# data[].attributes.body
הרכיב 555 הוא רכיב שמשתמשים בו מאד באלקטרוניקה לעבודה בתור טיימר

# data[].attributes.attachment_link.title
555 Timer IC: Internal Structure, Working, Pin Diagram and Description

# data[].attributes.attachment_link.description
node:summary555 Timer IC is one of the commonly used IC among students and hobbyists. There are a lot of applications of this IC, mostly used as vibrators like, ASTABLE MULTIVIBRATOR, MONOSTABLE MULTIVIBRATOR, and BISTABLE MULTIVIBRATOR. You can find here some circuits based on 5555 IC.

# data[].attributes.headline
ירין.מ ואופיר.ב 

# data[].attributes.subject
ירין.מ ואופיר.ב 

# data[].attributes.body
הרכיב 555 הוא רכיב שיכול להיות מחובר בצורה של Monostable ובכך לייצר טיימר של זמן קבוע הרכיב 555 ידוע בשמו moltivibrator
http://www.electronics-tutorials.ws/waveforms/555_oscillator.html

# data[].attributes.attachment_link.readable_text
The 555 Timer IC can be connected either in its Monostable mode thereby producing a precision timer of a fixed time duration, or in its Bistable mode to produce a flip-flop type switching action. But we can also connect the 555 timer IC in an Astable mode to produce a very stable 555 Oscillator circuit for generating highly accurate free running waveforms whose output frequency can be adjusted by means of an externally connected RC tank circuit consisting of just two resistors and a capacitor.

The 555 Oscillator is another type of relaxation oscillator for generating stabilized square wave output waveforms of either a fixed frequency of up to 500kHz or of varying duty cycles from 50 to 100%. In the previous 555 Timer tutorial we saw that the Monostable circuit produces a single output one-shot pulse when triggered on its pin 2 trigger input.

Whereas the 555 monostable circuit stopped after a preset time waiting for the next trigger pulse to start over again, in order to get the 555 Oscillator to operate as an astable multivibrator it is necessary to continuously re-trigger the 555 IC after each and every timing cycle.

This re-triggering is basically achieved by connecting the trigger input (pin 2) and the threshold input (pin 6) together, thereby allowing the device to act as an astable oscillator. Then the 555 Oscillator has no stable states as it continuously switches from one state to the other. Also the single timing resistor of the previous monostable multivibrator circuit has been split into two separate resistors, R1 and R2 with their junction connected to the discharge input (pin 7) as shown below.

Basic Astable 555 Oscillator Circuit

In the 555 Oscillator circuit above, pin 2 and pin 6 are connected together allowing the circuit to re-trigger itself on each and every cycle allowing it to operate as a free running oscillator. During each cycle capacitor, C charges up through both timing resistors, R1 and R2 but discharges itself only through resistor, R2 as the other side of R2 is connected to the discharge terminal, pin 7.

Then the capacitor charges up to 2/3Vcc (the upper comparator limit) which is determined by the 0.693(R1+R2)C combination and discharges itself down to 1/3Vcc (the lower comparator limit) determined by the 0.693(R2*C) combination. This results in an output waveform whose voltage level is approximately equal to Vcc - 1.5V and whose output "ON" and "OFF" time periods are determined by the capacitor and resistors combinations. The individual times required to complete one charge and discharge cycle of the output is therefore given as:

Astable 555 Oscillator Charge and Discharge Times

Where, R is in Ω and C in Farads.

When connected as an astable multivibrator, the output from the 555 Oscillator will continue indefinitely charging and discharging between 2/3Vcc and 1/3Vcc until the power supply is removed. As with the monostable multivibrator these charge and discharge times and therefore the frequency are independent on the supply voltage.

The duration of one full timing cycle is therefore equal to the sum of the two individual times that the capacitor charges and discharges added together and is given as:

555 Oscillator Cycle Time

The output frequency of oscillations can be found by inverting the equation above for the total cycle time giving a final equation for the output frequency of an Astable 555 Oscillator as:

555 Oscillator Frequency Equation

By altering the time constant of just one of the RC combinations, the Duty Cycle better known as the "Mark-to-Space" ratio of the output waveform can be accurately set and is given as the ratio of resistor R2 to resistor R1. The Duty Cycle for the 555 Oscillator, which is the ratio of the "ON" time divided by the "OFF" time is given by:

555 Oscillator Duty Cycle

The duty cycle has no units as it is a ratio but can be expressed as a percentage ( % ). If both timing resistors, R1 and R2 are equal in value, then the output duty cycle will be 2:1 that is, 66% ON time and 33% OFF time with respect to the period.

555 Oscillator Example No1

An Astable 555 Oscillator is constructed using the following components, R1 = 1kΩ, R2 = 2kΩ and capacitor C = 10uF. Calculate the output frequency from the 555 oscillator and the duty cycle of the output waveform.

- capacitor charge "ON" time is calculated as:

- capacitor discharge "OFF" time is calculated as:

Total periodic time ( T ) is therefore calculated as:

The output frequency, ƒ is therefore given as:

Giving a duty cycle value of:

As the timing capacitor, C charges through resistors R1 and R2 but only discharges through resistor R2 the output duty cycle can be varied between 50 and 100% by changing the value of resistor R2. By decreasing the value of R2 the duty cycle increases towards 100% and by increasing R2 the duty cycle reduces towards 50%. If resistor, R2 is very large relative to resistor R1 the output frequency of the 555 astable circuit will determined by R2 x C only.

The problem with this basic astable 555 oscillator configuration is that the duty cycle, the "mark to-space" ratio will never go below 50% as the presence of resistor R2 prevents this. In other words we cannot make the outputs "ON" time shorter than the "OFF" time, as (R1 + R2)C will always be greater than the value of R1 x C. One way to overcome this problem is to connect a signal bypassing diode in parallel with resistor R2 as shown below.

Improved 555 Oscillator Duty Cycle

By connecting this diode, D1 between the trigger input and the discharge input, the timing capacitor will now charge up directly through resistor R1 only, as resistor R2 is effectively shorted out by the diode. The capacitor discharges as normal through resistor, R2.

An additional diode, D2 can be connected in series with the discharge resistor, R2 if required to ensure that the timing capacitor will only charge up through D1 and not through the parallel path of R2. This is because during the charging process diode D2 is connected in reverse bias blocking the flow of current through itself.

Now the previous charging time of t ₁ = 0.693(R1 + R2)C is modified to take account of this new charging circuit and is given as: 0.693(R1 x C). The duty cycle is therefore given as D = R1/(R1 + R2). Then to generate a duty cycle of less than 50%, resistor R1 needs to be less than resistor R2.

Although the previous circuit improves the duty cycle of the output waveform by charging the timing capacitor, C1 through the R1 + D1 combination and then discharging it through the D2 + R2 combination, the problem with this circuit arrangement is that the 555 oscillator circuit uses additional components, i.e. two diodes.

We can improve on this idea and produce a fixed square wave output waveform with an exact 50% duty cycle very easily and without the need for any extra diodes by simply moving the position of the charging resistor, R2 to the output ( pin 3 ) as shown.

50% Duty Cycle Astable Oscillator

The 555 oscillator now produces a 50% duty cycle as the timing capacitor, C1 is now charging and discharging through the same resistor, R2 rather than discharging through the timers discharge pin 7 as before. When the output from the 555 oscillator is HIGH, the capacitor charges up through R2 and when the output is LOW, it discharges through R2. Resistor R1 is used to ensure that the capacitor charges up fully to the same value as the supply voltage.

However, as the capacitor charges and discharges through the same resistor, the above equation for the output frequency of oscillations has to be modified a little to reflect this circuit change. Then the new equation for the 50% Astable 555 Oscillator is given as:

50% Duty Cycle Frequency Equation

Note that resistor R1 needs to be sufficiently high enough to ensure it does not interfere with the charging of the capacitor to produce the required 50% duty cycle. Also changing the value of the timing capacitor, C1 changes the oscillation frequency of the astable circuit.

555 Oscillator Applications

We said previously that the maximum output to either sink or source the load current via pin 3 is about 200mA and this value is more than enough to drive or switch other logic IC's, a few LED's or a small lamp etc and that we would need to use a bipolar transistor or MOSFET to amplify the 555's output to drive larger current loads such as motor or relays.

But the 555 Oscillator can also be used in a wide range of waveform generator circuits and applications that require very little output current such as in electronic test equipment for producing a whole range of different output test frequencies.

The 555 can also be used to produce very accurate sine, square and pulse waveforms or as LED or lamp flashers and dimmers to simple noise making circuits such as metronomes, tone and sound effects generators and even musical toys for Christmas.

We could very easily build a simple 555 oscillator circuit to flash a few LED's "ON" and "OFF" similar to the one shown, or to produce a high frequency noise from a loudspeaker. But one very nice and simple to build science project using an astable based 555 oscillator is that of an Electronic Metronome.

Metronomes are devices used to mark time in pieces of music by producing a regular and recurring musical beat or click. A simple electronic metronome can be made using a 555 oscillator as the main timing device and by adjusting the output frequency of the oscillator the tempo or "Beats per Minute" can be set.

So for example, a tempo of 60 beats per minute means that one beat will occur every second and in electronics terms that equates to 1Hz. So by using some very common musical definitions we can easily build a table of the different frequencies required for our metronome circuit as shown below.

Metronome Frequency Table

The output frequency range of the metronome was simply calculated as the reciprocal of 1 minute or 60 seconds divided by the number of beats per minute required, for example (1/(60 secs / 90 bpm) = 1.5Hz) and 120bpm is equivalent to 2Hz, and so on. So by using our now familiar equation above for calculating the output frequency of an astable 555 oscillator circuit the individual values of R1, R2 and C can be found.

The time period of the output waveform for an astable 555 Oscillator is given as:

For our electronic metronome circuit, the value of the timing resistor R1 can be found by rearranging the equation above to give:

Assuming a value for resistor R2 = 1kΩ and capacitor C = 10uF the value of the timing resistor R1 for our frequency range is given as 142k3Ω at 60 beats per minute to 46k1Ω at 180 beats per minute, so a variable resistor (potentiometer) of 150kΩ would be more than enough for the metronome circuit to produce the full range of beats required and some more. Then the final circuit for our electronic metronome example would be given as:

555 Electronic Metronome

This simple metronome circuit demonstrates just one simple way of using a 555 oscillator to produce an audible sound or note. It uses a 150kΩ potentiometer to control the full range of output pulses or beats, and as it has a 150kΩ value it can be easily calibrated to give an equivalent percentage value corresponding to the position of the potentiometer. For example, 60 beats per minute equals 142.3kΩ or 95% rotation.

Likewise, 120 beats per minute equals 70.1kΩ or 47% rotation, etc. Additional resistors or trimmer's can be connected in series with the potentiometer to pre-set the outputs upper and lower limits to predefined values, but these additional components will need to be taken into account when calculating the output frequency or time period.

While the above circuit is a very simple and amusing example of sound generation, it is possible to use the 555 Oscillator as a noise generator/synthesizer or to make musical sounds, tones and alarms by constructing a variable-frequency, variable-mark/space ratio waveform generator.

In this tutorial we have used just a single 555 oscillator circuit to produce a sound but by cascading together two or more 555 oscillator chips, various circuits can be constructed to produce a whole range of musical and sound effects. One such novelty circuit is the police car "Dee-Dah" siren given in the example below.

555 Oscillator Police "Dee-Dah" Siren

The circuit simulates a warble-tone alarm signal that simulates the sound of a police siren. IC1 is connected as a 2Hz non-symmetrical astable multivibrator which is used to frequency modulate IC2 via the 10kΩ resistor. The output of IC2 alternates symmetrically between 300Hz and 660Hz taking 0.5 seconds to complete each alternating cycle.

# data[].attributes.attachment_link.title
555 Oscillator Tutorial - The Astable Multivibrator

# data[].attributes.attachment_link.description
The 555 Timer IC can be connected either in its Monostable mode thereby producing a precision timer of a fixed time duration, or in its Bistable mode to produce a flip-flop type switching action.

# data[].attributes.headline
אליסה ואופיר

# data[].attributes.subject
אליסה ואופיר

# data[].attributes.body
הרכיב 555 הוא טיימר/שעון אשר נפוץ בתעשיית האלקטרוניקה והחשמל.  http://www.jameco.com/jameco/workshop/techtip/555-timer-tutorial.html

# data[].attributes.body
http://www.electronics.dit.ie/staff/mtully/555%20folder/555%20timer.htm

# data[].attributes.body
הרכיב 555 יכול לשמש בתור טיימר לתדר שמוכנס לתוך המגבר

http://www.555-timer-circuits.com/555-amplifier.html

# data[].attributes.body
זהו שבב שעון/מתנד 555 בסיסי וידוע מימי בית הספר. כיב קלסי לבניית מעגלים ראשונים איפה שיש צורך לנדנד לד, לייצר צפצוף או אלפי סוגי פרוייקטים אחרים המשתמשים במתנד זה. (multi vibrator)
https://www.4project.co.il/product/ne555-555-timer

# data[].attributes.headline
ליטל,זהר,יותם טי

# data[].attributes.body
ליטל,זהר,יותם
טיימר 555 בפני עצמו אינו רכיב דיגיטלי אלא מעגל משולב לינארי, אולם משתמשים בו במעגלים דיגיטליים רבים בתור מחולל גל ריבועי לאות השעון ∅.

# data[].attributes.headline
משימה (יש לסיים את המשימה בתוך 5 דקות )

# data[].attributes.subject
משימה (יש לסיים את המשימה בתוך 5 דקות )

# data[].attributes.body
1. על כל זוג תלמידים לפתוח חלון כמו החלון הנוכחי על ידי דבל קליק במקום כלשהו בלוח

2. לרשום בו את שמם הפרטי (בלבד) בכותרת למעלה (היכן שנרשם באדום)

3.למצוא אתר יחודי (כזה שלא נמצא כבר על הפדלט) ברשת ,בעברית או באנגלית, המסביר את הרכיב 555.

4. להעתיק את הקישור של האתר לחלון שפתחתם.

4.לרשום במשפט אחד או שניים, מתוך האתר שמצאתם, מהו הרכיב 555.

# data[].attributes.headline
גדי   (דוגמה)

# data[].attributes.subject
גדי   (דוגמה)

# data[].attributes.body
הרכיב 555 הינו "קוצב זמן" מתוך האתר הבא

# data[].attributes.attachment_link.readable_text
אלקטרוניקה

מבנה פנימי של הרכיב:

ההתקן מורכב משני משוונים (comperator), דלגלג (FF) ומהפך:

- המשוון משווה את פתחי 2 הכניסות שלו כאשר מתח היציאה שלו עולה כאשר המתח ב-2 הכניסות זהה.

- ה-flip flop מגדיר את רוחב הפולס ביציאה ובדרך כלל Low ונעשה High לאחר Set ושוב פעם Low לאחר Reset.

- המהפך מבטיח שרמת מתח היציאה תשתנה מהאדמה ל- Low ו-VDD ל-High. מהפך זה גם חוצץ בין ההתקן לעומס על ההתקן. במעגל יש גם מחלק מתח המורכב מ-3 נגדים זהים כך שהמתח בין 2 קצוות המחלק יהיו אדמה ומקור ובין הנגדים המתח יהיה שליש VDD ושני שליש VDD בהתאם.

הכניסות והיציאות מההתקן:

כניסות פולס הדרבון להפעלת המעגל או להחלפת מחזור, פולס זה הוא שלילי כך שהרמה שם תהיה VDD. המעגל מושפע כאשר המתח יורד לשליש VDD.

מתח המוצא Vout

פולס במבוא הדרוש לאפס את המתח ביציאה. פולס זה שולט על פעולת כל ההתקן ומבטל כל כניסה אחרת.
כפי שנאמר לעיל פעולת ה-trigger רק כאשר הוא יורד למתח של שליש VDD כדי להבטיח שפולס זה יהיה קצר ושירד מתחת למתח הנדרש יש שמכניסים מעגל דרבון

ה. Voltage Control - רגל 5

המתח בנקודה זו הוא שני שליש VDD היוצא ממחלק המתח - מתח ייחוס. לנקודה זו מחובר קבל בעל ערך של .1µF כדי למנוע רעשים שנובעים מהמיתוג. יש אפשרות לשנוי בצורה אלקטרונית של זמני המיתוג ואז כניסה זו קובעת את תחום המתחים לפעולת ההתקן.

המתח הדרוש כדי להפסיק את הפעולה או המחזור וכתוצאה להתחלת מחזור של פריקת הקבל. מתח זה פעיל רק כאשר ערכו שני שליש VDD ולא פעיל כאשר המתח קטן מזה.

קובע את רמת המתח שבו מתחיל תהליך פירוק הקבל, הזרם נכנס לטרנזיסטור כאשר הוא נמצא בהולכה. מחברים בדרך כלל את הדק ה - Discharge למעגל RC החיצוני.

מימוש רכיב הזמנן 555 כמתנד Astable

אנו נשתמש ברכיב ה555 כמתנד רב- יציב Astable ולכן התדר וזמן המחזור יקבעו על ידי 2 נגדים וקבל חיצוניים.

במצב ההתחלתי (הדלקת ההתקן) המתח על הדקTrigger הוא 0V ולכן המשוון השני בפעולה וכתוצאה ה- FF במצב set והיציאה Vo ב-HIGH .

כאשר מתח הקבל מגיע לרמה של /3V CC 2, המשוון הראשון נכנס לפעולה ומחליף את מצב ה-FF ל-Reset וכתוצאה היציאה תעבור ל-Low .

טרנזיסטור כמפסק:
אם Q יהיה '0' אין זרם ולכן הטרנזיסטור בנתק. (בין הקולקטור לאמיטר) - טעינה של הקבל.
אם Q יהיה '1' יזרום זרם בבסיס והטרנזיסטור יהיה בקצר (בין הקולקטור לאמיטר) - פריקה של הקבל.

התחלפות מצב ה-FF ל-Reset מכניסה את טרנזיסטורDischarge לרוויה וכתוצאה מתח הקולקטור יורד ל-Vc=0.2V, מתח זה מועבר לנקודת התחברות בין נגדים R A ו-R B כאשר נגד R A משמש כנגד Rc של מעגל ה-Discharge. מתחVc גורם לקבל להתחיל להתפרק עם מקדם זמן של τ ₂=R BC (בגלל טרנזיסטור Discharge R A איננו חלק ממעגל הפירוק).

הקבל מתפרק דרך הנגד R B עד שמגיע לרמת מתח של 1/3V CC ואז המשוון הראשון נכנס לפעולה וגורם ל-FF לעבור למצב SET. כל הפעולה חוזרת על עצמה .

· ככל שR A יהיה קטן ביחס לR B זמני הפריקה והטעינה יהיו קרובים זה לזה.

· ככל שR B יהיה גדול יותר זמני הפריקה והטעינה יהיו גדולים יותר

· אם R A יהיה גדול באופן משמעותי זמן הטעינה יהיה גדול יותר מזמן הפריקה.

במשווה A1 ברגל השלילית (2\3v) יש יותר מתח מאשר ברגל החיובית (6, Vc) ולכן המשווה מוציא "0" לוגי אל R בפילפלופ (F.F).

במשווה A2 ברגל החיובית (1\3v) יש יותר מתח מאשר ברגל השלילית (2, Vc) ולכן המשווה מוציא "1" אל S בפליפלופ (F.F).

ע"פ טבלת האמת של ה-F.F, ב-Q גג יתקבל "0". אין זרם בבסיס הטרנזיסטור, הטרנ' נתק והקבל נטען.

Vout="1" (לאחר המהפך)

במשווה A1 ברגל השלילית (2\3v) יש יותר מתח מאשר ברגל החיובית (6, Vc) ולכן המשווה מוציא "0" לוגי אל R בפילפלופ (F.F).

במשווה A2 ברגל החיובית (1\3v) יש פחות מתח מאשר ברגל השלילית (2, Vc) ולכן המשווה מוציא "0" אל S בפליפלופ (F.F).

ע"פ טבלת האמת של ה-F.F, נשמר מצב. כלומר: ב-Q גג יתקבל "0". אין זרם בבסיס הטרנזיסטור, הטנ' נתק והקבל נטען.

Vout="1" (לאחר המהפך)

במשווה A1 ברגל השלילית (2\3v) יש פחות מתח מאשר ברגל החיובית (6, Vc) ולכן המשווה מוציא "1" לוגי אל R בפילפלופ (F.F).

במשווה A2 ברגל החיובית (1\3v) יש פחות מתח מאשר ברגל השלילית (2, Vc) ולכן המשווה מוציא "0" אל S בפליפלופ (F.F).

ע"פ טבלת האמת של ה-F.F, ב-Q גג יתקבל "1". זורם זרם בבסיס הטרנזיסטור, הטרנ' נכנס לרוויה (מצב קצר), רגל 7 מתקצרת לאדמה, והקבל מתפרק (המתח שהוא שואף להגיע אליו עכשיו הוא 0v).

Vout="0" (לאחר המהפך)

מיד עם תחילת הפריקה, מתח הקבל יגיע טיפה מתחת ל- ⅔V :

במשווה A1 ברגל השלילית (2\3v) יש יותר מתח מאשר ברגל החיובית (6, Vc) ולכן המשווה מוציא "0" לוגי אל R בפילפלופ (F.F).

במשווה A2 ברגל החיובית (1\3v) יש פחות מתח מאשר ברגל השלילית (2, Vc) ולכן המשווה מוציא "0" אל S בפליפלופ (F.F).

ע"פ טבלת האמת של ה-F.F, נשמר מצב. כלומר, ב-Q גג מתקבל "1", הטרנ' ממשיך להיות קצר והקבל ממשיך להתפרק.

Vout="0" (לאחר המהפך)

במשווה A1 ברגל השלילית (2\3v) יש יותר מתח מאשר ברגל החיובית (6, Vc) ולכן המשווה מוציא "0" לוגי אל R בפילפלופ (F.F).

במשווה A2 ברגל החיובית (1\3v) יש יותר מתח מאשר ברגל השלילית (2, Vc) ולכן המשווה מוציא "1" אל S בפליפלופ (F.F).

ע"פ טבלת האמת של ה-F.F, ב-Q גג יתקבל "0". אין זרם בבסיס הטרנזיסטור- הטרנ' נכנס לקיטעון (נתק). פריקת הקבל נפסקת והוא מתחיל להטען.

Vout="1" (לאחר המהפך)

*התהליך הוא תהליך מחזורי וחוזר על עצמו. רק בהפעלה הראשונה של המעגל הקבל נטען מ-0v ל-⅓V.

ה-DUTY CYCLE ("גורם מחזור") מחזיר פעולה כלומר יחס הזמן שבו היציאה במצב "1" לוגי לזמן המחזור כולו.

Duty Cycle =

= תדרF

# data[].attributes.attachment_link.title
אלקומפ | אלקטרוניקה ומחשבים

# data[].attributes.attachment_link.description
אלקטרוניקה מבנה פנימי של הרכיב: ההתקן מורכב משני משוונים (comperator), דלגלג (FF) ומהפך: - המשוון משווה את פתחי 2 הכניסות שלו כאשר מתח היציאה שלו עולה כאשר המתח ב-2 הכניסות זהה. - ה-flip flop מגדיר את רוחב הפולס ביציאה ובדרך כלל Low ונעשה High לאחר Set ושוב פעם Low לאחר Reset.

# data[].attributes.headline
דניאל ואוריאל אוהבים אותך גדי

# data[].attributes.subject
דניאל ואוריאל אוהבים אותך גדי

# data[].attributes.body
555 הוא טיימר , מעגל משולב (שבב) ,

# data[].attributes.attachment_link.readable_text
The 555 timer IC is an integrated circuit (chip) used in a variety of timer, delay, pulse generation, and oscillator applications. Derivatives provide two ( 556) or four ( 558) timing circuits in one package. It was commercialized in 1972 by Signetics. Numerous companies have made the original bipolar timers and similar low-power CMOS timers too. In 2017, it was said over a billion 555 timers are produced annually by some estimates, and "probably the most popular integrated circuit ever made."

The timer IC was designed in 1971 by Hans Camenzind under contract to Signetics. In 1968, he was hired by Signetics to develop a phase-locked loop (PLL) IC. He designed an oscillator for PLLs such that the frequency did not depend on the power supply voltage or temperature. Signetics subsequently laid off half of its employees due to the 1970 recession, and development on the PLL was thus frozen. Camenzind proposed the development of a universal circuit based on the oscillator for PLLs and asked that he develop it alone, borrowing equipment from Signetics instead of having his pay cut in half. Camenzind's idea was originally rejected, since other engineers argued the product could be built from existing parts sold by the company; however, the marketing manager approved the idea.

The first design for the 555 was reviewed in the summer of 1971. Assessed to be without error, it proceeded to layout design. A few days later, Camenzind got the idea of using a direct resistance instead of a constant current source finding later that it worked. The change decreased the required 9 pins to 8 so the IC could be fit in an 8-pin package instead of a 14-pin package. This revised design passed a second design review with the prototypes completed in October 1971 as the NE555V (plastic DIP) and SE555T (metal TO-5). The 9-pin copy had been already released by another company founded by an engineer who attended the first review and retired from Signetics; that firm withdrew its version soon after the 555 was released. The 555 timer was manufactured by 12 companies in 1972 and it became a best selling product.

Several books report the name 555 comes from the three 5 kilohm resistors inside the chip. However, in a recorded interview with an online transistor museum curator, Hans Camenzind said "It was just arbitrarily chosen. It was Art Fury (Marketing Manager) who thought the circuit was gonna sell big who picked the name '555'."

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 dual in-line package (DIP-8). Variants available include the 556 (a DIP-14 combining two complete 555s on one chip), and 558 / 559 (both a DIP-16 combining four reduced-functionality timers on one chip).

The NE555 parts were commercial temperature range, 0 °C to +70 °C, and the SE555 part number designated the military temperature range, −55 °C to +125 °C. These were available in both high-reliability metal can (T package) and inexpensive epoxy plastic (V package) packages. Thus the full part numbers were NE555V, NE555T, SE555V, and SE555T.

Low-power CMOS versions of the 555 are also available, such as the Intersil ICM7555 and Texas Instruments LMC555, TLC555, TLC551. CMOS timers use significantly less power than bipolar timers; CMOS timers also cause less supply noise than bipolar version when the output switches states.[citation needed ]

The internal block diagram and schematic of the 555 timer are highlighted with the same color across all three drawings to clarify how the chip is implemented:

Green: Between the positive supply voltage VCC and the ground GND is a voltage divider consisting of three identical resistors, which create two reference voltages at 1⁄3 VCC and 2⁄3 VCC. The latter is connected to the "Control" pin. All three resistors have the same resistance, 5 kΩ for bipolar timers, 100 kΩ (or higher) for CMOS timers.

Yellow: The comparator negative input is connected to the higher-reference voltage divider of 2⁄3 VCC (and "Control" pin), and comparator positive input is connected to the "Threshold" pin.

Red: The comparator positive input is connected to the lower reference voltage divider of 1⁄3 VCC, and comparator negative input is connected to the "Trigger" pin.

Purple: An SR flip-flop stores the state of the timer and is controlled by the two comparators. The "Reset" pin overrides the other two inputs, thus the flip-flop (and therefore the entire timer) can be reset at any time.

Pink: The output of the flip-flop is followed by an output stage with push-pull (P.P.) output drivers that can load the "Output" pin with up to 200 mA for bipolar timers, lower for CMOS timers.

Cyan: Also, the output of the flip-flop turns on a transistor that connects the "Discharge" pin to the ground.

555 internal block diagram[1]

555 internal schematic of bipolar version

555 internal schematic of CMOS version

The pinout of the 8-pin 555 timer and 14-pin 556 dual timer are shown in the following table. Since the 556 is conceptually two 555 timers that share power pins, the pin numbers for each half is split across two columns.

In the following table, longer pin names are used, because manufacturers never standardized the abbreviated pin names across all datasheets.

1

Ground supply: this pin is the ground reference voltage (zero volts).

2

Trigger: when the voltage at this pin falls below of the voltage of CONTROL ( V CC, except when CONTROL is driven by an external signal), the OUTPUT goes to the high state and a timing interval starts. As long as this pin continues to be kept at a low voltage, the OUTPUT will remain in the high state.

3

Output: this pin is a push-pull (P.P.) output that is driven to either a low state (GND) or a high state (for bipolar timers, V CC minus approximately 1.7 volts) (for CMOS timers, V CC). For bipolar timers, this pin can drive up to 200 mA, but CMOS timers are able to drive less (varies by chip). For bipolar timers, if this pin drives an edge-sensitive input of a digital logic chip, a 100 to 1000 pF decoupling capacitor (between this pin and GND) may need to be added to prevent double triggering.

4

Reset: a timing interval may be reset by driving this pin to GND, but the timing does not begin again until this pin rises above approximately 0.7 volts. This pin overrides TRIGGER, which in turn overrides THRESHOLD. If this pin is not used, it should be connected to V CC to prevent electrical noise accidentally causing a reset.

5

Control: this pin provides access to the internal voltage divider ( V CC by default). By applying a voltage to this pin, the timing characteristics can be changed. In astable mode, this pin can be used to frequency-modulate the OUTPUT state. If this pin is not used, it should be connected to a 10 nF decoupling capacitor (between this pin and GND) to ensure electrical noise doesn't affect the internal voltage divider.

6

Threshold: when the voltage at this pin is greater than the voltage at CONTROL ( V CC except when CONTROL is driven by an external signal), then the OUTPUT high state timing interval ends, causing the OUTPUT to go to the low state.

7

Discharge: For bipolar timers, this pin is an open-collector (O.C.) output, CMOS timers are open-drain (O.D.). This pin can be used to discharge a capacitor between intervals, in phase with the OUTPUT. In bistable mode and schmitt trigger mode, this pin is unused, which allows it to be used as an alternate output.

8

Positive supply: For bipolar timers, the voltage range is typically 4.5 to 16 volts, some are spec'ed for up to 18 volts, though most will operate as low as 3 volts. For CMOS timers, the voltage range is typically 2 to 15 volts, some are spec'ed for up to 18 volts, and some are spec'ed as low as 1 volt. See the supply min and max columns in the derivatives table in this article. Decoupling capacitor(s) are generally applied (between this pin and GND) as a good practice.

Pinout of 555 single timer.[1][2]

The 555 IC has the following operating modes:

1. Astable (free-running) mode - the 555 can operate as an electronic oscillator. Uses include LED and lamp flashers, pulse generation, logic clocks, tone generation, security alarms, pulse position modulation and so on. The 555 can be used as a simple ADC, converting an analog value to a pulse length (e.g., selecting a thermistor as timing resistor allows the use of the 555 in a temperature sensor and the period of the output pulse is determined by the temperature). The use of a microprocessor-based circuit can then convert the pulse period to temperature, linearize it and even provide calibration means.

2. Monostable (one-shot) mode - in this mode, the 555 functions as a "one-shot" pulse generator. Applications include timers, missing pulse detection, bounce-free switches, touch switches, frequency divider, capacitance measurement, pulse-width modulation (PWM), and so on.

3. Bistable (flip-flop) mode - the 555 operates as an SR flip-flop. Uses include bounce-free latched switches.

4. Schmitt Trigger (inverter) mode - the 555 operates as a Schmitt trigger inverter gate which converts a noisy input into a clean digital output.

In the astable configuration, the 555 timer puts out a continuous stream of rectangular pulses having a specific frequency. The astable configuration is implemented using two resistors, and , and one capacitor . In this configuration, the control pin is not used, thus it is connected to ground through a 10 nF decoupling capacitor to shunt electrical noise. The threshold and trigger pins are connected to the capacitor , thus they have the same voltage. Initially, the capacitor is not charged, thus the trigger pin receives zero voltage which is less than a third of the supply voltage. Consequently, the trigger pin causes the output to go high and the internal discharge transistor to go to cut-off mode. Since the discharge pin is no longer short-circuited to ground, the current flows through the two resistors, and , to the capacitor charging it. The capacitor starts charging until the voltage becomes two-thirds of the supply voltage. At this instance, the threshold pin causes the output to go low and the internal discharge transistor to go into saturation mode. Consequently, the capacitor starts discharging through till it becomes less than a third of the supply voltage, in which case, the trigger pin causes the output to go high and the internal discharge transistor to go to cut-off mode once again. And the cycle repeats.

In the first pulse, the capacitor charges from zero to two-thirds of the supply voltage, however, in later pulses, it only charges from one-third to two-thirds of the supply voltage. Consequently, the first pulse has a longer high time interval compared to later pulses. Moreover, the capacitor charges through both resistors but only discharges through , thus the high interval is longer than the low interval. This is shown in the following equations.

The high time interval of each pulse is given by:

The low time interval of each pulse is given by:

Hence, the frequency of the pulse is given by:

[24]

and the duty cycle (%) is given by:

where is in seconds (time), is in ohms (resistance), is in farads (capacitance), is the natural log of 2 constant, which is 0.693147 (rounded to 6 trailing digits), but it is commonly rounded to fewer digits in 555 timer books and datasheets as 0.7 or 0.69 or 0.693.

Resistor requirements:

power capability of must be greater than , per Ohm's law.

Particularly with bipolar 555s, low values of must be avoided so that the output stays saturated near zero volts during discharge, as assumed by the above equation. Otherwise, the output low time will be greater than calculated above.

The first cycle will take appreciably longer than the calculated time, as the capacitor must charge from 0 V to of V CC from power-up, but only from of V CC to of V CC on subsequent cycles.

Shorter duty cycle

To create an output high time shorter than the low time (i.e., a duty cycle less than 50%) a fast diode (i.e. 1N4148 signal diode) can be placed in parallel with R ₂, with the cathode on the capacitor side. This bypasses R ₂ during the high part of the cycle so that the high interval depends only on R ₁ and C, with an adjustment based the voltage drop across the diode. The voltage drop across the diode slows charging on the capacitor so that the high time is longer than the expected and often-cited ln(2)*R ₁C = 0.693 R ₁C. The low time will be the same as above, 0.693 R ₂ C. With the bypass diode, the high time is

where V diode is when the diode's "on" current is of V cc/R ₁ which can be determined from its datasheet or by testing. As an extreme example, when V cc = 5 V and V diode= 0.7 V, high time = 1.00 R ₁C which is 45% longer than the "expected" 0.693 R ₁C. At the other extreme, when V cc= 15 V and V diode= 0.3 V, the high time = 0.725 R ₁C which is closer to the expected 0.693 R ₁C. The equation reduces to the expected 0.693 R ₁C if V diode = 0 V.

In monostable mode, the output pulse ends when the voltage on the capacitor equals of the supply voltage. The output pulse width can be lengthened or shortened to the need of the specific application by adjusting the values of R and C.

The output pulse is of width t, which is the time it takes to charge C to of the supply voltage. It is given by

where is in seconds (time), is in ohms (resistance), is in farads (capacitance), is the natural log of 3 constant, which is 1.098612 (rounded to 6 trailing digits), but it is commonly rounded to fewer digits in 555 timer books and datasheets as 1.1 or 1.099.

While using the timer IC in monostable mode, the time span between any two triggering pulses must be greater than the RC time constant.

In bistable mode, the 555 timer acts as an SR flip-flop. The trigger and reset inputs are held high via pull-up resistors while the threshold input is grounded. Thus configured, pulling the trigger momentarily to ground acts as a 'set' and transitions the output pin to V CC (high state). Pulling the reset input to ground acts as a 'reset' and transitions the output pin to ground (low state). No timing capacitors are required in a bistable configuration. The discharge pin is left unconnected, or may be used as an open-collector output.

A 555 timer can be used to create a Schmitt trigger inverter gate which converts a noisy input into a clean digital output. The input signal should be connected through a series capacitor which then connects to the trigger and threshold pins. A resistor divider, from V CC to GND, is connected to the previous tied pins. The reset pin is tied to V CC.

In 1972, Signetics originally released the 555 timer in DIP-8 and TO5-8 metal can packages, and the 556 timer was released in DIP-14 package.

In 2012, the 555 was available in through-hole packages as DIP-8 (2.54 mm pitch), and surface-mount packages as SO-8 (1.27 mm pitch), SSOP-8 / TSSOP-8 / VSSOP-8 (0.65 mm pitch), BGA (0.5 mm pitch).

In 2006, the dual 556 timer was available in through-hole packages as DIP-14 (2.54 mm pitch), and surface-mount packages as SO-14 (1.27 mm pitch) and SSOP-14 (0.65 mm pitch).

The MIC1555 is a CMOS 555-type timer with three fewer pins available in SOT23-5 (0.95 mm pitch) surface-mount package.

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

Numerous companies have manufactured one or more variants of the 555, 556, 558 timers over the past decades as many different part numbers. The following is a partial list:

Table notes

All information in the above table was pulled from references in the datasheet column, except where denoted below.

For the "Timer Total" column, a "*" denotes parts that are missing 555 timer features.

For "Iq" column, a 5 volt supply was chosen as a common voltage to make it easier to compare. The value for Signetics NE558 is an estimate because NE558 datasheets don't state Iq at 5V. The value listed in this table was estimated by comparing the 5V to 15V ratio of other bipolar datasheets, then derating the 15V parameter for the NE558 part, which is denoted by the "*".

For the "Frequency Max" column, a "*" denotes values that may not be the actual maximum frequency limit of the part. The MIC1555 datasheet discusses limitations from 1 to 5 MHz. Though most bipolar timers don't state the maximum frequency in their datasheets, they all have a maximum frequency limitation of hundreds of kHz across their full temperature range. Section 8.1 of the Texas Instruments NE555 datasheet states a value of 100 kHz, and their website shows a value of 100 kHz in timer comparison tables. In Signetics App Note 170, states that most devices will oscillate up to 1 MHz, however when considering temperature stability it should be limited to about 500 kHz. The application note from HFO mentions that at higher supply voltages the maximum power dissipation of the circuit might limit the operating frequency, as the supply current increases with frequency.

For the "Manufacturer" column, the following associates historical 555 timer manufacturers to current company names.

The dual version is called 556. It features two complete 555 timers in a 14 pin package; only the two power supply pins are shared between the two timers. In 2020, the bipolar version was available as the NE556, and the CMOS versions were available as the Intersil ICM7556 and Texas Instruments TLC556 and TLC552. See derivatives table in this article.

The quad version is called 558 that has four reduced-functionality timers in a 16 pin package designed primarily for " monostable multivibrator" applications. By 2014, many versions of 16-pin NE558 have become obsolete.

Partial list of differences between 558 and 555 chips:

One V CC and one GND, similar to 556 chip.

Four "Reset" are tied together internally to one external pin (558).

Four "Control Voltage" are tied together internally to one external pin (558).

Four "Triggers" are falling-edge sensitive (558), instead of level sensitive (555).

Two resistors in the voltage divider (558), instead of three resistors (555).

One comparator (558), instead of two comparators (555).

Four "Output" are open-collector (O.C.) type (558), instead of push-pull (P.P.) type (555). Since the 558 outputs are open-collector, pull-up resistors are required to "pull up" the output to the positive voltage rail when the output is in a high state. This means the high state only sources a small amount of current through the pull-up resistor.

Books with timer chapters

Datasheets

See links in "Derivatives" table and "References" section in this article.

# data[].attributes.attachment_link.description
The 555 timer IC is an integrated circuit (chip) used in a variety of timer, delay, pulse generation, and oscillator applications. Derivatives provide two ( 556) or four ( 558) timing circuits in one package. It was commercialized in 1972 by Signetics. Numerous companies have made the original bipolar timers and similar low-power CMOS timers too.