A new approach to motor drive current measurement

Abstract

Even though motor drives are increasingly digitally controlled, motor current measurement has traditionally remained analog-based. Moreover, the analog approach has required large bandwidths in order to faithfully reproduce the PWM ripple current. This paper proposes a new topology in which the sample and hold function occurs early in the signal processing chain, instead of after the isolation function, as is often the case. This simplifies the signal processing chain and improves accuracy of the measured current. The reason is that sample timing accuracy can be a far more important accuracy parameter than gain or offset performance. A new high voltage IC topology is presented that accomplishes this function in a single, monolithic structure.