4 Achieving reliable detection and protection in electric motor drives

Designers must incorporate multiple levels of reliable detection and protection to prevent damage to motor-drive circuits. Power switching transistors such as IGBTs have relatively short withstand times (less than 10 µs) and can quickly overheat and become damaged from excessive currents.

Current-limiting fuses and circuit breakers provide excellent overcurrent protection, but have slow reaction times and require user intervention. They are often the last resort for protection during a failure event.

To detect and quickly protect the motor drive against these fault conditions, one solution senses the current and voltage at critical electrical paths within the motor drive. The measured current and voltage are received by a host microcontroller that controls high-side power circuits such as power switching transistors and circuit breakers. To suppress overcurrents or overvoltage faults, the host microcontroller either turns off or modifies the switching characteristics of power transistors, or trips the circuit breakers.

Figure 4-1 shows the Texas Instruments (TI) AMC23C14 family of low-latency reinforced isolated comparators in short-circuit current, overcurrent, undercurrent, overvoltage, undervoltage and overtemperature fault-detection scenarios. These devices integrate adjustable comparator threshold functions, include a high-side low-dropout regulator for the power supply, and have a response time of sub-0.5 µs in an eight-pin small-outline integrated circuit package.

Next, review the several use cases for AMC23C14 family of isolated comparators in electric motor drives.