9V Battery life when used with 5V DC/DC step down converter?

[HankMcSpank]

An alkaline PP3 is rated at about 550maH @9V.

Does this mean if I use a DC/DC step down converter to convert it down to 5V that I'd get something in the order of 850maH out of the same PP3? (I've lobbed a bit off for losses attributed to the DC/DC conversion).

I'm looking to feed a circuit with 5V (which has a PIC onboard - along with some analogue stuff)...but I'm constrained to a PP3 (I'd much rather use AAs!)...just trying to work out the best way forward for maximising battery life.


Also just wondering what the pros/cons are of say a PWM LDO regulator to regulate 9V down to 5V vs a dedicated DC/DC converter?

[Ioannis]

I really want this PP3 battery you have at 550mA!!!

Are you sure you have the correct mA/h figures?

Usually these are in the range 150 to 170mAh.

What requirements has your circuit? (I flow, time to operate before die etc).

I would surely use AA, maybe 3 of them for about 4,5 Volts or 2 of them with a boost regulator.

Ioannis

[ScaleRobotics]

You have to get the energizer bunny type. They are above 600 mah for low current draw. But that is measured going down to 4.8v

[Dave]

Hank, I have used 2 with a boost converter in the past with great success on a DDR Pad remote transmitter. The converter was a MAX1724 boost reg. You should give one a try... 2 aa's are have higher Mah. than a 9 volt. That is what I was going to use originally....

Dave Purola,
N8NTA

[schu4647]

I have never tried this so it may not work. What about a pFET sourcing your regulator. Have your on switch be a button that takes the pFET gate low and turns on your micro. The pFET gate is also tied to a micro IO pin which immediately goes low holding the pFET on. When you have a period of inactivity you make your gate high shutting off the entire board until that button is pressed again.

[schu4647]

I have never tried this so it may not work. What about a pFET sourcing your regulator. Have your on switch be a button that takes the pFET gate low and turns on your micro. The pFET gate is also tied to a micro IO pin which immediately goes low holding the pFET on. When you have a period of inactivity you make your gate high shutting off the entire board until that button is pressed again.

You probably need an NPN with the collector pulled up to the 9V through a 1k. Tie the collector to the gate of the pFET. The base of the transistor will go to the button and to the micro pin. When the button is pushed the base goes high turning it on and pulling the gate low. Your board is now on and your micro pin needs to go high to keep it on. During inactivity you make the pin low. That turns off the NPN which then takes the gate high and turns off your board. I am so brilliant. I think anyway.