What is the NE555 and How Does it Work?
14 March 2024
Ⅰ. The birth background of NE555
Ⅳ. Internal composition of NE555
Ⅴ. Operating modes of the NE555
Ⅷ. Five classic circuits of NE555
NE555 is a monolithic integrated circuit timer that can generate various types of timing signals. It is widely used in various electronic devices in areas such as electronic clocks, power management, calculators and LED displays. The purpose of this article is to provide detailed information of NE555, including its birth background, design, internal structure, pin description, operating modes and principle, as well as applications, to help you better use the chip.
Dating back to the early 1970s, the NE555 IC timer chip was designed by Hans Camenzind, an engineer at Signetics Corporation (now part of NXP Semiconductors, Inc.) in the U.S., and was released in 1971. The NE555 was originally designed to provide an affordable and powerful timer solution. The background of its creation is mainly related to the following aspects:
1. Hans Camenzind's design: Hans Camenzind was an electrical engineer from Switzerland who specialized in developing innovative integrated circuit designs. His design philosophy is to create a chip that is versatile, easy to use and widely applicable. Based on this philosophy, he successfully designed the NE555 and brought it to market.
2. Development of integrated circuit technology: The 1960s and 1970s were a period of rapid development of integrated circuit technology. With the advancement of technology and improvement of manufacturing process, chip designers had the ability to integrate more functions into a single chip, thus providing more applications and solutions.
3. The emergence of demand: In the electronics industry at the time, timers played a vital role in all types of circuits and systems. However, early timer solutions generally had some limitations, such as high cost, large size or functional limitations. Therefore, there is an urgent need for an affordable and powerful timer chip in the market.
The NE555 is one of the models in the 555 series of timing ICs. The pin functions and applications of this series of ICs are compatible with each other, but the stability, power-saving performance, and oscillation frequency of the different models of the chip due to price differences may also vary. 555 is a widely used and extremely common timing IC, only a small number of resistors and capacitors, can produce a variety of different frequency pulse signals required for digital circuits. 555 is the main role of the NE555 is to use its internal timer to form a time base circuit to provide timing pulses for other circuits. The main function of the NE555 is to utilize its internal timer to form a time base circuit to provide timing pulses for other circuits. The NE555 time base circuit is available in two main packages: one is a DIP double in-line 8-pin package, and the other is a SOP-8 small package.
Alternatives and equivalents:
• BL5372
• NA555
• KR3225Y
The 555 timer was designed by Hans R. Camenzind in 1971 for Sigognitik. Sigognitik was subsequently acquired by Philips. The 555 chips produced by different manufacturers vary in construction, with the standard 555 chip integrating 25 transistors, 2 diodes, and 15 resistors, which are led out through 8 pins (in a DIP-8 package.) Derivatives of the 555 include the 556 (a DIP-14 chip integrating two 555s) as well as the 558 and 559.
The NE555 has an operating temperature range of 0°C to 70°C, while the military-grade SE555 is capable of operating in extreme temperatures from -55°C to 125°C. The packaging forms of 555 include high-reliability metal packaging (represented by T) and low-cost epoxy resin packaging (represented by V). Therefore, the complete labels of 555 are NE555V, NE555T, SE555V and SE555T, etc. Although there is a common belief that the name of the 555 chip comes from the three 5KQ resistors inside it, Hans Camenzind himself denied this and claimed that he chose the three numbers at random.
There are also low-power versions of the 555, including the 7555 and the TLC555 using CMOS circuits. Compared with the standard 555, the 7555 has lower power consumption. In addition, the manufacturer claims that the 7555 control pin does not require a ground capacitor like other 555 chips, and there is no need for glitch-eliminating decoupling capacitors between the power supply and ground.
NE555 is a classic integrated circuit. Its internal circuit structure includes three main functional modules: voltage comparator and output stage, comparator and RS flip-flop. The following will provide a detailed analysis of the internal circuit of NE555:
1. Voltage comparator
There is a voltage comparator inside the NE555 for detecting the power supply voltage. The output of this voltage comparator is connected to the RS flip-flop.
2. Output stage
The output stage is connected to the RS flip-flop and is responsible for controlling the state of the output pin (i.e. pin 3). The output architecture of the NE555 is an open-drain design, which means that it cannot directly provide a high-level signal, but can only pull the output pin low. Therefore, when a high-level signal needs to be output, it is usually necessary to use an external pull-up resistor to pull the output pin to a high-level state.
3. Comparator
There are two comparators inside the NE555, namely Threshold comparator and Trigger comparator. The Threshold comparator is connected to pin 6 (THR) and the trigger comparator is connected to pin 2 (TRIG). These two comparators are used to detect changes in threshold voltage and trigger voltage.
(1) Threshold comparator: When the voltage rises at the Threshold pin (pin 6), this comparator will output a high level signal. When the Threshold voltage exceeds the Trigger voltage, the output of the comparator will change.
(2) Trigger comparator: When the voltage drops at the Trigger pin (pin 2), this comparator will output a low level signal. When the Trigger voltage is lower than the Threshold voltage, the output of the comparator will change.
4. RS trigger
The NE555 contains an RS flip-flop internally to store the state of the output pin (pin 3). The input of the RS flip-flop is controlled by the outputs of the Threshold comparator and the Trigger comparator.
(1) R input: It is connected to the output of the Threshold comparator and controls the reset of the RS flip-flop.
(2) Input: It is connected to the output of the Trigger comparator and controls the setting of the RS flip-flop.
The NE555 timer can work in three modes of operation:
1. Unstable mode: It refers to no stable state. The NE555's unstable mode is often used in strobe lights, tone generators, pulse signal generators, logic circuits such as clocks and other circuits.
2. Bi-stable mode: This mode is like a bicycle bracket, which can be stabilized in the lifted state as well as in the lowered state, and will only change when it is subjected to external force. It is called bistable because it has two stabilized states.
3. Monostable mode: This mode is like a door equipped with a door closer, which can be stabilized in the closed state and can only reach the open state when an external force is applied. Once the external force is withdrawn, the door will automatically return to the closed state. Since it has only one stable state, it is called monostable, and the NE555's monostable mode can be used for applications such as timers, flick switches, and capacitance measurements.
When the power supply voltage Vcc is turned on, the circuit starts to work, and the capacitor C starts charging immediately. When the voltage of capacitor C reaches 2/3 of Vcc, the output of the internal comparator will change to high level, and the output OUT will also change from low level to high level. Subsequently, when the voltage of capacitor C drops to 1/3 of Vcc, the output of the internal comparator will become low level, and at this time the output OUT will also change from high level back to low level. After that, the capacitor C starts charging again, and the circuit enters a new working cycle.
The period T (seconds) is determined by the values of the external capacitor C and the two external resistors R1 and R2. The formula is: T = 0.693×(R1 + 2×R2)×C. The duty cycle D describes the proportion of high level time in the square wave cycle, and its formula is: D = (R1 + R2) / (R1 + 2×R2). Therefore, by adjusting the values of capacitor C and resistors R1 and R2, we can change the period and duty cycle of the square wave waveform.
In short, the working principle of NE555 is based on the construction of a sequential circuit. By adjusting the values of external capacitors and resistors, we can control the period and duty cycle to generate various required pulse waveforms.
1. NE555 infrared remote control time-delay light
Modern homes are commonly equipped with infrared remote controls, and we can utilize these existing remotes to control an infrared remote control time delay lamp. In the illustration, H represents the integrated infrared receiver head, while C1 is the filter capacitor. As the remote control emits a string of digital pulse signals, after C1 filter, it will get a negative pulse, this pulse can trigger the 555 monostable circuit to start working.
2. NE555 water boil alarm
The water alarm is mainly composed of three parts: temperature control circuit, low frequency oscillation circuit and high frequency oscillation circuit. Among them, RP, RT and VT1 together form a temperature control circuit. The low-frequency oscillation circuit is composed of IC1, R2, R3, C1 and other components, and its forced reset terminal ④ pin is controlled by VT1. The high-frequency oscillator is composed of IC2, R4, R5, C2 and other components, and its forced reset terminal ④ foot is controlled by IC1. When the water temperature reaches the preset temperature, the resistance value of RT will become smaller, causing VT1 to cut off. At this time, pin ④ of IC1 becomes high, and IC1 starts to oscillate and output low frequency pulses. These pulses modulate the high-frequency oscillator composed of IC2 so that it starts to work and emits a ticking sound.
3. NE555 touch timer switch
IC1 is a piece of 555 timing circuit which is configured here as a monostable circuit. Normally, since there is no induced voltage at the P terminal of the touch pad, capacitor C1 will be completely discharged through pin 7 of the 555, causing pin 3 to output a low level and relay KS to be in the released state, so the light will not come on.
When we need to turn on the light, just touch the metal plate P with your hand, the stray signal voltage generated by human body induction will be added to the trigger terminal of 555 through C2, making the output of 555 change from low level to high level. At this time, the relay KS will be absorbed, and the lamp is then lit. At the same time, pin 7 of the 555 is internally cut off, and the power supply will charge C1 through R1, which marks the beginning of timing. When the voltage on capacitor C1 rises to 2/3 of the supply voltage, pin 7 of the 555 will conduct, discharging C1, which causes the output of pin 3 to change from high to low. At this point, the relay will be released, the light goes out, and the timing ends. Timing time is mainly determined by the value of R1 and C1, the formula is: T1 = 1.1R1 * C1. According to the values marked in the figure, the timing time is about 4 minutes. For D1, we can choose 1N4148 or 1N4001 these two models.
1. NE555 basic timer circuit
This is one of the most common circuits, which consists of components such as the NE555 chip, resistors and capacitors. By adjusting the values of the resistors and capacitors, the user can set different timing times. This circuit is often used to generate millisecond-level timing signals, such as pulse signals and square wave signals. The circuit is characterized by its simple structure, easy to implement, and can produce more accurate timing signals.
2. NE555 monostable trigger circuit
This is a circuit that can generate a single pulse signal. The circuit mainly consists of NE555 and several resistors and capacitors and other components. By adjusting the values of the resistors and capacitors, the user can change the width and delay time of the pulse. This circuit is commonly used to generate single-pulse signals such as trigger signals and synchronization signals. The circuit is characterized by its ability to generate a single pulse signal, and the width and delay time of the pulse can be adjusted.
3. NE555 bistable flip-flop circuit
This is a circuit that realizes the logic flip-flop function. By adjusting the values of resistors and capacitors, the user can change the flip-flop time and threshold voltage of the circuit. This circuit is commonly used to implement applications such as logic flip-flops and voltage comparisons. The circuit is characterized by its ability to implement the logic flip-flop function, and the flip-flop time and threshold voltage can be adjusted, so it is suitable for a variety of different logic application scenarios.
4. NE555 square wave generator circuit
This is a circuit that generates a square wave signal. By adjusting the resistor and capacitor values, the user can change the frequency and duty cycle of the square wave. This circuit is commonly used to generate square wave signals such as digital signals and modulated signals. The circuit is characterized by its ability to generate square wave signals, and the frequency and duty cycle of the square wave can be adjusted, so it is suitable for a variety of digital and modulation application scenarios.
5. NE555 multi-harmonic oscillator circuit
This is a circuit that generates rectangular wave signals. The circuit mainly consists of two NE555 chips and several components such as resistors and capacitors. The user can flexibly change the frequency and duty cycle of the oscillation by adjusting the values of these resistors and capacitors. As a result, this circuit can be used to generate audio signals or modulated signals, for example. The circuit is characterized by its ability to generate rectangular wave signals with adjustable frequency and duty cycle.
Frequently Asked Questions
1. What is the function of NE555?
The SE 555 Timer IC works between the temperature range of -55°C to 125°C in SE and the IC NE 555 is used for where the temperature ranges from 0°C to 70°C. It has a wide range of usages in the electronic field as a timer, delay, pulse generation, oscillator, etc.
2. Is NE555 and IC 555 same?
Yes, NE555 Timer IC and 555 Timer IC are same. The NE555 is the part number to the timer IC. Generally, the NE555 IC is called by the name 555 Timer IC.
3. What is the working principle of NE555?
A 555 timer can act as an active-low SR latch (though without an inverted Q output) by connecting a Reset input signal to the RESET pin and connecting a Set input signal to the TR pin. Thus, pulling Set momentarily low acts as a "set" and transitions the output to the high state (VCC).
