General-purpose comparator with flexible output drive
The LM311PSR is a single general-purpose comparator from Texas Instruments, designed for level detection, zero-crossing, and pulse-width modulation circuits where the output must interface with multiple logic families or drive a load directly. Its output stage supports DTL, MOS, open-collector, open-emitter, RTL, and TTL — meaning it can pull down a relay coil, drive a CMOS gate input, or feed a TTL counter without an external buffer. Typical output current is 50 mA, enough to switch a small relay or LED indicator directly from the comparator pin.
Runs on a single supply from 3.5 V to 30 V, or dual supplies from ±1.75 V to ±15 V — covers 5 V logic rails, 12 V industrial buses, and ±15 V op-amp supplies without a separate regulator. Maximum input offset voltage is 7.5 mV at ±15 V, and maximum input bias current is 0.25 µA at the same condition — tight enough for precision threshold sensing in thermostat or battery-monitor circuits. Quiescent current maxes at 7.5 mA — not a low-power part, but acceptable for line-powered or moderate-duty-cycle applications.
Not rated for automotive or extended industrial environments; if the ambient drops below freezing or exceeds 70°C, look at the LM311M or LM311N variants with wider temperature grades.