In one of my products I use a TDA7052 amplifier in
essentially the same way you are describing here. I use a
PNP transistor in the amplifier positive rail supply to turn
it on when required. In low voltage applications you want a
transistor with low saturation voltage and high current gain
(beta). Zetex make some TO92 transistors (and another
similar package) with extremely high current ratings and
high betas at high current for this size package. You can
get Zetex transistors via Farnell - not as cheap as most
anywhere else but available anywhere. The 25 volt Vce ZTX749
has a beta of 100 at 1000ma and a Vsat of 0.5 volt at 2A.
(Farnell 432-970). The 15 volt ZTX788b (Farnell part number
707-790) has a beta of 300 (!) and saturation of 0.45 volts
at 2A

Then again, as others have suggested, you could use a P
channel FET. Beta now irrelevant but watch Rdson. A P
channel FET will be placed in the positive amplifier rail so
the amp is at ground when off. N channel FETS are a little
cheaper and a little more common but will be in the
amplifier ground lead so it floats to + supply when off.
This will not be a problem if you allow for it in your
design.

I have no connection with Farnell or Zetex (except that I
like their products :-) ).

From: Rick "The Notes Guy" Dickinson <rtd@NOTESGUY.COM>
To: PICLIST@MITVMA.MIT.EDU <PICLIST@MITVMA.MIT.EDU>
Date: Wednesday, 1 April 1998 12:33
Subject: Re: powersave during PIC sleep


On Tue, 31 Mar 1998 15:10:20 -0800, you wrote:

>I have a PIC controlled circuit that also includes an LM386
audio
>amplifier. When I put the PIC into sleep mode, I'd like to
eliminate the
>power drain of the amp. I can use a relay to do this but I
figure that
>there is probably some very clean solid state way to
accomplish this.
>Any ideas?

John,

Try powering the audio amp through a very low Rds(on)
N-channel
MOSFET.  Use a PIC pin to bias the gate high when you want
it on, and
make the PIC pin an input and use a 1 Meg resistor to ground
to turn
off the MOSFET when you want the amp turned off.

- Rick
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