Re: Solid State Voltage and Current Regulator (fwd)

From: 	bmack[SMTP:bmack-at-frontiernet-dot-net]
Sent: 	Saturday, January 10, 1998 8:55 PM
To: 	Tesla List
Subject: 	Re: Solid State Voltage and Current Regulator (fwd)

> From: 	Richard Wayne Wall[SMTP:rwall-at-ix-dot-netcom-dot-com]
> Sent: 	Thursday, January 08, 1998 4:16 PM
> To: 	Tesla List
> Subject: 	Re: Solid State Voltage and Current Regulator (fwd)
> You wrote: 
> snip
> >> Harri's observation about these series pass transistors are 
> analogous
> >> to large variable resistors is partially correct.  Resistor are 
> always
> >> 
> >Bipolar Transistors?  I hear that IGBTs have _very_ low forward drop, 
> >and I see them being used in some of the higher-end lighting dimmers 
> in
> >place of SCRs these days- their ability to turn on at any desired 
> speed
> >eliminates the need for a filter inductor.
> >
> >Following this thread with considerable interest,
> >Gomez
> =====================================================================
> snip
> These are bipolar transitor modules.  Not IGBTs.  Although I wish I had 
> a few IGBTs to play with, they are big bucks at these power levels.
I see no advantage to IGBT's in this application!
Essentially it's a hybrid that has the advantage of the FET gate input
without the resistive loss problems in the Drain source region.
At saturation it is more or less like a forward biased diode curve, just
a normal BPT.  This non-linear drop vs current is very desireable at very
high current levels by reducing the dissapation and voltage at saturation.
You already have that with the BPT and the input scheme is non-critical,
so save your $$.

The only down side to IGBT's is slow speed, although there have been some
recent advances in thin wafer technology that have brought them into the
500KHZ+ range.  Unfortunatly the yeild on these puppys is dismal at best,
thus the high price tag.
By the way those large die transistors are slow as snails too. But at 60HZ
who cares!
Saving my $ for the fuel bill
Jim Mcvey