LM311D
STMicroelectronics
IC COMPARATOR 1 GEN PUR 8SOIC
MOQ 1 · Tube · RoHS · EIA-481 · DAP/DDP · T/T
Technical specifications
| Parameter / Attribute | Specification / Value |
|---|---|
| Type | General Purpose |
| Output type | DTL, MOS, Open-Collector, Open-Emitter, RTL, TTL |
| Mounting | Surface Mount |
| Voltage - input offset | 7.5mV @ ±15V |
| Voltage - supply, single (Dual (±)) | 5V ~ 30V, ±2.5V ~ 15V |
| Output current | 50mA |
| Current - quiescent | 7.5mA |
| Current - input bias | 0.25µA @ ±15V |
| Operating temperature | 0°C ~ 70°C |
| Package | Tube |
| Case | 8-SOIC (0.154\", 3.90mm Width) |
| Number of elements | 1 |
Need Stock or a Drop-in Second-Source for LM311D?
Package: DIP-8 / SOIC-8 · Pin-compatible replacements with immediate Shenzhen spot stock
The LM311 is the single comparator with the flexible output stage: an open collector and open emitter both brought out, a strobe pin that gates the output, and balance pins for offset trimming - the part interface and threshold circuits reach for when the job needs more than a bare LM393. Its DIP-8 pinout deliberately does not follow op-amp conventions, which is exactly why the standing repair error is treating one of the op-amp-shaped 8-pin parts as a substitute. Driven within its ratings it switches up to 50V at 50mA and wire-ORs cleanly; driven by habit it sits in the wrong socket.
Verified Pin-Compatible Replacements (3 verified alternatives)
The Industrial-Temperature Grade
Shenzhen Spot Stock (24-48h Dispatch)
The LM311 die specified for the industrial temperature range (about -25 to +85 degC against the commercial 0 to +70) - same pins, same strobe, same output stage.
Same supply flexibility (single 5V to split +/-15V operation).
The Precision Upgrade
Shenzhen Spot Stock (24-48h Dispatch)
The long-established improved comparator designed against the LM311 socket: same pin functions with tighter offset performance for precision threshold work.
Same flexibility envelope; check the vendor datasheet windows before designing in.
The Other Comparator - Not the Same Socket
Shenzhen Spot Stock (24-48h Dispatch)
The dual comparator in the same 8-pin size - and a completely different pinout: outputs on pins 1 and 7, supplies on 4 and 8, no strobe, no balance, open collector only.
Single-supply design point; less output flexibility than the LM311.
Buyer & Quality Checklist for Sourcing Alternatives
- Read the LM311 pin map before assuming anything: pin 1 is the emitter of the output transistor (not a channel output), pins 5 and 6 are balance and balance/strobe, pin 7 is the output collector, supplies sit on pins 4 and 8. The body looks op-amp-familiar and is not.
- The dual output (collector at pin 7, emitter at pin 1) lets the comparator reference its output to ground, VCC+ or VCC-: use the emitter pin deliberately in level-shifting and wire-OR circuits, and do not ground it by reflex.
- The strobe pin (6) turns the output off from logic - used to multiplex several comparators onto one line. A floating or miswired strobe reads as a dead comparator; check it early in any fault hunt.
- Offset balance pins behave like a 741: a small potentiometer across pins 5 and 6 trims input offset if DC precision matters. Leave them floating or tied when unused.
- Output switch ratings: up to about 50V at 50mA through the open collector - enough to drive relays and optos directly with a pull-up on the load rail.
- Differential input range is wide (about +/-30V), but the supply pins are not symmetric - in split-supply circuits verify the negative rail arrangement against the datasheet before copying op-amp habits.
Frequently Asked Technical Questions
Q: What is the difference between LM311 and LM393?
A: LM311 is a single comparator with strobe, offset-balance pins and a two-sided output stage in the DIP-8; LM393 is a dual comparator with plain open-collector outputs and a different pinout in the same package. Same family of jobs, not the same socket.
Q: What does the strobe pin on the LM311 do?
A: Pulling it to logic low forces the output transistor off regardless of the inputs - used to gate the comparator off or to multiplex several comparators onto one wire-OR line. Left floating (or wired per the circuit), the comparator runs normally.
Q: Can I use an LM311 as a drop-in for a slow op-amp stage?
A: No - a comparator is not compensated for linear feedback and its output stage is not a linear amplifier (open collector or emitter, external pull-up required). It compares; it does not follow. Use it for thresholds and level detection only.