System for measuring current in multiple motor coils using a single sensing element

A method for sensing current in at least two leads of a three-phase motor comprising:

• supplying DC power to a primary winding of a current sense transformer;
• selectively coupling the primary winding of the current sense transformer to one or more leads in a three-phase motor;
• measuring a voltage across a resistor connected to a secondary winding of the current sense transformer;
• and
• comparing voltages measured across the resistor to identify currents in at least one lead of the three-phase motor.

A circuit for sensing current in at least two leads of a three-phase motor comprising:

• a DC power supply having a pair of output terminals;
• an H-bridge driver connected to one terminal of the DC power supply and being connected to leads of a three-phase motor to drive each lead to a voltage obtained from the DC power supply;
• a regulating circuit for identifying the voltage to which each lead is to be driven and for controlling switches within the H-bridge circuit to drive each lead to an identified voltage;
• and
• a single current sense resistor connected to the other terminal of the DC power supply and to the H-bridge driver;
• and
• the regulating circuit being configured to compare a voltage across the single current sense resistor at a first time with a voltage across the single current sense resistor at a second time to measure a current through a motor lead.