How to combine power supplies...

I have 2 small devices that have their own power supplies.  I want to combine the two boards into a single housing/device.

One of the devices uses a 3.7 volt 130mAh battery for power.  The second uses 2 AAA batteries (1.5 volts each).  What would be the best way to use only one power supply to power them both (if that is possible)?

I do understand that using a single power supply would drop the amount of time that the 2 devices could operate as compared to each using its own power supply.  That is acceptable.
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wire_workerConnect With a Mentor Commented:
How large (i.e. physical size) are you prepared for this single power supply to be?  If you were happy to use say 5xAA rechargeable batteries then you would probably get a longer life out of each of the two devices.

Configure the batteries in series to give a total supply range of about 6V when fresh and about 4.5V when flat.  Use two low drop out (LDO) voltage regulators (with minimal associated circuitry) to then supply 3.7V and 3.0V respectively.

If you need more advice re. choosing a LDO vreg. let me know.
cerkseesAuthor Commented:
Would it not be possible to just wire both devices to either the 3.7 volt lithium or the 2 AAA batteries?

I understand that the run time may be considerably less than the devices got when using their own power supplies.
_Connect With a Mentor Commented:
Not without some kind of splitter/regulator.
If you wire them both to the 3.7, you risk toasting one.
If you wire both to the AA batteries, you don't have enough juice to run the other one properly.
Thank you much.    : )
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