555 timer

2006-08-19T11:11:50Z

Flyingspuds2007:

File:Signetics NE555N.JPG

2006-08-19T11:09:51Z

Flyingspuds2007: Signetics NE555N, the original 555 type oscillator, in a dual-in-line plastic package, manufactured in 1978 (work week 28)

Signetics NE555N, the original 555 type oscillator, in a dual-in-line plastic package, manufactured in 1978 (work week 28)

555 timer

2006-08-19T11:04:22Z

Flyingspuds2007:

[[Image:Signetics NE555N.JPG|thumb|right|NE555 from [[Signetics]] in [[Dual in-line package|dual-in-line package]]]]
[[Image:555-schem.png|frame|right|Schematic symbol of the 555 timer]]
The '''555''' is an [[integrated circuit]] (chip) implementing a variety of [[timer]] and [[multivibrator]] applications. The IC was designed and invented by [[Hans R. Camenzind]]. 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. Even today, [[Samsung]] in [[Korea]] manufactures over 1 [[billion]] units per year ([[As of 2003|2003]]).

The 555 timer is one of the most popular and versatile integrated circuits ever produced. It includes 23 [[transistor]]s, 2 [[diode]]s and 16 [[resistor]]s on a silicon chip installed in an 8-pin mini dual-in-line package ([[Dual in-line package|DIP]]). The 556 is a 14-pin DIP that combines two 555s on a single chip. The 558 is a 16-pin DIP that combines four, slightly modified, 555s on a single chip (DIS & THR are connected internally, TR is falling edge sensitive instead of level sensitive). Also available are ultra-low power versions of the 555 such as the 7555. The 7555 requires slightly different wiring using fewer external components and less power.

The 555 has three 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.
*[[Bistable]] mode: the 555 can operate as a [[Flip-flop (electronics)|flip-flop]], if the DIS pin is not connected and no capacitor is used. Uses include bouncefree latched switches, etc.

==Usage==
The connection of the pins is as follows:
{| border=1
! Nr. !! Name !! Purpose
|-
| 1 || GND || '''G'''rou'''nd''', low level
|-
| 2 || TR || A short pulse high->low on the '''tr'''igger starts the timer
|-
| 3 || Q || During a timing interval, the '''o'''utput stays at [[Vcc|+VCC]]
|-
| 4 || R || A timing interval can be interrupted by applying a '''r'''eset pulse to low (0V)
|-
| 5 || CV || '''C'''ontrol '''v'''oltage allows access to the internal voltage divider (2/3 VCC)
|-
| 6 || THR || The '''thr'''eshold at which the interval ends (it ends if U.thr > 2/3 VCC)
|-
| 7 || DIS || Connected to a capacitor whose '''dis'''charge time will influence the timing interval
|-
| 8 || V+, VCC || The positive supply '''v'''oltage which must be between 5 and 15 V, high level
|}

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:

<center>[[Image:555-schem-2.png|Example 555 schematic]] Example 555 schematic </center>

The interval time ''t'' is given by

:<math>t = RC</math>

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.

In the astable mode, the high time from each pulse is given by

:<math>high = 0.69 \cdot (R1 + R2) \cdot C</math>

and the low time from each pulse is given by

:<math>low = 0.69 \cdot R2 \cdot C</math>

where R1 and R2 are the values of the resistor in [[ohm]]s and C is the value of the capacitor in [[farad]]s.

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

{| border=1 cellpadding=2
|Supply voltage (VCC)
|4.5 to 15 V
|-
|Supply current (VCC = +5 V)
|3 to 6 mA
|-
|Supply current (VCC = +15 V)
|10 to 15 mA
|-
|Output current (maximum)
|200 mA
|-
|Power dissipation
|600 mW
|-
|Operating temperature
|0 to 70° C
|}

==Derivatives==

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

{| border="1" cellpadding="2"
!Manufacturer
!Model
!Remark
|-
|ECG Philips
|ECG955M
|-
|Exar
|XR-555
|-
|Fairchild
|NE555/KA555
|-
|Harris
|HA555
|-
|Intersil
|SE555/NE555/ICM7555
|-
|Lithic Systems
|LC555
|-
|Maxim
|ICM7555
|-
|Motorola
|MC1455/MC1555
|-
|National
|LM1455/LM555C
|-
|NTE Sylvania
|NTE955M
|-
|Raytheon
|RM555/RC555
|-
|RCA
|CA555/CA555C
|-
|Sanyo
|LC7555
|-
|Texas Instruments
|SN52555/SN72555; TLC555
|-
|USSR
|K1006ВИ1
|-
|Zetex
|ZSCT1555
|down to 0.9V
|}

==External links==
*[http://www.uoguelph.ca/~antoon/gadgets/555/555.html 555 Timer Tutorial]
*[http://www.fairchildsemi.com/ds/NE/NE555.pdf Data Sheet (Fairchild) (PDF)]
*[http://www.falstad.com/circuit/ex-555.html Java simulation] of 555 oscillator circuit
*[http://www.datasheetarchive.com/search.php?q=NE555&sType=part&ExactDS=Starts 1972 Signetics NE555 datasheet (PDF)]

[[Category:Integrated circuits]]

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555 timer

File:Signetics NE555N.JPG

555 timer