Q.Describe the operation of opto coupler isolator circuit for MOSFET/IGBT.

An opto-coupler isolator circuit transfers the triggering gate signal to a MOSFET/IGBT gate without any direct electrical connection, using an infrared LED optically coupled to a phototransistor in the same package. …

[!TLDR]

An LED-and-phototransistor opto-coupler passes the gate signal to the MOSFET/IGBT by light, isolating the low-voltage controller from the high-voltage power device.

Some circuits, such as inverters, need the triggering gate signal to be transferred from the control circuit to the gates of MOSFETs/IGBTs without any direct ohmic (electrical) connection, because the gate signals and the power devices are often at very different voltage levels (for example a microcontroller at 5 V DC controlling IGBTs that switch 48 V DC in a UPS). The link must be isolated to protect the microcontroller from overvoltage damage.

An opto-coupler (opto-isolator) is an electronic component that transfers an electrical signal from one circuit to another while electrically isolating the two circuits. It consists of an infrared LED chip placed optically in line with a phototransistor, both enclosed in the same package (for example a 4-pin opto-coupler IC). …