27 Apr
2011
27 Apr
'11
8:24 p.m.
On 4/26/11 9:41 PM, Bob Bradlee wrote:
I promise you that I'm not trying to be either dense or argumentative
here, but we're just talking about (assuming we're talking about the
same thing) an electrically-controlled switch in series with a power
input with a capacitor to ground on the other side, and a resistive
voltage divider after the capacitor that generates a PWM control voltage
to the oscillator that drives the switch. Nowhere in this arrangement
is there any requirement for a load.
Based on your comments, though, I'm starting to suspect that we're
talking about two completely different circuit topologies. Why don't
you (if you're so inclined and have a moment) describe in more detail
the topology you're talking about, assuming I'm correct that it's
something different.
-Dave
--
Dave McGuire
Port Charlotte, FL
I'd
like to see the math on that. I have a pretty good grasp of
switching regulators; I've done a lot with them in various designs.
Admittedly only very small ones for portable equipment though, in the
sub-1A range, but the concepts are the same. PWM a transistor between
saturation and cutoff, smooth it out with a capacitor, sample the output
into an error amplifier to control the PWM duty cycle. No load there,
unless you're talking about leakage across the PCB and such.
Ohm's law comes unglued when R goes to infinity.
Capacitive reactance comes into play, maybe thats enough load?
But an RC circuit with infinate R will always seek the peek voltage of the pulse,
no matter the freq untill there is some load to regulate around.