Types of power supplies for LEDs. Power supply for LEDs, power supply for LEDs. Integrated current stabilizers

Judging by the comments, many people are interested not only in the parameters of LED lamps, but also in the theory of their internal structure. Therefore, I decided to talk a little about the basics of circuit solutions most often used in this area.

So, the core and main component of the LED light bulb is the LED. From the point of view of circuitry, light-emitting diodes are no different from any others, except that in the sense of using them as diodes themselves, they have terrible parameters - a very small allowable reverse voltage, a relatively large junction capacitance, a huge operating voltage drop (about 3.5 V for white LEDs - for example, for a rectifier diode, this would be a nightmare), etc.

However, we understand that the main value of LEDs for mankind is that they glow, and sometimes quite brightly. In order for an LED to glow happily ever after, it needs two conditions: a stable current through it and good heat dissipation from it. The quality of the heat sink is ensured by various design methods, so now we will not dwell on this issue. Let's talk about why and how modern humanity achieves the first goal - a stable current.

Speaking of white LEDs

It is clear that white LEDs are most interesting for lighting. They are made on the basis of a crystal that emits blue light, filled with a phosphor that re-radiates part of the energy in the yellow-green region. The title picture clearly shows that the current-carrying wires go into something yellow - this is the phosphor; the crystal is located underneath. On a typical spectrum of a white LED, a blue peak is clearly visible:

Spectra of LEDs with different color temperatures: 5000K (blue), 3700K (green), 2600K (red). Read more.

We have already figured out that in the circuitry sense, the LED differs from any other diode only in the parameter values. Here it must be said that the device is fundamentally nonlinear; that is, he does not obey the Ohm's law familiar from school at all. The dependence of the current on the applied voltage on such devices is described by the so-called. current-voltage characteristic (CVC), and for the diode it is exponential. It follows from this that the smallest change in the applied voltage leads to a huge change in current, but that's not all - with a change in temperature (as well as aging), the I–V characteristic shifts. In addition, the position of the IV characteristics is slightly different for different diodes. I will specify separately - not only for each type, but for each instance, even from the same batch. For this reason, the distribution of current through diodes connected in parallel will necessarily be uneven, which cannot have a good effect on the durability of the structure. In the manufacture of matrices, they try to either use a series connection, which solves the problem at the root, or choose diodes with approximately the same forward voltage drop. To facilitate the task, manufacturers usually indicate the so-called "bin" - the code for the selection by parameters (including voltage), into which a particular instance falls.

VAC of a white LED.

Accordingly, in order for everything to work well, the LED must be connected to a device that, regardless of external factors, will automatically select the voltage with high accuracy at which the specified current flows in the circuit (for example, 350 mA for one-watt LEDs), and control the process continuously. In general, such a device is called a current source, but in the case of LEDs, it is fashionable these days to use the overseas word "driver". In general, a driver is often referred to as solutions that are primarily designed to work in a specific application - for example, "MOSFET driver" - a microcircuit designed to drive specifically powerful field-effect transistors, "seven-segment indicator driver" - a solution to drive specifically seven-segment devices, etc. . That is, by calling a current source an LED driver, people are hinting that this current source is designed specifically to work with LEDs. For example, it can have specific functions - something like having a DMX-512 light interface, detecting an open and short circuit at the output (and a conventional current source, in general, should work without problems for a short circuit), etc. However, concepts are often confused, and, for example, they call the most common adapter (voltage source!) For LED strips a driver.

In addition, devices designed to set the lighting fixture mode are often called ballast.

So, current sources. The simplest current source can be a resistor in series with the LED. This is done at low power (somewhere up to half a watt), for example, in the same LED strips. As the power increases, the losses on the resistor become too high, and the requirements for current stability increase, and therefore there is a need for more advanced devices, the poetic image of which I drew above. All of them are built according to the same ideology - they have a regulatory element controlled by current feedback.

Current stabilizers are divided into two types - linear and pulse. Linear circuits are relatives of the resistor (the resistor itself and its analogues also belong to this class). They usually do not give a special gain in efficiency, but they increase the quality of current stabilization. Pulse circuits are the best solution, but they are more complex and expensive.

Let's now take a quick look at what you can see inside or around LED bulbs these days.

1. Capacitor ballast

The capacitor ballast is an extension of the idea of ​​putting a resistor in series with an LED. In principle, the LED can be connected to the outlet directly like this:

The back-to-back diode is necessary in order to prevent the breakdown of the LED at the moment when the mains voltage changes polarity - I have already mentioned that there are no LEDs with a permissible reverse voltage of hundreds of volts. In principle, instead of a reverse diode, you can put another LED.

The resistor value in the circuit above is calculated for the LED current of about 10 - 15 mA. Since the mains voltage is much greater than the drop across the diodes, the latter can be ignored and calculated directly according to Ohm's law: 220/20000 ~ 11 mA. You can substitute the peak value (311 V) and make sure that even in the limit case, the diode current will not exceed 20 mA. Everything turns out great, except that the resistor will dissipate about 2.5 watts of power, and about 40 mW on the LED. Thus, the efficiency of the system is about 1.5% (in the case of a single LED, it will be even less).

The idea of ​​the method under consideration is to replace the resistor with a capacitor, because it is known that in AC circuits, reactive elements have the ability to limit the current. By the way, you can also use a choke, moreover, they do it in classic electromagnetic ballasts for fluorescent lamps.

Counting according to the formula from the textbook, it is easy to get that in our case a 0.2 μF capacitor is required, or an inductance coil of about 60 H. Here it becomes clear why chokes are never found in such ballasts of LED lamps - a coil of such an inductance is a serious and expensive structure, but a 0.2 uF capacitor is much easier to get. Of course, it must be designed for the peak mains voltage, and better with a margin. In practice, capacitors with an operating voltage of at least 400 V are used. Having slightly supplemented the circuit, we get what we have already seen in the previous article.

Lyrical digression

"Microfarad" is abbreviated exactly as "uF". I dwell on this because I often see people writing "mF" in this context, while the latter is an abbreviation for "millifarad", that is, 1000 microfarads. In English, "microfarad", again, is not written as "mkF", but, on the contrary, "uF". This is because the letter "u" resembles the letter "μ" with its tail torn off.

So, 1 F/F = 1000 mF/mF = 1000000 uF/uF/μF, and nothing else!

In addition, "Farad" is masculine, as it is named after the great male physicist. So, "four microfarads", but not "four microfarads"!

As I have already said, such a ballast has only one advantage - simplicity and cheapness. Like a ballast with a resistor, current stabilization is not very good here, and, even worse, there is a significant reactive component, which is not very good for the network (especially at noticeable powers). In addition, as the desired current increases, the required capacitance of the capacitor will increase. For example, if we want to turn on a one-watt LED operating at 350 mA, we need a capacitor with a capacity of about 5 microfarads, designed for a voltage of 400 V. This is already more expensive, larger and more complex in terms of design. With the suppression of ripples, everything is also not easy here. In general, we can say that the capacitor ballast is only forgivable for small beacon lamps, nothing more.

2. Transformerless buck topology

This circuit solution belongs to the family of transformerless converters, which includes step-down, step-up and inverting topologies. In addition, transformerless converters also include SEPIC, Chuck converter and other exotics, such as switched capacitors. In principle, an LED driver can be built on the basis of any of them, but in practice they are much less common in this capacity (although boost topology is used, for example, in many flashlights).

One example of a driver based on a transformerless buck topology is shown in the figure below.

In wildlife, such inclusion can be observed on the example of the ZXLD1474 or the ZXSC310 inclusion option (which, by the way, is just a boost converter in the original switching circuit).

Here the LED is connected in series with the coil. The control circuit monitors the current through the measuring resistor R1 and controls the switch T1. If the current through the LED drops below a predetermined minimum, the transistor turns on and the coil with the LED connected in series with it is connected to the power source. The current in the coil begins to increase linearly (red area on the graph), diode D1 is locked at this time. As soon as the control circuit registers that the current has reached a predetermined maximum, the key closes. In accordance with the first switching law, the coil tends to maintain the current in the circuit due to the energy stored in the magnetic field. At this point, current flows through diode D1. The energy of the coil field is consumed, the current decreases linearly (green area on the graph). When the current drops below a predetermined minimum, the control circuit registers this and opens the transistor again, pumping power into the system - the process repeats. Thus, the current is maintained within the specified limits.

A distinctive feature of the step-down topology is the ability to make the ripple of the light flux arbitrarily small, since in such a connection the current through the LED is never interrupted. The way to approach the ideal lies through an increase in inductance and an increase in the switching frequency (today there are converters with operating frequencies up to several megahertz).

Based on such a topology, the Gauss lamp driver discussed in the previous article was made.

The disadvantage of the method is the lack of galvanic isolation - when the transistor is open, the circuit is directly connected to the voltage source, in the case of network LED lamps - to the network, which can be unsafe.

3. Flyback converter

Although the flyback converter contains something that looks like a transformer, in this case it is more correct to call this part a two-winding choke, since current never flows through both windings at the same time. In fact, flyback converters are similar in principle to transformerless topologies. When T1 is open, the current in the primary rises, energy is stored in the magnetic field; at the same time, the polarity of switching on the secondary winding is deliberately chosen so that the diode D3 is closed at this stage and no current flows on the secondary side. The load current at this moment supports the capacitor C1. When T1 closes, the polarity of the voltage on the secondary is reversed (because the derivative of the current in the primary reverses sign), D3 opens and the stored energy is transferred to the secondary. In terms of current stabilization, everything is the same - the control circuit analyzes the voltage drop across the resistor R1 and adjusts the time s e parameters so that the current through the LEDs remains constant. Most often, the flyback converter is used at powers not exceeding 50 W; further, it ceases to be appropriate due to increasing losses and the necessary dimensions of the inductor transformer.

I must say that there are options for flyback drivers without an opto-isolator (for example). They rely on the fact that the currents of the primary and secondary windings are coupled, and with certain reservations, one can limit oneself to analyzing the current of the primary winding (or, more often, a separate auxiliary winding) - this saves on details and, accordingly, reduces the cost of the solution.

The flyback converter is good because, firstly, it provides isolation of the secondary part from the mains (higher safety), and, secondly, it makes it relatively easy and cheap to manufacture lamps compatible with standard dimmers for incandescent lamps, as well as to arrange coefficient correction power.

Lyrical digression

The flyback converter is so called because a similar method was originally used to obtain high voltage in televisions based on cathode ray tubes. The high voltage source was circuitically combined with the horizontal sweep circuit, and a high voltage pulse was obtained at the time reverse electron beam.

A little about pulsations

As already mentioned, pulse sources operate at sufficiently high frequencies (in practice, from 30 kHz, more often about 100 kHz). Therefore, it is clear that a serviceable driver in itself cannot be a source of a large ripple factor - primarily because this parameter is simply not normalized at frequencies above 300 Hz, and, besides, high-frequency ripples are quite easy to filter out anyway. The problem is the mains voltage.

The fact is that, of course, all the circuits listed above (except for the circuit with a quenching capacitor) operate on direct voltage. Therefore, at the input of any electronic ballast, first of all, there is a rectifier and a storage capacitor. The purpose of the latter is to feed the ballast at those moments when the mains voltage goes below the threshold of the circuit. And here, alas, a compromise is needed - high-voltage high-capacity electrolytic capacitors, firstly, cost money, and, secondly, they take up precious space in the lamp housing. This is also the root cause of power factor problems. The described circuit with a rectifier has an uneven current consumption. This leads to the appearance of higher harmonics of it, which is the reason for the deterioration of the parameter of interest to us. Moreover, the better we try to filter the voltage at the ballast input, the lower the power factor we will get if we do not make separate efforts. This explains the fact that almost all the low ripple lamps that we have seen show a very mediocre power factor, and vice versa (of course, the introduction of an active power factor correction will affect the price, so they prefer to save on it for now).

Perhaps this is all that, as a first approximation, can be said about the electronics of LED lamps. I hope that with this article I to some extent answered all the circuitry questions that were asked to me in the comments and private messages.

There are many different types of LED power supplies on the market today. This article is intended to make it easier for you to choose the source you need.

First of all, let's look at the difference between a standard power supply and an LED driver. First you need to decide - what is a power supply? In the general case, this is a power supply of any type, which is a separate functional unit. Usually it has certain input and output parameters, and it doesn’t matter what kind of devices it is intended to power. The driver for powering the LEDs provides a stable output current. In other words, this is also a power supply. The driver is just a marketing designation - to avoid confusion. Before the advent of LEDs, current sources - and they are the driver - were not widely used. But then a super-bright LED appeared - and the development of current sources went by leaps and bounds. And not to be confused - they are called drivers. So let's agree on some terms. The power supply is a source of voltage (constant voltage), the Driver is a source of current (constant current). The load is what we connect to the power supply or driver.

Power Supply

Most electrical appliances and electronic components require a voltage source to operate. They are the usual electrical network, which is present in any apartment in the form of a socket. Everyone knows the phrase "220 volts". As you can see - not a word about the current. This means that if the device is designed to operate from a 220 V network, then it does not matter to you how much current it consumes. If only there were 220 - and he will take the current himself - as much as he needs. For example, a conventional electric kettle with a power of 2 kW (2,000 W), connected to a 220 V network, consumes the following current: 2,000/220 = 9 amperes. Quite a lot, given that most conventional electrical power strips are rated at 10 amps. This is the reason for the frequent operation of the protection (machine) when the kettles are plugged into the outlet through an extension cord, into which many devices are already inserted - a computer, for example. And it's good if the protection works, otherwise the extension cord may simply melt. And so - any device designed to be plugged into an outlet - knowing what its power is, you can calculate the current consumed.
But most household devices, such as a TV, DVD player, computer, need to lower the mains voltage from 220 V to the level they need - for example, 12 volts. The power supply is just the device that deals with such a decrease.
There are many ways to lower the voltage of the network. The most common power supplies are transformer and switching.

Power supply based on transformer

Such a power supply is based on a large, iron, buzzing contraption. :) Well, current transformers buzz less. The main advantage is the simplicity and relative safety of such blocks. They contain a minimum of details, but at the same time they have good characteristics. The main disadvantage is efficiency and dimensions. The more powerful the power supply, the heavier it is. Part of the energy is spent on "humming" and heating :) In addition, part of the energy is lost in the transformer itself. In other words - simple, reliable, but has a lot of weight and consumes a lot - efficiency at the level of 50-70%. It has an important integral plus - galvanic isolation from the network. This means that if a malfunction occurs or you accidentally get into the secondary power circuit with your hand, you won’t be shocked :) Another definite plus is that the power supply can be connected to the network without load - this will not harm it.
But let's see what happens if overload the power supply.
Available: transformer power supply with an output voltage of 12 volts and a power of 10 watts. Connect a 12 volt 5 watt light bulb to it. The light bulb will glow at all its 5 watts and consume current 5 / 12 \u003d 0.42 A.

Connect the second bulb in series to the first, like this:

Both bulbs will glow, but very dimly. When connected in series, the current in the circuit will remain the same - 0.42 A, but the voltage will be distributed between two bulbs, that is, each will receive 6 volts. It is clear that they will glow barely. Yes, and each will consume approximately 2.5 watts.
Now let's change the conditions - connect the bulbs in parallel:

As a result, the voltage on each lamp will be the same - 12 volts, but the current they will take is 0.42 A each. That is, the current in the circuit will double. Considering that we have a unit with a power of 10 W - it won’t seem enough to him - when connected in parallel, the load power, that is, the light bulbs, is summed up. If we also connect a third one, then the power supply will start to heat up wildly and eventually burn out, possibly taking your apartment with it. And all this because he does not know how to limit the current. Therefore, it is very important to correctly calculate the load on the power supply. Of course, more complex units contain overload protection and automatically turn off. But you should not count on this - protection, sometimes, also does not work.

Impulse power block

The simplest and brightest representative is Chinese power supply for halogen lamps 12 V. Contains few parts, light, small. The dimensions of the 150 W block are 100x50x50 mm, the weight is 100 grams. The same transformer power supply would weigh three kilograms, or even more. The power supply for halogen lamps also has a transformer, but it is small because it operates at an increased frequency. It should be noted that the efficiency of such a unit is also not up to par - about 70-80%, while it produces decent interference in the electrical network. There are many more blocks based on a similar principle - for laptops, printers, etc. So, the main advantage is small dimensions and low weight. Galvanic isolation is also present. The disadvantage is the same as that of its transformer counterpart. It can burn out from overload :) So if you decide to make 12 V halogen lighting at home, calculate the allowable load on each transformer.
It is desirable to create from 20 to 30% of the stock. That is, if you have a 150 W transformer, it’s better not to hang more than 100 W loads on it. And keep a close eye on the Ravshans if they make repairs for you. They should not be trusted to calculate power. It is also worth noting that the impulse blocks do not like switching on without load. That is why it is not recommended to leave cell phone chargers in the outlet after charging is completed. However, everyone does this, so most of the current impulse blocks contain protection against turning on without load.

These two simple members of the power supply family share a common task - providing the right voltage level to power the devices that are connected to them. As mentioned above, the devices themselves decide how much current they need.

Driver

In general driver is a current source for LEDs. For him, there is usually no "output voltage" parameter. Only output current and power. However, you already know how to determine the allowable output voltage - we divide the power in watts by the current in amperes.
In practice, this means the following. Suppose the driver parameters are as follows: current - 300 milliamps, power - 3 watts. Divide 3 by 0.3 - we get 10 volts. This is the maximum output voltage that the driver can provide. Suppose we have three LEDs, each rated at 300 mA, and the voltage across the diode should be about 3 volts. If we connect one diode to our driver, then the voltage at its output will be 3 volts, and the current will be 300 mA. Connect the second diode successively(see the example with lamps above) with the first - the output will be 6 volts 300 mA, connect the third - 9 volts 300 mA. If we connect the LEDs in parallel, then these 300 mA will be distributed between them approximately equally, that is, approximately 100 mA each. If we connect three-watt LEDs with a working current of 700 mA to a 300 mA driver, they will receive only 300 mA.
I hope the principle is clear. A working driver under no circumstances will give out more current than it is designed for - no matter how you connect the diodes. It should be noted that there are drivers that are designed for any number of LEDs, so long as their total power does not exceed the power of the driver, and there are those that are designed for a certain number - 6 diodes, for example. However, they allow some spread to a smaller side - you can connect five diodes or even four. efficiency universal drivers worse than their counterparts, designed for a fixed number of diodes due to some features of the operation of pulse circuits. Also, drivers with a fixed number of diodes usually contain protection against abnormal situations. If the driver is designed for 5 diodes, and you connected three, it is quite possible that the protection will work and the diodes will either not turn on or will blink, signaling an emergency mode. It should be noted that most drivers do not tolerate the connection to the supply voltage without load - in this they are very different from a conventional voltage source.

So, we have determined the difference between the power supply and the driver. Now let's look at the main types of LED drivers, starting with the simplest ones.

Resistor

This is the simplest LED driver. It looks like a barrel with two leads. The resistor can limit the current in the circuit by selecting the desired resistance. How to do this is described in detail in the article "Connecting LEDs in a car"
The disadvantage is low efficiency, lack of galvanic isolation. There is no way to reliably power an LED from a 220 V network through a resistor, although many household switches use a similar circuit.

capacitor circuit.

Similar to a resistor circuit. The disadvantages are the same. It is possible to make a capacitor circuit of sufficient reliability, but the cost and complexity of the circuit will greatly increase.

Chip LM317

This is the next member of the protozoan family drivers for LEDs. Details are in the aforementioned article about LEDs in cars. The disadvantage is low efficiency, a primary power source is required. The advantage is reliability, simplicity of the circuit.

Driver on chip type HV9910

This type of driver has gained considerable popularity due to the simplicity of the circuit, the low cost of components and small dimensions.
Advantage - versatility, accessibility. The disadvantage is that it requires skill and care when assembling. There is no galvanic isolation from the 220 V network. High impulse noise in the network. Low power factor.

Driver with low voltage input

This category includes drivers designed to be connected to a primary voltage source - a power supply or a battery. For example, these are drivers for LED lights or lamps designed to replace halogen 12 V. The advantage is small size and weight, high efficiency, reliability, and safety in operation. The disadvantage is that a primary voltage source is required.

network driver

Completely ready to use and contain all the necessary elements to power the LEDs. The advantage is high efficiency, reliability, galvanic isolation, operational safety. The disadvantage is the high cost, difficult to obtain. They can be both in the case and without the case. The latter are usually used as part of lamps or other light sources.

Application of drivers in practice

Most people planning to use LEDs are making a common mistake. Buy yourself first LED, then under them is selected driver. This can be considered a mistake because at present there are not so many places where you can purchase a sufficient assortment of drivers. As a result, having the coveted LEDs in your hands, you are racking your brains - how to choose a driver from the available one. So you bought 10 LEDs - and there are only 9 drivers. And you have to rack your brains - what to do with this extra LED. Maybe it was easier to count on 9 at once. Therefore, driver selection should occur simultaneously with the selection of LEDs. Next, you need to take into account the features of the LEDs, namely the voltage drop across them. For example, a red 1 W LED has an operating current of 300 mA and a voltage drop of 1.8-2 V. The power consumed by it will be 0.3 x 2 \u003d 0.6 W. But a blue or white LED has a voltage drop of 3-3.4 V at the same current, that is, a power of 1 W. Therefore, a driver with a current of 300 mA and a power of 10 W will "pull" 10 white or 15 red LEDs. The difference is significant. A typical diagram for connecting 1 W LEDs to a driver with an output current of 300 mA looks like this:

For standard 1W LEDs, the negative terminal is larger than the positive one, so it is easy to distinguish it.

What if only 700mA drivers are available? Then you have to use even number of LEDs including two of them in parallel.

I want to note that many mistakenly assume that the operating current of 1 W of LEDs is 350 mA. It's not, 350mA is the MAXIMUM operating current. This means that when working for a long time it is necessary to use source of power with a current of 300-330 mA. The same is true for parallel connection - the current per LED should not exceed the specified figure of 300-330 mA. It does not mean at all that operating at increased current will cause the LED to fail. But with insufficient heat dissipation, each extra milliamp can reduce the service life. In addition, the higher the current, the lower the efficiency of the LED, which means that its heating is stronger.

When it comes to connecting an LED strip or modules designed for 12 or 24 volts, you need to take into account that the power supplies offered for them limit the voltage, not the current, that is, they are not drivers in the accepted terminology. This means, firstly, that you need to carefully monitor the load power connected to a particular power supply. Secondly, if the unit is not stable enough, the output voltage spike can kill your tape. It makes life a little easier that resistors are installed in the tapes and modules (clusters), which allow you to limit the current to a certain extent. I must say, the LED strip consumes a relatively large current. For example, smd 5050 tape, which has 60 LEDs per meter, consumes about 1.2 A per meter. That is, to power 5 meters, you need a power supply with a current of at least 7-8 amperes. At the same time, the tape itself will consume 6 amperes, and one or two amperes must be left in reserve so as not to overload the unit. And 8 amps is almost 100 watts. These blocks are not cheap.
Drivers are more optimal for connecting a tape, but finding such specific drivers is problematic.

Summing up, we can say that the choice of a driver for LEDs should be given no less, if not more attention than LEDs. Carelessness when choosing is fraught with failure of LEDs, drivers, excessive consumption and other delights :)

Yuri Ruban, Rubikon LLC, 2010 .

Over the past 10-20 years, the number of consumer electronics has increased many times over. A huge variety of electronic components and ready-made modules appeared. Power requirements have also increased, many require a stabilized voltage or a stable current.

The driver is most often used as a current stabilizer for LEDs and charging car batteries. Such a source is now in every LED spotlight, lamp or luminaire. Consider all options for stabilization, ranging from old and simple to the most effective and modern. They are also called led driver.

• 1. Types of stabilizers
• 2. Popular models
• 3. Stabilizer for LEDs
• 4. Driver for 220V
• 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 chip and its analogues, which belongs to the class of linear stabilizers, remain the most popular and popular.

At the moment, there are several types of voltage and current stabilizers:

1. linear up to 10A and input voltage up to 40V;
2. pulse with a high input voltage, lowering;
3. pulse with low input voltage, increasing.

On a pulse PWM controller, usually from 3 to 7 amperes according to the characteristics. In reality, it depends on the cooling system and efficiency in a particular mode. Boosting from a low input voltage makes a higher output voltage. This option is used for power supplies with a small number of volts. For example, in a car, when you need to make 19V or 45V out of 12V. With a buck, it's easier, the high is reduced to the desired level.

Read about all the ways to power LEDs in the article "to 12 and 220V". Connection schemes are described separately from the simplest ones for 20 rubles to full-fledged blocks with good functionality.

By functionality, they are divided into specialized and universal. Universal modules usually have 2 variable resistances to adjust the Volts and Amps output. Specialized ones most often do not have building elements and the output values ​​\u200b\u200bare fixed. Among the specialized ones, current stabilizers for LEDs are common, there are a large number of circuits on the Internet.

Popular Models

Lm2596

Among the impulse ones, the LM2596 has become popular, but by modern standards it has a low efficiency. If more than 1 amp, then a heatsink is required. A small list of similar ones:

1. LM317
2. LM2576
3. LM2577
4. LM2596
5. MC34063

I will supplement with a modern Chinese assortment, which is good in terms of characteristics, but is much less common. On Aliexpress, the search for the marking helps. The list is compiled by online stores:

• MP2307DN
• XL4015
• MP1584EN
• XL6009
• XL6019
• XL4016
• XL4005
• L7986A

Also suitable for Chinese DRL daytime running lights. Due to the 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. Chances are you've seen flashing DRLs or running lights where some of the LEDs don't work.

Do-it-yourself circuit assembly on these elements will be simple. Mostly these are voltage stabilizers, which are switched on in the current stabilization mode.

Do not confuse the maximum voltage of the entire unit and the maximum voltage of the PWM controller. Low-voltage 20V capacitors can be installed on the block when the pulse chip has an input up to 35V.

LED Stabilizer

It is easiest to make a current stabilizer for LEDs with your own hands on the LM317, you only need to calculate the resistor for the LED on an online calculator. Food can be used at hand, for example:

1. 19V laptop power supply;
2. from the printer for 24V and 32V;
3. 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 complicated, then it becomes not rational to assemble it with your own hands. If you are not a radio amateur, then a switching 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 section "Ready-made modules".

Driver for 220 V

..

If you are interested in a driver for a 220v LED, then it is better to order or buy it. They are of medium difficulty to manufacture, but setup will take more time and setup experience will be required.

The 220 LED driver can be removed from faulty LED lamps, fixtures 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. Look at the datasheet to see what resistance should be in order to get the required amps.

If you put an adjustable resistor of the calculated value, then the number of amperes at the output will be configurable. 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, it takes time to find the minimum price. But thanks to this I make an order for 2-3 pieces for tests. I buy for reviews and consultations of manufacturers who buy components in China.

In June 2016, the universal module on the XL4015 became the best choice, the price of which is 110 rubles with free delivery. Its characteristics are suitable for connecting powerful LEDs up to 100 watts.

Schematic in driver mode.

In the standard version, the XL4015 case is soldered to the board, which serves as a heatsink. To improve cooling on the XL4015 case, you need to put a radiator. Most put it on top, but the effectiveness of such an installation is low. It is better to put the cooling system on the bottom of the board, opposite the place where the microcircuit is soldered. Ideally, it is better to unsolder it and put it on a full-fledged radiator through thermal paste. The legs will most likely need to be lengthened with wires. If such serious cooling is required for the controller, then the Schottky diode will also need it. It will also have to be put on a radiator. Such a refinement 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

Application (roll) does not even require any skills and 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 possibilities and application have been repeatedly tested and verified. Only it requires good cooling, this is its main drawback. The only thing to be wary of is low-quality Chinese LM317 microcircuits, which have worse parameters.

Due to the absence of unnecessary noise at the output, linear stabilization microcircuits were used to power high-quality Hi-Fi and Hi-End DACs. For DACs, power cleanliness 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. It will be possible to get up to 10A at the output, it is set by low-resistance. In this scheme, the KT825 transistor takes on the main load.

Another way is to put an analog with higher specifications 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 for sale. Now you can assemble any device from ready-made blocks in a minimum time.

I began to lose confidence in Chinese products after I saw in the "Tank Biathlon" how the best Chinese tank had a wheel fall off.

Chinese online stores have become the leader in the range of power supplies, DC-DC current converters, drivers. In their free sale, you can find almost any modules, if you look better, then 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 a 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 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 switching circuits 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 microcircuit. If above 3A, then cooling of the PWM and a powerful Schottky diode is required. The inductor is rewound with a thicker wire or replaced with a suitable one.

The efficiency depends on the operating mode, 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 shipping is included in the price. I used to think that because of the goods for 30-50 rubles, the Chinese will not even get dirty, a lot of work with a low income. But as practice has shown, I was wrong. Any penny nonsense they pack and send. It comes in 98% of cases, and I have been buying on Aliexpress for more than 7 years and for large amounts, probably already about 1 million rubles.

Therefore, I place an order in advance, usually 2-3 pieces of the same name. Unnecessary sell on a local forum or Avito, everything sells like hot cakes.

Despite the objective problems with the introduction of LED lighting, more and more enterprises are engaged in the development and production of semiconductor lighting devices. Scientific and production company "Plazmaininform" entered this market in 2010 and currently positions itself as a developer and serial manufacturer of current sources for LED lamps.

Power supplies (PS) of LEDs are the most important part of a semiconductor lamp, which largely determines the functional, lighting performance and reliability of the lighting device. For companies involved in the design and installation of lighting systems, in addition to luminous flux and color temperature, other characteristics such as electrical safety, efficiency, power factor, luminous flux ripple factor, electromagnetic compatibility and cost are also important. As a result of cooperation between Plazmaininform SPC and a number of enterprises that develop and manufacture lighting devices, open-type current sources were born and put into mass production, providing electric power of 15, 20, 30, 35, 50 and 100 W.

An analysis of the IP for LED lamps produced by a number of companies shows that the circuitry of the current sources is determined by the required output power of the lamp: if it is less than 60 W, then a flyback power factor corrector (PFC) with output current stabilization is usually selected. At a higher output power, a separate PFC and a separate converter with output current stabilization and input/output galvanic isolation, performed according to the flyback, forward or resonant LLC-type circuitry, are used. Converters without galvanic isolation (step-down type, SEPIC, etc.) from the point of view of ensuring safety during the operation of LED lamps are not widely used.

During development, great attention was paid to parameters such as output current ripple, electromagnetic compatibility (EMC) and cost. The choice of output current pulsations is determined by the requirements for luminous flux pulsations, which are regulated by standards and amount to 10–20% for general-purpose lamps, and 5–10% for table lamps during prolonged work at a computer. For street lamps, the pulsation of the luminous flux is not regulated and must be set for each specific application.

Taking into account that the luminaires can be connected to electric networks of a sufficiently large length, to which high-current equipment can be connected, the power sources must withstand the test voltage of 1.5 kV wire-to-wire and wire-to-case, as well as nanosecond and microsecond impulse surges and dips with an amplitude of up to 1.0 kV. In addition, televisions, receivers and other equipment susceptible to interference can be connected to the same electrical networks. Therefore, it is necessary to ensure that the IP complies with the following main EMC standards: GOST R 51318.15-99, GOST R 51514-99, GOST R 51317.3.2.2006 (sections 6, 7), GOST R 51317.3.3.2008, GOST R 51317.4.2.99, GOST R 51317.4 .4.2007, GOST R 51317.4.5.99, GOST R 51317.4.6.99, GOST R 51317.4.11.2007.

PSL (Power Supply Led) sources are made according to the scheme of a flyback power factor corrector with output current stabilization and voltage limitation. A typical block diagram is shown in fig. 1. The basis of the converter is the PFC controller, which controls the power switch and provides a power factor above 0.9. Oscillograms of the input voltage and current, as well as the effective and limiting values ​​of the current harmonics of the PSL50 source are shown in fig. 2 and 3. The EMC filter ensures electromagnetic compatibility in accordance with luminaire standards.

Rice. one. Source Block Diagram

Rice. 2. PSL50 input voltage and current waveforms

Rice. 3. RMS and harmonic limits of input current PSL50

As an example, Table 1 shows the level of radio interference at the PSL50 mains terminals in the frequency range 0.009-30 MHz (quasi-peak values).

Table 1 . Radio interference level PSL50

Frequency, MHz	Voltage value radio interference, dB (μV)
	measured	Permissible (norm)
0,009	56	110
0,04	25	92
0,15	37	66
0,16	35	65,5
0,24	21	62,1
0,55	13	55,2
1	at the level noise	56
3,5	11	56
6	31	56
7,7	37	56
10	32	60
15,6	51	60
28	42	60
30	41	60

The output filter provides the required level of output current ripple and, accordingly, luminous flux ripple. The level and shape of current and voltage ripples for two ratings of the PSL50 output filter are shown in fig. 4–7.

Rice. four. Output current ripple at rated load. Filter capacitance 300uF (10mV corresponds to 100mA)	Rice. 5. Output voltage ripple at rated load. Filter capacitance 300uF (DC 120V)
Rice. 6. Output current ripple at rated load. Filter capacitance 500uF (10mV corresponds to 100mA)	Rice. 7. Output voltage ripple at rated load. Filter capacitance 500uF (DC 120V)

The oscillograms show that an increase in the output capacitance by 60% reduces the current ripple by half and, accordingly, reduces the luminous flux ripple, since the relationship between them is almost linear. When turned on, the sources provide a smooth voltage supply for 50 ms. The shape of the output voltage at the start of the PSL50 is shown in fig. eight.

Rice. eight. Output voltage of PSL50 at switch-on

The error signal amplifier (USO) for current provides the formation of an error signal, maintaining the current through the LEDs at a given level. USO voltage limits the output voltage at idle. The galvanic isolation unit is designed to transmit an error signal to the controller, to the primary circuit. The damper limits the voltage surge at the drain of the power switch, which allows the use of a lower voltage and cheaper transistor.

The source is powered by an alternating current network. Galvanic isolation of input and output circuits between themselves and the housing withstands 1.5 kV and ensures safe operation. The sources comply with domestic and international standards regarding EMC. There is a built-in protection against short circuit at the output, idling operation is provided. The main technical characteristics of the sources are given in Table 2.

Table 2 . Power supply parameters

Parameter name	Source type
	PSL15	PSL20	PSL30	PSL35	PSL50	PSL100
Supply voltage	176-264V, 50/60Hz
Maximum power, W	20	20	20	20	20	20
Output voltage range, V	24–32	36–48	44–50	25–38	100–144	200–300
Output current, mA	500±30	360±20	600±20	900±30	360±20	370±20
Output current instability, % (no more)	5	5	5	5	5	5
Output current ripple, % (no more)	20	20	20	20	10	10
Efficiency, % (at least)	85	85	85	85	90	90
Power factor, % (at least)	90	90	90	90	97	95
Operating temperature, °C	–25…+65	0…+40	0…+40	0…+40	0…+40	–45…+60
Average resource, h	50 000
Overall dimensions, mm (no more)	135×40×25	145×30×25	145×30×25	145×30×25	160×33×25	180×40×36
Weight, g (no more)	100	100	100	100	110	160

The appearance of PSL15, PSL35, PSL50 and PSL100 is shown in fig. 9–12, respectively. Sources PSL20 and PSL30 have a design similar to PSL35.

Rice. 9. Source PSL15	Rice. ten. Source PSL35
Rice. eleven. Source PSL50	Rice. 12. Source PSL100

For special designs of luminaires, an inexpensive network non-isolated current source with a power of 9 W (PSL9) has been developed. It is a buck converter with passive power factor correction. The source diagram is shown in fig. 13, appearance - in fig. 14. The basis of the source is the HV9910 driver chip. Chain С1–VD2–VD3–VD4–C2 - passive cash register. The output current is set by resistors R4, R5, R6. C3 is the output filter capacitor. PSL9 source parameters are shown in Table 3.

Rice. 13. Schema PSL9

Rice. fourteen. Source PSL9

T a b l e 3 . PSL9 Source Options

Supply voltage	176-264V, 50/60Hz
Efficiency, % (not less than)	80
Power factor, % (not less than)	84
Minimum output operating voltage, V	20
Maximum output operating voltage, V	32
Maximum open circuit voltage, V	350
Stabilized output current, mA	350±10
Output current instability, % (no more)	5
Output current ripple, % (no more)	15
Overall dimensions (L×W×H), mm	45×33×25
Operating temperature range, °C	0…+40

Luminaires, in the design of which PSL9, PSL15, PSL30, PSL100 are used, are undergoing trial operation. Luminaires with PSL20, PSL35 and PSL50 are mass-produced.

The chosen scheme for constructing power sources makes it possible to modify the design at no great cost to obtain other values ​​of the output voltage and current within the declared power, providing power to luminaires with a different scheme for switching on LEDs.

To date, there are hundreds of varieties of LEDs that differ in appearance, glow color and electrical parameters. But all of them are united by a common principle of operation, which means that the circuits for connecting to an electrical circuit are also based on general principles. It is enough to understand how to connect one indicator LED, in order to then learn how to draw up and calculate any circuits.

LED pinout

Before proceeding to consider the issue of the correct connection of the LED, you need to learn how to determine its polarity. Most often, indicator LEDs have two outputs: an anode and a cathode. Much less often in a case with a diameter of 5 mm there are instances that have 3 or 4 leads for connection. But it’s also easy to figure out their pinout.

SMD LEDs can have 4 outputs (2 anodes and 2 cathodes), which is due to the technology of their production. The third and fourth conclusions can be electrically unused, but used as an additional heat sink. The pinout shown is not a standard. To calculate the polarity, it is better to first look at the datasheet, and then confirm what you see with a multimeter. You can visually determine the polarity of a SMD LED with two leads by a cut. The cut (key) in one of the corners of the housing is always located closer to the cathode (minus).

The simplest LED wiring diagram

There is nothing easier than connecting an LED to a low-voltage constant voltage source. It can be a battery, a rechargeable battery or a low-power power supply. It is better if the voltage is at least 5 V and not more than 24 V. Such a connection will be safe, and for its implementation you will need only 1 additional element - a low-power resistor. Its task is to limit the current flowing through the p-n junction at a level no higher than the nominal value. To do this, the resistor is always installed in series with the emitting diode.

Always respect polarity when connecting an LED to a constant voltage (current) source.

If the resistor is excluded from the circuit, then the current in the circuit will be limited only by the internal resistance of the EMF source, which is very small. The result of such a connection will be an instant failure of the radiating crystal.

Limiting Resistor Calculation

Looking at the current-voltage characteristic of the LED, it becomes clear how important it is not to make a mistake when calculating the limiting resistor. Even a small increase in the rated current will lead to overheating of the crystal and, as a result, to a decrease in the working life. The choice of a resistor is made according to two parameters: resistance and power. Resistance is calculated by the formula:

• U – supply voltage, V;
• U LED - direct voltage drop across the LED (passport value), V;
• I - rated current (passport value), A.

The result obtained should be rounded up to the nearest value from the E24 series up, and then calculate the power that the resistor will have to dissipate:

R is the resistance of the resistor accepted for installation, Ohm.

More detailed information about calculations with practical examples can be found in the article. And those who do not want to dive into the nuances can quickly calculate the parameters of the resistor using an online calculator.

Turning on the LEDs from the power supply

We are talking about power supplies (PSUs) operating on 220 V AC. But even they can differ greatly from each other in output parameters. It can be:

• alternating voltage sources, inside which there is only a step-down transformer;
• unstabilized direct voltage sources (PSV);
• stabilized PPIs;
• stabilized constant current sources (LED drivers).

You can connect an LED to any of them by supplementing the circuit with the necessary radio elements. Most often, stabilized 5 V or 12 V PSIs are used as a power supply. This type of PSU implies that with possible fluctuations in the mains voltage, as well as with a change in the load current in a given range, the output voltage will not change. This advantage allows you to connect LEDs to the PSU using only resistors. And it is precisely this connection principle that is implemented in circuits with indicator LEDs.
Powerful LEDs must be connected through a current stabilizer (driver). Despite their higher cost, this is the only way to guarantee stable brightness and long-term operation, as well as to avoid premature replacement of an expensive light emitting element. Such a connection does not require an additional resistor, and the LED is connected directly to the output of the driver, subject to the condition:

• I driver - driver current according to the passport, A;
• I LED - rated current of the LED, A.

If the condition is not met, the connected LED will burn out due to overcurrent.

Serial connection

It is not difficult to assemble a working circuit on a single LED. Another thing is when there are several of them. How to connect 2, 3 ... N LEDs correctly? To do this, you need to learn how to calculate more complex switching schemes. A daisy chain circuit is a circuit of several LEDs, in which the cathode of the first LED is connected to the anode of the second, the cathode of the second to the anode of the third, and so on. A current of the same magnitude flows through all elements of the circuit:

And the voltage drops are summarized:

Based on this, we can draw the following conclusions:

• it is advisable to combine in a series circuit only LEDs with the same operating current;
• if one LED fails, the circuit will open;
• The number of LEDs is limited by the PSU voltage.

Parallel connection

If it is necessary to light several LEDs from a power supply unit with a voltage of, for example, 5 V, then they will have to be connected in parallel. In this case, in series with each LED, you need to put a resistor. Formulas for calculating currents and voltages will take the following form:

Thus, the sum of currents in each branch should not exceed the maximum allowable current of the PSU. When connecting the same type of LEDs in parallel, it is enough to calculate the parameters of one resistor, and the rest will be of the same value.

All the rules for serial and parallel connection, illustrative examples, as well as information on how not to turn on LEDs can be found in.

mixed inclusion

Having dealt with the schemes of serial and parallel connection, it's time to combine. One of the options for the combined connection of LEDs is shown in the figure.

By the way, this is how each LED strip is arranged.

Inclusion in the alternating current network

Connecting LEDs from a PSU is not always advisable. Especially when it comes to the need to make a switch backlight or an indicator of the presence of voltage in the power strip. For such purposes, it will be enough to assemble one of the simple ones. For example, a circuit with a current-limiting resistor and a rectifier diode that protects the LED from reverse voltage. The resistance and power of the resistor are calculated using a simplified formula, neglecting the voltage drop across the LED and diode, since it is 2 orders of magnitude less than the mains voltage:

Due to the high power dissipation (2-5 W), the resistor is often replaced with a non-polar capacitor. Working on alternating current, it kind of "extinguishes" the excess voltage and almost does not heat up.

Connecting flashing and multi-color LEDs

Externally, blinking LEDs are no different from conventional analogues and can blink in one, two or three colors according to the algorithm specified by the manufacturer. The internal difference consists in the presence of another substrate under the case, on which the integrated pulse generator is located. The rated operating current, as a rule, does not exceed 20 mA, and the voltage drop can vary from 3 to 14 V. Therefore, before connecting a flashing LED, you need to familiarize yourself with its characteristics. If they are not there, then you can find out the parameters experimentally by connecting to an adjustable 5-15 V power supply through a 51-100 Ohm resistor.

In the case of the multicolor there are 3 independent crystals of green, red and blue. Therefore, when calculating the resistor values, it must be remembered that each color of the glow corresponds to its own voltage drop.

Once again about three important points

1. Direct rated current is the main parameter of any LED. Underestimating it, we lose in brightness, and overestimating it, we sharply reduce the service life. Therefore, the best power source is an LED driver, when connected to which a constant current of the desired amount will always flow through the LED.
2. The voltage given in the datasheet to the LED is not decisive and only indicates how many volts will drop at the p-n junction when the rated current flows. Its value must be known in order to correctly calculate the resistance of the resistor if the LED is powered by a conventional PSU.
3. To connect high-power LEDs, it is important not only a reliable power supply, but also a high-quality cooling system. Installing LEDs with a power consumption of more than 0.5 W on a radiator will guarantee their stable and long-term operation.

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