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Old 03-21-2011, 07:34 PM   #11 (permalink)
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Originally Posted by bobski View Post
Sounds safe. :/
Maybe if you use high value resistors for your divider. Low values might pass enough current to out-feed the power regulator. If the regulator can basically run backwards, that might not be a problem. If it can't, you'll end up with greater than 5V as VCC.
Also, the forward bias voltage of the diode would mean the input hits 5.7 volts (or so, depending on the diode) before it starts clamping down.
Low resistor divider values would be mistake - they would load your source and you might not get an accurate reading. And circuits that run on 5.0V generally have absolute maximums well above 6V, so a diode drop above 5.0V is not a big concern. If you could handle the leakage current, Shottky diodes have very low drops, they might be a good option.

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