Powering a 5v Arduino with 3.3v and using a resistor network for voltage droping

Hello, I am powering an Arduino Pro Mini 5v with a Lipo battery which has a maximum voltage of 4.2v and a minimum of 3.3v. I also need to power an NRF2401n+ with .9v - 3.6v but the voltage from a fully charged lipo is too high. I know I could lower the voltage with a diode, led or a resistor network but I was wondering which of these is most efficient?

Also, wouldn't using a resistor network limit the max current the NRF2401 would use?

Also, I have not seen any problems powering an Arduino pro mini 5v with 3.3v but does this cause any problems or damage the Arduino?

If anyone has any ideas, please let me know :)

Thanks!

5V promini powered with 3.3V is out of spec - Speed Grade diagram in the datasheet shows ~3.8V is needed for 16 MHz operation. None the less, folks do operate them that low and claim to see adequate operation. On other hand, there was a '1284P thread yesterday where serial operations were not okay for a 3.3V powered part & 16 MHz - raising the power solved the serial issues.

I would use a normal diode with ~0.7V drop between the battery and NRF2401n+. Try it with a resistor as a light load, simulating the NRF2401n+ current draw, see how it does.

Either that or get a switching regulator: http://www.pololu.com/category/131/step-down-voltage-regulators Or a really low LDO regulator that can take the 3.7V from a LiPo and make 3.3.

I agree onto using a normal diode to drop ~0.7V without energy consumption (or, better, no appreciable energy drawn).

To measure the voltage at the output you need to put something between the diode and GND, like a 220R resistor, then measure the voltage between the diode output and ground: that is what your nRF24 will get. I'm powering my mini with 4AAA cells and using two diodes in series to drop the voltage before it reaches the nRF24 board: so at no blue smoke.

serg10: Hello, I am powering an Arduino Pro Mini 5v with a Lipo battery which has a maximum voltage of 4.2v and a minimum of 3.3v. I also need to power an NRF2401n+ with .9v - 3.6v but the voltage from a fully charged lipo is too high. I know I could lower the voltage with a diode, led or a resistor network but I was wondering which of these is most efficient?

Neither. Diodes and resistors don't work as power supplies when current draw is variable (eg. NRF2401n+).

Voltage drop across diodes is highly dependent on current. Resistors are just rubbish for power supplies.

A LM317 voltage regulator costs about 30 cents.

Luckily, the load for the way my NRF240 is set up is relatively low and stable so I managed to use a diode to drop the voltage. Thanks for the input guys!

serg10: Luckily, the load for the way my NRF240 is set up is relatively low and stable so I managed to use a diode to drop the voltage. Thanks for the input guys!

Check very carefully.

Every time you switch between send/receive/standby the load will drop from about 14ma to about 1ma.

The voltage could rise a lot during those transitions if you're using a diode (and damage the chip).