555 Timer IC
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The 555 timer IC is an
integrated circuit An integrated circuit (IC), also known as a microchip or simply chip, is a set of electronic circuits, consisting of various electronic components (such as transistors, resistors, and capacitors) and their interconnections. These components a ...
used in a variety of
timer A timer or countdown timer is a type of clock that starts from a specified time duration and stops upon reaching 00:00. It can also usually be stopped manually before the whole duration has elapsed. An example of a simple timer is an hourglass ...
, delay, pulse generation, and
oscillator Oscillation is the repetitive or periodic variation, typically in time, of some measure about a central value (often a point of equilibrium) or between two or more different states. Familiar examples of oscillation include a swinging pendulum ...
applications. It is one of the most popular timing ICs due to its flexibility and price. Derivatives provide two ( 556) or four ( 558) timing circuits in one package. The design was first marketed in 1972 by
Signetics Signetics Corporation was an American electronics manufacturer specifically established to make integrated circuits. Founded in 1961, they went on to develop a number of early microprocessors and support chips, as well as the widely used 555 time ...
and used
bipolar junction transistor A bipolar junction transistor (BJT) is a type of transistor that uses both electrons and electron holes as charge carriers. In contrast, a unipolar transistor, such as a field-effect transistor (FET), uses only one kind of charge carrier. A ...
s. Since then, numerous companies have made the original timers and later similar low-power
CMOS Complementary metal–oxide–semiconductor (CMOS, pronounced "sea-moss ", , ) is a type of MOSFET, metal–oxide–semiconductor field-effect transistor (MOSFET) semiconductor device fabrication, fabrication process that uses complementary an ...
timers. In 2017, it was said that over a billion 555 timers are produced annually by some estimates, and that the design was "probably the most popular integrated circuit ever made".


History

The timer IC was designed in 1971 by Hans Camenzind under contract to
Signetics Signetics Corporation was an American electronics manufacturer specifically established to make integrated circuits. Founded in 1961, they went on to develop a number of early microprocessors and support chips, as well as the widely used 555 time ...
. In 1968, he was hired by Signetics to develop a
phase-locked loop A phase-locked loop or phase lock loop (PLL) is a control system that generates an output signal whose phase is fixed relative to the phase of an input signal. Keeping the input and output phase in lockstep also implies keeping the input and ou ...
(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. After this design was tested and found to be without errors, Camenzind got the idea of using a direct resistance instead of a constant current source, finding that it worked satisfactorily. The design change decreased the required 9 external pins to 8, so the IC could be fit in an 8-pin package instead of a 14-pin package. This revised version passed a second design review, and the prototypes were completed in October 1971 as the NE555V (plastic DIP) and SE555T (metal TO-5). The 9-pin version had already been released by another company founded by an engineer who had attended the first review and had 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. The 555 found many applications beyond timers. Camenzind noted in 1997 that "nine out of 10 of its applications were in areas and ways I had never contemplated. For months I was inundated by phone calls from engineers who had new ideas for using the device."


Name

Several books report the name "555" timer IC derived from the three 5 kΩ 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' timer IC."


Design

Depending on the manufacturer, the standard 555 package incorporated the equivalent of 25
transistor A transistor is a semiconductor device used to Electronic amplifier, amplify or electronic switch, switch electrical signals and electric power, power. It is one of the basic building blocks of modern electronics. It is composed of semicondu ...
s, 2
diode A diode is a two-Terminal (electronics), terminal electronic component that conducts electric current primarily in One-way traffic, one direction (asymmetric electrical conductance, conductance). It has low (ideally zero) Electrical resistance ...
s, and 15
resistor A resistor is a passive two-terminal electronic component that implements electrical resistance as a circuit element. In electronic circuits, resistors are used to reduce current flow, adjust signal levels, to divide voltages, bias active e ...
s on a
silicon Silicon is a chemical element; it has symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic lustre, and is a tetravalent metalloid (sometimes considered a non-metal) and semiconductor. It is a membe ...
chip packaged into an 8-pin
dual in-line package In microelectronics, a dual in-line package (DIP or DIL) is an Semiconductor package, electronic component package with a rectangular housing and two parallel rows of electrical connecting pins. The package may be through-hole technology, throu ...
(DIP-8). Variants available included the 556 (a DIP-14 combining two complete 555s on one chip), and 558 / 559 (both variants were a DIP-16 combining four reduced-functionality timers on one chip). The NE555 parts were commercial temperature range, 0 Â°C to +70 Â°C, and the SE555 part number designated the military temperature range, −55 Â°C to +125 Â°C. These chips were available in both high-reliability metal can (T package) and inexpensive epoxy plastic (V package) form factors. Thus, the full part numbers were NE555V, NE555T, SE555V, and SE555T. Low-power CMOS versions of the 555 are now available, such as the Intersil ICM7555 and Texas Instruments LMC555, TLC555, TLC551.


Internal schematic

The internal
block diagram A block diagram is a diagram of a system in which the principal parts or functions are represented by blocks connected by lines that show the relationships of the blocks.
and
schematic A schematic, or schematic diagram, is a designed representation of the elements of a system using abstract, graphic symbols rather than realistic pictures. A schematic usually omits all details that are not relevant to the key information the sc ...
of the 555 timer are highlighted with the same color across all three drawings to clarify how the chip is implemented: * : Between the positive supply voltage VCC and the ground GND is a
voltage divider In electronics, a voltage divider (also known as a potential divider) is a passive linear circuit that produces an output voltage (''V''out) that is a fraction of its input voltage (''V''in). Voltage division is the result of distributing the i ...
consisting of three identical
resistor A resistor is a passive two-terminal electronic component that implements electrical resistance as a circuit element. In electronic circuits, resistors are used to reduce current flow, adjust signal levels, to divide voltages, bias active e ...
s (5 kΩ for bipolar timers, 100kΩ or higher for CMOS) to create reference voltages for the analog comparators. CONTROL is connected between the upper two resistors, allowing an external voltage to control the reference voltages: ** When CONTROL is not driven, this divider creates an upper reference voltage of VCC and a lower reference voltage of VCC. ** When CONTROL is driven, the upper reference voltage will instead be VCONTROL and the lower reference voltage will be VCONTROL. * : The
comparator In electronics, a comparator is a device that compares two voltages or currents and outputs a digital signal indicating which is larger. It has two analog input terminals V_+ and V_- and one binary digital output V_\text. The output is ideally ...
's negative input is connected to voltage divider's upper reference voltage, and the comparator's positive input is connected to THRESHOLD. * : The
comparator In electronics, a comparator is a device that compares two voltages or currents and outputs a digital signal indicating which is larger. It has two analog input terminals V_+ and V_- and one binary digital output V_\text. The output is ideally ...
's positive input is connected to voltage divider's lower reference, and the comparator's negative input is connected to TRIGGER. * : A set-reset latch stores the
state State most commonly refers to: * State (polity), a centralized political organization that regulates law and society within a territory **Sovereign state, a sovereign polity in international law, commonly referred to as a country **Nation state, a ...
of the timer and is controlled by the two comparators. RESET overrides the other two inputs, thus the latch (and therefore the entire timer) can be reset at any time. * : The output of the latch is followed by an output stage with pushpull output drivers that can supply up to 200mA for bipolar timers, lower for CMOS timers. * : Also, the output of the latch controls a
transistor A transistor is a semiconductor device used to Electronic amplifier, amplify or electronic switch, switch electrical signals and electric power, power. It is one of the basic building blocks of modern electronics. It is composed of semicondu ...
acting as an
electronic switch In electronics, an electronic switch is a switch controlled by an Passivity (engineering), active electronic component or device. Without using moving parts, they are called solid state switches, which distinguishes them from mechanical switches. ...
that connects DISCHARGE to ground. File:NE555 Bloc Diagram.svg, 555 internal block diagram File:NE555 Internal Circuit.svg, 555 internal schematic of bipolar version File:C555 Internal Circuit.svg, 555 internal schematic of CMOS version


Pinout

The
pinout In electronics, a pinout (sometimes written "pin-out") is a cross-reference between the contacts, or ''pins'', of an electrical connector or electronic component, and their functions. "Pinout" now supersedes the term "basing diagram" which was the ...
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 are split across two columns. File:555 Pinout.svg, Pinout of 555 single timer File:NE556 pennen.svg, Pinout of 556 dual timer


Modes

The 555 IC has the following operating modes: # Astable (free-running) mode – The 555 operates as an
electronic oscillator An electronic oscillator is an electronic circuit that produces a periodic, oscillating or alternating current (AC) signal, usually a sine wave, square wave or a triangle wave, powered by a direct current (DC) source. Oscillators are found ...
. Applications include: #* Light emitting diode and lamp flashers, pulse generation,
pulse-width modulation Pulse-width modulation (PWM), also known as pulse-duration modulation (PDM) or pulse-length modulation (PLM), is any method of representing a signal as a rectangular wave with a varying duty cycle (and for some methods also a varying peri ...
(PWM), logic clocks, tone generation, security alarms,
pulse-position modulation Pulse-position modulation (PPM) is a form of signal modulation in which ''M'' message bits are encoded by transmitting a single pulse in one of 2^M possible required time shifts. This is repeated every ''T'' seconds, such that the transmitted b ...
, etc. #*
Analog-to-digital conversion In electronics, an analog-to-digital converter (ADC, A/D, or A-to-D) is a system that converts an analog signal, such as a sound picked up by a microphone or light entering a digital camera, into a digital signal. An ADC may also provide ...
(ADC) from an analog value represented by a resistance or capacitance into a digital pulse length. #** e.g., selecting a
thermistor A thermistor is a semiconductor type of resistor in which the resistance is strongly dependent on temperature. The word ''thermistor'' is a portmanteau of ''thermal'' and ''resistor''. The varying resistance with temperature allows these devices ...
as timing resistor allows the use of the 555 in a temperature sensor with the period of the output pulse determined by the
temperature Temperature is a physical quantity that quantitatively expresses the attribute of hotness or coldness. Temperature is measurement, measured with a thermometer. It reflects the average kinetic energy of the vibrating and colliding atoms making ...
. A microprocessor can then convert the pulse period to temperature, linearize it, and even provide calibration. # Monostable (one-shot) mode – The 555 operates as a "one-shot" pulse generator. Applications include: #* timers, missing pulse detection, bounce-free switches, touch switches, frequency dividers, triggered measurement of resistance or capacitance, PWM, etc. # Bistable (latch) mode – The 555 operates as a set-reset latch. Applications include: #* switch debouncing. #
Schmitt trigger In electronics, a Schmitt trigger is a comparator circuit with hysteresis implemented by applying positive feedback to the noninverting input of a comparator or differential amplifier. It is an passivity (engineering), active circuit which con ...
(inverter) mode – the 555 operates as a Schmitt trigger inverter gate. Application: #* Converts a noisy input into a clean digital output.


Astable

In the astable configuration, the 555 timer puts out a continuous stream of rectangular pulses having a specific period. The astable configuration is implemented using two resistors, R_1 and R_2 , and one capacitor C. The threshold and trigger pins are both connected to the capacitor; thus they have the same voltage. Its repeated operating cycle (starting with the capacitor uncharged) is: # Since the capacitor's voltage will be below  ''V''CC, the trigger pin causes the 555's internal latch to change state, causing OUT to go high and the internal discharge transistor to cut-off. # Since the discharge pin is no longer short-circuited to ground, the capacitor starts charging via current from Vcc through the resistors R_1 and R_2. # Once the capacitor charge reaches  Vcc, the threshold pin causes the 555's internal latch to change state, causing OUT to go low and the internal discharge transistor to go into saturation (maximal-conductivity) mode. # This discharge transistor provides a discharge path, so the capacitor starts discharging through R_2. # Once the capacitor's voltage drops below  ''V''CC, the cycle repeats from step 1. During the first pulse, the capacitor charges from 0 V to  ''V''CC, however, in later pulses, it only charges from  ''V''CC to  ''V''CC. 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 R_2, thus the output high interval is longer than the low interval. This is shown in the following equations: The output high time interval of each pulse is given by: : t_\text = \ln(2) \cdot (R_1 + R_2) \cdot C The output low time interval of each pulse is given by: : t_\text = \ln(2) \cdot R_2 \cdot C Hence, the
frequency Frequency is the number of occurrences of a repeating event per unit of time. Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as mechanical vibrations, audio ...
f of the pulse is given by: : f = \frac = \frac and the
duty cycle A duty cycle or power cycle is the fraction of one period in which a signal or system is active. Duty cycle is commonly expressed as a percentage or a ratio. A period is the time it takes for a signal to complete an on-and-off cycle. As a for ...
D is given by: : D~(\%) = \frac \cdot 100 = \frac \cdot 100 where t is the time in
second The second (symbol: s) is a unit of time derived from the division of the day first into 24 hours, then to 60 minutes, and finally to 60 seconds each (24 × 60 × 60 = 86400). The current and formal definition in the International System of U ...
s, R is the resistance in
ohm Ohm (symbol Ω) is a unit of electrical resistance named after Georg Ohm. Ohm or OHM may also refer to: People * Georg Ohm (1789–1854), German physicist and namesake of the term ''ohm'' * Germán Ohm (born 1936), Mexican boxer * Jörg Ohm (1 ...
s, C is the capacitance in
farad The farad (symbol: F) is the unit of electrical capacitance, the ability of a body to store an electrical charge, in the International System of Units, International System of Units (SI), equivalent to 1 coulomb per volt (C/V). It is named afte ...
s, and \ln(2) is the natural log of 2 constant. Resistor R_1 requirements: * The maximum current through R_1 must be lower than the maximum current rating of the internal transisor at the DISCHARGE pin, because this transistor "shorts" the DISCHARGE pin to the GND pin (per internal schematics above) to drain the capacitor. This is the reason why R_1 shouldn't be a very low resistance, such as when a variable trimmer or
potentiometer A potentiometer is a three- terminal resistor with a sliding or rotating contact that forms an adjustable voltage divider. If only two terminals are used, one end and the wiper, it acts as a variable resistor or rheostat. The measuring instrum ...
is used instead of a fixed value resistor. * The maximum power rating of R_1 must be greater than \frac, per
Ohm's law Ohm's law states that the electric current through a Electrical conductor, conductor between two Node (circuits), points is directly Proportionality (mathematics), proportional to the voltage across the two points. Introducing the constant of ...
.


Shorter duty cycle

To create an output high time shorter than the low time (i.e., a
duty cycle A duty cycle or power cycle is the fraction of one period in which a signal or system is active. Duty cycle is commonly expressed as a percentage or a ratio. A period is the time it takes for a signal to complete an on-and-off cycle. As a for ...
less than 50%) a fast diode (i.e. 1N4148 signal diode) can be placed in parallel with R2, with the cathode on the capacitor side. This bypasses R2 during the high part of the cycle, so that the high interval depends only on R1 and C, with an adjustment based on the voltage drop across the diode. The low time is unaffected by the diode and so remains \ln(2) \, R_2 \, C \, . But the diode's forward
voltage drop In electronics, voltage drop is the decrease of electric potential along the path of a current flowing in a circuit. Voltage drops in the internal resistance of the source, across conductors, across contacts, and across connectors are unde ...
''V''diode slows charging on the capacitor, so the high time is longer than the often-cited \ln(2) \, R_1 \, C to become: : t_\text = \ln\left(\frac\right) \cdot R_1 \cdot C, where ''V''diode is when the diode's "on" current is of ''V''CC/R1 (which depends on the type of diode and can be found in datasheets or measured). When Vdiode is small relative to ''V''cc, this charging is faster and approaches \ln(2) \, R_1 \, C but is slower the closer Vdiode is to ''V''cc:
As an extreme example, when ''V''CC = 5 V, and Vdiode = 0.7 V, high time is 1.00 R1C, which is 45% longer than the "expected" 0.693 R1C. At the other extreme, when ''V''cc = 15 V, and Vdiode = 0.3 V, the high time is 0.725 R1C, which is closer to the expected 0.693 R1C. The equation approaches 0.693 R1C as ''V''diode approaches 0 V.


Voltage-controlled pulse-width modulation

In the previous example schematics, the control pin was not used, thus it should connected to ground through a 10  nF decoupling capacitor to shunt electrical noise. However, if a time-varying voltage source was applied to the control pin, then the pulse widths would be dependent on the control voltage.


Monostable

Monostable mode produces an output pulse when the trigger signals drops below ''V''CC. An
RC circuit A resistor–capacitor circuit (RC circuit), or RC filter or RC network, is an electric circuit composed of resistors and capacitors. It may be driven by a voltage source, voltage or current source and these will produce different responses. A fi ...
sets the output pulse's duration as the time t in
second The second (symbol: s) is a unit of time derived from the division of the day first into 24 hours, then to 60 minutes, and finally to 60 seconds each (24 × 60 × 60 = 86400). The current and formal definition in the International System of U ...
s it takes to charge C to ''V''CC: : t = \ln(3) \cdot R \cdot C, where R is the resistance in
ohm Ohm (symbol Ω) is a unit of electrical resistance named after Georg Ohm. Ohm or OHM may also refer to: People * Georg Ohm (1789–1854), German physicist and namesake of the term ''ohm'' * Germán Ohm (born 1936), Mexican boxer * Jörg Ohm (1 ...
s, C is the capacitance in
farad The farad (symbol: F) is the unit of electrical capacitance, the ability of a body to store an electrical charge, in the International System of Units, International System of Units (SI), equivalent to 1 coulomb per volt (C/V). It is named afte ...
s, \ln(3) is the natural log of 3 constant. The output pulse duration can be lengthened or shortened as desired by adjusting the values of R and C. Subsequent triggering before the end of this timing interval won't affect the output pulse.


Example values

The timing table (right) shows common electronic component value solutions for various powers of 10 timings. Scaling R and C by opposite powers of 10 will provide the same timing. For instance: * 1ms ≅ 1nF and 910kΩ, * 1ms ≅ 10nF and 91kΩ (values from table), * 1ms ≅ 100nF and 9.1kΩ. For each row in the example table (right), additional timing values can easily be created by adding one to three of the same resistor value in parallel and/or series. A second resistor in parallel, the new timing is half the table time. A second resistor in series, the new timing is double the table time. * 2.5ms (0.25x) ≅ 100nF and 22.75kΩ (four 91kΩ resistors in parallel), * 5ms (0.5x) ≅ 100nF and 45.5kΩ (two 91kΩ resistors in parallel), * 10ms (1x) ≅ 100nF and 91kΩ (values from table), * 15ms (1.5x) ≅ 100nF and 136.5kΩ (one 91kΩ resistor in series with "two 91kΩ resistors in parallel"), * 20ms (2x) ≅ 100nF and 182kΩ (two 91kΩ resistors in
series Series may refer to: People with the name * Caroline Series (born 1951), English mathematician, daughter of George Series * George Series (1920–1995), English physicist Arts, entertainment, and media Music * Series, the ordered sets used i ...
), * 25ms (2.5x) ≅ 100nF and 227.5kΩ ("two 91kΩ resistors in series" in series with "two 91kΩ resistors in parallel"), * 30ms (3x) ≅ 100nF and 273kΩ (three 91kΩ resistors in series), * 40ms (4x) ≅ 100nF and 364kΩ (four 91kΩ resistors in series).


Bistable SR latch

A 555 timer can act as an active-low SR latch (though without an inverted output) with two outputs: output pin is a push-pull output, discharge pin is an open-collector output (requires a
pull-up resistor In electronic logic circuits, a pull-up resistor (PU) or pull-down resistor (PD) is a resistor used to ensure a known state for a signal. More specifically, a pull-up resistor or pull-down resistor ensures that a wire will have a high logic lev ...
). For the schematic on the right, a input signal connects to the pin and connecting a input signal to the pin. Thus, pulling momentarily low acts as a "set" and transitions the output to the high state (''V''CC). Conversely, pulling momentarily low acts as a "reset" and transitions the Out pin to the low state (GND). No timing capacitors are required in a bistable configuration. The threshold input is grounded because it is unused. The trigger and reset inputs may be held high via
pull-up resistor In electronic logic circuits, a pull-up resistor (PU) or pull-down resistor (PD) is a resistor used to ensure a known state for a signal. More specifically, a pull-up resistor or pull-down resistor ensures that a wire will have a high logic lev ...
s if they are normally Hi-Z and only enabled by connecting to ground.


Bistable Schmitt trigger inverter gate

A 555 timer can be used to create a
Schmitt trigger In electronics, a Schmitt trigger is a comparator circuit with hysteresis implemented by applying positive feedback to the noninverting input of a comparator or differential amplifier. It is an passivity (engineering), active circuit which con ...
inverter gate with two outputs: output pin is a push-pull output, discharge pin is an open-collector output (requires a
pull-up resistor In electronic logic circuits, a pull-up resistor (PU) or pull-down resistor (PD) is a resistor used to ensure a known state for a signal. More specifically, a pull-up resistor or pull-down resistor ensures that a wire will have a high logic lev ...
). For the schematic on the right, an input signal is AC-coupled through a low value series capacitor, then biased by identical high-resistance resistors R_1 and R_2, which causes the signal to be centered at ''V''cc. This centered signal is connected to both the trigger and threshold input pins of the timer. The input signal must be strong enough to excite the trigger levels of the comparators to exceed the lower ''V''CC and upper ''V''CC thresholds in order to cause them to change state, thus providing the Schmitt trigger feature. No timing capacitors are required in a bistable configuration.


Packages

In 1972,
Signetics Signetics Corporation was an American electronics manufacturer specifically established to make integrated circuits. Founded in 1961, they went on to develop a number of early microprocessors and support chips, as well as the widely used 555 time ...
originally released the 555 timer in DIP-8 and TO5-8 metal can packages, and the 556 timer was released in a DIP-14 package. 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). 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). The MIC1555 is a
CMOS Complementary metal–oxide–semiconductor (CMOS, pronounced "sea-moss ", , ) is a type of MOSFET, metal–oxide–semiconductor field-effect transistor (MOSFET) semiconductor device fabrication, fabrication process that uses complementary an ...
555-type timer with three fewer pins available in SOT23-5 (0.95 mm pitch) surface-mount package.


Specifications

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


Derivatives

Numerous companies have manufactured one or more variants of the 555, 556, 558 timers over the past decades, under 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 "Total timers" column, a "*" denotes parts that are missing 555 timer features. * For the "''I''q" 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 ''I''q at 5 V. The value listed in this table was estimated by comparing the 5 V to 15 V ratio of other bipolar datasheets, then derating the 15 V 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. 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. **
Fairchild Semiconductor Fairchild Semiconductor International, Inc. was an American semiconductor company based in San Jose, California. It was founded in 1957 as a division of Fairchild Camera and Instrument by the " traitorous eight" who defected from Shockley Semi ...
was sold to
ON Semiconductor ON Semiconductor Corporation (stylized and doing business as onsemi) is an American semiconductor supplier company, based in Scottsdale, Arizona. Products include power and signal management, logic, discrete, and custom devices for automotive, c ...
in 2016. ON Semiconductor was founded in 1999 as a spinoff of
Motorola Motorola, Inc. () was an American multinational telecommunications company based in Schaumburg, Illinois. It was founded by brothers Paul and Joseph Galvin in 1928 and had been named Motorola since 1947. Many of Motorola's products had been ...
Semiconductor Components Group. The MC1455 started as a Motorola product. **
Intersil Intersil is an American semiconductor company headquartered in Milpitas, California. , Intersil is a subsidiary of Renesas. The previous Intersil was formed in August 1999 through the acquisition of the semiconductor business of Harris Corpor ...
was sold to Renesas Electronics in 2017. The ICM7555 and ICM7556 started as Intersil products. ** Micrel was sold to
Microchip Technology Microchip Technology Incorporated is a publicly listed American semiconductor corporation that manufactures microcontroller, mixed-signal, analog, and Flash-IP integrated circuits. Its corporate headquarters is located in Chandler, Arizona. ...
in 2015. The MIC1555 started as a Micrel product. **
National Semiconductor National Semiconductor Corporation was an United States of America, American Semiconductor manufacturing, semiconductor manufacturer, which specialized in analogue electronics, analog devices and subsystems, formerly headquartered in Santa Clara, ...
was sold to
Texas Instruments Texas Instruments Incorporated (TI) is an American multinational semiconductor company headquartered in Dallas, Texas. It is one of the top 10 semiconductor companies worldwide based on sales volume. The company's focus is on developing analog ...
in 2011. The LM555 and LM556 started as a National Semiconductor products. **
Signetics Signetics Corporation was an American electronics manufacturer specifically established to make integrated circuits. Founded in 1961, they went on to develop a number of early microprocessors and support chips, as well as the widely used 555 time ...
was sold to Philips Semiconductor in 1975, later to
NXP Semiconductors NXP Semiconductors N.V. is a Dutch semiconductor manufacturing and design company with headquarters in Eindhoven, Netherlands. It is the third largest European semiconductor company by market capitalization as of 2024. The company employs approx ...
in 2006. ** Zetex Semiconductors was sold to Diodes Incorporated in 2008. The ZSCT1555 started as a Zetex product.


556 dual timer

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.


558 quad timer

The quad version is called 558 and has four reduced-functionality timers in a 16-pin package designed primarily for
monostable multivibrator A multivibrator is an electronic circuit used to implement a variety of simple two-state devices such as relaxation oscillators, timers, latches and flip-flops. The first multivibrator circuit, the astable multivibrator oscillator, was invented ...
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).


See also

*
RC circuit A resistor–capacitor circuit (RC circuit), or RC filter or RC network, is an electric circuit composed of resistors and capacitors. It may be driven by a voltage source, voltage or current source and these will produce different responses. A fi ...
*
Counter (digital) In digital electronics, a counter is a sequential logic circuit that counts and stores the number of positive or negative transitions of a clock signal. A counter typically consists of flip-flop (electronics), flip-flops, which store a value repr ...
*
Operational amplifier An operational amplifier (often op amp or opamp) is a direct coupling, DC-coupled Electronic component, electronic voltage amplifier with a differential input, a (usually) Single-ended signaling, single-ended output, and an extremely high gain ( ...
*
List of LM-series integrated circuits The following is a list of LM-series integrated circuits. Many were among the first analog integrated circuits commercially produced since late 1965; some were groundbreaking innovations. As of 2007, many are still being used. The LM series orig ...
*
List of linear integrated circuits The following is a list of linear integrated circuits. Many were among the first analog chip, analog integrated circuits commercially produced; some were groundbreaking innovations, and many are still being used. See also * Linear integrated ...
*
4000-series integrated circuits The 4000 series is a CMOS logic family of integrated circuits (ICs) first introduced in 1968 by RCA. It was slowly migrated into the 4000B buffered series after about 1975. It had a much wider supply voltage range than any contemporary logic fami ...
, List of 4000-series integrated circuits *
7400-series integrated circuits The 7400 series is a popular logic family of transistor–transistor logic (TTL) integrated circuits (ICs). In 1964, Texas Instruments introduced the SN5400 series of logic chips, in a ceramic semiconductor package. A low-cost plastic packa ...
,
List of 7400-series integrated circuits The following is a list of 7400-series digital logic integrated circuits. In the mid-1960s, the original 7400-series integrated circuits were introduced by Texas Instruments with the prefix "SN" to create the name SN74xx. Due to the popularity of ...
*
Push–pull output A push–pull amplifier is a type of electronic circuit that uses a pair of active devices that alternately supply current to, or absorb current from, a connected load. This kind of amplifier can enhance both the load capacity and switching s ...
, Open-collector/drain output, Three-state output


Notes


References


Further reading

;Books * ''555 Timer Applications Sourcebook With Experiments''; 2nd Ed; Howard Berlin; BPB Publications; 218 pages; 2008; . ''(1st Ed in 1978)''
/small> * ''Timer/Generator Circuits Manual''; 1st Ed; R.M. Marston; Newnes; 276 pages; 1990; . * ''Engineer's Mini-Notebook â€“ 555 Timer IC Circuits''; 3rd Ed; Forrest Mims III; Radio Shack; 33 pages; 1989; ASIN B000MN54A6. ''(1st Ed in 1984)''
/small> * ''IC Timer Cookbook''; 2nd Ed; Walt Jung; Sams Publishing; 384 pages; 1983; .
(1st Ed in 1977)
'
* ''110 IC Timer Projects''; Jules Gilder; Hayden; 115 pages; 1979; . * ''IC 555 Projects''; E.A. Parr; Bernard Babani Publishing; 144 pages; 1978; . ; Books with timer chapters *

- Volume VI - Experiments''; Tony Kuphaldt; Open Book Project; 423 pages; 2010. ''(Chapter 6 and 8)''
/small> * ''Designing Analog Chips''; Hans Camenzind (inventor of 555 timer); Virtual Bookworm; 244 pages; 2005; . ''(Chapter 11)''
/small> * ''Timer, Op Amp, and Optoelectronic Circuits and Projects''; Forrest Mims III; Master Publishing; 128 pages; 2004; . (Chapter 1) * ''Linear LSI Data and Applications Manual'';
Signetics Signetics Corporation was an American electronics manufacturer specifically established to make integrated circuits. Founded in 1961, they went on to develop a number of early microprocessors and support chips, as well as the widely used 555 time ...
; 1250 pages; 1985. ''(Appnotes AN170/171 and Datasheets NE555/6/8)''
/small> * ''Analog Applications Manual'';
Signetics Signetics Corporation was an American electronics manufacturer specifically established to make integrated circuits. Founded in 1961, they went on to develop a number of early microprocessors and support chips, as well as the widely used 555 time ...
; 418 pages; 1979. ''(Chapter 6)''
/small> * ''TTL Cookbook''; Don Lancaster; Sams Publishing; 412 pages; 1974; . ''(Chapter 4, pages 171-188)''
/small> ; Datasheets * See links in "Derivatives" table and "References" section in this article.


External links


Using the 555 Timer IC in Special or Unusual Circuits
- Nuts & Volts magazine

- Tony van Roon

* 555 timing calculators
astablemonostable




{{Authority control 1972 introductions Electronic oscillators Linear integrated circuits