A printer apparatus includes a photoreceptor, a magnetic roll, an electrode, a current source coupled to the electrode, the current source having a signal generator coupled to an input winding of a transformer that exhibits a parasitic capacitance; and a current measurement circuit. The current measurement circuit includes a simulation capacitor having a capacitance proportional to the parasitic capacitance, the simulation capacitor having a first electrode coupled to a hot terminal of the output winding of the transformer and a second electrode coupled to a first node, a second sense resistor coupled between the first node and ground so current flowing through the simulation capacitor flows through the second sense resistor, a first sense resistor coupled to a second node, and a differential amplifier having an inverting input coupled to the first node and a non-inverting input coupled to the second node.