From: Tony Williams
Subject: Re: An interesting little prob.
Date: Thu, 31 Oct 2002 07:57:02 +0000 (GMT)
References: <firstname.lastname@example.org> <email@example.com> <firstname.lastname@example.org>
NNTP-Posting-Date: Thu, 31 Oct 2002 08:32:21 +0000 (UTC)
User-Agent: Pluto/1.14i (RISC-OS/3.60)
In article ,
Winfield Hill wrote:
> Tony wrote...
> > I'm leaning towards an inverting opamp there Win
> Yes I can see the appeal of that. But a non-inverting emitter-
> follower approach avoids the painful issue of compensating the
> common-emitter stage, whose gain is g_m times the load, where
> g_m is a function of clamping current and the load is who knows
> what? The resulting compensation forces a slowing of the clamp.
> In contrast, the emitter-follower clamp is very fast (as fast
> as the EF transistor, the opamp doesn't have to move) and it's
> naturally compensated already, doesn't need more. Also, the
> opamp/BJT is always on, so an opamp diode limiter isn't needed.
Win. Are we talking at cross purposes here?
+---[R]--------+ +----+-[?]--|pnp |
Ana 0v------|+/| |\ |
| | |
? ? +
Just using the opamp as an inverter.
Notice the ?'s. I still have some minor decisions
> The BJT has to be a serious heat-sinked honker type, right?
> To handle full current at full voltage.
Yes it will be buried inside equipment, maybe even running
unloaded 24/7....TIP36C, heatsinks, fan, over-T switch, etc.