Suppose a particular ADC has an input voltage range of 5 volts to -5 volts, and therefore is suitable for digitizing AC input signals. A technician wants to use this ADC to digitize AC line voltage (120 volts RMS), and builds the following conditioning circuit to safely connect the ADC to the AC line:

Unfortunately, this ADC is not able to fully sample the AC waveform when tested. It overflows and underflows at the waveforms peaks, as though the input waveform is too large (outside of the 5/-5 volt ADC chip range). The technician re-checks his calculations, but still thinks the voltage division ratio provided by the potential transformer and resistor network should be sufficient for this task.



What is wrong with this circuit? Why does it over-range at the waveform peaks instead of sampling the 120 volt waveform with range to spare? Then, once having identified the problem, recommend a solution to fix the problem.