Mostly it depends on what other than the microcontroller you need to power.

KISS would dictate running straight from the battery without any regulators.
Depending on your circuit, it can often be done.

If you look through the specs of PIC's, you will find that there are a
number of them (especially the ones with L for low-voltage in their part
numbers) that are low enough voltage and tolerant enough of voltage
variations that they will work directly from a battery.

When designing this way, you need to study the discharge voltage
characteristics of the battery chemistry you are planning on, and make sure
that fresh cells won't blow up your circuit, and that the voltage where your
circuits give up is low enough that you can use most of the battery's
available energy.

For instance, we use primary lithium cells (readily available for digital
cameras).  New ones are around 3.2V per cell, and to use up 90% of the
useful energy, you have to take them down to around 2.1V.

One gotcha you need to be aware of is just what does your circuit do when
the battery dies?  The voltage will eventually taper off to the point that
it won't run, but on the way, it may do strange things.  That's why a lot of
newer PIC's have stuff like programmable brown-out detectors.

> -----Original Message-----
> From: John Waters [mailto:john_fm_waters@HOTMAIL.COM]
> Sent: Sunday, July 22, 2001 11:18 AM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: [OT]: How to reduce power consumption for battery operated
> circuits?
>
>
> Hi All,
>
> For a battery operated circuit, we want the power consumption
> to be as low
> as possible, but if the circuit involves a microcontroller,
> we will need a
> voltage regulator like the 78L05 or 7805 to keep the 5V
> stable. Since the
> supply voltage is at least 2V higher than the 5V, part of the
> current will
> be bypassed through the regulator, in other words, the
> regulator "consumes"
> some power even when there is no or little current demanding by the
> microcontroller circuit itself.
>
> Is using the regulator unavoidable? What is the usual methods
> to reduce
> power consumption for a battery operated microcontroller circuit?
>
> Thanks in advance!
>
> John
>
>
>
>
>
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