Slowing down a power IGBT switch

[sattar138]

Hi all:
Can you provide your comment on the following inquiry?

I am designing a power supply system in which I will be switching an IGBT (IXGT60N60B2 from IXYS).
I need to slow down the switching time of the IGBT.
I can add series resistance at the gate to slow down the switching.

Q1: Can I increase the input capacitance by adding a known capacitance (X7R) in parallel with the input to the IGBT and add resistance?

My concern with using the gate to emitter capacitance is that it isn’t clearly defined over temperature and the value has a typical value only.
Q2: Would you recommend using an externally applied capacitor instead of relying on the gate to emitter capacitance to slow the down the switching?

thanks,
Sattar

 

[FvM]

Adding a gate-emitter capacitor doesn't effectively increase the transition time of Vce respectively the switching time. It would only delay switch-on and switch-off. To understand why, look at the Vge vs. Qg diagram in a IGBT datasheet. During the rise/fall time of the output voltage, current flows out/into the gate terminal while the gate voltage is at a plateau. Adding a capacitor doesn't change it.

So: Q1, yes, Q2, not at all.

As an additional remark, switching losses usually set a limit for suitable switching time increment. The range of practical interest can be mostly achieved with series resistors.

 

[dick_freebird]

Are you sure you want to fix whatever the problem is, by
making the IGBT switch slowly and dissipate power? That
the IGBT will in fact tolerate it, switching as slowly as you
want to go?

Might there be some other approach like a RC drain snubber,
if it's an EMI or overshoot type problem?