Re: Disabling the freewheling diode

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Malcolm Watts" <m.j.watts-at-massey.ac.nz> 

On 1 Sep 2003, at 2:19, Tesla list wrote:

 > Original poster: dhmccauley-at-spacecatlighting-dot-com
 >
 >
 >  >  > The reason for this is that the freewheeling current is much less than
 >  >  > the current that the MOSFET conducts when it
 >  >  > is ON.
 >  >  >
 >  >  > The Captain
 >  >
 >  > But, but.... the Schottky diode has to handle the conduction current
 >  > doesn't it??  There is a real cheap source of 30A/40A Schottky diodes
 >  > out there too - any old scrapped computer SMPS has a dual unit
 >  > rectifying its +5V supply. Note that a single dual diode (common
 >  > anode) would serve both upper MOSFETs in an H-bridge arrangement.
 >  >
 >  > Malcolm
 >
 >
 > No.  The FET takes the conduction current, not the series Schottky in
 > parallel with it.

I confess to being absolutely lost. Series Schottky in parallel?? Is
not the Schottky diode in series with the drain? What other ON-
conduction path is there?

Malcolm

   The Rds of the FET is much lower (and less voltage drop)
 > then the parallel Schottky
 > diode, therefore, most of the current goes through the FET.  On the
 > otherhand, for reverse freewheeling current, the Schottky diode will
 > conductor first and take the bulk of
 > any reverse freewheeling current in the circuit.
 >
 > The Captain
 >
 >
 >