Re: Using Batteries For Odd Voltages
From: Fritz Schlunder (me_at_privacy.net)
Date: 03/26/05
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Date: Sat, 26 Mar 2005 03:38:09 -0700
"phaeton" <blahbleh666@hotmail.com> wrote in message
news:1111787776.848585.3330@f14g2000cwb.googlegroups.com...
> Robert- That amp design looks interesting too! I actually just
> ordered a bunch of TDA2002 (replacement for the LM383) and some LM386s
> from Jameco. Futurlec is awesome but they take forever to ship. The
> LM386 is typically 1/2W, and the LM383 amp is 8W. My tube amp is
> switchable between 5W and 15W.
The TDA2002 has a quiescent current draw (current draw when powered, but
with the output unloaded) of typically 45mA. Add to that maybe say 20mA for
the required current for producing your audio output and that yields a
typical power consumption of say 65mA.
Standard 9V alkaline batteries have a rated capacity of around 600mAh, so
expect battery life of something vaguely around ten hours. Although the
TDA2002 expects a supply voltage of 18V (or two 9V batteries in series), it
will probably operate acceptably with much lower voltage (since you don't
need 8W output capability). Nevertheless if you use two 9V batteries, the
operating cost could be quite significant. The TDA2002 is massive overkill
for driving headphones. When operating from 18V it would probably be very
easy to configure the TDA2002 to produce way too much power which will end
up burning out your headphones and/or eardrums.
The LM386 is a much more suitable part for your application. It operates
from lower voltage, so a single 9V battery would supply it just fine. The
quiescent current draw is typically around 4mA, so expect dramatically
better battery life (and you only need one to begin with). As it is the
LM386 is still a fair amount more powerful than you actually need to drive a
set of headphones, however it should do just fine. As an added bonus the
LM386 is available in a DIP8 package, whereas those TDA2002 devices come in
what appears to be a relatively cumbersome TO-220-5 package. Five legged
TO-220 parts don't fit properly in a solderless breadboard, while the DIP8
fits nicely. I highly recommend playing with your circuits on a solderless
breadboard.
Standard headphone rail to rail input and output amplifiers can operate from
as low as 3V or less and still yield adequate volume for use with
headphones. A more advanced design running from two AA or AAA batteries
could be built from a part such as the TPA6100A2.
http://focus.ti.com/lit/ds/symlink/tpa6100a2.pdf
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