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555 timer IC

  

555 timer IC


The 555 is an integrated circuit (chip) implementing a variety of timer and multivibrator applications. The IC was was designed and invented by Hans R. Camezind. It was designed in 1970 and introduced in 1971 by Signetics (later acquired by Philips). The original name was the SE555/NE555 and was called "The IC Time Machine". It is still in wide use, thanks to its ease of use, low price and good stability. Still today, Samsung in Korea manufactures over 1 billion a year (2003).

The 555 timer is one of the most popular and versatile integrated circuits ever produced. It includes 23 transistors, 2 diodes and 16 resistors on a silicon chip installed in an 8-pin mini dual-in-line package (DIP). The 556 is a 14-pin DIP that combines two 555's on a single chip. Also available are ultra-low power versions of the 555. The 555 has two principle operating modes:

  • Monostable mode: In this mode, the 555 functions as a "one-shot." applications include timers, missing pulse detection, bouncefree switches, touch switches, etc.

  • Astable mode: The 555 can operate as an oscillator. Uses include LED and lamp flashers, pulse generation, logic clocks, tone generation, security alarms, etc.

    Usage

The connection of the pins is as follows:

Using simply a capacitor and a resistor, the timing interval, i.e. the time during which the output stays low, can be adjusted to the need of the specific application. An example configuration is shown below:


Example 555 schematic

The interval time t is given by

which is the time it takes to charge C to 63% of the applied voltage (exact figure: (1-1/e)V). See RC circuit for an explanation of this effect.

Specifications


These specifications apply to the NE555. Other 555 timers can have better specifications depending on the grade (military, medical, etc).

Derivatives

Many pin-compatible variants, including CMOS versions, have been built by various companies. The 555 is also known under the following type numbers:

External links

  • 555 Timer Tutorial
  • Data Sheet (Fairchild)

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