JPH06181431A - Solid-state relay - Google Patents

Abstract

PURPOSE:To attain a snap action at switching and to drive a high frequency MOSFET with a low input capacitance. CONSTITUTION:When a thyristor 5 discharges a charge of a gate of a MOSFET 9, photo transistors (TRs) 6,7 are connected to an N channel gate 12A and a P channel gate 12B of the thyristor 5. Furthermore, a leakage element 8 is provided between the N-channel gate 12A and the P channel gate 12B of the thyristor 5. When an electronic force is generated in a photovoltaic diode array 4 by the photo TRs 6,7 and the leakage element 8, a leakage is caused in the leakage element 8, a sensing current is controlled and the operation of the thyristor 5 is controlled to be released independently of the potential difference between photovoltaic diode array 4 and a gate of the MOSFET 9, then the high frequency MOSFET9 with a low capacitance between the gate and the source is driven.

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 optical coupling by a light emitting diode or a photovoltaic diode array.

[0002]

2. Description of the Related Art In a conventional solid state relay, various circuits are used to drive an output stage MOS transistor.

FIG. 7 is a circuit diagram of a solid state relay showing a conventional example. As shown in FIG. 7, such a solid-state relay includes a light emitting diode 3 connected between input terminals 1 and 2, a photovoltaic diode array 4 optically coupled to the light emitting diode 3, and a photovoltaic diode array 4 connected in parallel with the photovoltaic diode array 4. It has a resistor 18 and an n-channel enhancement-type field effect transistor (MOSFET) 9 connected to each other, and output terminals 10 and 1 are provided to a drain electrode and a source electrode.
1 is connected. In such a solid state relay, when an input current flows between the input terminals 1 and 2, a photovoltaic voltage is generated across the photovoltaic diode array 4. This generated voltage is applied to the gate of MOSFET 9
By applying the voltage across the substrates, the state between the output terminals 10 and 11 connected to the source / drain electrodes of the MOSFET 9 changes from the off state to the on state. That is, this solid-state relay does not have a mechanically movable part (switch) and has the same function as an electromechanical relay. Here, the resistor 18 has a function of discharging the electric charge accumulated in the electrostatic capacitance between the gate and the substrate of the MOSFET 9. If the resistor 18 does not exist, when the input terminals 1 and 2 are disconnected in the above circuit example, the output terminals 10 and 11 are disconnected.
It becomes impossible to return to the OFF state.

FIG. 8 is a circuit diagram of another conventional solid-state relay. As shown in FIG. 8, this relay circuit improves the on / off operation speed of the circuit in FIG. 7, and includes a light emitting diode 3, a photovoltaic diode array 4, and a MOSFET 9, and the resistor 18 described above. Instead of diode 19, PNP transistor 2
0 and a resistor 21.

In this relay circuit, the input terminals 1 and 2 are
When an input current flows in the meantime, an optical signal is generated from the light emitting diode 3, so an electromotive force is generated at both ends of the photovoltaic diode array 4. A current based on this photoelectromotive force flows through the diode 19 to the gate of the MOSFET 9 and charges between the gate and the substrate. Further, due to this charging current, the diode 19 causes a voltage drop in the forward direction.
The base and emitter of the transistor 20 are reverse biased. Therefore, the transistor 20 remains off. On the other hand, the resistor 21 has a very high impedance, for example, 5M.
Has Ω. Since the photocurrent of the photovoltaic diode array 4 is applied to the high input impedance circuit defined by the resistor 21, a very high speed response is realized.

Next, when the input current is cut off, the transistor 20 is turned on when the output voltage of the photovoltaic diode array 4 drops to a value lower than the gate voltage (about 0.6 V). As a result, the charge between the gate and the substrate of the MOSFET 9 is discharged fairly rapidly, so that the MOS
The FET 9 is rapidly turned off.

FIG. 9 is a circuit diagram of another conventional solid-state relay. As shown in FIG. 9, this relay circuit is an example configured by only active elements in order to eliminate waste of the chip area due to the high resistance 21 of FIG. 8 described above.
That is, the thyristor 5 and the diodes 22 and 23 are provided, and the switching characteristics of the thyristor 5 are used to make the MOS.
Control the FET 9.

First, when an input current flows between the input terminals 1 and 2, electromotive force is generated at both ends of the photovoltaic diode array 4, as in the above-mentioned example. As a result, the charging current flows through the diode 22, so that a forward voltage drop occurs. Therefore, the N-pole gate 12A of the thyristor 5 is reverse-biased, so that the thyristor 5 remains off. Since the current from the photovoltaic diode array 4 flows from the anode side to the cathode side of the diodes 22 and 23 in this manner, both the N-pole gate 12A and the P-pole gate 12B of the thyristor 5 are strongly reverse biased. Therefore,
The thyristor 5 does not turn on by malfunction because it is sufficiently stable against external noise. By the voltage generated in the photovoltaic diode array 4 in this state,
Since a charging current flows between the gate and the substrate of the MOSFET 9 via the diodes 22 and 23, the output terminals 10 and 11 connected to the drain and source electrodes, which are the current-carrying electrodes of the MOSFET 9, are switched from the off state to the on state.

Next, when the input current is cut off, the voltage of the photovoltaic diode array 4 begins to drop, so that the diodes 22 and 23 are reverse biased and are brought into a non-conducting state. On the other hand, since the gate voltage of the MOSFET 9 does not change, the potential difference with the photovoltaic diode array 4 decreases. When this potential difference reaches about 1.2 V, the N-pole gate 12A and the P-pole gate 12B of the thyristor 5 are forward biased and the thyristor 5 is turned on. Therefore, the output terminals 10 and 11 connected to the current-carrying electrodes of the MOSFET 9 are switched from the ON state to the OFF state.

FIG. 10 is a circuit diagram of a conventional solid state relay showing another example. As shown in FIG.
This relay circuit is a circuit in which the diodes 22 and 23 in the circuit of FIG. 9 described above are replaced with NPN phototransistors 24 and 25, and the anode of the diode 22 is replaced with the collector of the phototransistor 24 and the cathode is connected with the emitter. I am doing it. Similar to the photovoltaic diode array 4, the bases of these phototransistors 24 and 25 have a structure in which the light of the light emitting diode 3 is irradiated. The operation of this circuit operates in the same manner as in FIG. An example of such a circuit is described in, for example, Japanese Patent Laid-Open No. 63-2422.

[0011]

The above-mentioned conventional solid-state relay has been put into practical use by making some improvements, but it has various drawbacks as described below.

First, the circuits shown in FIG. 7 and FIG.
With the relay circuit of 0, the operating characteristics are improved considerably. However, in the configuration example shown in FIG. 9 or FIG. 10, when a current is applied between the input terminals to turn it on, the electric charge generated by the electromotive force generated in the photovoltaic diode array passes through the diodes to the gate of the output MOSFET. Since the voltage is applied immediately, the minimum input current (sensing current: Ion) required to operate the relay becomes extremely sensitive. That is, the output MOSFET is turned on with a current of several μA. In such a solid state relay, on / off snap action operation on the output side of the relay cannot be obtained, and the solid state relay is sensitive to noise.

[0013] Next, FIG. 9 discharge circuit in solid-state relay in and FIG. 10, the anode-cathode voltage V ₁ and the anode-cathode of the thyristor voltage V ₂ and the V ₂ of the photovoltaic diode array> V ₁ It works when it comes to the relationship. However, when the light emitting diode is turned off and the V1 voltage of the photovoltaic diode array starts to drop, the high frequency MOSFET has a small input capacitance (C _iss
= About 10 pF), the condition of V2> V1 is not satisfied. That is, the discharge circuit is not operated and the MO is gradually increased.
The SFET turns off. Therefore, the first object of the present invention is that the switching operation speed of the MOSFET is significantly slowed down. The first object of the present invention is to easily set such a moving current value, thereby realizing an on / off snap action operation and a malfunction. It is to provide a solid state relay capable of preventing the above.

A second object of the present invention is to provide a solid state relay which can use a MOSFET having a low input capacitance and has a high switching speed.

[0015]

A solid state relay according to the present invention comprises a semiconductor light emitting device connected between input terminals, a photovoltaic diode array for generating electromotive force by light from the semiconductor light emitting device, and A thyristor having an anode electrode and a cathode electrode connected in parallel to both ends of the photovoltaic diode array and having an N-pole gate and a P-pole gate; and applying a voltage generated from the photovoltaic diode array to the gate. A field effect transistor that is rendered conductive by the first phototransistor, a first phototransistor connected between the N-pole gate of the thyristor and the anode electrode of the photovoltaic diode array, the P-pole gate of the thyristor, and the phototransistor. A second phototransistor connected between the cathode electrodes of the electromotive force diode array. And register configured to have a leakage element connected between the N-pole gate and the P-pole gate of the thyristor.

[0016]

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, this embodiment uses a light emitting diode 3, a photovoltaic diode array 4, a thyristor 5, and an enhancement type MOSFET 9.
In addition to the same as in the conventional example (FIG. 9), the phototransistors 6 and 7 connected to the N-pole gate 12A and the P-pole gate 12B of the thyristor 5 and the leak element 8 connected between these gates are provided. Have The diodes 22 and 23 of the conventional example (FIG. 9) are unnecessary.

In such a relay circuit, the input terminals 1,
When the light emitting diode 3 is turned on by the voltage applied between the two, the generated light causes an electromotive force in the photovoltaic diode array 4. Both ends of the photovoltaic diode array 4 are connected to both ends of the thyristor 5,
The collector of the NPN phototransistor 6 is connected to the connection point between the anode of the photovoltaic diode array 4 and the anode of the thyristor 5, and N is connected to the connection point between the cathode of the photovoltaic diode array 4 and the cathode of the thyristor 5.
The emitter of the PN phototransistor 7 is connected. Moreover, the NPN is connected to the N-pole gate 12A of the thyristor 5.
The emitter of the phototransistor 6 is connected, and the P-pole gate 12B of the thyristor 5 is connected to the NPN phototransistor 7
The collector of is connected. Further, the leak element 8 is connected between the N-pole gate 12A and the P-pole gate 12B of the thyristor 5. The anode and cathode of the thyristor 5 are connected to the gate electrode a and the source electrode b of the n-channel enhancement type MOSFET 9, respectively. Therefore, when the MOSFET 9 is turned on, the output terminal 1 connected to the drain electrode c and the source electrode b
The load circuit is closed via 0 and 11.

FIG. 2 is a voltage characteristic diagram of the MOSFET in FIG. As shown in FIG. 2, here, a MOSFET is used.
9 shows the gate voltage and drain voltage characteristics, and at time t
_{When a} signal voltage is input to the light emitting diode 3 between the input terminals 1 and 2 at ₀ , the NPN photodiodes 6 and 7 are simultaneously turned on by the light from the light emitting diode 3 at this time, and the N-pole gate 12A of the thyristor 5 is turned on. Since the P pole gate 12B and the P pole gate 12B are short-circuited with the anode and the cathode of the thyristor 5, respectively, the thyristor 5 is maintained in the OFF state. In this state, the voltage generated in the photovoltaic diode array 4 causes the charging current to start flowing in the gate electrode a of the MOSFET 9.

Next, at time t ₁ , as shown in the characteristic 13A, when the gate voltage VG of the MOSFET 9 reaches the threshold value V _TH , the MOSFET 9 is turned on. After that, the gate voltage V _G is held at a substantially constant voltage due to the Miller effect, and the drain voltage V _D of the MOSFET 9 starts to decrease as shown in the characteristic 13B.

Subsequently, at time t2, the drain voltage V
When D drops to the ON voltage, the gate voltage VG starts to rise again. In the operation at the time of this input, by branching the photocurrent from the photovoltaic diode array 4 by the leaf element 8 connected between the N-pole gate 12A and the P-pole gate 12B of the thyristor 5, the input current (sensing current) : I _on ), the snap action operation is possible.

Next, when the light emitting diode 3 is turned off at the time t ₃ , the NPN phototransistors 6 and 7 are turned off, so that the N-pole gate 12A and the P-pole gate 12B of the thyristor 5 are set to a high impedance state and the light is turned on. The anode and cathode of the electromotive force diode array 4 and the thyristor 5 are electrically cut off, and the sensitivity of the thyristor 5 is very high. In this state, the MOSFET 9 applied between the anode and cathode of the thyristor 5
Since a leak current flows through the thyristor 5 due to the gate voltage V _G of the gate voltage V _G and the residual voltage of the photovoltaic diode array 4, the thyristor 5 is turned on to discharge the electric charge held in the gate capacitance of the MOSFET 9, and the gate voltage V _G Begins to fall.

Next, when the gate voltage V _G reaches the threshold value V _TH at time t ₄ , the MOSFET 9 starts to turn off, and the drain voltage is V _D = V _DD due to the Miller effect as described above.
The gate voltage V _G maintains the same value until After that, the gate voltage V _G decreases, the MOSFET 9 is turned off, and time t ₅ is reached.

In the off-time operation of the MOSFET 9, the leak element 8 connected between the N-pole gate 12A and the P-pole gate 12B of the thyristor 5 increases the leak of the thyristor 5 and makes it easier to turn on the thyristor 5. Have a function. Further, the circuit composed of the solid state relay shown in FIG. 1 is operated by the thyristor 5 in comparison with the circuit composed of the solid state relay shown in FIG.
Since the off operation is performed irrespective of the potential difference between the gate and the gate of 9, the high frequency MOSFET having a small input capacitance can be driven.

FIG. 3 is a switching characteristic diagram of the solid state relay shown in FIG. As shown in FIG. 3, here, the load current of the output terminal with respect to the input current from the input terminal is shown. In that case, the characteristic 14A shown by the solid line is the characteristic of the present embodiment, and the characteristic 14B shown by the dotted line is the characteristic when the leak element 8 is not inserted. As described above, according to the present embodiment, the leak element 8 does not appear as a load current for an input such as noise.

FIG. 4 is a circuit diagram of a solid state relay showing a second embodiment of the present invention. As shown in FIG.
This embodiment is the leak element 8 in the first embodiment described above.
This is an example in which the diode 15 is used for. In this case, the cathode electrode of the diode 15 is connected to the N-pole gate 12A of the thyristor 5 and the anode electrode of the diode 15 is connected to the P-pole gate 12B of the thyristor 5. Other light emitting diode 3 to phototransistor 7 and MOSF
ET9 is exactly the same as that of the first embodiment described above.

FIG. 5 is a circuit diagram of a solid state relay showing a third embodiment of the present invention. As shown in FIG.
This embodiment is the leak element 8 in the first embodiment described above.
This is an example in which a resistor 16 equivalent to several μΩ is used. This embodiment has a circuit configuration in which a high resistance is connected between the N-pole gate 12A and the P-pole gate 12B of the thyristor 5, and the same characteristics as those of the first embodiment can be obtained.

FIG. 6 is a circuit diagram of a solid state relay showing a fourth embodiment of the present invention. As shown in FIG.
This embodiment is the leak element 8 in the first embodiment described above.
In this example, an NPN phototransistor 17 similar to the NPN phototransistors 6 and 7 is used. In this case, the phototransistor 17 is connected to the N-pole gate 12A of the thyristor 5.
2 is a circuit configuration using an NPN phototransistor 17 in which the emitter electrode is connected and the collector electrode is connected to the P-pole gate 12B of the thyristor 5. Particularly, in this embodiment, the phototransistor 17 and the photovoltaic diode array 4 which are not driven by the same light emitting diode 3 are used.

[0029]

As described above, in the solid-state relay of the present invention, the phototransistor is used to drive the thyristor used in the discharge circuit of the gate electrode of the output MOSFET, and a leak element for controlling the input current sensitivity is used. By providing between the N-pole gate and the P-pole gate, the moving current value can be easily set and the output side ON / OFF
In addition to obtaining the off snap action operation, it is also resistant to the noise on the input terminal side, which has the effect of preventing malfunction.

Further, according to the present invention, since the operation control of the thyristor is turned off regardless of the potential difference between the photovoltaic diode array and the gate of the MOSFET, a high-capacity high-frequency MOSFET having a low capacitance between the gate and the source can be used. There is an effect that the switching speed can be increased.

[Brief description of drawings]

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

FIG. 2 is a voltage characteristic diagram of the MOSFET in FIG.

3 is a switching characteristic diagram of the solid state relay in FIG.

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

FIG. 5 is a circuit diagram of a solid state relay showing a third embodiment of the present invention.

FIG. 6 is a circuit diagram of a solid state relay showing a fourth embodiment of the present invention.

FIG. 7 is a circuit diagram of a solid-state relay showing a conventional example.

FIG. 8 is a circuit diagram of a solid state relay showing another conventional example.

FIG. 9 is a circuit diagram of a solid state relay showing another conventional example.

FIG. 10 is a circuit diagram of a conventional solid state relay showing another example.

[Explanation of symbols]

 1, 2 Input terminal 3 Light emitting diode 4 Photovoltaic diode array 5 Thyristor 6, 7, 17 Phototransistor 8 Leak element 9 Enhancement type MOSFET 10, 11 Output terminal 12A N-pole gate 12B P-pole gate 15 Diode 16 Resistance a Gate electrode b Source electrode c Drain electrode

Claims (5)

[Claims] 1. A semiconductor light emitting device connected between input terminals, a photovoltaic diode array that generates electromotive force by light from the semiconductor light emitting device, and an anode electrode and a cathode at both ends of the photovoltaic diode array. A thyristor having correspondingly connected electrodes in parallel and having an N-pole gate and a P-pole gate; a field-effect transistor which becomes conductive by applying a voltage generated from the photovoltaic diode array to the gate; A first phototransistor connected between the N-pole gate of the thyristor and the anode electrode of the photovoltaic diode array, and a P-gate of the thyristor and the cathode electrode of the photovoltaic diode array. A second phototransistor and the N-pole gate and front of the thyristor A solid-state relay having a leak element connected between P-pole gates. 2. A first NPN phototransistor having an emitter electrode connected to the N-pole gate of the thyristor and a collector electrode connected to the anode electrode of the photovoltaic diode array. Wherein the second phototransistor is a second NPN phototransistor having a collector electrode connected to the P-pole gate of the thyristor and an emitter electrode connected to the cathode electrode of the photovoltaic diode array, The solid state relay according to claim 1, wherein the first and second NPN phototransistors and the photovoltaic diode array are driven by the semiconductor light emitting element. 3. The solid-state relay according to claim 1, wherein the leak element is a diode, the cathode electrode of which is connected to the N-pole gate of the thyristor and the anode electrode of which is connected to the P-pole gate of the thyristor. . 4. The solid state relay according to claim 1, wherein the leak element is a resistance element. 5. The leak element uses a third NPN phototransistor, wherein an emitter electrode is connected to the N-pole gate of the thyristor and a collector electrode is connected to the P-pole gate of the thyristor. Solid state relay.