BETAPIN 1 · Output transistor
Output emitterEMIT
Function
Emitter of the output transistor, separate from the negative supply.
How to connect
Connect to ground for the illustrated logic output.
Electrical note
Do not leave the emitter floating.
Single differential voltage comparator
LM311 Pinout
Explore LM311 pins, signal names, electrical functions and connection guidance for each package.
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8Physical pins
LM311PPDIP-8
Manufacturer-referencedTexas Instruments
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PIN 2 · Comparison inputs
Non-inverting inputIN+
Function
Signal input in the threshold detector.
How to connect
Connect VIN; keep it within 0.5–3.5 V for the 5 V example.
PIN 3 · Comparison inputs
Inverting inputIN−
Function
Reference input in the threshold detector.
How to connect
Connect the 2.00 V divider node.
PIN 4 · Supply
Negative supplyV−
Function
Negative power rail for the comparator.
How to connect
Connect to ground in the single-supply example.
Electrical note
This is a supply pin; it is not internally interchangeable with output emitter pin 1.
PIN 5 · Balance & strobe
Offset balanceBAL
Function
Optional offset-balance connection.
How to connect
Leave open when offset trimming is not used.
PIN 6 · Balance & strobe
Balance / strobeBAL/STB
Function
Optional balance and current-driven output-disable connection.
How to connect
Leave open in this unstrobbed circuit.
Electrical note
Do not short to ground. Use the manufacturer’s current-driven strobe network when required.
PIN 7 · Output transistor
Output collectorCOL
Function
Collector of the output transistor.
How to connect
Add 10 kΩ to +5 V and read this node.
Electrical note
HIGH requires an external pull-up; this pin sinks current when the transistor is on.
PIN 8 · Supply
Positive supplyV+
Function
Positive comparator supply.
How to connect
Connect +5 V with 100 nF bypass to pin 4.