Integral timer NE555 - history, structure and principles of work. Variety of simple circuits on NE555

In the previous post on electronics, we got acquainted with a fairly simple integrated circuit, the 4026 counter. The chip, which will be discussed in this post, is much more interesting, at least, because it can perform not one single function, but several at once. Moreover, with its help we will finally learn not only how to flash LEDs, but also generate sounds. The name of the chip is 555 timer.

How the 555 timer works

I have seen various explanations of how this microcircuit works. But the best, it seems to me, is given in the same book by Charles Platt. Platt suggests imagining that a virtual switch is hidden inside the microcircuit:

Legs 1 and 8 are simply plugged into power. You can forget about pin 5 (control) for now, because it is rarely used and is usually connected to ground. Moreover, through a small capacitor to prevent interference. Why it is actually needed will be explained a little later.

The mentioned switch is shown in the picture in green. Initially, it connects outputs 3 and 7 to ground. When the voltage on pin 2 (trigger) drops to 1/3 of the supply voltage, comparator A (also virtual, of course) notices this and moves the switch down. In this state, output 3 becomes positive and output 7 is open. When the voltage at pin 6 (threshold) rises to 2/3 of the supply voltage, comparator B notices this and turns the switch up. Actually, leg 5 (control) is needed in order to choose some other value instead of 2/3. Finally, by lowering the voltage on pin 4 (reset), you can return the microcircuit to its original state.

To understand why the 555 timer is called a "timer", consider three modes of operation.

Monostable mode

Also sometimes referred to as single shot mode. Below is a diagram of using the chip in this mode:

Note that, as is often the case, the location of the chip pins on the schematic does not match their physical locations. This and the following diagrams do not indicate the voltage of the power source, since it can be changed in a certain range. Personally, I tested the performance of circuits at voltages from 3 to 6 V. All circuits have a 100 μF capacitor connected in parallel with the load. As we already know, it plays the role of a smoothing filter. In two out of three circuits, pin 5 (control) is connected to a 100 nF ceramic capacitor. Why this is done has already been described above. This is what all schemes have in common. Now let's talk about the differences.

Fun fact! According to the specification, the 555 timer is not designed to operate at less than 4.5 V. However, in practice, it does not perform so badly at 3 V.

So what's going on here. In the initial state, the LED is off. When you press the button connected to leg 2 (trigger), the LED lights up for about 2.5 seconds and then goes out. If, while the LED is on, press the button connected to leg 4 (reset), the LED will immediately go out before the time expires.

How it works? Pay attention to the right side of the diagram. At the initial moment in time, pin 7 is connected to the minus, so the current goes through the resistor directly to it, without reaching the capacitor at the bottom of the circuit. Pin 3 (out) is also connected to minus, so no current flows through the LED and, accordingly, it does not light up. When you click on the button connected to pin 2 (trigger), pin 7 starts to lead to nothing, and pin 3 is connected to positive. As a result, the current goes to the LED and it lights up. In addition, the capacitor at the bottom of the circuit begins to charge. When the capacitor reaches 2/3 of the supply voltage, the timer sees it through pin 6 (threshold) and resets the chip to its original state. As a result, the LED goes out, and the capacitor is completely discharged. The user can prematurely reset the chip to its original state by pressing the second button.

The time during which the LED is on can be adjusted using the capacitance of the capacitor and the resistance of the resistor using the following formula:

\u003e\u003e\u003e import math
\u003e\u003e\u003e R \u003d 100 * 1000
\u003e\u003e\u003e C \u003d 22/1000/1000
\u003e\u003e\u003e T \u003d math.log (3) * R * C
\u003e\u003e\u003e T
2.4169470350698417

Here R is the resistance of the resistor in ohms, C is the capacitance of the capacitor in farads, and T is the LED burning time in seconds. Note, however, that in practice, the characteristics of all elements are determined with some error. For resistors, for example, it is typically either 5% (gold bar) or 10% (silver bar).

Self-oscillating mode (astable mode)

Corresponding circuit:

What's going on here? The LED simply blinks at a rate of about 3 times per second. No buttons or other interactive features are provided.

How it works. Due to the fact that initially pin 7 (discharge) supplies a low voltage and is connected to pin 2 (trigger) through a 10 kΩ resistor, the chip immediately switches to its "down" state. The LED lights up and the capacitor at the bottom of the circuit starts charging through the two resistors on the right. When the voltage across the capacitor reaches 2/3 of the full voltage, the chip sees it through pin 6 (threshold) and switches to the "high" state. The capacitor begins to discharge through pin 7 (discharge), but it does so more slowly than in the previous circuit, since this time it is discharged through a 10 kΩ resistor. When the voltage across the capacitor drops to 1/3 of the full voltage, the chip sees it through pin 2 (trigger). As a result, it again goes to the "lower" state and the process is repeated.

How the LED will blink can be determined by the formulas:

\u003e\u003e\u003e import math
\u003e\u003e\u003e C \u003d 22/1000/1000
\u003e\u003e\u003e R1 \u003d 1 * 1000
\u003e\u003e\u003e R2 \u003d 10 * 1000
\u003e\u003e\u003e H \u003d math.log (2) * C * (R1 + R2)
\u003e\u003e\u003e H
0.16774161769550675
\u003e\u003e\u003e L \u003d math.log (2) * C * R2
\u003e\u003e\u003e L
0.15249237972318797
\u003e\u003e\u003e F \u003d 1 / (H + L)
\u003e\u003e\u003e F
3.1227165387207

Here F is the blinking frequency in hertz, H is the time in seconds during which the LED is on, and L is the time in seconds during which the LED is off. Interestingly, a diode can be connected in parallel with resistor R2, thereby forcing the capacitor to charge only through R1, and discharge, as before, through R2. Thus, it is possible to achieve complete independence of time H from time L and vice versa.

Fun fact! By connecting a speaker or a piezo buzzer instead of an LED in this circuit, and also choosing C equal to 100 nF or 47 nF, you can enjoy sound with a frequency of 687 Hz or 1462 Hz, respectively. In fact, this is far from pure sound of a certain frequency, since the 555 chip generates a square wave, and for a pure sound you need a sine wave. The easiest way to feel the difference between a square wave and a sine wave is in Audacity by saying Generate → Tone. Note that you can adjust R2, and therefore the sound frequency, by replacing the corresponding resistor with a potentiometer. In addition, a resistor connected in series with a speaker or piezo buzzer can also be replaced with a potentiometer and the volume can be adjusted with it. Finally, instead of a capacitor, you can also connect a potentiometer to pin 5 (control) and use it to fine-tune the signal frequency.

Bistable mode

And, finally, the bistable mode diagram:

What's happening. Initially, the LED is off. When you press the button connected to leg 2 (trigger), it lights up and stays on indefinitely. When you press another button connected to leg 4 (reset), the LED goes out. That is, it turned out something like the "enable" and "off" buttons.

How it works. The mode is similar to monostable (the first one considered), only there is no capacitor that could return the chip from the "lower" state back to the "upper" one. Instead, pin 6 (threshold) is connected directly to ground, and pins 5 (control) and 7 (discharge) are not connected to anything at all. In this case, this is normal, since any signal applied to these pins will still be ignored. In general, this is the same monostable mode, only the chip does not change its state automatically. Only the user can change the state by explicitly applying a low voltage to pin 2 (trigger) or 4 (reset).

Conclusion

Agree, it was not so difficult! The following photo shows all the modes described above, assembled on a breadboard:

From left to right - monostable, self-oscillating and bistable modes. The variant where the self-oscillating mode is used with a speaker and two potentiometers looks much more impressive, but less illustrative, so I do not show it here.

You will find the sources for the above circuits created in gschem. Some more information can be found in article 555 timer IC on Wikipedia, and also further links.

As always, I will be glad to receive your questions and additions. How often do you need to use the 555 timer?

Fun fact! There are enthusiasts who do absolutely crazy things on the 555 timer. For example, with a strong desire on its basis, you can make operational amplifiers or logic gates, and therefore, theoretically, and entire processors. Details can be found, for example, in the post You Know You Can Do That with a 555 at hackaday.com.

Addition: You may also be interested in posts

With the modern development of electronics in China, it seems that you can buy anything your heart desires: from home theaters and computers to such simple products as electrical outlets and plugs.

Somewhere between them are flashing Christmas tree garlands, clocks with thermometers, power regulators, thermostats, photo relays and much more. As the great satirist Arkady Raikin said in a monologue about deficit: “Let everything be, but let something be missing!” In general, what is missing is what is included in the "repertoire" of simple radio amateur designs.

Despite such competition from the Chinese industry, the interest of amateur designers in these simple designs has not been lost to this day. They continue to be developed and in some cases find a worthy application in small home automation devices. Many of these devices were born thanks to (domestic analogue of KR1006VI1).

These are the already mentioned photo relays, various simple alarm systems, voltage converters, PWM - DC motor controllers and much more. Several practical designs available for home review will be described below.

Photo relay on timer 555

The photo relay shown in Figure 1 is designed to control lighting.

Picture 1.

The control algorithm is traditional: in the evening, when the illumination decreases, the lamp turns on. The light is turned off in the morning when the illumination reaches the normal level. The circuit consists of three units: an illumination meter, a load switching unit and a power supply unit. It is better to start the description of the operation of the circuit backwards - in front, - the power supply unit, the load switching unit and the light meter.

Power Supply

In such designs, just the very case when it is reasonable to apply, in violation of all safety recommendations, a power supply unit that does not have galvanic isolation from the network. When asked why this is possible, the answer is: after setting up the device, no one will climb into it, everything will be in an insulating housing.

External adjustments are also not expected, after the adjustment, it remains only to close the lid and hang the finished one in place, let it work. Of course, if necessary, the only “sensitivity” setting can be brought out using a long plastic tube.

Security can be achieved in two ways during the configuration process. Either use an isolation transformer () or power the device from a laboratory power supply. In this case, the mains voltage and the light bulb can be not connected, and the operation of the photocell can be monitored by the LED1 LED.

The power supply circuit is quite simple. It represents a bridge rectifier Br1 with a quenching capacitor C2 for at least 400V AC. Resistor R5 is designed to smooth the inrush current through the capacitor C14 (500.0 μF * 50V) when the device is turned on, and also serves as a fuse.

Zener diode D1 is designed to stabilize the voltage at C14. A 1N4467 or 1N5022A is suitable as a Zener diode. For the Br1 rectifier, 1N4407 diodes or any low-power bridge, with a reverse voltage of 400V and a rectified current of at least 500mA, are quite suitable.

Capacitor C2 should be shunted with a resistor of about 1MΩ (not shown in the diagram) so that after turning off the device it does not "click" with current: it certainly doesn’t kill it, but it is still quite sensitive and unpleasant.

Load switching unit

Made with the use of a specialized microcircuit KR1182PM1A, which allows you to make a lot of useful devices. In this case, it is used to control the KU208G triac. The best results are obtained by the imported "analog" BT139 - 600: the load current is 16A at a reverse voltage of 600V, and the current of the control electrode is much less than that of the KU208G (sometimes the KU208G has to be selected according to this indicator). BT139 is capable of withstanding impulse overloads up to 240A, making it extremely reliable in a variety of applications.

If BT139 is installed on a radiator, then the switched power can reach 1KW, without a radiator, load control up to 400W is permissible. In the case when the power of the light bulb does not exceed 150W, you can completely do without a triac. To do this, the right output of the La1 lamp according to the scheme should be connected directly to the terminals 14, 15 of the microcircuit, and the resistor R3 and the triac T1 should be excluded from the circuit.

Let's go further. The KR1182PM1A microcircuit is controlled through pins 5 and 6: when they are closed, the lamp is extinguished. There may be an ordinary contact switch, however, working the other way around - the switch is closed, and the lamp is off. It's much easier to remember this "logic".

If this contact is opened, then the capacitor C13 begins to charge and, as the voltage on it increases, the brightness of the lamp gradually increases. For incandescent lamps, this is very important, since it increases their service life.

By selecting the resistor R4, you can adjust the state of charge of the capacitor C13 and the brightness of the lamp. In the case of using energy-saving lamps, the capacitor C13 can be omitted, as is the KR1182PM1A itself. But this will be discussed below.

Now we are approaching the main thing. Instead of a relay, simply out of a desire to get rid of contacts, the control was entrusted to the transistor optocoupler AOT128, which can be successfully replaced with an imported "analogue" 4N35, however, with such a replacement, the value of the resistor R6 should be increased to 800KΩ ... 1MΩ, since at 100KΩ the imported 4N35 does not work will be. Proven by practice!

If the optocoupler transistor is open, its K-E junction, like a contact, will close pins 5 and 6 of the KR1182PM1A microcircuit and the lamp will be turned off. To open this transistor, you need to light up the LED of the optocoupler. In general, the opposite is true: the LED is off, and the lamp is on.

Based on 555, it turns out very simple. To do this, it is enough to connect the photoresistor LDR1 and the trimming resistor R7 to the timer inputs, with its help the threshold of the photo relay is adjusted. Switching hysteresis (dark - light) is provided by the timer itself, its. Remember these "magic" numbers 1 / 3U and 2 / 3U?

If the photosensor is in the dark, its resistance is high, so the voltage across the resistor R7 is low, which leads to the fact that the output of the timer (pin 3) is set to a high level and the optocoupler LED is off, and the transistor is closed. Consequently, the light will be turned on, as it was written earlier in the subheading "Load switching node".

In the case of lighting the photosensor, its resistance becomes small, on the order of several KOhms, so the voltage across the resistor R7 increases to 2 / 3U, and a low voltage level appears at the timer output, the optocoupler LED lights up, and the load lamp goes out.

Here someone may say: "It will be difficult!" But almost always, everything can be simplified to the limit. If it is supposed to light energy-saving lamps, then a soft start is not required, and a conventional relay can be used. And who said that only lamps and only turn on?

If the relay has several contacts, then you can do whatever your heart desires, and not only turn it on, but also turn it off. Such a scheme is shown in Figure 2 and does not need any special comments. The relay is selected so that the coil current is no more than 200mA at an operating voltage of 12V.

Figure 2.

Pre-installation diagrams

In some cases, it is required to turn on something with some delay in relation to the power on of the device. For example, first apply voltage to logic microcircuits, and after a while power supply of output stages.

These delays are easy to implement with the 555 timer. Schemes of such delays and timing diagrams of operation are shown in Figures 3 and 4. The dashed line shows the voltage of the power source, and the solid line at the output of the microcircuit.

Figure 3. After power-up, the delayed output is high.

Figure 4. After power-up, the output is delayed low.

Most often, these "installers" are used as part of more complex circuits.

Alarm devices on timer 555

The circuit of the signaling device is one with which we have already met for a long time.

Figure 5.

In a container with water, for example, a pool, two electrodes are immersed. While they are in the water, the resistance between them is small (water is a good conductor), so the capacitor C1 is shunted, the voltage across it is close to zero. Also, there is zero voltage at the timer input (pins 2 and 6), therefore, at the output (pin 3), a high level will be set, the generator does not work.

If the water level for some reason falls and the electrodes end up in the air, the resistance between them will increase, ideally just a break, and the capacitor C1 will not be shunted. Therefore, our multivibrator will work - pulses will appear at the output.

The frequency of these pulses depends on our imagination and on the parameters of the RC circuit: it will be either a blinking light or a nasty squeak of the speaker. Along the way, you can turn on the water topping up. To avoid overflow and turn off the pump in time, it is necessary to add another electrode and a similar circuit to the device. Here the reader can already experiment.

Figure 6.

When the limit switch S2 is pressed, a high level voltage appears at the timer output, and will remain so even if S2 is released and no longer held. The device can be removed from this state only by pressing the "Reset" button.

For now, let's dwell on this, maybe someone will need time to take a soldering iron and try to solder the devices under consideration, investigate how they work, at least experiment with the parameters of RC circuits. Listen to how the speaker beeps or the LED blinks, compare what the calculations give, whether the practical results differ much from the calculated ones.

Chip NE555 (analogue KR1006VI1) is a universal timer designed to generate single and repetitive pulses with stable time characteristics. It is not expensive and is widely used in various amateur radio schemes. It can be used to assemble various generators, modulators, converters, time relays, threshold devices and other components of electronic equipment ...

Dimensions for different types of enclosures

CASE - DIMENSIONS
PDIP (8) - 9.81mm × 6.35mm
SOP - (8) - 6.20mm × 5.30mm
TSSOP (8) - 3.00 mm × 4.40 mm
SOIC (8) - 4.90 mm × 3.91 mm

Block diagram of NE555

Electrical characteristics

(1) This parameter affects the maximum values \u200b\u200bof the timing resistors R A and R B in the circuit. 12. For example, when V CC \u003d 5 V R \u003d R A + R B ≉ 3.4 MΩ, and for V CC \u003d 15 V, the maximum value is 10 mΩ.

Performance characteristics

(1) Meets MIL-PRF-38535 and has not been factory tested.

(2) For conditions specified as Min. and Max. , use the appropriate value specified in the recommended operating conditions.

(3) The time interval error is defined as the difference between measured value and average random sample from each process.

(4) Values \u200b\u200bshown are for a monostable circuit with the following component values \u200b\u200bR A \u003d 2 kΩ to 100 kΩ, C \u003d 0.1 μF.

(5) Values \u200b\u200bshown are for an astable circuit with the following component values \u200b\u200bR A \u003d 1 kΩ to 100 kΩ, C \u003d 0.1 μF.

Metal detector on one chip

Coil diameter 70-90 mm, 250-290 turns of wire in varnish insulation (PEL, PEV ...), 0.2-0.4 mm in diameter.

Instead of a speaker, you can use headphones or a piezo emitter.

Video of this metal detector

Voltage converter from 12V to 24V

Animation of toys

Together with the counter 4017 and 555, you can make a "running fire" to animate some kind of toy or souvenir. At power up, the generator starts running for 555 only for a few minutes, then turns off. At the same time, the current consumption drops - the batteries will last for a long time. The time is set with a variable resistor of 500 kOhm.

Light driven generator

Dark detector with LM555. This scheme will generate sound when light hits the Cds photosensor. Sveta . The sensor, when exposed to light, closes the circuit and the 555 generates oscillations about 1 kHz through open transistor BC158.

Musical keyboard

A very simple musical instrument (keyboard) for playing music can be made using the 555 chip. You can assemble the unusual musical instrument in the photo above. Graphite is used as a keyboard and a sheet of paper with notes is represented as holes in paper.

The same circuit, but with conventional resistors and buttons.

Timer for 10 minutes

The timer is started with the S1 button after 10 minutes. LED1 and LED2 flash alternately. The time is set by a 550 kΩ resistor and a 150 μF capacitor.

Car alarm simulator

The LED flashes as if an alarm is installed in the car. Install the LED in a visible place. The thief will see that the car is under an alarm and will go around it

Simple Police Siren Simulator

The circuit is assembled on a breadboard.

Two NE555s can be used to make a simple police siren generator. It is recommended that you make the following parameters of the timer R1 \u003d 68 kOhm (timer no. 1) is set to slow generation mode and the timer with R4 \u003d 10 kOhm (timer no. 2) is set to fast generation mode. Myou can change the characteristics of the timer. The output frequency is changed by means of a chain of resistors R1, R2 and C1 for timer # 1 and R4, R5 and C3 for timer # 2.

A similar circuit below with a transistor at the output:

Liquid level sound generator

You can use this water level control circuit toalarm anywhere like level indicator water, for example in reservoirs, tanks, swimming pools or anywhere else.

These are not all the capabilities of the timer microcircuit. See also the video of the microcircuit.

Timer NE555 is perhaps the most popular integrated circuit of its time. Despite the fact that it was developed over 40 years ago (in 1972), it is still produced by many manufacturers today. In this article, we will try to cover in detail the description and application of the NE555 timer.

Clever comparator connections, a resettable flip-flop and an inverting amplifier in a single monolithic integrated circuit, along with several other elements, have spawned the nearly immortal circuitry of devices used by many radio amateurs today.

555 Timer was developed by the American company Signetics in 1972 and is registered on the world market. Two years later, the same company developed a microcircuit with the designation 556, which combined two separate NE555 timers with only common power pins. Even later, the 557, 558 and 559 chips were developed using up to four NE555 timers in one package. But later they were discontinued and almost forgotten.

The NE555 integrated circuit was designed as a timer and contains a combination of analog and digital elements in a single chip. It is available in various designs, ranging from the classic DIP package for standard and SOIC for SMD mounting and up to a miniature package version SSOP or SOT23-5. (Prices for timer NE555)

The NE555 timer, in addition to the standard version, is also produced in a low-power CMOS design. The NE555's power supply is 4.5 to 15 volts (18 volts maximum), and the CMOS version uses 3 volts. The maximum output load of the NE555 output is 200mA, the low-power version of the timer only has 20mA at 9 volts.

The stability of the standard 555 is highly dependent on the quality of the power supply. This does not affect so much in simple circuits using a timer, however, in more complex designs, it is advisable to install a buffer capacitor along the power circuit with a capacity of 100 microfarads.

Main characteristics of the integral timer NE555

• The maximum frequency is more than 500 kHz.
• The length of one pulse is from 1 msec to an hour.
• It can work as a monostable multi-vibrator.
• High output current (up to 200mA)
• Adjustable pulse duty cycle (the ratio of the pulse period to its duration).
• Compatible with TTL levels.
• Temperature stability 0.005% per degree Celsius.

The NE555 microcircuit contains just over 20 transistors and 10 resistors. The following figure shows a block diagram of a timer from Philips Semiconductors.

The following table lists the main properties of NE555

Purpose of terminals of timer NE555

# 2 - Start (trigger)

The flip-flop switches if the voltage at this pin drops below 1/3 of the supply voltage. This pin has a high input impedance, more than 2 mΩ. In the unstable mode, it is used to control the voltage across the timing capacitor; in the bistable mode, a switching element is connected to it, for example, a button.

# 4 - Reset

If the voltage at this pin is below 0.7 volts, then the internal comparator is reset. In case of non-use, supply voltage must be applied to this pin of the NE555 timer. The lead resistance is about 10 kΩ.

No. 5 - Control

It can be used to adjust the output pulse duration by applying a voltage 2/3 of the supply voltage. If this pin is not used, then it is advisable to connect it to the minus of the power supply through a 0.01 microfarad capacitor.

No. 6 - Stop (comparator)

Stops the timer if the voltage on this pin is higher than 2/3 of the supply voltage. The pin has a high input impedance, more than 10 mΩ. It is commonly used to measure the voltage across a timing capacitor.

No. 7 - Discharge

The pin through the internal transistor is connected to ground when the internal flip-flop is active. The lead (open collector) is mainly used to discharge the timing capacitor.

# 3 - Exit

The NE555 microcircuit has only one output with a current of up to 200 mA. This is significantly more than conventional integrated circuits. The output is capable of driving, for example, LEDs (with a current-limiting resistor), small light bulbs, a piezoelectric transformer, a speaker (with a capacitor), an electromagnetic relay (with a protective diode) or even low-power DC motors. If a higher output current is required, a suitable transistor can be connected as an amplifier.

Timer NE555 - wiring diagram

The ability of pin 3 of the NE555 timer to create both a high voltage level and a low (almost 0 volt) level allows you to control the load connected to both power supply minus and plus. As an example, connecting LEDs. This, of course, is not a requirement, and the load (LED) can be connected to either the negative or the positive of the power supply.

If the NE555 timer operates in an unstable state (generator mode), then a speaker can be connected to its output. It is connected after the blocking capacitor (for example, 100 μF) and must have a resistance of at least 64 Ohm due to the limited maximum load current of the timer output. The capacitor is designed to separate the DC component of the signal and only conducts the audio signal.

A speaker with a coil resistance lower than 64 ohms can be connected either through a capacitor with a lower capacitance (reactance), which is an additional resistance, or by using an amplifier. The amplifier can also be used to connect a more powerful speaker.

Like all integrated circuits, the NE555 timer output that controls an inductive load (relay) must be protected from overvoltage surges created at the time of shutdown. A diode (e.g. 1N4148) is always connected in parallel to the relay coil in the opposite direction.

However, the NE555 requires a second diode in series with the relay coil. It limits the low voltage that is at output 3 of the timer and prevents the relay from being energized by a small current.

Such a diode can be, for example, 1N4001 (1N4148 diode is not suitable) or an LED.

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It should be noted right away when describing the NE 555 microcircuit that it is produced in both standard TTL logic and CMOS, so it can operate in a wide voltage range and is used in many types of devices as a clock pulse generator or a universal timer. The microcircuit can generate both single and repetitive pulses, which depends on the switching circuit and the choice of a specific mode of operation.

The first version of the IP was developed back in 1971 by the then famous Signetics company. In terms of its characteristics and functionality, it is widely demanded, as evidenced by its active use in devices for controlling the speed of rotation of motors and thyristor power controllers.

It can also be used to construct a unified pulse generator with a variable pulse train output frequency. For a detailed description characteristics of the microcircuit look at the ne 555 datasheet. It lists not only the main characteristics, but also presents diagrams of work. And in this description ne 555 we will provide general information sufficient for the development of electronic devices with your own hands.

Background of IP creation

In the 70s. Signetics fell under the influence of the crisis and was forced to cut its staff by at least 50%, including the developer of the presented scheme. Therefore she was created literally on his knees in a garage, and the NE 566 developed by him was taken as a basis. The platform of the future IC already consisted of the main functional blocks necessary for the operation:

There are different types of switching circuits on the ne 555 for the operation of the microcircuit, it was enough to have an external RC circuit, which was the timing. And inner voltage divider, in proportion to which the amplitude of the output signal was formed. After some time and minor improvements, in particular, replacing the built-in stable current generator to charge the internal capacitor with a resistor, it entered the series.

As for the timer structure, it contained:

• 23 transistors;
• 16 resistors;
• 2 diodes.

Microcircuit analogs

The universal timer soon acquired functional analogues, which became Soviet microcircuits from the KR series:

• 1006VI1;
• 1008VI1;
• 1087VI2;
• 1087VI3.

Also, the ne555 microcircuit has an analogue, for example, KR10006VI1, then it is worth considering the fact that the reset input R has priority over the installation. This moment for some reason missed in the technical description of the MS, which is an important fact in the construction of electronic circuits. In other microcircuits, the pins have priority up to the opposite S over R.

All of the above presented analogs of timers are based on standard TTL logic. If you want to design ne555 devices with more economical performance, then it is better to use an MS from the CMOS series. These are the devices:

• ICM 7555 IPA;
• GLC 555;
• KR1441VI1.

Chip characteristics

The functional diagram of the presented microcircuit is quite simple and consists of the following blocks:

• a voltage divider that compares the input signal with two reference levels;
• 2 high-precision comparators for high and low signal levels;
• trigger with built-in RS-inputs and additional reset, medium-power output transistor bipolar or field, depending on the technology.

Also, in hardware, a power amplifier is provided in the design of the microcircuit, which increases the load capacity of the device and its quality of work.

The microcircuit is universal, no matter how you look, from all sides. For example, the basic version NE 555 is designed on supply voltage in the range from 4.5 to 16.5 V, which greatly simplifies the process of designing many circuits, since there is no need to adhere to a specific power supply.

But if it is necessary to power the pulse generator from a reduced level of the order of 2-3 V, then it is better to use circuits based on CMOS logic. They not only can to function freely at low voltage, but also have increased indicators of immunity to interference and power instability.

Also, modifications of devices with an increased threshold of the supply voltage, which can reach 18 V, are produced. These MCs can be used in pulse devices and generators.

According to the information provided by the western on the ne555 datasheet, the current consumed by the device depends on the magnitude of the input pulse. If it lies at a nominal level of about 5 V, then current magnitude is no more than 6 mA. But if the voltage rises to 15V, then the current also rises to 15mA. Usually, devices are developed with their own hands for an average current rate, which leaves about 10 mA, which indicates a supply voltage in the range from 9 to 12 V. But this is typical for TTL logic.

Microcircuits based on CMOS transistors consume even less - 100-200 μA, which makes them even more economical. But the maximum value of the consumed current does not exceed 100 mA. If it takes more than this value from you, it means that the device is defective and requires replacement.

Some problems and features of working with a microcircuit

An 8-pin package is a good idea, but this form factor makes it difficult to work with the timer. Namely, it is deprived of the ability to independently compare the signals of the upper and lower thresholds, which quite often required in conversion devices, for example, the same ADC. To realize this possibility, radio amateurs resort to using another series of devices, for example, NE 521, or install 3I-NOT elements at the input, if appropriate.

In bipolar devices, there is such a drawback as a pulse current when switching on and off, the value of which can reach 400 mA, which can cause a breakdown output transistor or other elements of the circuit into which it was soldered. The reason for this phenomenon is the through-current of the output stage, which arises from the same high power supply pulses.

To eliminate the problem, it is recommended to use a special blocking capacitor connected to inputs 5 and a common (power supply min) with a capacity of about 0.01–0.1 μF. Due to the charge of its plates, the internal voltage in the MC, input to the output stage, is smoothed, which excludes the possibility of breakdown. It also protects the internal divider from external interference that can cause false alarms.

Also, as is the case with many other TTL logic chips, it is recommended to bypass the NE 555 with a 1 μF quenching capacitor with ceramic plates.

Purpose and arrangement of microcircuit pins

The basic version of NE 555 has an 8-pin DIP package, but other modifications are also available that are analogous. Therefore, orient exclusively of this description when building devices with your own hands, it is not worth it. For each microcircuit, you need to view your datasheet.

The schematic designation of the device is displayed in the form of the inscription "G 1 / GN". In foreign reference books, this inscription can be deciphered as a generator of single and series of pulses. what regarding pinout and their purpose, then all the same type of MS are standardized and can be interchangeable without making any modifications.

The table below shows the pinouts in a standard MS package:

Operating modes and application of the microcircuit

The simplest circuit implementation used in various digital devices is a one-shot. On the example of this circuit, you can also see a typical connection using a quenching and shunt capacitors. It is in this design that this microcircuit is most often used. And it works as follows:

When a signal with a low level arrives at the MS input at number 2, the timer starts working in the time counting mode. In this case, a high level is set at the output of the device throughout the entire duration of the time interval... This time can be set independently by choosing the necessary external components, which are a resistor and a capacitor, connected to the plus of the power supply and pin number 6.

The time delay is determined using the standard formula, taking into account the correction constant: t \u003d 1.1 RC. At the end of the counting (capacitor discharge), the timer returns to its original state. And the output signal is reversed. So until the next arrival of the low-level input pulse.

Moreover, if there is a low level at the input, then the output is high. And when a pulse is applied to the reset input of the trigger, the timer stops counting and the signal level at the output changes to the opposite.

Independent generator mode

To turn on the microcircuit in multivibrator mode, there is a circuit shown in the figure below. Here everything is as simple as in the previous version, but there are some features of the calculation of the element and the characteristics of the output signal sequence. To set a specific frequency change the output signal and the subsequent switching to the opposite stable state, it will be necessary to combine pins 2 and 6 and set another resistor in the divide, reducing the capacitor charge current, but at the same time connecting the input signal with the trigger setting input. And to calculate the parameters used by the element, you will need to use the following simple calculation formulas:

Change in the duty cycle of the output pulse

Often it is required to use a 555 chip with the ability to set the duty cycle of the output signal. For example, to make it larger than 2, then this will require an additional chain between 7 and 6 pinsby connecting a diode to them. In this case, the anode terminal contacts with terminal 7 of the MC. Such inclusion of an additional component shunts the resistor R 2, providing the capacitor charging circuit through R 1. Then, when calculating the duration of the high signal level at the output, it will occur according to the formula without taking into account R 2.

In reverse loop discharge current will flow through R 2, and R 1 is no longer involved in the process. And it is determined by the formula that was indicated above without changes.