Relay module, 24 V AC,

The Texas Instruments LM139, LM239, LM339 and LM2901 are quad differential input voltage comparators designed to operate from a single power supply over a wide range of voltages. The common mode input voltage range includes ground and the devices have open collector outputs.

Comparators, Texas Instruments

Texas Instruments’ range of voltage comparators includes not only conventional single, dual and quad comparator packages but also window comparators and over- & under-voltage supervisors.

Although comparators and operational amplifiers are superficially similar devices their operation in practical applications is very different. Op amps are intended for linear operation accompanied by suitable feedback whereas comparators are tailored for rapid switching and generally operated in open-loop mode. Dedicated voltage comparators have significantly shorter propagation delays and are capable of faster response times under saturated conditions. Most comparators are also more tolerant of high differential input voltages and many have open-collector outputs allowing parallel operation with other devices.