Simple IGBT failure

Thread Starter


Joined Aug 20, 2011
Hello All,

I am an English student currently in Fort Portal, Uganda, attempting to build an induction generator controller with very limited resources. As part of the design, I intend to to PWM the ~240V RMS produced by the generator. Right now, I am attempting to simply switch mains on/off at low frequency to test some IGBTs. I have a 12V transformer, that after RMS peak and a regulation of around 1.4 gives around 20V pk-pk AC out. I rectify this, then divide it using two 1kOhm resistors to give 0V, ~10V and ~20V connections.

The IGBTs have integrated antiparallel diodes, so I place them in antiseries, with common emitters. I connect the emitters to the ~10V connection. I then run a wire from the two IGBT gates, and manually touch it to the 0V and 20V connections, in an attempt to give gate-emitter voltages of -10V and 10V. The IGBTs do not respond, seemingly blocking in one direction regardless of connection. I have attached a diagram of the circuit I intend to use this method in; ignore everything in grey, and ignore the transistor; as I said, I am manually connecting the wire to avoid any complications.

I would greatly appreciate any insight into the IGBT's lack of response.



Joined Jul 9, 2011
The IGBTs do not respond, seemingly blocking in one direction regardless of connection.
Please post the whole circuit you are using right now to test the IGBTs. E.g. what are the collectors connected to? If I ignore everything in grey, then the collectors are open.


Joined Jul 9, 2011
I drew your schematic again and attached it.

First of all I think it's dangerous to experiment with a circuit at this high voltage if you are not exactly sure if/how it works. Why not use a smaller voltage to switch?

Then, when turning ON both IGBTs you are applying to one of them a reverse voltage (+ on emitter and - on collector) depending on the 230VAC polarity.
This is not a valid condition for a conducting IGBT.
Are u sure they are still ok?

If you want to use 1 conducting IGBT and the body diode of the other (blocking) IGBT, you have to alternate the gate signals for each IGBT (1 OFF , the other ON)

It would be be helpful to explain what your final goal is in terms of voltage / current etc. and the components you want to use.