JPS62213414A - Semiconductor relay circuit - Google Patents

Abstract

PURPOSE:To realize a semiconductor relay subject to high speed switching control by using complementary signals as input signals, using one signal as a gate drive signal of an output MOSFET and employing the other as a gate- source storage charge discharging signal. CONSTITUTION:When an input electric signal is given between input terminals 1 and 2, a photovoltaic element 6 generates a voltage. In this case, a light emitting 5 is not lighted and a photovoltaic element 9 generates no voltage. Thus, the 2nd MOSFET pair 8 is turned off. When a potential across the element 6 gets higher, an output MOSFET 10 is turned on. When the voltage is higher, the voltage exceeds a threshold value of the 1st MOSFET pair 7, the impedance of the 1st MOSFET pair 7 is lowered to discharge the 2nd MOSFET pair 8 and the photovoltaic element 9. When the input signal is lost, the element 5 is lighted and the element 9 generates a voltage to the turn on the 2nd MOSFET pair 8 thereby discharging the stored charge of the output MOSFET 10.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a semiconductor relay circuit using isolation by optical coupling. The present invention relates to a controllable semiconductor relay circuit.

(Background technique 1) Conventionally, a photocoupler and MO as shown in Fig. 3 have been used.
A semiconductor relay circuit combining SFET has been proposed. In this conventional example, the relay input terminal (1)
, (2) is connected to a light emitting element (3) made of a light emitting diode (LED), and a photovoltaic element made of a photodiode array that receives an optical signal from the light emitting element (3) and generates an electric signal. (6) is provided to constitute a so-called photocoupler.

The voltage generated in the photovoltaic element (6) is transferred to the output MOS
applied between the gate and source of FET<10),
The OSFET (10) is made conductive. by this,
The relay output terminals (11) and (12) are electrically connected.

Next, when the input voltage between the relay input terminals (1) and (2) is removed and the optical signal from the light emitting element (3) is blocked, the photovoltaic element (6) stops generating an electrical signal. Stop. Since the resistor (13) is connected in parallel to the photovoltaic element (6), the electric charge of the photovoltaic element (6) is transferred to the resistor (13).
) is discharged through. Similarly, MOS F for output
The accumulated charge between the gate and source of E T (10) is also discharged via the resistor (13). As a result, the output MOSFET (10) becomes non-conductive, and the relay output terminals (11) and (12) become disconnected.

In this conventional example, the current generated in the photovoltaic element (6) during the light emitting operation of the light emitting element (3) is transferred to the output MOS.
Charge between the gate and source of FET (10) to create a MOSF
The ET (10) is made conductive, but the discharge resistor (1
3) is connected, not all of the current is used for charging between the gate and the source, and current is also shunted to the discharging resistor (13). For this reason, MOSF
The rise of the gate voltage of ET (10) is delayed. After the light emitting element (3) stops emitting light, the resistor 3 (13) connects the \ft product charge of the photovoltaic element (6) with the MOS F E
This is for discharging the accumulated charge between the gate and source of MOS FET (10), and has the role of promoting a drop in the gate voltage of MOS FET (10). therefore,
If the resistance value of the resistor (13) is high, the gate voltage will rise quickly and fall slowly.On the other hand, if the resistance value of the resistor (13) is low, the gate voltage will rise slowly and fall slowly. The decline will be faster. In order to speed up both the rise and fall of the gate voltage, the resistance value of the resistor (13) should be high resistance (preferably infinite) when the gate voltage rises, and low resistance when the gate voltage falls. (preferably 0), and in the conventional example, this movement 1r cannot be realized.

(Object of the Invention) The present invention has been made in view of the above-mentioned points, and its object is to realize a semiconductor relay circuit that can control opening and closing of an output MOSFET at high speed.

(Disclosure of the Invention) Hereinafter, the configuration of the present invention will be explained with reference to illustrated embodiments.
As shown in FIG. 1, a first light emitting element (3) generates an optical signal in response to an input electrical signal, and a second light emitting element (3) generates an optical signal in response to a signal having a phase opposite to that of the input electrical signal.
5), and first and second light emitting elements (3), which receive the optical signals of the first and second light emitting elements (5), respectively, and generate electric signals, respectively.
The electromotive force of the photovoltaic elements (6), (9) and the first photovoltaic element (6) is applied between the gate 1 and the substrate, and the relay output terminal (11) is applied between the source and drain. ), (12)
The electromotive forces of the output MOSFET (10) and the first photovoltaic element (6) are converted to the closing control II lightning voltage, and the output M
Enhancement type MOSFET with substantially the same characteristics and a higher threshold voltage than OSFET (10)
The first MOSFET pair formed by combining T (7a) and (7b) and the enhancement type MOSFET ( 8a) and a second MOSFET pair (8) consisting of a combination of (8b), one of the first and second MOSFET pairs (8)
FETs (7a) and (8a) are connected in parallel to the first and second photovoltaic elements (6) and (9), respectively;
The other M of (8) of the first and second MOSFET pair
OS FET (7b) and (8b) are connected in parallel to the second and first photovoltaic elements (9) and (6), respectively.

In the embodiment of FIG. 1, the output MOSFET (10)
As for Enhancement 1~ type N channel MOS
FET is used, and the substrate terminal is commonly connected to the source terminal. This output MO9FET (10)
is used with the train terminal held at a positive potential as the relay output terminal (11) and the source terminal held at a negative potential as the relay output terminal (12) when in the off state. At times, it operates so that current flows from one output terminal (11) to the other output terminal (12).

As the light emitting elements (3) and (5), light emitting diodes (L
ED) is used. The first light emitting element (3) is directly connected to the input terminals (1) and (2) of the relay, and generates an optical signal when a voltage of the polarity shown is applied. ing. The second light emitting element (5) is the first light emitting element (5).
The light emitting element (3) generates an optical signal using a signal having a phase opposite to that of the input electric signal, and in this embodiment, an inverter (4) is used to obtain a signal having a phase opposite to the input electrical signal. Further, as the photovoltaic elements (6) and (9), a series array of photodiodes is used, and the electromotive force is output from the output MOS
F E T (10), MOSFET pair ()), (
8) is set higher than the threshold voltage. The first photovoltaic element (6) is a first light emitting element (
3), and the second photovoltaic element (9) is optically coupled to the second light emitting element (5). The anode of the first photovoltaic element (6) has an output M OS F' E
It is connected to the gate of T (10), and its cathode is connected to the source of the output MOSFET (10).

The MOSFET pair (8) is formed by combining N-channel MOSFETs of Enhancement 1 to type having substantially the same characteristics, and is a MOSFET (7a).

(7b), (8a), and (8b) are formed on the same chip for each pair. The threshold voltage VTH of the MOSFET pair is the output MOSFET (10)
is set slightly higher than the threshold voltage.

Each MOS FET (7m), (7b), (8a), (
8b), the source and the substrate are commonly connected. Each gate of the first and second MOSFET pair is connected to the anode of the first and second photovoltaic element (6), (9), respectively, and each source of the first and second MOSFET pair is connected to the anode of the first and second photovoltaic element (6), (9), respectively. photovoltaic device (6).

(9) are respectively connected to the cathodes. 1st and 2nd
One of the MOSFET pairs in (8)4;:
The drains of FET (7a) and (8a) are
connected to the anodes of the first and second photovoltaic elements (6) and (9), respectively, and the other MOS FET (7b),
The drains of (8b) are connected to the anodes of the second and first photovoltaic elements (9) and (6), respectively.

The operation of this embodiment will be explained below. When an input electrical signal of the polarity shown is applied between the relay input terminals (1), (2), the first light emitting element (3) emits an optical signal. This optical signal is applied to the first photovoltaic element (6), and the photovoltaic element (6) generates a voltage such that the 7th node is at a positive potential and the cathode is at a negative potential. On the other hand, on the output side of the inverter (4).

Since a signal with the opposite phase to the input electric signal is generated, no voltage is applied to the second light emitting element (5), and this light emitting element (5)
) does not emit an optical signal, therefore the second photovoltaic element (9) optically coupled with the second light emitting element (5) does not generate a voltage, therefore the second photovoltaic element ( 9), the second MOSFET pair (
Each MO9FET (8a), (8) in 8)
b) is in the off state. Since MOSFET (8b) in the second MOSFET pair (8) is in the off state, the voltage across the photovoltaic element (6) increases rapidly. The voltage across the photovoltaic element (6) is the threshold voltage VT of the MOSFET (71I) in the first MOSFET pair.
When R is reached, the impedance of MO3FET (7a) decreases, so the voltage across the photovoltaic element (6) is regulated to this threshold voltage VTH (see Figure 2(b)). As in, the output MOSFET (10
) is the threshold voltage of MOS FET (7a
) is set slightly lower than the threshold voltage VTH of the output MOS FET (10). The other MOSFET (7b) in the 1471M03FET pair (f) has substantially the same characteristics as the one MOSFET (7a), so it has low impedance and is a photovoltaic element ( 9) and the second MOSFET pair (8).
) to discharge the accumulated charge between the gate and source of the output M
MO for discharging accumulated charge of OS FET (10)
S F E T <8b) is kept in a reliable cutoff state.

Next, when the input electrical signal between the relay input terminals (1) and (2) is removed, the optical signal of the first light emitting element (3) is blocked. Therefore, the first photovoltaic element (6) stops generating photovoltaic force. On the other hand, on the output side of the inverter (4), a signal with the opposite phase to the input electrical signal is generated, so
A voltage is applied to the second light-emitting element (5), and this light-emitting element (5) emits a light signal. This optical signal is applied to the second photovoltaic element (9), and the photovoltaic element (9) generates a voltage such that its anode is at a positive potential and its cathode is at a negative potential.

When the first photovoltaic element (6) stops generating photovoltaic force, the voltage across the photovoltaic element (6) begins to decrease. Since this voltage is regulated by the threshold voltage VTH of the MOSFET (7a) as described above, it immediately becomes a voltage smaller than the threshold voltage V'l'H, and the voltage of the MOSFET (7a) in the first MOSFET pair immediately becomes smaller than the threshold voltage V'l'H.
) and (7b) are both in a high impedance state. Therefore, the voltage across the photovoltaic element (9) quickly increases. The voltage across the photovoltaic element (9) is
When the threshold voltage of one MOSFET (8a) in the FET pair (8) reaches ■t+n (=Vt14), the impedance of the MOSFET (8a) decreases, so the voltage across the photovoltaic element (9) decreases. is regulated by this threshold voltage VTH (see Figure 2(c)), the other MOSFET in the first MOSFET pair (8)
S F E T (8b) is one of the M OS F
Since it has almost the same characteristics as E T (8 m), it has low impedance and is similar to the photovoltaic element (6 m).
) and the accumulated charge between the gate and source of the first output MOSFET (10) are discharged, and the first output MOSFET (10) is discharged.
This is to keep the OSFET (10) in a reliable cutoff state.

Therefore, the relay input terminals (1) and (2) shown in Figure 2 (
, ) is applied, the output M
As shown in FIG. 2(d), the OS FET (10) is controlled to open and close according to an input electric signal.

Moreover, until the voltage across the first photovoltaic element (6) reaches the threshold voltage VTH, there is virtually no impedance that prevents this voltage increase. The voltage rises quickly.

In addition, the second photovoltaic element (9) allows the output MOSF
Since the MOSFET (8b) for discharging the accumulated charge between the gate and source of ET (10) is controlled to close, the voltage between the gate and source of the output MOSFET (10) also falls rapidly. It is done. This allows high-speed rmr? (It is something that can be controlled. In addition, MO3F E T <7a)
In (8a), by regulating the voltage across the photovoltaic elements (6) and (9) to a threshold voltage of 7 H, one photovoltaic element (6) (or (9)) generates a photovoltaic voltage. When the generation of the charge discharging MOSFET (7b) (or (8b)) is stopped, the charge discharging MOSFET (7b) (or (8b)) is immediately turned off.
This prevents the S FET (7b) (or (8b)) from interfering with the increase in the voltage across the photovoltaic element (9) (or (6)).

In the example, an inverter (4) is used to obtain a signal with a phase opposite to the input electric signal, but by connecting two LEDs in antiparallel and reversing the polarity of the applied voltage, 2f
l! The configuration may be such that the LEDs of J are lit alternately.

In addition, as the output MOSFET (10), although an enhancement type N-channel MOSFET was used, a depletion type MOSFET,
Even if P channel (7,1M03FET is used), it will not be flat.

(Effect of Q light) As described above, in the present invention, the voltage across the first photovoltaic element that increases the limiting voltage of the output MOSFET by 4 is the first
Until the threshold voltage of the MOSFET pair is reached, there is virtually no impedance that prevents this voltage from rising, which has the effect that the gate-source voltage of the output MOSFET rises rapidly. MO3r? for discharging the accumulated charge between the gate and source of the output MOSFET by the second photovoltaic element.
Since the opening of ET is controlled, the output MO8
The voltage between the gate and source of the FET also falls rapidly, which causes the output MOSFET to
This has the effect of realizing a semiconductor relay circuit that can control opening and closing at high speed.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a semiconductor relay circuit according to one embodiment of the present invention, FIG. 2 is an explanatory diagram of the same operation, and FIG. 3 is a circuit diagram of a conventional example. (3) and (5) are light emitting elements, (6) and (9) are photovoltaic elements, (8) is a MOSFET pair, and (10) is an output MO8FET.

Claims (1)

[Claims] (1) A first light emitting element that generates an optical signal in response to an input electrical signal, a second light emitting element that generates an optical signal in response to a signal that is in opposite phase to the input electrical signal, and first and second light emitting elements. The electromotive force of the first photovoltaic element is applied between the gate and the substrate, and the electromotive force of the first photovoltaic element is applied between the gate and the substrate, and the electromotive force of the first photovoltaic element is applied between the gate and the substrate. The output MOSFET used as a relay output terminal and the electromotive force of the first photovoltaic element are used as the closing control voltage, and the output MOSFET
A first MOSFET pair consisting of a combination of enhancement type MOSFETs having substantially the same characteristics and having a threshold voltage higher than T, and an enhancement type MOSFET having substantially the same characteristics whose closing control voltage is the electromotive force of the second photovoltaic element. a second MOSFET pair consisting of a combination of MOSFETs; one MOSFET of the first and second MOSFET pairs;
The SFETs are connected in parallel to the first and second photovoltaic elements, respectively, and the other MOSFET of the first and second MOSFET pairs
A semiconductor relay circuit characterized in that ET is connected in parallel to the second and first photovoltaic elements, respectively.