As shown in Figure 14, a motor drive takes power from AC mains, rectifies it to a DC voltage, and inverts the DC back to AC with variable magnitude and frequency based on motor load demand.

A motor drive typically has an isolation barrier between power and control circuits through isolated semiconductor components. An isolated amplifier or modulator measures and isolates current and voltage feedback signals from the power circuits. An isolated gate driver provides isolation between the MCU generating the pulse-width modulation (PWM) control signals and power transistors such as IGBTs. An isolated comparator checks for any overcurrent, overvoltage or overtemperature conditions and provides a fault signal to the MCU. Optional interface isolation with digital isolators can help meet any additional system safety requirements.

It’s important for a galvanically isolated motor drive to minimize noise interference between power and control circuits and ensure safety for human operators. Modern motor-drive systems must also meet IEC 61800-5-1 safety standards.

Increasing measurement accuracy for current and voltage feedback loops helps minimize torque ripple and provides smooth speed and torque current profiles to the motor. Isolated amplifiers such as the AMC1300 and AMC1311B and isolated modulators such as the AMC1306M25 and AMC1336 support accurate current and voltage measurements with high CMTI that improves system reliability with reduced noise coupling.

With low propagation delay, high CMTI, and reduced rise and fall times, isolated gate drivers enable higher PWM frequencies and minimal switching losses, making it easier for designers to adopt SiC and gallium nitride (GaN) transistors in their motor-drive systems. For accurate and fast fault detection in fault-tolerant systems, the AMC23C12 family of reinforced isolated comparators provides a cost-effective solution with <3% accuracy, <400-ns latency, and up to 50% space and bill-of-materials (BOM) reductions.

Digital isolators such as the ISO6760L with integrated interlock and low EMI ensure the transmission of digital signals with high signal integrity between the power and control circuit or (optionally) between the MCU and interface. The Isolated Delta-Sigma Modulator Based AC/DC Voltage and Current Measurement Module Reference Design provides a cost-optimized and highly reliable solution to achieve sub-1% accuracy for isolated current and voltage measurements.