I have a 5V hobby circuit that will be externally powered from a wall wart, with way less than 1 amp. For full flexibility, I'm thinking of using a simple LM7805 regulator - but that has a 7V minimum. Since 5V supplies are becoming ubiquitous, I'd like to allow that too - but then I'd need to bypass the regulator.
What would be the impact / effect / damage if I simply provided a jumper that shorted the regulator's input to the output for semi-permanent use with a 5V supply? Use a 9-12V supply: remove the jumper. Use a 5V supply: add the jumper. I'd leave the input and output capacitors to do their thing: it won't harm the 5V case.
Would the regulator be at minimum consumption because the output was already at 5V? Or would it struggle at full load with the less-than 7V input - or worse, short output to ground?