Apparatus and method for current sensing for motor driver in pwm mode
AssigneeSGS-Thomson Microelectronics S.A.
InventorLarry B. Li
Life of this patent
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Abstract
A motor drive control circuit for operation in the PWM mode includes a feedack circuit from a resistor for sensing motor coil current modified to switchably connect the resistor to the drive input in accordance with operation of a sample-hold switch. The sample-hold switch is controlled to sample a signal proportional to motor coil current only at the middle of the coil current rise during each PWM ON time, thus providing a reliable indication of average coil current. A signal storage capacitor connected in the feedback circuit receives the sampled signal and retains it for use in feedback control throughout PWM operation until the next sample.
Claims18
A circuit for providing a signal proportional to the average current flowing through coils of a motor operated in a PWM control mode, comprising:
- a sense resistor across which a voltage representing drive current supplied to the coils is developed;
- a sense amplifier having an input and an output;
- a signal storage capacitor connected in parallel with the sense resistor and connected to the input of the sense amplifier;
- a sample-hold switch connected between the sense resistor and the signal storage capacitor for (a) connecting the sense amplifier and the signal storage capacitor with the sense resistor at times t.sub.m mid-way between times t.sub.1 of initiation of PWM drive pulses to the coils and times t.sub.2 of termination of PWM drive pulses to the coils, when voltage developed across the sense resistor is at a middle value representing average coil current for a PWM drive pulse, and (b) disconnecting the sense amplifier and the signal storage capacitor from the sense resistor at other times, whereby the sense amplifier is provided a signal substantially proportional to the coil current during operation in the PWM control mode.
A motor control system providing average motor coil current sensing throughout operation in a drive mode that provides discontinuous coil energization, comprising:
- a drive circuit for supplying energizing current to motor coils in pulses;
- a current sensing and feedback circuit, for providing to the drive circuit a signal representing average current in the motor coils both during and between drive pulses, comprising:
- means for sampling and storing a signal representing coil current during drive pulses, and
- means for providing a feedback signal, proportional to the stored signal, to the drive circuit during operation between pulses.
A method of operating a PWM drive system for deriving average load current for control purposes throughout operation, both during and between drive pulses, comprising:
- sensing and developing a signal proportional to load current;
- sampling the signal proportional to load current at a time during a PWM drive pulse, other than a time of pulse initialization or termination, to derive a sampled current signal, wherein the time of the sampling is substantially at the average of load current during the PWM drive pulse and the sampled current signal is an average current signal;
- and
- applying the sampled current signal as a feedback signal during PWM drive operation.
A drive system providing drive pulses for a load comprising:
- means for sensing and developing a signal proportional to load current;
- means for sampling the signal proportional to load current at a time during a drive pulse to derive a sampled current signal;
- means for applying the sampled current signal as a control feedback signal
- means for holding the sampled current signal so it is available for applying as a feedback signal throughout operation until a further sampled signal is taken, and wherein
- the time at which the means for sampling samples the signal proportional to load current is substantially at an average of load current during a drive pulse and the sampled current signal is an average current signal;
- the sampling time of the means for sampling is limited to a time interval that is short compared to a duration of a drive pulse, and
- the means for holding includes a signal storage capacitor that substantially maintains its charge until a subsequent sampled current signal is taken.
Dependencies are inferred from the claim text.