an active filter for reducing the common mode current in a pulse width modulated drive circuit driving a load , said drive circuit comprising an a - c source , a rectifier connected to said a - c source and producing a rectified output voltage connected to a positive d - c bus and a negative d - c bus , a pwm inverter having input terminals coupled to said positive d - c bus and negative d - c bus and having a controlled a - c output , a load driven by said a - c output of said pwm inverter , a ground wire extending from said load , and a current sensor for measuring the common mode current in said drive circuit in said ground wire , said current sensor producing an output current related to said common mode current , said active filter comprising a first and second mosfet transistor , each having first and second main electrodes and a control electrode , and an amplifier driving a respective one of the transistors ; said first electrode of said first and second transistor coupled to a common node , said second electrodes of said first and second transistors being coupled to said positive d - c bus and said negative d - c respectively ; each of said amplifiers having an input coupled to said output of said current sensor and each having an output connected to a respective one of said control electrodes ; and a d - c isolating capacitor connecting said common node of said first electrode of said first and second transistors to said ground wire .