The times when LEDs were used only as indicators for turning on devices are long gone. Modern LED devices can completely replace incandescent lamps in household, industrial and. This is facilitated by the various characteristics of LEDs, knowing which you can choose the right LED analogue. The use of LEDs, given their basic parameters, opens up a wealth of possibilities in the field of lighting.
A light-emitting diode (denoted as LED, LED, LED in English) is a device based on an artificial semiconductor crystal. When an electric current is passed through it, the phenomenon of emission of photons is created, which leads to a glow. This glow has a very narrow spectral range, and its color depends on the semiconductor material.
LEDs with red and yellow emission are made from inorganic semiconductor materials based on gallium arsenide, green and blue ones are made on the basis of indium gallium nitride. To increase the brightness of the luminous flux, various additives are used or the multilayer method is used, when a layer of pure aluminum nitride is placed between semiconductors. As a result of the formation of several electron-hole (p-n) transitions in one crystal, the brightness of its glow increases.
There are two types of LEDs: for indication and lighting. The former are used to indicate the inclusion of various devices in the network, and also as sources of decorative lighting. They are colored diodes placed in a translucent case, each of them has four terminals. Devices emitting infrared light are used in devices for remote control of devices (remote control).
In the lighting area, LEDs are used that emit white light. LEDs are classified by color into cool white, neutral white and warm white. There is a classification of LEDs used for lighting according to the installation method. The SMD LED designation means that the device consists of an aluminum or copper substrate on which the diode crystal is placed. The substrate itself is located in a housing, the contacts of which are connected to the contacts of the LED.
Another type of LED is designated OCB. In such a device, many crystals coated with phosphor are placed on one board. Thanks to this design, a high brightness of the glow is achieved. This technology is used in production with a large luminous flux in a relatively small area. In turn, this makes the production of LED lamps the most accessible and inexpensive.
Note! Comparing lamps based on SMD and COB LEDs, it can be noted that the former can be repaired by replacing a failed LED. If a COB LED lamp does not work, you will have to change the entire board with diodes.
When choosing a suitable LED lamp for lighting, you should take into account the parameters of the LEDs. These include supply voltage, power, operating current, efficiency (luminous output), glow temperature (color), radiation angle, dimensions, degradation period. Knowing the basic parameters, it will be possible to easily select devices to obtain a particular illumination result.
As a rule, a current of 0.02A is provided for conventional LEDs. However, there are LEDs rated at 0.08A. These LEDs include more powerful devices, the design of which involves four crystals. They are located in one building. Since each of the crystals consumes 0.02A, in total one device will consume 0.08A.
The stability of LED devices depends on the current value. Even a slight increase in current helps to reduce the radiation intensity (aging) of the crystal and increase the color temperature. This ultimately leads to the LEDs turning blue and failing prematurely. And if the current increases significantly, the LED immediately burns out.
To limit the current consumption, the designs of LED lamps and luminaires include current stabilizers for LEDs (drivers). They convert the current, bringing it to the value required by the LEDs. In the case when you need to connect a separate LED to the network, you need to use current-limiting resistors. The resistor resistance for an LED is calculated taking into account its specific characteristics.
Helpful advice! To choose the right resistor, you can use the LED resistor calculator available on the Internet.
How to find out the LED voltage? The fact is that LEDs do not have a supply voltage parameter as such. Instead, the voltage drop characteristic of the LED is used, which means the amount of voltage the LED outputs when the rated current passes through it. The voltage value indicated on the packaging reflects the voltage drop. Knowing this value, you can determine the voltage remaining on the crystal. It is this value that is taken into account in the calculations.
Given the use of various semiconductors for LEDs, the voltage for each of them may be different. How to find out how many volts an LED is? You can determine it by the color of the devices. For example, for blue, green and white crystals the voltage is about 3V, for yellow and red crystals it is from 1.8 to 2.4V.
When using a parallel connection of LEDs of identical ratings with a voltage value of 2V, you may encounter the following: as a result of variations in parameters, some emitting diodes will fail (burn out), while others will glow very faintly. This will happen due to the fact that when the voltage increases even by 0.1V, the current passing through the LED increases by 1.5 times. Therefore, it is so important to ensure that the current matches the LED rating.
The luminous flux of diodes is compared with other light sources, taking into account the strength of the radiation they emit. Devices measuring about 5 mm in diameter produce from 1 to 5 lumens of light. While the luminous flux of a 100W incandescent lamp is 1000 lm. But when comparing, it is necessary to take into account that a regular lamp has diffused light, while an LED has directional light. Therefore, the dispersion angle of the LEDs must be taken into account.
The scattering angle of different LEDs can range from 20 to 120 degrees. When illuminated, LEDs produce brighter light in the center and reduce illumination towards the edges of the dispersion angle. Thus, LEDs illuminate a specific space better while using less power. However, if it is necessary to increase the illumination area, diverging lenses are used in the design of the lamp.
How to determine the power of LEDs? To determine the power of an LED lamp required to replace an incandescent lamp, it is necessary to apply a coefficient of 8. Thus, you can replace a conventional 100W lamp with an LED device with a power of at least 12.5W (100W/8). For convenience, you can use the data from the table of correspondence between the power of incandescent lamps and LED light sources:
| Incandescent lamp power, W | Corresponding power of LED lamp, W |
| 100 | 12-12,5 |
| 75 | 10 |
| 60 | 7,5-8 |
| 40 | 5 |
| 25 | 3 |
When using LEDs for lighting, the efficiency indicator is very important, which is determined by the ratio of luminous flux (lm) to power (W). Comparing these parameters for different light sources, we find that the efficiency of an incandescent lamp is 10-12 lm/W, a fluorescent lamp is 35-40 lm/W, and an LED lamp is 130-140 lm/W.
One of the important parameters of LED sources is the glow temperature. The units of measurement for this quantity are degrees Kelvin (K). It should be noted that all light sources are divided into three classes according to their glow temperature, among which warm white has a color temperature of less than 3300 K, daylight white - from 3300 to 5300 K, and cool white over 5300 K.
Note! The comfortable perception of LED radiation by the human eye directly depends on the color temperature of the LED source.
The color temperature is usually indicated on the labeling of LED lamps. It is designated by a four-digit number and the letter K. The choice of LED lamps with a certain color temperature directly depends on the characteristics of its use for lighting. The table below displays options for using LED sources with different glow temperatures:
| LED color | Color temperature, K | Lighting Use Cases | |
| White | Warm | 2700-3500 | Lighting for domestic and office premises as the most suitable analogue of an incandescent lamp |
| Neutral (daytime) | 3500-5300 | The excellent color rendition of such lamps allows them to be used for lighting workplaces in production. | |
| Cold | over 5300 | Mainly used for street lighting, and also used in hand-held lanterns | |
| Red | 1800 | As a source of decorative and phyto-lighting | |
| Green | - | ||
| Yellow | 3300 | Lighting design of interiors | |
| Blue | 7500 | Illumination of surfaces in the interior, phyto-lighting | |
The wave nature of color allows the color temperature of LEDs to be expressed using wavelength. The marking of some LED devices reflects the color temperature precisely in the form of an interval of different wavelengths. The wavelength is designated λ and is measured in nanometers (nm).
Considering the size of SMD LEDs, devices are classified into groups with different characteristics. The most popular LEDs with standard sizes are 3528, 5050, 5730, 2835, 3014 and 5630. The characteristics of SMD LEDs vary depending on the size. Thus, different types of SMD LEDs differ in brightness, color temperature, and power. In LED markings, the first two digits indicate the length and width of the device.
The main characteristics of SMD LEDs 2835 include an increased radiation area. Compared to the SMD 3528 device, which has a round working surface, the SMD 2835 radiation area has a rectangular shape, which contributes to greater light output with a smaller element height (about 0.8 mm). The luminous flux of such a device is 50 lm.
The SMD 2835 LED housing is made of heat-resistant polymer and can withstand temperatures up to 240°C. It should be noted that the radiation degradation in these elements is less than 5% over 3000 hours of operation. In addition, the device has a fairly low thermal resistance of the crystal-substrate junction (4 C/W). The maximum operating current is 0.18A, the crystal temperature is 130°C.
Based on the color of the glow, there are warm white with a glow temperature of 4000 K, daytime white - 4800 K, pure white - from 5000 to 5800 K and cool white with a color temperature of 6500-7500 K. It is worth noting that the maximum luminous flux is for devices with cool white glow, the minimum is for warm white LEDs. The design of the device has enlarged contact pads, which promotes better heat dissipation.
Helpful advice! SMD 2835 LEDs can be used for any type of installation.
The SMD 5050 housing design contains three LEDs of the same type. LED sources of blue, red and green colors have technical characteristics similar to SMD 3528 crystals. The operating current of each of the three LEDs is 0.02A, therefore the total current of the entire device is 0.06A. To ensure that the LEDs do not fail, it is recommended not to exceed this value.
LED devices SMD 5050 have a forward voltage of 3-3.3V and a light output (mains flux) of 18-21 lm. The power of one LED is the sum of three power values of each crystal (0.7 W) and amounts to 0.21 W. The color of the glow emitted by the devices can be white in all shades, green, blue, yellow and multi-colored.
The close arrangement of LEDs of different colors in one SMD 5050 package made it possible to implement multi-color LEDs with separate control of each color. To regulate luminaires using SMD 5050 LEDs, controllers are used, so that the color of the glow can be smoothly changed from one to another after a given amount of time. Typically, such devices have several control modes and can adjust the brightness of the LEDs.
SMD 5730 LEDs are modern representatives of LED devices, the housing of which has geometric dimensions of 5.7x3 mm. They belong to ultra-bright LEDs, the characteristics of which are stable and qualitatively different from the parameters of their predecessors. Manufactured using new materials, these LEDs are characterized by increased power and highly efficient luminous flux. In addition, they can work in conditions of high humidity, are resistant to temperature changes and vibration, and have a long service life.
There are two types of devices: SMD 5730-0.5 with a power of 0.5 W and SMD 5730-1 with a power of 1 W. A distinctive feature of the devices is the ability to operate on pulsed current. The rated current of SMD 5730-0.5 is 0.15A; during pulse operation, the device can withstand current up to 0.18A. This type of LEDs provides a luminous flux of up to 45 lm.
SMD 5730-1 LEDs operate at a constant current of 0.35A, in pulsed mode - up to 0.8A. The light output efficiency of such a device can be up to 110 lm. Thanks to the heat-resistant polymer, the device body can withstand temperatures up to 250°C. The dispersion angle of both types of SMD 5730 is 120 degrees. The degree of luminous flux degradation is less than 1% when operating for 3000 hours.
The Cree company (USA) is engaged in the development and production of ultra-bright and most powerful LEDs. One of the Cree LED groups is represented by the Xlamp series of devices, which are divided into single-chip and multi-chip. One of the features of single-crystal sources is the distribution of radiation along the edges of the device. This innovation made it possible to produce lamps with a large luminous angle using a minimum number of crystals.
In the XQ-E High Intensity series of LED sources, the beam angle ranges from 100 to 145 degrees. Having small geometric dimensions of 1.6x1.6 mm, the power of ultra-bright LEDs is 3 Volts, and the luminous flux is 330 lm. This is one of the newest developments from Cree. All LEDs, the design of which is developed on the basis of a single crystal, have high-quality color rendering within CRE 70-90.
Related article:
How to make or repair an LED garland yourself. Prices and main characteristics of the most popular models.
Cree has released several versions of multi-chip LED devices with the latest power types from 6 to 72 Volts. Multichip LEDs are divided into three groups, which include devices with high voltage, power up to 4W and above 4W. Sources up to 4W contain 6 crystals in MX and ML type housings. The dispersion angle is 120 degrees. You can buy Cree LEDs of this type with white warm and cool colors.
Helpful advice! Despite the high reliability and quality of light, you can buy powerful LEDs of the MX and ML series at a relatively low price.
The group over 4W includes LEDs made from several crystals. The largest in the group are the 25W devices represented by the MT-G series. The company's new product is XHP model LEDs. One of the large LED devices has a 7x7 mm body, its power is 12W, and the light output is 1710 lm. High voltage LEDs combine small dimensions and high light output.
There are certain rules for connecting LEDs. Taking into account that the current passing through the device moves only in one direction, for long-term and stable operation of LED devices it is important to take into account not only a certain voltage, but also the optimal current value.
Depending on the power source used, there are two types of circuits for connecting LEDs to 220V. In one of the cases it is used with limited current, in the second - a special one that stabilizes the voltage. The first option takes into account the use of a special source with a certain current strength. A resistor is not required in this circuit, and the number of connected LEDs is limited by the driver power.
To designate LEDs in the diagram, two types of pictograms are used. Above each schematic image there are two small parallel arrows pointing upward. They symbolize the bright glow of the LED device. Before connecting the LED to 220V using a power supply, you must include a resistor in the circuit. If this condition is not met, this will lead to the fact that the working life of the LED will be significantly reduced or it will simply fail.
If you use a power supply when connecting, then only the voltage in the circuit will be stable. Considering the insignificant internal resistance of an LED device, turning it on without a current limiter will lead to the device burning out. That is why a corresponding resistor is introduced into the LED switching circuit. It should be noted that resistors come in different values, so they must be calculated correctly.
Helpful advice! The negative aspect of circuits for connecting an LED to a 220 Volt network using a resistor is the dissipation of high power when it is necessary to connect a load with increased current consumption. In this case, the resistor is replaced with a quenching capacitor.
When calculating the resistance for an LED, they are guided by the formula:
U = IхR,
where U is voltage, I is current, R is resistance (Ohm’s law). Let's say you need to connect an LED with the following parameters: 3V - voltage and 0.02A - current. So that when connecting an LED to 5 Volts on the power supply it does not fail, you need to remove the extra 2V (5-3 = 2V). To do this, you need to include a resistor with a certain resistance in the circuit, which is calculated using Ohm’s law:
R = U/I.
Thus, the ratio of 2V to 0.02A will be 100 Ohms, i.e. This is exactly the resistor needed.
It often happens that, given the parameters of the LEDs, the resistance of the resistor has a value that is non-standard for the device. Such current limiters cannot be found at points of sale, for example, 128 or 112.8 ohms. Then you should use resistors whose resistance is the closest value compared to the calculated value. In this case, the LEDs will not function at full capacity, but only at 90-97%, but this will be invisible to the eye and will have a positive effect on the life of the device.
There are many options for LED calculation calculators on the Internet. They take into account the main parameters: voltage drop, rated current, output voltage, number of devices in the circuit. By specifying the parameters of LED devices and current sources in the form field, you can find out the corresponding characteristics of resistors. To determine the resistance of color-coded current limiters, there are also online calculations of resistors for LEDs.
When assembling structures from several LED devices, circuits for connecting LEDs to a 220 Volt network with a serial or parallel connection are used. At the same time, for correct connection, it should be taken into account that when LEDs are connected in series, the required voltage is the sum of the voltage drops of each device. While when LEDs are connected in parallel, the current strength is added up.
If the circuits use LED devices with different parameters, then for stable operation it is necessary to calculate the resistor for each LED separately. It should be noted that no two LEDs are exactly alike. Even devices of the same model have minor differences in parameters. This leads to the fact that when a large number of them are connected in a series or parallel circuit with one resistor, they can quickly degrade and fail.
Note! When using one resistor in a parallel or series circuit, you can only connect LED devices with identical characteristics.
The discrepancy in parameters when connecting several LEDs in parallel, say 4-5 pieces, will not affect the operation of the devices. But if you connect a lot of LEDs to such a circuit, it will be a bad decision. Even if LED sources have a slight variation in characteristics, this will cause some devices to emit bright light and burn out quickly, while others will glow dimly. Therefore, when connecting in parallel, you should always use a separate resistor for each device.
As for the series connection, there is economical consumption here, since the entire circuit consumes an amount of current equal to the consumption of one LED. In a parallel circuit, the consumption is the sum of the consumption of all LED sources included in the circuit.
In the design of some devices, resistors are provided at the manufacturing stage, which makes it possible to connect LEDs to 12 Volts or 5 Volts. However, such devices cannot always be found on sale. Therefore, in the circuit for connecting LEDs to 12 volts, a current limiter is provided. The first step is to find out the characteristics of the connected LEDs.
Such a parameter as the forward voltage drop for typical LED devices is about 2V. The rated current of these LEDs corresponds to 0.02A. If you need to connect such an LED to 12V, then the “extra” 10V (12 minus 2) must be extinguished with a limiting resistor. Using Ohm's law you can calculate the resistance for it. We get that 10/0.02 = 500 (Ohm). Thus, a resistor with a nominal value of 510 Ohms is required, which is the closest in the range of E24 electronic components.
In order for such a circuit to work stably, it is also necessary to calculate the power of the limiter. Using the formula based on which power is equal to the product of voltage and current, we calculate its value. We multiply a voltage of 10V by a current of 0.02A and get 0.2W. Thus, a resistor is required, the standard power rating of which is 0.25W.
If it is necessary to include two LED devices in the circuit, then it should be taken into account that the voltage dropped across them will already be 4V. Accordingly, the resistor will have to extinguish not 10V, but 8V. Consequently, further calculation of the resistance and power of the resistor is done based on this value. The location of the resistor in the circuit can be provided anywhere: on the anode side, cathode side, between the LEDs.
One way to check the operating condition of LEDs is to test with a multimeter. This device can diagnose LEDs of any design. Before checking the LED with a tester, the device switch is set in the “testing” mode, and the probes are applied to the terminals. When the red probe is connected to the anode and the black probe to the cathode, the crystal should emit light. If the polarity is reversed, the device display should display “1”.
Helpful advice! Before testing the LED for functionality, it is recommended to dim the main lighting, since during testing the current is very low and the LED will emit light so weakly that in normal lighting it may not be noticeable.
Testing LED devices can be done without using probes. To do this, insert the anode into the holes located in the lower corner of the device into the hole with the symbol “E”, and the cathode into the hole with the indicator “C”. If the LED is in working condition, it should light up. This testing method is suitable for LEDs with sufficiently long contacts that have been cleared of solder. The position of the switch does not matter with this method of checking.
How to check LEDs with a multimeter without desoldering? To do this, you need to solder pieces of a regular paper clip to the tester probes. A textolite gasket, which is placed between the wires and then treated with electrical tape, is suitable as insulation. The output is a kind of adapter for connecting probes. The clips spring well and are securely fixed in the connectors. In this form, you can connect the probes to the LEDs without removing them from the circuit.
Many radio amateurs practice assembling various designs from LEDs with their own hands. Self-assembled products are not inferior in quality, and sometimes even surpass their manufactured counterparts. These can be color and music devices, flashing LED designs, do-it-yourself LED running lights and much more.
To prevent the LED's life from being exhausted ahead of schedule, it is necessary that the current flowing through it has a stable value. It is known that red, yellow and green LEDs can cope with increased current load. While blue-green and white LED sources, even with a slight overload, burn out in 2 hours. Thus, for the LED to operate normally, it is necessary to resolve the issue with its power supply.
If you assemble a chain of series- or parallel-connected LEDs, you can provide them with identical radiation if the current passing through them has the same strength. In addition, reverse current pulses can negatively affect the life of LED sources. To prevent this from happening, it is necessary to include a current stabilizer for the LEDs in the circuit.
The qualitative characteristics of LED lamps depend on the driver used - a device that converts voltage into a stabilized current with a specific value. Many radio amateurs assemble a 220V LED power supply circuit with their own hands based on the LM317 microcircuit. The elements for such an electronic circuit are low cost and such a stabilizer is easy to construct.
When using a current stabilizer on LM317 for LEDs, the current is adjusted within 1A. A rectifier based on LM317L stabilizes the current to 0.1A. The device circuit uses only one resistor. It is calculated using an online LED resistance calculator. Available devices are suitable for power supply: power supplies from a printer, laptop or other consumer electronics. It is not profitable to assemble more complex circuits yourself, since they are easier to purchase ready-made.
The use of daytime running lights (DRLs) on cars significantly increases the visibility of the car during daylight hours by other road users. Many car enthusiasts practice self-assembly of DRLs using LEDs. One of the options is a DRL device of 5-7 LEDs with a power of 1W and 3W for each block. If you use less powerful LED sources, the luminous flux will not meet the standards for such lights.
Helpful advice! When making DRLs with your own hands, take into account the requirements of GOST: luminous flux 400-800 cd, luminous angle in the horizontal plane - 55 degrees, in the vertical plane - 25 degrees, area - 40 cm².
For the base, you can use a board made of aluminum profile with pads for mounting LEDs. The LEDs are fixed to the board using a thermally conductive adhesive. Optics are selected according to the type of LED sources. In this case, lenses with a luminous angle of 35 degrees are suitable. Lenses are installed on each LED separately. The wires are routed in any convenient direction.
Next, a housing is made for the DRLs, which also serves as a radiator. For this you can use a U-shaped profile. The finished LED module is placed inside the profile, secured with screws. All free space can be filled with transparent silicone-based sealant, leaving only the lenses on the surface. This coating will serve as a moisture barrier.
Connecting the DRL to the power supply requires the mandatory use of a resistor, the resistance of which is pre-calculated and tested. Connection methods may vary depending on the car model. Connection diagrams can be found on the Internet.
The most popular flashing LEDs, which can be purchased ready-made, are devices that are controlled by the potential level. The blinking of the crystal occurs due to a change in power supply at the terminals of the device. Thus, a two-color red-green LED device emits light depending on the direction of the current passing through it. The blinking effect in the RGB LED is achieved by connecting three separate control pins to a specific control system.
But you can make an ordinary single-color LED blink, having a minimum of electronic components in your arsenal. Before you make a flashing LED, you need to choose a working circuit that is simple and reliable. You can use a flashing LED circuit, which will be powered from a 12V source.
The circuit consists of a low-power transistor Q1 (silicon high-frequency KTZ 315 or its analogues are suitable), a resistor R1 820-1000 Ohms, a 16-volt capacitor C1 with a capacity of 470 μF and an LED source. When the circuit is turned on, the capacitor is charged to 9-10V, after which the transistor opens for a moment and transfers the accumulated energy to the LED, which begins to blink. This circuit can only be implemented when powered from a 12V source.
You can assemble a more advanced circuit that works in a similar way to a transistor multivibrator. The circuit includes transistors KTZ 102 (2 pcs.), resistors R1 and R4 of 300 Ohms each to limit the current, resistors R2 and R3 of 27000 Ohms each to set the base current of the transistors, 16-volt polar capacitors (2 pcs. with a capacity of 10 uF) and two LED sources. This circuit is powered by a 5V DC voltage source.
The circuit operates on the “Darlington pair” principle: capacitors C1 and C2 are alternately charged and discharged, which causes a particular transistor to open. When one transistor supplies energy to C1, one LED lights up. Next, C2 is smoothly charged, and the base current of VT1 is reduced, which leads to the closing of VT1 and the opening of VT2 and another LED lights up.
Helpful advice! If you use a supply voltage above 5V, you will need to use resistors with a different value to prevent failure of the LEDs.
To implement fairly complex color music circuits on LEDs with your own hands, you must first understand how the simplest color music circuit works. It consists of one transistor, a resistor and an LED device. Such a circuit can be powered from a source rated from 6 to 12V. The operation of the circuit occurs due to cascade amplification with a common radiator (emitter).
The VT1 base receives a signal with varying amplitude and frequency. When signal fluctuations exceed a specified threshold, the transistor opens and the LED lights up. The disadvantage of this scheme is the dependence of blinking on the degree of the sound signal. Thus, the effect of color music will appear only at a certain level of sound volume. If you increase the sound. The LED will be on all the time, and when it decreases, it will flash slightly.
To achieve a full effect, they use a color music circuit using LEDs, dividing the sound range into three parts. The circuit with a three-channel audio converter is powered from a 9V source. A huge number of color music schemes can be found on the Internet at various amateur radio forums. These can be color music schemes using a single-color strip, an RGB LED strip, as well as a scheme for smoothly switching LEDs on and off. You can also find diagrams of running LED lights online.
The voltage indicator circuit includes resistor R1 (variable resistance 10 kOhm), resistors R1, R2 (1 kOhm), two transistors VT1 KT315B, VT2 KT361B, three LEDs - HL1, HL2 (red), HLЗ (green). X1, X2 – 6-volt power supplies. In this circuit, it is recommended to use LED devices with a voltage of 1.5V.
The operating algorithm of a homemade LED voltage indicator is as follows: when voltage is applied, the central green LED source lights up. In the event of a voltage drop, the red LED located on the left turns on. An increase in voltage causes the red LED on the right to light up. With the resistor in the middle position, all transistors will be in the closed position, and voltage will only flow to the central green LED.
Transistor VT1 opens when the resistor slider is moved up, thereby increasing the voltage. In this case, the voltage supply to HL3 stops, and it is supplied to HL1. When the slider moves down (voltage decreases), transistor VT1 closes and VT2 opens, which will provide power to the LED HL2. With a slight delay, LED HL1 will go out, HL3 will flash once and HL2 will light up.
Such a circuit can be assembled using radio components from outdated equipment. Some assemble it on a textolite board, observing a 1:1 scale with the dimensions of the parts so that all elements can fit on the board.
The limitless potential of LED lighting makes it possible to independently design various lighting devices from LEDs with excellent characteristics and a fairly low cost.
We are all familiar with Christmas tree garlands consisting of multi-colored light bulbs. However, recently products based on LEDs have become very popular.
How they are designed, what kind of connection diagram they have and what to do if the garland stops glowing will be discussed in detail in this article.
What does a Christmas tree garland consist of?
What is a garland of LEDs, is it worse or better than a regular one?
Externally, this is almost the same product as before - wires, light bulbs (LED), control unit.
The most important element is, of course, the control unit. A small plastic box on which various operating modes of the backlight are indicated. 
They can be changed by simply pressing a button. The unit itself can be quite well protected with IP44 level of moisture and dust protection. 
What's inside? To open it, use the sharp tip of a knife or a thin screwdriver to pry the latches from the bottom and take off the protective cover. 
By the way, sometimes it is glued, and not just sitting on the latches.
First of all, inside you will see wires soldered to the board. The thicker wire is usually the network wire, supplying 220V voltage. 
Soldered on the board:
The number of board elements depends primarily on the number of light channels of the garland. More expensive models may have a fuse. 
LED garland diagram
The AC mains voltage is supplied to the power controller through resistors and a diode bridge, already rectified and smoothed through a capacitor. 
In this case, this voltage is supplied through the button, which is open in the normal state. When you close it, the controller modes switch.
The controller in turn controls the thyristors. Their number depends on the number of backlight channels. And after the thyristors, the output power goes directly to the LEDs in the garland.
The more such outputs, the more varied the colors the product can have. If there are only two of them, this means that only two parts (or halves) of the garland will work in different modes - some bulbs will go out, others will light up, etc. 
In fact, these two lines of diodes will be connected on two channels in series. They will connect to each other at the end point - the last LED. 
If for some reason you are annoyed by the blinking of the garland and you want it to glow evenly with only one color, it is enough to short-circuit the cathode and anode of the thyristor on the back side of the board using soldering. 
The more expensive the garland you have, the more outgoing channels and wiring will leave the control board.
At the same time, if you follow the traces of the board, one of the mains voltage outputs is always supplied directly to the final LED of the garland, bypassing all elements of the circuit. 
Causes of malfunction
Situations with garland malfunctions are very diverse.
At the same time, remember that the most important element - the microcircuit on the board - “burns” very, very rarely.
In approximately 5-10% of all cases.
Bad soldering
If your backlight suddenly stops working, first of all always check the soldering of the supply and output wires. It is quite possible that the entire contact was held only by hot glue. 
It’s worth moving the wiring and contacts as usual.
The most common problem with Chinese garlands is the use of very thin wires, which simply break off at the solder points on the board.
To prevent this from happening, all contacts after soldering must be filled with a thick layer of hot melt adhesive. 
And when stripping such veins, it is advised to use not a knife, but a lighter. Instead of whittling away the insulation with a blade, lightly heat and melt it with a lighter. 
After that, simply remove the outer layer with your nails without damaging the veins themselves.
LED damage
If the wire contacts are OK and you are sinning on one of the diodes, how can you check if it is faulty? And most importantly, how to find it among the whole series of light bulbs? 
First of all, unplug the garland from the outlet. Start with the last diode. The power wire comes to it directly from the control unit.
An outgoing conductor is soldered to the same leg. He goes to the next branch of the light channel. You also need to test the diode between its two power wires (input-output). 
You will need a multimeter and its somewhat modernized probes. 
Thin needles are tightly tied to the tips of the tester probes with a thread so that their points protrude a maximum of 5-8mm. 
Wrap everything on top with a thick layer of electrical tape. 
Since the LEDs are soldered, you won’t be able to simply pull them out of the light bulb like in regular garlands.
Therefore, you will have to pierce the insulation of the conductors to get to the copper conductors of the wiring. Switch the multimeter to diode testing mode. 
And you begin to sequentially pierce the supply wires near each suspicious diode. 
If you have a garland not 220V, but 12V or 24V, which is connected from this power supply: 
then the working LED from the multimeter battery should light up. 
If this is a 220V backlight, then check the multimeter readings.
On working elements they will be approximately the same, but the faulty one will show a break.
The method is of course barbaric and damages the insulation, but it works quite well. True, after such punctures, it is better not to use outdoor garlands outdoors.
Chaotic blinking
There is a situation when you turn on a garland and it starts blinking chaotically, sometimes brighter, sometimes dimmer. It sorts through the channels on its own.
In general, one gets the impression that this is not some kind of factory effect, but as if the garland has “gone crazy.”
Most often the problem here is the electrolytic capacitor. It may swell and swell a little, and this will be clearly visible even to the naked eye. 
Everything can be solved by replacing it. The denomination is indicated on the case, so you can easily purchase and select a similar one in radio parts stores. 
If you replaced the capacitor, but it did not give any effect, where to look next? Most likely one of the resistors has burned out (broken). It is quite problematic to visually determine the breakdown. You will need a tester.
You take resistance measurements, having previously learned its nominal (normal) value from the markings. If it doesn't match, change it. 
Part of the garland does not shine
When any of the channels on the garland does not work completely, there may be two reasons.
For example, a breakdown on one of the thyristors or diodes responsible for it.
To make sure of this for sure, simply unsolder the wiring of this channel on the board from its place and connect there the adjacent channel, which is known to be working. 
And if at the same time another channel also stops working, then the problem is not in the garland itself, but in the components of its board - a thyristor or diode. 
You check them with a multimeter, find the ones that match the parameters and change them.
The garland shines dimly
There are also not entirely obvious accidents, when the LEDs of a separate channel seem to be on, but rather dimly compared to the others. 
What does it mean? The controller circuit is working fine. When you press the button, all modes are switched.
Testing the parameters of the diode bridge and resistance with a tester also does not reveal any problems. In this case, the only thing left to blame is the wires. They are already quite frail, and when such a stranded wire is torn, its cross section decreases even more.
As a result, the garland is simply not able to start the LEDs in the nominal brightness mode, since they simply do not have enough voltage. How to find this torn vein in a long garland? 
To do this, you will have to walk along the entire line with your hands. Turn on the garland and start moving the wires near each LED until the entire backlight lights up in full force.
According to Murphy's law, this may be the very last segment of the garland, so be patient.
As soon as you find this area, pick up a soldering iron and disassemble the wires on the LED. Clean them with a lighter and solder everything again. 
Then insulate the soldering area with heat shrink. 
The topic of this article is inspired by the inevitably approaching New Year. Many of us in our collections, and just on the farm, have several old New Year's electric garlands at once. December is the best time for their prevention and repair. Probably, garlands with miniature incandescent bulbs require maximum attention, to which we will first of all pay attention. However, much of what has been said will somehow apply to more modern LED-based garlands.
Of course, the most common malfunction is called “the garland does not light.” This can be caused not only by the burnout of one of the light bulbs, but also by a violation of the contact in the plugs and sockets (for example, self-turning of the lamps), an internal break (kink) in the wires and the failure of additional, not always noticeable circuit elements (for example, fuses, hidden in the power cord, etc.). Sometimes the search for such a malfunction can take a very long time, and in the end there may even be a desire to “give up”
The simplest and at the same time effective way to find a defective section of the circuit is a phased continuity, followed by removing each light bulb from the cartridge. However, because of this, this method is also the longest, and besides, not all garlands are collapsible (in some places the bulbs are soldered). The so-called “miracle screwdriver” (field detector), equipped with batteries and a built-in field-effect transistor amplifier, will help to significantly reduce the search time for a problem area. The problematic garland is connected to the network, after which it is carefully carried out with a screwdriver along its entire length. Near the break point (or the bulb of a burnt-out lamp), a buzzer starts to sound and a green LED lights up (see photo on the right). Troubleshooting using this method takes a matter of seconds, but unfortunately it does not work if the garland has more than one break.
So, the burnt out lamp has been successfully detected. It’s good if it’s a Soviet light bulb with an E10 socket on which its parameters are written! However, garlands (especially imported ones) often use baseless lamps without any markings. Moreover, despite almost the same appearance, these lamps can differ significantly in parameters, i.e. be completely non-fungible. How to be? First you need to find out the required parameters of such a lamp. A burnt-out light bulb removed from the garland will not help us in any way with this, so for research we will have to remove another one - a working one. To find out its characteristics, we need an adjustable (laboratory) power supply and a tester for measuring current. The proposed measurement technique is as follows: the voltage on the lamp turned on through the tester is carefully raised from zero until the moment when it begins to glow with sufficient intensity. Attention! Do not overheat the lamp; it is better to let it glow a little dimmer than it should. At this moment, you should record the operating voltage and especially the lamp current. Next, it is easy to determine the rated voltage as the closest of the series 1; 1.5; 2.5; 3; 3.5; 5; 6; 9; 10; 12; 13.5; 14; 16; 18; 24; 26 V and current from the series 0.06; 0.1; 0.16; 0.2; 0.25; 0.3 A. Now all that remains is to find in stock or purchase a lamp with exactly the same parameters.
But what to do if you can’t find exactly the lamp you need? For example, some types of lamps were not sold at all separately from garlands. Sometimes in such cases they resort to short-circuiting the burnt-out lamp, but this is the wrong approach, which greatly brings the moment of complete failure of the garland closer. In other cases, instead of a burnt-out lamp, another one is installed with “from-the-lantern” parameters, which either also leads to an overload of the remaining lamps (in this case, the new lamp barely glows, as in the photo on the right), or to the immediate burnout of the new lamp. How to choose the right replacement?
Let's start with the fact that the most correct replacement is still exactly the same light bulb as all the others, i.e. "native". But if it is not there, a replacement must be selected primarily based on its operating current, so that the garland can retain its previous appearance when turned on.
For example, if the lamps in a garland are designed for 5V, 0.12A, then instead of one of them it is quite possible to try installing the lamp on 3 V, 0.16 A. By the way, the result of this particular replacement can be seen in the photo on the left (the “non-original” light bulb is the left one). However, it must be remembered that as the number of lamps being replaced increases, the load on the remaining lamps increases, so it will not be possible to abuse such a replacement indefinitely.
Another, more radical and more correct way to revive an old garland is to completely replace all the light bulbs with new ones of a different type (from among those currently freely sold). However, we must remember that the initial number of lamps in the garland dictates the range of rated voltages for the selected lamps. For example, with 10 lamps in a garland these should be 24-26 V bulbs, with 16 - 16-18 V, with 20 - 12-14 V, with 50 - 5-6 V, etc. At the same time, we still have the freedom to choose lamps with any operating current at a given voltage, the main thing is that they are all the same.
In garlands of the 1990s...2000s, lamps with the so-called self-shorting (see photo on the right) were often used - a special element that is broken through when the filament burns out and short-circuits the lamp, so that the rest of the garland continues to work. As you can see, this solution is essentially an automatic replacement of burnt-out lamps with jumpers - the very option that we recommended avoiding. As shorted lamps accumulate in the garland, the voltage on the remaining ones increases more and more, which accelerates their failure and increases the likelihood of an avalanche burnout of many lamps at once, accompanied by tripping of the garland's fuse (if there is one!) and, in fact, its final failure. Therefore, when extinguished light bulbs appear in a garland, it is still advisable to change them as soon as possible. However, sometimes it turns out that self-shorting, for some reason, also works for lamps with a working filament. In this case, you can try to extend the life of such light bulbs by burning out the short-circuiting element with increased current. To do this, such a lamp is connected to a laboratory source with adjustable current. The voltage should be set at a level not exceeding the rated voltage of the lamp. Next, the current is carefully increased until the short-circuiting element gradually melts. You should not immediately apply high current to the lamp, as this can lead to melting of its electrodes and final failure.
Old electric garlands did not contain any electronic controllers or control devices, so the only lighting effects available were the blinking of the entire chain, provided by including a specially designed lamp with a bimetallic contact inside the circuit. Unfortunately, it was these lamps that were the first to fail; sometimes this was expressed in the fact that the built-in contact stopped opening. You can replace such a lamp with a starter can, or even better, with a whole starter connected in series with the garland (the burnt out flashing lamp is replaced with a regular one). The whole problem lies in selecting the type of starter that would ensure beautiful flashing of the lamps, similar to what was originally intended. This topic has become the subject of a separate study, but in short, starters in a full-size (extension) flask with a lilac-colored filling gas, in particular the “old” Philips S10, have proven themselves to be the best starters. Soviet starters with neon filling turned out to be completely unsuitable for this purpose. However, you need to remember that such an abnormal operating mode greatly wears out and overheats the starter, so such a repaired flashing garland needs to be given a “rest” from time to time.
How to extend the life of an old garlandTime moves inexorably forward, and incandescent lamps are just as inexorably becoming a thing of the past. Therefore, old electric garlands, especially those made in the Soviet Union, are increasingly becoming rarities every year and are beginning to require especially careful handling. How to extend their life? The answer is suggested by one feature of incandescent lamps, namely the dependence of their service life on the operating voltage (and, accordingly, current). This relationship is nonlinear, for example, reducing the voltage by 10% doubles the lamp life. Sometimes, to achieve this effect, garlands are connected to the network through a diode, but this creates an unpleasant flickering effect of the lamps, noticeable to the eye. Instead, we can recommend powering the garland through an autotransformer (if you happen to have one lying around the household), and if it is absent, turn it on through a ballast choke (recommended) or a capacitor. A choke with the required parameters can always be selected from among the standard ones for turning on fluorescent lamps.
The rest of the advice will be quite banal: do not subject the garland to strong shocks (especially when it is turned on), do not connect it to a network with increased voltage or voltage surges, do not reduce the number of lamps in the garland and do not short-circuit burnt-out lamps. A simple set of these preventive measures can already ensure a long life for your favorite garland to the delight of your household and all lovers of New Year's decorations.
The New Year is coming - and now Christmas tree decorations and garlands come out of the boxes. And if the toy is simply hung in the place chosen for it, then there are various accidents with the garlands. This is especially true for cheap options. Anyone who has ever repaired this miracle of technology knows that the Chinese garland, whose circuit is simple, has some features.
Most often, Chinese craftsmen are attracted to New Year's decorations by their attractive price (from 150 rubles per piece) and bright lights that flash in several modes. Four types of light bulbs, and sometimes LEDs, are pleasing to the eye and wallet. True, after a while one or several colors stop burning. There may be several reasons, but the fact remains that the garland no longer works 100%.
If the product is damaged, it is not necessary to replace it with a new one. Although it is customary to enter the New Year with everything new, our hands are not made for boredom. Is it really difficult to change a burnt out light bulb? The point here is not the price or the time spent on repairs. It's a matter of principle. And every person who decides to repair a Chinese garland for the first time begins to be surprised.
The most unpleasant surprise during repairs is thin wire strands. You begin to wonder how it all works and has not yet fallen apart. Both the price of the product and the reliability of operation become clear. This is the Chinese garland. Scheme, repair and search for gaps - this is your future fate. The wiring connection is naturally the weakest point. Therefore, you should start searching for a gap with the switching box.
In addition to surprisingly thin wiring, the Chinese product can please you with the quick failure of the thyristors that control the color lines, as well as the main controller. To replace faulty elements, you most often have to look for domestic analogues or redo the entire circuit.
Let's consider some of the possible cases when the Chinese garland circuit is not needed. From the electrical engineering course, only 2 problems associated with electrical problems are known: short circuit and open circuit. In the case of a non-working garland, you need to look for a gap. Let's say the blue light is off. 2 options are possible:
Now you need to find a break or a burnt out light bulb. As a rule, a visual inspection will help us with this. Most often, the gap is visible to the naked eye, and the repair quickly ends. To connect the two ends of the wire, you don’t even need to have a soldering iron on hand - simple twisting helps. It is imperative to wrap it with electrical tape.
Attention! Any repair of an electrical product is carried out without connecting to the network.
If the gap is not visible, you should pay attention to the box with the button. The Chinese garland, the design of which does not differ from the standard one, has a control unit in a flat box. By unscrewing 2 or more screws, you can see a small printed circuit board with several elements. It comes with 2 wires from the plug: phase and neutral, as well as 4 wires with light bulbs of four different colors. Breaks most often occur at the junction of wire strands.
A number of malfunctions are associated with malfunction. Here, the mode switching button itself may fail. This problem can be “cured” by cleaning the contacts or completely replacing them. A Chinese garland, the circuit of which is standard, necessarily includes a controller. It can also go bad and can be replaced too. The weak link can be any of the 4 thyristors - one for each color.
To replace faulty elements, Chinese colleagues offer their own. The problem is that lamps become outdated quite quickly, and finding the right Chinese-made version can be problematic. In this case, the domestic element base comes to the rescue. The most important thing is to choose the right analogue.
To select an analogue of the desired element, it is important to know the parameters of the Chinese product. The PCR406J transistor is often searched for on forums. The Chinese garland, the diagram of which is made on such elements, is familiar. Only the desired element actually turns out to be a thyristor, and its Russian analogue MCR100 is almost identical in parameters.
What to do if no breaks are found? The design of a Chinese garland is simple. All light bulbs are connected to each other in series. This means that if the blue line is not lit, you need to find at least one burnt out one. There are two options.
The second method can be avoided if you use a multimeter with thin needles attached to the ends of the probes. However, the conductor strands used in Chinese products are so thin that they can be torn even by a needle.
It happens that there is no second damaged garland and a new light bulb at hand. In this case, you can simply connect the two ends together. This is fraught with an increase in voltage on the remaining light bulbs, since according to the laws of electrical engineering in a series circuit, the voltage is divided equally. But if you remove one or two elements, this will not greatly affect the service life. Despite the fact that they are Chinese, everything works on general principles.
Such products have recently become widespread. In this regard, low-power elements appeared on the garlands instead of light bulbs. The Chinese scheme differs little from the standard one. But, given the fact that the LED is designed for a much lower voltage, each of them will have a resistor in the circuit for a 220 V network. In another embodiment, a step-down transformer will be implemented at the system input.
In addition to the usual circuit, where the elements are arranged in series, there is a circuit of a Chinese garland with LEDs placed in parallel. With this option, even the burnout of several light elements at once will not introduce dissonance into the overall picture.
A Chinese garland, the circuit of which is built on LEDs, has a number of advantages.
LED Chinese garlands are very convenient to use to decorate the outdoor part of the house. Due to their high moisture and frost resistance, such products will please the eye for a long time without repair.
When buying such a product, it is not always possible to please yourself and your loved ones with high-quality jewelry. Sometimes, behind bright lights and an attractive price, a rather simple and cheap Chinese garland is hidden. Its circuit will be easy to study and convenient for applying electrical skills. Repairing a product can also bring moral satisfaction. Everyone determines for themselves whether it is worth the time and effort. Or maybe it’s better to immediately take the more expensive option? After all, even Chinese garlands for a high price are much better quality than their cheap “compatriots”. The choice is yours!
Despite the fact that the No. 1 electrical parameter for an LED is the rated current, it is often necessary to know the voltage at its terminals for calculations. The term “LED voltage” refers to the potential difference across the pn junction in the open state. It is a reference parameter and, together with other characteristics, is indicated in the passport for the semiconductor device. 3, 9 or 12 volts... Often you come across specimens about which nothing is known. So how do you find out the voltage drop across an LED?
An excellent clue in this case is the color of the glow, the external shape and dimensions of the semiconductor device. If the LED housing is made of a transparent compound, then its color remains a mystery, which a multimeter will help you solve. To do this, turn the switch of the digital tester to the “check for break” position and touch the LED terminals one by one with the probes. A healthy element in forward bias will exhibit a slight glow from the crystal. Thus, we can draw a conclusion not only about the color of the glow, but also about the performance of the semiconductor device. There are other ways to test emitting diodes, which are described in detail in.
Light-emitting diodes of different colors are made from different semiconductor materials. It is the chemical composition of the semiconductor that largely determines the supply voltage of the LEDs, or more precisely, the voltage drop across the pn junction. Due to the fact that dozens of chemical compounds are used in the production of crystals, there is no exact voltage for all LEDs of the same color. However, there is a certain range of values, which are often sufficient to carry out preliminary calculations of the elements of an electronic circuit. On the one hand, the size and appearance of the housing do not affect the forward voltage of the LED. But in other way. through the lens you can see the number of emitting crystals that can be connected in series. The phosphor layer in SMD LEDs can hide an entire chain of crystals. A striking example is the miniature multi-chip LEDs from the company, the voltage drop of which often significantly exceeds 3 volts.
In recent years, white SMD LEDs have appeared, the housing of which contains 3 crystals connected in series. They can often be found in Chinese 220 volt LED lamps. Naturally, it will not be possible to verify the serviceability of the LED crystals in such a lamp using a multimeter. The standard tester battery produces 9 V, and the minimum response voltage of a three-crystal white light-emitting diode is 9.6 V. There is also a two-crystal modification with a response threshold of 6 volts.
You can find out all the technical characteristics of the LED from the Internet. To do this, you need to download a datasheet for a model that is similar in appearance, necessarily with the same glow color, check the passport dimensions with the actual ones, and write down the nominal values of the current and voltage drop. It should be borne in mind that this technique is very approximate, since 20 mA and 150 mA LEDs with a voltage spread of up to 0.5 volts can be manufactured in the same housing.
The most accurate data on the forward voltage drop across an LED can be obtained through practical measurements. To do this, you will need an adjustable DC power supply (PSU) with a voltage from 0 to 12 volts, a voltmeter or multimeter and a 510 Ohm resistor (more is possible). The laboratory circuit for testing is shown in the figure. 
Everything is simple here: a resistor limits the current, and a voltmeter monitors the forward voltage of the LED. Smoothly increasing the voltage from the power source, observe the increase in readings on the voltmeter. When the triggering threshold is reached, the LED will begin to emit light. At some point, the brightness will reach the nominal value, and the voltmeter readings will stop increasing sharply. This means that the p-n junction is open, and a further increase in voltage from the output of the power supply will be applied only to the resistor.
The current reading on the screen will be the nominal forward voltage of the LED. If you continue to increase the power supply to the circuit, then only the current through the semiconductor will increase, and the potential difference across it will change by no more than 0.1-0.2 volts. Excessive current will lead to overheating of the crystal and electrical breakdown of the p-n junction.
If the operating voltage on the LED is set to about 1.9 volts, but there is no glow, then the infrared diode may be tested. To verify this, you need to direct the radiation flow to the turned on phone camera. A white spot should appear on the screen.
In the absence of an regulated power supply, you can use a 9 V “crown”. You can also use a 3 or 9 volt network adapter in the measurements, which produces a rectified stabilized voltage, and recalculate the value of the resistor.
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