AC Cap Dropper DC Power Supply

Well, sure; you could use a JFET with gate shorted to source... as a current regulator (pass element). Or, a regulated DC/DC converter. but, of course, there still has to be some provision for lightning and other surges.

How about a mag amp? ;)

Cheers

Phil Hobbs

Chewing on some authentic Australian licorice, I almost choked ;-) ...Jim Thompson

-- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at

A long,long time ago in a place not so far away I used a transformer made by Sola that had a matched resonant capacitor.

Tom

Will it fit in 1" x 1" ?:-) ...Jim Thompson

Not hardly. And it was heavy too.

Tom

I remember them. Nice scheme if you stand the space/weight. ...Jim Thompson

If your looking for a junk don't care 120V low current supply..

this works on the starting cycle and uses only a portion.. it kinds of semi regulates, it's only good for low current..

I think that was around 5 volts out..

Jamie

-Lasse

Not sure exactly what you are looking for, but if you are using caps to drop voltage I'm guessing this is a "cheap and cheerful"-type application.

I use a super-simple regulator to drop "dead" 9V batteries down to 1.5V to run various low-drain devices like clocks and timers. It's just an NPN (2N3904, etc) with collector from battery, and emitter driving load. Base "reference" is a green LED to ground, with a selected resistor from base to collector. Small enough to wire the whole works onto a 9V battery clip. Lots of variations: More LEDs for higher output voltage, Darlingtons for more sensitivity/higher power, etc.

Forward-biased LEDs have super-sharp knees at low currents, and the parts bins are full of them.

Best regards,

Bob Masta DAQARTA v7.00 Data AcQuisition And Real-Time Analysis

-- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at

Power level? Input range?

RL

That's unfortunate, because a lot of tweaking with nonlinear dielectrics can be done on the lower domestic voltage range. This reduces the effect of varying input voltage and can reduce the brute in the force. Also 800mW is a lot to ask of this technique. An ~ 1uF

Maybe you should mess with a few more numbers, before examining improvements in the technique? Also, be warned that this isn't a circuit you can just slip into a pre-existing device that has other biasing dependencies.

I like the non-simplistic self-oscillating DC-DC stuff. The off-shore demonstrated capability to produce this circuitry for nothing is the only upside. Might as well be happy....

RL

The capacitor must go between the AC line and input to the bridge. It uses the reactance of the capacitor as a dropping resistor.

Nonsense, all it requires is a _changing_ input. ...Jim Thompson

Or a PFC path... that's all I can say right now ;-) ...Jim Thompson

If it's full-wave rectified you can turn a HV part 'off' when the voltage exceeds your desired output voltage and lose the series cap. Your output cap need only be as big as a full-wave rectified low voltage supply would required.

The cap is better with transients most likely, but if it's behind a bunch of electronics anyway, the above might be a good solution.

Best regards, Spehro Pefhany

With appropriate discharge paths. If the cap is before the rectifier, the source can do this, otherwise........

RL

You know, Jim really shocks me, he designs IC's and yet, he has this dilemma

Getting information from him is like pulling teeth.. It would be nice to know the output voltage requirement. We already know the watts (0.8), but at what voltage on the output?

I offered up a bad idea of a design, just like him asking for something that should be trivial on his part.

WHen he said a "Cap dropper" I miss read and gave him a "Crap dropper" or did I?

The circuit I offered up however, works great as a line noise detector. :)

Jamie