On Sun, 4 Oct 1998 12:32:18 +1000 "Paul B. Webster VK2BZC"
<paulb@midcoast.com.au> writes:
>Seth Fischer wrote:
>
>> Is there a better or more efficient way of obtaining 5V d.c. with a
>> small compact circuit?
>
>  Yes, use a series capacitor (mains rated) with a 1/8W (fusible)
>resistor in series and a bridge rectifier if the application is not
>linked to one mains terminal, or a "voltage doubler"-style pair of
>rectifiers if it is.
>
>  Note that this arrangement will not allow you to detect the mains
>zero-crossing; if you want that you can use a low-power resistor *as
>well*.
>
>  You tell me how much current you need, what ripple you will
>tolerate,
>and I'll give you the (rough) values.



        Maxim has a shunt regulator chip just for this purpose.  Their chip
includes the diodes (I think there are two part numbers, one half wave,
the other bridge), a zener shunt regulator, and perhaps a series linear
regulator.  Check out the Maxim web site.


Harold


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