JPH05268042A - Solid-state relay - Google Patents

Abstract

PURPOSE:To attain high speed drive of the solid-state relay employing a high frequency use MOSFET with a low input capacitance and its miniaturization. CONSTITUTION:A 3rd diode 9 connects between an anode and a cathode of a photo electromotive force element 3. When a voltage impressed to an input terminal is decreased and a light from a light emitting diode 2 starts decreasing, if an input capacitance of the MOSFET7 is small, the MOSFET7 is gradually turned off while a discharge circuit consisted with a thyristor 6 and diodes 4, 5 is inactive and the operation remarkably slows down. Thus, the high frequency M0SFET7 with a low input capacitance is driven by providing the diode 9 to cause a leakage current thereby activating the discharge circuit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical coupling type solid state relay having the same function as that of an electromechanical relay without having any mechanical moving parts, and particularly to a high frequency signal such as an RF signal or a video signal. Solid-state relay for controlling the signal of.

[0002]

2. Description of the Related Art Conventionally, such a solid-state relay has a light emitting diode, an optical coupling element, and an output stage MOSFE.
It is configured with T and the like.

FIG. 5 is a circuit diagram of a conventional solid state relay. As shown in FIG. 5, a conventional solid state relay is a photovoltaic device in which a light emitting diode 2 is turned on by a voltage applied between input terminals 1 and 1A, and a plurality of photodiodes 10 are cascade-connected by the emitted light. An electromotive force is generated in the power element 3. Both ends of the thyristor 6 are connected between the anode electrode and the cathode electrode at both ends of the photovoltaic element 3 via the first diode 4 and the second diode 5, respectively. The N-pole gate of the thyristor 6 is connected to the connection point between the anode electrode of the photovoltaic element 3 and the anode electrode of the first diode 4, and similarly the cathode electrode of the photovoltaic element 3 and the second diode are connected. The P-pole gate of the thyristor 6 is connected to the connection point of the cathode electrode 5 of FIG. And thyristor 6
There are two enhancement type DMOSFETs 7 each for the anode electrode (hereinafter, the electrode is omitted) and the cathode.
Connected to the gate 7a and back gate 7b of
When these MOSFETs 7 are turned on, the load between the output terminals 8 and 8A connected to the drain electrodes 7c-7c is closed.

In such a solid state relay, the thyristor 6 is in the off state with the light emitting diode 2 turned on, and the resistance value is extremely high. Therefore, the electric charge generated by the electromotive force generated in the photovoltaic element 3 is immediately applied to the gate 7a of the output DMOSFET 7 via the first diode 4 and the second diode 5. Next, input terminals 1, 1
The voltage applied to A disappears and the light emitting diode 2
When is turned off, the voltage generated by the photovoltaic 3 disappears,
The gate voltage of the output enhancement type DMOSFET 7 is maintained as it is by the diodes 4, 5 and the thyristor 6. In this state, the voltage of the photovoltaic element 3 decreases due to self-discharge.
Turns off. Therefore, the impedance of the N-pole gate and the P-pole gate of the thyristor 6 becomes extremely high, and the thyristor 6 is turned on with an extremely small current. When the voltage further decreases, the N pole gate or P pole gate of the thyristor 6 is forward biased. Since the gate sensitivity of the thyristor 6 is extremely high, the thyristor 6 is turned on by a slight self-discharge current of the photovoltaic element 3. Furthermore, since the thyristor 6 has a self-holding characteristic, the voltage between the anode and the cathode becomes 1 when it is turned on once.
The ON state is maintained until the voltage drops to about V. Therefore, the charge accumulated in the gate 7a of the output enhancement DMOSFET 7 is quickly discharged through the thyristor 6,
The DMOSFET 7 is turned off.

[0005]

The conventional solid state relay described above has an isolation loss of 40d when controlling high frequency signals such as RF signals and video signals.
High frequency MOS with low input capacitance of B or more (1 MHz)
It is necessary to use field effect transistors.

However, the discharge circuit of the solid-state relay has a voltage V1 between the anode and the cathode of the photovoltaic element 3.
And the voltage V2 between the anode and cathode of the thyristor 6 is V
It operates when the relationship of 2> V1 is satisfied. However,
When the light emitting diode 2 is turned off and the voltage of the photovoltaic element V1 starts to drop, the high frequency MOS field effect transistor has a small input capacitance (Ciss, about 10 pF),
The condition of V2> V1 is not established, and the MOS field effect transistor is gradually turned off without operating the discharge circuit. Therefore, there is a drawback that the switching operation speed of the field effect transistor is significantly slowed down.

An object of the present invention is to provide a small-sized solid state relay which can use such a field effect transistor having a low input capacitance and has a high switching speed.

[0008]

A solid state relay of the present invention comprises a semiconductor light emitting device, a photovoltaic device in which a plurality of photodiodes for generating electromotive force by light from the semiconductor light emitting device are cascade-connected, A MOS field effect transistor which becomes conductive when a voltage generated from a photovoltaic element is applied to its gate, an anode electrode is connected to a gate electrode of the MOS field effect transistor, and a cathode electrode is connected to a back gate electrode. A thyristor in which an N-pole gate and a P-pole gate are connected to an anode electrode and a cathode electrode of the photovoltaic element, respectively, and an anode electrode is connected to the N-pole gate of the thyristor and a cathode electrode is connected to the anode electrode of the thyristor. The connected first diode and the P-pole gate of the thyristor. A second diode connected to the cathode electrode of the thyristor and an anode electrode connected to the cathode electrode of the thyristor, and a third diode connected between the anode electrode and the cathode electrode of the photovoltaic element, The MOS field effect transistor is used as a switching element that opens and closes a load circuit.

[0009]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a circuit diagram of a solid state relay showing an embodiment of the present invention. As shown in FIG. 1, in the present embodiment, the third diode 9 is connected between the anode electrode and the cathode electrode of the photovoltaic element 3 in which a plurality of photodiodes 10 are cascaded in the conventional example of FIG. It has been configured. Other configurations are shown in FIG.
It is similar to the circuit of.

First, when an input current flows between the input terminals 1 and 1A to turn on the light emitting diode 2, electromotive force is generated at both ends of the photovoltaic element 3. This voltage is applied between the gate 7a and the back gate 7b of the high frequency enhancement type DMOSFET 7 to enhance the high frequency enhancement type DMOSFET 7.
The drain electrodes 7c-7c of the MOSFET 7 are turned on.

Next, when the input current between the input terminals 1 and 1A is cut off, the light emission of the light emitting diode 2 stops and the voltage of the photovoltaic element 3 starts to drop. When this voltage starts to drop, the voltage across the photovoltaic element 3 is quickly lowered, so that a leak current is generated in the diode 9 connected between the anode and cathode electrodes of the photovoltaic element 3 to reduce the input voltage. Enhancement type DMOS for high frequency of capacitance
The discharge circuit composed of the diodes 4 and 5 and the thyristor 6 can be operated by the electric charge charged to the low capacity between the gate and the source of the FET 7, and the above-mentioned conventional example is turned off.
It can be realized similarly to the operation. Further, the diode 9 is adjusted to have a reverse saturation current of 10 ⁻⁷ A (ampere) at the time of reverse bias.

FIG. 2 is a plan view of a chip of the relay shown in FIG. As shown in FIG. 2, this chip is an example in which the drive circuit portion surrounded by the dotted line in FIG. 1 is integrated into one chip.
This chip includes a photovoltaic element 3, wiring pads 12 and 13 connected between the gate and back gate of a high-frequency enhancement type DMOSFET 7, a thyristor 6, diodes 4 and 5, which form a discharge circuit, and a diode. 9 and.

FIG. 3 is a partially cutaway perspective view of the relay shown in FIG. 1 assembled in a mold package. As shown in FIG. 3, the solid-state relay in which the chip is molded in the mold package 14 has the LED 2, the drive circuit element of FIG. Two high-frequency enhancement type DMOSFETs 7 and Ag
It is mounted with a paste, and each element is connected by a bonding wire 18 according to the connection of the circuit shown in FIG.

FIG. 4 is a circuit diagram of a solid state relay showing another embodiment of the present invention. As shown in FIG. 4, this embodiment uses the diode 9 in the embodiment of FIG. 1 described above.
Is replaced with a high resistance element 11 made of polysilicon. That is, the high resistance element 11 is set to have a high resistance of several MΩ in order to generate a leak current similarly to the diode 9. Therefore, in this embodiment, when the LED 2 is turned off, the high resistance element 11 helps the voltage drop across the photovoltaic element 3 and the discharge circuit can be operated in the same manner as in the above-described embodiment.

[0015]

As described above, in the solid state relay of the present invention, the diode or the high resistance element is connected between the anode electrode and the cathode electrode of the photovoltaic element so that the photovoltaic element is turned on when the LED is turned off. Since a leak current can be generated in the power element, there is an effect that a high-capacity high-frequency MOSFET having a low capacitance between the gate and the source can be driven. Further, the present invention has an effect that it can be easily realized with almost no influence on the chip occupying area.

[Brief description of drawings]

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

FIG. 2 is a plan view of a chip of the relay shown in FIG.

FIG. 3 is a partially cutaway perspective view of the relay shown in FIG. 1 assembled in a mold package.

FIG. 4 is a circuit diagram of a solid state relay showing another embodiment of the present invention.

FIG. 5 is a circuit diagram of a conventional solid-state relay.

[Explanation of symbols]

 1,1A Input terminal 2 Light emitting diode 3 Photovoltaic element 4,5,9 Diode 6 Thyristor 7 High frequency enhancement type DMOSFET 8,8A Output terminal 10 Photodiode 11 High resistance element 12,13 Wiring pad 14 Mold package 15 Lead Frame 16 Internal lead 18 Bonding wire

Claims (2)

[Claims] 1. A semiconductor light emitting element, a photovoltaic element in which a plurality of photodiodes that generate electromotive force by light from the semiconductor light emitting element are cascade-connected, and a voltage generated from the photovoltaic element is applied to a gate. The MOS field effect transistor which becomes conductive by connecting the anode to the gate electrode of the MOS field effect transistor and the cathode electrode to the back gate electrode of the MOS field effect transistor, and the N pole gate and the P pole gate of the photovoltaic field effect transistor, respectively. A thyristor connected to an anode electrode and a cathode electrode of a power device; a first diode having an anode electrode connected to the N-pole gate of the thyristor and a cathode electrode connected to the anode electrode of the thyristor; The cathode electrode is connected to the P-pole gate and the thyristor is A second diode having an anode electrode connected to a cathode electrode and a third diode connected between the anode electrode and the cathode electrode of the photovoltaic element are provided, and the MOS field effect transistor opens and closes a load circuit. A solid-state relay characterized by being used as a switching element. 2. The solid state relay according to claim 1, wherein the third diode is replaced with a high resistance element.