Difference between revisions of "555 timer"
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[[Image:Signetics NE555N.JPG|thumb|right|NE555 from [[Signetics]] in [[Dual in-line package|dual-in-line package]]]]
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[[Image:555-schem.png|frame|right|Schematic symbol of the 555 timer]]
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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]]).
  
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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.
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The 555 has three operating modes:
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*[[Monostable]] mode: in this mode, the 555 functions as a "one-shot". Applications include timers, missing pulse detection, bouncefree switches, touch switches, etc.
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*[[Astable]] mode: the 555 can operate as an [[oscillator]]. Uses include [[LED]] and lamp flashers, pulse generation, logic clocks, tone generation, security alarms, etc.
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*[[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.
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==Usage==
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The connection of the pins is as follows:
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{| border=1
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! Nr. !! Name !! Purpose
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|-
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| 1 || GND || '''G'''rou'''nd''', low level
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|-
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| 2 || TR  || A short pulse high->low on the '''tr'''igger starts the timer
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|-
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| 3 || Q  || During a timing interval, the '''o'''utput stays at [[Vcc|+V<sub>CC</sub>]]
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|-
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| 4 || R  || A timing interval can be interrupted by applying a '''r'''eset pulse to low (0V)
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|-
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| 5 || CV  || '''C'''ontrol '''v'''oltage allows access to the internal voltage divider (2/3 V<sub>CC</sub>)
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|-
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| 6 || THR || The '''thr'''eshold at which the interval ends (it ends if U.thr > 2/3 V<sub>CC</sub>)
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|-
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| 7 || DIS || Connected to a capacitor whose '''dis'''charge time will influence the timing interval
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|-
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| 8 || V+, V<sub>CC</sub> || The positive supply '''v'''oltage which must be between 5 and 15 V, high level
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|}
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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:
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<center>[[Image:555-schem-2.png|Example 555 schematic]]<br />Example 555 schematic </center>
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The interval time ''t'' is given by
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:<math>t = RC</math>
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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.
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In the astable mode, the high time from each pulse is given by
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:<math>high = 0.69 \cdot (R1 + R2) \cdot C</math>
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and the low time from each pulse is given by
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:<math>low = 0.69 \cdot R2 \cdot C</math>
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where R1 and R2 are the values of the resistor in [[ohm]]s and C is the value of the capacitor in [[farad]]s.
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==Specifications==
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These specifications apply to the NE555. Other 555 timers can have better specifications depending on the grade (military, medical, etc).
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{| border=1 cellpadding=2
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|Supply voltage (V<sub>CC</sub>)
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|4.5 to 15 V
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|-
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|Supply current (V<sub>CC</sub> = +5 V)
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|3 to 6 mA
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|-
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|Supply current (V<sub>CC</sub> = +15 V)
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|10 to 15 mA
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|-
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|Output current (maximum)
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|200 mA
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|-
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|Power dissipation
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|600 mW
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|-
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|Operating temperature
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|0 to 70° C
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|}
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==Derivatives==
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Many pin-compatible variants, including [[CMOS]] versions, have been built by various companies. The 555 is also known under the following type numbers:
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{| border="1" cellpadding="2"
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!Manufacturer
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!Model
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!Remark
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|-
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|ECG Philips
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|ECG955M
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|-
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|Exar
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|XR-555
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|-
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|Fairchild
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|NE555/KA555
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|-
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|Harris
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|HA555
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|-
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|Intersil
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|SE555/NE555/ICM7555
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|-
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|Lithic Systems
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|LC555
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|-
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|Maxim
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|ICM7555
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|-
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|Motorola
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|MC1455/MC1555
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|-
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|National
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|LM1455/LM555C
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|-
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|NTE Sylvania
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|NTE955M
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|-
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|Raytheon
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|RM555/RC555
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|-
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|RCA
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|CA555/CA555C
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|-
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|Sanyo
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|LC7555
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|-
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|Texas Instruments
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|SN52555/SN72555; TLC555
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|-
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|USSR
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|K1006ВИ1
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|-
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|Zetex
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|ZSCT1555
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|down to 0.9V
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|}
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==External links==
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*[http://www.uoguelph.ca/~antoon/gadgets/555/555.html 555 Timer Tutorial]
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*[http://www.fairchildsemi.com/ds/NE/NE555.pdf Data Sheet (Fairchild) (PDF)]
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*[http://www.falstad.com/circuit/ex-555.html Java simulation] of 555 oscillator circuit
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*[http://www.datasheetarchive.com/search.php?q=NE555&sType=part&ExactDS=Starts 1972 Signetics NE555 datasheet (PDF)]
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[[Category:Integrated circuits]]
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[[da:555 timer ic]]
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[[de:NE555]]
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[[es:Circuito integrado 555]]
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[[it:NE555]]
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[[lt:NE 555]]
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[[nl:555 timer IC]]
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[[pt:CI 555]]
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[[sk:NE555]]
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[[th:ไอซี 555]]

Revision as of 05:55, 6 January 2007

NE555 from Signetics in dual-in-line package
File:555-schem.png
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 (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 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, 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:

Nr. Name Purpose
1 GND Ground, low level
2 TR A short pulse high->low on the trigger starts the timer
3 Q During a timing interval, the output stays at +VCC
4 R A timing interval can be interrupted by applying a reset pulse to low (0V)
5 CV Control voltage allows access to the internal voltage divider (2/3 VCC)
6 THR The threshold at which the interval ends (it ends if U.thr > 2/3 VCC)
7 DIS Connected to a capacitor whose discharge time will influence the timing interval
8 V+, VCC The positive supply voltage 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:

Example 555 schematic
Example 555 schematic

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 ohms and C is the value of the capacitor in farads.

Specifications

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

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:

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

da:555 timer ic de:NE555 es:Circuito integrado 555 it:NE555 lt:NE 555 nl:555 timer IC pt:CI 555 sk:NE555 th:ไอซี 555

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