The calculation for an LED is quite simple, quick and does not contain anything “military”, only Ohm’s law. Although there are many online calculators on the World Wide Web that help determine various parameters, in my personal opinion, it is better to figure it out yourself and understand the physics of the process than to blindly use such calculators.
The most common example is connecting an LED to a 5 V power source, such as a computer USB port. The second example is a connection to a car battery, the nominal voltage of which is 12 V. If a semiconductor device is directly connected to such a power source, the latter will simply fail under the influence of a flowing current that exceeds the permissible value - thermal breakdown of the semiconductor crystal will occur. Therefore, it is necessary to limit the amount of current.
For the purpose of better clarity, let’s take two types of LEDs with the most common characteristics:
voltage:
U VD 1 = 2.2 V;
U VD 2 = 3.5 V;
current:
I VD 1 = 0.01 A;
I VD 2 = 0.02 A.
Calculation of a resistor for an LED
Let's determine the resistance R 1.5 for VD 1 at Uip = 5 V.
To calculate the resistance value, according to Ohm's law, you need to know the current and voltage:
R=U/I.
We know the magnitude of the current flowing in the circuit, including through VD, from the given condition I VD 1 = 0.01 A, therefore the voltage drop across R 1.5 should be determined. It is equal to the difference between the supplied Uip = 5 V and the voltage drop across the LED U VD 1 = 2.2 V:
Now we find R 1.5
From the standard series of resistances, we select the closest one in the direction of increase, so we take R 1.5 = 300 Ohms.
In the same way, let's calculate R for VD 2:
Let's carry out similar calculations with a value of Uip = 12 V.
We accept R 1.12 = 1000 Ohm = 1 kOhm.
We take R 2.12 = 430 Ohm.
For convenience, we write down the obtained resistance values of all resistors:
It should be noted that the resistance selected from the standard range exceeds the calculated one, so the current in the circuit will be significantly reduced. However, this decrease can be neglected due to its small value.
Calculation of power dissipation
Identifying resistance is only half the battle. The resistor is also characterized important parameter, which is called dissipation power P, is the power that it can withstand for a long time without overheating above a certain temperature. It depends on the squared current, since the latter flowing in the circuit causes heating of its elements.
P = I 2 R.
Visually, a resistor with a higher P is larger in size. 
LEDs are modern, economical, reliable radioelements used for light indication. We think everyone knows about this! It is based on this experience that there is such a high desire to use LEDs for designing a wide variety of electrical circuits, both in consumer electronics and for cars. But here certain difficulties arise. After all, the most common LEDs have a supply voltage of 3...3.3 volts, and the on-board voltage of the car is nominally 12 volts, and sometimes rises to 14 volts. Of course, a logical assumption arises here that in order to connect the LEDs to the 12 volt network of the machine, it will be necessary to lower the voltage. The article will be devoted to this topic, connecting the LED to the vehicle’s on-board network and reducing the voltage.
Two basic principles on how you can connect an LED to 12 volts or reduce the voltage at the load
Before moving on to specific schemes and their descriptions, I would like to talk about two fundamentally different, but possible options connecting the LED to a 12 volt network.
The first is when the voltage drops due to the fact that an additional consumer resistance is connected in series with the LED, which is a voltage stabilizer microcircuit. In this case, a certain part of the voltage is lost in the microcircuit, turning into heat. This means that the second, remaining one goes directly to our consumer - the LED. Because of this, it does not burn out, since not all of the total voltage passes through it, but only a part. The advantage of using a microcircuit is the fact that it is capable of automatically maintaining a given voltage. However, there are also disadvantages. You will not be able to reduce the voltage below the level for which it is designed. Second. Since the microcircuit has a certain efficiency, the drop relative to the input and output will differ by 1-1.5 volts downwards. Also, to use the microcircuit, you will need to use a good dissipative radiator installed on it. After all, in essence, the heat generated by the microcircuit is the loss we have not claimed. That is, what we cut off from a larger potential in order to get a smaller one.
The second option for powering the LED is when the voltage is limited by a resistor. It's akin to having a big water pipe would take it and narrow it down. In this case, the flow (flow and pressure) would decrease significantly. In this case, only part of the voltage reaches the LED. This means that he can also work without the danger of being burned. The disadvantage of using a resistor is that it also has its own efficiency, that is, it also wastes unclaimed voltage into heat. In this case, it can be difficult to install the resistor on the heatsink. As a result, it is not always suitable for inclusion in a circuit. Another disadvantage is the fact that the resistor does not automatically maintain the voltage within a given limit. When the voltage in the common circuit drops, it will supply the same lower voltage to the LED. Accordingly, the opposite situation will occur when the voltage in the common circuit increases.
Of course, both options are not ideal, since when operating from portable energy sources, each of them will spend part of the useful energy on heat. And this is relevant! But what to do, this is the principle of their work. In this case, the power source will spend part of its energy not on useful action, but on heat. Here the panacea is to use pulse-width modulation, but this significantly complicates the circuit... Therefore, we will still focus on the first two options, which we will consider in practice.
Connecting an LED through a resistance to 12 volts in a car (via a resistor)
Let's start, as in the paragraph above, with the option of connecting the LED to a voltage of 12 volts through a resistor. In order for you to better understand how the voltage drop occurs, we will present several options. When 3 LEDs are connected to 12 volts, 2 and 1.
Connecting 1 LED through a resistance to 12 volts in a car (via a resistor)
So we have an LED. Its supply voltage is 3.3 volts. That is, if we took a 3.3 volt power source and connected an LED to it, then everything would be great. But in our case, there is an increased voltage, which is not difficult to calculate using the formula. 14.5-3.3= 11.2 volts. That is, we need to initially reduce the voltage by 11.2 volts, and then only apply voltage to the LED. In order for us to calculate the resistance, we need to know what current flows in the circuit, that is, the current consumed by the LED. On average, this is about 0.02 A. If you wish, you can look rated current in the datasheet to the LED. As a result, according to Ohm's law, it turns out. R=11.2/0.02=560 Ohm. The resistance of the resistor is calculated. Well, drawing a diagram is even easier.
The resistor power is calculated using the formula P=UI=11.2*0.02=0.224 W. We take the closest one according to the standard series.
Connecting 2 LEDs through a resistance to 12 volts in a car (via a resistor)
By analogy with the previous example, everything is calculated the same way, but with one condition. Since there are already two LEDs, the voltage drop across them will be 6.6 volts, and the remaining 14.5-6.6 = 7.9 volts will remain for the resistor. Based on this, the scheme will be as follows.
Since the current in the circuit has not changed, the power of the resistor remains unchanged.
Connecting 3 LEDs through a resistance to 12 volts in a car (via a resistor)
And one more option, when almost all the voltage is extinguished by LEDs. This means that the resistor will be even smaller in value. Total 240 ohms. A diagram for connecting 3 LEDs to the machine's on-board network is attached.
Finally, all we have to say is that the calculations used a voltage of not 12, but 14.5 volts. It is this increased voltage that usually occurs in the electrical network of the car when it is started.
It is also not difficult to estimate that when connecting 4 LEDs, you will not need to use any resistor at all, because each LED will have 3.6 volts, which is quite acceptable.
Connecting an LED through a voltage stabilizer to 12 volts in a car (via a microcircuit)
Now let's move on to a stabilized 12-volt LED power supply circuit. Here, as we have already said, there is a circuit that regulates its own internal resistance. Thus, the LED will be powered steadily, regardless of voltage surges in the on-board network. Unfortunately, the disadvantage of using the microcircuit is the fact that the minimum stabilized voltage that can be achieved will be 5 volts. It is with this voltage that you can find the most widely known microcircuits - stabilizers KR142 EH 5B or foreign analogue L7805 or L7805CV. Here the only difference is in the manufacturer and the rated operating current from 1 to 1.5 A.
So, the remaining voltage from 5 to 3.3 volts will have to be extinguished according to the same example as in previous cases, that is, by using a resistor. However, reducing the voltage with a resistor by 1.7 volts is no longer as critical as by 8-9 volts. Voltage stabilization in this case will still be observed! Here is a wiring diagram for the stabilizer chip.
As you can see, it is very simple. Anyone can implement it. No more difficult than soldering the same resistor. The only condition is the installation of a radiator that will remove heat from the microcircuit. It is necessary to install it. The diagram says that the microcircuit can power 10 LED circuits, but in fact this parameter is underestimated. In fact, if about 0.02 A passes through the LED, then it can power up to 50 LEDs. If you need to provide power to a larger quantity, then use a second identical independent circuit. Using two microcircuits connected in parallel is not correct. Since their characteristics are slightly different from each other, due to individual characteristics. As a result, one of the microcircuits will have a chance to burn out much faster, since its operating modes will be different - overestimated.
We have already talked about the use of similar microcircuits in the article “5-volt charger in a car.” By the way, if you still decide to power the LED using PWM, although it’s hardly worth it, then this article will also reveal to you all the secrets of implementing such a project.
To summarize about connecting an LED to 12 volts in a car with your own hands
To sum up, about connecting an LED to a 12 volt network, we can say about the simplicity of the circuit design. Both with the case where a resistor is used, and with a microcircuit - stabilizer. All this is easy and simple. At least this is the simplest thing you can come across in electronics. So everyone should be able to connect an LED to the car’s on-board 12-volt network, for sure. If this is too tough, then you shouldn’t take on something more complex at all.
Video on connecting an LED to a network in a car
And now, to make it easier for you to estimate what resistance value you need and what power for your specific case, you can use the resistor selection calculator
Every year, the popularity of LED lighting, which is organized not using light bulbs, but special strips, is growing in the world. These are special lighting products that have many advantages over other types of lamps. But in order for them to work efficiently and for a long time, LED strips must be connected to the power supply through a special unit.
It is worth noting that not every power supply unit (PSU) sold will be suitable for your LED strip. Therefore, in order for its operation to proceed as it should, in this situation it is necessary to calculate the required power consumption that the power supply connected to the tape must have. This article will help you understand this issue.
Features of the product and why an adapter is needed
The popularity of LED products (strips and light bulbs) led to the appearance on the market lighting fixtures a wide range of such products. Moreover, tapes do not occupy the last place in this matter. Everything is connected with the high popularity of LED strips, which have the following advantages:
- easy to install on any surface, as they have a self-adhesive base;
- have a variety of glow colors;
- can be controlled by a remote control when connected to a controller circuit;
- the ability to extend the product as much as needed depending on the length of the backlight;
- low power consumption;
Note! Such products consume the minimum amount of electricity.
- long service period.
The biggest problem that can arise with this type of LED products is right choice and connecting the power supply. Moreover, it is not enough to simply calculate what kind of power supply you will need. Connection rules must be followed. Only if the calculations and connections were correct, you can admire the bright and colorful glow of your new LED backlight.
The need for a power supply for LED strips is based on the fact that these products are low-voltage. They are usually rated for 12 or 24 volts. At the same time, the power supply network through which current flows in our houses and apartments has 220 volts. As a result of this mismatch, an adapter (power supply) is required that will allow the current coming from the network to correspond to the required voltage parameters. Only with the help of a power supply can you change the current to the required parameters applicable for this type of LED product.
Note! If the power supplied by the power supply is not suitable, then the current coming from the network may cause the LEDs to burn out.
Therefore, when choosing a power supply, you should find out how much its power should be for an LED of a certain length.
Selecting a converter: important nuances of choice
Waterproof converter
When selecting a unit for a given type of lighting product, you should rely on the following indicators:
- available supply voltage: 12 or 24 volts;
- the total power consumed by the purchased product;
- the need to protect the unit from high humidity.
Note! If you are purchasing lighting products for installation in rooms with a humid climate (bathroom, swimming pool, kitchen, loggia or balcony), the converter must be protected from moisture.
In addition, the choice of block should be made based on your own financial capabilities. The better and higher quality the block is, the more expensive it will cost. But remember that a low-quality converter, passing current of different voltages through itself, can quickly fail.
The most important parameter for choosing a power supply is its power. Its calculation is based on the length of the product (how many meters it is), as well as other parameters, which we will talk about in the next section.
Converter power calculation parameters
The converter, which changes the current characteristic, is an integral part of the connection diagram for this lighting product. If it is not there, the current will immediately damage the LED, making it unfit for further use. Moreover, the product itself may have different voltages and lengths (each meter has great importance). Therefore, each individual situation requires its own power calculation.
Note! You can find out which power supply is needed for a particular LED strip from a special table. This table is shown below.
Table for choosing a power supply
Most often, people purchase 12-volt products, since they are easier to find and are somewhat cheaper.
Power for a power supply is the main parameter. Therefore, to ensure that the current does not lead to burnout of the product, the calculation should be carried out correctly. And for this you need to know the following parameters:
- length of the lighting product;
Note! Since LED can easily increase its length, each meter here affects the total energy consumption. Each additional meter will increase this indicator.
- how many diodes are there (per meter). The table above shows how many LEDs each meter of a particular type of strip has.
Placement of diodes on the base
These two parameters (length and number of LEDs for each meter) are the basis for calculating the power of the power supply. For example, you want to connect 2 five-meter SMD 5050 RGB strips to the converter. This means that the table shows that there are 30 LEDs per meter of such a product, and the length of the LED itself is two meters.
A detailed example of calculating the required indicator
Power is a parameter whose unit of measurement is watt. To calculate it for a specific LED strip, you need to carry out the following algorithm:
- First you need to determine how much energy one meter consumes. This parameter can be easily determined from the table above. For example, for SMD5050 tapes per meter this figure will be 7.2 watts;
- Then you can easily calculate the power that the LED consumes in total. To do this, you just need to multiply the indicator for one meter by the length. For example, you want to make a backlight from a 10-meter SMD5050 model. In this situation, we multiply 7.2 watts by 10 and get 72 watts.
This is the power, 72 watts, that will be consumed by a ten-meter SMD5050. But here it follows the fate that a certain number of watts will be spent on converting the current. Therefore, it is important to choose a converter with a uniquely large watt rating so that there is a small margin. It will compensate for possible losses and maintain the performance of the lighting products connected to it at the proper level.
Note! The minimum power reserve (watts) that the power supply must have should be 30% of the final figure of your calculations. In our case, 20% should be calculated from 72 watts.
Thus, the final figure of your calculations for products with a total consumption of 72 watts, taking into account 30%, will already be 93.4 watts. You can find data that you should take 20-25% as a reserve. Which calculation option you ultimately use depends on you and the proposed range of power supplies.
Types of converters for LED products
Now all that remains is to go to the store or market for the converter we need. You can choose a rounded value, but one that is as close as possible to the final figure of your calculations.
Conclusion
Despite the large number of advantages of LED products, when using strips you need to be careful in calculating the power for the power supply used. If an error has crept into the calculations, then when the product is connected to the network, it may simply burn out. The operation of LED strips will be of high quality only with a correctly selected converter.
How to select and install volume sensors for automatic control light
Homemade adjustable transistor blocks power supplies: assembly, practical application
In circuits with LEDs, they are necessarily used for limitation. They protect against burnout and premature failure of LED elements. The main problem is the accurate selection of the required parameters, which is why the resistance calculator for LEDs is widely popular among specialists. To obtain the most accurate results, you will need data on the voltage of the power source, the forward voltage of the LED itself and its calculated current, as well as the connection diagram and number of elements.
How to calculate the resistance of current limiting resistors
In the simplest case, when the necessary initial data is missing, the value of the forward voltage of the LEDs can be determined with high accuracy by the color of the glow. Typical data on this physical phenomenon are summarized in a table.
Many LEDs have a current rating of 20 mA. There are other types of elements in which this parameter can reach a value of 150 mA and higher. Therefore, in order to accurately determine the rated current, data on technical specifications LED. If the necessary information is completely missing, the rated current of the element is conventionally taken to be 10 mA, and the forward voltage is 1.5-2 volts.
The number of current-limiting resistors directly depends on the connection diagram of the semiconductor elements. For example, if you use, you can completely get by with one resistor, since the current strength at all points will be the same.
In the case of a parallel connection, one quenching resistor will no longer be enough. This is due to the fact that the characteristics of LEDs cannot be exactly the same. They all have their own resistances and the same different current consumption. That is, an element with minimal resistance consumes large quantity current and may fail prematurely.
Consequently, if at least one LED connected in parallel fails, this will lead to increased voltage for which the remaining elements are not designed. As a result, they will also stop working. Therefore, with a parallel connection, each LED is provided with its own resistor.
All these features are taken into account in the online calculator. The calculations are based on the formula for determining the resistance: R = Uquenching/ILED. In turn, Uquenching = Upower - ULED.
The operation of an LED is based on the emission of light quanta that occurs when current flows through it. Depending on this, the brightness of the element changes. At low current it glows dimly, but at high current it flares up and burns out. The easiest way to limit the current flowing through it is to use a resistance. It is not difficult to correctly calculate the resistor, but you should remember that it only limits, but does not stabilize the current.
Operating principle and properties
LED is a device having the ability to emit light. On printed circuit boards and in diagrams it is denoted by the Latin letters LED (Light Emitting Diode), which translated means “light emitting diode”. Physically, it is a crystal placed in a housing. Classically, it is considered a cylinder, one side of which has a convex round shape, which is a hemispherical lens, and the other has a flat base, and the leads are located on it.
With the development of solid-state technologies and reduction technological process The industry began to produce SMD diodes intended for surface mounting. Despite this, the physical operating principle of the LED has not changed and is the same for any type and color of the device.
The manufacturing process of a radiation device can be described as follows. At the first stage, the crystal is grown. This happens by placing an artificially made sapphire in a chamber filled with a gaseous mixture. This gas contains doping additives and a semiconductor. When the chamber is heated, the resulting substance is deposited onto the plate, and the thickness of such a layer does not exceed several microns. After the deposition process is completed by sputtering, contact pads are formed and this entire structure is placed in the housing.
Due to the nature of production, there are no LEDs that are identical in parameters and characteristics. Therefore, although manufacturers try to sort out devices that are similar in value, often in one batch there are products that differ in color temperature and operating current.
Radio element device
A light emitting diode (LED) is a semiconductor radio element whose operation is based on the properties of the electron-hole junction. When a current passes through it in the forward direction, recombination processes occur at the interface of the two materials, accompanied by radiation in the visible spectrum.
For a very long time, the industry could not produce a blue LED, which is why it was impossible to obtain a white light emitter. Only in 1990, researchers at the Japanese corporation Nichia Chemical Industries invented a technology for producing a crystal that emits light in the blue spectrum. This automatically allowed, by mixing green, red and of blue color get white.
The radiation process is based on the release of energy during the recombination of charges in the electron-hole transition zone. It is formed by contact of two semiconductor materials with different conductivities. As a result of injection, transition of minority charge carriers, a blocking layer is formed.
On the side of the material with n-conductivity, a barrier of holes appears, and on the side with p-conductivity, a barrier of electrons appears. There is a balance. When a forward bias voltage is applied, there is a massive movement of charges into the band gap on both sides. As a result, they collide and energy is released in the form of light emission.
This light may or may not be visible to the human eye. This depends on the composition of the semiconductor, the amount of impurities, and the band gap. Therefore, the visible spectrum is achieved by manufacturing multilayer semiconductor structures.
LED characteristics
The color of the glow depends on the type of semiconductor and the degree of its doping, which determines the bandgap width zones p-n transition. The service life of LEDs primarily depends on temperature conditions his works. The higher the heating of the device, the faster its aging occurs. And the temperature, in turn, is related to the current passing through the LED. The lower the power of the light source, the longer its service life. Aging is expressed as a decrease in the brightness of a light fixture. Therefore, it is so important to choose the right resistance for the LED.
The main characteristics of LED diodes include:
Connection methods
For trouble-free operation of the LED, the operating current is very important. Incorrect connection of radiation sources or a significant spread in their parameters when working together will lead to an excess of the current flowing through them and further burnout of the devices. This is due to an increase in temperature, due to which the LED crystal is simply deformed, and p-n junction will break through. Therefore, it is so important to limit the amount of current supplied to the light source, that is, limit the supply voltage.
The easiest way to do this is to use a resistor connected in series to the emitter circuit. An ordinary resistor is used in this capacity, but it must have a certain value. Its large value will not be able to provide the required potential difference for the occurrence of the recombination process, and a smaller value will burn it. In this case, you need not only to know how to calculate the resistance for an LED, but also to understand how to install it correctly, especially if the circuit is saturated with radio elements.
An electrical circuit can use one or several LEDs. In this case, there are three schemes for their inclusion:
- single;
- sequential;
- parallel.
Single element
When only one LED is used in an electrical circuit, then one resistor is placed in series with it. As a result of such a connection, the total voltage applied to this circuit will be equal to the sum of the potential difference drops across each element of the circuit. If we designate these losses on the resistor as Ur, and on the LED as Us, then the total voltage of the EMF source will be equal to: Uo = Ur + Us.
Paraphrasing Ohm's law for the network section I = U / R, the formula is obtained: U = I * R. Substituting the resulting expression into the formula for finding the total voltage, we get:
Uo = IrRr + IsRs, where
- Ir is the current flowing through the resistor, A.
- Rr - calculated resistance of the resistor, Ohm.
- Is is the current passing through the LED, A.
- Rs - internal impedance of the LED, Ohm.
The value of Rs varies depending on the operating conditions of the radiation source and its value depends on the current strength and potential difference. This dependence can be seen by studying the current-voltage characteristic of the diode. At the initial stage, there is a smooth increase in current, and Rs has a high value. After this, the impedance drops sharply and the current rapidly increases even with a slight increase in voltage.
If you combine the formulas, you get the following expression:
Rr = (Uo - Us) / Io, Ohm
It is taken into account that the current strength flowing in the series circuit of a section of the circuit is the same at any point, that is, Io = Ir = Is. This expression is also suitable for connecting LEDs in series, because it also uses only one resistor for the entire circuit.
Thus, to find the required resistance, it remains to find out the value of Us. The value of the voltage drop across the LED is a reference value and it is different for each radio element. To obtain data, you will need to use the datasheet on the device. A datasheet is a set of information sheets that contain comprehensive information about the parameters, operating modes, as well as circuit diagrams for switching on a radio element. It is produced by the product manufacturer.
Parallel circuit
In a parallel connection, radioelements contact each other at two points - nodes. For this type of circuit, two rules are valid: the current strength entering the node is equal to the sum of the current strengths emanating from the node, and the potential difference at all points of the nodes is the same. Based on these definitions, we can conclude that in the case of parallel connection of LEDs, the desired resistor, located at the beginning of the node, is found according to the formula: Rr = Uo / Is1+In, Ohm, where:
- Uo is the potential difference applied to the nodes.
- Is1 is the current flowing through the first LED.
- In is the current passing through the nth LED.
But such a circuit with a common resistance located in front of the parallel connection of the LEDs is not used. This is due to the fact that if one emitter burns out, according to the law, the current entering the node will remain unchanged. This means that it will be distributed among the remaining working elements and at the same time more current will flow through them. As a result, a chain reaction will occur and all semiconductor emitters will eventually burn out.
Therefore, it would be correct to use your own resistor for each parallel branch with its own LED and calculate the resistor for the LED separately for each arm. This approach is also advantageous in that the circuit can use radioelements with different characteristics.
The calculation of the resistance of each arm occurs similarly to a single connection: Rn = (Uo - Us) / In, Ohm, where:
- Rn is the required resistance of the nth branch.
- Uo - Us - voltage drop difference.
- In is the current through the nth LED.
Calculation example
Let it go electrical diagram power is supplied from the source DC voltage, equal to 32 volts. In this circuit there are two brand LEDs connected in parallel to each other: Cree C503B-RAS and Cree XM-L T6. To calculate the required impedance, you will need to find out the typical voltage drop across these LEDs from the datasheet. So, for the first it is 2.1 V at a current of 0.2, and for the second it is 2.9 V at the same current value.
Substituting these values into the formula for a series circuit, you get the following result:
- R1 =(U0-Us1)/ I=(32−2.1)/0.2 = 21.5 Ohm.
- R2 = (U0-Us2)/ I=(32−2.9)/0.2 = 17.5 Ohm.
The closest values are selected from the standard series. They will be: R1 = 22 Ohms and R2 = 18 Ohms. If desired, you can also calculate the power dissipated by resistors using the formula: P = I*I*U. For the found resistors it will be P= 0.001 W.
Browser-based online calculators
At large quantities LEDs in the circuit, calculating the resistance for each is a rather tedious process, especially since you can make a mistake. Therefore, the easiest way to make calculations is to use online calculators.
They are a program written to run in a browser. On the Internet you can find many such calculators for LEDs., but the principle of operation is the same. You will need to enter reference data in the provided forms, select a connection diagram and click the “Result” or “Calculation” button. Then all that remains is to wait for an answer.
By recalculating it manually, you can check it, but there will be little point in this, since the programs use similar formulas when calculating.