Method of sensing motor winding current in integrated stepper motor buffer
AssigneeTexas Instruments Incorporated
InventorJim D. Childers
Life of this patent
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Abstract
A method and motor controller for sensing motor winding current. An FET drive transistor has its ON resistance periodically increased to about five times the normal ON resistance for short sensing intervals during motor drive. An analog-to-digital converting senses the voltage across this FET during the sensing intervals. The resulting digital signal is used to calculate motor current. The time at high ON resistance is much less than the time at normal. The ON resistance can be changed using two FETs or one FET with gate fingers over differing parts of the channel region.
Claims10
A method of sensing motor winding current comprising the steps of:
- periodically during current drive
- increasing the ON resistance of a drive circuit driving the motor winding to a first level above a non-zero second level,
- measuring the voltage across the drive circuit,
- returning the ON resistance of the drive circuit to the second level, and
- calculating motor current from the measured voltage.
A motor controller comprising:
- a plurality of drive circuits connected to a motor winding for driving the motor, one of said drive circuits being a current sensing drive circuit having a variable ON resistance;
- an analog-to-digital converter having an analog sensing input sensing a voltage across said current sensing drive circuit and a digital output corresponding to said voltage;
- a microcontroller connected to said plurality of drive circuits and said analog-to-digital converter, said microcontroller
- controlling ON and OFF operation of said plurality of drive circuits to control motor operation,
- said microcontroller further controlling said sensor drive circuit to periodically have a high ON resistance during ON operation during a sensing interval and otherwise have a non-zero normal ON resistance,
- controlling said analog-to-digital converter to sense said voltage during said sensing interval, and
- calculating a motor current from said digital output of said analog-to-digital converter.
Dependencies are inferred from the claim text.