[sdiy] LED current source needed for 'digital' outputs?

Neil Johnson neil.johnson71 at gmail.com
Tue Mar 4 17:07:30 CET 2014


Hi,

Richie wrote:
> I've seen VU meter designs in pro-audio kit where all of the LEDs are
> connected together in series and driven from the supply rails via a constant
> current source.  Current is allowed to pass through the LEDs that we want
> illuminated, and "diverted around" the LEDs that are meant to not be
> illuminated.  The total current drawn from the power supply is therefore
> 20mA regardless of whether all the LEDs are lit, all are extinguished, or
> any combination in between.  That way it doesn't trash the power supply
> rails with switching transients.

I've done similar with little VU meter driver chips and some
low-current LEDs, again fixing the current consumption to 20mA
irrespective of how many LEDs are lit.  For the minimal added cost it
does help to minimise switching noise off the floor.

Neil
--
http://www.njohnson.co.uk



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