NE555

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NE555 from Signetics in housing DIP -8, manufactured in 1978 week 28

The integrated circuit NE555 is an active electronic component that switches an output on or off under certain conditions. It is very suitable for timing controls and clock generators and is sometimes even used in switched-mode power supplies . The NE555 - often referred to as 555 for short - was first introduced in 1972 by the US semiconductor manufacturer Signetics . Due to its robustness and reliability, it is still used today, with areas of application ranging from toys to space travel. The NE555 is the world's best-selling integrated circuit.

history

Close-up of the of the NE555 and the bonding wires

The NE555 was developed between 1970 and 1971 by the Swiss engineer Hans R. Camenzind for the US semiconductor manufacturer Signetics (later Philips Semiconductors, now NXP ). At first, the project was very controversial: Timing circuits were mostly built with operational amplifiers or comparators , which made up a large part of the analog circuits manufactured by Signetics . On the one hand it was doubted that there was even a market for specialized timer ICs, on the other hand it was feared that a timer IC could reduce sales of the operational amplifiers - this is known in the economy as the cannibalism effect. The name NE555 comes from Art Fury , at that time Marketing Manager at Signetics. The fact that the development of the NE555 was commissioned to Hans Camenzind despite the company's internal resistance goes back to him.

Camenzind had previously developed the NE565 / NE567 (a phase-locked loop , PLL) and the NE566 (a voltage-controlled oscillator , VCO), each of which contains a stable oscillator that is largely unaffected by temperature and supply voltage. The first draft of the NE555 was therefore based on a similar oscillator in which an external capacitor was also charged or discharged linearly by a voltage-to-current converter , which serves as a constant current source , and several current mirrors and produced a triangular voltage .

After the design was finalized and Signetics reviewed and approved it, Camenzind rejected his design again: he replaced the constant current source with a single external resistor. This meant that an 8-pin housing could be used instead of the 14-pin housing - with a constant current source 9 connections would have been necessary; However, Signetics only made 8 or 14 pin DIP . Although the capacitor is not charged or discharged linearly via a resistor, a change in the supply voltage has no effect, as the timer determines the state of charge of the capacitor ratiometrically , i.e. H. in relation to the supply voltage, compares. As a side effect, the new circuit was more stable against temperature fluctuations.

From 1972 the NE555 was mass- produced. Demand exceeded all expectations, with Signetics selling more than half a million units in the first quarter. The other semiconductor manufacturers rebuilt the NE555 very quickly: just six months after its appearance, 555 copies from eight different manufacturers were on the market. Sometimes other type designations are used for the replicas, such as MC1455 from ON Semiconductor (formerly Motorola ), LM555 from National Semiconductor , KA555 from Fairchild Semiconductor (formerly Samsung ) or the SN72555 from Texas Instruments . Replicas were also made in the Eastern Bloc , such as the КР1006ВИ1 from the former USSR . Such replicas were common in the 1970s up to the Semiconductor Chip Protection Act of 1984 (SCPA). Even more than 30 years after its market launch, around one billion units were still produced annually in 2003.

The available chip housings have also changed over the years: The NE555 was manufactured from the start in a plastic housing, the dual in-line package (DIP), and in the round metal housing (TO-78 "metal can" ) (which is no longer common today ) . For military and space applications, the NE555 is also packaged in ceramic housings (CERDIP, LCC). In the 1980s, housing variants as Surface Mounted Devices (SMD) such as SOIC, SSOP or TSSOP followed .

Dual timer 556 in a 14-pin DIP housing

Variants with two and four timer circuits in one housing also came on the market, which allow more complex circuits to be constructed in a compact manner. The dual variant NE556 contains two identical and independent 555 timers on one chip in a chip housing with 14 pins. The NE558 variant contains four timers in a 16-pin housing, also known as "quad timers". Due to the combined connections, the timers in the latter variant are not completely independent of one another.

A few years after the bipolar version was launched, Intersil brought a largely compatible CMOS variant onto the market. It has the same pinout and identical function with significantly lower power consumption. No Darlington steps are required in the chip design . Due to the lower input current, it allows higher resistance values ​​and the outputs can be controlled up to the supply voltage. However, the CMOS variant delivers a smaller maximum output current compared to the bipolar version. Today, CMOS variants are available from various manufacturers, such as the LMC555 (National Semiconductor), TLC555 (Texas Instruments), ICM7555 (various manufacturers). There is also a dual version of this with the designation ICM7556 .

Altered bipolar versions have also been released, e.g. B. the ZSCT1555 from the company Zetex , which works down to 0.9 V supply voltage and is therefore suitable for operation from a single battery cell. This design also comes from Hans Camenzind.

The disadvantages of the original, bipolar design, such as the relatively large quiescent current of up to 15 mA, the relatively high minimum supply voltage of 4.5 V for today's conditions and the significant current peaks when switching the output stage are partially avoided in newer replicas. Nevertheless, the IC from various manufacturers is still produced in unaltered circuit, only the manufacturing processes were to smaller feature sizes changed, so does the size of the chip thereby reduced ( english the shrink ), see. Scaling (microelectronics) . After a fire in a factory in Caen , in which the last production line for the processes used was destroyed, Philips stopped production of the NE555 in 2003 and has only offered the CMOS version ICM7555 (today as NXP ).

construction

Pin assignment
connection Surname Description / purpose
1 GND Ground (0 V)
2 TRIG "Trigger": OUT rises and the interval begins when this input falls below 1 ⁄ 3 V CC .
3 OUT Output: This output is pulled to V CC or GND by the IC .
4th RESET A time interval can be interrupted if this input is set to GND.
5 CTRL "Control": Access to the internal voltage divider (usually 2 ⁄ 3 V CC )
6th THR "Threshold": The interval ends when the voltage at THR is greater than at CTRL.
7th DIS "Discharge": Open collector output : can discharge a capacitor between the intervals.
8th V +, V CC Supply voltage (between 3 and 15 V)

The NE555 contains the equivalent of 24 bipolar transistors , two diodes and 15 resistors ( Small Scale Integration , SSI), which together form six function blocks (these are highlighted in color in the block diagram and circuit diagram below):

  • Between the supply voltage V CC (+) and the ground GND (-) there is a voltage divider made of three identical resistors, which, if not connected externally, supplies the two reference voltages 1 ⁄ 3  V CC and 2 ⁄ 3  V CC . The latter is available at the Control Voltage connection pin . (green)
  • Two comparators are each connected to one of the reference voltages, while the other two inputs are routed directly to the trigger and threshold connections . (yellow and red)
  • A flip-flop saves the status of the timer and is controlled via the two comparators. The flip-flop (and thus the entire timer module) can be reset at any time via the reset connection, which overrides the other two inputs . (purple)
  • At the output of the flip-flop there is an output stage with a totem pole output , which can be loaded with up to 200 mA at the output connection . (pink)
  • A transistor is connected in parallel to the output stage, the collector of which is connected to the Discharge connection . This transistor is always switched through when the output is low . (Light Blue)

  • Block diagram of the 555

  • Circuit of the bipolar NE555

  • Switching the CMOS version

Basic circuits

The NE555 has three basic modes of operation described below. In addition, there are a number of other circuit variants derived from them, such as electronic tachometers , trigger switches in oscilloscopes , basic functions in cable testers or temperature controllers in which the NE555 is used as a circuit component.

Monostable multivibrator

Switching example for the 555 in monostable mode
The relationships of the trigger signal, the voltage on the capacitor C and the pulse width

As a monostable multivibrator , the NE555 works as a one-time pulse generator. Applications in this mode include timers, frequency dividers, capacitance measurement and pulse width modulation (PWM).

The pulse begins when the NE555 timer receives a signal at the trigger input. This is the case when the voltage at the trigger input falls below 1 ⁄ 3 of the supply voltage. The width of the output pulse is determined by the time constant of an external RC network, which consists of a capacitor C and a resistor R, as shown in the adjacent circuit diagram. The output pulse ends when the voltage on the capacitor corresponds to 2 ⁄ 3 of the supply voltage, provided that the trigger pulse ended before. The pulse width τ of the output pulse can be changed by adjusting the values ​​of R and C according to the following equation:

In this simple basic circuit, the monostable multivibrator cannot be retriggered. A new trigger signal is only accepted after the time τ has elapsed . By expanding the circuit, a retriggerable monostable multivibrator can also be implemented with the NE555. One only makes use of its function as a precision Schmitt trigger.

One application of the monostable multivibrator with the quadruple timer circuit NE558 was the analog joystick interface on the so-called game port of the IBM PC in the 1980s: The NE558 represents part of a simple AD converter with four channels, which measures the resistance value of the potentiometer per axis for two joysticks into a pulse duration dependent on the deflection. The triggering of the NE558 and the determination of the duration of a pulse are implemented via the software.

Bistable multivibrator

Switching example for the 555 in bistable mode

When operated as a bistable multivibrator , only the flip-flop built into the NE555 is used in principle . Areas of application are e.g. B. bounce-free switches.

The trigger input (pin 2) serves as a SET for the flip-flop , with which the bistable multivibrator is set by a short pulse. A short pulse at the reset input (pin 4) serves as a RESET , the bistable multivibrator is thus reset. Both the set impulse and the reset impulse correspond to the negative logic - this fact is indicated by crossing over the signal names.

Since there is no time-dependent function with a bistable multivibrator, no additional capacitors are necessary in principle. The smoothing capacitor shown in the circuit with 10  nF at the CTRL connection is used, as in the other circuit modes, only to smooth the internal reference voltage and can be omitted if the accuracy requirements are low.

Astable multivibrator

Switching example for the 555 in astable mode

As an astable multivibrator , the NE555 works as an oscillator and generates a periodic signal at its output. Depending on the wiring, different waveforms , such as the simplest form a square wave , can be generated with a variable pulse width ratio. The applications include, among other things, all forms of blinkers, pulse generators, electronic clocks, applications for sound generation or as a clock source in DC voltage converters .

The circuit is constituted by two resistors R 1 and R 2 , and a charging capacitor C is formed. The charging capacitor is initially uncharged, as a result of which the internal flip-flop is set via the TRIG input, the DIS output is kept high-resistance and the capacitor is charged via the two resistors. When the supply voltage on capacitor C reaches 2 ⁄ 3 , the internal flip-flop is reset, which switches the DIS output to ground (GND). This causes the capacitor to discharge to ground via resistor R 2 and the DIS output. The discharge continues until the capacitor is discharged to 1 ⁄ 3 of the supply voltage. Then the flip-flop is set again and the process begins again.

This allows the oscillator frequency f to be determined as a function of the components R 1 , R 2 and C as follows:

Different pulse width ratios can be selected by choosing R 1 and R 2 differently. The duration t high for the high pulse at the output is

The duration t low for the low pulse at the output is given as:

By feeding a voltage to the CTRL input, you can shift the trigger level. In this way the charging time and thus the frequency of the multivibrator is changed. The resistance values ​​must not be selected to be too low in order to avoid overloading the output stages. For example, with this simple basic circuit , a pulse width ratio of 50:50 cannot be achieved, since the resistor R 1 would then represent a short circuit with a required value of 0 Ω . If a diode is connected in parallel to R 2 , a pulse width ratio of 50:50 can be achieved. For the generation of almost any pulse width ratio, e.g. For example, for a range between 1% and 99%, comparatively inexpensive connection circuits can be used.

Operating data and variants

The following technical details apply to the NE555. Other versions of the timer may have different specifications, which can be found in the respective data sheets.

parameter value
Supply voltage (V CC ) 4.5-16V
Supply current (V CC = +5 V) 3-6 mA
Supply current (V CC = +15 V) 10-15 mA
Maximum output current 200 mA
Maximum power dissipation 600 mW
Minimal power consumption 30 mW (at 5 V), 225 mW (at 15 V)
operating temperatur 0-70 ° C

The following table compiles a selection of current and former manufacturers of the 555 timer circuit with their type designation and special features.

Manufacturer model annotation
Avago Technologies Av-555M
Custom Silicon Solutions CSS555 / CSS555C CMOS (from 1.2 V), I DD  <5 µA
IP core for ASICs
CEMI ULY7855
ECG Philips ECG955M
Exar XR-555
Fairchild Semiconductor NE555 / KA555
HFO (GDR) B555
Harris HA555
Hitachi HA17555
IK Semicon ILC555 CMOS (from 2 V)
Intersil SE555 / NE555
Intersil ICM7555 CMOS
Lithic Systems LC555
Maxim ICM7555 CMOS (from 2 V)
Motorola MC1455 / MC1555
National Semiconductor LM1455 / LM555 / LM555C
National Semiconductor LMC555 CMOS (from 1.5 V)
NXP Semiconductors ICM7555 CMOS
Raytheon RM555 / RC555
RCA CA555 / CA555C
Signetics / Philips Semiconductors NE555 / SE555 Original version
STMicroelectronics NE555N / TS555CN / K3T647
NDE Sylvania NTE955M
Texas Instruments SN52555 / SN72555
Texas Instruments TLC555 CMOS (from 2 V)
Replica from the USSR КР1006ВИ1
Zetex ZSCT1555 up to 0.9V

Data Sheets

literature

  • Roland Jeschke: Flashing, sounding, controlling with the 555 timer . 2nd Edition. Frech-Verlag, Stuttgart 1982, ISBN 3-7724-0332-8 .
  • Karl-Heinz Bläsing, Klaus Schlenzig: Timer circuits B 555 D and B 556 D information and applications . MV – Berlin, 1984.
  • Patrick Schnabel, Thomas Schaerer: Timer 555. Basics, application-oriented circuits and extracts from data sheets for an electronics workshop. The electronics compendium . ( Online ).

Web links

Commons : NE555  - Collection of Images, Videos and Audio Files

Individual evidence

  1. ↑ a b c Hans Camenzind: Designing Analog Chips . 2nd Edition. Virtualbookworm.com Publishing, College Station, Texas in 2005, ISBN 1-58939-718-5 , Chapter 11 Timers and Oscillators: , S. 11-2 and 11-3 ( designinganalogchips.com ).
  2. ↑ a b Transistor Museum: Interview with Hans Camenzind about the design of the NE555 (English, text and audio)
  3. ↑ NE555: datasheet на русском, описание и схема включения. ledjournal.info, accessed October 31, 2018 (Russian).
  4. ^ Walter G. Jung: IC Timer Cookbook , Second Edition, Sams Technical Publishing 1983, ISBN 978-0-672-21932-0 , pp. 40-41
  5. ^ Hans R. Camenzind: Redesigning the old 555 . In: IEEE Spectrum , Volume 34, Number 9, September 1997. IEEE Press, ISSN  0018-9235 , pp. 80-85
  6. ↑ van Roon, chapter "Monostable Mode" (Using the 555 timer as a logic clock)
  7. ↑ Ulrich Tietze, Christoph Schenk: Semiconductor circuit technology . 10th edition. Springer, 1993, ISBN 3-540-56184-6 , pp. 190-191 .
  8. ↑ IBM-PC Gameport (joystick) , queried on June 8, 2012
  9. ↑ University of Applied Sciences Emden. Flip-flops with comparators ( Memento from March 4, 2016 in the Internet Archive ) (PDF, 212 kB)
  10. ↑ NE555 as an astable trigger stage / astable multivibrator. Retrieved June 11, 2019 .
  11. ↑ badenhausen.com: PWM speed controller for small DC motors , from 2016 (PDF), accessed on December 3, 2016
  12. ^ Custom Silicon Solutions