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Theory Of Operation 65
OV Circuit
The OV circuit consists of a comparator that compares the output voltage of the module with an overvoltage reference
signal and shuts down the output when the output of the supply exceeds the overvoltage reference level.
The microprocessor generates the overvoltage reference by putting out a pulse-width modulated signal that is filtered to
produce a 0 to 4 volts reference (OVREF). This reference is proportional to an overvoltage setting of about 0 to 110% of
full scale output and is applied to the + input of the overvoltage comparator.
The output of the supply goes to a voltage divider which steps down the output to a proportional voltage that also ranges
from 0 to 4 volts. This signal is applied to the negative input of the overvoltage comparator. When the voltage at the
negative input exceeds the voltage at the positive input, the output of the comparator changes state, informing the
microprocessor that an overvoltage condition has occurred. The microprocessor then turns off the pulse-width modulators,
which turns off the FETs.