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Re: Disabling the freewheling diode



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

On 1 Sep 2003, at 16:40, Tesla list wrote:

 > Original poster: dhmccauley-at-spacecatlighting-dot-com
 >
 >
 > There are two diodes both of which typically are Schottky diodes.  There is
 > the schottky ultrafast diode in parallel with the FET which is used to
 > bypass the intrinsic diode of the FET, and there is also the series schottky
 > diode of which you speak of in series with the drain of the FET which is
 > used to help keep the internal FET diode turned off during reverse current
 > (freewheeling)
 >
 > Dan

You will find that the parallel diode is not a Schottky and could
never be. Schottkys are not built with the necessary voltage ratings.
It appears then that the diode you are talking about with lower
current ratings is in fact the ultra-fast recovery parallel diode.
The one I am speaking about and which I think most recognize as being
a Schottky is the diode in series with the drain.

Malcolm

 >
 >  > 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
 >  >  >
 >  >  >
 >  >  >
 >  >
 >  >
 >  >
 >  >
 >  >
 >
 >
 >