555 Timer IC

  
IC 555 is a very 8 pin popular IC that is designed to work as a timer. And it is used to construct timer-based projects just like Astable, Monostable, bistable, and many more.

The 555 IC can operate from a wide range of supply voltages of + 5 V to +18 V. This makes 555 compatible with standard digital circuits whose voltage levels(0-state = 0V, 1-state = 5 V) are known as TTL (transistor-transistor logic) levels. 


IC 555 Timer



To better understand read the Timer and it uses


Timer

Applications such as square wave, ramp, pulse generators, and one-shot multi-vibrators, etc. require a circuit essentially capable of producing timing intervals. Due to the circuit components count and the delicacy in using transistors, integrated circuits(ICs) are preferred. One such most suitable and popular IC for producing timing intervals is the 555. This IC is popularly known as 555 timer





Modes of operation

The 555 IC timer has two modes of operation:

-  as an astable(free-running) multi-vibrator
-  as a mono-stable (one-shot) multi-vibrator



Block diagram of 555 Timer IC

Block Diagram of 555 timer Circuit

PIN Configuration

Pin No.1. It is meant to ground the IC.

Pin No.2. It is 'Trigger' terminal. On applying a negative-going trigger voltage to this terminal.

Pin No.3. It is 'Output' terminal. A load can be connected between the output terminal and Vcc terminal or between the output terminal and the ground terminal.

Pin No.4. It is 'reset' terminal. It allows the IC to be disabled and over-rides the command signals at the trigger input.

Pin No.5. It is 'control voltage' input terminal. It is used to change both the threshold (gate) and trigger voltage level.

Pin No.6. It is 'Threshold' (a short of gate ) terminal. On applying a positive-going threshold voltage to this terminal.

Pin No.7. It is 'Discharged' terminal. It is meant for discharging an external timing capacitor during the time when the output is 'low'.

Pin No.8. It is meant for supplying bias voltage i.e. Vcc +5v To +18 V.




Types of 555 timer IC packages


The 555 timer IC is available in two package styles metal can (TO) and DIP as shown in Fig



PIN Diagram of 555 Timer Circuit


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