Driving a 7805 or how else to get +5VDC reg (was Re: My first good find!!!) - test-drb@ccmp.vtda.org

6 Dec 2002

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 From: ard(a)p850ug1.demon.co.uk

  How can I take +6VDC of battery power and get
+5VDC regulated power
 from it?  If it matters, the currents involved will be under 1000mA,
 but probably over 200mA. 
Take a look at 'low dropout regulators'. National Semiconductor make 
(made?) them -- LM2940 series I think. They will work down to about 0.6V 
difference between input and output (so for a 5V regulator, you need at 
least 5.6V in). These are similar to the 7805 -- 3 terminals, and you 
need to put a couple of decoupling caps near the chip.

That probably won't let you use all the capacity of your '6V' battery, 
but it should let you use some of it.

Incidentally, I assuem the Zip drive produced 5V internally from this 
battery pack. Any ideas what it used?

-tony

Hi
 He didn't say what kind of batteries he was using
to provide 6V. Different batteries have different
discharge voltages. Even though a lead-acid battery
is fully discharged at 5V. Using it until 5.5V and
then recharging is a good idea for longer life.
 Even if the regulator drops below 5V on the output,
most circuits will work down to 4.8V someplace
or lower. A low dropout regulator, as you suggest,
might still be the best option.
Dwight