Using LEDs as lighting sources usually requires a specialized driver. But it happens that the necessary driver is not at hand, but you need to organize lighting, for example, in a car, or test the LED for brightness. In this case, you can do it yourself for LEDs.
How to make a driver for LEDs
The circuits below use the most common elements that can be purchased at any radio store. No special equipment is required during assembly; all necessary tools are widely available. Despite this, with a careful approach, the devices work for quite a long time and are not much inferior to commercial samples.
Required materials and tools
In order to assemble a homemade driver, you will need:
- Soldering iron with a power of 25-40 W. You can use more power, but this increases the risk of overheating of the elements and their failure. It is best to use a soldering iron with a ceramic heater and a non-burning tip, because... a regular copper tip oxidizes quite quickly and has to be cleaned.
- Flux for soldering (rosin, glycerin, FKET, etc.). It is advisable to use a neutral flux - unlike active fluxes (phosphoric and hydrochloric acids, zinc chloride, etc.), it does not oxidize the contacts over time and is less toxic. Regardless of the flux used, after assembling the device, it is better to wash it with alcohol. For active fluxes this procedure is mandatory, for neutral ones - to a lesser extent.
- Solder. The most common is low-melting tin-lead solder POS-61. Lead-free solders are less harmful when inhaling fumes during soldering, but have a higher melting point with lower fluidity and a tendency to degrade the weld over time.
- Small pliers for bending leads.
- Wire cutters or side cutters for cutting long ends of leads and wires.
- Installation wires are insulated. Stranded copper wires with a cross-section of 0.35 to 1 mm2 are best suited.
- Multimeter for monitoring voltage at nodal points.
- Electrical tape or heat shrink tubing.
- A small prototype board made of fiberglass. A board measuring 60x40 mm will be sufficient.
PCB development board for quick installation
Simple driver circuit for 1 W LED
One of the simplest circuits for powering a powerful LED is shown in the figure below:
As you can see, in addition to the LED, it includes only 4 elements: 2 transistors and 2 resistors.
The powerful n-channel field-effect transistor VT2 acts here as a regulator of the current passing through the LED. Resistor R2 determines the maximum current passing through the LED and also acts as a current sensor for transistor VT1 in the feedback circuit.
The more current passes through VT2, the greater the voltage drops across R2, accordingly VT1 opens and lowers the voltage at the gate of VT2, thereby reducing the LED current. In this way, stabilization of the output current is achieved.
The circuit is powered from a constant voltage source of 9 - 12 V, a current of at least 500 mA. The input voltage should be at least 1-2 V greater than the voltage drop across the LED.
Resistor R2 should dissipate 1-2 W of power, depending on the required current and supply voltage. Transistor VT2 is n-channel, designed for a current of at least 500 mA: IRF530, IRFZ48, IRFZ44N. VT1 – any low-power bipolar npn: 2N3904, 2N5088, 2N2222, BC547, etc. R1 - power 0.125 - 0.25 W with a resistance of 100 kOhm.
Due to the small number of elements, assembly can be carried out by hanging installation:
Another simple driver circuit based on the LM317 linear controlled voltage regulator:
Here the input voltage can be up to 35 V. The resistor resistance can be calculated using the formula:
where I is the current strength in amperes.
In this circuit, the LM317 will dissipate significant power given the large difference between the supply voltage and the LED drop. Therefore, it will have to be placed on a small one. The resistor must also be rated for at least 2 W.
This scheme is discussed more clearly in the following video:
Here we show how to connect a powerful LED using batteries with a voltage of about 8 V. When the voltage drop across the LED is about 6 V, the difference is small, and the chip does not heat up much, so you can do without a heatsink.
Please note that if there is a large difference between the supply voltage and the drop across the LED, it is necessary to place the microcircuit on a heat sink.
Power driver circuit with PWM input
Below is a circuit for powering high-power LEDs:
The driver is built on a dual comparator LM393. The circuit itself is a buck-converter, that is, a pulse step-down voltage converter.
Driver Features
- Supply voltage: 5 - 24 V, constant;
- Output current: up to 1 A, adjustable;
- Output power: up to 18 W;
- Output short circuit protection;
- The ability to control brightness using an external PWM signal (it will be interesting to read how).
Operating principle
Resistor R1 with diode D1 form a source of reference voltage of about 0.7 V, which is additionally regulated by variable resistor VR1. Resistors R10 and R11 serve as current sensors for the comparator. As soon as the voltage across them exceeds the reference one, the comparator will close, thus closing the pair of transistors Q1 and Q2, and they, in turn, will close the transistor Q3. However, inductor L1 at this moment tends to resume the flow of current, so the current will flow until the voltage at R10 and R11 becomes less than the reference voltage, and the comparator opens transistor Q3 again.
The pair of Q1 and Q2 acts as a buffer between the output of the comparator and the gate of Q3. This protects the circuit from false positives due to interference on the Q3 gate, and stabilizes its operation.
The second part of the comparator (IC1 2/2) is used for additional brightness control using PWM. To do this, the control signal is applied to the PWM input: when TTL logic levels (+5 and 0 V) are applied, the circuit will open and close Q3. The maximum signal frequency at the PWM input is about 2 KHz. This input can also be used to turn the device on and off using the remote control.
D3 is a Schottky diode rated for current up to 1 A. If you cannot find a Schottky diode, you can use a pulse diode, for example FR107, but the output power will then decrease slightly.
The maximum output current is adjusted by selecting R2 and turning on or off R11. This way you can get the following values:
- 350 mA (1 W LED): R2=10K, R11 disabled,
- 700 mA (3 W): R2=10K, R11 connected, nominal 1 Ohm,
- 1A (5W): R2=2.7K, R11 connected, nominal 1 Ohm.
Within narrower limits, adjustment is made using a variable resistor and a PWM signal.
Assembling and configuring the driver
The driver components are mounted on a breadboard. First, the LM393 chip is installed, then the smallest components: capacitors, resistors, diodes. Then transistors are installed, and lastly a variable resistor.
It is better to place elements on the board in such a way as to minimize the distance between the connected pins and use as few wires as jumpers as possible.
When connecting, it is important to observe the polarity of the diodes and the pinout of the transistors, which can be found in the technical description for these components. Diodes can also be used in resistance measurement mode: in the forward direction, the device will show a value of the order of 500-600 Ohms.
To power the circuit, you can use an external DC voltage source of 5-24 V or batteries. 6F22 (“crown”) and other batteries have too small a capacity, so their use is impractical when using high-power LEDs.
After assembly, you need to adjust the output current. To do this, LEDs are soldered to the output, and the VR1 engine is set to the lowest position according to the diagram (checked with a multimeter in the “testing” mode). Next, we apply the supply voltage to the input, and by rotating the VR1 knob we achieve the required brightness.
List of elements:
Conclusion
The first two of the considered circuits are very simple to manufacture, but they do not provide short circuit protection and have rather low efficiency. For long-term use, the third circuit on LM393 is recommended, since it does not have these disadvantages and has greater capabilities for adjusting the output power.
must be connected to the power supply through special devices that stabilize the current - drivers for LEDs. These are 220 V AC voltage converters to DC voltage with the parameters necessary for the operation of light diodes. Only with their presence can one guarantee stable operation, long service life of LED sources, declared brightness, protection against short circuits and overheating. The choice of drivers is small, so it is better to first purchase a converter and then select it for it. You can assemble the device yourself using a simple diagram. Read about what an LED driver is, which one to buy and how to use it correctly in our review.
- These are semiconductor elements. The brightness of their glow is determined by current, not voltage. For them to work, they need a stable current of a certain value. At a p-n junction, the voltage drops by the same number of volts for each element. Ensuring optimal operation of LED sources taking into account these parameters is the driver’s task.
Exactly what power is needed and how much it drops at the p-n junction should be indicated in the passport data of the LED device. The converter parameter range must fit within these values.
Essentially, a driver is a . But the main output parameter of this device is stabilized current. They are produced according to the principle of PWM conversion using special microcircuits or based on transistors. The latter are called simple.
The converter is powered from a regular network and outputs a voltage of a given range, which is indicated in the form of two numbers: the minimum and maximum values. Usually from 3 V to several tens. For example, using a converter with an output voltage of 9÷21 V and a power of 780 mA, it is possible to provide operation of 3÷6, each of which creates a drop in the network of 3 V.
Thus, a driver is a device that converts current from a 220 V network to the specified parameters of the lighting device, ensuring its normal operation and long service life.
Where is it used?
The demand for converters is growing along with the popularity of LEDs. - These are economical, powerful and compact devices. They are used for a variety of purposes:
- for lanterns;
- at home;
- for arrangement;
- in car and bicycle headlights;
- in small lanterns;
When connecting to a 220 V network, you always need a driver; if you use constant voltage, you can get by with a resistor.
How the device works
The principle of operation of LED drivers for LEDs is to maintain a given output current, regardless of voltage changes. The current passing through the resistances inside the device is stabilized and acquires the desired frequency. Then it passes through a rectifying diode bridge. At the output we get a stable forward current, sufficient to operate a certain number of LEDs.
Main characteristics of drivers
Key parameters of current conversion devices that you need to rely on when choosing:
- Rated power of the device. It is indicated in the range. The maximum value must be slightly greater than the power consumption of the connected lighting fixture.
- Output voltage. The value must be greater than or equal to the total voltage drop across each circuit element.
- Rated current. Must match the power of the device to provide sufficient brightness.
Depending on these characteristics, it is determined which LED sources can be connected using a specific driver.
Types of current converters by device type
Drivers are produced in two types: linear and pulse. They have the same function, but the scope of application, technical features and cost differ. A comparison of converters of different types is presented in the table:
| Device type | Specifications | pros | Minuses | Scope of application |
| Current generator on a transistor with a p-channel, smoothly stabilizes the current at alternating voltage | No interference, inexpensive | Efficiency less than 80%, gets very hot | Low-power LED lamps, strips, flashlights |
| Operates on the basis of pulse width modulation | High efficiency (up to 95%), suitable for powerful devices, extends the service life of elements | Creates electromagnetic interference | Car tuning, street lighting, household LED sources |
How to choose a driver for LEDs and calculate its technical parameters
A driver for an LED strip will not be suitable for a powerful street lamp and vice versa, so it is necessary to calculate the main parameters of the device as accurately as possible and take into account the operating conditions.
| Parameter | What does it depend on | How to calculate |
| Device power calculation | Determined by the power of all connected LEDs | Calculated using the formula P = PLED source × n , Where P – is the driver power; PLED source – power of one connected element; n - amount of elements. For a power reserve of 30% you need to multiply P by 1.3. The resulting value is the maximum driver power required to connect the lighting fixture |
| Output voltage calculation | Determined by the voltage drop across each element | The value depends on the glow color of the elements; it is indicated on the device itself or on the packaging. For example, you can connect 9 green or 16 red LEDs to a 12V driver. |
| Current calculation | Depends on the power and brightness of the LEDs | Determined by the parameters of the connected device |
Converters are available with or without housing. The former look more aesthetically pleasing and are protected from moisture and dust, the latter are used for hidden installation and are cheaper. Another characteristic that must be taken into account is the permissible operating temperature. It is different for linear and pulse converters.
Important! The packaging with the device must indicate its main parameters and manufacturer.
Methods for connecting current converters
LEDs can be connected to the device in two ways: in parallel (several chains with the same number of elements) and in series (one by one in one chain).
To connect 6 elements with a voltage drop of 2 V in parallel in two lines, you will need a 6 V 600 mA driver. And when connected in series, the converter must be designed for 12 V and 300 mA.
A serial connection is better because all the LEDs will glow equally, whereas with a parallel connection the brightness of the lines may vary. When connecting a large number of elements in series, a driver with a high output voltage will be required.
Dimmable current converters for LEDs
- This is the regulation of the intensity of light emanating from a lighting fixture. Dimmable drivers allow you to change the input and output current parameters. Due to this, the brightness of the LEDs increases or decreases. When using regulation, it is possible to change the color of the glow. If the power is less, then the white elements may turn yellow, if more, then blue.
Chinese drivers: is it worth saving?
Drivers are produced in China in huge quantities. They are low cost, so they are quite in demand. They have galvanic isolation. Their technical parameters are often overestimated, so it’s worth taking this into account when buying a cheap device.
Most often these are pulse converters, with a power of 350÷700 mA. They do not always have a housing, which is even convenient if the device is purchased for the purpose of experimentation or training.
Disadvantages of Chinese products:
- simple and cheap microcircuits are used as the basis;
- devices do not have protection against power fluctuations and overheating;
- create radio interference;
- create high-level ripple at the output;
- They do not last long and are not guaranteed.
Not all Chinese drivers are bad; more reliable devices are also produced, for example, based on PT4115. They can be used to connect household LED sources, flashlights, and strips.
Driver lifespan
The service life of an ice driver for LED lamps depends on external conditions and the original quality of the device. The estimated service life of the driver is from 20 to 100 thousand hours.
The following factors can affect the service life:
- temperature changes;
- high humidity;
- power surges;
- incomplete load of the device (if the driver is designed for 100 W, but uses 50 W, the voltage returns back, which causes an overload).
Well-known manufacturers provide a warranty on drivers for an average of 30 thousand hours. But if the device was used incorrectly, the buyer is responsible. If the LED source does not turn on, or perhaps the problem is in the converter, incorrect connection, or malfunction of the lighting fixture itself.
How to check the LED driver for functionality, see the video below:
DIY driver circuit for LEDs with a brightness controller based on RT4115
A simple current converter can be assembled based on a ready-made Chinese PT4115 microcircuit. It is reliable enough for use. Chip characteristics:
- Efficiency up to 97%;
- there is an output for a device that regulates brightness;
- protected from load breaks;
- maximum stabilization deviation 5%;
- input voltage 6÷30 V;
- output power 1.2 A.
The chip is suitable for powering an LED source over 1 W. Has a minimum of strapping components.
Decoding the outputs of the microcircuit:
- S.W.– output switch;
- DIM– dimming;
- GND– signal and power element;
- CIN– capacitor
- CSN– current sensor;
- VIN- supply voltage.
Even a novice master can assemble a driver based on this chip.
220V LED lamp driver circuit
In the case of the current stabilizer, it is installed in the base of the device. And it is based on inexpensive microcircuits, for example, CPC9909. Such lamps must be equipped with a cooling system. They last much longer than any other, but it is better to give preference to trusted manufacturers, since the Chinese ones have noticeable hand soldering, asymmetry, lack of thermal paste and other shortcomings that reduce service life.
How to make a driver for LEDs with your own hands
The device can be made from any unnecessary phone charger. It is necessary to make only minimal improvements and the microcircuit can be connected to LEDs. It is enough to power 3 1 W elements. To connect a more powerful source, you can use boards from fluorescent lamps.
Important! During work it is necessary to observe safety precautions. Touching exposed parts may result in an electric shock of up to 400 V.
| Photo | Stage of assembling the driver from the charger |
 | Remove the housing from the charger. |
 | Using a soldering iron, remove the resistor that limits the voltage supplied to the phone. |
 | Install a tuning resistor in its place until it needs to be set to 5 kOhm. |
 | Using a serial connection, solder the LEDs to the output channel of the device. |
 | Remove the input channels with a soldering iron, and in their place solder a power cord to connect to a 220 V network. |
 | Check the operation of the circuit, set the regulator on the trimming resistor to the required voltage so that the LEDs shine brightly but do not change color. |
Example of a driver circuit for LEDs from a 220 V network Drivers for LEDs: where to buy and how much they cost
You can purchase stabilizers for LED lamps and microcircuits for them in radio components stores, electrical equipment stores, and on many online trading platforms. The last option is the most economical. The cost of the device depends on its technical characteristics, type and manufacturer. Average prices for some types of drivers are shown in the table below.
LEDs for their power supply require the use of devices that will stabilize the current passing through them. In the case of indicator and other low-power LEDs, you can get by with resistors. Their simple calculation can be further simplified by using the LED Calculator.
To use high-power LEDs, you cannot do without using current-stabilizing devices - drivers. The right drivers have a very high efficiency - up to 90-95%. In addition, they provide stable current even when the power supply voltage changes. And this may be relevant if the LED is powered, for example, by batteries. The simplest current limiters - resistors - cannot provide this by their nature.
You can learn a little about the theory of linear and pulsed current stabilizers in the article “Drivers for LEDs”.
Of course, you can buy a ready-made driver. But it’s much more interesting to make it yourself. This will require basic skills in reading electrical diagrams and using a soldering iron. Let's look at a few simple homemade driver circuits for high-power LEDs.
Simple driver. Assembled on a breadboard, powers the mighty Cree MT-G2
A very simple linear driver circuit for an LED. Q1 – N-channel field-effect transistor of sufficient power. Suitable, for example, IRFZ48 or IRF530. Q2 is a bipolar NPN transistor. I used 2N3004, you can use any similar one. Resistor R2 is a 0.5-2W resistor that will determine the driver current. Resistance R2 2.2Ohm provides a current of 200-300mA. The input voltage should not be very high - it is advisable not to exceed 12-15V. The driver is linear, so the driver efficiency will be determined by the ratio V LED / V IN, where V LED is the voltage drop across the LED, and V IN is the input voltage. The greater the difference between the input voltage and the drop across the LED and the greater the driver current, the more the transistor Q1 and resistor R2 will heat up. However, V IN should be greater than V LED by at least 1-2V.
For tests, I assembled the circuit on a breadboard and powered it with a powerful CREE MT-G2 LED. The power supply voltage is 9V, the voltage drop across the LED is 6V. The driver worked immediately. And even with such a small current (240mA), the mosfet dissipates 0.24 * 3 = 0.72 W of heat, which is not small at all.
The circuit is very simple and can even be mounted in a finished device.
The circuit of the next homemade driver is also extremely simple. It involves the use of a step-down voltage converter chip LM317. This microcircuit can be used as a current stabilizer.
An even simpler driver on the LM317 chip
The input voltage can be up to 37V, it must be at least 3V higher than the voltage drop across the LED. The resistance of resistor R1 is calculated by the formula R1 = 1.2 / I, where I is the required current. The current should not exceed 1.5A. But at this current, resistor R1 should be able to dissipate 1.5 * 1.5 * 0.8 = 1.8 W of heat. The LM317 chip will also get very hot and will not be possible without a heatsink. The driver is also linear, so in order for the efficiency to be maximum, the difference between V IN and V LED should be as small as possible. Since the circuit is very simple, it can also be assembled by hanging installation.
On the same breadboard, a circuit was assembled with two one-watt resistors with a resistance of 2.2 Ohms. The current strength turned out to be less than the calculated one, since the contacts in the breadboard are not ideal and add resistance.
The next driver is a pulse buck driver. It is assembled on the QX5241 chip.
The circuit is also simple, but consists of a slightly larger number of parts and here you can’t do without making a printed circuit board. In addition, the QX5241 chip itself is made in a fairly small SOT23-6 package and requires attention when soldering.
The input voltage should not exceed 36V, the maximum stabilization current is 3A. The input capacitor C1 can be anything - electrolytic, ceramic or tantalum. Its capacity is up to 100 µF, the maximum operating voltage is no less than 2 times greater than the input. Capacitor C2 is ceramic. Capacitor C3 is ceramic, capacity 10 μF, voltage - no less than 2 times greater than the input. Resistor R1 must have a power of at least 1W. Its resistance is calculated by the formula R1 = 0.2 / I, where I is the required driver current. Resistor R2 - any resistance 20-100 kOhm. The Schottky diode D1 must withstand the reverse voltage with a reserve - at least 2 times the value of the input. And it must be designed for a current not less than the required driver current. One of the most important elements of the circuit is field-effect transistor Q1. This should be an N-channel field device with the lowest possible resistance in the open state; of course, it should withstand the input voltage and the required current strength with a reserve. A good option is field-effect transistors SI4178, IRF7201, etc. Inductor L1 should have an inductance of 20-40 μH and a maximum operating current not less than the required driver current.
The number of parts of this driver is very small, all of them are compact in size. The result may be a fairly miniature and, at the same time, powerful driver. This is a pulse driver, its efficiency is significantly higher than that of linear drivers. However, it is recommended to select an input voltage that is only 2-3V higher than the voltage drop across the LEDs. The driver is also interesting because output 2 (DIM) of the QX5241 chip can be used for dimming - regulating the driver current and, accordingly, the brightness of the LED. To do this, pulses (PWM) with a frequency of up to 20 KHz must be supplied to this output. Any suitable microcontroller can handle this. The result may be a driver with several operating modes.
(13 ratings, average 4.58 out of 5)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:
- 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.
- 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 exactly 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.
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 in various 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 of the LED driver is the 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.
