[{"data":1,"prerenderedAt":-1},["ShallowReactive",2],{"doc-seo-670872-105":3,"detail-sidebar-cat-0-en-105":84,"doc-detail-670872-en":134},{"code":4,"msg":5,"data":6},0,"ok",{"site_id":7,"language":8,"slug":9,"title":10,"keywords":11,"description":12,"schema_data":13,"social_meta":77,"head_meta":79,"extra_data":81,"updated_unix":83},105,"en","the-555-timer-ic","The 555 Timer IC","","The document explains the 555 timer IC, including its historical introduction, key electrical characteristics, and why it remains useful for monostable and astable timing circuits. It describes the internal functional organization using simplified block-diagram reasoning, contrasts common packaging options (metal-can and 8-pin DIP), and summarizes device relationships such as the 556 and 558. It further develops the external RC timing concept, including capacitor charge behavior, time constant calculation, and practical guidance for capacitor timing, trigger/pin functions, and stability considerations.",{"@graph":14,"@context":76},[15,34,55],{"@type":16,"itemListElement":17},"BreadcrumbList",[18,23,27,31],{"item":19,"name":20,"@type":21,"position":22},"https://docshare.wps.com","Home","ListItem",1,{"item":24,"name":25,"@type":21,"position":26},"https://docshare.wps.com/document/","Document",2,{"item":28,"name":29,"@type":21,"position":30},"https://docshare.wps.com/document/technology/","Technology",3,{"item":32,"name":10,"@type":21,"position":33},"https://docshare.wps.com/document/the-555-timer-ic/670872/",4,{"url":32,"name":10,"@type":35,"image":36,"author":41,"headline":10,"publisher":44,"fileFormat":47,"inLanguage":8,"description":12,"dateModified":48,"datePublished":49,"encodingFormat":47,"isAccessibleForFree":50,"interactionStatistic":51},"DigitalDocument",{"url":37,"@type":38,"width":39,"height":40},"https://docshare.wps.com/thumbnails/the-555-timer-ic/670872.png","ImageObject",300,407,{"name":42,"@type":43},"Oliver","Person",{"url":19,"name":45,"@type":46},"DocShare","Organization","application/pdf","2026-11-02","2026-11-01",true,{"@type":52,"interactionType":53,"userInteractionCount":26},"InteractionCounter",{"@type":54},"ViewAction",{"@type":56,"mainEntity":57},"FAQPage",[58,64,68,72],{"name":59,"@type":60,"acceptedAnswer":61},"What are the main timing modes supported by the 555 timer IC?","Question",{"text":62,"@type":63},"The 555 timer supports monostable and astable applications. It can be used alone or combined with other solid-state devices for timing functions.","Answer",{"name":65,"@type":60,"acceptedAnswer":66},"How is the time constant for the 555 timer determined?",{"text":67,"@type":63},"The time constant is calculated using t = R × C. It represents the time for the capacitor voltage to reach about 63.7% of the applied voltage in the charging process.",{"name":69,"@type":60,"acceptedAnswer":70},"What does the Trigger (Pin 2) do in monostable operation?",{"text":71,"@type":63},"Pin 2 drives the lower comparator to set the latch, causing the output to go high and starting the monostable timing sequence. Triggering is level-sensitive and requires the input to go below a threshold (about 1/3 V+).",{"name":73,"@type":60,"acceptedAnswer":74},"What precautions are needed for the trigger input signal?",{"text":75,"@type":63},"The trigger input must not remain lower than 1/3 V+ for longer than the intended timing cycle. If it does, the timer can retrigger itself at the end of the first output pulse.","https://schema.org",{"og:url":32,"og:type":78,"og:title":10,"og:site_name":45,"og:description":12},"article",{"robots":80,"canonical":32},"index,follow",{"doc_id":82,"site_id":7},670872,1793572441,{"code":4,"msg":85,"data":86},"success",[87,91,95,99,104,108,113,118,123,126,130],{"id":22,"doc_module":4,"doc_module_name":25,"category_name":88,"show_sort_weight":89,"slug":90},"Story & Novel",90,"story-novel",{"id":26,"doc_module":4,"doc_module_name":25,"category_name":92,"show_sort_weight":93,"slug":94},"Literature",80,"literature",{"id":33,"doc_module":4,"doc_module_name":25,"category_name":96,"show_sort_weight":97,"slug":98},"Exam",70,"exam",{"id":100,"doc_module":4,"doc_module_name":25,"category_name":101,"show_sort_weight":102,"slug":103},5,"Comic",60,"comic",{"id":105,"doc_module":4,"doc_module_name":25,"category_name":29,"show_sort_weight":106,"slug":107},6,50,"technology",{"id":109,"doc_module":4,"doc_module_name":25,"category_name":110,"show_sort_weight":111,"slug":112},7,"Healthcare",40,"healthcare",{"id":114,"doc_module":4,"doc_module_name":25,"category_name":115,"show_sort_weight":116,"slug":117},8,"Research & Report",30,"research-report",{"id":119,"doc_module":4,"doc_module_name":25,"category_name":120,"show_sort_weight":121,"slug":122},9,"Religion & Spirituality",20,"religion-spirituality",{"id":121,"doc_module":4,"doc_module_name":25,"category_name":124,"show_sort_weight":121,"slug":125},"World Cup","world-cup",{"id":127,"doc_module":4,"doc_module_name":25,"category_name":128,"show_sort_weight":127,"slug":129},10,"Lifestyle","lifestyle",{"id":131,"doc_module":4,"doc_module_name":25,"category_name":132,"show_sort_weight":100,"slug":133},19,"General","general",{"code":4,"msg":85,"data":135},{"doc_id":82,"user_id":136,"nickname":42,"user_avatar":137,"doc_module":4,"category_id":105,"category_name":29,"doc_title":10,"doc_description":12,"doc_content":138,"file_id":139,"file_url":140,"file_type":141,"file_size":142,"view_count":26,"is_deleted":4,"is_public":22,"is_downloadable":22,"audit_status":22,"page_count":143,"language":144,"language_code":8,"site_id":7,"html_lang":8,"table_of_contents":145,"faqs":146,"seo_title":147,"seo_description":12,"update_tm":83,"read_time":116},8796095461610,"https://ap-avatar.wpscdn.com/davatar_276721f389ce27ea32af1340a28f341c","The 555 Timer IC  \n(Adapted from [http://www.electronics.dit.ie/staff/mtully/555%20folder/555%20timer.htm](http://www.electronics.dit.ie/staff/mtully/555%20folder/555%20timer.htm))  \nThe 555 timer IC was first introduced around 1971 by the Signetics Corporation as the SE555/NE555 and was called \"The IC Time Machine\" and was also the very first and only commercial timer IC available. It provided circuit designers with a relatively cheap, stable, and user-friendly integrated circuit for both monostable and astable applications. Since this device was first made commercially available, a myriad of novel and unique circuits have been developed and presented in several trade, professional, and hobby publications. The past ten years some manufacturers stopped making these timers because of competition or other reasons. Yet other companies, like NTE (a subdivision of Philips) picked up where some left off.  \nAlthough these days the CMOS version of this IC, like the Motorola MC1455, is mostly used, the regular type is still available, however there have been many improvements and variations in the circuitry. But all types are pin-forpin plug compatible.  \nIn this tutorial the 555 timer is examined in detail along with its uses, either by itself or in combination with other solid state devices. This timer uses a maze of transistors, diodes and resistors and for this complex reason a more simplified (but accurate) block diagram is used to explain the internal organizations of the 555.  \nThe 555, in fig. 1 and fig. 2 above, comes in two packages, either the round metal-can called the 'T' package or the more familiar 8-pin DIP 'V'package. About 20-years ago the metal-can type was pretty much the standard (SE/NE types) . The 556 timer is a dual 555 version and comes in a 14-pin DIP package, the 558 is a quad version with four 555's also in a 14 pin DIP case.  \nInside the 555 timer, at fig. 3, are the equivalent of over 20 transistors, 15 resistors, and 2 diodes, depending of the manufacturer. The equivalent circuit, in block diagram, providing the functions of control, triggering, level sensing or comparison, discharge, and power output. Some of the more attractive features of the 555 timerare: Supply voltage between 4.5 and 18 volt, supply current 3 to 6 mA, and a Rise/Fall time of 100 nSec. It can also withstand quite a bit of abuse. The Threshold current determine the maximum value of Ra + Rb. For 15 volt operation the maximum total resistance for R (Ra +Rb) is 20 MΩ.  \nThe supply current, when the output is 'high', is typically 1 milli-amp (mA) or less. The initial monostable timing accuracy is typically within 1% of its calculated value, and exhibits negligible (0 . 1%/V) drift with supply voltage. Thus long-term supply variations can be ignored, and the temperature variation is only 50ppm/°C (0 .005%/°C) .  \nAll IC timers rely upon an external capacitor to determine the off-on time intervals of the output pulses. It takes a finite period of time for a capacitor (C) to charge or discharge through a resistor (R) . Those times are clearly defined and can be calculated given the values of resistance and capacitance.  \nThe basic RC charging circuit is shown in fig. 4. Assume that the capacitor is initially discharged. When the  \nswitch is closed, the capacitor begins to charge through the resistor. The voltage across the capacitor rises from zero up to the value of the applied DC voltage. The charge curve for the circuit is shown in fig. 6. The time that it takes for the capacitor to charge to 63.7% of the applied voltage is known as the time constant (t) . That time can be calculated with the simple expression:  \nt = R X C  \nAssume a resistor value of 1 MΩ and a capacitor value of 1uF. The time constant in that case is:  \nt = 1,000,000 X 0.000001 = 1 second  \nAssume further that the applied voltage is 6 volts. That means that it will take one time constant for the voltage across the capacitor to reach 63.2% of the applied voltage. Therefo","cbCaigCETB971LSB","https://ap.wps.com/l/cbCaigCETB971LSB","pdf",162878,12,"English","# Overview\n## Historical background and compatibility\n# Internal organization and features\n## Functional blocks and packaging\n# RC timing fundamentals\n## Capacitor charging and time constant\n# Monostable timing and pulse detection\n## Missing pulse detector rule\n# Pin functions\n## Ground and trigger pins","[{\"question\":\"What are the main timing modes supported by the 555 timer IC?\",\"answer\":\"The 555 timer supports monostable and astable applications. It can be used alone or combined with other solid-state devices for timing functions.\"},{\"question\":\"How is the time constant for the 555 timer determined?\",\"answer\":\"The time constant is calculated using t = R × C. It represents the time for the capacitor voltage to reach about 63.7% of the applied voltage in the charging process.\"},{\"question\":\"What does the Trigger (Pin 2) do in monostable operation?\",\"answer\":\"Pin 2 drives the lower comparator to set the latch, causing the output to go high and starting the monostable timing sequence. Triggering is level-sensitive and requires the input to go below a threshold (about 1/3 V+).\"},{\"question\":\"What precautions are needed for the trigger input signal?\",\"answer\":\"The trigger input must not remain lower than 1/3 V+ for longer than the intended timing cycle. If it does, the timer can retrigger itself at the end of the first output pulse.\"}]","The 555 Timer IC | PDF"]