Regular readers are often interested in how to properly power LEDs to maximize their service life. This is especially true for LEDs of unknown manufacture with poor technical characteristics or overestimated ones.
It is impossible to determine quality by appearance and parameters. We often have to tell you how to calculate a power supply for LEDs, which one is better to buy or make yourself. Basically, I recommend buying a ready-made one; any circuit after assembly requires testing and adjustment.
- 1. Basic types
- 2. How to make the calculation
- 3. Calculator for calculation
- 4. Connection in the car
- 5. LED supply voltage
- 6. Connection from 12V
- 7. Connection from 1.5V
- 8. How to calculate the driver
- 9. Low voltage from 9V to 50V
- 10. Built-in driver, hit 2016
- 11. Characteristics
Main types
A LED is a semiconductor electronic element with low internal resistance. If you apply a stabilized voltage to it, for example 3V, a large current will flow through it, for example 4 Amperes, instead of the required 1A. The power on it will be 12W, and the thin conductors that connect the crystal will burn out. Conductors are clearly visible on color and RGB diodes, because they do not have a yellow phosphor.
If the power supply for LEDs is 12V with a stabilized voltage, then a resistor is installed in series to limit the current. The disadvantage of this connection will be higher energy consumption, the resistor also consumes some energy. For 1.5V LED rechargeable flashlights, it is irrational to use such a circuit. The number of volts on the battery decreases quickly, and the brightness will decrease accordingly. And without increasing it to at least 3V, the diode will not work.
Specialized LED drivers based on PWM controllers do not have these disadvantages. When the voltage changes, the current remains constant.
How to make a calculation
- rated power consumption or desired;
- drop voltage.
The total energy consumption of the connected electrical circuit should not exceed the power of the unit.
The voltage drop depends on how much light the ice chip emits. I recommend buying branded LEDs, such as Bridgelux, since their range of parameters is minimal. They are guaranteed to keep the declared characteristics and have a reserve for them. If you buy at a Chinese market, such as Aliexpress, then don’t expect a miracle, 90% of the time they will deceive you and send you junk with parameters 2-5 times worse. This was checked many times by my colleagues, who ordered inexpensive LED 5730 sometimes 10 times. They received SMD5730 at 0.1W, instead of 0.5W. This was determined by the current-voltage characteristic.
In addition, the cheap ones have a very wide range of parameters. To determine this at home with your own hands, connect 5-10 of them in series. I adjust the number of volts until they glow slightly. You will see that some shine brighter, others are barely noticeable. Therefore, some will heat up more in the nominal operating mode, others less. The power on them will be different, so the most loaded ones will fail before the rest.
Calculator for calculation
The calculator takes into account 4 parameters:
- number of volts at the output;
- voltage reduction on one LED;
- rated operating current;
- number of LEDs in the circuit.
Connection in the car
When the engine is running, there is an average of 13.5V - 14.5V, and when the engine is off, 12V - 12.5V. Special requirements when plugged into a car cigarette lighter or on-board network. Short-term surges can be up to 30V. If you use a current-limiting resistor, then the current increases in direct proportion to the increase in the LED supply voltage. For this reason, it is better to install a stabilizer on the microcircuit.
The disadvantage of using it in a car may be the appearance of interference on the radio in the VHF range. The PWM controller operates at high frequencies and will interfere with your radio. You can try replacing it with another or linear type. Sometimes shielding with metal and placing it away from the car's head unit helps.
LED supply voltage
From the tables it can be seen that for low-power ones at 1W, 3W this indicator is 2B for red, yellow, orange. For white, blue, green it is from 3.2V to 3.4V. For powerful ones from 7V to 34V. These numbers will have to be used for calculations.
Table for LED at 1W, 3W, 5W
Table for high-power LEDs 10W, 20W, 30W, 50W, 100W
Connection from 12V
One of the most common voltages is 12 Volts, they are present in household appliances, cars and automotive electronics. Using 12V you can fully connect 3 LED diodes. An example is a 12V LED strip, in which 3 pieces and a resistor are connected in series.
Example on diode 1W, its rated current is 300mA.
- If one LED drops 3.2V, then for 3 pieces it will be 9.6V;
- the resistor will have 12V – 9.6V = 2.4V;
- 2.4 / 0.3 = 8 Ohms nominal required resistance;
- 2.4 * 0.3 = 0.72W will be dissipated by the resistor;
- 1W + 1W + 1W + 0.72 = 3.72W total power consumption of the entire circuit.
Similarly, you can calculate for another number of elements in the circuit.
Connection from 1.5V
The power source for the LEDs can be a simple 1.5V AA battery. An LED diode usually requires a minimum of 3V; there is no way to do this without a stabilizer. These specialized LED drivers are used in hand-held flashlights on the Cree Q5 and Cree XML T6. A miniature microcircuit increases the number of volts to 3V and stabilizes 700mA. Switching on from 1.5 volts using a current-limiting resistor is impossible. If we use two 1.5 volt batteries, connecting them in series, we get 3V. But the batteries run out quite quickly, and the brightness will drop even faster. At 2.5V there will still be a lot of capacity left in the batteries, but the diode will almost go out. And the LED driver will maintain the nominal brightness even at 1V.
I usually order such modules on Aliexpress, the Chinese cost 50-100 rubles, in Russia they are a bit expensive.
How to calculate the driver
- draw up a connection diagram on paper;
- if the driver is Chinese, then it is advisable to check whether it can withstand the declared power or not;
- keep in mind that different colors (blue, red, green) have different volt drops;
- the total power should not be higher than that of the current source.
Draw a connection diagram on which you will distribute the elements if they are connected not just in series, but in combination with a parallel connection.
On a Chinese power supply from an unknown manufacturer, the power may be significantly lower. They easily indicate the maximum peak power, and not the rated long-term power. It is more difficult to check; you need to load the power supply to the maximum and measure the parameters.
For the third point, use the example tables for 1W,3W, 5W, 10W, 20W, 30W, 50W, 100W, which are given above. But trust more in the characteristics that the seller gave you. For single-chip ones there are 3V, 6V, 12V.
If the total power consumption of the circuit exceeds the rated power of the power source, the current will drop and heating will increase. It will recover to normal levels if the load is reduced.
For LED strips, the calculation is very simple. Measure the number of watts per meter and multiply by the number of meters. Just measure, in most cases the power is overestimated and instead of 14.4 W/m you will get 7 W/m. All too often disappointed customers come to me with this problem.
Low voltage from 9V to 50V
I’ll briefly tell you what I use to switch on 12V, 19V, 24V units and to connect to 12V automobiles.
Most often I buy ready-made modules on PWM chips:
- there are boosters, for example, 12V at the input, 22V at the output;
- step-down, for example from 24V to 17V.
Not everyone wants to spend a lot of money on buying a ready-made spotlight for a car, an LED lamp, or order a ready-made driver. Therefore, they turn to me to assemble something decent from available components. The price of such modules starts from 50 rubles to 300 rubles for a 5A model with a radiator. I buy several pieces in advance, they sell out quickly.
The most popular option is the linear IC, a simple, reliable, outdated one.
Models based on LM2596 are very popular, but it is already outdated and I advise you to pay attention to a more modern one with good efficiency. Such blocks have from 1 to 3 tuning resistances, which can be used to adjust any parameters up to 30V and up to 5A.
Built-in driver, hit 2016
At the beginning of 2016, LED modules and COB diodes with an integrated driver began to gain popularity. They are connected directly to a 220V network, ideal for assembling lighting equipment with your own hands. All elements are located on one heat-conducting plate. PWM controllers are miniature, thanks to good contact with the cooling system. We have not yet tested the reliability and stability; the first reviews will appear after at least six months of use. I have already ordered the cheapest and most affordable COB model at 50W. To find these on the Aliexpress Chinese bazaar, enter “integrated led driver” in the search.
Characteristics
A global problem is counterfeiting of Cree and Philips LEDs on an industrial scale. The Chinese have entire enterprises for this; they copy 95-99% of them externally; it is impossible for an ordinary buyer to tell the difference. The worst thing is when such a fake is sold to you under the guise of the original Cree T6. You will connect the fake one according to the technical specifications of the original one. A fake has characteristics that are on average 30% worse. Less luminous flux, lower maximum operating temperature, lower power consumption. You will not find out about the deception very soon; it will work about 5-10 times less than the real one, especially at double current.
Recently I measured the luminous flux of my flashlights on the left Cree made by LatticeBright. I took out the entire board with the driver and placed it in a photometric ball. The result was 180-200 lumens, the original had 280-300 lumens. Without serious equipment, which is mainly found in laboratories, you will not be able to measure and therefore find out the truth.
Sometimes you come across overclocked diodes, the current strength of which is 30% -60% higher than the rated one, and, accordingly, the power. An unscrupulous manufacturer, especially a basement Chinese one, takes advantage of the fact that service life is difficult to measure in hours. After all, no one records the time worked, and when a lamp or LED spotlight fails, the seller can no longer be found. And it’s pointless to search; the warranty period for such products is always shorter than the service life.
There is an LED lamp consisting of 50 pieces of OSRAM GW PUSRA1.PM LEDs connected in series. The operating current of the lamp is 700 mA. The lamp will be operated in the temperature range from -30 to +50 degrees Celsius.
Necessary: select a power source for this LED lamp.
Let's look at the characteristics of the GW PUSRA1.PM LEDs that the manufacturer gives us:
From the documentation it can be seen that the typical voltage drop across one LED is 2.80 V at a current of 700 mA.
Therefore, the typical voltage drop of an LED luminaire (50 LEDs connected in series) is 2.80 X 50 = 140 V.
In the production of LEDs, there is an important problem - repeatability of parameters. The most high-tech production does not make it possible to produce devices with the same specified operating parameters.
To take this into account in the calculations, look in the technical documentation to find out what the minimum and maximum voltage drop across the LED is at a current of 700mA. The manufacturer indicated the maximum voltage drop: 3.20 V, minimum: 2.70 V.
Taking these deviations into account, the calculated voltage drops across the LED lamp will be:
minimum: 2.70 x 50 = 135V
maximum: 3.20 x 50 = 160V
We obtained an intermediate operating range of LED lamp voltage drop of 135…160 V at an operating current of 700 mA.
When calculating the intermediate operating voltage drop range, we did not take into account the operating temperature range of the LED lamp. This range is determined by the planned climatic conditions of operation of the LED lamp (from -30 to +50 degrees Celsius).
Let's look at the graph of the voltage drop across the LED versus temperature: 
The graph shows that the lower the temperature, the greater the voltage drop across the LED.
The increase in voltage drop across the LED at -30 degrees relative to 85 degrees will be approximately 0.2 V
The increase in voltage drop across the LED at +50 degrees relative to 85 degrees will be approximately 0.05 V
Therefore, the voltage drops across the LED lamp, taking into account the temperature range, will be:
from (2.7 + 0.05) x 50 pcs. = 137.5 V to (3.2 +0.2) x 50 pcs. = 170 V
That is, with a typical voltage drop across the lamp of 140 V, the calculated voltage drop range will be: 137.5 ... 170 V
Note: in a real lamp, the temperature of the LEDs due to heating may exceed the calculated +50 degrees Celsius. Strictly speaking, this can lead to a decrease in the voltage drop across the LEDs and, accordingly, a slight decrease in the value of the lower limit of the voltage range of the lamp. But since we use these calculations to select power supplies, we allow ourselves to neglect this small correction, since the source still needs to be purchased with a decent margin in terms of the lower and upper limits of the output voltage. Or, if there is a need to know the lower limit absolutely precisely, you need to make practical measurements of the temperature of the LEDs in a real lamp.
Please note that this calculation was carried out for the typical current of these LEDs: 700 mA. But in general, the current range for these LEDs is 200 ... 1500 mA. That is, if desired, another current from this range can be selected. In this case, you can use the chart:
Returning to our calculation for a current of 700 mA, we will select a power source for an LED lamp.
Let's estimate the maximum power consumption of the lamp: 170 V x 0.7 A = 119 W
When choosing a power source, MEAN WELL recommends having a power reserve of approximately 30%. Consequently, the rated power of the source will be about 150 W.
We choose the model ELG-150-C700.
The main characteristics of the ELG-150-C700 are presented in the table:
As you can see, the ELG-150-C700 source provides a stabilized current of 700 mA at the output in the range of 107 ... 214 V
The 700 mA current is the same as the set current of the LED lamp. The source voltage range 107 … 214 V is wider than the LED lamp voltage range 137.5 … 170 V
Therefore, together they should work fine.
Let's analyze how the source behaves in different temperature conditions:
It can be seen that in a given temperature range from -30 to +50 degrees Celsius, the nominal power of the source does not change and is at the level of 100%.
The ELG-150-C700 source has been matched to the luminaire.
Over the past 10-20 years, the number of consumer electronics has increased manifold. A huge variety of electronic components and ready-made modules has appeared. Power requirements have also increased; many require stabilized voltage or stable current.
The driver is most often used as a current stabilizer for LEDs and charging car batteries. Such a source now exists in every LED spotlight, lamp or luminaire. Let's consider all stabilization options, from the old and simple to the most effective and modern. They are also called led drivers.
- 1. Types of stabilizers
- 2. Popular models
- 3. Stabilizer for LEDs
- 4. 220V driver
- 5. Current stabilizer, circuit
- 6.LM317
- 7. Adjustable current stabilizer
- 8. Prices in China
Types of stabilizers
Pulse adjustable DC
15 years ago, in my first year, I took tests in the subject “Power Sources” for electronic equipment. From then until today, the LM317 microcircuit and its analogues, which belong to the class of linear stabilizers, remain the most popular and popular.
At the moment there are several types of voltage and current stabilizers:
- linear up to 10A and input voltage up to 40V;
- pulse with high input voltage, step-down;
- pulse with low input voltage, boost.
On a pulse PWM controller, the characteristics are usually from 3 to 7 amperes. In reality, it depends on the cooling system and efficiency in a particular mode. Boosting a low input voltage makes the output higher. This option is used for power supplies with a low number of volts. For example, in a car, when you need to make 19V or 45V from 12V. With a lowering one it is easier, the high is reduced to the desired level.
Read about all the ways to power LEDs in the article “12 and 220V”. Connection diagrams are described separately, from the simplest ones for 20 rubles to full-fledged units with good functionality.
Based on functionality, they are divided into specialized and universal. Universal modules usually have 2 variable resistances to adjust the Volt and Ampere output. Specialized ones most often do not have building elements and the output values are fixed. Among specialized ones, current stabilizers for LEDs are common; circuit diagrams are available in large quantities on the Internet.
Popular models
Lm2596
The LM2596 has become popular among pulsed ones, but by modern standards it has low efficiency. If more than 1 amp, then a radiator is required. A small list of similar ones:
- LM317
- LM2576
- LM2577
- LM2596
- MC34063
I’ll add a modern Chinese assortment, which has good characteristics, but is much less common. On Aliexpress, searching by marking helps. The list is compiled by online stores:
- MP2307DN
- XL4015
- MP1584EN
- XL6009
- XL6019
- XL4016
- XL4005
- L7986A
Also suitable for Chinese daytime running lights DRL. Due to their low cost, LEDs are connected through a resistor to a car battery or car network. But the voltage jumps up to 30 volts in pulses. Low-quality LEDs cannot withstand such surges and begin to die. Most likely, you have seen flashing DRLs or running lights where some LEDs do not work.
Assembling a circuit with your own hands using these elements will be simple. These are mainly voltage stabilizers, which are switched on in current stabilization mode.
Do not confuse the maximum voltage of the entire block and the maximum voltage of the PWM controller. Low-voltage capacitors of 20V can be installed on the block when the pulse microcircuit has an input of up to 35V.
Stabilizer for LEDs
The easiest way to make a current stabilizer for LEDs with your own hands is using LM317; you just need to calculate the resistor for the LED using an online calculator. Food can be used at hand, for example:
- laptop power supply 19V;
- from the printer at 24V and 32V;
- from consumer electronics at 12 volts, 9V.
The advantages of such a converter are low price, easy to buy, minimum parts, high reliability. If the current stabilizer circuit is more complex, then assembling it with your own hands becomes irrational. If you are not a radio amateur, then a pulse current stabilizer is easier and faster to buy. In the future, it can be modified to the required parameters. You can find out more in the “Ready-made modules” section.
220 V driver
If you are interested in a driver for a 220V LED, then it is better to order or buy it. They have an average manufacturing complexity, but setup will take more time and will require setup experience.
The 220 LED driver can be removed from faulty LED lamps, luminaires and spotlights that have a faulty LED circuit. In addition, almost any existing driver can be modified. To do this, find out the model of the PWM controller on which the converter is assembled. Typically, the output parameters are set by a resistor or several. Using the datasheet, look at what resistance should be in order to get the required Amps.
If you install an adjustable resistor of the calculated value, then the number of Amperes at the output will be adjustable. Just do not exceed the rated power that was indicated.
Current stabilizer, circuit
I often have to look through the assortment on Aliexpress in search of inexpensive but high-quality modules. The difference in cost can be 2-3 times; time is spent searching for the minimum price. But thanks to this, I order 2-3 pieces for testing. I buy for reviews and consultations with manufacturers who buy components in China.
In June 2016, the optimal choice was the universal module based on the XL4015, the price of which was 110 rubles with free delivery. Its characteristics are suitable for connecting high-power LEDs up to 100 Watts.
Circuit in driver mode.
In the standard version, the XL4015 case is soldered to a board, which serves as a heatsink. To improve cooling, you need to install a radiator on the XL4015 case. Most people put it on top, but the efficiency of such an installation is low. It is better to install the cooling system at the bottom of the board, opposite the place where the microcircuit is soldered. Ideally, it is better to unsolder it and place it on a full-fledged radiator using thermal paste. The legs will most likely have to be extended with wires. If the controller requires such serious cooling, then the Schottky diode will also need it. It will also have to be placed on the radiator. This modification will significantly increase the reliability of the entire circuit.
In general, the modules do not have protection against incorrect power supply. This instantly disables them, be careful.
LM317
The application (rolling) does not even require any skills or knowledge of electronics. The number of external elements in the circuits is minimal, so this is an affordable option for anyone. Its price is very low, its capabilities and applications have been tested and verified many times. Only it requires good cooling, this is its main drawback. The only thing you should be wary of is low-quality Chinese LM317 microcircuits, which have worse parameters.
Due to the absence of excess noise at the output, linear stabilization microcircuits were used to power high-quality Hi-Fi and Hi-End DACs. For DACs, cleanliness of power plays a huge role, so some use batteries for this.
The maximum power for the LM317 is 1.5 Amps. To increase the number of amperes, you can add a field-effect transistor or a regular one to the circuit. The output can be up to 10A, set by low-resistance resistance. In this diagram, the KT825 transistor takes on the main load.
Another way is to install an analogue with higher technical characteristics on a larger cooling system.
Adjustable current stabilizer
As a radio amateur with 20 years of experience, I am pleased with the range of ready-made blocks and modules sold. Now you can assemble any device from ready-made blocks in a minimum amount of time.
I began to lose confidence in Chinese products after I saw in “Tank Biathlon” how the wheel of the best Chinese tank fell off.
Chinese online stores have become the leaders in the range of power supplies, DC-DC current converters, and drivers. They have almost any modules available for free sale; if you look harder, you can also find very highly specialized ones. For example, for 10,000 thousand rubles you can assemble a spectrometer worth 100,000 rubles. Where 90% of the price is a markup for the brand and slightly modified Chinese software.
The price starts from 35 rubles. for a DC-DC voltage converter, the driver is more expensive and has two or three trimming resistors instead of one.
For more versatile use, an adjustable driver is better. The main difference is the installation of a variable resistor in the circuit that sets the output amperes. These characteristics can be indicated in typical connection diagrams in the specifications for the microcircuit, datasheet, datasheet.
The weak points of such drivers are the heating of the inductor and the Schottky diode. Depending on the PWM controller model, they can withstand 1A to 3A without additional cooling of the chip. If above 3A, then cooling of the PWM and a powerful Schottky diode is required. The choke is rewound with a thicker wire or replaced with a suitable one.
The efficiency depends on the operating mode and the voltage difference between the input and output. The higher the efficiency, the lower the heating of the stabilizer.
Prices in China
The cost is very low, considering that delivery is included in the price. I used to think that because of a product that costs 30-50 rubles, the Chinese wouldn’t even get dirty; it’s a lot of work for a low income. But as practice has shown, I was wrong. They pack up any cheap nonsense and send it out. It arrives in 98% of cases, and I have been purchasing on Aliexpress for more than 7 years and for large sums, probably already about 1 million rubles.
Therefore, I place an order in advance, usually 2-3 pieces of the same name. I sell what I don’t need on the local forum or Avito, everything sells like hot cakes.
Lighting devices containing a regular LED have recently begun to be used to create artificial decorative lighting for rooms. This new direction has proven itself to be very promising, widely used not only in interiors, but also for bright, effective lighting of architectural and landscape objects. To ensure that energy consumption is minimal and light output is maximum, it is recommended to use high-power LEDs, which our company offers to buy in Moscow.
What current sources should you buy for high-power LEDs?
In order for a powerful LED to work stably and without interruptions, it is necessary to provide it with constant power through a current source, which is also called drivers. The devices are designed to power LED circuits and modules with high power values, and operate under constant high load. Current sources for high-power LEDs reduce the current in the electrical network to a predetermined value, thereby ensuring uninterrupted lighting, operational safety and long service life of the entire system.
The current source for high-power LEDs is a simple, ordinary and small-sized device that is necessary to provide power to electronic devices that operate on direct current. These devices support a specific output current and power. Current sources are needed to ensure uninterrupted operation of powerful LEDs and module spotlights.
Current sources for high-power LED devices and modules are characterized by a stabilized output current value. The sources operate in high-power multi-chip LED systems with high power values.
How to choose and buy current sources for high-power LEDs
Power supplies for high power LED lighting sources are selected based on certain parameters:
- Output current value. The output current source has a certain current value, which is constant and does not change during operation. The driver can also operate at a current different from the permissible one. If the current is less than the rated current, the lighting will not be very bright. If the output current value is greater than the permissible value, then the lighting will be very bright, but the equipment will overheat, due to which the service life of the device will be significantly reduced. That is why you should not exceed the permissible output current value.
- Maximum output power value. It shows the maximum load that the driver can withstand. However, you should not load it to the upper limit value, since in this case there is a high probability of the device overheating, which will reduce its service life.
Today we have a wide range of drivers for high-power LEDs. In all these devices, the current value does not change, only the output voltage changes depending on the connected load. The housing of the current source for high-power LEDs can be made of plastic or aluminum.
All current sources that our company offers to buy can be classified according to the principle of housing design:
- Sealed. They are used for working in open areas or in rooms with high levels of humidity and dust.
- Leaky. They are designed to work in dry indoor areas.
We currently offer a wide range of different current sources. There are universal drivers that are designed for an indefinite number of LEDs, the main thing is that the power of the current source does not exceed the total power of all connected LEDs. You can also find current sources that are designed for a certain number of diodes.
The efficiency of universal current sources for high-power LEDs is slightly less than that of conventional drivers due to the features of their circuitry. Current sources with a certain number of diodes are made with built-in overload protection. But if you connect a smaller number of diodes to them, then most likely the protection will work and the system will display an alarm message.
When using the driver, you must follow some rules so that the system operates normally throughout its entire service life:
- The current source must be connected to the supply voltage directly under load.
- LEDs connected to a current source must have sufficient cooling, especially if additional current is planned to be used.
Our store employs experienced consultants who will tell you all the necessary parameters for your needs, help you correctly calculate the power of the device for specific equipment and decide on the choice of power supply model.
Author's note: “There is a fairly large amount of information on the Internet about the power supply of LED products, but when I was preparing material for this article, I found a large amount of absurd information on sites from the top search engine results. In this case, there is either a complete absence or incorrect perception of basic theoretical information and concepts.”
LEDs are the most efficient of all common light sources today. Behind the efficiency there are also problems, for example, a high requirement for the stability of the current that powers them, poor tolerance of complex thermal operating conditions (at elevated temperatures). Hence the task of solving these problems. Let's see how the concepts of power supply and driver differ. First, let's delve into the theory.
Current source and voltage source
power unit is a generalized name for a part of an electronic device or other electrical equipment that supplies and regulates electricity to power this equipment. It can be located both inside the device and outside, in a separate housing.
Driver- a generalized name for a specialized source, switch or power regulator for specific electrical equipment.
There are two main types of power supplies:
Voltage source.
Current source.
Let's look at their differences.
Voltage source- this is a power source whose output voltage does not change when the output current changes.
An ideal voltage source has zero internal resistance, but the output current can be infinitely large. In reality, the situation is different.
Any voltage source has internal resistance. In this regard, the voltage may deviate slightly from the nominal when connecting a powerful load (powerful - low resistance, high current consumption), and the output current is determined by its internal structure.
For a real voltage source, the emergency mode of operation is the short circuit mode. In this mode, the current increases sharply; it is limited only by the internal resistance of the power source. If the power supply does not have short circuit protection, it will fail
Current source- this is a power source whose current remains set regardless of the resistance of the connected load.
Since the purpose of a current source is to maintain a given current level. The emergency operating mode for it is idle mode.
To explain the reason in simple words, the situation is as follows: let’s say you connected a load with a resistance of 1 Ohm to a current source with a rated 1 Ampere, then the voltage at its output will be set to 1 Volt. A power of 1 W will be released.
If you increase the load resistance, say, to 10 Ohms, then the current will still be 1A, and the voltage will already be set at 10V. This means that 10W of power will be released. Conversely, if you reduce the resistance to 0.1 Ohm, the current will still be 1A, and the voltage will be 0.1V.
Idling is a state when nothing is connected to the terminals of the power source. Then we can say that at idle the load resistance is very large (infinite). The voltage will increase until a current of 1A flows. In practice, an example of such a situation is the ignition coil of a car.
The voltage on the electrodes of the spark plug, when the power circuit of the primary winding of the coil opens, increases until its value reaches the breakdown voltage of the spark gap, after which current flows through the resulting spark and the energy accumulated in the coil is dissipated.
A short circuit condition for a current source is not an emergency operation mode. During a short circuit, the load resistance of the power source tends to zero, i.e. it is infinitely small. Then the voltage at the output of the current source will be appropriate for the flow of a given current, and the released power will be negligible.
Let's move on to practice
If we talk about modern nomenclature or names that are given to power supplies more by marketers than by engineers, then power supply it is commonly called a voltage source.
These include:
Charger for a mobile phone (in them, the conversion of values until the required charging current and voltage is achieved is carried out by converters installed on the board of the device being charged.
Power supply for laptop.
Power supply for LED strip.
The driver is the current source. Its main use in everyday life is to power individual and both of them with ordinary high power from 0.5 W.
LED Power
At the beginning of the article it was mentioned that LEDs have very high power requirements. The fact is that the LED is powered by current. It's connected with . Look at her.
The picture shows the current-voltage characteristics of diodes of different colors:
This branch shape (close to a parabola) is due to the characteristics of semiconductors and the impurities that are introduced into them, as well as the features of the pn junction. The current, when the voltage applied to the diode is less than the threshold, almost does not increase, or rather its increase is negligible. When the voltage at the diode terminals reaches a threshold level, the current through the diode begins to increase sharply.
If the current through a resistor grows linearly and depends on its resistance and applied voltage, then the increase in current through a diode does not obey this law. And with an increase in voltage by 1%, the current can increase by 100% or more.
Plus to this: for metals, the resistance increases as its temperature increases, but for semiconductors, on the contrary, the resistance drops, and the current begins to increase.
To find out the reasons for this in more detail, you need to delve into the course “Physical Foundations of Electronics” and learn about the types of charge carriers, the band gap and other interesting things, but we will not do this, we briefly considered these issues.
In technical specifications, the threshold voltage is designated as the voltage drop in forward bias; for white LEDs it is usually about 3 volts.
At first glance, it may seem that at the stage of design and production of the lamp it is enough to set a stable voltage at the output of the power supply and everything will be fine. They do this on LED strips, but they are powered from stabilized power supplies, and besides, the power of the LEDs used in strips is often * small, tenths and hundredths of a watt.
If such an LED is powered by a driver with a stable output current, then when the LED heats up, the current through it will not increase, but will remain unchanged, and the voltage at its terminals will therefore decrease slightly.
And if from the power supply (voltage source), after heating the current will increase, which will make the heating even stronger.
There is one more factor - the characteristics of all LEDs (as well as other elements) are always different.
Driver selection: characteristics, connection
To choose the right driver, you need to familiarize yourself with its technical characteristics, the main ones are:
Rated output current;
Maximum power;
Minimum power. Not always indicated. The fact is that some drivers will not start if a load less than a certain power is connected to them.
Often in stores, instead of power, they indicate:
Rated output current;
Output voltage range in the form of (min.)V...(max.)V, for example 3-15V.
The number of connected LEDs depends on the voltage range, written in the form (min)...(max), for example 1-3 LEDs.
Since the current through all elements is the same when connected in series, therefore the LEDs are connected to the driver in series.
It is not advisable (or rather impossible) to connect LEDs in parallel to the driver, because the voltage drops on the LEDs may differ slightly and one will be overloaded, and the other, on the contrary, will operate in a mode below the nominal one.
It is not recommended to connect more LEDs than specified by the driver design. The fact is that any power source has a certain maximum permissible power, which cannot be exceeded. And for each LED connected to a source of stabilized current, the voltage at its outputs will increase by approximately 3V (if the LED is white), and the power will be equal to the product of current and voltage, as usual.
Based on this, we will draw conclusions: in order to buy the right driver for LEDs, you need to determine the current that the LEDs consume and the voltage that drops across them, and select the driver according to the parameters.
For example, this driver supports connecting up to 12 powerful 1W LEDs with a current consumption of 0.4A.
This one produces a current of 1.5A and a voltage from 20 to 39V, which means you can connect to it, for example, a 1.5A LED, 32-36V and a power of 50W.
Conclusion
A driver is one type of power supply designed to provide LEDs with a given current. In principle, it doesn’t matter what this power source is called. Power supplies are called power supplies for 12 or 24 Volt LED strips; they can supply any current below the maximum. Knowing the correct names, you are unlikely to make a mistake when purchasing a product in stores, and you will not have to change it.
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