Why and how to choose a driver for LED lighting. Drivers for LEDs - everything a home master needs to know Driver for an LED lamp operating principle

Author's note: “There is a fairly large amount of information on the Internet about the power supply of LED products, but when I was preparing material for this article, I found a large amount of absurd information on sites from the top search engine results. In this case, there is either a complete absence or incorrect perception of basic theoretical information and concepts.”

LEDs are the most efficient of all common light sources today. Behind the efficiency there are also problems, for example, a high requirement for the stability of the current that powers them, poor tolerance of complex thermal operating conditions (at elevated temperatures). Hence the task of solving these problems. Let's see how the concepts of power supply and driver differ. First, let's delve into the theory.

Current source and voltage source

power unit is a generalized name for a part of an electronic device or other electrical equipment that supplies and regulates electricity to power this equipment. It can be located both inside the device and outside, in a separate housing.

Driver- a generalized name for a specialized source, switch or power regulator for specific electrical equipment.

There are two main types of power supplies:

Voltage source.

Current source.

Let's look at their differences.

Voltage source- this is a power source whose output voltage does not change when the output current changes.

An ideal voltage source has zero internal resistance, but the output current can be infinitely large. In reality, the situation is different.

Any voltage source has internal resistance. In this regard, the voltage may deviate slightly from the nominal when connecting a powerful load (powerful - low resistance, high current consumption), and the output current is determined by its internal structure.

For a real voltage source, the emergency mode of operation is the short circuit mode. In this mode, the current increases sharply; it is limited only by the internal resistance of the power source. If the power supply does not have short circuit protection, it will fail

Current source- this is a power source whose current remains set regardless of the resistance of the connected load.

Since the purpose of a current source is to maintain a given current level. The emergency operating mode for it is idle mode.

To explain the reason in simple words, the situation is as follows: let’s say you connected a load with a resistance of 1 Ohm to a current source with a rated 1 Ampere, then the voltage at its output will be set to 1 Volt. A power of 1 W will be released.

If you increase the load resistance, say, to 10 Ohms, then the current will still be 1A, and the voltage will already be set at 10V. This means that 10W of power will be released. Conversely, if you reduce the resistance to 0.1 Ohm, the current will still be 1A, and the voltage will be 0.1V.

Idling is a state when nothing is connected to the terminals of the power source. Then we can say that at idle the load resistance is very large (infinite). The voltage will increase until a current of 1A flows. In practice, an example of such a situation is the ignition coil of a car.

The voltage on the electrodes of the spark plug, when the power circuit of the primary winding of the coil opens, increases until its value reaches the breakdown voltage of the spark gap, after which current flows through the resulting spark and the energy accumulated in the coil is dissipated.

A short circuit condition for a current source is not an emergency operation mode. During a short circuit, the load resistance of the power source tends to zero, i.e. it is infinitely small. Then the voltage at the output of the current source will be appropriate for the flow of a given current, and the released power will be negligible.

Let's move on to practice

If we talk about modern nomenclature or names that are given to power supplies more by marketers than by engineers, then power supply it is commonly called a voltage source.

These include:

Charger for a mobile phone (in them, the conversion of values ​​until the required charging current and voltage is achieved is carried out by converters installed on the board of the device being charged.

Power supply for laptop.

Power supply for LED strip.

The driver is the current source. Its main use in everyday life is to power individual and both of them with ordinary high power from 0.5 W.

LED Power

At the beginning of the article it was mentioned that LEDs have very high power requirements. The fact is that the LED is powered by current. It's connected with . Look at her.

The picture shows the current-voltage characteristics of diodes of different colors:

This branch shape (close to a parabola) is due to the characteristics of semiconductors and the impurities that are introduced into them, as well as the features of the pn junction. The current, when the voltage applied to the diode is less than the threshold, almost does not increase, or rather its increase is negligible. When the voltage at the diode terminals reaches a threshold level, the current through the diode begins to increase sharply.

If the current through a resistor grows linearly and depends on its resistance and applied voltage, then the increase in current through a diode does not obey this law. And with an increase in voltage by 1%, the current can increase by 100% or more.

Plus to this: for metals, the resistance increases as its temperature increases, but for semiconductors, on the contrary, the resistance drops, and the current begins to increase.

To find out the reasons for this in more detail, you need to delve into the course “Physical Foundations of Electronics” and learn about the types of charge carriers, the band gap and other interesting things, but we will not do this, we briefly considered these issues.

In technical specifications, the threshold voltage is designated as the voltage drop in forward bias; for white LEDs it is usually about 3 volts.

At first glance, it may seem that at the stage of design and production of the lamp it is enough to set a stable voltage at the output of the power supply and everything will be fine. They do this on LED strips, but they are powered from stabilized power supplies, and besides, the power of the LEDs used in strips is often * small, tenths and hundredths of a watt.

If such an LED is powered by a driver with a stable output current, then when the LED heats up, the current through it will not increase, but will remain unchanged, and the voltage at its terminals will therefore decrease slightly.

And if from the power supply (voltage source), after heating the current will increase, which will make the heating even stronger.

There is one more factor - the characteristics of all LEDs (as well as other elements) are always different.

Driver selection: characteristics, connection

To choose the right driver, you need to familiarize yourself with its technical characteristics, the main ones are:

Rated output current;

Maximum power;

Minimum power. Not always indicated. The fact is that some drivers will not start if a load less than a certain power is connected to them.

Often in stores, instead of power, they indicate:

Rated output current;

Output voltage range in the form of (min.)V...(max.)V, for example 3-15V.

The number of connected LEDs depends on the voltage range, written in the form (min)...(max), for example 1-3 LEDs.

Since the current through all elements is the same when connected in series, therefore the LEDs are connected to the driver in series.

It is not advisable (or rather impossible) to connect LEDs in parallel to the driver, because the voltage drops on the LEDs may differ slightly and one will be overloaded, and the other, on the contrary, will operate in a mode below the nominal one.

It is not recommended to connect more LEDs than specified by the driver design. The fact is that any power source has a certain maximum permissible power, which cannot be exceeded. And for each LED connected to a source of stabilized current, the voltage at its outputs will increase by approximately 3V (if the LED is white), and the power will be equal to the product of current and voltage, as usual.

Based on this, we will draw conclusions: in order to buy the right driver for LEDs, you need to determine the current that the LEDs consume and the voltage that drops across them, and select the driver according to the parameters.

For example, this driver supports connecting up to 12 powerful 1W LEDs with a current consumption of 0.4A.

This one produces a current of 1.5A and a voltage from 20 to 39V, which means you can connect to it, for example, a 1.5A LED, 32-36V and a power of 50W.

Conclusion

A driver is one type of power supply designed to provide LEDs with a given current. In principle, it doesn’t matter what this power source is called. Power supplies are called power supplies for 12 or 24 Volt LED strips; they can supply any current below the maximum. Knowing the correct names, you are unlikely to make a mistake when purchasing a product in stores, and you will not have to change it.

The most optimal way to connect to 220V, 12V is to use a current stabilizer or LED driver. In the language of the intended enemy it is written “led driver”. By adding the desired power to this request, you can easily find a suitable product on Aliexpress or Ebay.

• 1. Features of Chinese
• 2. Service life
• 3. LED driver 220V
• 4. RGB driver 220V
• 5. Module for assembly
• 6. Driver for LED lamps
• 7. Power supply for LED strip
• 8. DIY LED driver
• 9. Low voltage
• 10. Brightness adjustment

Features of Chinese

Many people like to buy from the largest Chinese bazaar, Aliexpress. prices and assortment are good. LED driver is most often chosen due to its low cost and good performance.

But with the rise in the dollar exchange rate, it became unprofitable to buy from the Chinese, the cost became equal to the Russian one, and there was no guarantee or possibility of exchange. For cheap electronics, the characteristics are always overestimated. For example, if the power specified is 50 watts, at best this is the maximum short-term power, not constant. The nominal will be 35W - 40W.

In addition, they save a lot on the filling to reduce the price. In some places there are not enough elements that ensure stable operation. The cheapest components are used, with a short service life and low quality, so the defect rate is relatively high. As a rule, components operate at the limit of their parameters, without any reserve.

If the manufacturer is not listed, then he does not have to be responsible for the quality and no review will be written about his product. And the same product is produced by several factories in different configurations. For good products, the brand must be indicated, which means that he is not afraid to be responsible for the quality of his products.

One of the best is the MeanWell brand, which values ​​the quality of its products and does not produce junk.

Life time

Like any electronic device, the LED driver has a service life that depends on operating conditions. Branded modern LEDs already work up to 50-100 thousand hours, so the power fails earlier.

Classification:

1. consumer goods up to 20,000 hours;
2. average quality up to 50,000 hours;
3. up to 70,000h. power supply using high-quality Japanese components.

This indicator is important when calculating long-term payback. There is enough consumer goods for household use. Although the miser pays twice, and this works great in LED spotlights and lamps.

LED driver 220V

Modern LED drivers are designed using a PWM controller, which can stabilize the current very well.

Main parameters:

1. rated power;
2. operating current;
3. number of connected LEDs;
4. degree of protection against moisture and dust
5. Power factor;
6. Stabilizer efficiency.

Housings for outdoor use are made of metal or impact-resistant plastic. When the case is made of aluminum, it can act as a cooling system for electronic components. This is especially true when filling the body with compound.

The markings often indicate how many LEDs can be connected and what power. This value can be not only fixed, but also in the form of a range. For example, 4 to 7 pieces of 1W are possible. It depends on the LED driver circuit design.

RGB driver 220V

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Three-color RGB LEDs differ from single-color LEDs in that they contain crystals of different colors (red, blue, and green) in one housing. To control them, each color must be lit separately. For diode strips, an RGB controller and power supply are used for this.

If a power of 50W is indicated for an RGB LED, then this is the total for all 3 colors. To find out the approximate load on each channel, divide 50W by 3, we get about 17W.

In addition to powerful led drivers, there are also 1W, 3W, 5W, 10W.

There are 2 types of remote controls. With infrared control, like a TV. With radio control, the remote control does not need to be pointed at the signal receiver.

Assembly module

If you are interested in an LED driver for assembling an LED spotlight or lamp with your own hands, then you can use an LED driver without a housing.

Before making a 50W led driver with your own hands, it’s worth searching a little, for example, every diode lamp contains it. If you have a faulty light bulb whose diodes are faulty, then you can use the driver from it.

Low voltage

We will analyze in detail the types of low-voltage ice drivers operating from voltages up to 40 volts. Our Chinese brothers-in-mind offer many options. Voltage stabilizers and current stabilizers are produced on the basis of PWM controllers. The main difference is that the module with the ability to stabilize the current has 2-3 blue regulators on the board, in the form of variable resistors.

The technical characteristics of the entire module are indicated by the PWM parameters of the microcircuit on which it is assembled. For example, the outdated but popular LM2596 according to its specifications holds up to 3 Amperes. But without a radiator it will only handle 1 Ampere.

A more modern option with improved efficiency is the XL4015 PWM controller designed for 5A. With a miniature cooling system, it can operate up to 2.5A.

If you have very powerful, super-bright LEDs, then you need an LED driver for LED lamps. Two radiators cool the Schottky diode and the XL4015 chip. In this configuration, it is capable of operating up to 5A with voltage up to 35V. It is advisable that it does not operate in extreme conditions, this will significantly increase its reliability and service life.

If you have a small lamp or pocket spotlight, then a miniature voltage stabilizer with a current of up to 1.5A is suitable for you. Input voltage from 5 to 23V, output up to 17V.

Brightness adjustment

To regulate the brightness of the LED, you can use compact LED dimmers that have appeared recently. If its power is not enough, then you can install a larger dimmer. They usually operate in two ranges: 12V and 24V.

You can control it using an infrared or radio remote control (RC). They cost from 100 rubles for a simple model and from 200 rubles for a model with a remote control. Basically, such remote controls are used for 12V diode strips. But it can easily be connected to a low-voltage driver.

Dimming can be analog in the form of a rotary knob or digital in the form of buttons.

LED lamps have become widespread, as a result of which the active production of secondary power supplies has begun. The LED lamp driver is capable of stably maintaining the specified current values ​​at the output of the device, stabilizing the voltage passing through the diode chain.

We will tell you everything about the types and principles of operation of a current conversion device for operating a diode light bulb. Our article provides guidelines for choosing a driver and provides useful recommendations. Independent home electricians will find connection diagrams proven in practice.

Diode crystals consist of two semiconductors - anode (plus) and cathode (minus), which are responsible for the transformation of electrical signals. One area has P-type conductivity, the second – N. When a power source is connected, current will flow through these elements.

Due to this polarity, electrons from the P-type zone rush to the N-type zone, and vice versa, charges from point N rush to P. However, each section of the region has its own boundaries, called P-N junctions. At these sites, particles meet and are mutually absorbed or recombine.

A diode is a semiconductor element and has only one p-n junction. For this reason, the main characteristic that determines the brightness of their glow is not voltage, but current

During P-N transitions, the voltage decreases by a certain number of volts, always the same for each element of the circuit. Taking these values ​​into account, the driver stabilizes the incoming current and produces a constant value at the output.

What power is required and what values ​​of losses during P-N passage are indicated in the passport of the LED device. Therefore, it is necessary to take into account the parameters of the power supply, the range of which must be sufficient to compensate for lost energy.

In order for high-power LEDs to work for the time specified in the characteristics, a stabilizing device is required - a driver. The body of the electronic mechanism always shows its output voltage

Power supplies with voltages from 10 to 36 V are used to equip lighting devices.

Equipment can be of various types:

• headlights of cars, bicycles, motorcycles, etc.;
• small portable or street lamps;
• , tapes, and modules.

However, for, as well as in the case of using constant voltage, it is permissible not to use drivers. Instead, a resistor is added to the circuit, also powered from a 220 V network.

Operating principle of the power supply

Let's figure out what the differences are between a voltage source and a power supply. As an example, consider the diagram shown below.

By connecting a 40 ohm resistor to a 12 V power source, a current of 300 mA will flow through it (Figure A). When a second resistor is connected in parallel to the circuit, the current value will be 600 mA (B). However, the voltage will remain unchanged.

Despite connecting two resistors to the power source, the second one will create a constant voltage at the output, because under ideal conditions it is not subject to the load

Now let's look at how the values ​​change if resistors are connected to the power supply in the circuit. Similarly, we introduce a 40 Ohm rheostat with a 300 mA driver. The latter creates a voltage of 12 V on it (circuit B).

If the circuit is made up of two resistors, then the current value is unchanged, and the voltage will be 6 V (G).

The driver, unlike the voltage source, maintains the specified current parameters at the output, but the voltage power can vary

Drawing conclusions, we can say that a high-quality converter supplies the load with the rated current even when the voltage drops. Accordingly, diode crystals with 2 V or 3 V and a current of 300 mA will burn equally brightly with a reduced voltage.

Distinctive characteristics of the converter

One of the most important indicators is the transmitted power under load. Do not overload the device and try to get the best possible results.

Incorrect use contributes to the rapid failure of not only the viewing mechanism, but also the LED chips.

The main factors influencing work include:

• constituent elements used in the assembly process;
• degree of protection (IP);
• minimum and maximum values ​​at the input and output;
• manufacturer.

Modern models of converters are produced on the basis of microcircuits and use pulse-width conversion (PWM) technology.

During operation of the power supply, a pulse-width modulation method has been introduced to regulate the output voltage, while the same kind of current is maintained at the output as at the input

Such devices are characterized by a high degree of protection against short circuits, network overloads, and also have increased efficiency.

Rules for selecting a current converter

To purchase an LED lamp converter, you should study the key ones. It is worth relying on the output voltage, rated current and output power.

LED power

Let us initially analyze the output voltage, which is subject to several factors:

• the value of voltage losses at the P-N junctions of the crystals;
• number of light diodes in the chain;
• connection diagram.

The parameters of the rated current can be determined by the characteristic features of the consumer, namely the power of the LED elements and the degree of their brightness.

This indicator will affect the current consumed by the crystals, the range of which varies based on the required brightness. The task of the converter is to provide these elements with the required amount of energy.

The output voltage value must be greater than or identical to the total amount of energy expended on each block of the electrical circuit

The power of the device depends on the strength of each LED element, their color and quantity.

To calculate the energy consumed, use the following formula:

P H = P LED * N,

N is the number of crystals in the chain.

The obtained indicators should not be less than the driver power. Now it is necessary to determine the required nominal value.

Maximum power of the device

It should also be taken into account that in order to ensure stable operation of the converter, its nominal values ​​must exceed the obtained PH value by 20-30%.

Thus the formula takes the form:

P max ≥ (1.2..1.3) * P H,

where P max is the rated power of the power supply.

In addition to the power and number of consumers on the board, the load strength is also subject to the color factors of the consumer. With the same current, depending on the shade, they have different voltage drops.

The driver for the LED lamp must supply the amount of current necessary to ensure maximum brightness. When selecting a device, the buyer must remember that the power must be greater than what all LEDs use

Let's take, for example, LEDs from the American company Cree from the XP-E line in red.

Their characteristics are as follows:

• voltage drop 1.9-2.4 V;
• current 350 mA;
• average power consumption 750 mW.

A green analogue at the same current will have completely different indicators: losses at P-N junctions are 3.3-3.9 V, and the power is 1.25 W.

Accordingly, we can draw conclusions: a driver rated at 10 W is used to power twelve red crystals or eight green ones.

LED connection diagram

The choice of driver should be made after determining the connection diagram for LED consumers. If you first purchase light diodes and then select a converter for them, this process will be accompanied by a lot of difficulties.

To find a device that ensures the operation of exactly this number of consumers with a given connection diagram, you will have to spend a lot of time.

Let's give an example with six consumers. Their voltage loss is 3 V, current consumption is 300 mA. To connect them, you can use one of the methods, and in each individual case the required parameters of the power supply will differ.

The disadvantage of alternating diodes is the need for a higher voltage power supply if there are a lot of crystals in the circuit

In our case, when connected in series, an 18 V unit with a current of 300 mA is required. The main advantage of this method is that the same power passes through the entire line, and accordingly, all diodes burn with identical brightness.

The disadvantage of parallel placement of consumers is the difference in the brightness of each chain. This negative phenomenon occurs due to the scattering of diode parameters due to differences between the current passing through each line

If parallel placement is used, it is enough to use a 9 V converter, however, the consumed current will be doubled compared to the previous method.

The method of sequential arrangement of two diodes cannot be used with a change in the number of crystals included in the group - 3 or more. Such restrictions are due to the fact that too much current can pass through one element, and this creates the likelihood of failure of the entire circuit

If a sequential method is used with the formation of pairs of two LEDs, a driver with similar performance is used as in the previous case. In this case, the brightness of the lighting will be uniform.

However, even here there are some negative nuances: when power is supplied to the group, due to the variation in characteristics, one of the LEDs can open faster than the second, and accordingly, a current twice the nominal value will flow through it.

Many types are designed for such short-term jumps, but this method is less popular.

Types of drivers by device type

Devices that convert 220 V power to the required indicators for LEDs are conventionally divided into three categories: electronic; based on capacitors; dimmable.

The lighting accessories market is represented by a wide variety of driver models, mainly from Chinese manufacturers. And despite the low price range, you can choose a very decent option from these devices. However, you should pay attention to the warranty card, because Not all products presented are of acceptable quality.

Electronic view of the device

Ideally, the electronic converter should be equipped with a transistor. Its role is to unload the control microcircuit. To eliminate or smooth out ripple as much as possible, a capacitor is mounted at the output.

This type of device belongs to the expensive category, but it is capable of stabilizing current up to 750 mA, which ballast mechanisms are not capable of.

The newest drivers are mainly installed on light bulbs with an E27 socket. An exception to the rule is Gauss GU5.3 products. They are equipped with a transformerless converter. However, the degree of pulsation in them reaches several hundred Hz

Pulsation is not the only drawback of converters. The second can be called electromagnetic interference in the high frequency (HF) range. So, if other electrical appliances are connected to the socket connected to the lamp, for example, a radio, you can expect interference when receiving digital FM frequencies, television, router, etc.

The optional device of a quality device must have two capacitors: one is electrolytic to smooth out ripples, the other is ceramic to reduce RF. However, such a combination can be found rarely, especially when talking about Chinese products.

Those who have general concepts in such electrical circuits can independently select the output parameters of the electronic converter by changing the value of the resistors

Due to their high efficiency (up to 95%), such mechanisms are suitable for powerful devices used in various fields, for example, for car tuning, street lighting, and household LED sources.

Capacitor based power supply

Now let's move on to less popular devices - those based on capacitors. Almost all low-cost LED lamp circuits that use this type of driver have similar characteristics.

However, due to modifications by the manufacturer, they undergo changes, for example, the removal of some circuit element. Especially often this part is one of the capacitors - a smoothing one.

Due to the uncontrolled filling of the market with cheap and low-quality goods, users can “feel” one hundred percent pulsation in the lamps. Even without delving into their design, we can say that the smoothing element has been removed from the circuit

Such mechanisms have only two advantages: they are available for self-assembly, and their efficiency is equal to one hundred percent, since losses will only occur at p-n junctions and resistances.

There are the same number of negative aspects: low electrical safety and high degree of pulsation. The second disadvantage is around 100 Hz and is formed as a result of rectification of the alternating voltage. GOST specifies a norm of permissible pulsation of 10-20%, depending on the purpose of the room where the lighting device is installed.

The only way to mitigate this drawback is to select a capacitor with the correct rating. However, you should not count on completely eliminating the problem - such a solution can only smooth out the intensity of the bursts.

Dimmable current converters

Drivers-dimmers allow you to change the incoming and outgoing current indicators, while reducing or increasing the brightness of the light emitted by the diodes.

There are two connection methods:

• the first involves a soft start;
• the second is impulse.

Consider the operating principle of dimmable drivers based on the CPC9909 chip, used as a regulating device for LED circuits, including those with high brightness.

Diagram of standard connection of CPC9909 with 220 V power supply. According to the schematic instructions, it is possible to control one or more powerful consumers

During a soft start, the microcircuit with the driver ensures gradual switching on of the diodes with increasing brightness. This process involves two resistors connected to the LD pin, designed to perform the task of smooth dimming. This is how an important task is achieved – extending the service life of LED elements.

The same output also provides analog regulation - the 2.2 kOhm resistor is replaced with a more powerful variable analogue - 5.1 kOhm. In this way, a smooth change in output potential is achieved.

The use of the second method involves supplying rectangular pulses to the low-frequency output of the PWMD. In this case, either a microcontroller or a pulse generator is used, which are necessarily separated by an optocoupler.

With or without housing?

Drivers are available with or without a housing. The first option is the most common and more expensive. Such devices are protected from moisture and dust particles.

Devices of the second type are used for hidden installation and, accordingly, are inexpensive.

All presented devices can be powered from a 12 V or 220 V network. Despite the fact that open-frame models benefit in price, they lag significantly behind in terms of safety and reliability of the mechanism

Each of them differs in the permissible temperature during operation - this must also be taken into account when selecting.

Classic driver circuit

To independently assemble an LED power supply, we will deal with the simplest pulse-type device that does not have galvanic isolation. The main advantage of this type of circuit is simple connection and reliable operation.

The scheme of such a mechanism is composed of three main cascade areas:

1. Capacitive voltage separator.
2. Rectifier.
3. Surge Protectors.

The first section is the resistance provided to alternating current on capacitor C1 with a resistor. The latter is required solely for self-charging of the inert element. It does not affect the operation of the circuit.

When the generated half-wave voltage passes through the capacitor, current flows until the plates are fully charged. The smaller the capacity of the mechanism, the less time it will take to fully charge it.

For example, a device with a volume of 0.3-0.4 μF is charged during 1/10 of the half-wave period, i.e., only a tenth of the passing voltage will pass through this section.

The straightening process in this section is carried out according to the Graetz scheme. The diode bridge is selected based on the rated current and reverse voltage. In this case, the last value should not be less than 600 V

The second stage is an electrical device that converts (rectifies) alternating current into pulsating current. This process is called full-wave. Since one part of the half-wave has been smoothed by a capacitor, the output of this section will have a DC current of 20-25 V.

Since the LED power supply should not exceed 12 V, a stabilizing element must be used for the circuit. For this purpose, a capacitive filter is introduced. For example, you can use model L7812

The third stage operates on the basis of a smoothing stabilizing filter - an electrolytic capacitor. The choice of its capacitive parameters depends on the load strength.

Since the assembled circuit reproduces its operation immediately, you cannot touch the bare wires, since the conducted current reaches tens of amperes - the lines are first insulated.

Conclusions and useful video on the topic

All the difficulties that a radio amateur may encounter when selecting a converter for powerful LED lamps are described in detail in the video:

Key features of independently connecting a converter device to an electrical circuit:

Step-by-step instructions describing the process of assembling an LED driver with your own hands using improvised means:

Despite the tens of thousands of hours of uninterrupted operation of LED lamps declared by the manufacturer, there are many factors that significantly reduce these indicators.

Drivers are designed to smooth out all current jumps in the electrical system. Their selection or self-assembly must be approached responsibly after calculating all the necessary parameters.

Tell us about how you selected the driver for the LED light bulb. Share your arguments and ways to stabilize the voltage supply to a diode lighting device. Leave comments in the block below, ask questions, post photographs on the topic of the article.

Regular readers are often interested in how to properly power LEDs to maximize their service life. This is especially true for LEDs of unknown manufacture with poor technical characteristics or overestimated ones.

It is impossible to determine quality by appearance and parameters. We often have to tell you how to calculate a power supply for LEDs, which one is better to buy or make yourself. Basically, I recommend buying a ready-made one; any circuit after assembly requires testing and adjustment.

• 1. Basic types
• 2. How to make the calculation
• 3. Calculator for calculation
• 4. Connection in the car
• 5. LED supply voltage
• 6. Connection from 12V
• 7. Connection from 1.5V
• 8. How to calculate the driver
• 9. Low voltage from 9V to 50V
• 10. Built-in driver, hit 2016
• 11. Characteristics

Main types

A LED is a semiconductor electronic element with low internal resistance. If you apply a stabilized voltage to it, for example 3V, a large current will flow through it, for example 4 Amperes, instead of the required 1A. The power on it will be 12W, and the thin conductors that connect the crystal will burn out. Conductors are clearly visible on color and RGB diodes, because they do not have a yellow phosphor.

If the power supply for LEDs is 12V with a stabilized voltage, then a resistor is installed in series to limit the current. The disadvantage of this connection will be higher energy consumption; the resistor also consumes some energy. For 1.5V LED rechargeable flashlights, it is irrational to use such a circuit. The number of volts on the battery decreases quickly, and the brightness will decrease accordingly. And without increasing it to at least 3V, the diode will not work.

Specialized LED drivers based on PWM controllers do not have these disadvantages. When the voltage changes, the current remains constant.

How to make a calculation

1. rated power consumption or desired;
2. drop voltage.

The total energy consumption of the connected electrical circuit should not exceed the power of the unit.

The voltage drop depends on how much light the ice chip emits. I recommend buying branded LEDs, such as Bridgelux, their variation in parameters is minimal. They are guaranteed to keep the declared characteristics and have a reserve for them. If you buy at a Chinese market, such as Aliexpress, then don’t expect a miracle, 90% of the time they will deceive you and send you junk with parameters 2-5 times worse. This was checked many times by my colleagues, who ordered inexpensive LED 5730 sometimes 10 times. They received SMD5730 at 0.1W, instead of 0.5W. This was determined by the current-voltage characteristic.

In addition, the cheap ones have a very wide range of parameters. To determine this at home with your own hands, connect 5-10 of them in series. I adjust the number of volts until they glow slightly. You will see that some shine brighter, others are barely noticeable. Therefore, some will heat up more in the nominal operating mode, others less. The power on them will be different, so the most loaded ones will fail before the rest.

Calculator for calculation

The calculator takes into account 4 parameters:

• number of volts at the output;
• voltage reduction on one LED;
• rated operating current;
• number of LEDs in the circuit.

Connection in the car

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When the engine is running, there is an average of 13.5V - 14.5V, and when the engine is off, 12V - 12.5V. Special requirements when plugged into a car cigarette lighter or on-board network. Short-term surges can be up to 30V. If you use a current-limiting resistor, then the current increases in direct proportion to the increase in the LED supply voltage. For this reason, it is better to install a stabilizer on the microcircuit.

The disadvantage of using it in a car may be the appearance of interference on the radio in the VHF range. The PWM controller operates at high frequencies and will interfere with your radio. You can try replacing it with another or linear type. Sometimes shielding with metal and placing it away from the car's head unit helps.

LED supply voltage

From the tables it can be seen that for low-power ones at 1W, 3W this indicator is 2B for red, yellow, orange. For white, blue, green it is from 3.2V to 3.4V. For powerful ones from 7V to 34V. These numbers will have to be used for calculations.

Table for LED at 1W, 3W, 5W

Table for high-power LEDs 10W, 20W, 30W, 50W, 100W

Connection from 12V

One of the most common voltages is 12 Volts, they are present in household appliances, cars and automotive electronics. Using 12V you can fully connect 3 LED diodes. An example is a 12V LED strip, in which 3 pieces and a resistor are connected in series.

Example on diode 1W, its rated current is 300mA.

• If one LED drops 3.2V, then for 3 pieces it will be 9.6V;
• the resistor will have 12V – 9.6V = 2.4V;
• 2.4 / 0.3 = 8 Ohms nominal required resistance;
• 2.4 * 0.3 = 0.72W will be dissipated by the resistor;
• 1W + 1W + 1W + 0.72 = 3.72W total power consumption of the entire circuit.

Similarly, you can calculate for another number of elements in the circuit.

Connection from 1.5V

The power source for the LEDs can be a simple 1.5V AA battery. An LED diode usually requires a minimum of 3V; there is no way to do this without a stabilizer. These specialized LED drivers are used in hand-held flashlights on the Cree Q5 and Cree XML T6. A miniature microcircuit increases the number of volts to 3V and stabilizes 700mA. Switching on from 1.5 volts using a current-limiting resistor is impossible. If we use two 1.5 volt batteries, connecting them in series, we get 3V. But the batteries run out quite quickly, and the brightness will drop even faster. At 2.5V there will still be a lot of capacity left in the batteries, but the diode will almost go out. And the LED driver will maintain the nominal brightness even at 1V.

I usually order such modules on Aliexpress, the Chinese cost 50-100 rubles, in Russia they are a bit expensive.

How to calculate the driver

1. draw up a connection diagram on paper;
2. if the driver is Chinese, then it is advisable to check whether it can withstand the declared power or not;
3. keep in mind that different colors (blue, red, green) have different volt drops;
4. the total power should not be higher than that of the current source.

Draw a connection diagram on which you will distribute the elements if they are connected not just in series, but in combination with a parallel connection.

On a Chinese power supply from an unknown manufacturer, the power may be significantly lower. They easily indicate the maximum peak power, and not the rated long-term power. It is more difficult to check; you need to load the power supply to the maximum and measure the parameters.

For the third point, use the example tables for 1W,3W, 5W, 10W, 20W, 30W, 50W, 100W, which are given above. But trust more in the characteristics that the seller gave you. For single-chip ones there are 3V, 6V, 12V.

If the total power consumption of the circuit exceeds the rated power of the power source, the current will drop and heating will increase. It will recover to normal levels if the load is reduced.

For LED strips, the calculation is very simple. Measure the number of watts per meter and multiply by the number of meters. Just measure, in most cases the power is overestimated and instead of 14.4 W/m you will get 7 W/m. All too often disappointed customers come to me with this problem.

Low voltage from 9V to 50V

I’ll briefly tell you what I use to switch on 12V, 19V, 24V units and to connect to 12V automobiles.

Most often I buy ready-made modules on PWM chips:

1. there are boosters, for example, 12V at the input, 22V at the output;
2. step-down, for example from 24V to 17V.

Not everyone wants to spend a lot of money on buying a ready-made spotlight for a car, an LED lamp, or order a ready-made driver. Therefore, they turn to me to assemble something decent from available components. The price of such modules starts from 50 rubles to 300 rubles for a 5A model with a radiator. I buy several pieces in advance, they sell out quickly.

The most popular option is the linear IC, a simple, reliable, outdated one.

Models based on LM2596 are very popular, but it is already outdated and I advise you to pay attention to a more modern one with good efficiency. Such blocks have from 1 to 3 tuning resistances, which can be used to adjust any parameters up to 30V and up to 5A.

Built-in driver, hit 2016

At the beginning of 2016, LED modules and COB diodes with an integrated driver began to gain popularity. They are connected directly to a 220V network, ideal for assembling lighting equipment with your own hands. All elements are located on one heat-conducting plate. PWM controllers are miniature, thanks to good contact with the cooling system. We have not yet tested the reliability and stability; the first reviews will appear after at least six months of use. I have already ordered the cheapest and most affordable COB model at 50W. To find these on the Aliexpress Chinese bazaar, enter “integrated led driver” in the search.

Characteristics

A global problem is counterfeiting of Cree and Philips LEDs on an industrial scale. The Chinese have entire enterprises for this; they copy 95-99% of them externally; it is impossible for an ordinary buyer to tell the difference. The worst thing is when such a fake is sold to you under the guise of the original Cree T6. You will connect the fake one according to the technical specifications of the original one. A fake has characteristics that are on average 30% worse. Less luminous flux, lower maximum operating temperature, lower power consumption. You will not find out about the deception very soon; it will work about 5-10 times less than the real one, especially at double current.

Recently I measured the luminous flux of my flashlights on the left Cree made by LatticeBright. I took out the entire board with the driver and placed it in a photometric ball. The result was 180-200 lumens, the original had 280-300 lumens. Without serious equipment, which is mainly found in laboratories, you will not be able to measure and therefore find out the truth.

Sometimes you come across overclocked diodes, the current on which is 30%-60% higher than the rated one, and accordingly the power. An unscrupulous manufacturer, especially a basement Chinese one, takes advantage of the fact that service life is difficult to measure in hours. After all, no one records the time worked, and when a lamp or LED spotlight fails, the seller can no longer be found. And there is no point in searching, the warranty period for such products is always shorter than the service life.

The standard RT4115 LED driver circuit is shown in the figure below:

The supply voltage should be at least 1.5-2 volts higher than the total voltage across the LEDs. Accordingly, in the supply voltage range from 6 to 30 volts, from 1 to 7-8 LEDs can be connected to the driver.

Maximum supply voltage of the microcircuit 45 V, but operation in this mode is not guaranteed (better pay attention to a similar microcircuit).

The current through the LEDs has a triangular shape with a maximum deviation from the average value of ±15%. The average current through the LEDs is set by a resistor and calculated by the formula:

I LED = 0.1 / R

The minimum permissible value is R = 0.082 Ohm, which corresponds to a maximum current of 1.2 A.

The deviation of the current through the LED from the calculated one does not exceed 5%, provided that resistor R is installed with a maximum deviation from the nominal value of 1%.

So, to turn on the LED at constant brightness, we leave the DIM pin hanging in the air (it is pulled up to the 5V level inside the PT4115). In this case, the output current is determined solely by resistance R.

If we connect a capacitor between the DIM pin and ground, we get the effect of smooth lighting of the LEDs. The time it takes to reach maximum brightness will depend on the capacitor capacity; the larger it is, the longer the lamp will light up.

For reference: Each nanofarad of capacitance increases the turn-on time by 0.8 ms.

If you want to make a dimmable driver for LEDs with brightness adjustment from 0 to 100%, then you can resort to one of two methods:

1. First way assumes that a constant voltage in the range from 0 to 6V is supplied to the DIM input. In this case, brightness adjustment from 0 to 100% is carried out at a voltage at the DIM pin from 0.5 to 2.5 volts. Increasing the voltage above 2.5 V (and up to 6 V) does not affect the current through the LEDs (the brightness does not change). On the contrary, reducing the voltage to a level of 0.3V or lower leads to the circuit turning off and putting it into standby mode (the current consumption drops to 95 μA). Thus, you can effectively control the operation of the driver without removing the supply voltage.
2. Second way involves supplying a signal from a pulse-width converter with an output frequency of 100-20000 Hz, the brightness will be determined by the duty cycle (pulse duty cycle). For example, if the high level lasts 1/4 of the period, and the low level, respectively, 3/4, then this will correspond to a brightness level of 25% of the maximum. You must understand that the driver operating frequency is determined by the inductance of the inductor and in no way depends on the dimming frequency.

The PT4115 LED driver circuit with constant voltage dimmer is shown in the figure below:

This circuit for adjusting the brightness of the LEDs works great due to the fact that inside the chip the DIM pin is “pulled up” to the 5V bus through a 200 kOhm resistor. Therefore, when the potentiometer slider is in its lowest position, a voltage divider of 200 + 200 kOhm is formed and a potential of 5/2 = 2.5V is formed at the DIM pin, which corresponds to 100% brightness.

How the scheme works

At the first moment of time, when the input voltage is applied, the current through R and L is zero and the output switch built into the microcircuit is open. The current through the LEDs begins to gradually increase. The rate of current rise depends on the magnitude of the inductance and supply voltage. The in-circuit comparator compares the potentials before and after resistor R and, as soon as the difference is 115 mV, a low level appears at its output, which closes the output switch.

Thanks to the energy stored in the inductance, the current through the LEDs does not disappear instantly, but begins to gradually decrease. The voltage drop across the resistor R gradually decreases. As soon as it reaches a value of 85 mV, the comparator will again issue a signal to open the output switch. And the whole cycle repeats all over again.

If it is necessary to reduce the range of current ripples through the LEDs, it is possible to connect a capacitor in parallel with the LEDs. The larger its capacity, the more the triangular shape of the current through the LEDs will be smoothed out and the more similar it will become to a sinusoidal one. The capacitor does not affect the operating frequency or efficiency of the driver, but increases the time it takes for the specified current through the LED to settle.

Important assembly details

An important element of the circuit is capacitor C1. It not only smoothes out ripples, but also compensates for the energy accumulated in the inductor at the moment the output switch is closed. Without C1, the energy stored in the inductor will flow through the Schottky diode to the power bus and can cause a breakdown of the microcircuit. Therefore, if you turn on the driver without a capacitor shunting the power supply, the microcircuit is almost guaranteed to shut down. And the greater the inductance of the inductor, the greater the chance of burning the microcontroller.

The minimum capacitance of capacitor C1 is 4.7 µF (and when the circuit is powered with a pulsating voltage after the diode bridge - at least 100 µF).

The capacitor should be located as close to the chip as possible and have the lowest possible ESR value (i.e. tantalum capacitors are welcome).

It is also very important to take a responsible approach to choosing a diode. It must have a low forward voltage drop, short recovery time during switching, and stability of parameters as the temperature of the p-n junction increases, in order to prevent an increase in leakage current.

In principle, you can take a regular diode, but Schottky diodes are best suited to these requirements. For example, STPS2H100A in SMD version (forward voltage 0.65V, reverse - 100V, pulse current up to 75A, operating temperature up to 156°C) or FR103 in DO-41 housing (reverse voltage up to 200V, current up to 30A, temperature up to 150 °C). The common SS34s performed very well, which you can pull out of old boards or buy a whole pack for 90 rubles.

The inductance of the inductor depends on the output current (see table below). An incorrectly selected inductance value can lead to an increase in the power dissipated on the microcircuit and exceeding the operating temperature limits.

If it overheats above 160°C, the microcircuit will automatically turn off and remain in the off state until it cools down to 140°C, after which it will start automatically.

Despite the available tabular data, it is permissible to install a coil with an inductance deviation greater than the nominal value. In this case, the efficiency of the entire circuit changes, but it remains operational.

You can take a factory choke, or you can make it yourself from a ferrite ring from a burnt motherboard and PEL-0.35 wire.

If maximum autonomy of the device is important (portable lamps, lanterns), then, in order to increase the efficiency of the circuit, it makes sense to spend time carefully selecting the inductor. At low currents, the inductance must be larger to minimize current control errors resulting from the delay in switching the transistor.

The inductor should be located as close as possible to the SW pin, ideally connected directly to it.

And finally, the most precision element of the LED driver circuit is resistor R. As already mentioned, its minimum value is 0.082 Ohms, which corresponds to a current of 1.2 A.

Unfortunately, it is not always possible to find a resistor of a suitable value, so it’s time to remember the formulas for calculating the equivalent resistance when resistors are connected in series and in parallel:

• R last = R 1 +R 2 +…+R n;
• R pairs = (R 1 xR 2) / (R 1 +R 2).

By combining different connection methods, you can obtain the required resistance from several resistors at hand.

It is important to route the board so that the Schottky diode current does not flow along the path between R and VIN, as this can lead to errors in measuring the load current.

The low cost, high reliability and stability of driver characteristics on the RT4115 contribute to its widespread use in LED lamps. Almost every second 12-volt LED lamp with an MR16 base is assembled on PT4115 (or CL6808).

The resistance of the current-setting resistor (in Ohms) is calculated using exactly the same formula:

R = 0.1 / I LED[A]

A typical connection diagram looks like this:

As you can see, everything is very similar to the circuit of an LED lamp with a RT4515 driver. The description of the operation, signal levels, features of the elements used and the layout of the printed circuit board are exactly the same as those, so there is no point in repeating.

CL6807 sells for 12 rubles/pcs, you just need to be careful that they don’t slip soldered ones (I recommend taking them).

SN3350

SN3350 is another inexpensive chip for LED drivers (13 rubles/piece). It is almost a complete analogue of PT4115 with the only difference being that the supply voltage can range from 6 to 40 volts, and the maximum output current is limited to 750 milliamps (continuous current should not exceed 700 mA).

Like all the microcircuits described above, the SN3350 is a pulsed step-down converter with an output current stabilization function. As usual, the current in the load (and in our case, one or more LEDs act as the load) is set by the resistance of the resistor R:

R = 0.1 / I LED

To avoid exceeding the maximum output current, resistance R should not be lower than 0.15 Ohm.

The chip is available in two packages: SOT23-5 (maximum 350 mA) and SOT89-5 (700 mA).

As usual, by applying a constant voltage to the ADJ pin, we turn the circuit into a simple adjustable driver for LEDs.

A feature of this microcircuit is a slightly different adjustment range: from 25% (0.3V) to 100% (1.2V). When the potential at the ADJ pin drops to 0.2V, the microcircuit goes into sleep mode with a consumption of around 60 µA.

Typical connection diagram:

For other details, see the specifications for the microcircuit (pdf file).

ZXLD1350

Despite the fact that this microcircuit is another clone, some differences in technical characteristics do not allow their direct replacement with each other.

Here are the main differences:

• the microcircuit starts at 4.8V, but reaches normal operation only with a supply voltage of 7 to 30 Volts (up to 40V can be supplied for half a second);
• maximum load current - 350 mA;
• resistance of the output switch in the open state is 1.5 - 2 Ohms;
• By changing the potential at the ADJ pin from 0.3 to 2.5V, you can change the output current (LED brightness) in the range from 25 to 200%. At a voltage of 0.2V for at least 100 µs, the driver goes into sleep mode with low power consumption (about 15-20 µA);
• if the adjustment is carried out by a PWM signal, then at a pulse repetition rate below 500 Hz, the range of brightness changes is 1-100%. If the frequency is above 10 kHz, then from 25% to 100%;

The maximum voltage that can be applied to the ADJ input is 6V. In this case, in the range from 2.5 to 6V, the driver produces the maximum current, which is set by the current-limiting resistor. The resistor resistance is calculated in the same way as in all of the above microcircuits:

R = 0.1 / I LED

The minimum resistor resistance is 0.27 Ohm.

A typical connection diagram is no different from its counterparts:

Without capacitor C1 it is IMPOSSIBLE to supply power to the circuit!!! At best, the microcircuit will overheat and produce unstable characteristics. In the worst case, it will fail instantly.

More detailed characteristics of the ZXLD1350 can be found in the datasheet for this chip.

The cost of the microcircuit is unreasonably high (), despite the fact that the output current is quite small. In general, it’s very much for everyone. I wouldn't get involved.

QX5241

QX5241 is a Chinese analogue of MAX16819 (MAX16820), but in a more convenient package. Also available under the names KF5241, 5241B. It is marked "5241a" (see photo).

In one well-known store they are sold almost by weight (10 pieces for 90 rubles).

The driver operates on exactly the same principle as all those described above (continuous step-down converter), but does not contain an output switch, so operation requires the connection of an external field-effect transistor.

You can take any N-channel MOSFET with suitable drain current and drain-source voltage. For example, the following are suitable: SQ2310ES (up to 20V!!!), 40N06, IRF7413, IPD090N03L, IRF7201. In general, the lower the opening voltage, the better.

Here are some key features of the LED driver on the QX5241:

• maximum output current - 2.5 A;
• Efficiency up to 96%;
• maximum dimming frequency - 5 kHz;
• maximum operating frequency of the converter is 1 MHz;
• accuracy of current stabilization through LEDs - 1%;
• supply voltage - 5.5 - 36 Volts (works normally at 38!);
• output current is calculated by the formula: R = 0.2 / I LED

Read the specification (in English) for more details.

The LED driver on the QX5241 contains few parts and is always assembled according to this scheme:

The 5241 chip comes only in the SOT23-6 package, so it’s best not to approach it with a soldering iron for soldering pans. After installation, the board should be thoroughly washed to remove flux; any unknown contamination can negatively affect the operation of the microcircuit.

The difference between the supply voltage and the total voltage drop across the diodes should be 4 volts (or more). If it is less, then some glitches in operation are observed (current instability and inductor whistling). So take it with reserve. Moreover, the greater the output current, the greater the voltage reserve. Although, perhaps I just came across a bad copy of the microcircuit.

If the input voltage is less than the total drop across the LEDs, then generation fails. In this case, the output field switch opens completely and the LEDs light up (of course, not at full power, since the voltage is not enough).

AL9910

Diodes Incorporated has created one very interesting LED driver IC: the AL9910. It is curious in that its operating voltage range allows it to be connected directly to a 220V network (via a simple diode rectifier).

Here are its main characteristics:

• input voltage - up to 500V (up to 277V for alternating);
• built-in voltage stabilizer for powering the microcircuit, which does not require a quenching resistor;
• the ability to adjust brightness by changing the potential on the control leg from 0.045 to 0.25V;
• built-in overheating protection (triggered at 150°C);
• operating frequency (25-300 kHz) is set by an external resistor;
• an external field-effect transistor is required for operation;
• Available in eight-legged SO-8 and SO-8EP packages.

The driver assembled on the AL9910 chip does not have galvanic isolation from the network, so it should be used only where direct contact with the circuit elements is impossible.