John Larkin wrote:
On Thu, 18 Nov 2004 10:09:19 GMT, "Kevin Aylward"
wrote:


It's actually not a bad idea to have an opamp per output transistor,
if you do it right, which this guy clearly hasn't. I make a power
amp that uses 32 300-watt fets in the output (16 p-ch, 16 n-ch,
+-200 volt rails) and do just that.

Bloody hell. That's some amp, probably about 20KW out. This will
certainly kick the **** out of you at 50 Hz.

How did you get the opamp voltage rating, or was it a discrete one?


It's a transconductance amp, so the fet sources are at the rails
(through current-sense resistors) and the drains are the output. So
the gate-drive fets work on the +-200 power supply rails (with small
floating local supplies) and only need to swing enough to drive the
gates.

I have recently been playing with both source out and drain out
configurations for that super duper amp I mentioned in one post. One
issue with the drain out is x-over spikes. I was getting 100A thick
x-over spikes in the drain output, verses essentially, none in the
source output. The gates tied together prevents the spike when slewing.
So, worth noting if you want the utmost in speed without frying the
devices in a linear amp.



Kevin Aylward

http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
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