1. Optical coupling structure difference
The main internal structure of optocouplers and OCMOSFET.
Photocoupler When a light emitting diode (LED) lights up a phototransistor, the light creates a photocurrent that flows from the collector to the base of the phototransistor. Therefore, when the LED is not lit, the phototransistor is cut off, and when the LED is strongly lit, a large photocurrent flows from the collector to the base, and the phototransistor is stably switched on. Unlike when the base-collector is simply short-circuited, even if the collector-emitter voltage is less than the base-emitter forward voltage of the transistor, the photocurrent still flows and the phototransistor is on.
The OCMOSFET is equipped with a photovoltaic cell, and when the LED is lit, the photovoltaic cell charges the gate capacitor to increase the gate-source voltage, thus conducting the MOSFET in the MOSFET. Contact type of situation. For open type contacts, the FET conducts without gate source voltage. However, when the LED is lit, the photovoltaic cell will reverse bias the gate-source voltage, thus cutting off the FET. When the make-typeOCMOSFET is off, the photovoltaic cell not only stops charging, but the internal discharger switch automatically closes, forcing the gate to discharge. As a result, the grid-source voltage drops immediately.
Two FETs in an OCMOSFET are connected in series in reverse. Therefore, when the OCMOSFET is on, the two FETs are double-wizard on. However, when the OCMOSFET is not on, it is only on the forward FET where the applied voltage is cut off, while the parasitic diode of the other FET is on.
2. Differences in optocoupler features
As a result of these structural differences, optocouplers and OCMOSFETs have the following characteristics:
1. Although the optical coupler conducts only DC (direct current) in the output, the OCMOSFET can conduct DC and AC (alternating current) in the FET.
2. Usually, the optical coupler operates at a speed of microseconds or higher, while the OCMOSFET operates at a speed of milliseconds.
3. Although the output conduction characteristics of the optical coupler vary with the input current value, the output conduction characteristics of the OCMOSFET are independent of the input current value.
4. The optical coupler corresponding to the input becomes conductive. However, when an input is applied, there are two types of OCmosFETs: one that conducts (a contact: closed contact) and one that breaks (b contact: open contact). Therefore, although OCmosFETs cannot expect high-speed operation like photocouplers, OCMOSFETs can switch alternating current with very small input currents (as small as a few milliamps) as well as large currents in the amperage range.
3. Application differences
Typically, optical couplers are only used to transmit DC signals. Its applications include:
1. Pulse transmission (in conventional digital circuits) On the other hand, because the OCMOSFET operates at a slower speed than the photocoupler, it is rarely used for signal transmission. However, due to the bidirectional conduction and low on-resistance characteristics of MOSFETs, it is mainly used as an \"electronic switch\" to interrupt AC signals. Therefore, OCMOSFET is also known as SSR (solid State relay).