Re: FET/IGBT drivers

To: tesla-at-pupman-dot-com
Subject: Re: FET/IGBT drivers
From: "The Flavored Coffee Guy" <elgersmad-at-msn-dot-com> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
Date: Tue, 28 Dec 1999 06:47:41 -0700
Approved: twftesla-at-uswest-dot-net
Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme

Typically the best way to preserve a semiconductor is a pair of zener diodes
rated at the voltage the power transisor is biased at.  You simply connect
them in series so that one is forward biased, and the other is reverse
biased.  Then they are placed in parallel with the source and drain, or
Collector and Emitter. That way no matter which direction the polarity of a
spike from the coil goes, if it goes beyond the supply voltage for the FET,
or transistor, it goes around as a short.

    For transistors diodes are used to prevent the base biasing voltages
from being reversed in the voltage divider, and sent back through the
emitter, or the collector to ground because your primary in circuit
transient protection is the zener diodes in parallel with the collector and
emitter..


James.





-----Original Message-----
From: Tesla List +ADw-tesla+AEA-pupman-dot-com+AD4-
To: tesla+AEA-pupman-dot-com +ADw-tesla+AEA-pupman-dot-com+AD4-
Date: Monday, December 27, 1999 11:15 PM
Subject: Re: FET/IGBT drivers


+AD4-Original Poster: +ACI-Bill the arcstarter+ACI-
+ADw-arcstarter+AEA-hotmail-dot-com+AD4-
+AD4-
+AD4-Kennan C Herrick +ADw-kcha1+AEA-juno-dot-com+AD4- wrote:
+AD4-
+AD4APA-snip+AD4-
+AD4APg-I tried a fast diode between ground and the H bridge central leg:
no help,
+AD4APg-a diode was too slow (I am talking about 10-100 ns spikes). Then I
tried
+AD4APg-the Motorola cure: a 20 ohms resistor between the chip pin and the H
bridge
+AD4APg-central leg. THAT WORKED+ACE- I made a lot of shorts
+AD4APA-snip+AD4-
+AD4-
+AD4-Thanks for the interesting post+ACE-  Any posts on how to increase the
longevity
+AD4-of semiconductor devices is always appreciated.  At work - we found that
+AD4-using an extra 2-transistor +ACI-totem pole+ACI- drive stage for the
FET gate
+AD4-produced better results than just relying on the gate drive pin of our
SMPS
+AD4-control chip (even though it was rated for it).  Buck mode
architecture but
+AD4-still involves driving fets etc.
+AD4-
+AD4-Anyone noticed you can get fets with practically negligible Rds ratings?
+AD4-Our part had a stated Rds of 0.006 ohms+ACE-  I said B.S. - can't be
true so I
+AD4-pumped 10 amps through it - and measured Vds +AD0- 40 mV.  Now I'm a
believer+ACE-
+AD4-:)
+AD4-
+AD4-The bit about the 20 ohm shunt resistor presumes that the source of this
+AD4-bounce is (?) high impedence and thusly 'quenched' out by the 20 ohm
+AD4-resistance?  Did this ground bounce couple into the circut via a conducted
+AD4-or radiated path?
+AD4-
+AD4-Please hurry and get your circuit working again so you can tell us all
your
+AD4-tricks+ACE-
+AD4-
+AD4--Bill
+AD4-(surrounded by 2 volt 60 amp smps laser diode drivers...)
+AD4-
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+AD4-Get Your Private, Free Email at http://www.hotmail-dot-com
+AD4-
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