An LED is a diode that glows when current flows through it. In English, the LED is called light emitting diode, or LED.
The color of the LED glow depends on the additives added to the semiconductor. So, for example, impurities of aluminum, helium, indium, phosphorus cause a glow from red to yellow. Indium, gallium, nitrogen causes the LED to glow from blue to green. When a phosphor is added to a blue glow crystal, the LED will glow white. Currently, the industry produces glowing LEDs of all colors of the rainbow, but the color does not depend on the color of the LED case, but on the chemical additives in its crystal. LED of any color can have a transparent body.
The first LED was made in 1962 at the University of Illinois. In the early 1990s, bright LEDs appeared, and a little later super bright ones.
The advantage of LEDs over incandescent bulbs is undeniable, namely:
* Low power consumption - 10 times more efficient than light bulbs
* Long service life - up to 11 years of continuous operation
* High durability resource - not afraid of vibrations and shocks
* Large variety of colors
* Ability to work at low voltages
* Environmental and fire safety - the absence of toxic substances in the LEDs. LEDs do not heat up, which prevents fires.
LED marking
Rice. 1. The design of indicator 5 mm LEDs
An LED crystal is placed in the reflector. This reflector sets the initial scattering angle.
The light then passes through the epoxy resin housing. It reaches the lens - and then it begins to scatter on the sides at an angle depending on the design of the lens, in practice - from 5 to 160 degrees.
Emitting LEDs can be divided into two large groups: visible radiation LEDs and infrared (IR) LEDs. The former are used as indicators and backlight sources, the latter - in devices remote control, IR transceivers, sensors.
Light emitting diodes are marked with a color code (Table 1). First you need to determine the type of LED by the design of its housing (Fig. 1), and then clarify it by color marking according to the table.
Rice. 2. Types of LED housings
LED colors
LEDs come in almost all colors: red, orange, yellow, yellow, green, blue and white. Blue and white LED is a little more expensive than other colors.
The color of LEDs is determined by the type of semiconductor material they are made of, not by the color of the plastic in their housing. LEDs of any color come in a colorless case, in which case the color can only be recognized by turning it on ...
Table 1. LED marking
Multicolor LEDs
A multi-color LED is arranged simply, as a rule, it is red and green combined into one housing with three legs. By changing the brightness or the number of pulses on each of the crystals, you can achieve different colors of glow.
LEDs are connected to a current source, anode to plus, cathode to minus. The minus (cathode) of the LED is usually marked with a small case cut or a shorter lead, but there are exceptions, so it is better to clarify this fact in technical specifications specific LED.
In the absence of these marks, the polarity can also be determined empirically by briefly connecting the LED to the supply voltage through the appropriate resistor. However, this is not the best way to determine polarity. In addition, in order to avoid thermal breakdown of the LED or a sharp reduction in its service life, it is impossible to determine the polarity by the “poke method” without a current-limiting resistor. For quick testing, a resistor with a nominal resistance of 1kΩ is suitable for most LEDs if the voltage is 12V or less.
You should immediately warn: you should not direct the LED beam directly into your eye (as well as into the eye of a friend) at close range, which can damage your eyesight.
Supply voltage
The two main characteristics of LEDs are voltage drop and current. Usually LEDs are rated at 20mA, but there are exceptions, for example, four-chip LEDs are usually rated at 80mA, since one LED package contains four semiconductor crystals, each of which consumes 20mA. For each LED, there are permissible values of the supply voltage Umax and Umaxrev (respectively for direct and reverse switching). When voltages above these values are applied, an electrical breakdown occurs, as a result of which the LED fails. There is also a minimum value of the supply voltage Umin, at which the LED glows. The range of supply voltages between Umin and Umax is called the "working" zone, since this is where the operation of the LED is ensured.
Supply voltage - the parameter for the LED is not applicable. LEDs do not have this characteristic, so you cannot connect LEDs to a power source directly. The main thing is that the voltage from which (through a resistor) the LED is powered should be higher than the direct voltage drop of the LED (the direct voltage drop is indicated in the characteristic instead of the supply voltage and for conventional indicator LEDs it ranges from 1.8 to 3.6 volts on average).
The voltage indicated on the packaging of the LEDs is not the supply voltage. This is the voltage drop across the LED. This value is needed to calculate the remaining voltage that “did not drop” on the LED, which takes part in the formula for calculating the resistance of the current limiting resistor, since it is it that needs to be regulated.
Changing the supply voltage by just one tenth of a volt at a conditional LED (from 1.9 to 2 volts) will cause a fifty percent increase in the current flowing through the LED (from 20 to 30 milliamps).
For each instance of an LED of the same rating, the voltage suitable for it may be different. By turning on several LEDs of the same rating in parallel, and connecting them to a voltage of, for example, 2 volts, we run the risk of quickly burning some copies and underlighting others due to the spread of characteristics. Therefore, when connecting the LED, it is necessary to monitor not the voltage, but the current.
The amount of current for the LED is the main parameter, and as a rule, it is 10 or 20 milliamps. It doesn't matter what the tension is. The main thing is that the current flowing in the LED circuit matches the nominal current for the LED. And the current is regulated by a resistor connected in series, the value of which is calculated by the formula:
R
Upit is the power supply voltage in volts.
Down- direct voltage drop across the LED in volts (indicated in the specifications and is usually in the region of 2 volts). When several LEDs are switched on in series, the magnitudes of the voltage drops add up.
I- the maximum forward current of the LED in amperes (indicated in the characteristics and is usually either 10 or 20 milliamps, i.e. 0.01 or 0.02 amperes). When several LEDs are connected in series, the forward current does not increase.
0,75
is the reliability factor for the LED.
You should also not forget about the power of the resistor. You can calculate the power using the formula:
P is the power of the resistor in watts.
Upit- effective (effective, rms) voltage of the power source in volts.
Down- direct voltage drop across the LED in volts (indicated in the specifications and is usually in the region of 2 volts). When several LEDs are switched on in series, the magnitudes of the voltage drops add up. .
R is the resistance of the resistor in ohms.
Calculation of the current-limiting resistor and its power for one LED
Typical characteristics of LEDs
Typical parameters of the white indicator LED: current 20 mA, voltage 3.2 V. Thus, its power is 0.06 W.
Also referred to low-power LEDs are surface-mounted - SMD. They illuminate the buttons in your cell phone, the screen of your monitor, if it is LED-backlit, they are used to make decorative LED strips on a self-adhesive basis and much more. There are two most common types: SMD 3528 and SMD 5050. The former contain the same crystal as indicator LEDs with leads, that is, its power is 0.06 W. But the second one - three such crystals, so it can no longer be called an LED - this is an LED assembly. It is customary to call SMD 5050 LEDs, but this is not entirely correct. These are assemblies. Their total power, respectively, is 0.2 watts.
The operating voltage of an LED depends on the semiconductor material from which it is made, respectively, there is a relationship between the color of the LED and its operating voltage.
LED voltage drop table depending on color
By the magnitude of the voltage drop when testing the LEDs with a multimeter, you can determine the approximate color of the LED glow according to the table.
Serial and parallel switching of LEDs
When connecting LEDs in series, the resistance of the limiting resistor is calculated in the same way as with one LED, just the voltage drops of all LEDs are added together according to the formula:
When connecting LEDs in series, it is important to know that all LEDs used in a garland must be of the same brand. This statement should not be taken as a rule, but as a law.
To find out what is the maximum number of LEDs that can be used in a garland, you should use the formula
* Nmax - the maximum allowable number of LEDs in a garland
* Upit - The voltage of the power source, such as a battery or accumulator. In volts.
* Upr - Direct voltage of the LED taken from its passport characteristics (usually in the range from 2 to 4 volts). In volts.
* As the temperature changes and the LED ages, Upr may increase. Coeff. 1.5 gives a margin for such a case.
In this count, "N" can be a fraction, such as 5.8. Naturally, you will not be able to use 5.8 LEDs, therefore, the fractional part of the number should be discarded, leaving only an integer, that is, 5.
The limiting resistor for series connection of LEDs is calculated in the same way as for a single connection. But in the formulas, one more variable “N” is added - the number of LEDs in the garland. It is very important that the number of LEDs in a garland be less than or equal to “Nmax” - the maximum allowable number of LEDs. In general, the following condition must be fulfilled: N = 
All other calculations are carried out in the same way as calculating a resistor when the LED is turned on alone.
If the power supply voltage is not enough even for two series-connected LEDs, then each LED must have its own limiting resistor.
Paralleling LEDs with a common resistor is a bad idea. As a rule, LEDs have a spread of parameters, require slightly different voltages each, which makes such a connection practically inoperative. One of the diodes will glow brighter and take on more current until it fails. Such a connection greatly accelerates the natural degradation of the LED crystal. If LEDs are connected in parallel, each LED must have its own limiting resistor.
Serial connection of LEDs is also preferable from the point of view of economical consumption of the power source: the entire series circuit consumes exactly as much current as one LED. And when they are connected in parallel, the current is as many times greater than how many parallel LEDs we have.
Calculating the limiting resistor for series-connected LEDs is as simple as for a single one. We simply sum up the voltage of all the LEDs, subtract the resulting sum from the power supply voltage (this will be the voltage drop across the resistor) and divide by the current of the LEDs (usually 15 - 20 mA).
And if we have a lot of LEDs, several dozen, and the power source does not allow us to connect them all in series (not enough voltage)? Then we determine, based on the voltage of the power source, how many LEDs we can connect in series. For example, for 12 volts, these are 5 two-volt LEDs. Why not 6? But after all, something must also fall on the limiting resistor. Here are the remaining 2 volts (12 - 5x2) and take it for calculation. For a current of 15 mA, the resistance will be 2/0.015 = 133 ohms. The closest standard is 150 ohms. But such chains of five LEDs and a resistor each, we can already connect as many as we like. This method is called a parallel-serial connection.
If there are LEDs of different brands, then we combine them in such a way that each branch has LEDs of only ONE type (or with the same operating current). In this case, it is not necessary to observe the same voltage, because we calculate our own resistance for each branch.
Next, consider a stabilized LED switching circuit. Let's touch on the manufacture of a current stabilizer. There is a KR142EN12 chip (foreign analogue of LM317), which allows you to build a very simple current stabilizer. To connect the LED (see figure), the resistance value is calculated R = 1.2 / I (1.2 - voltage drop not stabilizer) That is, at a current of 20 mA, R = 1.2 / 0.02 = 60 Ohm. Stabilizers are designed for a maximum voltage of 35 volts. It is better not to strain them like that and apply a maximum of 20 volts. With this inclusion, for example, a white LED of 3.3 volts, it is possible to supply voltage to the stabilizer from 4.5 to 20 volts, while the current on the LED will correspond to a constant value of 20 mA. At a voltage of 20V, we find that 5 white LEDs can be connected in series to such a stabilizer, without worrying about the voltage on each of them, the current in the circuit will flow 20mA (the excess voltage will be extinguished on the stabilizer).
Important! In a device with a large number of LEDs, a large current flows. It is strictly forbidden to connect such a device to the switched on power supply. In this case, a spark occurs at the connection point, which leads to the appearance of a large current pulse in the circuit. This pulse disables the LEDs (especially the blue and white ones). If the LEDs operate in a dynamic mode (constantly on, off and blinking) and this mode is based on the use of a relay, then sparks on the relay contacts should be excluded.
Each chain should be assembled from LEDs of the same parameters and from the same manufacturer.
Also important! Temperature change environment affects the current flowing through the crystal. Therefore, it is desirable to manufacture the device so that the current flowing through the LED is not 20 mA, but 17-18 mA. The loss of brightness will be insignificant, but a long service life is guaranteed.
How to power an LED from a 220 V network.
It would seem that everything is simple: we put a resistor in series, and that's it. But you need to remember one important characteristic of the LED: the maximum allowable reverse voltage. Most LEDs have about 20 volts. And when you connect it to the network with reverse polarity (the current is alternating, half a period goes in one direction, and the other half goes in the opposite direction), the full amplitude voltage of the network will be applied to it - 315 volts! Where does such a figure come from? 220 V is the effective voltage, while the amplitude is in (root of 2) \u003d 1.41 times more.
Therefore, in order to save the LED, you need to put a diode in series with it, which will not let the reverse voltage pass to it.
Another option for connecting the LED to the mains 220v:
Or put two LEDs back-to-back.
The mains supply option with a quenching resistor is not the most optimal: significant power will be released on the resistor. Indeed, if we apply a 24 kΩ resistor (maximum current 13 mA), then the power dissipated on it will be about 3 watts. You can reduce it by half by turning on the diode in series (then heat will be released only during one half-cycle). The diode must be for a reverse voltage of at least 400 V. When you turn on two counter LEDs (there are even those with two crystals in one case, usually of different colors, one crystal is red, the other is green), you can put two two-watt resistors, each with a resistance twice less.
I will make a reservation that by using a high resistance resistor (for example, 200 kOhm), you can turn on the LED without a protective diode. The reverse breakdown current will be too low to cause crystal destruction. Of course, the brightness is very small, but for example, to illuminate the switch in the bedroom in the dark, it will be quite enough.
Due to the fact that the current in the network is alternating, it is possible to avoid unnecessary waste of electricity for heating the air with a limiting resistor. Its role can be played by a capacitor that passes alternating current without heating up. Why this is so is a separate question, we will consider it later. Now we need to know that in order for the capacitor to pass alternating current, both half-cycles of the network must necessarily pass through it. But an LED only conducts current in one direction. So, we put an ordinary diode (or a second LED) in opposite parallel to the LED, and it will skip the second half-cycle.
But now we have disconnected our circuit from the network. Some voltage remained on the capacitor (up to the full amplitude, if we remember, equal to 315 V). To avoid accidental electric shock, we will provide a high-value discharge resistor in parallel with the capacitor (so that during normal operation a small current flows through it, which does not cause it to heat up), which, when disconnected from the network, will discharge the capacitor in a fraction of a second. And to protect against pulsed charging current, we also put a low-resistance resistor. It will also play the role of a fuse, instantly burning out if the capacitor accidentally breaks down (nothing lasts forever, and this also happens).
The capacitor must be at least 400 volts, or special for alternating current circuits with a voltage of at least 250 volts.
And if we want to make an LED light bulb from several LEDs? We turn them all on in series, the oncoming diode is enough for one at all.
The diode must be designed for a current not less than the current through the LEDs, reverse voltage - not less than the sum of the voltage on the LEDs. Better yet, take even number LEDs and turn them on in parallel.
In the figure, three LEDs are drawn in each chain, in fact there may be more than a dozen of them.
How to calculate a capacitor? From the amplitude voltage of the 315V network, we subtract the sum of the voltage drop across the LEDs (for example, for three white ones, this is about 12 volts). We get the voltage drop across the capacitor Up \u003d 303 V. The capacitance in microfarads will be equal to (4.45 * I) / Up, where I is the required current through the LEDs in milliamps. In our case, for 20 mA, the capacitance will be (4.45 * 20) / 303 = 89/303 ~= 0.3 uF. You can put two 0.15uF (150nF) capacitors in parallel.
The most common mistakes when connecting LEDs
1. Connecting the LED directly to a power source without a current limiter (resistor or special driver chip). Discussed above. The LED quickly fails due to a poorly controlled amount of current.
2. Connecting LEDs connected in parallel to a common resistor. Firstly, due to the possible scatter of parameters, the LEDs will light up with different brightness. Secondly, and more significantly, if one of the LEDs fails, the current of the second will double, and it may also burn out. In the case of using a single resistor, it is more expedient to connect the LEDs in series. Then, when calculating the resistor, we leave the current the same (for example, 10 mA), and add the forward voltage drop of the LEDs (for example, 1.8 V + 2.1 V = 3.9 V).
3. Turning on LEDs in series, designed for different currents. In this case, one of the LEDs will either wear out or glow dimly - depending on the current setting of the limiting resistor.
4. Installation of a resistor of insufficient resistance. As a result, the current flowing through the LED is too large. Since part of the energy is converted into heat due to defects in the crystal lattice, it becomes too much at high currents. The crystal overheats, as a result of which its service life is significantly reduced. With an even greater overestimation of the current, due to the heating of the p-n junction region, the internal quantum yield decreases, the brightness of the LED drops (this is especially noticeable for red LEDs), and the crystal begins to disintegrate catastrophically.
5. Connecting the LED to AC mains (eg 220V) without taking measures to limit reverse voltage. Most LEDs have a reverse voltage limit of about 2 volts, while the reverse half-cycle voltage when the LED is off creates a voltage drop across it equal to the supply voltage. There are many different schemes that exclude the destructive effect of reverse voltage. The simplest one is discussed above.
6. Installation of a resistor of insufficient power. As a result, the resistor gets very hot and begins to melt the insulation of the wires touching it. Then the paint burns on it, and in the end it collapses under the influence of high temperature. The resistor can painlessly dissipate no more than the power for which it is designed.
Flashing LEDs
The flashing LED (MSD) is a LED with a built-in integrated pulse generator with a flash frequency of 1.5-3 Hz.
Despite the compactness, the blinking LED includes a semiconductor chip generator and some additional elements. It is also worth noting that the flashing LED is quite versatile - the supply voltage of such an LED can range from 3 to 14 volts for high-voltage, and from 1.8 to 5 volts for low-voltage specimens.
Distinctive qualities of flashing set-diode:
- Small size
Compact light signaling device
Wide supply voltage range (up to 14 volts)
Different color of radiation.
In some variants of flashing LEDs, several (usually 3) multi-colored LEDs with different flash intervals can be built in.
The use of flashing LEDs is justified in compact devices, where there are high requirements for the dimensions of radio elements and power supply - flashing LEDs are very economical, because the MSD electronic circuit is made on MOS structures. A flashing LED can easily replace an entire functional unit.
The symbolic graphic designation of a blinking LED on schematic diagrams is no different from the designation of a conventional LED, except that the arrow lines are dotted and symbolize the blinking properties of the LED.
If you look through the transparent housing of the flashing LED, you will notice that it is structurally composed of two parts. On the basis of the cathode (negative terminal), a light-emitting diode crystal is placed.
The oscillator chip is located on the base of the anode terminal.
By means of three gold wire jumpers all parts of this combined device are connected.
It is easy to distinguish an MSD from a conventional LED by its appearance, looking at its case through the light. Inside the MSD are two substrates of approximately the same size. On the first of them is a crystalline light emitter cube made of a rare earth alloy.
A parabolic aluminum reflector (2) is used to increase the light flux, focus and shape the radiation pattern. In the MSD, it is slightly smaller in diameter than in a conventional LED, since the second part of the package is occupied by a substrate with an integrated circuit (3).
Both substrates are electrically connected to each other by two gold wire jumpers (4). The MSD body (5) is made of matte light-scattering plastic or transparent plastic.
The emitter in the MSD is not located on the axis of symmetry of the body, therefore, to ensure uniform illumination, a monolithic colored diffuse light guide is most often used. The transparent case is found only in MSDs of large diameters with a narrow radiation pattern.
The oscillator chip consists of a high-frequency master oscillator - it works constantly - its frequency, according to various estimates, fluctuates around 100 kHz. Together with the RF generator, a divider on logic elements works, which divides the high frequency to a value of 1.5-3 Hz. The use of a high-frequency generator in conjunction with a frequency divider is due to the fact that the implementation of a low-frequency generator requires the use of a capacitor with a large capacitance for the timing circuit.
To bring the high frequency to a value of 1-3 Hz, dividers on logical elements are used, which are easy to place on a small area of \u200b\u200bthe semiconductor crystal.
In addition to the master RF oscillator and the divider, an electronic key and a protective diode are made on the semiconductor substrate. For flashing LEDs, designed for a supply voltage of 3-12 volts, a limiting resistor is also built in. Low-voltage MSDs do not have a limiting resistor. A protective diode is required to prevent damage to the microcircuit when the power is reversed.
For reliable and long-term operation of high-voltage MSDs, it is desirable to limit the supply voltage to 9 volts. With an increase in voltage, the dissipated power of the MSD increases, and, consequently, the heating of the semiconductor crystal. Over time, excessive heat can cause the flashing LED to rapidly degrade.
You can safely check the serviceability of a flashing LED using a 4.5 volt battery and a 51 ohm resistor connected in series with the LED, with a power of at least 0.25 watts.
The health of the IR diode can be checked using a cell phone camera.
We turn on the camera in shooting mode, catch the diode on the device (for example, the remote control), press the buttons on the remote control, the working IR diode should flash in this case.
In conclusion, you should pay attention to issues such as soldering and mounting LEDs. These are also very important issues that affect their viability.
LEDs and microcircuits are afraid of static, improper connection and overheating, the soldering of these parts should be as fast as possible. You should use a low-power soldering iron with a tip temperature of no more than 260 degrees and soldering for no more than 3-5 seconds (manufacturer's recommendations). It will not be superfluous to use medical tweezers when soldering. The LED is taken with tweezers higher to the body, which provides additional heat removal from the crystal during soldering.
The legs of the LED should be bent with a small radius (so that they do not break). As a result of the intricate curves, the legs at the base of the case should remain in the factory position and should be parallel and not tense (otherwise it will get tired and the crystal will fall off the legs).
Today, there are hundreds of varieties of LEDs, differing appearance, glow color and electrical parameters. But all of them are united by a common principle of operation, which means that the circuits for connecting to an electrical circuit are also based on general principles. It is enough to understand how to connect one indicator LED, in order to then learn how to draw up and calculate any circuits.
LED pinout
Before proceeding to consider the issue of the correct connection of the LED, you need to learn how to determine its polarity. Most often, indicator LEDs have two outputs: an anode and a cathode. Much less often in a case with a diameter of 5 mm there are instances that have 3 or 4 leads for connection. But it’s also easy to figure out their pinout.
SMD LEDs can have 4 outputs (2 anodes and 2 cathodes), which is due to the technology of their production. The third and fourth conclusions can be electrically unused, but used as an additional heat sink. 
The pinout shown is not a standard. To calculate the polarity, it is better to first look at the datasheet, and then confirm what you see with a multimeter. You can visually determine the polarity of a SMD LED with two leads by a cut. The cut (key) in one of the corners of the housing is always located closer to the cathode (minus). 
The simplest LED wiring diagram
There is nothing easier than connecting an LED to a low-voltage constant voltage source. It can be a battery, a rechargeable battery or a low-power power supply. It is better if the voltage is at least 5 V and not more than 24 V. Such a connection will be safe, and for its implementation you will need only 1 additional element - a low-power resistor. Its task is to limit the current flowing through the p-n junction at a level no higher than the nominal value. To do this, the resistor is always installed in series with the emitting diode. 
Always respect polarity when connecting an LED to a constant voltage (current) source.
If the resistor is excluded from the circuit, then the current in the circuit will be limited only by the internal resistance of the EMF source, which is very small. The result of such a connection will be an instant failure of the radiating crystal.
Limiting Resistor Calculation
Looking at the current-voltage characteristic of the LED, it becomes clear how important it is not to make a mistake when calculating the limiting resistor. 
Even a small increase in the rated current will lead to overheating of the crystal and, as a result, to a decrease in the working life. The choice of a resistor is made according to two parameters: resistance and power. Resistance is calculated by the formula: 
- U – supply voltage, V;
- U LED - direct voltage drop across the LED (passport value), V;
- I - rated current (passport value), A.
The result obtained should be rounded up to the nearest value from the E24 series up, and then calculate the power that the resistor will have to dissipate:
R is the resistance of the resistor accepted for installation, Ohm.
More detailed information about calculations with practical examples can be found in the article. And those who do not want to dive into the nuances can quickly calculate the parameters of the resistor using an online calculator.
Turning on the LEDs from the power supply
We are talking about power supplies (PSUs) operating on 220 V AC. But even they can differ greatly from each other in output parameters. It can be:
- alternating voltage sources, inside which there is only a step-down transformer;
- unstabilized direct voltage sources (PSV);
- stabilized PPIs;
- stabilized constant current sources (LED drivers).
You can connect an LED to any of them by supplementing the circuit with the necessary radio elements. Most often, stabilized 5 V or 12 V PSIs are used as a power supply. This type of PSU implies that with possible fluctuations in the mains voltage, as well as with changes in the load current in a given range, the output voltage will not change. This advantage allows you to connect LEDs to the PSU using only resistors. And it is precisely this connection principle that is implemented in circuits with indicator LEDs. 
Powerful LEDs must be connected through a current stabilizer (driver). Despite their higher cost, this is the only way to guarantee stable brightness and long-term operation, as well as to avoid premature replacement of an expensive light emitting element. 
Such a connection does not require an additional resistor, and the LED is connected directly to the output of the driver, subject to the condition: 
- I driver - driver current according to the passport, A;
- I LED - rated current of the LED, A.
If the condition is not met, the connected LED will burn out due to overcurrent.
Serial connection
It is not difficult to assemble a working circuit on a single LED. Another thing is when there are several of them. How to connect 2, 3 ... N LEDs correctly? To do this, you need to learn how to calculate more complex switching schemes. A daisy chain circuit is a circuit of several LEDs, in which the cathode of the first LED is connected to the anode of the second, the cathode of the second to the anode of the third, and so on. A current of the same magnitude flows through all elements of the circuit:
And the voltage drops are summarized:
Based on this, we can draw the following conclusions:
- it is advisable to combine in a series circuit only LEDs with the same operating current;
- if one LED fails, the circuit will open;
- The number of LEDs is limited by the PSU voltage.
Parallel connection
If it is necessary to light several LEDs from a power supply unit with a voltage of, for example, 5 V, then they will have to be connected in parallel. In this case, in series with each LED, you need to put a resistor. 
Formulas for calculating currents and voltages will take the following form: 
Thus, the sum of currents in each branch should not exceed the maximum allowable current of the PSU. When connecting the same type of LEDs in parallel, it is enough to calculate the parameters of one resistor, and the rest will be of the same value.
All the rules for serial and parallel connection, illustrative examples, as well as information on how not to turn on LEDs can be found in.
mixed inclusion
Having dealt with the schemes of serial and parallel connection, it's time to combine. One of the options for the combined connection of LEDs is shown in the figure. 
By the way, this is how each LED strip is arranged.
Inclusion in the alternating current network
Connecting LEDs from a PSU is not always advisable. Especially when it comes to the need to make a switch backlight or an indicator of the presence of voltage in the power strip. For such purposes, it will be enough to assemble one of the simple ones. For example, a circuit with a current-limiting resistor and a rectifier diode that protects the LED from reverse voltage. 
The resistance and power of the resistor are calculated using a simplified formula, neglecting the voltage drop across the LED and diode, since it is 2 orders of magnitude less than the mains voltage: 
Due to the high power dissipation (2-5 W), the resistor is often replaced with a non-polar capacitor. Working on alternating current, it kind of "extinguishes" the excess voltage and almost does not heat up.
Connecting flashing and multi-color LEDs
Externally, flashing LEDs are no different from conventional counterparts and can flash in one, two or three colors according to the algorithm specified by the manufacturer. The internal difference consists in the presence of another substrate under the case, on which the integrated pulse generator is located. The rated operating current, as a rule, does not exceed 20 mA, and the voltage drop can vary from 3 to 14 V. Therefore, before connecting a flashing LED, you need to familiarize yourself with its characteristics. If they are not there, then you can find out the parameters experimentally by connecting to an adjustable 5-15 V power supply through a 51-100 Ohm resistor.
In the case of the multicolor there are 3 independent crystals of green, red and blue. Therefore, when calculating the resistor values, it must be remembered that each color of the glow corresponds to its own voltage drop.
Once again about three important points
- Direct rated current is the main parameter of any LED. Underestimating it, we lose in brightness, and overestimating it, we sharply reduce the service life. Therefore, the best power source is an LED driver, when connected to which a constant current of the desired amount will always flow through the LED.
- The voltage given in the datasheet to the LED is not decisive and only indicates how many volts will drop at the p-n junction when the rated current flows. Its value must be known in order to correctly calculate the resistance of the resistor if the LED is powered by a conventional PSU.
- To connect high-power LEDs, it is important not only to have a reliable power supply, but also quality system cooling. Installing LEDs with a power consumption of more than 0.5 W on a radiator will guarantee their stable and long-term operation.
Read also
In the era of Zeus and Hercules, every earthly day began with the fact that the goddess of the morning dawn, Eos, went to heaven. She was carried by two immortal horses - Phaeton and ... Lamp. Note that there was definitely no horse named LED on Olympus. However, mankind has decided to abandon incandescent lamps and gas-discharge analogues in favor of more economical and durable semiconductor light sources. Today they are installed in the head lighting equipment of even relatively inexpensive cars.
Down with the halogens!
Automotive LEDs at the beginning of their career spoiled their own reputation: the secondary market was inundated with outright "leftist". As a rule, the light source for the head optics was a dozen dead LEDs that shone in different directions - it was not worth even dreaming about the correct light distribution. However, Philips LED headlight soon appeared, in which narrow strips of LEDs exactly corresponded to the location of the filament in a conventional light bulb. And soon many Chinese manufactories began to produce similar designs.
In fact, you cannot install LEDs in headlights homologated for halogens, and we have talked about this more than once. But Eastern manufacturers stubbornly write H4 or H7 on the packaging of their products! Illegal? Undoubtedly. However, let's leave the legal side of the issue for now. Our the main task- test the LEDs for professional suitability. To this end, we purchased five kits for installation in headlights designed to work with H4 lamps. Please note that all purchased LEDs are capable of operating at both 12 V and 24 V. This indicates that they use high-quality power stabilization units - the so-called drivers.
The difference between a lamp trying to be correct (top photo) and a completely unusable one: the correct lamp has separate lines of LEDs for high and low beams. These rulers are similar in size and arrangement to the incandescent spiral in a conventional lamp. The correct lamp has a screen that covers the lower hemisphere of the low beam luminous element. In addition, the right lamp is equipped with a driver that allows you to work at a voltage of 12-24 V, as well as a cooling radiator.The difference between a lamp trying to be correct (top photo) and a completely unusable one: the correct lamp has separate lines of LEDs for high and low beams. These rulers are similar in size and arrangement to the incandescent spiral in a conventional lamp. The correct lamp has a screen that covers the lower hemisphere of the low beam luminous element. In addition, the right lamp is equipped with a driver that allows you to work at a voltage of 12-24 V, as well as a cooling radiator.
The regloscope is listening
Let's start with a simple check - perhaps everything will end there. We go to the service station to the old friend of the magazine Anatoly Vaysman to test the LEDs directly on the car. We took the popular Kia Rio as a carrier. This car was also chosen because. By the way, many people put LEDs instead of halogens solely in order to change lamps less often, because on some machines this operation is time-consuming (for example, you have to remove the bumper) and, accordingly, expensive.
The car service master drives the car to the site and installs a regloscope in front of the headlight - such a device is used to check lighting equipment during a mandatory technical inspection. We start with a standard halogen lamp. Everything is okay! Now let's see what light distribution will give luminous semiconductors.Three out of five products failed: instead of the exemplary “tick”, something that looked like a UFO from a television horror story appeared on the screen. But two subjects - Philips LED headlight and G7 Head light conversion kit - gave an acceptable picture. And if, during the inspection, the inspecting inspector does not carefully look through the transparent cap of the headlight, which lamp is installed in it, then, in theory, he should not have any complaints. In addition, in headlights with a diffuser or lensed optics, it will not be possible to see the light bulb from the outside! In general, the probability of slipping through the inspection is very high.
It turns out that some LEDs can still (at least from a technical point of view) be installed in headlights? In order to get an accurate confirmation, we turned to the "highest court" - the test center of NTC AE LLC, where we conducted control tests of LED sources for compliance with the requirements of UNECE Regulation No. 112-00 regarding low beam.
| approximate price 2000 rub. Current consumption - 1.37 A (regular "halogen" eats about 4.16 A). The regloscope immediately caught a flare on the left in the headlight. Laboratory measurements confirmed: at the B50L point, the luminous intensity is 2.0 cd instead of the allowable 0.6 cd. In zone III - a sevenfold excess of light intensity. The only advantage is that Kia managed to close the cover on the headlight. | approximate price 4650 rub. Current consumption - 1.57 A. Kia headlight cover closed. The lamp makes it possible to adjust the angular position relative to the holder. Checking in garage conditions gave the green light to the product: I liked the light distribution. However, more careful measurements in the test center still revealed deviations from the norm: at point B50L it turned out to be 0.8 cd instead of 0.6 cd, in zone III - 1.6 cd instead of 1.0 cd. It's a pity, but it doesn't meet the standards. |
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| approximate price 10 000 rub. The current consumption is 1.65 A. The description honestly says that free space is required: 70 mm behind the headlight and 60 mm in diameter. The lamp allows you to adjust the angular position relative to the holder. The lid on the Kia did not close due to the huge driver block. The light distribution according to the regloscope brought the product to the forefront. However, all at the same points, the experts identified deviations from the tolerance: 2.0 cd instead of 0.6 cd at point B50L and 2.82 cd instead of 1.0 cd in zone III. In general, these lamps shine better than others that have been tested, but you cannot travel with them on public roads. | approximate price 2300 rub. Current consumption - 1.35 A. Kia headlight cover closed. But the parameters - nowhere worse. Deviations were noted at points B50L, 75R and in zone III (as much as 13.2 times!). Verdict: Deny! | approximate price 4500 rub. The current consumption is 1.48 A. The Kia headlight cover was closed. The mount wobbles a lot. The light distribution does not correspond to the norm at point B50L and zone III, many times exceeding the permissible limit. Is it possible to expect otherwise from a lamp whose LEDs are in the form of fat circles that do not resemble spirals in any way? Verdict: don't buy. |
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Refuse!
Semiconductors…failed. The whole crowd. All the LEDs, alternately placed by the test laboratory employees in the headlight of the GAZelle, blinded the oncoming driver, and the cheapest ones, in addition, refused to properly illuminate the right side of the road. Better than others, of course, looked like those that showed a normal picture on the regloscope - Philips LED headlight and G7 Head light conversion kit. By the way, their light intensity is amazing: for example, Philips at the 50R point gave out 100 cd (candela - a unit of light intensity), exceeding the standard tenfold. But they also turned out to be outside the law, the results are in the table.In addition, some light sources do not sit tightly in the workplace and rotate slightly around their longitudinal axis. It is clear that when moving, the picture of the light distribution will go astray. And the operating temperature of the various cooling radiators is such that we were even afraid for the safety of the plastic casing of the headlight.
We also note that in most cases, the rear cover of the Rio headlight can be closed when installing LED bulbs - only a huge Philips lamp block simply did not fit under the cover. The headlight of the GAZelle, on which bench tests were carried out, turned out to be less hospitable. How do you ride without a cover? The headlight will quickly turn into a trash can.
LIGHT DISTRIBUTION ON THE REGLOSCOPE SCREEN |
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As for the statements of the manufacturers of LED light sources about their full compliance with the original, as well as the H4 inscriptions on the boxes, this is an outright deception. Only the letter L should be used to designate LEDs, and only the car manufacturer or can approve their installation instead of halogen lamps.
By the way, Philips representatives officially answered our request that you should not drive on public roads with such light. These lamps are designed primarily for ATVs, snowmobiles and other off-road vehicles. However, sellers of oriental lamps, all these subtleties, sorry for the pun, don't care. Is it shining? Is the connector suitable? Use on health!
In general, it was no coincidence that there was no LED horse in the Olympic stable. The gods preferred to use the services of the faithful Lamp ... Which is what we advise you!
TEST RESULTS OF LIGHTS WITH LED LIGHT SOURCES
| Checkpoints | Normalized value of light intensity, cd | The actual value of the light intensity, cd |
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| clear light | V16 Turbo |
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| B50L | ≤ 0,4 (0,6)* | 2,0 | 0,8 | 2,0 | 0,6 | 4,0 |
| ≥ 12 (9,6) | 34,6 | 27,0 | 50,0 | 4,4 | 33,4 |
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| ≥ 12 (9,6) | 55,0 | 36,0 | 100,0 | 12,4 | 47,6 |
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| ≥ 6, 0 (4,8) | 42,22 | 24,0 | 66,0 | 45,6 |
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| Zone III** | ≤ 0,7 (1,0) | 7,0 | ||||
An LED is a conventional diode in which substances are added to the crystal that emit light when an electric current passes through them. When a positive voltage is applied to the anode and a negative voltage to the cathode, a glow occurs. The most common cause of failure is exceeding the supply voltage rating.
On the schematic diagrams, the pinout is clear. We always apply a “minus” to the cathode, which is why it is indicated by a straight line at the top of the triangle. Usually the cathode is the contact on which the light emitting crystal is located. It is wider than the anode.
In ultra-bright LEDs, polarity is usually marked on the contacts or on the housing. If there are no markings on the legs, the leg with a wider base is the cathode.
LED wiring diagram
In the classical circuit, it is recommended to connect through a current-limiting resistor. Indeed, by choosing the right resistor or inductive resistance, you can connect a diode designed for a supply voltage of 3V, even to an alternating current network.
The main requirement for power parameters is the current limitation of the circuit.
Since the current strength is a parameter that reflects the density of the electron flux through the conductor, if this parameter is exceeded, the diode will simply explode due to the instantaneous and significant heat release on the semiconductor crystal.
How to Calculate Limiting Resistor
- R is the resistance of the limiting resistor in ohms;
- Upit - voltage of the power supply in volts;
- Upad - LED supply voltage;
- I is the rated current of the LED in amperes.
If the power of the resistor is significantly less than required, it will simply burn out due to overheating.
Turning on the LED through the power supply without a resistor
I have had a table lamp upgraded to LED for several years now. Six bright LEDs are used as a light source, and an old charger from mobile phone Nokia. Here is my LED wiring diagram:
The nominal voltage of the diodes is 3.5V, the current is 140mA, the power is 1W.
If an external power supply is selected, current limiting is required. Connecting these LEDs to modern chargers with a supply voltage of 5V 1-2A will require a limiting resistor.
To adapt this circuit to a 5V charger, use a 10-20 ohm 0.3A resistor.
If you have a different power supply, make sure it has a current stabilization circuit.
Scheme charger from mobile phone | Power supply for most low-voltage household appliances |
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How to connect LEDs correctly
Parallel connection
The easiest way to determine diode compatibility is with a low-voltage or regulated power supply. You can navigate by the "ignition voltage", when the crystal begins to glow only slightly. With a “starting” voltage spread of 0.3-0.5 V, a parallel connection without a current-limiting resistor is unacceptable.
Serial connection
Calculation of resistance for a circuit of several diodes: R = (Upit - N * Usd) / I * 0.75
Maximum number of serial diodes: N \u003d (Upit * 0.75) / Usd
When you turn on several LED strings in series, it is advisable to calculate a different resistor for each circuit.
How to turn on the LED in AC power
If, when an LED is connected to a DC source, the electrons move only in one direction, and it is enough to limit the current with a resistor, in an AC voltage network, the direction of movement of the electrons constantly changes.
With the passage of a positive half-wave, the current, passing through the resistor, extinguishing excess power, will ignite the light source. The negative half-wave will go through the closed diode. For LEDs, the reverse voltage is small, about 20V, and the amplitude voltage of the network is about 320V.
For some time, the semiconductor will operate in this mode, but at any time a reverse breakdown of the crystal is possible. To avoid this, an ordinary rectifier diode is installed in front of the light source, which can withstand reverse current up to 1000 V. It will not pass the reverse half-wave into the electrical circuit.
AC connection diagram in the figure on the right.
Other types of LED
Flashing
A design feature of a flashing LED is that each contact is both a cathode and an anode. Inside it are two light-emitting crystals with different polarities. If such a light source is connected through a step-down transformer to an alternating current network, it will flash at a frequency of 25 times per second.
For a different flashing frequency, special drivers are used. Now such diodes are no longer used.
colorful
Multi-colored LED - two or more diodes combined into one package. Such models have one common anode and several cathodes.
By changing the brightness of each matrix through a special power driver, you can achieve any glow light.
When using such elements in home-made circuits, do not forget that multi-colored crystals have different supply voltages. This point must also be taken into account when connecting a large number of multi-colored LED sources.
Another option is a diode with a built-in driver. Such models can be two-color with alternate inclusion of each color. The flashing frequency is set by the built-in driver.
A more advanced option is an RGB diode that changes color according to a program pre-installed in the chip. Here, the glow options are limited only by the imagination of the manufacturer.
The use of LED strip as a means of lighting has a number of advantages. First of all, this is saving electricity, ease of installation, the absence of high voltages and other advantages. This one appeared relatively recently and has already been widely used for various purposes.
The LED strip is a flexible plastic strip on which LEDs are soldered and connected to an electrical circuit. Thus, they are already ready for operation and for this you only need to connect the power supply to it.
The main application of the device is the decoration of any place with light or spot lighting. Due to its brightness and multi-coloredness, it is used in car tuning, in the interiors of restaurants and cafes, in individual home design.
However, with all the ease of operation and installation, there are features when using this type of lighting. Before you install the LED strip, you need to choose it correctly and decide on the power of the power supply. You also need to know how to properly cut the desired length and connect the power wires. The lines of this article will tell about all this.
Choosing an LED strip by glow
Before you make an LED strip, you need to decide what color glow you need. There is just white light and multi-colored. Ribbon with different colors labeled as RGB (R - red, G - green, B - blue). In the case of the usual one-color version, there are only two contacts, and in the color version there are four. It is worth noting that a multi-colored ribbon can have different glow modes, and a single-colored ribbon can have only one.
The choice will also affect the characteristics of the power supply. It must provide the necessary power and polarity of the supply. In addition, the power supply must have a power margin of 20% up.
It is also worth considering that before connecting the RGB LED strip, you need to plan where the controller for it will be located. Since it is often controlled by a remote control, access to it must be within line of sight.
Calculation of LED strip and power supply
The density of LEDs per meter of tape can be different. Basically it is within 30, 60 and 120 pieces. There is also a double wide tape for 240 diodes. The method of how to calculate the LED strip for its correct operation depends on this.
For diodes brand SMD 3528 is:
- 60 diodes per meter consume 4.8 watts.
- 120 diodes per meter consume 7.2 watts.
- 240 diodes per meter consume 16 watts.
For SMD 5050 brand diodes, the power consumption is:
- 30 diodes per meter consume 7.2 watts.
- 60 diodes per meter consume 14 watts.
- 240 diodes per meter consume 25 watts.
For all cases, if the length of the tape is more than one meter, it is necessary to sum up the entire load and select the appropriate power supply. For example, if there are diodes of the SMD 5050 brand on the tape with a density of 60 pieces per meter, and the tape length is 5 meters, then the power of the power supply must be at least 70 watts.
Selecting a power supply
In order to do it qualitatively, you need to choose the right one for it. After the power consumption has been determined, you need to decide on the type of power supply. This procedure depends on where the backlight is installed. If the tape will work in harsh outdoor conditions, then you should pay attention to sealed plastic or metal versions. They are completely protected from harmful effects and have a compact size. But for these advantages you will have to pay a little more.
If the installation site is indoors and there is enough space for installation, it is advisable to choose an open power supply. It, in comparison with the previous options, is larger in size, but its cost is much lower.
There are also portable power supplies that are similar to phone chargers. They are designed to operate in portable devices that do not exceed a power consumption of 60 watts.
Determining the protective properties
To protect against external influences, the LED strip can be covered on top with a protective layer of silicone or transparent plastic. This applies to those options when outdoor installation is needed. If everything will be mounted indoors, then you can use tapes without protection.
The tape in silicone is suitable for use in corridors, large rooms or other places where both mechanical impacts and the likelihood of liquids are possible. For outdoor use, full protection is required. This tape is a round elastic rod. It has full protection against all influences, including temperature. Therefore, special fasteners may be required before installing this type of LED strip.
How to connect two ribbons together
In order for the diodes to work properly, you need to know how to connect the LED strip correctly. There are two options for this purpose. The first and easiest way, in which you need to purchase special connectors, when using them, you can make a connection in a matter of seconds. The disadvantage of this method is the possibility of contact oxidation and, as a result, power loss.
Another method is more reliable, but requires some skills in handling a soldering iron. The two ends of the tape are soldered with a special solder. In this case, the connection is very reliable. After this procedure, it is advisable to close the contacts with heat shrink tape or special glue. In both cases, in order to know how to properly connect the LED strip, you need not to reverse the polarity of the conductors. They are connected according to the principle "+" to "+" and "-" to "-". It is worth noting that a multi-colored ribbon cannot be combined with a single-colored one. Only tapes of the same type can be summed.
Ribbon connection by soldering
Before you tape to the power wire or connect two segments to each other, you need to purchase the necessary tools and supplies. We will need:
- Low power soldering iron.
- Solder based on tin.
- Flux.
- Connecting wires.
- Sharp knife for stripping insulation.
First of all, we clean the contacts on the tape. If there is silicone protection, then carefully remove it with a knife. We also clean the wires for soldering. The length of the bare conductor should be approximately one centimeter. Then we take a heated soldering iron and lower it into the flux, and then quickly into the solder. After making sure that part of the solder stuck to the tip, we apply a stripped conductor to it. After this operation, part of the solder should go to the conductor. The next step is to solder the prepared conductor to the corresponding pins on the tape. To do this, a conductor is applied in the right place, and a little flux is applied on top of it. After that, you need to touch the assembly with a soldering iron tip for one second. The result should be soldering the conductor.
Tape connection with connectors
Before connecting the tape to power or another tape using connectors, you need to choose them correctly and attach them with high quality. In the case of connecting two segments, you will need a pair of connectors, which must first be soldered together. For soldering, you can use the guide described above.
After the two connectors are ready, insert the stripped edge of the tape into its special slot with the locking buttons open. After that, you need to press these buttons and fix the tape contacts. In the case of a power connection, everything will happen the same way, but with one connector.
In both cases, care must be taken to ensure that the polarity of the connection matches correctly. If something is mixed up, then the tape will not burn. But do not be very upset with this outcome, it will not burn out from this.
How to cut the desired length of tape
Before attaching the LED strip, you need to make a segment of the required length. To simplify this operation, the strip with LEDs has a clear location of places for possible cutting. Often these places are every four light elements, but there may be a different cutting ratio. Therefore, we find a suitable place and with a sharp knife or scissors we make an even cut. It should turn out so that at both ends there will be two contacts to which you can connect power.
If the tape has special protection in the form of silicone or plastic, then before cutting it off, you need to clean a small gap. For this purpose, you can use a knife. You need to act very carefully so as not to damage the contacts.
Preparing for installation
Before attaching the LED strip in the selected location, the entire system must be checked for operability. To do this, the entire electrical circuit is assembled on the table and checked. If there are no comments in the work, then you can proceed to inspect the installation site. To do this, you need to make sure that the tape will not be affected by negative factors in the form of liquids and mechanical influences. It is necessary to design the place for laying the tape so that the bending radius is not less than 20 millimeters. Otherwise, strong bending may damage the tape.
Sometimes the LED strip has an adhesive side for installation. It allows you to attach it to any hard surface. But before you do this, you need to clean and degrease this surface with gasoline or acetone. In the absence of funds for installation, you can use double-sided tape or other means.
Features of connecting RGB tape
Before connecting this type of LED strip to the power supply, you need to check its operation with a special controller that regulates the voltage. It supplies power to those LEDs that should be lit. When connecting, you need to match all four contacts. On the controller and power supply, all terminals are signed, and this operation is not difficult. If everything worked out, and the tape works in all color modes, then you can proceed to install it on the workplace.
Special plugs and sockets can also be used to connect the power supply. They greatly simplify all the work and allow you to ensure a reliable connection. To do this, a socket with the required number of contacts is soldered onto the tape, and the corresponding plug is connected to the power wire.
Installation in a car
Before you install the LED strip in the car, you need to make sure that it is not affected by harmful factors. It can be physical exercise, kinks and increased vibration. To do this, it is usually installed in specially prepared places. For example, it can be a special corner made of plastic or metal, which is attached to the case.
In addition to the right place for installation, you need to use a stabilized voltage to power the backlight. To do this, a special electronic stabilizer is connected to the circuit. It will allow you to equalize the voltage to 12 volts when lowering and raising it in the on-board network. This device can be purchased at any auto parts store. It always comes with instructions for connecting, and if not, then the seller must explain everything.
During direct mounting and when connecting the power wire, it is necessary to remove the terminals from the battery. This action will avoid short circuits and other unpleasant situations.
This article provided basic tips on how to install an LED strip and connect it correctly. Compliance with these rules will help to avoid in the process, as well as in the future, unpleasant situations in operation.
If you decide to make a spectacular backlight in the car or beautifully decorate certain places in the house, then for this purpose it is better to choose a ribbon with a multi-colored glow. This will allow you to flexibly manage the external design.
For lighting, which should be extremely practical, white light is more suitable. It does not impose additional shades on the surrounding objects and will be more natural.
Finally
LED strip is one of the long-lasting light sources. It is preferred when low voltage power is required. When it is connected, electric shock is impossible, since it is too small for this. Therefore, such lighting can be safely used in damp rooms and basements.
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