Patent ID: 8724275

Claim:
A method comprising: receiving N power signals, each having a different one of N phases, over N power supply lines that supply power to a motor, wherein N is an integer greater than two; using a first isolator, selectively activating a first switch to allow a first current to flow from a first one of the N power supply lines to a second one of the N power supply lines; using a second isolator, generating a signal based on the first current; and selectively generating a phase failure signal when the signal is less than a predetermined threshold, wherein the first isolator includes a first optocoupler, wherein activating the first switch using the first isolator includes supplying current to a light emitter of the first optocoupler, wherein the second isolator includes a second optocoupler, and wherein generating the signal includes supplying a total current including the first current to a light emitter of the second optocoupler.