Re: Very low power, power supply

From: Ken Smith (kensmith_at_green.rahul.net)
Date: 03/17/05 

Date: Thu, 17 Mar 2005 15:12:28 +0000 (UTC)

In article <gU3dD2CxLWOCFwGE@jmwa.demon.co.uk>,
John Woodgate <noone@yuk.yuk> wrote:
>I read in sci.electronics.design that Paul Burke <paul@scazon.com> wrote
>(in <39t14hF4mtp4kU1@individual.net>) about 'Very low power, power
>supply', on Thu, 17 Mar 2005:
>>Don Pearce wrote:
>>
>>> You don't need a power supply. Put all the LEDs in series with each
>>> other, and with a 5.6k resistor. Get a resistor with a power rating of
>>> about 5 watts.
>>
>>Or a 250Vdc/160Vac 0.47uF cap. (assuming 60Hz) (about 50p from Farnell),
>>then it doesn't get warm.
>
>You need some resistance in series to prevent the inrush current zapping
>the LEDs and/or the cap. For 120 V mains, 470 ohms 0.5 W may be enough.

Also: Make 2 banks of series out of the LEDs. Hook the two banks in
reverse parallel.

   ----/\/\/---!!-----+------------
                      ! !
                     --- V
                      ^ ---
                      ! !
                     --- V
                      ^ ---
                      ! !
                     --- V
                      ^ ---
                      ! !
  --------------------+-----------

This way, the current has a path for both directions.
                         

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