I THINK you have two questions:

1. You want to drop the 400VAC supply down to
5V to run the PIC12F675.

2. You want to switch the power to the heater or
fan that draws 400V@4A.

If that is the case:

1. The easiest way is to get a transformer that will reduce
400V to 10VAC, then you can build a simply AC to DC supply
and regulate it with a 78L05.

You CAN directly drop it using a capacitor, but it is dangerous
to work with, especially if none of the main AC legs are neutral
(usually the case with 400-440VAC). The thermistor, for example,
might be 400V above safety ground.

2. The easiest way is to use a TRIAC with a zero-crossing optical
switch. Some people (CRYDOM) make these ready to use, with 3V DC input and
capable of switching 600VAC @ 20A or so.

--Bob

At 10:28 AM 12/3/2003, you wrote:
>Hello!
>
>I want to use a PIC 12F675 to compare and
>switch with in a temperature regulator circuit.
>My problem is how I have to handle the high
>voltage and current 400/4 A ~ .
>It=B4s possible to drop this to a supply voltage
>+5V=3D with any components without to cause
>to much heat.
>Can I use a triac to switch the phase on/off
>with the PIC?
>
>Will be grateful for any kinds of suggestions.
>
>Regards
>=C5keN
>
>--
>http://www.piclist.com hint: PICList Posts must start with ONE topic:
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--------------
Bob Axtell
PIC Hardware & Firmware Dev
Tucson, AZ
1-520-219-2363
"I lose some on each sale but make it up in volume."

--
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