Jaguars vs Victors

[dsirovica]

Originally Posted by Mark McLeod

The Victor FETs used are IRL3103 (International Rectifier) or an equivalent like FDB6035AL

OK Houston we have a problem.

The IRL3103 has 16mOhms, and FDB6035AL 12.5mOhms.
For a 40A motor curent through a 3-FET Vic, this is 2.8W and 2.2W respectively and an operating temp of 201 and 163 C.

Compare that to a two FET FDP8441 Jag: 1.08W and 92 C.

According to this the Jag has superior power.

Reality says different...

Could it be that the Vics are simply driven red hot and we may be operating in out-of spec areas - we do see a lot of failed Vics?

Also my temp calcs assume no fan so that may increase power dissipation significantly - anyone care to analyse forced air vs ambient power dissipation for these geometries?


Now back to the switching power dissipation:

1. anything less than 100% duty cycle increases the number of FETS dissipating power. At 50% cycle we double the dissipation power.

3. I am worried by the "Single Pulse Avalanche Energy (Note 1) 947 mJ"
of the FDP8441. If that means you turn 1Joule into heat on every swichover - we are trullly fried!

So we need help with (1) forced air power dissipation, and (2) switching energy loss in FETs.

I think we stumbled on a structural problem with FIRST: the kids are too young to know this level of detail, and the mentors are too old to know about this new MOSFET stuff, and object oriented programming - for me that meant you have a chair and desk object and a punch-card object ?