Drain current differs from source current? NMOS

Thread Starter

KaloyanP

Joined May 27, 2012
5
Hi, I have been researching transistors for a PWM drive for a small motor and the one I have chosen for now is the RSQ 035 NO3 (it will form the lower half of a discrete H-bridge). However, I noticed that the maximum current for the drain is about 3.5 times bigger than the one for the source. How does that work? Where would the current go if it doesn't go through from the drain to the source?
 

crutschow

Joined Mar 14, 2008
25,634
All the drain current has to go through the source.

Could you post a reference to the data sheet for that MOSFET? I couldn't find it.
 

Thread Starter

KaloyanP

Joined May 27, 2012
5
All the drain current has to go through the source.

Could you post a reference to the data sheet for that MOSFET? I couldn't find it.
Exactly, that's what I know as well, but they keep insisting on the two currents being different throughout the datasheet :)

I goofed up with the spacing in the name, heres a reference to the datasheet :)

http://datasheet.elcodis.com/pdf/5/78/57838/rsq035p03tr.pdf

P.S. I probably should think twice before posting so late in the night... Just noticed that the second rating is for the body diode, which now makes a lot more sense :) The moral of the story is: kids, read your datasheets twice, they don't lie unless they are totally wrong.
 

cabraham

Joined Oct 29, 2011
82
Is = Id +Ig. Is = source current, Id = drain current, Ig = gate current.

With high frequency PWM rectangular drive waveforms, the gate current is not negligible. So Id & Is will not exactly match because their difference is the gate current Ig, which is non-zero. Make sense?

Claude
 
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