Quote:
Originally Posted by MPaulHolmes
Some igbts don't have this problem because of the Kelvin emitter connection, which has a separate path to the emitter inside the igbt from the power path.
|
IGBTs also avoid turn-off ringing because they don't (can't) turn off quickly. You have to wait for the minority carriers to decay (recombine) before the device is fully off. This absorbs some of the inductive energy that would otherwise "slosh" around the cables, capacitors and controller structure.
There is a lot of design effort around turning off IGBTs. You can't get rid of the tail end of the minority carrier recombination, but you can immediately stop generation of new carriers by a negative gate voltage, and bypassing the gate resistor with a diode.
MOSFETs don't have same issue and are relatively easy to turn off.
We have (had) a turn-off ringing issue which we "fixed" by using 39 ohm gate resistors. That costs us a little in the turn-on speed, but it's easier to change resistors and add cooling than building a better capacitor board or physically reducing the current loop area in our controller.