What ist the best way to reduce Vin to 5.5V when using 4 Alkaline Batteries?

[tvetter1976]

I would like to use 4 Alkaline Batteries to power a Fipy through its Vin pin. I am wondering what is the best way to keep battery voltage below 5.5V? Any suggestions?

[kjm]

stick a diode in series, 4x1.5-0.6=5.4v

[robert-hh]

@kjm Fresh Alkalines are at 1.6V. But since the maximum rating of the LM3281 regulator is 6V, that would still be within the limit. The good thing about the diode is, that it also protects against wrong polarity. On the downside you will have that voltage drop too, when the batteries are exhausted.
A more elegant solution is to add a up/down regulator in between. Pololu has a nice selection of such regulators. My personal favorite is the S7V8A (adjustable), which deliver the output voltage of your choice with input voltages between 2.7 and 11.8 V. it does both up and down conversion.
There are fixed voltage versions of that module too (5V and 3.3V).
This is a little bit of overkill, since the built-in regulator is also present. But if you lower the input voltage below 3.4V, the built-in regulator switches to bypass mode.

[tvetter1976]

@robert-hh
Thanks for the suggestions. Also quiescent current seems to be quite low. Data sheet says 50 uA. This regulator will add a lot of flexibility regarding different power sources.

[robert-hh]

@tvetter1976 The shutdown current of 50µA is set by a 100k resistor on the board. If you replace that by a higher value, the shutdown current will be lower.
Replacing may be hard. But you can take it off and connect an resistor between Vin and EN externally.

[tvetter1976]

Actually, I don't want to shut down the device via En pin. But its seems that the power consumtion is also quite low, when Iout is low(during deep sleep). I will test this device.