LED drivers: types, characteristics and criteria for selecting devices
The guarantee of the brightness of the glow, efficiency and durability of LED sources is the correct power supply, which can be provided by special electronic devices – drivers for LEDs. They convert the AC voltage in the 220V network into a DC voltage of a given value. An analysis of the main types and characteristics of the devices will help to understand what function the converters perform and what to pay attention to when choosing them.
Purpose of LED drivers for LEDs
The main function of the LED driver is to provide a stabilized current passing through the LED device. The value of the current flowing through the semiconductor crystal must correspond to the passport parameters of the LED. This will ensure the stability of the crystal glow and help to avoid its premature degradation. In addition, at a given current, the voltage drop will correspond to the value required for the p-n junction. You can find out the corresponding power supply voltage of the LED using the volt-ampere characteristic.
When lighting residential and office premises with LED lamps and fixtures, drivers are used, which are powered by AC 220V. In automotive lighting (headlights, DRL, etc.), bicycle headlights, portable flashlights use DC power sources in the range from 9 to 36V. Some low-power LEDs can be connected without a driver, but then a resistor must be inserted into the circuit for switching the LED to the 220 volt network.
The output voltage of the driver is indicated in the interval of two final values, between which stable operation is ensured. There are adapters with an interval from 3V to several dozen. To power a circuit of 3 white LEDs connected in series, each of which has a power of 1 W, you will need a driver with output values U – 9–12V, I – 350 mA. The voltage drop for each crystal will be about 3.3V, and in total 9.9V, which will enter the driver range.
Main characteristics of converters
Before you buy a driver for LEDs, you should familiarize yourself with the main characteristics of the devices. These include output voltage, rated current and power. The output voltage of the converter depends on the magnitude of the voltage drop on the LED source, as well as on the connection method and the number of LEDs in the circuit. The current depends on the power and brightness of the emitting diodes. The driver must provide the LEDs with the current they need to maintain the required brightness.
One of the important characteristics of the driver is the power that the device outputs as a load. The choice of driver power is influenced by the power of each LED device, the total number and color of the LEDs. The power calculation algorithm is that the maximum power of the device should not be lower than the consumption of all LEDs:
P = P(led) × n,
where P(led) is the power of a single LED source, and n is the number of LEDs.
In addition, a mandatory condition must be met, under which a power reserve within 25-30% would be provided. Thus, the maximum power value should not be less than the value (1.3 x P).
The color characteristics of the LEDs should also be taken into account. After all, semiconductor crystals of different colors have different voltage drops when a current of the same strength passes through them. So the voltage drop of the red LED at a current of 350 mA is 1.9-2.4 V, then the average value of its power will be 0.75 watts. The green analog has a voltage drop in the range from 3.3 to 3.9 V and at the same current the power will already be 1.25 watts. This means that 16 red LED sources or 9 green ones can be connected to the driver for 12V LEDs.
Useful advice! When choosing a driver for LEDs, experts advise not to neglect the maximum power value of the device.
What are the drivers for LEDs by device type
Drivers for LEDs are classified by device type into linear and pulsed. The structure and typical driver circuit for linear type LEDs is a current generator on a transistor with a p-channel. Such devices provide smooth current stabilization under the condition of unstable voltage on the input channel. They are simple and cheap devices, but they are characterized by low efficiency, emit a lot of heat during operation and cannot be used as drivers for high-power LEDs.
Pulse devices create a series of high-frequency pulses in the output channel. Their work is based on the principle of PWM (pulse width modulation), when the average output current is determined by the fill factor, i.e. the ratio of the pulse duration to the number of its repetitions. The change in the value of the average output current occurs due to the fact that the pulse frequency remains unchanged, and the fill factor varies from 10-80%.
Due to the high conversion efficiency (up to 95%) and the compactness of the devices, they have found wide application for portable LED designs. In addition, the efficiency of the devices has a positive effect on the duration of operation of autonomous power devices. Pulse type converters have compact dimensions and are distinguished by an extensive range of input voltages. The disadvantage of these devices is the high level of electromagnetic interference.
Useful advice! It is necessary to purchase an LED driver at the stage of choosing LED sources, having previously determined the scheme of LEDs from 220 volts.
Before choosing a driver for LEDs, it is necessary to know the conditions of its operation and the location of LED devices. Pulse-width drivers, which are based on a single chip, have miniature dimensions and are designed to be powered by autonomous low-voltage sources. The main application of these devices is car tuning and LED lighting. However, due to the use of a simplified electronic circuit, the quality of such converters is somewhat lower.
Dimmable drivers for LEDs
Modern drivers for LEDs are compatible with devices for regulating the brightness of semiconductor devices. The use of dimmable drivers allows you to control the level of illumination in the premises: reduce the intensity of the glow in the daytime, emphasize or hide individual elements in the interior, zone the space. This, in turn, makes it possible not only to use electricity efficiently, but also to save the resource of the LED light source.
There are two types of dimmable drivers. Some are connected between the power supply and LED sources. Such devices control the energy coming from the power source to the LEDs. Such devices are based on PWM control, in which energy is supplied to the load in the form of pulses. The pulse duration determines the amount of energy from the minimum to the maximum value. Drivers of this type are used for the most part for LED modules with fixed voltage, such as LED strips, running lines, etc.
Dimmable converters of the second type control the power supply directly. The principle of their operation consists both in PWM regulation and in controlling the amount of current flowing through the LEDs. Dimmable drivers of this type are used for LED devices with a stabilized current. It is worth noting that when LEDs are controlled by PWM regulation, there are negative effects on vision.
Comparing these two methods of regulation, it is worth noting that when adjusting the current value through LED sources, not only a change in the brightness of the glow is observed, but also a change in the color of the glow. So, white LEDs emit yellowish light at a lower current, and at an increase they glow blue. When LEDs are controlled by PWM regulation, there are negative effects on vision and a high level of electromagnetic interference. In this regard, PWM control is used quite rarely, unlike current regulation.
Driver diagrams for LEDs
Many manufacturers produce driver chips for LEDs that allow powering sources from low voltage. All existing drivers are divided into simple ones based on 1-3 transistors and more complex ones using special chips with pulse width modulation.
ON Semiconductor offers a wide range of chips as a basis for drivers. They are characterized by an acceptable cost, excellent conversion efficiency, cost-effectiveness and a low level of electromagnetic pulses. The manufacturer presents a UC3845 pulse type driver with an output current of up to 1A. On such a chip, it is possible to implement a driver circuit for a 10W LED.
HV9910 (Supertex) electronic components are a popular chip for drivers, thanks to their simple circuit resolution and low price. It has a built-in voltage regulator and pins for brightness control, as well as a pin for programming the switching frequency. The output current value is up to 0.01 A. On this chip, it is possible to implement a simple driver for LEDs.
Based on the UCC28810 chip (manufactured by Texas Instruments), you can create a driver circuit for high-power LEDs. In such a scheme of the LED driver, an output voltage of 70-85V can be created for LED modules consisting of 28 LED sources with a current of 3 A.
Useful advice! If you plan to buy ultra-bright LEDs with a power of 10 watts, you can use a pulse driver on the UCC28810 chip for the designs of them.
Clare company offers the creation of a simple pulse type driver based on the CPC 9909 chip. It includes a converter controller housed in a compact housing. Due to the built-in voltage stabilizer, the converter can be powered from a voltage of 8-550V. The CPC 9909 chip allows the driver to be operated in conditions of a wide range of temperature conditions from -50 to 80 ° C.
How to choose a driver for LEDs
The market offers a wide range of drivers for LEDs from different manufacturers. Many of them, especially Chinese-made, are characterized by a low price. However, it is not always profitable to buy such devices, since most of them do not meet the stated characteristics. In addition, such drivers are not accompanied by a warranty, and in case of a defect, they cannot be returned or replaced with high-quality ones.
So there is a possibility of acquiring a driver whose claimed power is 50 W. However, in fact it turns out that this characteristic has a non-permanent character and such power is only short-term. In reality, such a device will work as a 30W LED-driver or a maximum of 40W. It may also turn out that some components responsible for the stable functioning of the driver will not be enough in the filling. In addition, components of poor quality and with a short service life can be used, which is essentially a marriage.
When buying, you should pay attention to the indication of the brand of the product. A manufacturer who will provide a guarantee and will be ready to be responsible for their products will be indicated on a quality product. It should be noted that the service life of drivers from proven manufacturers will be much longer. The approximate operating time of the drivers is given below, depending on the manufacturer:
- driver from dubious manufacturers – no more than 20 thousand hours;
- devices of average quality – about 50 thousand hours;
- converter from a proven manufacturer using high–quality components – over 70 thousand hours.
Useful advice! What quality the LED driver will be is up to you to choose. However, it should be noted that it is especially important to purchase a proprietary converter when it comes to using it for LED spotlights and powerful lamps.
Calculation of drivers for LEDs
To determine the output voltage of the LED driver, it is necessary to calculate the ratio of power (W) to current (A). For example, the driver has the following characteristics: power 3 W and current 0.3 A. The calculated ratio is 10V. Thus, this will be the maximum value of the output voltage of this converter.
LED characteristics: current consumption, voltage, power and light output
Types. Wiring diagrams of LED sources. Calculation of resistance for LEDs. Checking the LED with a multimeter. LED designs with your own hands.
If it is necessary to connect 3 LED sources, the current of each of which is 0.3 mA at a supply voltage of 3V. By connecting one of the devices to the LED driver, the output voltage will be 3V and the current 0.3 A. By assembling two LED sources in series, the output voltage will be 6V and the current 0.3 A. By adding a third LED to the serial circuit, we get 9V and 0.3 A. With a parallel connection, 0.3 A will be equally distributed between the LEDs by 0.1 A. Connecting the LEDs to the device by 0.3 A at a current value of 0.7, they will get only 0.3 A.
This is the algorithm of operation of LED drivers. They give out the amount of current they are designed for. The method of connecting LED devices in this case does not matter. There are driver models that assume any number of LEDs connected to them. But then there is a limit on the power of LED sources: it should not exceed the power of the driver itself. Drivers designed for a certain number of connected LEDs are produced, fewer LEDs are allowed to be connected to them. But such drivers have low efficiency, unlike devices designed for a specific number of LED devices.
It should be noted that drivers designed for a fixed number of emitting diodes have emergency protection. Such converters do not work correctly if a smaller number of LEDs are connected to them: they will flicker or not glow at all. Thus, if you connect a voltage to the driver without an appropriate load, it will work unstable.
Where to buy drivers for LEDs
You can buy LED-driver at specialized points for the sale of radio components. In addition, it is much more convenient to get acquainted with the products and order the necessary product using the catalogs of the relevant sites. In addition, in online stores, you can buy not only converters, but also LED lighting devices and related products: power supplies, control devices, connection tools, electronic components for repairing and assembling a driver for LEDs with your own hands.
The implementing companies present a huge range of drivers for LEDs, the technical characteristics and prices of which can be seen in the price lists. As a rule, product prices are indicative and are specified when ordering from the project manager. The range includes converters of various capacities and degrees of protection used for outdoor and indoor lighting, as well as for lighting and tuning cars.
When choosing a driver, you should take into account the conditions of its use and the power consumption of the LED design. Therefore, it is necessary to purchase a driver before buying LEDs. So, before you buy a driver for 12 volt LEDs, you need to take into account that it should have a power reserve of about 25-30%. This is necessary in order to reduce the risk of damage or complete failure of the device in case of a short circuit or voltage drops in the network. The cost of the converter depends on the number of devices purchased, the form of payment and delivery time.
The table shows the main parameters and dimensions of 12 volt voltage stabilizers for LEDs with an indication of their approximate price:
|Modification of LD DC/AC 12 V||Dimensions, mm (h/w/d)||Output current, A||Power, W||Price, rub.|
|1x1W 3-4VDC 0.3A MR11||8/25/12||0,3||1×1||73|
|3x1W 9-12VDC 0.3A MR11||8/25/12||0,3||3×1||114|
|3x1W 9-12VDC 0.3A MR16||12/28/18||0,3||3×1||35|
|5-7x1W 15-24VDC 0.3A||12/14/14||0,3||5-7×1||80|
|10W 21-40V 0.3A AR111||21/30||0,3||10||338|
|12W 21-40V 0.3A AR11||18/30/22||0,3||12||321|
|3x2W 9-12VDC 0.4A MR16||12/28/18||0,4||3×2||18|
|3x2W 9-12VDC 0.45A||12/14/14||0,45||3×2||54|
Making drivers for LEDs with your own hands
Using ready-made chips, radio amateurs can independently assemble drivers for LEDs of different power. To do this, you need to be able to read electrical circuits and have skills working with a soldering iron. For example, you can consider several options for LED drivers with your own hands for LEDs.
The driver circuit for the 3W LED can be implemented on the basis of the PT4115 chip manufactured in China by PowTech. The chip can be used to power LED devices over 1W and includes control units that have a sufficiently powerful transistor at the output. The PT4115-based driver is highly efficient and has a minimal number of strapping components.
Overview of PT4115 and technical parameters of its components:
- luminance control function (dimming);
- input voltage – 6-30V;
- the value of the output current is 1.2 A;
- current stabilization deviation up to 5%;
- load break protection;
- presence of dimming pins;
- efficiency – up to 97%.
The chip has the following outputs:
- for the output switch – SW;
- for the signal and supply section of the circuit – GND;
- to adjust the brightness – DIM;
- input current sensor – CSN;
- supply voltage – VIN;
Driver diagram for LEDs with your own hands based on PT4115
The driver circuits for powering LED devices with a dissipating power of 3 W can be executed in two versions. The first assumes the presence of a power supply with a voltage from 6 to 30V. In another scheme, power is provided from an alternating current source with a voltage from 12 to 18V. In this case, a diode bridge is introduced into the circuit, at the output of which a capacitor is installed. It helps to smooth out voltage fluctuations, its capacity is 1000 UF.
For the first and second circuits, the capacitor (CIN) is of particular importance: this component is designed to reduce ripple and compensate for the energy accumulated by the inductor when the MOP transistor is closed. In the absence of a capacitor, all the inductance energy through the semiconductor diode DSHB (D) will get to the output of the supply voltage (VIN) and will cause a breakdown of the chip relative to the power supply.
Useful advice! It should be taken into account that the connection of a driver for LEDs in the absence of an input capacitor is not allowed.
Taking into account the quantity and how much the LEDs consume, the inductance (L) is calculated. In the circuit of the LED driver, the inductance should be selected, the value of which is 68-220 ΜGN. This is evidenced by the data of the technical documentation. It is possible to allow a slight increase in the value of L, but it should be taken into account that then the efficiency of the circuit as a whole will decrease.
As soon as the voltage is applied, the value of the current when it passes through the resistor RS (works as a current sensor) and L will be zero. Next, CS comparator analyzes the potential levels located before and after the resistor – as a result, a high concentration appears at the output. The current flowing into the load increases to a certain value controlled by RS. The current increases depending on the inductance value and the voltage value.
Assembling driver components
The components of the RT 4115 chip binding are selected taking into account the manufacturer’s instructions. For CIN, a low-impedance capacitor (a capacitor with a low ESR) should be used, since the use of other analogues will negatively affect the efficiency of the driver. If the device is powered from a block with a stabilized current, one capacitor with a capacity of 4.7 UF will be needed at the input. It is recommended to place it next to the chip. If the current is variable, you will need to introduce a solid-state tantalum capacitor with a capacity of at least 100 UF.
In the switching circuit for 3 W LEDs, it is necessary to install an inductor at 68 MCG. It should be located as close as possible to the SW pin. You can make the coil yourself. This will require a ring from a failed computer and a winding wire (PEL-0.35). The FR 103 diode can be used as the diode D. Its parameters: capacity 15 pF, recovery time 150 ns, temperature from -65 to 150 ° C. It can handle current pulses up to 30 A.
The minimum value of the RS resistor in the LED driver circuit is 0.082 ohms, the current is 1.2 A. To calculate the resistor, it is necessary to use the value of the current required for the LED. Below is the formula for calculating:
RS = 0,1 / I,
where I is the nominal value of the current of the LED source.
The RS value in the LED driver circuit is 0.13 ohms, respectively, the current value is 780 mA. If such a resistor cannot be found, several low-resistance components can be used, using the resistance formula for parallel and serial switching when calculating.
Layout of the driver for a 10 Watt LED with your own hands
You can assemble a driver for a powerful LED yourself, using electronic boards from failed fluorescent lamps. Most often, lamps burn out in such lamps. The electronic board remains operational, which allows its components to be used for homemade power supplies, drivers and other devices. Transistors, capacitors, diodes, inductors (chokes) may be needed for operation.
The faulty lamp must be carefully disassembled with a screwdriver. To make a driver for a 10-watt LED, you should use a fluorescent lamp with a power of 20 watts. This is necessary so that the throttle can withstand the load with a margin. For a more powerful lamp, you should either select the appropriate board, or replace the throttle itself with an analog with a large core. For LED sources with lower power, the number of turns of the winding can be adjusted.
Next, on top of the primary coils of the winding, it is necessary to make 20 turns of wire and connect this winding with a rectifier diode bridge using a soldering iron. After that, the voltage from the 220V network should be applied and the output voltage at the rectifier should be measured. Its value was 9.7 V. The LED source consumes 0.83 A through an ammeter. The nominal value of this LED is 900 mA, however, so that the low current consumption will increase its resource. The assembly of the diode bridge is carried out by mounting.
The new board and the diode bridge can be placed in the stand from the old table lamp. Thus, the LED driver can be assembled independently from the available radio components from failed devices.
Due to the fact that LEDs are quite demanding on power sources, it is necessary to choose the right driver for them. If the converter is selected correctly, you can be sure that the parameters of the LED sources will not deteriorate and the LEDs will last their allotted time.