Amplifier transistor matching?

My sincere apologies.

MrT.

By the way, while many op-amp circuits published specify a supply coltage of

+- 15 volts, or +- 9 volts, many circuit designs will work with +- 3 volts, which is easily achieved with two pairs of AA cells.

Also, many circuits will take more power from one side of the power supply than the other; so if you're using batteries to provide a +- power supply, it's worth testing them to see if only half need replacing.

Tim

transistor

cost

coltage of

volts,

supply

supply,

I just had to bash the hell out of a mini Maglite to get the innermost AA cell out of it. It had started to leak and the corrosion on the end was just enough to prevent it from coming out. I had to smakc it against a concrete floor, with a few layers of paper towel on it to give just a small amount of give.

Reason for saying this is that it'e really poor advice to give to reuse half spent batteries. Works really great if the equipment takes a single cell. But if you put a half spent battery in series with a new one, it's likely that the half spent one will be discharged to zero and beyond, leaking in the process. I think if I had two of four cells run down faster than the other two, I would swap the sets halfway thru their life. Better yet, get a piece of equipment that's not so poorly designed that it runs down one set faster than the other.

Measuring and matching used batteries is not that difficult, if you need to use them in pairs. Also, some sources for used batteries are applications where they were originally used in pairs. I collect and cull AA's from RF mics all the time with little ill-effect. Sometimes I come in from a gig with my pockets literally bulging with AA's. I usually just match them by open-circuit voltage and put them in different piles matched within a 0.1 or .05 volts of one another. Anything below 1.4 volts, I usually either relegate to the kids' CD/Mp3 players or discard.

It saves me hundred$ a year, at least.

jak

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

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

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?

2200mAh

provides -3v.

the

every

pairs of

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.

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.

This one is already assembled.

It doesn't have to be this fancy.

2200mAh

provides -3v.

the

every

pairs of

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.