RST Engineering wrote:

wrote in message
ups.com...

Trouble was, the thing was oscillating when at mid brightness
positions. Too much
capacitance on the output. A known problem with emitter followers.

Horsefeathers. Emitter followers have less than unity voltage gain and are
stable as rocks. And how does a resistive LED load become capacitive?
Difficult to imagine.

True for a real emitter follower, however if you have an N-stage
darlington with N=3, it can oscillate.

This was the subject of an IEEE Transactions article in the early 80's
and a source of great embarrassment for an engineer I worked with that
didn't read the article until after putting the design in production.

snip

--
Jim Pennino

Remove .spam.sux to reply.