LM311 (Voltage Comparator IC)

Description

LM311 – Voltage Comparator IC

Product Overview / Mini Datasheet

General Description

The LM311 is a single high-speed voltage comparator capable of driving TTL, MOS, and open-collector logic outputs. It’s designed to compare two input voltages and output a digital signal indicating which input is higher. The open-collector output allows for flexible interfacing and wired-AND logic configurations.

Specifications

Key Features

• Operates from single or dual supplies
• High output current drive (50 mA)
• Open-collector output for wired logic
• Wide input voltage range
• Fast response time (~200 ns)
• Compatible with TTL, CMOS, and MOS logic

Common Applications

• Zero-crossing detectors
• Pulse-width modulation
• Oscillators
• Window comparators
• Analog-to-digital converter circuits
• Voltage level detection

Pinout (8-pin DIP / SOIC)

       +--------+
  IN+ |1      8| V+
  IN- |2      7| Balance/Strobe
 GND |3      6| Output
 NC  |4      5| Balance
       +--------+

• Pin 1: Non-inverting Input
• Pin 2: Inverting Input
• Pin 3: Ground
• Pin 4: Not Connected
• Pin 5: Balance
• Pin 6: Output (Open Collector)
• Pin 7: Balance/Strobe
• Pin 8: V+ (Supply Voltage)

Pins 5 and 7 (Balance/Strobe) are used for offset adjustment and can often be left unconnected for typical applications.

How to Use

• Connect a pull-up resistor on the output (since it’s open-collector).
• Compare voltage levels: if V+ > V−, the output transistor turns off (output = HIGH via pull-up).
• If V+ < V−, transistor turns on (output = LOW / sinks current).
• Can be used in analog-to-digital conversion and logic level detection circuits.