Re: Disabling the freewheling diode

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

Original poster: "claude masetto" <claudmas-at-optusnet-dot-com.au> 

We still do not seem to be getting the answer as to why the series diode is
not rated for the same current as the mosfet
Claude
----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Tuesday, September 02, 2003 11:09 AM
Subject: 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
 >  >  >  >
 >  >  >  >
 >  >  >  >
 >  >  >
 >  >  >
 >  >  >
 >  >  >
 >  >  >
 >  >
 >  >
 >  >
 >
 >