A medium voltage adjustable frequency drive includes an input isolation transformer having a three-phase input and a three-phase output, a converter having a three-phase input electrically connected to the three-phase output of the input isolation transformer and an output providing a direct current bus, an inverter having an input electrically connected to the output of the converter and a three-phase output, and a pre-charge circuit. The pre-charge circuit includes a ferro-resonant transformer circuit having a primary winding structured to input a low voltage and a secondary winding structured to output a medium voltage and provide a constant current source. The pre-charge circuit also includes a medium voltage diode bridge having an input receiving the medium voltage from the secondary winding of the ferro-resonant transformer circuit and an output structured to provide the constant current source to the direct current bus.