piclist 2004\06\30\100509a >
Thread: Driving ATtiny11 with 9v battery
picon face BY : Michael Rigby-Jones email (remove spam text)

>-----Original Message-----
>From: Mr MCU [.....mikepEraseMEspam@spam@SGI.NET]
>Sent: 30 June 2004 13:48
>To: spamBeGonePICLISTTakeThisOuTspam@spam@MITVMA.MIT.EDU
>Subject: Re: [AVR:] Driving ATtiny11 with 9v battery
>Well not really - regulation is not needed.  The additional
>diode supplies the reverse polarity protection, and since it
>is not a shunt regulator, there is NO power loss if you put
>the micro into sleep mode - just what the micro would draw.
>This method is much more efficient and will handle varying
>loads without trouble.  To do so with a shunt regulator, you
>will waste most of your power heating up a series resistor.
>If you want that, you can use the shunt circuit as a hand warmer too!
>- Mike

It won't handle varying loads very well, a zener diodes have quite a high
dynamic resistance, especialy low voltage ones. (AKA a "soft knee").

A shunt regulator does not have to be grossly ineffecient.  If properly
designed, and the ciruit it's supplying draws a relatively constant voltage,
the current through the shunt should be quite small.

Neither circuit is good for a micropower design that may have a relatively
wide supply current range.  A micropower linear or switched regulator is the
only decent solution in this case.



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