Re: minimum supply voltage


Jerry Gaffke
 

The board is designed to operate at 12v.
I doubt it will work very well at 6v.

That said, in answer to your question, an LM2940-5 has a lower dropout voltage than the LM7805:
  http://www.ti.com/lit/ds/symlink/lm2940c.pdf
  http://www.ti.com/lit/ds/symlink/lm340.pdf

The "Dropout Voltage" at the bottom of page 5 of the LM2940c datasheet says worst case at 1 Amp is 1 Volt.
But the Raduino pulls far less than 1 Amp, likely well under a half volt.  So would work with 5.5v going in.

Near the bottom of page 6 of the second datasheet above (covers both LM340 and LM7805)
it says the "Dropout Voltage" is "typically" 2 volts at 1 Amp, they don't give a worst case.
Will probably be less than 2v since the Raduino is not pulling much current, but you'd be on very
shaky ground if trying to feed it only 6v.

Jerry, KE7ER


On Thu, Apr 26, 2018 at 09:35 am, vajra guru wrote:
Have received my uBITx but haven't started assembling yet... I was thinking along similar lines, using 6V to power the board, and using 24V for the PA... Does it make sense to change out the 7805 voltage regulator for something different to make this work? Thx, Calvin VE3EIT

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