Apparatus and method for measuring average motor current

Apparatus for measuring an average motor current in a motor driven in a pulse width modulation configuration by a PWM waveform, comprising:

• a sense resistor coupled to said motor for measuring a motor winding current flowing through said motor;
• a first current source coupled to said sense resistor generating a first current being proportional to said motor winding current;
• a current to voltage converter receiving said first current and generating an output voltage indicative of said average motor current in response thereto;
• circuitry for chopping said output voltage at substantially the same frequency and phase as said PWM waveform;
• a second current source coupled to said chopping circuitry and said first current to voltage converter for generating a second current being proportional to said chopped output voltage;
• and
• said current to voltage converter receiving a difference between said first and second currents.

A method for measuring an average motor current through a motor driven by a pulse width modulation waveform, comprising:

• sensing a motor winding current;
• generating a first current being proportional to said sensed motor winding current;
• generating a second current being proportional to a chopped output voltage having substantially the same frequency and phase as said pulse width modulation waveform;
• subtracting said first and second currents and converting to an output voltage indicative of said average motor current;
• chopping said output voltage at substantially the same rate and time as said pulse width modulation waveform for generating said second current.