ComponentsActive / Semiconductor

Logic Gates (74xx / CMOS)

IC (Digital)

Digital building blocks that perform Boolean logic (AND, OR, NOT, NAND, NOR, XOR, XNOR) on one or more binary inputs. The 74xx TTL and 4000 CMOS families contain hundreds of pre-built gate ICs.

Schematic symbol

Integrated circuit (DIP)

How logic gates (74xx / cmos) appears in a circuit diagram.

Types & variants

74xx (TTL, 5V)74HC / 74HCT (high-speed CMOS, TTL-pin compatible)74LVC / 74AHC (low-voltage, 3.3V capable)4000 series CMOS (3–15V, low power)Single gate (SOT-23 package, e.g. 74LVC1G08)Schmitt-trigger input variants (74xx14)Open-collector / open-drain variants (74xx03, 74xx09)

Key specs

Supply voltage

V

TTL: 4.75–5.25V. HC: 2–6V. 4000 CMOS: 3–15V. Check the family datasheet.

Propagation delay

ns

Time from input change to output change. TTL ~10ns, HC ~8ns, 4000 ~100ns at 5V.

Fan-out

—

How many gate inputs one output can drive. TTL: ~10. CMOS: very high (limited by capacitance).

Static current

µA

CMOS draws near-zero at DC; TTL draws 1–10mA per gate even when idle.

Input logic levels

V

TTL: VIH≥2.0V, VIL≤0.8V. CMOS: thresholds scale with VCC (~30% and ~70%).

Markings

Printed part number like 74HC00, 74LS08, CD4011. Date code + manufacturer logo below. SMD versions use shortened codes (e.g. HC00 → 00).

Standard values

Common gates per package: 7400 (quad NAND), 7402 (quad NOR), 7404 (hex NOT), 7408 (quad AND), 7432 (quad OR), 7486 (quad XOR), 74125 (quad buffer).

How to choose

1) Decide TTL vs CMOS — use HC/HCT for 5V general use, 74LVC for 3.3V, 4000 for high voltage (up to 15V) or low power. 2) Pick the gate function (AND/OR/NAND/NOR/XOR/NOT). 3) Check if you need Schmitt-trigger inputs for noisy signals. 4) Decide on through-hole DIP vs surface-mount SOIC/TSSOP. 5) For one-off gates, use single-gate SOT-23 parts to save board space.

Pinout & package

11A14VCC21B134B31Y124A42A114Y52B103B62Y93A7GND83Y

DIP-14 (7400 quad NAND) — top view, notch up

Check first: Shown for the 7400. Other 74xx gates keep pin 7 = GND and pin 14 = VCC, but the gate inputs move — the 7402 (quad NOR), for one, has its outputs on pins 1, 4, 10 and 13.

14-pin DIP/SOIC is the most common: pin 14 = VCC, pin 7 = GND, remaining 12 pins = 4 gates (2 in, 1 out each). Single-gate parts come in 5-pin SOT-23.

Example circuits

  • Push-button debounce with a Schmitt NAND latch (SR flip-flop)
  • Clock divider / oscillator with a 74HC14 Schmitt inverter
  • Simple burglar alarm using OR gates on multiple sensor inputs
  • XOR gate as a 1-bit comparator (signals-equal detector)
  • LED blinker with 4093 CMOS Schmitt NAND

Common failures

Outputs damaged by over-voltage or short circuits. Latch-up in CMOS if input exceeds supply rails. Static damage during handling (especially 4000 series). Symptoms: stuck output, excessive current draw, no switching.

How to test

Power the IC with VCC and GND. Apply known HIGH (VCC) or LOW (GND) inputs via jumper wires. Read the output with a multimeter or LED + 330Ω resistor. Compare against the gate's truth table. A logic probe is the fastest tool for this.

Substitutes

Other logic families with compatible pinouts (e.g. 74LS00 ↔ 74HC00 ↔ 74HCT00). For simple functions, a small microcontroller (ATtiny, PIC) can replace several gates.

Where to buy

DigiKeyMouserLCSCRobuAmazon