JP2003249676A - Optically coupled semiconductor relay device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optically coupled semiconductor relay device capable of attaining bidirectional current supply by sing one MOSFET as a switching element and capable of reducing output capacity. <P>SOLUTION: When an electric signal is supplied between input terminals 1a, 1b, the electric signal is converted into an optical signal by a light emitting diode (LED) 2 connected between the input terminals 1a, 1b and then converted into an electric signal by a photovoltaic diode array 4. The electric signal is supplied between gate and source of a normally-off n-channel MOSFET 6 acting as a switching element through a discharge circuit 5, so that the MOSFET 6 is turned on, an output contact signal to be supplied in a forward direction is obtained between terminals 8a, 8b through diodes 13, 16 of a diode bridge circuit 12, and an output contact signal to be energized in a negative direction is obtained through diodes 14, 15 of the diode bridge circuit 12. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optically coupled semiconductor relay device using a MOSFET as a switching element.

[0002]

2. Description of the Related Art An optical coupling type semiconductor relay device of this type is
A compact relay device instead of the conventional electromagnetic relay device,
Developed as a high-sensitivity, high-speed, high-reliability device, a semiconductor light emitting device, for example, a semiconductor photovoltaic device in which an electric signal is converted into an optical signal by a light emitting diode and is optically coupled with the light emitting diode For example, photovoltaic diodes (PV
D: Photo Voltaic Diode) array converts an optical signal into an electric signal, and the electric signal drives a MOSFET as a switching element to obtain an output contact signal. As this type of optical coupling type semiconductor relay device, a device capable of bidirectional energization is known, and for example, it is shown as a solid state relay in Japanese Patent No. 2522249.

The solid-state relay disclosed in the above publication will be described below with reference to FIG. 2 with a part of the name and reference numeral changed. When an electric signal is supplied between the input terminals 1a and 1b, it is converted into an optical signal by the light emitting diode 2 as a semiconductor light emitting element connected between the input terminals 1a and 1b. This optical signal is converted into an electric signal by a photovoltaic diode array 4 composed of a plurality of series-connected photovoltaic diodes 3 as semiconductor photovoltaic elements optically coupled to the light emitting diode 2. This electric signal is supplied via the discharge circuit 5 between the gates and sources of the two enhancement type (normally off type) N-channel MOSFETs 6 and 7 in which the sources as switching elements are commonly connected in anti-series. , MOSFETs 6 and 7 are turned on, and normally open output contact signals are obtained between the output terminals 8a and 8b connected to the drains of the MOSFETs 6 and 7, respectively.

The discharge circuit 5 is composed of diodes 9 and 10 and a thyristor 11. The diode 9 is the anode of the photovoltaic diode array 4 and the MOSFETs 6, 7
An anode is commonly connected to the respective gates of the diodes, and a cathode of the diode 10 is commonly connected to the cathodes of the photovoltaic diode array 4 and the sources of the MOSFETs 6 and 7. Thyristor 11
Is the cathode of the diode 9 and the MOSFET
6, 7 are connected to the connection point with the gates, the cathode is connected to the connection point between the anode of the diode 10 and the sources of the MOSFETs 6 and 7, and the N-pole gate is the anode of the photovoltaic diode array 4 and the anode of the diode 9. And the P-pole gate is connected to the connection point between the cathode of the photovoltaic diode array 4 and the cathode of the diode 10.

In the solid-state relay circuit having the above structure, when an electric signal is supplied between the input terminals 1a and 1b, it is converted into an optical signal by the light emitting diode 2 and again converted into an electric signal by the photovoltaic diode array 4. However, at this time, since the thyristor 11 used in the discharge circuit 5 is in the off state and has a very high resistance value, the electric signal from the photovoltaic diode array 4 causes the charge due to the diodes 9, 10
Is immediately applied to the respective gates of the MOSFETs 6 and 7 through.

Next, when the electric signal supplied between the input terminals 1a and 1b is no longer supplied, the light emitting diode 2
, And the electrical signal from the photovoltaic diode array 4 also disappears, but the gate voltages of the MOSFETs 6 and 7 are maintained as they are by the diodes 9 and 10 and the thyristor 11. In this state, the voltage drops in the photovoltaic diode array 4 due to self-discharge. Due to this voltage drop, first, the diodes 9 and 10 are turned off. Therefore, the N pole gate of the thyristor 11,
The impedance of the P-pole gate becomes extremely high, and the thyristor 11 turns on with a very small current. Further, when the voltage decreases, the N-pole gate or P-pole gate is forward biased. Since the sensitivity of the gate is extremely high, the thyristor 11 can be easily turned on by a slight self-discharge current of the photovoltaic diode array 4.

Since the thyristor 11 has a self-holding characteristic, once it is turned on, the potential between the anode and the cathode becomes 1
It keeps on until it drops to about V. Therefore, the MOS
The charges accumulated in the gates of the FETs 6 and 7 are quickly discharged through the thyristor 11 and the MOSFETs 6 and 7 are turned off.

[0008]

By the way, the above-mentioned conventional solid-state relay is a circuit in which two MOSFETs 6 and 7 are connected in anti-series in order to enable bidirectional energization. 2 chips are required, which is a problem in reducing the manufacturing cost. Further, in the solid state relay described in the above publication, reduction in output capacity has been required. The present invention solves the above problems and meets the above requirements by using a single MOS.
An object of the present invention is to provide an optical coupling type semiconductor relay device in which manufacturing cost is reduced by enabling bidirectional energization by using an FET and the output capacitance is further reduced.

[0009]

An optical coupling type semiconductor relay device of the present invention includes a semiconductor light emitting element, a semiconductor photovoltaic element for converting an optical signal from the semiconductor light emitting element into an electric signal, and driving by the electric signal. One MOSFET that is
A diode bridge circuit that obtains a bidirectionally energized output contact signal by energizing this MOSFET in one direction is provided. In the above, the normally open type optically coupled semiconductor relay device can be configured by using the enhancement type MOSFET as the MOSFET. Also, as a MOSFET, a depletion type MO
A normally closed optical coupling type semiconductor relay device can be constructed by using the SFET.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION A normally open type solid state relay according to one embodiment of the present invention will be described below with reference to FIG. The same parts as those in FIG. 2 are designated by the same reference numerals, the description thereof will be omitted, and only different points will be described. The difference from FIG. 1 is that
1 MOSFET instead of 2 MOSFETs 6 and 7
T6, the input terminals a and b of the diode bridge circuit 12 are connected to the output terminals 8a and 8b as bidirectional energizing means, and the output terminals c and d of the diode bridge circuit 12 are connected to the drain and source of the MOSFET 6, respectively. That is the point.

The diode bridge circuit 12 is composed of diodes 13, 14, 15, and 16. The anode of the diode 13 is connected to the input terminal a and the cathode is connected to the output terminal c.
The diode 14 has its anode connected to the input end b and its cathode connected to the output end c, and the diode 15 has its cathode connected to the input end a.
The anode is connected to the output end d, the cathode of the diode 16 is connected to the input end b, and the anode is connected to the output end d.

When an electric signal is supplied between the input terminals 1a and 1b, it is converted into an optical signal by the light emitting diode 2 connected between the input terminals 1a and 1b, and converted into an electric signal by the photovoltaic diode array 4. This electric signal is transmitted through the discharge circuit 5 to an N channel type MOS as a switching element.
It is supplied between the gate and source of FET6, and MOSFET
6 is turned on, and an output contact signal of positive direction conduction is applied between the terminals 8a and 8b via the diodes 13 and 16 of the diode bridge circuit 12, and a negative direction is applied via the diodes 14 and 15 of the diode bridge circuit 12. The output contact signal for energization is obtained.

With the above structure, bidirectional conduction can be achieved by reducing the number of MOSFETs from two to one by simply adding the diode bridge circuit 12, and the diode bridge circuit 12 can be manufactured with a smaller chip area than the MOSFET. The manufacturing cost can be reduced. Also, the terminals 8a, 8
Since two diodes are connected in series with the MOSFET between b, two MOSFs are provided between the terminals 8a and 8b.
The output capacity of the solid-state relay can be reduced as compared with the configuration in which ETs are connected in series.

In the above embodiment, the normally open type solid state relay has been described as an example, but it is also applicable to the normally closed type solid state relay. In this case, the MOSFET is a depletion type (normal) type. ON type) is used. Further, the discharge circuit 5 has been described as an example of the discharge circuit, but the discharge circuit is not limited to this and various other circuits can be used.

[0015]

According to the optically coupled semiconductor relay device of the present invention, one MOSFET is used as the switching element and the diode bridge circuit is used as the bidirectional energizing means to reduce the manufacturing cost of the optically coupled semiconductor relay device. The output capacity can be further reduced as well as the conventional value.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a solid state relay according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a conventional solid state relay.

[Explanation of symbols]

2 Light emitting diode (semiconductor light emitting element) 4 Photovoltaic diode array (semiconductor light emitting device) 6 MOSFET (switching element) 12 Diode bridge circuit (bidirectional energizing means)

Claims (3)

[Claims] 1. A semiconductor light emitting device, a semiconductor photovoltaic device for converting an optical signal from the semiconductor light emitting device into an electric signal, one MOSFET driven by this electric signal, and one-way conduction of this MOSFET. An optical coupling type semiconductor relay device comprising a diode bridge circuit for obtaining an output contact signal of bidirectional energization. 2. The optically coupled semiconductor relay device according to claim 1, wherein said MOSFET is a normally open type which is an enhancement type. 3. The optically coupled semiconductor relay device according to claim 1, wherein said MOSFET is a normally closed type, which is a depletion type.