IGBT and MOSFET gate driver photocouplers are a semiconductor device that provides a way to rapidly switch the input signal of high power IGBTs and MOSFETs while providing for high electrical isolation. Isolation is important because it blocks potential high voltages, isolates the ground and prevents noise currents from entering the low voltage control circuitry. Such signals can interfere with circuit operation and damage sensitive circuits. They are used in applications like motor control (where rapid switching can be used as a speed controller), Inverters and switched-mode power supplies. This may also be very important in meeting safety compliance regulations.

IGBT stands for insulated-gate bipolar transistor. MOSFET stands for metal oxide semiconductor field effect transistor. These are high-speed solid state switches not inside the device itself. They require extremely little current to turn them on relative to the current being switched. Because of the high currents these devices can switch (even hundreds of Amps), the switching currents required to switch the device on and off can still be quite high. The IGBT or MOSFETs gate input capacitance is in part created by an effect caused by negative feedback of the amplifier referred to as the Miller Effect or reverse transfer capacitance . This effect increases the capacitance roughly in proportion to the gain of the switch. The driver circuit needs to be capable of driving this load, being able to rapidly switch the voltage levels on the gate of the power IGBT or MOSFET to turn the device on and off. Time in the transition between on and off levels leads to power being dissipated in the IGBT or MOSFET, lowers efficiency or possibly even damages the device.

The device has a low voltage input that can turn the internal photodiode on or off.

This usually requires a voltage transition across the LEDs forward voltage typically around 1-1.4 Volts and current of around 10mA.  A beam of light from the LED crosses an electrically insulting barrier and is sensed by a photo detector. This signal is used to turn the IGBT or MOSFET Driver in the device on and off. The driver must be able to provide an extremely fast transition on either switching transition to maintain the efficiency of the external IGBT or MOSFET switch. This means the driver must be able to sink or source very large (even amps) of current during these edges to charge or discharge the input capacitance quickly.

The driver circuitry may have integrated fault detection circuitry to tell if the switch is being unduly stressed by the load, or some failure condition has occurred. These signals can be sent by some devices back across the photodiode isolated barrier to the low voltage side so that it can be detected by the isolated control circuitry.