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LM311Single differential voltage comparator
A fast voltage decision with a flexible output transistor.
LM311 is a single voltage comparator with separately accessible collector and emitter output pins. It compares two input voltages and switches its output transistor rather than amplifying a signal linearly. Our 5 V example compares VIN with a 2 V resistor reference. The emitter is grounded and the collector uses a 10 kΩ pull-up, giving a LOW output below the threshold and a HIGH output above it. Balance and strobe contacts add flexibility, but they require the correct external network. This reference follows TI’s commercial LM311P and LM311DR with both optional contacts left open in the basic circuit.
8Physical pins
LM311PPDIP-8
Manufacturer-referencedTexas Instruments
Pin diagram
Select a pin to explore its connection
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LM311PPDIP-8Top view
LM311DRSOIC-8Top view
Click a lead or use the arrow keys. Top view
PIN 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.
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.
Key specifications
The output collector and emitter are both exposed. The chosen emitter return and external pull-up determine the logic levels.
Recommended supply3.5–30 V · total span
Typical falling response165 ns · specified test
LM311 ambient0–70 °C
Output contactsC + E Separate collector and emitter
Package details
LM311P · PDIP-8
| Property | Details |
|---|---|
| Manufacturer | Texas Instruments |
| Part number | LM311P |
| Package | PDIP-8 |
| Connections | 8 pins |
| Mounting | Through-hole |
| Lead pitch | 2.54 mm |
| Package code | dip |
| Thermal reference | Board and package dependent; see manufacturer data |
Operating conditions
TI LM311 commercial grade
Manufacturer specifications 5 parameters
Scroll sideways to see all columns.
| Parameter | Value | Conditions / notes |
|---|---|---|
| Supply span | 3.5–30 V | V+ minus V− |
| Ambient range | 0 to +70°C | LM311 grade |
| Recommended input range | V− + 0.5 V to V+ − 1.5 V | Subject to the manufacturer supply conditions |
| Inputs in the 5 V example | 0.5–3.5 V | Both VIN and VREF |
| Balance / strobe | Open in the basic circuit | Optional networks shown in the manufacturer PDF |
No specifications match. Try a parameter name or a unit.
Supply range and input range are separate constraints.
Electrical characteristics
±15 V test supply unless stated
Manufacturer specifications 6 parameters
Scroll sideways to see all columns.
| Parameter | Value | Conditions / notes |
|---|---|---|
| Input offset voltage | 2 mV typical; 7.5 mV maximum | 25°C; 10 mV maximum over temperature |
| Input bias current | 100 nA typical; 250 nA maximum | 25°C; 300 nA maximum over temperature |
| Input offset current | 6 nA typical; 50 nA maximum | 25°C; 70 nA maximum over temperature |
| Collector-emitter LOW | 0.23 V typical; 0.4 V maximum | 4.5 V single supply; 8 mA sink; VID = −10 mV |
| Positive supply current | 5.1 mA typical; 7.5 mA maximum | Output LOW; no load; 25°C |
| Negative supply current magnitude | 4.1 mA typical; 5 mA maximum | Output HIGH; no load; 25°C |
No specifications match. Try a parameter name or a unit.
The LOW-voltage test is load dependent. It is not a fixed voltage for every collector current.
Response and output behavior
Manufacturer switching test
Manufacturer specifications 6 parameters
Scroll sideways to see all columns.
| Parameter | Value | Conditions / notes |
|---|---|---|
| LOW-to-HIGH response | 115 ns typical | ±15 V supply; 100 mV step; 5 mV overdrive |
| HIGH-to-LOW response | 165 ns typical | Same step and overdrive |
| Test output load | 500 Ω to 5 V; 5 pF | Different loading changes delay |
| VIN below VREF | Output transistor ON | Collector pulled toward emitter |
| VIN above VREF | Output transistor OFF | Pull-up creates HIGH |
| No pull-up, output OFF | Floating collector | Not a valid HIGH |
No specifications match. Try a parameter name or a unit.
Near equality, offset and noise can dominate. Typical response is not a guaranteed delay.
5 V threshold detector
A 2.00 V reference and 10 kΩ pull-up
Manufacturer specifications 7 parameters
Scroll sideways to see all columns.
| Parameter | Value | Conditions / notes |
|---|---|---|
| Reference upper resistor | 30 kΩ | +5 V to VREF |
| Reference lower resistor | 20 kΩ | VREF to ground |
| Reference result | 2.00 V | 5 × 20 / (30 + 20) |
| Signal input | 1.50 V initially | IN+ pin 2 |
| Output pull-up | 10 kΩ | +5 V to collector pin 7 |
| Emitter and negative rail | Pins 1 and 4 to ground | Two distinct terminals |
| Supply bypass | 100 nF | Pins 8–4; short local loop |
No specifications match. Try a parameter name or a unit.
The high-impedance output meter adds negligible loading.
Optional controls and stress limits
LM311P · PDIP-8
Manufacturer specifications 6 parameters
Scroll sideways to see all columns.
| Parameter | Value | Conditions / notes |
|---|---|---|
| Offset trim | Balance pins 5 and 6 | Use the manufacturer network |
| Strobe drive | Current driven, approximately −3 to −5 mA | Do not short the strobe contact to ground |
| Supply absolute maximum | 36 V total | Stress only; recommended maximum 30 V |
| Collector to V− absolute maximum | 40 V for LM311 | The 50 V rating belongs to other family members |
| Storage temperature | −65 to +150°C | Unpowered storage |
| Pin pitch | 2.54 mm | Through-hole |
No specifications match. Try a parameter name or a unit.
Stress ratings do not describe recommended continuous operation.
Connections by function
Select a pin for its function, connection guidance and electrical notes.
Output transistor2 pins
Comparison inputs2 pins
Supply2 pins
Balance & strobe2 pins
Output transistor2 pins
Comparison inputs2 pins
Supply2 pins
Balance & strobe2 pins
LM311 at a glance
Follow the labeled connections and functional stages
How it works
3 stages · Explore one step at a time
Compare VIN and VREF
VIN enters IN+ pin 2; the 2 V reference enters IN− pin 3. Their difference determines the unstrobbed output state.
Switch the output transistor
Below the threshold, the transistor conducts from collector pin 7 to emitter pin 1. Above it, the transistor releases the collector and the pull-up establishes HIGH.
Control the transition
Offset creates uncertainty around equality. Positive-feedback hysteresis can stabilize a noisy threshold; it is not included in this simple example.
Step 1 of 3
Find the switching threshold
Adjust VIN and the reference. Remove the pull-up to see why it matters.
IN+ − IN−—
Output state—
Pull-up current—
Enable JavaScript to explore the comparator.
Violet: offset-sensitive transition · Amber: input outside the recommended range.
Unstrobed DC teaching model with emitter pin 1 grounded. Valid input range is 0.5–3.5 V. The ±10 mV uncertainty band follows the full-temperature offset limit; it is not hysteresis. LOW uses an illustrative 0.23 V estimate from a different test load. Actual saturation, transient delay, leakage and noise are omitted.
LM311 in a circuit
Separate emitter return, reference divider and collector pull-up.
Connect it, step by step
Follow the component values and pin connections
Make the reference
30 kΩ over 20 kΩ gives 2 V from 5 V.
Connect the two returns
Ground pin 4 for power and pin 1 for the output transistor. Add 100 nF supply bypass.
Read the collector
Add 10 kΩ to +5 V at pin 7. VIN below 2 V gives LOW; above 2 V gives HIGH.
Inside LM311
A differential decision stage and an accessible output transistor.
Explore the circuit
Select a stage to see its role and connections
Differential input
Compare the input voltages within the permitted common-mode range.
Balance and strobe
Optional external networks adjust offset or release the output. Their electrical drive requirements matter.
Collector and emitter
The output transistor has both contacts available. The external circuit sets its return and HIGH level.
Selected packagePDIP-8LM311P
Physical connections8 pinsPackage-specific numbering
Reference collection6 tables30 parameters & pin functions
Pin reference
Signal names, electrical functions and connection guidance
Physical pin numbers8 pins
Scroll within the table to see all columns and rows.
| Pin | Signal | Type | Function & connection |
|---|---|---|---|
| EMIT | Output emitter | Emitter of the output transistor, separate from the negative supply.Connection guidanceConnect to ground for the illustrated logic output. Do not leave the emitter floating. | |
| IN+ | Non-inverting input | Signal input in the threshold detector.Connection guidanceConnect VIN; keep it within 0.5–3.5 V for the 5 V example. | |
| IN− | Inverting input | Reference input in the threshold detector.Connection guidanceConnect the 2.00 V divider node. | |
| V− | Negative supply | Negative power rail for the comparator.Connection guidanceConnect to ground in the single-supply example. This is a supply pin; it is not internally interchangeable with output emitter pin 1. | |
| BAL | Offset balance | Optional offset-balance connection.Connection guidanceLeave open when offset trimming is not used. | |
| BAL/STB | Balance / strobe | Optional balance and current-driven output-disable connection.Connection guidanceLeave open in this unstrobbed circuit. Do not short to ground. Use the manufacturer’s current-driven strobe network when required. | |
| COL | Output collector | Collector of the output transistor.Connection guidanceAdd 10 kΩ to +5 V and read this node. HIGH requires an external pull-up; this pin sinks current when the transistor is on. | |
| V+ | Positive supply | Positive comparator supply.Connection guidanceConnect +5 V with 100 nF bypass to pin 4. |
No pins match these filters. Try another signal name or reset the filters.
Operating conditions
TI LM311 commercial grade
Manufacturer-referenced values5 parameters
Scroll within the table to see all columns and rows.
| Parameter | Value | Conditions / notes |
|---|---|---|
| Supply span | 3.5–30 V | V+ minus V− |
| Ambient range | 0 to +70°C | LM311 grade |
| Recommended input range | V− + 0.5 V to V+ − 1.5 V | Subject to the manufacturer supply conditions |
| Inputs in the 5 V example | 0.5–3.5 V | Both VIN and VREF |
| Balance / strobe | Open in the basic circuit | Optional networks shown in the manufacturer PDF |
No specifications match. Try a parameter name or a unit.
Supply range and input range are separate constraints.
Electrical characteristics
±15 V test supply unless stated
Manufacturer-referenced values6 parameters
Scroll within the table to see all columns and rows.
| Parameter | Value | Conditions / notes |
|---|---|---|
| Input offset voltage | 2 mV typical; 7.5 mV maximum | 25°C; 10 mV maximum over temperature |
| Input bias current | 100 nA typical; 250 nA maximum | 25°C; 300 nA maximum over temperature |
| Input offset current | 6 nA typical; 50 nA maximum | 25°C; 70 nA maximum over temperature |
| Collector-emitter LOW | 0.23 V typical; 0.4 V maximum | 4.5 V single supply; 8 mA sink; VID = −10 mV |
| Positive supply current | 5.1 mA typical; 7.5 mA maximum | Output LOW; no load; 25°C |
| Negative supply current magnitude | 4.1 mA typical; 5 mA maximum | Output HIGH; no load; 25°C |
No specifications match. Try a parameter name or a unit.
The LOW-voltage test is load dependent. It is not a fixed voltage for every collector current.
Response and output behavior
Manufacturer switching test
Manufacturer-referenced values6 parameters
Scroll within the table to see all columns and rows.
| Parameter | Value | Conditions / notes |
|---|---|---|
| LOW-to-HIGH response | 115 ns typical | ±15 V supply; 100 mV step; 5 mV overdrive |
| HIGH-to-LOW response | 165 ns typical | Same step and overdrive |
| Test output load | 500 Ω to 5 V; 5 pF | Different loading changes delay |
| VIN below VREF | Output transistor ON | Collector pulled toward emitter |
| VIN above VREF | Output transistor OFF | Pull-up creates HIGH |
| No pull-up, output OFF | Floating collector | Not a valid HIGH |
No specifications match. Try a parameter name or a unit.
Near equality, offset and noise can dominate. Typical response is not a guaranteed delay.
5 V threshold detector
A 2.00 V reference and 10 kΩ pull-up
Manufacturer-referenced values7 parameters
Scroll within the table to see all columns and rows.
| Parameter | Value | Conditions / notes |
|---|---|---|
| Reference upper resistor | 30 kΩ | +5 V to VREF |
| Reference lower resistor | 20 kΩ | VREF to ground |
| Reference result | 2.00 V | 5 × 20 / (30 + 20) |
| Signal input | 1.50 V initially | IN+ pin 2 |
| Output pull-up | 10 kΩ | +5 V to collector pin 7 |
| Emitter and negative rail | Pins 1 and 4 to ground | Two distinct terminals |
| Supply bypass | 100 nF | Pins 8–4; short local loop |
No specifications match. Try a parameter name or a unit.
The high-impedance output meter adds negligible loading.
Optional controls and stress limits
LM311P · PDIP-8
Manufacturer-referenced values6 parameters
Scroll within the table to see all columns and rows.
| Parameter | Value | Conditions / notes |
|---|---|---|
| Offset trim | Balance pins 5 and 6 | Use the manufacturer network |
| Strobe drive | Current driven, approximately −3 to −5 mA | Do not short the strobe contact to ground |
| Supply absolute maximum | 36 V total | Stress only; recommended maximum 30 V |
| Collector to V− absolute maximum | 40 V for LM311 | The 50 V rating belongs to other family members |
| Storage temperature | −65 to +150°C | Unpowered storage |
| Pin pitch | 2.54 mm | Through-hole |
No specifications match. Try a parameter name or a unit.
Stress ratings do not describe recommended continuous operation.
No matching rowsTry a pin name, parameter, unit or test condition, or reset the filters.
Level detection
Turn a suitable sensor voltage into a logic decision with a defined pull-up.
Manufacturer application guideThreshold oscillators
Combine feedback and timing networks, including hysteresis and the actual propagation delay.
Manufacturer application guideLogic interfacing
Choose collector pull-up and emitter return to suit the receiving logic while observing every voltage/current limit.
Manufacturer application guideTake it into ProTech
Find LM311 in the Components Library to place its schematic symbol and connect its pins.
Reference page · circuit simulation model not yet availableOpen ProTech