Commutated relay switching system

A basic electronic control scheme which allows relays to be utilized at fast switching rates with long lifetimes and is applicable with standard microprocessor-based systems is described. The basic power-switching circuit consists of a commutating diode connected in parallel with the contacts of a single master relay, and this combination connected in series with a parallel combination of slave switching relays and associated loads. Timing and control is provided in such a way that the relays are switched at a high frequency but never with current flowing through the contacts. An actual range application with multiple loads is described, along with the necessary circuitry and logic. In addition, a diagnostic scheme is described which takes advantage of the commutated system to determine component failures in the power switching loads