On Sep 11, 2:32*pm, "Dave Plowman (News)"
wrote:
I've got a low voltage PWM unit which is controlled by a DC voltage. Can
be used for motor or light control etc.

In this case I want to use it to drive high power LEDs. Which it does just
fine. *

What I want to do is have it ramp up to max when a switch is made, and
ramp down to minimum when it's opened. I've experimented with RC circuits
which do sort of work - but don't give a linear fade in and fade out.
Any clever ideas? Preferably using just one cheap IC that I'll have in my
box...;-)

It would also be nice to arrange things so it takes no current when the
switch is off. Although I can get round this.

There are fairly simple methods using opamps. Eg set one to deliver a
constant current, feed this to a cap on the output. Or set one to
deliver a fixed b drop across an output R, which gives constant i,
etc.

Or more basically, stay with a CR and just use a percentage of the v
scale, making it somewhat more linear.


NT