Years ago we had threads about the ugly but seemingly simple scheme to get 12V DC at 5mA, etc, with a film capacitor straight to the AC line. We said, gotta have a series resistor to minimize the startup inrush current.
Does anybody recall a specific instance of this scheme being used commercially?
Paul and I are days away from turning in the manuscript on our new x-Chapters book, and I decided to add this and a few other cheap AC-to-DC-power circuits, for entertainment. So I created one with SPICE, 12V at 5mA, only a few parts, cost under $1.50, and the series resistor sized to limit the worst-case inrush (cap with -170V, new line connection at +170V) to 720 mA, with a 470-ohm 2-watt wirewound.
OK, the numbers look bad. Yes the cap current is 90-deg out of phase with the voltage, but not so for the 470-ohm resistor, swallowing up power. The efficiency is less than 5%. Yes I could reduce the 470, but its maximum pulsed instantaneous power (0.2ms) is already 245 W.
Maybe an NTC inrush limiter, but I don't know if the time scales are right.