Russell McMahon <apptech@PARADISE.NET.NZ> wrote:
> National typically recommend a 240r resistor from Vout to Vref giving
> 1.2/240 = 5mA "regulation" current. A change of 5uA in the bias current
> mentioned above will lead to a 5uA/5mA = 0.1% change in the regulated
> voltage. This order of effect is probably fairly acceptable in this class of
> regulator.

There's a second reason for passing 5 mA through the feedback divider:
Since the LM317 dumps (nearly) all of its operating current to the OUT pin,
it has a minimum load requirement of about 5 mA worst case (2-3 mA typical)
in order to maintain regulation. Putting this current through the divider
means that you don't need a separate load to drain the quiescent current.

-- Dave Tweed

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