At 08:48 AM 5/13/98 +0000, Lawrence Lile wrote:
>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
>
>

Maybe try a condensor-divider (in stead of resistors) in comb. ith some
diodes???? Should dissipate a lot less. .

(for replies contact me private, i'm temporarily off the list)
Hans de Vries - H.P.d.Vries@stud.tue.nl
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