JPH02100417A - Optical mos relay - Google Patents

Abstract

PURPOSE:To execute both an ON operation and an OFF operation at a high speed by using a photoconductive type photodetector as a photodetector and bringing a power MOSFET to ON/OFF control in accordance with whether a photocurrent of the photoconductive type photodetector exists or not. CONSTITUTION:The title relay is provided with a photodiode 21 being a photoconductive type photodetector connected between a gate and a source of power MOSFETs 4-1, 4-2, and a power source circuit 30 for applying a reverse voltage to this photodiode 21. When a light emission diode 1 emits light, the photodiode 21 conducts, and a photocurrent flows to the photodiode 21 through a resistance 28 from a capacitor 26 and an FET 25. Subsequently, the voltage drop of the resistance 27 is applied to gates G of the power MOSFETs 4-1, 4-2, and the power MOSFETs 4-1, 4-2 become an OFF state. In such a way, ON/OFF driving of the power MOSFETs is attained at a high speed.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an optical MOS relay (optical MOS relay) which combines a power MOSFET with an optical coupler consisting of a light emitting element and a light receiving element.
OS switch).

[Conventional technology]

Conventionally, in general, in this type of optical MO3IJ Ray, a photovoltaic element is used as a light receiving element, and by receiving light from a light emitting element, the photovoltaic element generates an electromotive force, and this electromotive force is Puff-M by being applied to the gate
Since the OSFET is driven ON/OFF, it has the advantage that it can be used for both AC and DC applications.

Figure 2 shows an example of the circuit configuration of a conventional optical MOS relay. In this example, an N-channel enhancement type is used as the power MOSFET 4-1.4-2. A channel enhancement type or a depressing type can be used.

When no forward current is flowing through the light emitting diode (LED) 1 as a light emitting element, no electromotive force is generated yet in the solar cell array 2 as a photovoltaic element. Therefore, the potential difference between the gate and source of power MOSFET4-1゜4-2 is OV, and the potential difference between the gate and source of power MOSFET4-1゜4-2 is OV,
2 is in the OFF state, and no current flows even if a voltage is applied between the output electrodes 12 and 13. On the other hand, when a voltage is applied between the input electrodes 10 and 11 so that the light emitting diode 1 becomes forward biased, a forward current flows through the light emitting diode 1, causing it to emit light. This light emission causes solar cell array 2
A photovoltaic force is generated, and the power MOSFET4-1.4
-2 gate-source capacitance is charged, and when the gate potential exceeds the gate threshold, the power MOSFET
4-1.4-2 becomes ON state, output electrode 12.13
A current flows when a voltage is applied between the two. In addition, power MOS
FET4-1゜4-2 is connected in anti-series between the output electrodes 12 and 13, and there is a parasitic diode in the opposite direction of power MOSFET4-1.4-2, so current can flow in both directions. It is possible. Therefore, this example can be used as a semiconductor relay for both AC and DC, but when used only for DC, one power MOSFET may be omitted.

Next, when the forward current of the light emitting diode 1 is turned off, the photovoltaic force of the solar cell array 2 disappears, and the power MO5
When the charge accumulated between the gate and source of FET4-1 and FET4-2 begins to discharge, and the voltage between the gate and source becomes below the threshold, power MO5FET4-1.4-2
becomes OFF again. By the way, solar cell array 2
has a high impedance at a voltage lower than the forward voltage of the diode, so the discharge time constant of the gate charge is very long. It's late. Therefore, in this example, a discharge resistor 3 is added to shorten the discharge time constant in order to bypass the discharge.

However, due to the addition of the discharge resistor 3, a part of the current generated from the solar cell array 2 is dissipated through the discharge resistor 3 when charging the gate-source capacitance of the power MOSFET 4-1.4-2. , from the start of light emission of light emitting diode 1 to power MO5FET4-1.4-2
This has the disadvantage that the response time until it reaches the ON state is longer.

Figure 3 shows another optical MO3I that improves the drawbacks of the conventional example.
In this circuit diagram, the single discharge resistor 3 shown in the second figure is replaced by a discharge FET 5. A discharge circuit consisting of a discharge solar cell array 6 and a discharge resistor 7 is provided. The discharge FET 5 is a depression type FET, and is in the ON state when the discharge solar cell array 6 does not receive light, so that the voltage between the gate and source of the power MOSFET 4-1, 4-2 is Ov, and its output is in the OFF state. It is. When a forward current flows through the light emitting diode 1, a photovoltaic force is generated in the solar cell array 2.6 that receives light from the light emitting diode 1. The photovoltaic force of the solar cell array 6 charges the gate-source capacitance so that the gate potential of the FET 5 becomes equal to or lower than the source potential. Its gate potential is FE
When the threshold value of T5 is exceeded, FET5 is turned off, and the photovoltaic force of the solar cell array 2 is transferred to the power MOSFE.
The voltage is directly applied between the gate and source of T4-1.4-2 to charge the gate-source capacitance, and when the voltage exceeds the threshold, the power MOSFET 41.4-2 is turned on. The discharge resistor 7 has the same function as the discharge resistor 3 shown in the second diagram. The current that discharge FET5 should flow is the power MOSFET4-. Since the drive current is sufficiently small compared to the drive current of 1.4-2, the discharge FET 5 can be realized with a small element. For this reason, the gate-source capacitance of the discharge FET 5 is sufficiently small, and even if there is a leak due to the discharge resistor 7 during charging of the gate-source capacitance, the discharge FET 5 is sufficiently powered by the photovoltaic force of the solar cell array 6. The response operation is quick, and the OFF operation is performed at a fairly high speed.

[Problem to be solved by the invention]

However, originally the power MOSFET4-1.4
-2's ON operation depends on the photovoltaic force of the solar cell array 2 and the power MOSFET fl-1,
It is determined by the gate-source capacitance of 4-2, and installing the solar cell array 6 for opening and closing the discharge circuit will reduce the photovoltaic force of the solar cell array 2 accordingly. The ON operation response speed of the optical MO3IJ relay shown in FIG. 2 is several 100 μs to several ms or more, which is considerably slower than that of a normal semiconductor relay.

The purpose of the present invention is to perform ON operation and OFF! The object of the present invention is to provide an optical MO3IJ laser capable of speeding up both II and II production.

[Means to solve the problem]

The configuration of the optical MO3IJ laser according to the present invention uses a photoconductive light receiving element instead of a photovoltaic light receiving element, and has a built-in power supply circuit that is supplied with power from an output electrode and applies a voltage to the photoconductive light receiving element. This eliminates the need for discharging operations during ON/OFF operation, and controls ON/OFF of the power MOSFET based on no photocurrent.

[Effect]

According to such means, since there is a photocurrent when the photoconductive light receiving element receives light or stops receiving light, the power MOSFET is affected by the presence or absence of a voltage drop across a resistor in the power supply circuit or changes in charging and discharging of a capacitor, for example. The gate voltage etc. of the power MOSFET are controlled, and the ON/O of the power MOSFET is controlled.
FF drive can be achieved at high speed.

〔Example〕

Next, one embodiment of the present invention will be described based on the accompanying drawings.

FIG. 1 shows an optical MOS FET IJ according to the present invention.
FIG. 2 is a circuit configuration diagram showing one embodiment of the circuit. Note that in FIG. 1, the same parts as those shown in FIG. 2 or 3 are given the same reference numerals, and their explanations will be omitted. 21 is
Unlike conventional solar cells, power MOSFET4
-1.4-2 is a photodiode as a photoconductive type light-receiving element connected between the gate and source. 30 surrounded by a broken line
is a power supply circuit that applies a reverse voltage to this photodiode 21.

The power supply circuit 30 includes diodes 22-1 and 22-2 as rectifiers that obtain direct current from the output electrodes 12.13, and a capacitor 26 that applies a reverse voltage to the photodiode 21.
A resistor 27 that applies a voltage drop due to the reverse current of the photodiode 21 to the gate G of the power MOSFET 4-1.4-2, and the photodiode 21. Source follower MOS FET with resistor 27 and capacitor 26 as load
25, and an N-channel depletion type MOSFET 23 that stabilizes the potential of the gate G of this MOSFET 25.
and a Zener diode 24.

The capacitor 26 has output electrodes 12 and 13, and a diode 2.
2-1.22-2, an electric charge is charged through the MO5FET 25, and the potential of the photodiode 21 is maintained at a potential lower than the gate potential of the FET 25 by its gate threshold voltage. Therefore, when the light emitting diode 1 is not emitting light (when the photodiode is non-conducting), the power M
The gate voltage of OSFET4-1.4-2 is connected to capacitor 2.
6 voltage, higher than the source voltage, power MO5F
ET4-1°4-2 is in the ON state. On the other hand, when a forward current flows through the light emitting diode 1 and emits light, the photodiode 21 becomes conductive, and the capacitor 26 and F E T2
A photocurrent flows from the photodiode 21 through the resistor 27 from the resistor 27, and the voltage drop across the resistor 27 is applied to the gate G of the power MO5FET4-1゜4-2.
FET4-1.4-2 becomes OFF state.

In this way, since the photodiode 21 is used as a light receiving element, the response speed is generally faster than that of a solar cell array. can exclusively receive light,
The speed can be increased compared to the conventional optical MOS relay. The charge of the capacitor 26, which is partially lost when the photodiode 21 is turned on, is compensated for when the photodiode 21 is turned off, but F
Since E T25 is used as a source follower, the power supply capacitor 26 is charged at high speed when the photodiode 21 is off, and when the photodiode 21 is on, the MO6
A photocurrent is also supplied from the FET 25 to the resistor 27, and O
Fast response when switching between N/OFF. Also, MOSFET
A stabilizing circuit (FET2) that keeps the gate voltage of FET25 constant
3. Since a Zener diode 24) is provided,
This contributes to stabilizing the operation of MOSFET 25. Furthermore,
In the conventional semiconductor manufacturing process for optical MO3'J arrays using solar cell arrays, processes such as conductor separation are required, but in this example, this process is not necessary, and the power supply is achieved using an inexpensive normal process. The circuit 30 and the like can be integrated on the same chip.

〔Effect of the invention〕

As explained above, the optical MOSFET relay according to the present invention uses a photoconductive type light receiving element instead of the solar cell array as the light receiving element in the conventional optical MOSFET relay, and has a built-in power supply circuit to apply voltage to the photoconductive type light receiving element. However, since the ON/OFF control of the power MOSFET is performed based on the presence or absence of photocurrent of the photoconductive type light receiving element, the following effects are achieved.

■The photoconductive light-receiving element itself has a faster response speed than a solar cell array, and a single photoconductive light-receiving element can exclusively receive all of the light emitted, making it possible to capture large changes in brightness and darkness. Therefore, faster switching can be realized compared to the conventional method.

■It goes without saying that power supply circuits etc. can be integrated on the same chip.
It does not require separation means such as dielectric separation, and can be manufactured at low cost using normal processes.

[Brief explanation of drawings]

FIG. 1 shows the optical MO3! according to the present invention. FIG. 2 is a circuit configuration diagram showing an embodiment of the J-ray. FIG. 2 is a circuit configuration diagram showing an example of a conventional optical MO3IJ relay. Figure 3 shows another conventional optical MO5! FIG. 2 is a circuit configuration diagram showing a J-ray. 1 Light emitting diode, 4-1.4-2 Power MOS
FET, 10.11 Human electrode, 12.13
Output electrode, 21 Light emitting diode, 22-1.22
-2 Diode, 23 Constant current source FET, 24
Zener diode, 25-MOS FET,
26 capacitor, 27 resistor, 30 power supply circuit. Figure 2 Figure 1 Figure 3

Claims (1)

[Claims] 1) A light emitting element, a light receiving element that receives future light,
A power MOSFE driven by the output of this light receiving element
In the optical MOS relay including T, a photoconductive type light receiving element is used as the light receiving element, a power supply circuit to apply a voltage is built in, and the power MOSFET is turned on depending on the presence or absence of a photocurrent of the photoconductive type light receiving element. An optical MOS relay characterized by /OFF control.