Method and apparatus for Kelvin current sensing in a multi-phase driver for a polyphase DC motor

A kelvin current sensing circuit in a control circuit for operating a polyphase DC motor having a rotor and a plurality of stator coils, said control circuit having a plurality of control transistors to sequentially energize the stator coils, and having a plurality of output nodes for connection to a sense resistor, said output nodes being connected to at least some of the control transistors wherein a current flowing in the stator coils flows through the sense resistor, the kelvin current sensing circuit comprising:

• an amplifier having an inverting input and a noninverting input and operative to produce an output signal corresponding to the difference in the voltages at the inverting input and the noninverting input, the output signal from the amplifier being applied to the control transistors connected to said output nodes;
• a plurality of voltage sensing transistors, each having a current path connected in parallel between a first current source and a first bias voltage, and each having a current control element controlled by an associated one of the control transistors
• a first transistor having a current path between a second current source and the first bias voltage, and having a control element controlled by an input reference voltage;
• a second transistor having a current path between a third current source and a first load element, and having a current control element coupled to the plurality of voltage sensing transistors, so that a voltage produced across the first load element is responsive to the currents conducted by the plurality of voltage sensing transistors and is applied to the inverting input of the amplifier;
• and
• a third transistor having a current path between the third current source and a second load element, and having a current control element coupled to the first transistor, so that a voltage produced across the second load element is responsive to the current conducted by the first transistor and is applied to the noninverting input of the amplifier.

A kelvin current sensing circuit that is part of a control circuit for operating a polyphase DC motor having a rotor and a plurality of stator coils, said control circuit having a plurality of control transistors to sequentially energize the stator coils, and having a plurality of output nodes for connection to a sense resistor, said output nodes being connected to at least some of the control transistors wherein a current flowing in the stator coils flows through the sense resistor, the kelvin current sensing circuit comprising:

• an amplifier having an inverting input and a noninverting input and operative to produce an output signal corresponding to the difference in the voltages at the inverting input and the noninverting input, the output signal from the amplifier being applied to the control transistors connected to said output nodes;
• a first transistor having a current path between a first current source and a first load element, and having a current control element controlled by an input reference voltage, so that a voltage produced across the first load element responsive to the input reference voltage is applied to the noninverting input of the amplifier;
• and
• a plurality of voltage sensing transistors, each having a current path connected in parallel between the current source and a second load element, each of the plurality of voltage sensing transistors having a control element coupled to an associated one of the control transistors to produce a voltage across the second load element responsive to the currents conducted by the plurality of voltage sensing transistors that is applied to the inverting input of the amplifier.

A method of kelvin current sensing in a control circuit for operating a polyphase DC motor having a rotor and a plurality of stator coils, said control circuit having a plurality of control transistors to sequentially energize the stator coils, and having a plurality of output nodes for connection to a sense resistor, said output nodes being connected to at least some of the control transistors, wherein a current flowing in the stator coils flows through the sense resistor, said method comprising the steps of:

• sensing a plurality of output voltages, each output voltage corresponding to the current conducted by a corresponding one of the control transistors;
• determining a lowest one of the plurality of output voltages;
• comparing the lowest one of the plurality of output voltages to a reference voltage to produce an output signal;
• and
• applying the output signal to the control transistors.