555 timer IC working and Diagram

This is a Timer IC you can use this IC in PCB for maintain Timing  The 555 timer IC is an integral part of electronics projects. Be it a simple project involving a single 8 bit micro-controller and some peripherals or a complex one involving system on chips (SoCs), 555 timer working is involved. These provide time delays, as an oscillator and as a flip-flop element among other applications..The 555 operates in 3 modes. (Astable, Mono-stable and Bi-stable modes.)

Depending on the manufacturer, the standard 555 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 consists of combining multiple chips on one board. However 555 is still the most popular

Pin Name Purpose
1 GND Ground reference voltage, low level (0 V)

The OUT pin goes high and a timing interval starts when this input falls below 1/2 of CTRL voltage (which is typically 1/3 Vcc, CTRL being 2/3 Vcc by default if CTRL is left open). In other words, OUT is high as long as the trigger low. Output of the timer totally depends upon the amplitude of the external trigger voltage applied to this pin.

3 OUT This output is driven to approximately 1.7 V below +Vcc, or to GND.

A timing interval may be reset by driving this input to GND, but the timing does not begin again until RESET rises above approximately 0.7 volts. Overrides TRIG which overrides threshold.


Provides “control” access to the internal voltage divider (by default, 2/3 Vcc).


The timing (OUT high) interval ends when the voltage at threshold is greater than that at CTRL (2/3 Vcc if CTRL is open).


Open collector output which may discharge a capacitor between intervals. In phase with output.

8 Vcc

Positive supply voltage, which is usually between 3 and 15 V depending on the variation.



Supply voltage                                    4.5 to 15 V
Supply current (+5 V)                       3 to 6 mA
Supply current (+15 V)                     10 to 15 mA
Output current (maximum)            200 mA
Maximum Power dissipation          600 mW
Operating temperature                    0 to 75 °C
Power consumption                          30 mW@5V, 225 mW@15V