A method for operating a charge pump that supplies switching current for a plurality of transistors includes a capacitor generating a pumped voltage. A comparator generates a pump control signal for turning on and off charging of the pump capacitor based on a difference between a comparison voltage and a reference voltage. A direct voltage sensor receives a feedback signal reflecting the pumped voltage and generates the comparison voltage in response to the feedback signal. The sensor includes a sensor resistor, a current source configured to drive a sensor current through the sensor resistor, and a differential op-amp that drives the sensor current to cause the voltage drop across the sensor resistor to remain constant as the pumped voltage experiences the voltage drop. The charge pump may include two similar direct voltage sensor controlling positive and negative pumped voltages.