Re: FET/IGBT drivers

• To: tesla-at-pupman-dot-com
• Subject: Re: FET/IGBT drivers
• From: "Bill the arcstarter" <arcstarter-at-hotmail-dot-com> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
• Date: Mon, 27 Dec 1999 20:01:33 -0700
• Approved: twftesla-at-uswest-dot-net
• Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme

Kennan C Herrick <kcha1-at-juno-dot-com> wrote:

<snip>
>I tried a fast diode between ground and the H bridge central leg: no help, 
>a diode was too slow (I am talking about 10-100 ns spikes). Then I tried 
>the Motorola cure: a 20 ohms resistor between the chip pin and the H bridge 
>central leg. THAT WORKED! I made a lot of shorts
<snip>

Thanks for the interesting post!  Any posts on how to increase the longevity 
of semiconductor devices is always appreciated.  At work - we found that 
using an extra 2-transistor "totem pole" drive stage for the FET gate 
produced better results than just relying on the gate drive pin of our SMPS 
control chip (even though it was rated for it).  Buck mode architecture but 
still involves driving fets etc.

Anyone noticed you can get fets with practically negligible Rds ratings?  
Our part had a stated Rds of 0.006 ohms!  I said B.S. - can't be true so I 
pumped 10 amps through it - and measured Vds = 40 mV.  Now I'm a believer! 
:)

The bit about the 20 ohm shunt resistor presumes that the source of this 
bounce is (?) high impedence and thusly 'quenched' out by the 20 ohm 
resistance?  Did this ground bounce couple into the circut via a conducted 
or radiated path?

Please hurry and get your circuit working again so you can tell us all your 
tricks!

-Bill
(surrounded by 2 volt 60 amp smps laser diode drivers...)

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