Negative Power Input

[nsypid]

What do people usually do when designing circuits with negative voltage input ? for example -48 volts ?. What if a external 5 volts used as digital input signal on these circuits ? How do they make sure they won't be ground reference problem ? for example ground reference for -48 volts and +5 volt is different ?

 

[albbg]

Sorry, but your question is not clear at all. What kind of circuit you are referring to ?

 

[nsypid]

I used buck converter to convert +48 input to +5 (the plus and minus -48V is switched to +48) to power a microcontroller. suppose i want to use digital input of the microcontroller to detect +5V, i suppose there would be some ground reference problem. should i isolate the input or is there another way to convert -48volt to +5volt ?

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i mean the +5 volt i want to detect with microcontroller is from external sources, which have the same reference ground from -48 volts

 

[BradtheRad]

Many IC's are liable to be damaged if you expose their inputs to a voltage outside the supply rails.

For this reason it may be necessary to level-shift a negative voltage up to the positive.

This can be done in various ways. A resistor network is among the simplest.