NE555

The NE555 is a widely used 8-pin bipolar timer integrated circuit designed to generate precise time delays and oscillations. It was designed by Hans Camenzind for Signetics and released in 1972, becoming one of the most popular and enduring ICs in electronics. The device is known for its simplicity, versatility, and broad voltage and temperature range, which contributed to its widespread adoption in both hobbyist and professional projects.

Inside the NE555, a three-resistor voltage divider creates reference levels at one-third and two-thirds of the supply voltage. Two comparators monitor the trigger and threshold inputs, and their outputs feed a set-reset flip-flop. A discharge transistor in the chip sinks current from an external timing capacitor connected to pin 6, 2, and 7 in various configurations. Pinout typically includes: pin 1 ground, pin 2 trigger, pin 3 output, pin 4 reset, pin 5 control voltage, pin 6 threshold, pin 7 discharge, and pin 8 Vcc.

The NE555 supports several modes of operation. In monostable mode, a trigger on pin 2 causes the output to go high for a time determined by an external resistor and capacitor, with the period approximated by t ≈ 1.1 × R × C. In astable mode, the circuit continuously oscillates with timing set by two resistors and a capacitor; the frequency is roughly f ≈ 1.44 / ((RA + 2RB) × C), and the duty cycle is adjustable via resistor values. In bistable mode, the output acts as a latch that is set or reset by input pulses.

Variants and derivatives, including CMOS versions, extend the family’s power and voltage ranges. The NE555 remains a foundational component for timers, oscillators, PWM controllers, and debouncing circuits across countless applications.