Microcontroller Controls Current-Loop AFE Protection

By: Anatoly Andrusevich

Abstract: The fragile current-shunt resistor in the analog front end of an isolated 0–20mA precision current loop can be protected by a fast fuse or an automatic current-limiting switch. The circuit shown, however, is faster than a fuse, requires no replacement, and (unlike the switch) provides microprocessor control with an option to log the fault events. The circuit includes a comparator (MAX9910), a microprocessor supervisor with watchdog timer (MAX6706), a D-type flip-flop, an NOR gate, an OR gate, and a solid-state relay.