain and source of the control transistor 8 composed of a depletion-type JFET.
The gate and source of the transistor 8 are connected to both ends of the resistor 9. Further, in order to reduce the charge accumulation time between the gate and the source of the output MOSFET 3, a high-speed circuit composed of a series circuit of a diode 6 and a phototransistor 5 is connected between the drain and the gate.

In this optically coupled relay circuit, the light emitting diode 1
When a photoelectromotive force is generated in the photodiode array 2, a photocurrent flows between the drain and source of the depletion-type control transistor 8 and the resistor 9, and a voltage is generated across the resistor 9. . Since the control transistor 8 is biased to a high resistance state by this voltage, the photoelectromotive force of the photodiode array 2 is applied between the gate and the source of the output MOSFET 3, and the output MOSFET 3 is turned on. At this time, charge flows from the drain of the output MOSFET 3 to the gate via the phototransistor 5 which has been short-circuited by receiving the optical signal from the light emitting diode 1, and the ON time of the output MOSFET 3 is greatly reduced. Further, when the output MOSFET 3 is turned on, the drain current becomes lower than the gate potential, thereby preventing the charge from flowing from the gate to the drain by the diode 6 between the drain and the gate.

Next, when the input signal to the light emitting diode 1 is cut off, the photoelectromotive force of the photodiode array 2 disappears, and the voltage across the resistor 9 disappears, so that the depression type control transistor 8 returns to the on state. At the same time, the phototransistor 5 is turned off, so that the output
The accumulated charge between the gate and the source of the MOSFET 3 is discharged via the control transistor 8, and the output MOSFET 3 is turned off.

[Problems to be Solved by the Invention] Generally, a semiconductor relay is required to have a high switching speed at the time of ON / OFF, and the switching speed of a semiconductor relay using a MOS between output terminals is determined by the gate / source of the MOS. It greatly depends on the charge / discharge time of the inter-charge. For this reason, in the conventional circuit shown in FIG. 2, when an optical signal is applied to the phototransistor 5 between the drain and the gate of the output MOSFET 3 at the time of ON, the drain and the drain are applied.
Since the gate is short-circuited and charge flows from the drain to the gate, the on-time is significantly reduced as compared with a relay having no circuit between the drain and the gate. On the other hand, the response of the phototransistor 5 from when the optical signal is cut off to when the collector and the emitter are opened is slow.
At the time of off, charge flows from the drain of the output MOSFET 3 to the gate, and there is a problem that the off time is greatly delayed as compared with a relay having no circuit between the drain and the gate.

The present invention has been made in view of such a point,
It is an object of the present invention to provide an optically-coupled relay circuit capable of shortening an off-time while utilizing a high-speed operation of the conventional circuit at an on-time.

[Means for Solving the Problems] In an optically coupled relay circuit according to the present invention, in order to solve the above problems, as shown in FIG. 1, light emission for generating an optical signal in response to an input signal is provided. A diode 1, a photodiode array 2 arranged to receive an optical signal of the light emitting diode 1, and a photo-electromotive force of the photodiode array 2 applied between a gate and a source to make a conductive state and a non-conductive state between a drain and a source. Output switching MOSFET3
And a control circuit 4 for forming a discharge path for accumulated charges between the gate and source of the output MOSFET 3, wherein the light of the light emitting diode 1 is disposed between the drain and gate of the output MOSFET 3. A series circuit consisting of a phototransistor 5 arranged to receive signals and a backflow preventing diode 6 is connected, and the output MO
A constant voltage element 7 for opening the drain-gate of the output MOSFET 3 until the phototransistor 5 is completely opened when the SFET 3 is turned off is inserted in the series circuit.

[Operation] In the present invention, since a constant-voltage element 7 having a high threshold is interposed in a series circuit of the diode 6 and the phototransistor 5 connected between the drain and the gate of the output MOSFET 3, an optical signal is cut off. Between the time when the voltage between the drain and the gate of the output MOSFET 3 reaches the threshold voltage of the constant voltage element 7, the voltage between the drain and the gate of the output MOSFET 3 is completely open.・
This covers the delay in response before the emitter is opened, thereby achieving a faster off-time.

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 10a and 10b, and is optically coupled to a photodiode array 2 and a phototransistor 5. The positive electrode of the diode array 2 is an output MOSF
The gate of ET3 and the negative electrode are connected to the source of MOSFET3 via a resistor 9, respectively. The gate of the output MOSFET 3 is connected to the drain of a normally-on type control transistor 8 composed of a depletion type JFET. The source of the control transistor 8 is connected to the source of the output MOSFET 3 and the gate is connected to the photodiode array 2. Is connected to the negative electrode. The drain of output MOSFET 3 is connected to one output terminal 1
In 1a, the source is connected to the other output terminal 11b, and a series circuit of a DC power supply 12 and a load 13 is connected between the output terminals 11a and 11b. Also, the drain of the output MOSFET 3
The anode of the diode 6 is connected, and the cathode of the diode 6 has a constant voltage element 7 having a drain and a gate short-circuited.
The drain side of the MOSFET is connected. The source side of the constant voltage element 7 is connected to the collector of the phototransistor 5, and the emitter of the phototransistor 5 is connected to the gate of the output MOSFET 3.

Next, the operation of the above embodiment will be described. First, the input terminal
When an input signal is applied between 10a and 10b, the light emitting diode 1 generates an optical signal, and the photodiode array 2 receives the optical signal, and generates a photoelectromotive force. This photoelectromotive force causes a photocurrent to flow between the drain and source of the depletion type control transistor 8 and the resistor 9, and a voltage is generated across the resistor 9.

This voltage biases the control transistor 8 to a high resistance state, so that the photovoltaic power of the photodiode array 2 is applied between the gate and the source of the output MOSFET 3. On the other hand, when the phototransistor 5 receives the optical signal from the light emitting diode 1, the drain-gate of the output MOSFET 3 is short-circuited, and the drain-gate voltage reaches the threshold voltage of the constant voltage element 7. Until the charge flows from the drain to the gate, and together with the photovoltaic power from the photodiode array 2, the output MOSF
ET3 is 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 8 is turned on, through which the charge between the gate and source of the output MOSFET 3 is discharged.

On the other hand, since the response speed of the phototransistor 5 when turned off is slow, an energized state exists even after the input signal is cut off, but the drain-gate voltage of the output MOSFET 3 is higher than the threshold voltage of the constant voltage element 7. Until the constant voltage element 7
Is open. When the drain-gate voltage of the output MOSFET 3 becomes equal to or higher than the threshold voltage of the constant voltage element 7, the phototransistor 5 is almost open.
The flow of electric charge from the drain to the gate of the output MOSFET 3 at the time of off is minimized, and the output MOSFET 3 is rapidly turned off.

In the above embodiment, the control circuit 4 for forming the discharge path of the accumulated charge between the gate and the source of the output MOSFET 3 is constituted by the control transistor 8 and the resistor 9. However, the present invention is not limited to this. Of course.

[Effects of the Invention] In the present invention, a constant-voltage element is inserted into a high-speed on-time circuit composed of a diode and a phototransistor between a drain and a source of an output MOSFET, whereby the output MOSFET is turned off. Leakage of charge from the drain to the gate can be prevented, and the off time can be reduced. Therefore, according to the present invention, it is possible to obtain an optically coupled relay circuit capable of shortening the off-time while utilizing the high-speed operation of the conventional circuit when it is on.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing one embodiment of the present invention, and FIG. 2 is a circuit diagram showing a conventional example. 1 ... light-emitting diode, 2 ... photodiode array, 3 ... output MOSFET, 4 ... control transistor,
5 ... Phototransistor, 6 ... Diode, 7 ...
Constant voltage element.

────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Takeshi Matsumoto 1048 Odakadoma, Kadoma, Osaka Prefecture Inside Matsushita Electric Works, Ltd. (56) References JP-A-3-297219 (JP, A) JP-A-2-292912 (JP, A) JP-A-2-7478 (JP, A) JP-A-2-20119 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H03K 17/00-17 / 98

Claims (1)

(57) [Claims] 1. A light emitting diode which generates an optical signal in response to an input signal, a photodiode array arranged to receive an optical signal of the light emitting diode, and a photoelectromotive force of the photodiode array is applied between a gate and a source. An optically coupled relay circuit comprising: an output MOSFET that is switched between a conductive state and a nonconductive state between a drain and a source when applied; and a control circuit that forms a discharge path of accumulated charge between the gate and the source of the output MOSFET. A series circuit comprising a phototransistor arranged to receive the light signal of the light emitting diode and a reverse current blocking diode is connected between the drain and the gate of the output MOSFET;
An optically coupled relay circuit, wherein a constant voltage element for opening the drain and gate of the output MOSFET is inserted into the series circuit until the phototransistor is completely opened when the MOSFET is turned off.