Ned Seith wrote:
>
> Vasile,
>
> Your series capacitance voltage divider circuit has certainly received
> criticism.
> So I hope that I'm not kicking a dead horse.
> While a transformer would definitely be the safest approach for the typical
> hobbyist, I'm glad to see that there is someone who is willing to be more
> intimate with the electrons.
> The concept and configuration of your series capacitance voltage divider
> circuit is fine.
> I have designed industrial applications which have provided several amps of
> current at low voltages from 220 Vac and 277 Vac mains using a series
> capacitor. Industrial equipment and machines frequently use a series
> capacitor instead of a transformer for providing lower voltages.
> A few points:
> I would not add a resistor in series with the capacitor (C9) as this will
> vary the effective capacitance reactance which is providing the desirable
> voltage drop and will also dissipate heat.
> I would not add a resistor in parallel to the capacitor (C9) as this will
> vary the effective capacitance reactance which is providing the desirable
> voltage drop. This resistor would also dissipate heat.
> I would not be too concerned with the capacitor (C9) remaining charged as
> the approximate 6 mA current consumption from the voltage regulator will
> quickly discharge the capacitor. UL and TUV stipulate that the voltage
> potential on an unplugged power cord must diminish to 1/3 of the mains
> voltage within 10 seconds. So, If I wanted to increase the rate at which
> the capacitor discharges, I would place a resistor in parallel to (C5) on
> the low voltage side of the circuit.
> I would want a 1/4 amp fuse between the 220 Vac main and the series
> capacitor (C9).
> I would also want the series capacitor (C9) rated for 800 V to 1000 V.
> If the series capacitor (C9) is getting warm at all, then the voltage
> rating should be increased.
> I would want the diode rectifiers voltage rating increased to 800 V to 1000
> V (1N4006, 1N4007) to assure that there is not any brief reverse conduction
> during the delay of the capacitors charge cycle.
> Otherwise, looks good to me.
> Just a few comments from an old engineer.
>
> Sincerely,
> Ned Seith


Hi Ned, I find these type of supplies very interesting,
and have been playing with them for many years. Since
before they were legal. :o)

I'm really interested in your "several amps" applications,
can you give any more info? Size/cost of the capacitors?
Or custom built capacitors? I've made some medium supplies
with the 630v poly types, pref the blue milspec ones.
They are still going good now after many years. Never
been brave enough to sell one though, just for personal
use in my workshop.

Do you have any specific tricks for handling current
under-loads or spike conditions? Regulation? Sorry to fire
questions at you. :o)
-Roman

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