Solon Wrote:


> Engineers:
>
> For a project based on PIC, How it can be feed from a source of 110
> V AC 60 Hz without using a transformer?
>
> Thanks in advance

Use a big, ugly, high power dropping resistor and a half wave diode.
As dumb as a post, this is the cheapest simplest power supply
available.  Also one of the worst performing.  PIC's work fine on it.


I do this all the time.  Several other folks have noted some problems
- high power dissipation, and danger of people coming in contact with
the AC line.  These things must be in an insulated case, or a
grounded enclosure.

I've used a half wave rectirfier - dropping resistor - capacitor
power supply in several appliances.  Someone suggested not using a
zener diode - that's a bad idea.  Zeners are neccesary.  The AC power
line is not very well regulated and fulla spikes.  A zener will do a
little toward mitigating spikes (but not much!).

You'll get lots better ripple and regulation if you drop in two steps
- first go from half wave AC to 24 volts, then to 5 volts.  I often
need 24 volts to power a relay anyway, so this works well.  In my
designs the 24 volt line goes to 40 or 50 volts when the relay is
off, so use a higher voltage capacitor.

A better design, still cheap, is to use a metallized polyester film
capacitor of about .68 to 1.5 mfd, followed by a full wave bridge and
a much smaller, lower power dropping resistor.  This avoids all that
heat and the expensive power resistor.  It won't work with a half
wave bridge.


Best Regards,

Lawrence Lile