Driver markings for LEDs. Drivers for LEDs: types, purpose, connection

Recently, a friend asked me to help with a problem. He is developing LED lamps, selling them along the way. He has accumulated a number of lamps that are not working correctly. Outwardly, this is expressed as follows: when turned on, the lamp flashes for a short time (less than a second), goes out for a second, and so repeats endlessly. He gave me three such lamps to study, I solved the problem, the fault turned out to be very interesting (just in the style of Hercule Poirot) and I want to tell you about the way to find the fault.

The LED lamp looks like this:

Fig 1. Appearance disassembled LED lamp

The developer has used an interesting solution - the heat from the operating LEDs is taken by a heat pipe and transferred to a classic aluminum radiator. According to the author, this solution allows us to ensure the correct thermal conditions for LEDs, minimizing thermal degradation and ensuring the longest possible service life of the diodes. At the same time, the service life of the diode power driver increases, since the driver board is removed from the thermal circuit and the board temperature does not exceed 50 degrees Celsius.

This solution - to separate the functional zones of light emission, heat removal and power current generation - made it possible to obtain high performance characteristics of the lamp in terms of reliability, durability and maintainability.
The disadvantage of such lamps, oddly enough, directly follows from its advantages - manufacturers do not need a durable lamp :). Does everyone remember the story about the conspiracy among incandescent lamp manufacturers about the maximum service life of 1000 hours?

Well, I can’t help but note the characteristic appearance of the product. My “state control” (wife) did not allow me to put these lamps in the chandelier where they are visible.

Let's return to the driver problems.

This is what the driver board looks like:

Fig 2. Appearance of the LED driver board from the surface mount side

And on the reverse side:

Fig 3. Appearance of the LED driver board from the power parts side

Studying it under a microscope made it possible to determine the type of control chip - it is MT7930. This is a flyback converter control chip (Fly Back), hung with various protections, like a Christmas tree with toys.

The MT7930 has built-in protection:

From excess current of the key element
supply voltage reduction
increasing supply voltage
short circuit in the load and load break.
from exceeding the temperature of the crystal

Declaring protection against short circuit in the load for a current source is rather of a marketing nature :)

It was not possible to obtain a schematic diagram for just such a driver, but a search on the Internet yielded several very similar diagrams. The closest one is shown in the figure:

Fig 4. LED Driver MT7930. Electrical circuit diagram

Analysis of this circuit and thoughtful reading of the manual for the microcircuit led me to the conclusion that the source of the blinking problem is the activation of the protection after the start. Those. the initial start-up procedure goes through (the lamp flashes - that’s what it is), but then the converter turns off due to one of the protections, the power capacitors are discharged and the cycle begins again.

Attention! The circuit contains life-threatening voltages! Do not repeat without proper understanding of what you are doing!

To study signals with an oscilloscope, you need to decouple the circuit from the network so that there is no galvanic contact. For this I used an isolation transformer. On the balcony, two Soviet-made TN36 transformers, dated 1975, were found in the reserves. Well, these are timeless devices, massive, covered in completely green varnish. I connected it according to the scheme 220 – 24 – 24 -220. Those. First I lowered the voltage to 24 volts (4 secondary windings of 6.3 volts each), and then increased it. Having multiple tapped primary windings gave me the opportunity to play with different supply voltages - from 110 volts to 238 volts. This solution is, of course, somewhat redundant, but quite suitable for one-time measurements.

Fig 5. Photo of the isolation transformer

From the description of the start in the manual it follows that when power is applied, capacitor C8 begins to charge through resistors R1 and R2 with a total resistance of about 600 kohms. Two resistors are used for safety reasons, so that if one breaks down, the current through this circuit does not exceed the safe value.

So, the power capacitor slowly charges (this time is about 300-400 ms) and when the voltage on it reaches 18.5 volts, the converter start procedure starts. The microcircuit begins to generate a sequence of pulses to the key field-effect transistor, which leads to the appearance of voltage on the Na winding. This voltage is used in two ways - to generate pulses feedback to control the output current (circuit R5 R6 C5) and to generate the operating supply voltage of the microcircuit (circuit D2 R9). At the same time, a current arises in the output circuit, which leads to the ignition of the lamp.

Why does the protection work and by what parameter?

First guess

Triggering of protection when output voltage is exceeded?

To test this assumption, I unsoldered and tested the resistors in the divider circuit (R5 10 kohm and R6 39 kohm). You can't check them without soldering them, since they are paralleled through the transformer winding. The elements turned out to be fine, but at some point the circuit started working!

I checked the shapes and voltages of the signals at all points of the converter with an oscilloscope and was surprised to see that they were all completely certified. No deviations from the norm...

I let the circuit run for an hour - everything was OK.

What if you let it cool? After 20 minutes in the off state it does not work.

Very good, apparently it’s a matter of heating some element?

But which one? And what element parameters can float away?

At this point I concluded that there was some kind of temperature sensitive element on the converter board. Heating this element completely normalizes the operation of the circuit.
What is this element?

Second guess

Suspicion fell on the transformer. The problem was thought like this: the transformer, due to manufacturing inaccuracies (say, the winding was underwound by a couple of turns), operates in the saturation region and due to sharp fall inductance and a sharp increase in current, the current protection of the field switch is triggered. This is a resistor R4 R8 R19 in the drain circuit, the signal from which is supplied to pin 8 (CS, apparently Current Sense) of the microcircuit and is used for the current feedback circuit and, when the setting of 2.4 volts is exceeded, turns off the generation for protection field effect transistor and transformer from damage. On the board under study there are two resistors R15 R16 in parallel with an equivalent resistance of 2.3 ohms.

But as far as I know, the parameters of the transformer deteriorate when heated, i.e. The behavior of the system should be different - turn on, work for 5-10 minutes and turn off. The transformer on the board is quite massive and its thermal constant is no less than a few minutes.
Maybe, of course, there is a short-circuited turn in it that disappears when heated?

Resoldering the transformer to a guaranteed working one was impossible at that moment (they had not yet delivered a guaranteed working board), so I left this option for later, when there were no versions left at all :). Plus the intuitive feeling is not it. I trust my engineering intuition.

At this point, I tested the hypothesis about the operation of the current protection by reducing the current current resistor by half by soldering the same one in parallel to it - this did not affect the blinking of the lamp in any way.

This means that everything is normal with the current of the field-effect transistor and there is no excess current. This was clearly visible from the signal shape on the oscilloscope screen. The peak of the sawtooth signal was 1.8 volts and clearly did not reach the value of 2.4 volts, at which the microcircuit turns off generation.

The circuit also turned out to be insensitive to changes in load - neither connecting the second head in parallel, nor switching a warm head to a cold one and back changed anything.

Third guess

I examined the supply voltage of the microcircuit. When operating in normal mode, all voltages were absolutely normal. In flashing mode too, as far as one could judge from the waveforms on the oscilloscope screen.

As before, the system blinked in a cold state and began to work normally when the transformer leg was warmed up with a soldering iron. Warm it up for 15 seconds and everything starts up fine.

Warming up the microcircuit with a soldering iron did nothing.

And the short heating time was very confusing... what could change in 15 seconds?

At some point, I sat down and methodically, logically cut off everything that was guaranteed to work. Once the lamp lights up, it means the starting circuits are working.
Once heating the board manages to start the system and it works for hours, it means the power systems are working properly.
It cools down and stops working - something depends on the temperature...
Is there a crack on the board in the feedback circuit? It cools and contracts, the contact is broken, it heats up, expands and the contact is restored?
I climbed a cold board with a tester - there are no breaks.

What else can interfere with the transition from startup mode to operating mode?!!!

Out of complete hopelessness, I intuitively soldered a 10 uF 35 volt electrolytic capacitor parallel to the same power supply for the microcircuit.

And then happiness came. It's working!

Replacing the 10 uF capacitor with a 22 uF capacitor completely solved the problem.

Here it is, the culprit of the problem:

Figure 6. Capacitor with incorrect capacitance

Now the mechanism of the malfunction has become clear. The circuit has two power circuits for the microcircuit. The first, triggering, slowly charges capacitor C8 when 220 volts are supplied through a 600 kΩ resistor. After it is charged, the microcircuit begins to generate impulses for the field operator, starting the power part of the circuit. This leads to the generation of power for the microcircuit in operating mode on a separate winding, which is supplied to the capacitor through a diode with a resistor. The signal from this winding is also used to stabilize the output current.

Until the system enters operating mode, the microcircuit is powered by the stored energy in the capacitor. And it was missing just a little - literally a couple or three percent.
The voltage drop was enough for the microcircuit protection system to trigger due to low power and turn off everything. And the cycle began again.

It was not possible to detect this drop in the supply voltage with an oscilloscope - it was too rough an estimate. It seemed to me that everything was fine.

Warming up the board increased the capacitor capacity by the missing percentage - and there was already enough energy for a normal start-up.

It is clear why only some of the drivers failed even though the elements were completely serviceable. A bizarre combination of the following factors played a role:

Low power capacitor capacity. The tolerance for the capacitance of electrolytic capacitors (-20% +80%) played a positive role, i.e. capacitances with a nominal value of 10 microfarads in 80% of cases have a real capacity of about 18 microfarads. Over time, the capacity decreases due to the drying out of the electrolyte.
Positive temperature dependence of the capacitance of electrolytic capacitors on temperature. Increased temperature at the output control point - just a couple of degrees is enough and the capacity is enough for normal startup. If we assume that at the exit control site it was not 20 degrees, but 25-27, then this turned out to be enough for almost 100% passing of the exit control.

The driver manufacturer saved money, of course, by using capacitors with a lower nominal value compared to the reference design from the manual (22 µF is indicated there), but fresh capacitors at elevated temperatures and taking into account the +80% spread allowed the batch of drivers to be delivered to the customer. The customer received seemingly working drivers, but over time they began to fail for some unknown reason. It would be interesting to know whether the manufacturer’s engineers took into account the peculiarities of the behavior of electrolytic capacitors with increasing temperature and the natural scatter, or did this happen by chance?

LEDs have become very popular. The main role in this was played by the LED driver, which maintains a constant output current of a certain value. We can say that this device is a current source for LED devices. This current driver, working together with the LED, provides long service life and reliable brightness. Analysis of the characteristics and types of these devices allows you to understand what functions they perform and how to choose them correctly.

What is a driver and what is its purpose?

An LED driver is an electronic device whose output produces a direct current after stabilization. IN in this case It is not voltage that is generated, but rather current. Devices that stabilize voltage are called power supplies. On their body it is indicated output voltage. 12 V power supplies are used to power LED strips, LED strips and modules.

The main parameter of the LED driver, which it can provide to the consumer for a long time at a certain load, is the output current. Individual LEDs or assemblies of similar elements are used as a load.

The LED driver is usually powered from a 220 V mains voltage. In most cases, the operating output voltage range is from three volts and can reach several tens of volts. To connect six 3W LEDs, you will need a driver with an output voltage from 9 to 21 V, rated at 780 mA. Despite its versatility, it has low efficiency if a minimum load is applied to it.

When lighting in cars, in the headlights of bicycles, motorcycles, mopeds, etc., when equipping portable lamps, constant voltage power is used, the value of which varies from 9 to 36 V. You can not use a driver for LEDs with low power, but in such In cases, it will be necessary to add a corresponding resistor to the 220 V supply network. Despite the fact that this element is used in household switches, connecting an LED to a 220 V network and counting on reliability is quite problematic.

Main Features

The power that these devices are capable of delivering under load is an important indicator. Don't overload it trying to achieve maximum results. As a result of such actions, drivers for LEDs or the LED elements themselves may fail.

The electronic content of the device is influenced by many reasons:

• device protection class;
• elemental component that is used for assembly;
• input and output parameters;
• manufacturer's brand.

The production of modern drivers is carried out using microcircuits using pulse-width conversion technology, which include pulse converters and current-stabilizing circuits. PWM converters are powered from 220 V, have a high class of protection against short circuits, overloads, as well as high efficiency.

Specifications

Before purchasing an LED converter, you should study the characteristics of the device. These include the following parameters:

• output power;
• output voltage;
• rated current.

The output voltage is affected by the connection diagram to the power source and the number of LEDs in it. The current value depends proportionally on the power of the diodes and the brightness of their radiation. The LED driver must supply as much current to the LEDs as required to ensure constant brightness. It is worth remembering that the power of the required device should be greater than that consumed by all LEDs. It can be calculated using the following formula:

P(led) – power of one LED element;

n- number of LED elements.

To ensure long-term and stable operation of the driver, the device’s power reserve should be 20–30% of the nominal one.

When performing calculations, you should take into account the color factor of the consumer, as it affects the voltage drop. It will have different meanings for different colors.

Best before date

LED drivers, like all electronics, have a certain service life, which is greatly influenced by operating conditions. LED elements manufactured by well-known brands are designed to last up to 100 thousand hours, which is much longer than power supplies. Based on the quality, the calculated driver can be classified into three types:

• low quality, with service life up to 20 thousand hours;
• with average parameters - up to 50 thousand hours;
• converter consisting of components from well-known brands - up to 70 thousand hours.

Many people don’t even know why they should pay attention to this parameter. This will be needed to select a device for long-term use and further payback. For use in domestic premises, the first category is suitable (up to 20 thousand hours).

How to choose a driver?

There are many types of drivers used for LED lighting. Most of the products presented are made in China and do not have the required quality, but they stand out due to their low price range. If you need a good driver, it is better not to go for the cheap ones made in China, since their characteristics do not always coincide with those declared, and they rarely come with a warranty. There may be a defect on the microcircuit or rapid failure of the device; in this case, it will not be possible to exchange for a better product or return the funds.

The most commonly chosen option is a boxless driver, powered by 220 V or 12 V. Various modifications allow them to be used for one or more LEDs. These devices can be chosen for organizing research in the laboratory or conducting experiments. For phyto-lamps and household use, drivers for LEDs located in the housing are chosen. Frameless devices win in terms of price, but lose in aesthetics, safety and reliability.

Types of drivers

Devices that supply power to LEDs can be divided into:

• pulse;
• linear.

Pulse-type devices produce multiple current pulses at the output high frequency and operate on the PWM principle, their efficiency is up to 95%. Pulse converters have one significant drawback - strong electromagnetic interference occurs during operation. To ensure a stable output current, a current generator is installed in the linear driver, which plays the role of an output. Such devices have low efficiency (up to 80%), but are technically simple and inexpensive. Such devices cannot be used for high power consumers.

From the above, we can conclude that the power source for LEDs should be chosen very carefully. An example would be a fluorescent lamp, which is supplied with a current that exceeds the norm by 20%. There will be virtually no changes in its characteristics, but the performance of the LED will decrease several times.

Many people quite often confuse power supplies and drivers, connecting LEDs and LED strips from the wrong sources.

As a result, after a short period of time they fail, and you have no idea what the reason was and begin to mistakenly blame the “low-quality” manufacturer.

Let's take a closer look at what their differences are and when you need to use one or another power source. But first, let's briefly look at the types of power supplies.

Transformer block

Today it is quite rare to see the use of a transformer power supply. The scheme of their assembly and operation is quite simple and understandable.

The most important element here is definitely the transformer. At home, it converts 220V into 12 or 24V. That is, there is a direct conversion of one voltage to another.

The network frequency is the usual 50 Hertz.

Next behind it is a rectifier. It rectifies a sinusoid of alternating voltage and produces a “constant” voltage at the output. That is, 12V supplied to the consumer is already a constant voltage of 12V, and not alternating.

This scheme has 3 main advantages:

• its simplicity

• simplicity of design

• relative reliability

However, there are also disadvantages here that made the developers think and come up with something more modern.

• first of all this heavy weight and decent dimensions

• as a consequence of the first drawback - a large consumption of metal for assembling the entire structure

• Well, the low cosine phi and low efficiency make the whole thing worse

This is why switching power supplies were invented. There is a slightly different operating principle here.

Switching power supplies

Firstly, voltage rectification occurs immediately. That is, AC 220V is supplied to the input and immediately converted to DC 220V at the input.

Next is the pulse generator. Its main task is to create artificially alternating voltage with a very high frequency. Several tens or even hundreds of kilohertz (from 30 to 150 kHz). Compare this to the 50 Hz we are used to in home sockets.

By the way, due to such a huge frequency, we practically do not hear the hum of pulse transformers. This is explained by the fact that the human ear is capable of distinguishing sound up to 20 kHz, no more.

The third element in the circuit is a pulse transformer. It resembles a regular one in shape and design. However, its main difference is its small overall dimensions.

This is precisely what is achieved due to high frequency.

Of these three elements, the most important is the pulse generator. Without it, there would not be such a relatively small power supply.

Advantages of pulse blocks:

• low price, if of course you compare it in terms of power, and the same unit assembled on a conventional transformer

• Efficiency from 90 to 98%

• supply voltage can be supplied in a wide range

• with a high-quality power supply manufacturer, switching UPSs have a higher cosine fi

There are also disadvantages:

• complexity of the assembly diagram

• complex design

• If you come across a low-quality pulse unit, it will release a bunch of high-frequency interference into the network, which will affect the operation of other equipment

Simply put, a power supply, whether regular or switching, is a device with strictly one output voltage. Of course, it can be “twisted”, but not in large ranges.

Such blocks are not suitable for LED lamps. Therefore, drivers are used to power them.

What are the differences between a driver and a power supply?

Why can’t a simple power supply be used for LEDs, and why exactly is a driver needed?

A driver is a device similar to a power supply.

However, as soon as you connect a load to it, it forces not the voltage, but the current to stabilize at the same level!

LEDs are “powered” by electric current. They also have such a characteristic as voltage drop.

If you see the inscription 10mA and 2.7V on the LED, this means that the maximum permissible current for it is 10mA, no more.

When a current of this magnitude flows, the LED will lose 2.7 Volts. It will be lost, and not required for work. You will achieve current stabilization and the LED will work long and brightly.

Moreover, LED is a semiconductor. And the resistance of this semiconductor depends on the voltage that is applied to it. The resistance changes according to the graph - the current-voltage characteristic.

If you look at it, you can see that even if you do not increase or decrease the voltage much, it will dramatically change the current value several times over.

Moreover, the dependence is not directly proportional.

It would seem that once you set the exact voltage, you can get the rated current that is required for the LED. At the same time, it will not exceed the limit values. It seems that a regular block should cope with this.

However, all LEDs have unique parameters and characteristics. At the same voltage, they can “eat” different currents.

Moreover, these parameters can also change with changes in ambient temperature.

And the operating temperature range of LED lamps is very wide.
For example, in winter it can be -30 degrees outside, and in summer it’s already +40. And this is in the same place.

Therefore, if you connect such lamps from a regular switching power supply, and not from a driver, then their operating mode will be absolutely unpredictable.

Of course they will work, but in what light output mode and for how long is unknown. Such work always ends the same way - with the LED burning out.

By the way, when the temperature rises, the luminous flux of LED lamps always drops, even for those connected via a driver. For low-quality specimens, the luminous flux drops very strongly, once they have been running for about an hour and warmed up.

For high-quality products, the luminous flux decreases slightly with heating, but still decreases.

Therefore, after startup, each lamp must be given time so that it reaches its operating mode and the luminous flux stabilizes. Its change should be no more than 10% of the initial one.

Many unscrupulous manufacturers cheat and measure these parameters immediately after switching on, when the flow is still at its maximum.

If you need to connect several LEDs, then they are connected in series. This is necessary so that the same current flows through all the elements, despite their different current-voltage characteristics (volt-ampere characteristics).

And this serial chain is connected to the driver. These chains can be combined in various ways. Create series-parallel or hybrid circuits.

Driver Disadvantages

Of course, drivers also have their undeniable disadvantages:

• firstly, they are designed only for a certain current and power

This means that for each driver you will have to select a certain number of LEDs each time. If one of them accidentally fails during operation, the driver will send all the current to the remaining ones.

Which will lead to their overheating and subsequent burnout. That is, the loss of one LED entails a breakdown of the entire chain.

There are also universal driver models; for them, the number of LEDs is not important, the main thing is that their total power does not exceed the permissible limit. But they are much more expensive.

• highly specialized in LEDs

Simple power supplies can be used for various needs, wherever 12V or more is needed, for example for video surveillance systems.

The main purpose of the drivers is LEDs.

Are there driverless factory lamps? Eat. Not long ago, many such LED lamps and spotlights appeared on the market.

However, their energy efficiency is not very high, at the level of conventional fluorescent lamps. And how it will behave in the event of possible changes in parameters in our networks is a big question.

LED strips - connection from a power supply or driver?

A separate issue is LED strips. They do not require drivers at all, and as you know, they are connected from the usual 12-36 Volt power supplies.

It would seem that there is a catch? There are also LEDs there.

But the fact is that the driver is already automatically present in the tape itself.

You have all seen soldered resistances (resistors) on LED strips.

They are precisely responsible for limiting the current to the nominal value. One resistor is installed across three LEDs connected in series.

Such sections of tape designed for a voltage of 12 Volts are called clusters. These individual clusters are connected to each other in parallel throughout the entire length of the tape.

And it is precisely thanks to this parallel connection that the same voltage of 12V is supplied to all LEDs. Thanks to clustering when installing the low-voltage strip, it can be easily cut into small pieces consisting of at least 3 LEDs.

It would seem that a solution has been found, but where is the drawback? And the main disadvantage of such a device is that these resistors do not do any useful work.

They only additionally heat the surrounding space and the LED itself near it. This is why LED strips do not shine as brightly as we would like. As a result, they are used only as additional interior light.

Compare 60-70 lumens/watt for LED strips, versus 120-140 lumens/watt for lamps and driver-based solutions.

LEDs occupy the leading position among the most effective sources of artificial light today. This is largely due to the high-quality power sources for them. When working in conjunction with a properly selected driver, the LED will maintain stable light brightness for a long time, and the service life of the LED will be very, very long, measured in tens of thousands of hours.

Thus, a correctly selected driver for LEDs is the key to long and reliable operation of the light source. And in this article we will try to cover the topic of how to choose the right driver for an LED, what to look for, and what they generally are.

An LED driver is a stabilized constant voltage or constant current power supply. In general, initially, an LED driver is a , but today even constant voltage sources for LEDs are called LED drivers. That is, we can say that the main condition is stable power characteristics DC.

An electronic device (essentially a stabilized pulse converter) is selected for the required load, be it a set of individual LEDs assembled in a series chain, or a parallel set of such chains, or maybe a strip or even one powerful LED.

A stabilized constant voltage power supply is well suited for LED strips, or for powering a set of several high-power LEDs connected one at a time in parallel - that is, when the rated voltage of the LED load is precisely known, and it is only necessary to select a power supply for the rated voltage at the corresponding maximum power .

Usually this does not cause problems, for example: 10 LEDs at 12 volts, 10 watts each, will require a 100 watt 12 volt power supply, rated for a maximum current of 8.3 amperes. All you have to do is adjust the output voltage using the adjusting resistor on the side, and you're done.

For more complex LED assemblies, especially when several LEDs are connected in series, you need not just a power supply with a stabilized output voltage, but a full-fledged LED driver - an electronic device with a stabilized output current. Here, current is the main parameter, and the supply voltage of the LED assembly can automatically vary within certain limits.

For an even glow of the LED assembly, it is necessary to ensure the rated current through all the crystals, however, the voltage drop across the crystals may differ for different LEDs (since the I-V characteristics of each of the LEDs in the assembly are slightly different), so the voltage will not be the same on each LED, but the current should be the same.

LED drivers are produced mainly for power supply from a 220 volt network or from a 12 volt vehicle on-board network. The driver output parameters are specified in the form of voltage range and rated current.

For example, a driver with an output of 40-50 volts, 600 mA will allow you to connect four 12-volt LEDs with a power of 5-7 watts in series. Each LED will drop approximately 12 volts, the current through the series chain will be exactly 600 mA, while the voltage of 48 volts falls within the operating range of the driver.

A driver for LEDs with stabilized current is a universal power supply for LED assemblies, and its efficiency is quite high and here's why.

The power of the LED assembly is an important criterion, but what determines this load power? If the current were not stabilized, then a significant part of the power would be dissipated on the equalizing resistors of the assembly, that is, the efficiency would be low. But with a current-stabilized driver, equalizing resistors are not needed, and the resulting efficiency of the light source will be very high.

Drivers different manufacturers differ in output power, protection class and used element base. As a rule, it is based on current output stabilization and protection against short circuit and overload.

Powered by 220 volt AC or 12 volt DC. The simplest compact drivers with low-voltage power supply can be implemented on a single universal chip, but their reliability, due to simplification, is lower. Nevertheless, such solutions are popular in auto tuning.

When choosing a driver for LEDs, you should understand that the use of resistors does not protect against interference, nor does the use of simplified circuits with quenching capacitors. Any voltage surges pass through resistors and capacitors, and the nonlinear I-V characteristic of the LED will necessarily be reflected in the form of a current surge through the crystal, and this is harmful for the semiconductor. Linear stabilizers are also not the best option in terms of immunity to interference, and the efficiency of such solutions is lower.

It is best if the exact quantity, power, and switching circuit of the LEDs are known in advance, and all LEDs in the assembly will be the same model and from the same batch. Then select the driver.

The range of input voltages, output voltages, and rated current must be indicated on the case. Based on these parameters, a driver is selected. Pay attention to the protection class of the housing.

For research tasks, for example, packageless LED drivers are suitable; such models are widely represented on the market today. If you need to place the product in a housing, the user can make the housing independently.

Andrey Povny

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In recent years, it has become increasingly popular. This is due to the fact that the LEDs used in the lamps, also called light-emitting diodes (LEDs), are quite bright, economical and durable. Using LED elements, interesting and original lighting effects are created that can be used in a wide variety of interiors. However, such lighting devices are very demanding on the parameters of electrical networks, especially on the current value. Therefore for normal operation LED drivers must be included in the lighting circuit. In this article we will try to figure out what LED drivers are, what are their main characteristics, how not to make a mistake when choosing, and whether it is possible to make one yourself.

Without such a miniature device, the LEDs will not work

Since LEDs are current devices, they are therefore very sensitive to this parameter. For normal lighting operation, a stabilized current with a nominal value must pass through the LED element. For these purposes, a driver for LED lamps was created.

Some readers, when they see the word driver, will be at a loss, since we are all accustomed to the fact that this term refers to some software that allows us to manage programs and devices. Translated from English language driver means: driver, driver, leash, mast, control program and more than 10 more values, but they are all united by one function - control. This is the case with drivers for, only they control the current. So, we’ve sorted out the term, now let’s get to the point.

LED driver is an electronic device, at the output of which, after stabilization, a constant current of the required magnitude is generated, ensuring normal operation of the LED elements. In this case, it is the current, not the voltage, that is stabilized. Devices that stabilize the output voltage are called, which are also used to power LED lighting elements.

As we already understood, the main parameter of the driver for LEDs is the output current, which the device can provide for a long time when the load is turned on. For normal and stable glow of LED elements, it is required that a current flow through the LED, the value of which must coincide with the values ​​​​specified in the technical data sheet of the semiconductor.

Where are LED drivers used?

As a rule, LED drivers are designed to operate with voltages of 10, 12, 24, 220 V and a constant current of 350 mA, 700 mA and 1 A. Current stabilizers for LEDs are produced mainly for specific products, but there are also universal devices that suitable for LED elements from leading manufacturers.

LED drivers in AC networks are mainly used for:

In electrical circuits with direct current, stabilizers are needed for the normal operation of on-board lighting and car headlights, portable lights, etc.

Current stabilizers are adapted to work with control systems and photocell sensors, and due to their compactness can be easily installed in distribution boxes. Also, using drivers, you can easily change the brightness and color of the LED elements, reducing the current through digital control.

How do stabilizing devices for LEDs work?

The principle of operation of the converter for and tapes is to maintain a given current value regardless of the output voltage. This is the difference between a power supply and an LED driver.

If we look at the diagram presented above, we will see that the current, thanks to resistor R1, is stabilized, and capacitor C1 sets the required frequency. Next, the diode bridge is switched on, as a result of which a stabilized current is supplied to the LEDs.

Device Features You Need to Pay Attention to

When choosing an LED driver for LED lamps, it is necessary to take into account the main parameters, namely: current, output voltage and power consumed by the connected load.

The output voltage of the current stabilizer depends on the following factors:

• number of LED elements;
• LED voltage drop;
• connection method.

The current at the output of the device is determined by the power and. The power of the load affects the current it consumes depending on the required glow intensity. It is the stabilizer that provides the LEDs with the required current.

Power LED lamp depends directly on:

• power of each LED element;
• total number of LEDs;
• colors.

The power consumed by the load can be calculated using the following formula:

P N = PLED × N , Where

• P N – total load power;
• P LED – power of an individual LED;
• N – number of LED elements connected to the load.

The maximum power of the current stabilizer should not be less than PH. For normal operation of the LED driver, it is recommended to provide a power reserve of at least 20÷30%.

In addition to the power and number of LEDs, the power of the load connected to the driver also depends on the color of the LED elements. The fact is that LEDs of different colors have different voltage drops at the same current value. So, for example, for a red CREE XP-E LED, the voltage drop at a current of 350 mA is 1.9÷2.4 V, and the average power consumption will be about 750 mW. For a green LED element at the same current, the voltage drop will be 3.3÷3.9 V, and the average power will be almost 1.25 W. Accordingly, a current stabilizer designed for a power of 10 W can power 12÷13 red LEDs or 7-8 green LEDs.

Types of stabilizers by device type

Current stabilizers for light-emitting diodes are divided according to the type of device into pulsed and linear.

For a linear driver, the output is a current generator, which provides smooth stabilization of the output current when the input voltage is unstable, without creating high-frequency electromagnetic interference. Such devices have a simple design and low cost, but the not very high efficiency (up to 80%) narrows the scope of their use to low-power LED elements and strips.

Pulse-type devices allow you to create a series of high-frequency current pulses at the output. Such drivers operate on the principle of pulse width modulation (PWM), that is, the average output current is determined by the ratio of the pulse width to their frequency. Such devices are more in demand due to their compactness and more high efficiency, which is about 95%. However, compared to linear PWM drivers, stabilizers have a higher level of electromagnetic interference.

How to choose a driver for LEDs

It should be immediately noted that a resistor cannot be a full replacement for a driver, since it is not able to protect the LEDs from power surges and impulse noise. Also, using a linear current source would not be the best option due to its low efficiency, which limits the capabilities of the stabilizer.

When choosing an LED driver for LEDs, you should adhere to the following basic recommendations:

• It is best to purchase a current stabilizer at the same time as the load;
• take into account the voltage drop across the LEDs;
• a high current rating reduces the efficiency of the LED and causes it to overheat;
• take into account the power of the load connected to the driver.

It is also necessary to pay attention that the stabilizer case indicates its power, operating ranges of input and output voltage, rated stabilized current and the degree of moisture and dust protection of the device.

Recommendation! How powerful and high-quality the driver for the LED strip or LED will be, of course, is up to you. However, it should be remembered that for the normal operation of the entire lighting system being created, it is best to buy a proprietary converter, especially if we are talking about LED spotlights and other powerful lighting devices.

Connecting current converters for LEDs: driver circuit for a 220 V LED lamp

Most manufacturers produce drivers on integrated circuits (ICs), which allow them to be powered from a reduced voltage. All converters for LED lighting that currently exist are divided into simple ones, created on the basis of 1÷3 transistors, and more complex ones, made using PWM microcircuits.

Above is an IC based driver circuit, but as we mentioned, there are connection methods using resistors and transistors. In fact, there are many connection options and it is simply impossible to consider them all in detail in one review. On the Internet you can find almost any scheme suitable for your situation.

How to calculate a current stabilizer for LED lighting

To determine the output voltage of the converter, it is necessary to calculate the ratio of power and current. So, for example, with a power of 3 W and a current of 0.3 A, the maximum output voltage will be 10 V.Next, you need to decide on the connection method, parallel or serial, as well as the number of LEDs. The fact is that the rated power and voltage at the driver output depend on this. After calculating all these parameters, you can select the appropriate stabilizer.

It is worth noting that converters designed for a certain number of LED elements have protection against emergency situations. This type of device is characterized by incorrect operation when connecting a smaller number of LEDs - flickering is observed or does not work at all.

Dimmable driver for LED elements - what is it?

The latest models of converters for LEDs are adapted to work with dimmers of semiconductor crystals -. The use of these devices allows for more efficient use of electricity and increases the life of the LED element.

Dimmable converters come in two types. Some are included in the circuit between the stabilizer and LED lighting elements and operate via PWM control. Converters of this type are used to work with LED strips, creeping line, etc.

In the second option, the dimmer is installed at the gap between the power source and the stabilizer, and the operating principle consists of both controlling the parameters of the current passing through the LEDs and using pulse-width modulation.

Features of Chinese current converters for LEDs

The high demand for drivers for LED lighting has led to their mass production in the Asian region, particularly in China. And this country is famous not only for high-quality electronics, but also for the mass production of all kinds of counterfeits. Chinese-made LED drivers are pulsed current converters, usually designed for 350÷700 mA and in a packageless design.

The advantages of Chinese current converters are only low cost and the presence of galvanic isolation, but there are still more disadvantages and they consist of:

• high level of radio interference;
• unreliability caused by cheap circuit solutions;
• vulnerability to network fluctuations and overheating;
• high level of ripple at the output of the stabilizer;
• short service life.

Typically, Chinese-made components operate at the limit of their capabilities, without any reserve. Therefore, if you want to create a reliably operating lighting system, it is best to buy a converter for LEDs from a well-known, trusted manufacturer.

Service life of current converters

Like any electronic device, the driver for an LED current source has a certain service life, which depends on the following factors:

• network voltage stability;
• temperature changes;
• humidity level.

Well-known manufacturers guarantee their products for an average of 30,000 hours of operation. The cheapest, simplest stabilizers are designed to operate for 20,000 hours, average quality - 20,000 hours, and Japanese ones - up to 70,000 hours.

LED driver circuit based on RT 4115

Thanks to the emergence large quantity LED elements with a power of 1÷3 W and a low price, most people prefer to use them to make home and car lighting. However, this requires a driver that will stabilize the current to the nominal value.

For correct operation of the converter, it is recommended to use tantalum capacitors. If you do not install a capacitor on the power supply, the integrated circuit (IC) will simply fail when the device is connected to the network. Above is a driver circuit for an LED on the PT4115 IC.

How to make your own LED driver

Using ready-made microcircuits, even a novice radio amateur can assemble a converter for LEDs of various powers. This requires the ability to read electrical diagrams and experience with a soldering iron.

You can assemble a current stabilizer for 3-watt stabilizers using a microcircuit from the Chinese manufacturer PowTech - PT4115. This IC can be used for LED elements with a power of more than 1 W and consists of control units with a fairly powerful transistor at the output. The converter, based on PT4115, has high efficiency and a minimum set of components.

As you can see, if you have experience, knowledge and desire, you can assemble an LED driver according to almost any scheme. Now let's consider step by step instructions creating a simple current converter for 3 LED elements with a power of 1 W each, from a charger for mobile phone. By the way, this will help you better understand the operation of the device and later move on to more complex schemes, designed for a larger number of LEDs and strips.

Instructions for assembling a driver for LEDs

Image	Description of the stage
	To assemble the stabilizer, you will not need an old mobile phone charger. We took them from Samsung, they are so reliable. Charger with parameters 5 V and 700 mA, carefully disassemble.
	We also need a 10 kOhm variable (tuning) resistor, 3 1 W LEDs and a cord with a plug.
	This is what the disassembled charger looks like, which we will redo.
	We unsolder the 5 kOhm output resistor and put a “tuner” in its place.
	Next, we find the output to the load and, having determined the polarity, solder the LEDs, pre-assembled in series.
	We unsolder the old contacts from the cord and connect the wire and plug in their place. Before checking the functionality of the driver for LEDs, you need to make sure that the connections are correct, that they are strong, and that nothing creates a short circuit. Only after this can you start testing.
	We start adjusting with a trimming resistor until the LEDs start to glow.
	As you can see, the LED elements are lit.
	Using a tester, we check the parameters we need: output voltage, current and power. If necessary, make adjustments with a resistor.
	That's it! The LEDs burn normally, nothing sparks or smokes anywhere, which means the conversion was successful, for which we congratulate you.

As you can see, making a simple driver for LEDs is very simple. Of course, experienced radio amateurs may not be interested in this scheme, but for a beginner it is perfect for practice.