My question is what significant advantage does using this HCPL3180 opto-coupler have to drive the gate of an FET over using other methods, such as using an op-amp or BJTs ??? and also does it have anything to do with ground bounce ?? enter image description here

  • 6
    \$\begingroup\$ Hi, Please be careful. You have deleted and (as near as makes no difference) repeated your question from yesterday, which you deleted 2 hours ago. You were able to delete it because there were not yet any answers. However members had invested already in some comments to help you clarify and refine the question, as well as helpful technical points. Their time has now been wasted by your deletion of that question (and those comments). :-( In future, whenever possible improve the original question, instead of deleting & reporting. Thanks \$\endgroup\$ – SamGibson Feb 7 at 23:08

An opto-coupler offers common ground isolation between sections with different voltages and currents. Also isolation between the digital and analog sections of a board, allowing digital control of analog circuits, and feedback of analog levels to a digital side with a MPU in control of analog circuits.

They also offer isolation from the high and low sections of an H-bridge, as the upper MOSFET is not at common ground, but usually between Vcc and ground, rapidly changing with the pulses. As shown in the drawing the MOSFET gate driver is powered by an isolated supply, so the gate can be properly driven regardless of the voltage at the source pin. Some half and full bridge driver IC's offer an internal offset and raised voltage for the upper MOSFETs and IGBTs, but they have voltage limits and may not be suited for a supply rail of +2,000 volts.

Optocouplers solve many connection problems where common grounds are not the same, or cannot be shared except at the power connector where all the various power grounds merge.

The optocoupler you refer to is designed to drive medium power MOSFETs with up to so many amps of gate drive current. It is not a general purpose optocoupler where a sharp rise and fall time at high current levels are not needed.

Other methods work but have a higher parts count. A transformer coupled design can be found with dual secondary windings, but additional Schottky diodes and resistors are needed so the MOSFET gates see only a positive pulse with a fast ON time and faster OFF time. This design is more common if IGBTs are used at very high voltage levels, far beyond what IC's can tolerate.

Extra transistors used to level shift the voltages for the upper MOSFET get complex, so if the voltage is not too high IC's that do that can be found for low to medium power applications.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.