Drivers for LEDs: types, characteristics and criteria for selecting devices. Homemade driver for high-power LEDs Homemade driver for 10 W LED

Probably everyone, even a novice radio amateur, knows that in order to connect a regular LED to a power source, you only need one resistor. But what if the LED is powerful? Watt so 10. What to do then?
I'll show you a way to make a simple driver for a high-power LED using just two components.

For the stabilizer driver we need:
1. Resistor – .
2. Microcircuit – LM317 – .

LM317 is a stabilizer chip. Great for designing regulated power supplies or drivers to power LEDs, as in our case.

Advantages of LM317

The voltage stabilization range is from 1.7 (including LED voltage - 3 V) to 37 V. An excellent characteristic for motorists: the brightness will not fluctuate at any speed;
Output current up to 1.5, you can connect several powerful LEDs;
The stabilizer has a built-in protection system against overheating and short circuit.
The negative power of the LED in the switching circuit is taken from the power source, so when attached to the car body, the number of mounting wires is reduced, and the body can act as a large heat sink for the LED.

Driver circuit for high power LED

I will connect a 3 Watt LED. As a result, we will need to calculate the resistance for our LED. A 1 W LED consumes 350 mA, and a 3 W LED consumes 700 mA (you can see it in the datasheet). The LM317 microcircuit has a stabilizer reference voltage of 1.25 - this number is constant. It needs to be divided by the current and you get the resistance of the resistor. That is: 1.25 / 0.7 = 1.78 Ohm. We take the current in amperes. We select the closest resistor in terms of resistance, since there are no resistors with a resistance of 1.78. We take 1.8 and assemble the circuit.

If the power of your LED exceeds 1 W, then the chip must be installed on a radiator. In general, LM317 is designed for current up to 1.5.
Our circuit can be powered with voltage from 3 to 37 volts. Agree, a solid range of nutrition is obtained. But the higher the voltage, the more the microcircuit heats up, keep this in mind.

The widespread use of LEDs has led to the mass production of power supplies for them. Such blocks are called drivers. Their main feature is that they are able to stably maintain a given current at the output. In other words, a driver for light emitting diodes (LEDs) is a source of current to power them.

Purpose

Since LEDs are semiconductor elements, the key characteristic that determines the brightness of their glow is not voltage, but current. In order for them to be guaranteed to work for the stated number of hours, a driver is needed - it stabilizes the current flowing through the LED circuit. It is possible to use low-power light-emitting diodes without a driver; in this case, its role is played by a resistor.

Application

Drivers are used both when powering the LED from a 220V network, and from DC voltage sources of 9-36 V. The former are used when lighting rooms with LED lamps and strips, the latter are more often found in cars, bicycle headlights, portable lanterns, etc.

Principle of operation

As already mentioned, the driver is a current source. Its differences from a voltage source are illustrated below.

The voltage source produces a certain voltage at its output, ideally independent of the load.

For example, if you connect a 40 Ohm resistor to a 12 V source, a current of 300 mA will flow through it.

If you connect two resistors in parallel, the total current will be 600 mA at the same voltage.

The driver maintains the specified current at its output. The voltage may change in this case.

Let's also connect a 40 Ohm resistor to the 300 mA driver.

The driver will create a 12V voltage drop across the resistor.

If you connect two resistors in parallel, the current will still be 300 mA, but the voltage will drop to 6 V:

Thus, an ideal driver is capable of delivering the rated current to the load regardless of voltage drop. That is, an LED with a voltage drop of 2 V and a current of 300 mA will burn as brightly as an LED with a voltage of 3 V and a current of 300 mA.

Main characteristics

When selecting, you need to take into account three main parameters: output voltage, current and power consumed by the load.

The driver output voltage depends on several factors:

LED voltage drop;
number of LEDs;
connection method.

The driver output current is determined by the characteristics of the LEDs and depends on the following parameters:

LED power;
brightness.

The power of LEDs affects the current they consume, which can vary depending on the required brightness. The driver must provide them with this current.

Load power depends on:

power of each LED;
their quantities;
colors.

In general, power consumption can be calculated as

where Pled is the LED power,

N is the number of connected LEDs.

The maximum driver power should not be less.

It is worth considering that for stable operation of the driver and to prevent its failure, a power reserve of at least 20-30% should be provided. That is, the following relationship must be satisfied:

where Pmax is the maximum driver power.

In addition to the power and number of LEDs, the load power also depends on their color. LEDs of different colors have different voltage drops for the same current. For example, the red XP-E LED has a voltage drop of 1.9-2.4 V at 350 mA. Its average power consumption is thus about 750 mW.

The green XP-E has a drop of 3.3-3.9 V at the same current, and its average power will be about 1.25 W. That is, a driver rated at 10 watts can power either 12-13 red LEDs or 7-8 green ones.

How to choose a driver for LEDs. LED connection methods

Let's say there are 6 LEDs with a voltage drop of 2 V and a current of 300 mA. You can connect them different ways, and in each case you will need a driver with certain parameters:

It is unacceptable to connect 3 or more LEDs in parallel in this way, since too much current may flow through them, as a result of which they will quickly fail.

Please note that in all cases the driver power is 3.6 W and does not depend on the method of connecting the load.

Thus, it is more advisable to select a driver for LEDs already at the stage of purchasing the latter, having previously determined the connection diagram. If you first purchase the LEDs themselves, and then select a driver for them, this may not be an easy task, since the likelihood that you will find exactly the power source that can ensure the operation of exactly this number of LEDs connected according to a specific circuit is small.

Kinds

In general, LED drivers can be divided into two categories: linear and switching.

The linear output is a current generator. It provides stabilization of the output current with an unstable input voltage; Moreover, the adjustment occurs smoothly, without creating high-frequency electromagnetic interference. They are simple and cheap, but their low efficiency (less than 80%) limits their scope of application to low-power LEDs and strips.

Pulse devices are devices that create a series of high-frequency current pulses at the output.

They usually operate on the principle of pulse width modulation (PWM), that is, the average value of the output current is determined by the ratio of the pulse width to their repetition period (this value is called the duty cycle).

The diagram above shows the operating principle of a PWM driver: the pulse frequency remains constant, but the duty cycle varies from 10% to 80%. This leads to a change in the average value of the output current I cp.

Such drivers are widely used due to their compactness and high efficiency (about 95%). The main disadvantage is the higher level of electromagnetic interference compared to linear ones.

220V LED driver

For inclusion in a 220 V network, both linear and pulsed ones are produced. There are drivers with and without galvanic isolation from the network. The main advantages of the former are high efficiency, reliability and safety.

Without galvanic isolation are usually cheaper, but less reliable and require care when connecting, as there is a risk of electric shock.

Chinese drivers

The demand for drivers for LEDs contributes to their mass production in China. These devices are pulsed current sources, usually 350-700 mA, often without a housing.

Chinese driver for 3w LED

Their main advantages are low price and the presence of galvanic isolation. The disadvantages are the following:

low reliability due to the use of cheap circuit solutions;
lack of protection against overheating and fluctuations in the network;
high level of radio interference;
high level of output ripple;
fragility.

Life time

Typically, the service life of the driver is shorter than that of the optical part - manufacturers provide a guarantee of 30,000 hours of operation. This is due to factors such as:

instability of mains voltage;
temperature changes;
humidity level;
driver load.

The weakest link LED driver are smoothing capacitors, which tend to evaporate the electrolyte, especially in conditions of high humidity and unstable supply voltage. As a result, the level of ripple at the driver output increases, which negatively affects the operation of the LEDs.

Also, the service life is affected by incomplete driver load. That is, if it is designed for 150 W, but operates at a load of 70 W, half of its power returns to the network, causing it to overload. This causes frequent power failures. We recommend reading about.

Driver circuits (chips) for LEDs

Many manufacturers produce specialized driver chips. Let's look at some of them.

ON Semiconductor UC3845 is a pulse driver with an output current of up to 1A. The driver circuit for a 10w LED on this chip is shown below.

Supertex HV9910 is a very common pulse driver chip. The output current does not exceed 10 mA and has no galvanic isolation.

A simple current driver on this chip is shown below.

Texas Instruments UCC28810. Network pulse driver has the ability to organize galvanic isolation. Output current up to 750 mA.

Another microcircuit from this company, a driver for powering powerful LM3404HV LEDs, is described in this video:

The device operates on the principle of a Buck Converter type resonant converter, that is, the function of maintaining the required current here is partially assigned to a resonant circuit in the form of coil L1 and Schottky diode D1 (a typical circuit is shown below). It is also possible to set the switching frequency by selecting a resistor R ON.

Maxim MAX16800 is a linear microcircuit that operates at low voltages, so you can build a 12 volt driver on it. The output current is up to 350 mA, so it can be used as a power driver for a powerful LED, flashlight, etc. There is a possibility of dimming. A typical diagram and structure is presented below.

Conclusion

LEDs are much more demanding on the power supply than other light sources. For example, exceeding the current by 20% for a fluorescent lamp will not entail a serious deterioration in performance, but for LEDs the service life will be reduced several times. Therefore, you should choose a driver for LEDs especially carefully.

Powerful LEDs in lighting devices are connected through electronic drivers that stabilize the current at their output.

Nowadays, so-called energy-saving fluorescent lamps (compact fluorescent lamps - CFLs) have become widespread. But over time, they fail. One of the causes of the malfunction is burnout of the lamp filament. Do not rush to dispose of such lamps because the electronic board contains many components that can be used in the future in other home-made devices. These are chokes, transistors, diodes, capacitors. Typically, these lamps have a functional electronic board, which makes it possible to use them as a power supply or driver for an LED. As a result, in this way we will get a free driver for connecting LEDs, which is even more interesting.

You can watch the process of making homemade products in the video:

List of tools and materials
-energy saving fluorescent lamp;
-screwdriver;
- soldering iron;
-tester;
-white LED 10W;
-enamel wire with a diameter of 0.4 mm;
-thermal paste;
- diodes of the HER, FR, UF brand for 1-2A
-desk lamp.

Step one. Disassembling the lamp.
We disassemble the energy-saving fluorescent lamp by carefully prying it off with a screwdriver. The lamp bulb cannot be broken as there is mercury vapor inside. We call the filament of the bulb with a tester. If at least one thread shows a break, then the bulb is faulty. If there is a working similar lamp, then you can connect the bulb from it to the electronic board being converted to make sure that it is working properly.

Step two. Remaking the electronic converter.
For the modification, I used a 20W lamp, the choke of which can withstand a load of up to 20 W. For a 10W LED this is enough. If you need to connect a more powerful load, you can use an electronic lamp converter board with the appropriate power, or change the inductor with a larger core.

It is also possible to power LEDs of lower power by selecting the required voltage by the number of turns on the inductor.
I mounted wire jumpers on the pins to connect the lamp filaments.

20 turns of enamel wire need to be wound over the primary winding of the inductor. Then we solder the secondary wound winding to the rectifier diode bridge. We connect 220V voltage to the lamp and measure the voltage at the output from the rectifier. It was 9.7V. An LED connected through an ammeter consumes a current of 0.83A. This LED has a rated current of 900mA, but in order to increase its service life, the current consumption is specially reduced. The diode bridge can be assembled on the board by surface mounting.

Diagram of the converted electronic converter board. As a result, from the inductor we get a transformer with a connected rectifier. Added components are shown in green.

Step three. LED assembly table lamp.
We remove the 220 volt lamp socket. I installed a 10W LED using thermal paste on a metal lampshade of an old table lamp. The table lamp shade serves as a heat sink for the LED.

The electronic power board and diode bridge were placed in the housing of the table lamp stand.

10 and 15 watt LED drivers for BP3105 and BP3106

These are the drivers they offer. We managed to find out that they are built on a 3106 (BP3106) chip, which has the following parameters:

conversion frequency: 380kHz
built-in special field switch (although the board has an external SVF4N65M)
Efficiency: up to 96%
built-in overheat protection
built-in current protection

Stated driver parameters:

voltage: 8-15 volts
current: 900 milliamps
load power: 10 watts

A tiny chip labeled 3106 (BP3106) is a PWM controller. Has a minimal set of external body kit. That, in fact, is all that we managed to find out about her. There is also a calculator:

This module cannot be converted without rewinding the transformer to a higher voltage. But it can be converted to lower power within small limits by increasing the resistance of the current-setting resistor on the CS line.

It is stated that this driver is for a 10-watt LED. The board does not have the usual PC817 and TL431: Feedback probably implemented using an additional transformer winding. The transformer is tiny, how it produces 10 watts is not clear. Probably thanks to high frequency transformations. In operation - tested, when powering the LED it produces 12 volts, with the replacement of the resistor - 10 volts.

The printed circuit board is double-sided, the flux has not been washed off. The primary and secondary circuits are isolated. The mains electrolyte is 12 uF 400 volts. Output - 100uF. At the output, two SF26 diodes are used in parallel. Apparently their schottkas are more expensive. Wires are soldered with thick, brittle insulation at the bend. There is no interference filtering of any kind.

Based on this driver and a powerful LED, it is quite possible to build a light bulb in a suitable energy-saving housing.

UP 03/30/2016 A good driver with an external field-effect transistor for 9-15 watt LEDs.

As a matter of fact, this driver was needed in order to power a twenty-watt LED at half the power. A ten-watt driver does not start with it, since the LED needs more high voltage- 30-36 volts.

The 15-watt driver in question has the following characteristics:

voltage: 27-48 volts
current: 300 milliamps
load power: 9-15 watts

It is assembled on the popular BP3105 chip, a relative of the BP3106. A KIA4N60H field-effect transistor without a radiator is installed here, at the input there are two 10uF 400V electrolytes and a fuse, at the output there are two 100uF 35V capacitors. Current-setting resistance - 7.5 Ohm + 1.2 Ohm + 1.2 Ohm, connected in parallel (total 0.55 Ohm).

If you unsolder two resistors and leave one at 1.2 ohms, then with a twenty-watt LED the current drops to 185 mA at 29 volts - a power of about 5.5 W.

With a 20-watt LED, this driver performs excellently, delivering 33 volts at 0.3 amps, powering it at half power as required. Of course, in this case the efficiency of the LED drops significantly, but these Chinese stoves can only operate in this mode. Of course, this driver can also be used to fully power fifteen watts, and it wouldn’t hurt to screw a radiator to the transistor.

How to connect 10W LEDs, And what use can they find?

The 10 W LED matrix is manufactured using MCOV technology and consists of 9 crystals connected 3 in series and 3 chains in parallel. Each crystal is designed for a voltage of 3.2-4.0 V, so in total three series-connected crystals open at 9.6 V and operate normally up to 12 V, which makes it quite easy to use them in cars and for emergency lighting by connecting them directly to battery through current limitingresistancepower 2W.
The resistance value is calculated using Ohm's law. With such a connection to the battery, due to heating of the resistance, losses can amount to 15-25% of the nominal value of the matrix, which is not critical in cars, but significantly reduces the battery discharge time during emergency lighting, therefore, for emergency lighting, DC-DC converters with an efficiency higher than 92% are often used. .

The quality of an LED matrix is determined by three main components: crystal, phosphor, and substrate. For a crystal, in addition to the light output Lm/W, its geometric dimensions are of great importance; the larger the crystal, the larger the contact area with the substrate, which allows for more efficient heat removal, and this is one of the main tasks. Working temperature 60-65 degrees C, but this does not mean that the radiator can heat up to such a temperature because... The temperature of the radiator and the matrix substrate are significantly different. Overheating of the crystal leads to its degradation and a decrease in the service life of the LEDs by times or tens of times, and subsequently to failure of the matrix. The minimum required radiator area is 200-300 sq. cm. depending on parameters and operating conditions. Brighter and higher-quality matrices have a copper substrate, while less bright ones have an aluminum substrate. Copper has a high thermal conductivity, so it is preferable, but even on aluminum, LEDs work normally with a sufficient heatsink, and if you use the matrix not at the full rated power, but at 80% of the nominal power, then even on aluminum the matrices will be able to work for the 50,000-100,000 hours declared by the manufacturer.

From technical characteristics It follows that the 10 W LED assembly is powered by a constant voltage of 12 volts with a current of 900-1000 mA and can heat up to +60 ° C.

First, let's try turning on a 10 W LED.

For a test run, we use a 12-volt DC source, in this case a battery, and a current stabilizer. Also, to test turn on the LED, we will need a radiator-cooler with an area of at least 600 cm 2.

The simplest current stabilizer can be assembled using an LM317 microcircuit and one resistor.

Current stabilizer circuit on LM 317 (hereinafter we will call it a driver)

Using the formula at the bottom of the figure, it is very easy to calculate the resistance value of the resistor for the required current. That is, the resistor resistance is equal to 1.25 divided by the required current. For stabilizers up to 0.1 A, a resistor power of 0.25 W is suitable. For currents from 350 mA to 1 A, 2 W is recommended. Below is a table of resistors for currents for widely used LEDs.

Current (specified current for a standard series resistor)	Resistor resistance	Note
20 mA	62 Ohm	standard LED
30 mA (29)	43 Ohm	"superflux" and similar
40 mA (38)	33 Ohm	"superflux" and similar
80 mA (78)	16 Ohm	four-crystal
350 mA (321)	3,9 Ohm	1 W
750 mA (694)	1,8 Ohm	3W
1000 mA (962)	1,3 Ohm	5 - 10 W

To connect a 10 W LED you will need a resistor with a value of 1,3 Ohm power 2W.

The LED is powered by a voltage of 10-12 volts. On the LM 317 stabilizer - a voltage drop of 1.25 volts when stabilized at 962 mA..

We add 12V diode + 1.25V stabilizer = 13.25V power supply voltage. A the battery has 13.4~13.8 volts, which is quite enough!

We assemble the circuit as follows:

We fix the LED on the aluminum radiator with self-tapping screws. Be sure to lubricate the entire contact area of the LED with the radiator with a thin layer of thermal conductive paste to improve heat transfer. Since there is no galvanic connection between the base of this LED and its contact terminals, we also attach the LM 317 chip in the TO 220 package to the same radiator using thermally conductive paste (it also heats up, because 1.25 volts drops on it!). Solder 3 parts according to the diagram

We connect the “-” terminal of the battery to the white wire, and the “+” terminal to the orange wire.

And, lo and behold! A 10 W LED illuminates at 1080 lm, which corresponds to the light intensity of a 100 W incandescent lamp. But unlike an incandescent lamp with a power of 100 W, the LED together with the driver heats up to only 45 degrees, and, most importantly, consumes only 10 W.

This design can be safely used in car headlights, for example, for low beam. The only thing that needs to be changed is to isolate the heat sink LM 317 from the car body, since the microcircuit has a galvanic connection with the heat sink via “+”, and in the car on the body “-”.