>> Bernd Grunwald wrote:
>> >
>> > Is there any efficient and not too expensive way to generate the ~5V for
>> > the PIC and some other devices out of the 230V AC Voltage from the net?
> Using
>>  a
>> > 7805 and other linear regulators is IMHO much too inefficient ...
>
>I know you can get some very nifty little ic's that do just that with
>no transformer etc. I know Maplin used to stock something like
>that...If you can wait till tomorrow, I'll see if I can get more
>details for you.
>

The series resistor/zener across the mains is hideously inefficient - and
if you want more than a few mA you need a very large heat-sinked resistor.
(I can provide circuit and design details if anyone wants.)

There is an IC HAR2405 from Harris Semiconductor that functions as a
direct-off-line 5V regulator. It uses a switching circuit to charge an
external reservoir capacitor to (Vout + a few volts) and an on-chip series
regulator to give a smooth output. You can add an external resistor to
adjust the output.

The Harris version supplies up to 50mA. There is also a Lucent (formerly
AT&T?) version that provides up to 100mA. I couldn't find the datasheet on
the web for the Lucent part, but I have the data-sheet for the Harris
(which I can eMail) so I can add:

        It needs external components (especially at higher current draws)
to current-limit the reservoir charging circuit

        It also needs a large series resistor (although not as big as the
zener/resistor method)

I think you should be able to build a direct off-mains supply using a
similar principle with an SCR as the switching element, and a
three-terminal micropower regulator (or even a 78L05). You could even use
the PIC to switch the gate of the SCR - if you can think of a way to start
the circuit up (and if the PIC locks up with the gate energised....BANG!!)

Oh yes... and with all these methods, remember that you have no mains
isolation, and one failed resistor results in 230v across the
pic/components/user/etc.