On 28 Sep 97 at 23:00, Wendell Wyly wrote:

>  I built the Transformerless Power Supply in Microchip application
>  note
> TB008 for an application that requires more than 40, but less than
> 80 ma at 5 volts directly from the ac power line.  The circuit is
> simple with a 47 ohm series resistor in series with a 1uf/250 volt
> electrolitic that is in parallel with a 1 meg resistor.  Then one
> 1N4005 diode conducts on the positive half cycles to the positive
> side of the 330 uf filter capacitor and the other 1N4005 diode
> conducts on the negative half cycles to the negative side of the 330
> uf filter capacitor.  So far, I cannot get over about 3 volts out
> and at 115 volts the 47 ohm series resistor burns up.  I used a
> electrolytic for the 1 uf/250 volt, but will try a back to back pair
> to get a non polarized one to try next.

If I'm visualising it right, the 1uf capacitor goes to active, the
47R resistor is connected to other end of 1uf, and the other end of
47R is connected to neutral? (with the rectifier gnd connected to
neutral)  According to my sums, this will give about 2.8 volts.
Not sure about resistor burning - but there's no way I'd use
electro's back-to-back like that.  Try those mains rated
polypropylene caps - they are available in those kind of values.

>
> Does anyone have a transformeless power supply that they have used
> successfully they would share with me.  I need one for 12 volts at
> 20 ma and another for 5 volts at about 60 - 80 ma.

Why transformerless?  You're making the circuit harder to interface
to.
MikeS
<mikesmith_ozNOSP*M.relaymail.net>
(remove the you know what before replying)