Electronics > Beginners

Measure reversible voltage without PD drop?

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David Hess:
If you have a second ADC channel, then add a second divider in parallel with the first divider which goes to the positive supply voltage or reference instead of ground.  Now one ADC channel reads positive voltage from ground and the second ADC channel measures negative voltage from the positive supply or reference.

ledtester:
Differential ADCs can measure negative voltages.

coppice:

--- Quote from: ledtester on August 10, 2019, 02:28:07 pm ---Differential ADCs can measure negative voltages.

--- End quote ---
Differential ADCs can normally measure negative differences, but many cannot tolerate either leg falling below ground.

David Hess:

--- Quote from: coppice on August 10, 2019, 02:41:51 pm ---
--- Quote from: ledtester on August 10, 2019, 02:28:07 pm ---Differential ADCs can measure negative voltages.
--- End quote ---

Differential ADCs can normally measure negative differences, but many cannot tolerate either leg falling below ground.
--- End quote ---

Some ADCs can measure negative voltages directly while operating only on a positive supply but few if any differential ADCs can operate this way because of input common mode limits.

coppice:

--- Quote from: David Hess on August 10, 2019, 03:49:12 pm ---Some ADCs can measure negative voltages directly while operating only on a positive supply but few if any differential ADCs can operate this way because of input common mode limits.

--- End quote ---
There are a number of ADCs designed specifically to interface to current shunts, which run from a single rail but allow the ADC  input pins to go slightly below ground. Typically 0.1V, which is enough to allow a well laid out shunt circuit to function properly. Most electrical energy measurement chips have a front end like this.

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