Why is IGBT used in VFD

Bidirectional AC switch with IGBTs

I came across a "Bidirectional IGBT Switch" on the internet while looking for a solution to my problem of protecting a TRIAC / SSR from a short circuit.

Since the TRIAC / SSR shutdown is beyond my control, I am very interested in the IGBT solution. However, since I was relatively unfamiliar with them, I wanted to ask here in case I don't fully understand the circuit.

Besides this circuit I also saw the following circuit which I can at least follow mentally and think it should work.

I have the following questions about this circuit:

  1. Can this switch be used sensibly for switching 220 V?

  2. Can I switch these devices off immediately, because they are IGBTs, if I perceive the current in the network and exceed a certain threshold value?

  3. Can other forms of transistors be used here? If not why

Spehro Pefhany

  1. Yes, it can be used to switch 220 V. Viable? Well, cost and complexity could be problems for static switching applications. It is seldom done what can be an indication.

  2. Yes, you can detect and prevent destruction with a short circuit (even if the short circuit occurs at peak mains voltage). However, you will need an IGBT with Short-circuit strength and need to detect the IGBT fast enough and turn it off (and strangely enough, too, can sound, not too fast). Follow the manufacturer's recommendations. These IGBTs are designed for use in VFD inverters (Variable Frequency Drive).

  3. I don't know any other devices that are supposed to withstand a short circuit on the network - maybe some beefy MOSFETs. Apart from that, an NPN transistor, an NPN Darlington or a MOSFET could be used. In the latter case, in your first circuit, the body diode shares the current with the external diode, so you may see additional heating in the MOSFET in addition to (forward) conduction losses.

To edit:

Here is the specification from a typical IGBT data sheet with short circuit rating:

As you can see, it can withstand a direct short for 10 μs under realistic conditions (hot, with 300V above).

For more information on IGBT behavior under the stressful conditions of a direct short circuit, see this reference. If you slow down the switching off of the IGBT a little (especially under short circuit conditions), the voltage spike can be reduced due to the inductance in the load circuit and the rapid change in current.


1) Can you explain in more detail what you mean by static switching? 2) Are short-circuit IGBTs designed to sustain large avalanche energies? Why shouldn't they be turned off too quickly?

Spehro Pefhany

The static switching just turns on and off, not very quickly. No PWM and no phase control. An old term. 2) not necessarily avalanche, which is caused by overvoltage rather than overcurrent. See Edit above for more information.