Guru
Joined: 02/02/2017
Location: AustraliaPosts: 1464
| Posted: 06:06am 19 Apr 2021 |
Haxby, my view is the internally generated voltage transients caused by the
fast voltage and/or fast current changes between Drain and Source are
not going to be a problem for the MOSFETs.
Even if these voltage transients were a problem for the FETS, what can we do
about them? Reduce the switching speeds via larger gate series resistance?
That would work to some degree or other.
The specifications for IR21844 and IR2110 and probably many other IR parts
have the gate drive outputs to remain within -0.3V of Vss (ground) and +0.3V
of Vdd (dc supply, usually 12 or 15V).
This is not unreasonable since the gate drive output stage within the IC is
a pair of MOSFETS and undoubtedly they are microscopic, not robust and easy to damage.
I have measured voltages that easily exceed the low limit by a volt.
This was when I drive a power board's FETS directly by a pair of IR21844 chips.
IF the internally generated transients, when added to the gate drive voltage
now exceeds the MOSFET specs then there will be trouble, eventually.
I have measured gate voltages carefully on the totem pole power boards
and the difference is profound.
I made a post on this subject I think it's here
https://www.thebackshed.com/forum/ViewTopic.php?PID=131988#131988#131988
here is a look at non-totem pole power board gate voltages
https://www.thebackshed.com/forum/ViewTopic.php?PID=131506#131506#131506
Back then I was wondering about potential damage to gate drive IC output stages.