JPH06177736A - Solid-state relay - Google Patents

Abstract

PURPOSE:To provide a solid-state relay in which only an input current of a prescribed limit flows with respect to a wide range of input voltage by connecting a depletion MOSFET whose gate and source are short-circuited via a resistive component in series with a light emitting element. CONSTITUTION:When a voltage is supplied between input terminals 6a and 6b, an input current flows via a resistance component 5. Thus, the gate of a depletion DMOSFET 8 is biased to a negative voltage with respect to a source by a voltage across the resistance component 5. An input current to the DMOSFET 8 is limited by the bias voltage. Thus, only a current of a prescribed limit flows to the light emitting element 1 against a wide range of input voltage in the voltage versus current characteristic between the input terminals 6A and 6B of the solid-state relay.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid state relay using an optical coupling system for isolation between input and output.

[0002]

2. Description of the Related Art A circuit diagram of a conventional solid state relay is shown in FIG. When an input signal is applied between the input terminals 6A and 6B,
The light emitting element 1 generates an optical signal according to an input signal. The photovoltaic diode array 2 generates photovoltaic power by this optical signal. This photovoltaic power is applied between the gate and source of the output MOSFET 3, and the high impedance state changes to the low impedance state between the relay output terminals 7A and 7B. Next, when the input signal between the input terminals 6A and 6B is cut off, the electromotive force of the photovoltaic diode array 2 disappears, and the charge accumulated in the gate capacitance of the output MOSFET 3 becomes the gate charge. It is discharged through the control circuit 4 which is a discharging means, and returns to a high impedance state between the relay output terminals 7A and 7B. As a result, the current flowing through the load can be turned on / off according to the input signal.

[0003]

The light emitting element 1 between the input terminals 6A and 6B of the above-mentioned conventional solid state relay has a voltage-current characteristic as shown in FIG. The rise is very steep. If an excessive voltage is applied between the input terminals, an excessive current will flow in the light emitting diode, and as a result, the light emitting diode will be destroyed, so the voltage range that can be applied between the input terminals of the solid state relay. Had the problem that it would be very small.

The present invention has been made in view of the above points, and an object thereof is to increase the allowable input voltage range between the input terminals of a solid-state relay.

[0005]

In order to solve the above-mentioned problems, in the solid-state relay according to the present invention, as shown in FIG. 1, a light-emitting element 1 for generating an optical signal in response to an input signal is provided.
And an output semiconductor element (photovoltaic diode array 2, output MOSFET 3 and output MOSFET 3 and an output MOSFET 3 which receives the optical signal, generates electron-hole pairs, and transits from a first impedance state to a second impedance state. In a solid-state relay composed of a control circuit 4), a current limiting element composed of a depletion type MOSFET 8 whose gate and source are short-circuited via a resistance component 5 is connected in series with the light emitting element 1. It is what

[0006]

In the present invention, in the depletion type MOSFET 8 connected in series with the light emitting element 1, the resistance component 5 connected between the gate and the source of the depletion type MOSFET 8 applies a voltage to the gate electrode which increases or decreases according to the input current. As a result, the current between the drain and the source is controlled. As a result, the terminals 6A between the inputs of the solid-state relay,
As shown in FIG. 4, the amount of current flowing between 6B can take a constant upper limit value for a wide range of input voltages.

[0007]

FIG. 1 is a circuit diagram of an embodiment of the present invention. The circuit configuration will be described below. One input terminal 6
The drain of the depletion type DMOSFET 8 is connected to A. Depletion type DMOSFET
The source of 8 is connected to the anode of the light emitting element 1 formed of a light emitting diode via the resistance component 5, and the gate of the DMOSFET 8 is connected to the connection point. The cathode of the light emitting element 1 is connected to the other input terminal 6B. The light emitting element 1 is optically coupled to the photovoltaic diode array 2. The photovoltaic power generated by the photovoltaic diode array 2 is output MOSFET
3 is applied between the gate and the source. Output MOS
The FET 3 has a drain connected to one output terminal 7A and a source connected to the other output terminal 7B.
The control circuit 4 is connected between the gate and the source of the output MOSFET 3. The control circuit 4 is in a high impedance state so that the gate-source voltage of the output MOSFET 3 rapidly rises when the photovoltaic diode array 2 generates a photovoltaic force. Further, when the photovoltaic diode array 2 stops the generation of photovoltaic power, the control circuit 4 is in a low impedance state so that the gate-source voltage of the output MOSFET 3 drops quickly. The DMOSFET 8 and the resistance component 5
Is preferably composed of one chip. Further, it is preferable that the output semiconductor element including the photovoltaic diode array 2, the output MOSFET 3 and the control circuit 4 is also configured by one chip.

The operation of the circuit shown in FIG. 1 will be described below. When a voltage is applied between the input terminals 6A and 6B, the input current flows through the resistance component 5. Therefore, the resistance component 5
Depletion type DMOSFET
The gate of 8 is biased negative with respect to the source.
With this bias voltage, depletion type DMOS
The FET 8 will limit the input current. Therefore, the voltage-current characteristic between the input terminals 6A and 6B of the solid state relay is as shown in FIG. That is, in the light emitting element 1, only a current up to a certain limit flows for a wide range of input voltage. While the voltage-current characteristic of the conventional example shown in FIG. 3 is the current input type, the voltage-current characteristic of the present invention shown in FIG. 4 is the voltage input type.

FIG. 5 shows a mounting structure on the input terminal side of the solid state relay of the present invention. On the comb of the input terminal 6A to which the positive voltage is applied, the depletion type DMOSFET 8 whose gate and source are short-circuited by the resistance component 5 is arranged. In general, the DMOSFET 8 has a drain on the back surface side of the device. In addition, the input terminal 6 to which a negative voltage is applied
On the comb of B, the light emitting element 1 having an anode on the front surface side and a cathode on the back surface side is arranged. Depletion type DMOS in which the gate and source are short-circuited by a resistance component 5.
By performing wire bonding 9 from the gate of the FET 8 to the anode on the surface side of the light emitting element 1, the input side circuit of the solid state relay of the present invention shown in FIG. 1 can be easily realized.

The present invention is not limited to the circuit of the illustrated embodiment, and the output side semiconductor element may be a phototransistor, a photothyristor, a phototriac or the like.

[0011]

According to the present invention, it is possible to realize a solid state relay in which only an input current up to a certain limit flows for a wide range of input voltage, and further, a feedback control circuit for constant current is not necessary, and therefore, a circuit is provided. There is an advantage that the driving power is not consumed and the loss in the input section is small.

As disclosed in the description of the embodiment, if a light emitting diode is used as a light emitting element and a depletion type DMOSFET is connected to the anode side of the chip, as shown in FIG. Since the current path can be formed, the mounting structure can be simplified.

[Brief description of drawings]

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

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

FIG. 3 is a diagram showing current-voltage characteristics between input terminals of a conventional solid state relay.

FIG. 4 is a diagram showing current-voltage characteristics between input terminals of the solid state relay of the present invention.

FIG. 5 is a plan view showing a mounting structure on the input terminal side of the solid-state relay of the present invention.

[Explanation of symbols]

 1 light emitting element 2 photovoltaic diode array 3 output MOSFET 4 control circuit 5 resistance component 6A input terminal 6B input terminal 7A output terminal 7B output terminal 8 depletion type DMOSFET

Claims (1)

[Claims] 1. A light-emitting element that generates an optical signal in response to an input signal, and an electron-hole pair that is generated by receiving the optical signal and transitions from a first impedance state to a second impedance state. In the solid-state relay composed of the output semiconductor element, a current limiting element composed of a depletion type MOSFET whose gate and source are short-circuited via a resistance component is connected in series with the light emitting element. And solid state relay.