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I'm looking at 5V LM7805 regulators data sheets to use with my MCU and most versions of the LM7805 seem to have a minimum input voltage from 7-8V, but looking at the $50 robot here, it is using 6.0V Nimh batteries with the LM7805. Why can he use 6.0V when the minimum for LM7805 is labelled at 7-8V?
I've never used diodes in the past with voltage regulators, but is it a good idea to put them in for protection? I have some 1N5818 30V/1A Schottky diodes, would I shove one in series with the input voltage and another one with the output voltage?
The best (as in minimal loss) way to apply a diode for reverse voltage protection is to use a fuse inline with the positive line and then the diode over the supply with the anode to ground and cathode to the positive line ("reverse biased"). with correct polarity nothing happens, but if you reverse the polarity, the diode conducts, shorting the supply and blowing the fuse (the fuse keep the reverse voltage from reaching dangerous levels (for the downstream circuitry) and the fuse protects the diode from shorting out permanently.
A different use of diodes with integrated voltage regulator circuits is for protecting the regulator against the backwards discharge of eg. large filter capacitors on the output side, while the input has gone to 0V, but that's not your everyday circuit.