JPS62250719A - Semiconductor relay circuit - Google Patents

Abstract

PURPOSE:To execute a quick switching by connecting the 2nd transistor in parallel with photodiode array and connecting a phototransistor between then so that the 2nd transistor can be turned off at the time of irradiating an optical signal and further connecting a resistance so that the 2nd transistor can be turned on at the time of blocking an optical signal. CONSTITUTION:When an input current flows between input terminals I1 and I2, the gate potential of an output FETQ1 rises thanks to the actions of a light emitting diode L and the photodiode array D, and a phototransistor TrP is turned on. At that time, the resistance R is made significantly great, and a current flowing from the photodiode array D is made minimal. A voltage across the gate and source of the FETQ1 is quickly boosted to speed up turning-on. When the input current between the input terminals I1 and I2 comes to zero, a voltage coexisting across the drain and source of a TrQ2 makes its gate potential at the level the same as the drain potential of the TrQ2 through the resistance R, and the TrQ2 is turned on. The charge fo the output FETQ1 is speedily discnaraged through the TrQ2 to shorten the turning-off time.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a semiconductor relay circuit using a photovoltaic element and a field effect transistor.

(Background Art) Conventionally, a semiconductor relay circuit as shown in FIG. 2 has been proposed. This circuit has input terminals (11), (I2)
When an input current flows between them, the light emitting diode (L) generates an optical signal, and the optical signal is transmitted to the photodiode array (D
) generates photovoltaic power.

This photovoltaic force is output by a field effect transistor (Q,)
is applied between the gate and source of Q to turn on the field effect transistor (Q).

Next, when the input current between the input terminals (I,) and (I2) disappears and the light emitted from the light emitting diode (L) disappears, the photodiode array (D) also stops generating photovoltaic force. do. At this time, the field effect transistor (Ql
) is discharged through the resistor (R). This lowers the gate potential of the field effect transistor (Ql).

The field effect transistor (Ql) is turned off.

In this circuit, the response time of the relay is determined by the resistance value of the resistor (R), and increasing this value shortens the turn-on time but increases the turn-off time. Conversely, if this value is decreased, the turn-off time will be shortened, but the turn-on time will be lengthened. In other words, it was not possible to shorten both the turn-on time and the turn-off time.

(Object of the invention) The present invention has been made in view of the above points, and
The object is to provide a semiconductor relay circuit that can shorten both turn-on time and turn-off time.

(Disclosure of the Invention) In the semiconductor relay circuit according to the present invention, as shown in FIG. In the semiconductor relay circuit, a second transistor (
Q2) is connected between one current-carrying terminal and the control terminal of the second transistor (Q2), and a photoconductive element, photoconductive element 1, is connected to the transistor ( P) is connected so that the second transistor (Q2) is turned off when the optical signal is irradiated, and the second
A resistor (R) is connected between the other conductive terminal and the control terminal of the transistor (Q2), and when the optical signal is cut off, the voltage accumulated between the gate and source of the field effect transistor (Q) is ) is applied to the control terminal to turn on the second transistor (Q2).

In the present invention, with this configuration, when an optical signal is irradiated, the impedance between the gate and source of the field effect transistor (Q) increases, and the gate potential rises rapidly. When the optical signal is interrupted, the impedance between the gate and source of the field effect transistor (Ql) decreases, causing the gate potential to drop rapidly. Therefore, both the turn-on time and turn-off time can be shortened. It is something.

Hereinafter, detailed embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram of a semiconductor relay circuit according to an embodiment of the present invention. Between the input terminals (I l) and (I2),
A series circuit of a voltage source (E) and a resistor (r) is connected. A light emitting diode (L) is connected to the input terminals (I 1) and (I z), and when there is an input current,
A light emitting diode (L) generates a light signal. This optical signal is simultaneously applied to the photodiode array (D) and the phototransistor (P).

The photodiode array (D) generates a photovoltaic force upon irradiation with an optical signal. This photovoltaic force is output by an enhancement mode MO3 type field effect transistor (Q,
) is applied between the gate and source. A photodiode array (D>) is composed of a plurality of photodiodes connected in series so that the photovoltaic force is higher than the threshold voltage between the gate and source of a field effect transistor (Ql). The transistor (P) is a photoconductive element that becomes conductive when receiving an optical signal and becomes non-conductive when the optical signal is interrupted.The phototransistor (P) is connected in series with the resistor (R). This series circuit is connected in parallel to both ends of the photodiode array (D).Also, at the voltage dividing point of this series circuit, there is an enhancement mode N-channel M
The gate of an O8 type transistor (Q2) is connected. The drain and source of this transistor (Q2) are connected in parallel with the photodiode array (D>) between the gate and source of the output field effect transistor (Ql). A resistor (R) is connected in parallel between the train and gate, and a phototransistor (P) is connected in parallel between the gate and source.
Between the drain and source of Ql) are the output terminals (0,) and (O
□) is connected to the series circuit of the load (Z) and the power supply (V), and by conducting between the train and source of the field effect transistor (Ql), the power supply (V) is connected to the load (Z). ), and by cutting off the drain and source of the field effect transistor (Q, ), the current supply from the power supply (V) to the load (Z) is cut off. .

The operation of the circuit shown in FIG. 1 will be explained below. First, when there is no input current between input terminals (II) and (12),
Since the light emitting diode (L) does not emit light and no photovoltaic force is generated in the photodiode array (D>), the output field effect transistor (Ql) is in the off state.
When input current flows between input terminals (II) and (12),
The light emitting diode (L) emits light in response to the input current, and a photovoltaic force is generated across the photodiode array (D), raising the gate potential of the output field effect transistor (Ql).

At this time, the phototransistor (P) connected between the gate and source of the transistor The voltage does not rise, so it remains off. Also, the current flowing from the photodiode array (D) at this time is only the current passing through the resistor (R), and by making this resistance sufficiently large, the current flowing from the photodiode array (D) can be reduced. and thereby,
The gate-source voltage of the field effect transistor (Ql) can be quickly increased, and the turn-on time can be accelerated.

Next, when the input current between the input terminals <1+) and (r2) becomes zero again, the light irradiation from the light emitting diode (L) disappears, and no photovoltaic force is generated in the photodiode array (D>). No photocurrent flows in the phototransistor (P) either, except for the output field effect transistor (Q,)
It takes some time for the gate potential to reach zero due to the charge stored between the gate and source. In order to make this time as small as possible, the transistor (Q
2) is connected between the gate and source of a field effect transistor (Ql). In other words, the phototransistor (P
) is no longer irradiated with light, the light Th current no longer flows, and a voltage exists between the drain and source of the transistor (Q2), and this voltage causes the transistor (Q2
) is applied to the transistor (
By becoming the same level as the drain potential of Q2),
The transistor (Q2) is turned on, and the charge accumulated between the gate and source of the output field effect transistor (Q,) is rapidly discharged via the transistor (Q2). Therefore, the output field effect transistor (Ql)
The turn-off time can be shortened.

The second transistor (Q2) may be a bipolar transistor; in this case, the collector may be connected to the drain, the base to the gate, and the emitter to the source. (P) may be any photoconductive element, and may be a photodiode or the like.

Furthermore, although the output field effect transistor has been described in the case of enhancement mode (normally off type), the same can be said for the case of depletion mode (normally on type), and the technical idea of the present invention applies. can be applied as is.

(Effects of the Invention) Since the present invention is configured as described above, the impedance between the gate and source of the output field effect transistor can be greatly changed between turn-on and turn-off, and both This has the effect of making high-speed switching possible.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a semiconductor relay circuit according to an embodiment of the present invention, and FIG. 2 is a circuit diagram of a conventional example. (D> is a photodiode array, (P) is a phototransistor, (Q, ) is a field effect transistor, (Q2)
is a transistor, and (R) is a resistor.

Claims (1)

[Claims] (1) In a semiconductor relay circuit in which a photovoltaic element is connected between the gate and source of a field effect transistor, a second transistor is connected in parallel with the photovoltaic element, and one current-carrying terminal of the second transistor is connected to the photovoltaic element. A photoconductive element that is made conductive by an optical signal that energizes the photovoltaic element is connected between the control terminal and the second transistor so that the second transistor is turned off when the optical signal is irradiated. A resistor is connected between the other energizing terminal and the control terminal, and when the optical signal is cut off, the voltage accumulated between the gate and source of the field effect transistor is applied to the control terminal via the resistor, and the second transistor is activated. A semiconductor relay circuit characterized in that it is connected to be turned on.