Circuit power supply question

[nemo000111]

Hi All,

This is my first project, and I could use a little help/advise from those with some more knowledge and wisdom than I have.  Here's what I came up with for a psu for it.  Not sure if it's the most efficient want of doing it or not.  It's a battery powered (2x AA batteries) circuit.  In it will be an xbee, attiny 84, and a few switches and sensors.  Then entire circuit is going to run at 3.3v.  It will need to run several months (ideally 6-8) without a battery change.  Meaning each component needs to have as little overhead as possible.  Most of the components after the psu either have near 0 constant current draw or are toggled on and off as needed via software.  The way the P-channel mosfet is hooked up should give me reverse voltage protection (with a drtop lower than that of a standalone diode if I looked at the right numbers) and the MCP1640 does the dc step-up conversion.  I can't figure out a cheap (money and electrically) way of doing over-voltage protection on the battery side (nothing over 5v).  Any advice would be helpful, espically if there's a better way to do the reverse voltage protection with less constant current loss.  Thanks again.

[user_ivo]

  Have you tried connect the circuit with reverse polarity? Since the chip has a EN(enable) pin probably the chip will not operate and you will not need the Mosfet,  if there isn´t any problem for you in burn the MCP1640 , i would try to connect the chip with reverse voltage and see what would happen . Regarding the over voltage protection, make one without get a increase of consuption, nothing come to my mind, at the moment  the most problem is you have a tradeoff between protection and consuption.