A single high-speed precision voltage comparator in SOIC-8, more flexible than a garden-variety comparator. Its output stage brings out both the transistor collector and emitter separately, so it can switch loads referenced to any level (drive a relay, a lamp, or logic at a different voltage), and a strobe input can force the output off on command. An offset-balance pair trims input offset for precision thresholds. It runs from a single supply or split supplies and drives up to 50 V / 50 mA on the output. Use it for level detection, zero-crossing, oscillators, and interfacing analog to logic.

Pinout

Pin	Name	Type	Function
1	EMIT OUT	output	Open-emitter output of the comparator's output transistor. Typically tied to VCC- (ground) or used as the low side of a level-shifted output; combined with COL OUT it forms a floating output that can drive loads referenced to either rail up to 50 V at 50 mA.
2	IN+	input	Non-inverting comparator input. Differential input range +/-30 V (VID), single-ended input range must remain within
3	IN-	input	Inverting comparator input. Differential and common-mode limits identical to IN+; typical input offset voltage 2 mV, input offset current 6 nA at 25 C.
4	VCC-	power_in	Negative supply pin. Absolute max -18 V; recommended supply span (VCC+ - VCC-) is 3.5 V to 30 V. In single-supply operation this pin is grounded.
5	BALANCE	input	Offset-balance trim pin. Connect an external network (typically a potentiometer between BALANCE and BAL/STRB with wiper to VCC+) to null input offset voltage. May be left open when trimming is not required.
6	BAL/STRB	input	Combined balance / strobe input. When current-driven at -3 mA to -5 mA (per datasheet note: the strobe must not be shorted to ground) the output is forced into the OFF (high-impedance) state regardless of the differential input. Also serves as the second terminal of the offset-balance network.
7	COL OUT	output	Open-collector output of the comparator's output transistor. Withstands up to 50 V (VCC- + 50 V) with the emitter grounded; sinks up to 50 mA (VOL <= 1.5 V at IOL = 50 mA). Requires an external pull-up resistor for logic-level output.
8	VCC+	power_in	Positive supply pin. Absolute max +18 V; recommended supply span (VCC+ - VCC-) is 3.5 V to 30 V. Positive-supply current ICC+ typ 5.1 mA (no load).

Key specifications

Parameter	Value
Type	Single precision comparator
Output	open-collector (separate emitter + collector)
Output rating	50 V / 50 mA
Strobe	yes (force output off)
Offset trim	balance pins
Response time	~200 ns
Supply	single 5 V or split up to ±15 V
Package	SOIC-8

Ordering variants

Same part, different packaging or reel option.

LM311D (SOIC-8, tube)
LM311DR (SOIC-8, tape & reel)

CAD (KiCad official)

Symbol: Comparator:LM311
Footprint: Package_SO:SOIC-8_3.9x4.9mm_P1.27mm
3D model: SOIC-8 (KiCad packages3D)

Provenance

Data extracted from the manufacturer datasheet, not a distributor listing:

Datasheet: Texas Instruments datasheet (42 pp, sha256 c4f907a0fa591db0, retrieved 2026-08-17, tier: manufacturer)
Extractor: ds2sf (Claude). Every pin and dimension is cited to a datasheet page; it refuses to fabricate.
CAD: KiCad official libraries (CC-BY-SA 4.0).

Datasheet PDF