Amplifier transistor matching?

[Mr.T]

"Kristian Ukkonen" <kristian.ukkonen@iki.fi> wrote in message
news:kkuEe.168$Dl5.67@read3.inet.fi...

Tim Martin wrote:
"Watson A.Name - "Watt Sun, the Dark Remover""
Better yet, get a piece of equipment that's not so poorly
designed that it runs down one set faster than the other.

OK. Suppose we have a circuit that draws 20 milliamps at -3v, and 220
milliamps at +3 volts. And suppose our power supply is four 1.5v
2200mAh
batteries, wired so one pair provides +3v, and the other pair
provides -3v.

Is it possible to redesign the power supply to do better than replace
the
+3v pair of batteries every 10 hours, and the -3v pair of batteries
every
110 hours? (So for 110 hours of operation, we'd need to replace 12
pairs of
batteries.)

Make a switching powersupply using 6V input and outputing
two 3V voltages?

Use a latching relay to switch the batteries (3V <> -3V)
every once and a while?

Seems like a lot of extra effort and expense for no net benefit.
If you improve the circuit by converting the 6V to +/- 15V instead,
(assuming that does provide some benefit for the circuit involved) at least
there may be some point to it all.
Otherwise it would probably be easier to provide a battery low indicator for
each pair of cells.

MrT.

 

[Watson A.Name - \"Watt Su]

"Tim Martin" <tim2718281@ntlworld.com> wrote in message
news:3PsEe.5181$YL5.2604@newsfe2-win.ntli.net...

"Watson A.Name - "Watt Sun, the Dark Remover""

Better yet, get a piece of equipment that's not so poorly
designed that it runs down one set faster than the other.

OK. Suppose we have a circuit that draws 20 milliamps at -3v, and 220
milliamps at +3 volts. And suppose our power supply is four 1.5v
2200mAh
batteries, wired so one pair provides +3v, and the other pair
provides -3v.

Is it possible to redesign the power supply to do better than replace
the
+3v pair of batteries every 10 hours, and the -3v pair of batteries
every
110 hours? (So for 110 hours of operation, we'd need to replace 12
pairs of
batteries.)

Tim

I would use a DC-DC converter to get the minus 3V, at 20mA. SHould take
just a 555 and a cap and a couple rectifiers. A V doubler with a zener
seems like it would do the trick.

http://ourworld.compuserve.com/homepages/Bill_Bowden/page10.htm#5volts.g
if
But use a CMOS 555 if the supply is less than 5V. But the CMOS 555 may
not source enough current, I'm not sure how much it can handle.

http://www.mpja.com/productview.asp?product=2308+PS This one is already
assembled.

http://www.build-it-electronics.com/page4.htm It doesn't have to be this
fancy.

http://www.national.com/ms/LB/LB-18.pdf