[R-390] Power Supply, Capacitors, and Dead Horses

[David Wise]

> From: Scott, Barry (Clyde B) [mailto:cbscott@ingr.com]
> 
> With a single cap across the rectifier, when power is 
> applied, isn't the current demand on the transformer and 
> rectifier components nearly infinite?  Is this a potential 
> problem?  Should there be some kind of current-limiting 
> resistor (or other component) in series with the cap?

At the instant of turn-on, if it happens at a point other
than the AC mains zero-crossing, there will be a current spike
limited only by impedance.  During steady-state operation,
the peak ripple current is limited not only by impedance
but by the fact that the voltage is not changing instantaneously.
I = C * dV/dt.  For 120VAC, the waveform is described by
V(t) = 170 * cos(377*t) so dV/dt = -64090 * sin(t), so
the peak rate of change is about 64V/mS.  I'm doing this from
memory, so take it for what you paid for it.

Bet you thought I wandered off.  No, I'm just still
messing around with VFO temperature compensation.
I'll do a fresh post for that.

Regards,
Dave Wise