Sunday, July 14, 2024

555 Timer IC Pinout, Circuit, Working, and Datasheet

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The 555 timer IC is an integral part of electronics projects. Be it a simple project involving a single 8-bit microcontroller and some peripherals or a complex one involving system on chips (SoCs), a 555 timer is involved. These provide time delays, as an oscillator and as a flip-flop element among other applications.

Introduced in 1971 by the American company Signetics, the 555 is still in widespread use due to its low price, ease of use, and stability. It is made by many companies in the original bipolar and low-power CMOS types. According to an estimate, a billion units were manufactured back in the year 2003 alone.

555 Timer IC Internal Circuit

Depending on the manufacturer, the standard 555 timer package includes 25 transistors, 2 diodes, and 15 resistors on a silicon chip installed in an 8-pin mini dual-in-line package (DIP-8). Variants consist of combining multiple chips on one board. However, 555 is still the most popular.

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555 Timer IC Internal Circuit
555 Timer IC Internal Circuit

Let us look at the pin diagram to have an idea about the timer Integrated Circuit (IC) before we talk about the 555 timers working.

555 Time IC Pin Diagram

555 Timer IC Pinout
Pin Diagram
555 Timer Pin Description
555 Timer Pin Description

555 Timer Specification

555 timer is used in almost every electronic circuit today. A 555 timer works as a flip-flop or as a multi-vibrator, it has a particular set of configurations. Some of the major features of the 555 timers would be,

  • It operates from a wide range of power ranging from +5 Volts to +18 Volts supply voltage.
  • Sinking or sourcing 200 mA of load current.
  • The external components should be selected properly so that the timing intervals can be made into several minutes along with the frequencies exceeding several hundred kilohertz.
  • The output pin of a 555 timer can drive a transistor-transistor logic (TTL) due to its high current output.
  • It has a temperature stability of 50 parts per million (ppm) per degree Celsius change in temperature which is equivalent to 0.005 %/ °C.
  • The duty cycle of the timer is adjustable.
  • Also, the maximum power dissipation per package is 600 mW, and its trigger pulse and reset inputs have logic compatibility.

555 Timer Working

The NE555 timer IC generally operates in 3 modes:

  1. Astable Mode
  2. Monostable Mode
  3. Bi-stable modes

Astable Mode

This means there will be no stable level of output. So the output will be swinging between high and low. This character of unstable output is used as a clock or square wave output for many applications.

Also Check: 555 Timer Calculator for Astable Circuit

Monostable Mode

This configuration consists of one stable and one unstable state. The stable state can be chosen as either high or low by the user. If the stable output is set at high (1), the output of the timer is high (1).

At the application of an interrupt, the timer output turns low (0). Since the low state is unstable it goes to high (1) automatically after the interrupt passes. Similar is the case for a low stable monostable mode.

Bi-stable Mode

In bistable mode, both the output states are stable. At each interrupt, the output changes from low (0) to high (1) and vice versa, and stays there. For example, if we have a high (1) output, it will go low(0) once it receives an interrupt and stays low (0) till the next interrupt changes the status.

More technical details can be found in the 555 Timer IC Datasheet.

IC 555 Timer-based Projects

You can also check the list of Interesting 555 timer projects.

More tutorials are available in the learning corner.

This article was first published on 4th June 2017 and recently updated in June 2024.


  1. i was making equal 3 sec stable out on and off pulse on astable mode and my positive peak was a small lengthier than negative peak. I tried a Lot but if i change the resistance and capacitor i will loose my either positive peak timing or negative peak timing and if i got it both as same then i will lose on and off time from 3 sec delay. but from your article i got idea about how monostable mode can help me. Now i am changing my path towards it. thanking you.


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