For uninterrupted operation in LED luminaires, a power source is required, which will be connected to the network. It is called a driver for an LED luminaire. The driver performs this function because this is the power source, the task of which is to stabilize the current and voltage in the network. But how do you choose the right driver? It is necessary to pay attention to its output parameters: the current parameter (in Amperes) and the voltage parameter (in Volts). There is also a parameter for the load power of the device (W). It is customary to select drivers with a power reserve and within the resolvable output voltage range and, of course, pay attention to the current stabilization characteristic. Otherwise, the luminaire must be recycled or sent for repair.
The driver also depends on such characteristics as:
- ripple level;
- electrical safety, etc.
The characteristic of the LED determines the luminous flux.
Driver selection
The choice of driver largely determines the place where the luminaire is planned to be installed.
For example, in a warehouse for a luminaire, you will need a driver with an operating temperature above 0 ° C and a degree of moisture resistance from IP 20. If we illuminate an office or any other administrative room where people work and high illumination is needed, then in this case it is necessary to take into account and the ripple factor: it should not be higher than 5%. Input voltage limits depend on specific conditions. For example, if a large number of equipment is installed in the room or it is powerful enough, then there is a possibility of voltage drop (surges) in the network. In this case, you need a power supply with a universal input.
The mains voltage in office premises is usually stable, and the standard input voltage range is more than sufficient. But in any case, the LED luminaire needs a power factor corrector, because the additional power turns out to be above the threshold of 25 watts. There are models for indoor lighting. These are PLD-40 and PLD-60 luminaire models. Their ripple coefficient is not higher than 20%, which means that they are suitable for lighting rooms that are not demanding on bright lighting. Drivers of such models are protected from short circuit and overheating, and also have full compliance with the requirements of electromagnetic compatibility. Thus, the example models PLD-40 and PLD-60 showed us an excellent match for standard luminaires without dimming.
Requirements for drivers depending on the purpose of the luminaire:
- If the luminaire is installed for outdoor lighting, then the main requirement for its driver is a wide range of tolerable temperatures, which guarantees proper operation after a long stay in the cold.
On top of that, the level of strength of the case will also have to be considered. Because the street luminaire must have absolute protection against any aggressive influences such as dust, dirt, chemical vapors, water (moisture resistance must be IP 65). The luminaire components should not be affected by cooling either.
The power supply (besides the fact that it must be protected in this way) must have a wide input voltage range due to the fact that the power lines are very unstable. It must be reliably protected from voltage surges.
- If the luminaire is installed to illuminate roads, railways, subways, then the driver of such a luminaire must be vibration-resistant. This is facilitated by the compound, which is poured into the power supplies, which allows it to not perceive vibrations. Otherwise, the elements will simply fall off the board at the first vibration attack.
All parameters and capabilities of the luminaire depend on the quality of the driver's parts. Among them are such important ones as ripple level, operating temperature range, resistance to voltage surges, temperature range. That is why the quality of the components of this device is so important. As you know, the LED luminaire itself is a very reliable lighting fixture that is distinguished by its durability. However, it will not be able to go through its entire service life if you do not properly approach the choice of driver in LED lamps. After all, the main reason for the failure of the luminaire is not a burned-out LED, but a bad driver. It is because of him that you will have to carry the lamp for repairs.
Lamp set and how to choose it
A typical LED luminaire contains only a few elements:
- lEDs;
- body;
- heat sink;
- radiator;
- driver.
If the kit is standard, how can you choose a lamp so that its pre-installed driver will last as long as possible?
As we have already found out, the driver is necessary in order to stabilize the current that powers the LEDs with a power of 1 Watt.
For proper operation of the LEDs from the power supply, you must lower the voltage. Each luminaire has the following parameters that must be considered when choosing the optimal driver. Let's talk about them in more detail:
- Power. The maximum power of the driver shows what maximum load it will withstand. For example, if the marking indicates (30x36) x1W, this means that 30 or 36 1 Watt LEDs can be connected to this driver. If we are talking about connecting a 12-24 Volt LED strip, then it should be borne in mind that the power supplies for them limit the voltage, and not the current at all.
This means that we must carefully monitor the power of the load connected to the power supply. In this case, the driver power should in no case be lower than the circuit power, otherwise the power supply will simply "burn out".
- Rated parameters of current and voltage. This parameter is indicated by the manufacturer on all LEDs, respectively, and the driver must be selected according to this mark. The maximum rated current is 350 mA. With this mark in the work, you must use a power source with a current strength in the range of 300-330 mA. This is true for any type of connection. This operating current range is recommended in order not to shorten the luminaire's shelf life, because the heat sink may not fully perform its functions.
- Class of tightness and moisture resistance (security). Currently, the protection class is defined by two digits after the IP. The first number indicates the degree of protection against solid influences (dust, dirt, sand, ice). The second is about liquid media (water, substances). However, there is no indication of the required temperature at which the luminaire can be used in the IP class. Whether or not it can be cooled depends on the strength of the case.
It is necessary to approach buying a driver for a luminaire with no less responsibility than buying the luminaire itself, because it is the power source that guarantees the long, serviceable service of the entire device. If you can't choose the right driver for the fixtures in any way, then you can do it yourself. The assembly diagram is quite simple.
The standard diagram of the PT4115 LED driver 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 range of supply voltages from 6 to 30 volts, from 1 to 7-8 LEDs can be connected to the driver.
The maximum supply voltage of the microcircuit is 45 V, but work in this mode is not guaranteed (better pay attention to a similar microcircuit).
The LED current is triangular with a maximum deviation of ± 15% from the mean. The average current through the LEDs is set by the resistor and is calculated using the formula:
I LED \u003d 0.1 / R
The minimum allowable value R \u003d 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 the resistor R is installed with a maximum deviation from the nominal value of 1%.
So, to turn on the LED at a constant brightness, the DIM pin is left hanging in the air (inside the PT4115 it is pulled up to 5V). In this case, the output current is determined exclusively by the resistance R.
If a capacitor is connected between the DIM pin and "ground", we get the effect of smooth lighting of the LEDs. The time to reach maximum brightness will depend on the capacitance of the capacitor, the larger it is, the longer the lamp will light up.
For reference: each nanofarad capacitance increases the turn-on time by 0.8 ms. 
If you need to make a dimmable driver for LEDs with dimming from 0 to 100%, then you can resort to one of two ways:
- The first way assumes supplying a constant voltage to the DIM input in the range from 0 to 6V. In this case, the brightness adjustment from 0 to 100% is carried out at a voltage at the DIM pin from 0.5 to 2.5 volts. An increase in voltage above 2.5 V (and up to 6 V) does not in any way affect the current through the LEDs (the brightness does not change). On the contrary, decreasing the voltage to a level of 0.3 V or lower leads to the shutdown of the circuit and putting it into standby mode (the current consumption in this case drops to 95 μA). Thus, it is possible to effectively control the operation of the driver without removing the supply voltage.
- Second way implies the supply of a signal from a pulse-width converter with an output frequency of 100-20000 Hz, the brightness will be determined by the duty cycle (duty cycle). For example, if a high level is kept for 1/4 of a period, and a low level, respectively, for 3/4, then this will correspond to a brightness level of 25% of the maximum. It should be understood that the frequency of the driver is determined by the inductance of the choke and in no way depends on the dimming frequency.
The diagram of a PT4115 LED driver with a constant voltage dimmer is shown in the figure below: 
This LED dimming circuit works great due to the fact that inside the microcircuit the DIM pin is pulled up to the 5V bus through a 200 kΩ resistor. Therefore, when the potentiometer slider is in the lowest position, a voltage divider of 200 + 200 kΩ is formed and a potential of 5/2 \u003d 2.5V is formed at the DIM pin, which corresponds to 100% brightness.
How the circuit works
At the first moment of time, when the input voltage is applied, the current through R and L is equal to zero and the output switch built into the microcircuit is open. The current through the LEDs begins to rise smoothly. The rate of rise of the current depends on the magnitude of the inductance and the supply voltage. The in-circuit comparator compares the potentials before and after the resistor R and, as soon as the difference is 115 mV, a low level appears at its output, which closes the output switch.
Due 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 also gradually decreases. As soon as it reaches a value of 85 mV, the comparator will again give a signal to open the output switch. And the whole cycle is repeated from the beginning.
If it is necessary to reduce the ripple current through the LEDs, it is allowed 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 it will become similar to a sinusoidal one. The capacitor does not affect the operating frequency or the efficiency of the driver, but increases the time it takes to establish a given current through the LED. 
Important assembly nuances
An important element of the circuit is the capacitor C1. It not only smooths out the ripple, but also compensates for the energy accumulated in the inductor when the output switch is closed. Without C1, the energy stored in the choke will flow through the Schottky diode to the power bus and can provoke a breakdown of the microcircuit. Therefore, if you turn on the driver without a bypass capacitor, the microcircuit is almost guaranteed to be covered. And the greater the inductance of the choke, the more chances to burn mikruhu.
The minimum capacitance of the C1 capacitor is 4.7 μF (and when the circuit is powered by a pulsating voltage after the diode bridge, it is at least 100 μF)
The capacitor should be located as close to the chip as possible and have as low ESR value as possible (i.e. tantalum capacitors are welcome).
It is also very important to take a responsible approach to the choice of a diode. It must have low forward voltage drop, short recovery time during switching, and stability as the temperature of the pn junction rises to prevent an increase in leakage current.
In principle, you can take an ordinary diode, but Schottky diodes are best suited for 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 package (reverse voltage up to 200V, current up to 30A, temperature up to 150 ° C). The common SS34s, which can be pulled from old boards or bought a whole pack for 90 rubles, have shown themselves very well.
The inductance of the choke depends on the output current (see table below). An incorrectly selected inductance value can lead to an increase in power dissipation on the microcircuit and an overshoot of the operating temperature range.
If it overheats above 160 ° C, the microcircuit will automatically turn off and will 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 allowed to install the coil with a deviation of the inductance upward from the nominal. In this case, the efficiency of the entire circuit changes, but it remains operational.
You can take a factory choke, or you can do it yourself from a ferrite ring from a burned-out motherboard and PEL-0.35 wire.
If the 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 on careful selection of the choke. At low currents, the inductance should be larger to minimize current control errors due to the switching delay of the transistor.
The choke should be located as close to the SW pin as possible, ideally connected directly to it.
And finally, the most precise element of the LED driver circuit is resistor R. As already mentioned, its minimum value is 0.082 Ohm, 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 recall the formulas for calculating the equivalent resistance for serial and parallel connection of resistors:
- R last \u003d R 1 + R 2 + ... + R n;
- R pairs \u003d (R 1 xR 2) / (R 1 + R 2).
By combining different switching methods, you can get the required resistance from several resistors at hand.
It is important to wire the board in such a way that the Schottky diode current does not flow along the path between R and VIN, as this can lead to errors in the measurement of the load current.
Low cost, high reliability and stability of the characteristics of the driver on the PT4115 contributes to its widespread use in LED lamps. Almost every second 12-volt LED lamp with 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 \u003d 0.1 / I LED [A]
A typical connection scheme looks like this: 
As you can see, everything is very similar to the circuit of an LED lamp with a driver on the PT4515. The description of work, signal levels, features of the elements used and the layout of the printed circuit board are exactly the same as that of, so it makes no sense to repeat.
CL6807 are sold at 12 rubles / piece, you just need to watch so as not to slip soldered ones (I recommend taking)
SN3350
SN3350 is another inexpensive microcircuit for LED drivers (13 rubles / piece). It is almost a complete analogue of PT4115 with the only difference that the supply voltage can be in the range from 6 to 40 volts, and the maximum output current is limited to 750 milliamperes (continuous current should not exceed 700 mA).
Like all the microcircuits described above, the SN3350 is a step-down pulse 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 \u003d 0.1 / I LED
In order not to exceed the value of the maximum output current, the resistance R should not be lower than 0.15 Ohm.
The microcircuit 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 the simplest adjustable LED driver.
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 about 60 μA.
Typical connection diagram: 
For the rest of the details, see the chip specification (pdf file).
ZXLD1350
Despite the fact that this microcircuit is another clone, some differences in technical characteristics do not allow them to be directly replaced with each other.
Here are the main differences:
- the microcircuit starts already at 4.8V, but it goes into normal operation only at a supply voltage of 7 to 30 Volts (it is allowed to supply up to 40V for half a second);
- maximum load current - 350 mA;
- the resistance of the output switch in the open state is 1.5 - 2 Ohm;
- 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 brightness range is 1-100%. If the frequency is higher than 10 kHz, then from 25% to 100%;
The maximum voltage that can be applied to the dimming input (ADJ) is 6V. In this case, in the range from 2.5 to 6V, the driver delivers the maximum current, which is set by the current-limiting resistor. Resistor resistance is calculated in the same way as in all of the above microcircuits:
R \u003d 0.1 / I LED
The minimum resistor resistance is 0.27 ohm.
A typical connection scheme is no different from its counterparts: 
Without capacitor C1, supply power to the circuit CANNOT !!! In the best case, the microcircuit will overheat and produce unstable characteristics. In the worst case, it will instantly fail.
More detailed characteristics of the ZXLD1350 can be found in the datasheet for this microcircuit.
The cost of the microcircuit is unreasonably high (), despite the fact that the output current is quite small. In general, it is strongly for an amateur. I would not have contacted.
QX5241
The QX5241 is the Chinese equivalent of the MAX16819 (MAX16820), but in a more convenient package. Also available under the designations 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 works on exactly the same principle as all of the above (continuous step-down converter), but does not contain an output switch, therefore, an external field-effect transistor must be connected for operation.
Any N-channel MOSFET with a suitable drain current and drain-source voltage can be taken. 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 of the key features of the QX5241 LED driver:
- maximum output current - 2.5 A;
- Efficiency up to 96%;
- maximum dimming frequency - 5 kHz;
- the maximum operating frequency of the converter is 1 MHz;
- current stabilization accuracy through LEDs - 1%;
- supply voltage - 5.5 - 36 Volts (it works fine even at 38!);
- the output current is calculated by the formula: R \u003d 0.2 / I LED
Read more in the specification (in English).
The LED driver on the QX5241 contains few details and is always assembled according to the following scheme: 
The 5241 microcircuit is only in the SOT23-6 case, so it is better not to approach it with a soldering iron for soldering pots. After installation, the board should be thoroughly washed from the flux, any incomprehensible contamination can adversely affect the operating mode of the microcircuit.
The difference between the supply voltage and the total voltage drop across the diodes must be 4 volts (or more). If less - then there are some glitches in the work (current instability and choke whistle). So take it with a margin. Moreover, the higher the output current, the greater the voltage margin. Although, perhaps I just came across an unsuccessful copy of the microcircuit.
If the input voltage is less than the total drop across the LEDs, then the generation is canceled. In this case, the output field is fully opened and the LEDs light up (naturally, not at full power, since the voltage is not enough).
AL9910
Diodes Incorporated has created one very interesting LED driver IC: AL9910. It is curious in that its operating voltage range allows you to connect it directly to a 220V network (through a simple diode rectifier).
Here are its main characteristics:
- input voltage - up to 500V (up to 277V for alternation);
- built-in voltage regulator for powering the microcircuit, which does not require a damping resistor;
- the ability to adjust the brightness by changing the potential on the control leg from 0.045 to 0.25V;
- built-in overheating protection (operates at 150 ° С);
- operating frequency (25-300 kHz) is set by an external resistor;
- an external field-effect transistor is required for operation;
- available in SO-8 and SO-8EP eight-legged housings.
The driver assembled on the AL9910 microcircuit does not have a galvanic isolation from the network, therefore it should be used only where direct contact with the circuit elements is impossible.
An integral part of any quality LED lamp or luminaire is the driver. With regard to lighting, the term "driver" should be understood as an electronic circuit that converts the input voltage into a stabilized current of a given value. The functionality of the driver is determined by the width of the input voltage range, the ability to adjust the output parameters, the susceptibility to fluctuations in the supply network, and efficiency.
The quality indicators of the lamp or lamp as a whole, service life and cost depend on the listed functions. All power supplies (IP) for LEDs are conventionally divided into linear and pulse converters. Linear power supplies can have a current or voltage stabilization unit. Often, radio amateurs construct circuits of this type with their own hands on the LM317 microcircuit. Such a device is easy to assemble and has a low cost. But, due to the very low efficiency and the obvious limitation on the power of the connected LEDs, the prospects for the development of linear converters are limited.
Pulse drivers can be more than 90% efficient and have a high degree of protection against network noise. Their power consumption is ten times less than the power supplied to the load. Thanks to this, they can be manufactured in a sealed case and are not afraid of overheating.
The first switching regulators had a complex device without idle protection. Then they were modernized and, in connection with the rapid development of LED technology, specialized microcircuits with frequency and pulse-width modulation appeared.
LED power supply circuit based on a capacitor divider
Unfortunately, the design of cheap 220V LED lamps from China does not provide for either a linear or a pulse stabilizer. Motivated by the extremely low price of the finished product, the Chinese industry was able to simplify the food scheme as much as possible. It is not correct to call it a driver, since there is no stabilization here. The figure shows that the electrical circuit of the lamp is designed to operate from a 220V network. The alternating voltage is lowered by the RC circuit and fed to the diode bridge. Then the rectified voltage is partially smoothed out by a capacitor and fed to the LEDs through a current-limiting resistor. This circuit has no galvanic isolation, that is, all elements are constantly at high potential.
As a result, frequent dips in the mains voltage lead to flickering of the LED lamp. And vice versa, overestimated mains voltage causes an irreversible aging process of the capacitor with a loss of capacity, and, sometimes, becomes the cause of its rupture. It is worth noting that another, serious negative side of this circuit is the accelerated degradation of LEDs due to unstable supply current.
Driver circuit for CPC9909
Modern pulse drivers for LED lamps have a simple circuit, so it can be easily made even with your own hands. Today, for the construction of drivers, a number of integrated circuits are produced, specially designed for driving high-power LEDs. To simplify the task for amateurs of electronic circuits, the developers of integrated drivers for LEDs in the documentation provide typical wiring diagrams and calculations of trim components.
General information
The American company Ixys has launched the release of the CPC9909 microcircuit designed to control LED assemblies and high-brightness LEDs. The CPC9909-based driver has a small size and does not require large investments. The CPC9909 IC is manufactured in a planar design with 8 pins (SOIC-8) and has a built-in voltage regulator.
Due to the presence of a stabilizer, the operating range of the input voltage is 12-550V from a DC source. The minimum voltage drop across LEDs is 10% of the supply voltage. Therefore, the CPC9909 is ideal for connecting high voltage LEDs. The IC works perfectly in the temperature range from -55 to + 85 ° C, which means it is suitable for the design of LED lamps and luminaires for outdoor lighting.
Pin assignment
It should be noted that with the help of CPC9909 you can not only turn on and off a powerful LED, but also control its glow. To learn about all the capabilities of the IC, consider the purpose of its conclusions. 
- VIN. Designed to supply voltage.
- Cs. Designed to connect an external current sensor (resistor), with which the maximum LED current is set.
- GND. General driver output.
- GATE. Chip output. Provides a modulated signal to the gate of the power transistor.
- PWMD. Low frequency dimming input.
- VDD. Output for regulating the supply voltage. In most cases, it is connected through a capacitor to a common wire.
- LD. Designed for setting analog dimming.
- RT. Designed to connect the timing resistor.
Scheme and its principle of operation
Typical switching on of CPC9909 with power supply from 220V network is shown in the figure The circuit is capable of driving one or more high-power LEDs or High Brightness LEDs. The circuit can be easily assembled by hand, even at home. The finished driver does not need adjustment, taking into account the competent choice of external elements and compliance with the rules for their installation. 
The driver for a 220V LED lamp based on CPC9909 works according to the method of frequency-pulse modulation. This means that the pause time is constant (time-off \u003d const). The alternating voltage is rectified by a diode bridge and smoothed by a capacitive filter C1, C2. Then it goes to the VIN input of the microcircuit and starts the process of forming current pulses at the GATE output. The IC's output current drives the power transistor Q1. At the moment of the open state of the transistor (pulse time "time-on"), the load current flows through the circuit: "+ diode bridge" - LED - L - Q1 - R S - "-diode bridge". 
During this time, the inductor stores energy in order to give it to the load during the pause. When the transistor turns off, the choke energy provides the load current in the circuit: L - D1 - LED - L. 
The process is cyclical, as a result of which the current through the LED has a sawtooth shape. The highest and lowest value of the saw depends on the inductance of the choke and the operating frequency. 
The pulse frequency is determined by the value of the resistance RT. The amplitude of the pulses depends on the resistance of the resistor RS. The LED current is stabilized by comparing the internal reference voltage of the IC with the voltage drop across RS. A fuse and a thermistor protect the circuit from possible emergency modes.
Calculation of external elements
Frequency setting resistor
The pause duration is set with an external resistor R T and is determined by the simplified formula:
pause t \u003d R T / 66000 + 0.8 (μs).
In turn, the pause time is related to the duty cycle and frequency:
pause t \u003d (1-D) / f (s), where D is the duty cycle, which is the ratio of the pulse time to the period.
Current sensor
The resistance rating R S sets the peak value of the current through the LED and is calculated by the formula: R S \u003d U CS / (I LED + 0.5 * I L pulse), where U CS is a calibrated reference voltage equal to 0.25V;
I LED - current through the LED;
I L pulse - the value of the load current ripple, which should not exceed 30%, that is, 0.3 * I LED.
After conversion, the formula will take the form: R S \u003d 0.25 / 1.15 * I LED (Ohm).
The power dissipated by the current sensor is determined by the formula: P S \u003d R S * I LED * D (W).
A resistor is accepted for installation with a power reserve of 1.5-2 times.
Throttle
As you know, the choke current cannot change abruptly, increasing during the pulse and decreasing during the pause. The task of the radio amateur is to choose a coil with an inductance that provides a compromise between the quality of the output signal and its dimensions. To do this, remember the level of pulsations, which should not exceed 30%. Then you need an inductance nominal:
L \u003d (US LED * t pauses) / I L pulse, where U LED is the voltage drop across the LED (s), taken from the VAC graph.
Power filter
Two capacitors are installed in the power circuit: C1 - to smooth the rectified voltage and C2 - to compensate for frequency interference. Since CPC9909 operates in a wide input voltage range, there is no need for a large electrolytic C1 capacity. 22 uF will be enough, but more is possible. The capacity of the metal-film C2 for a circuit of this type is standard - 0.1 μF. Both capacitors must withstand a voltage of at least 400V.
However, the microcircuit manufacturer insists on installing low equivalent series resistance (ESR) capacitors C1 and C2 in order to avoid the negative effects of high frequency interference that occurs when the driver is switched.
Rectifier
The diode bridge is selected based on the maximum forward current and reverse voltage. For operation in a 220V network, its reverse voltage must be at least 600V. The calculated value of the forward current directly depends on the load current and is determined as: I AC \u003d (π * I LED) / 2√2, A.
The resulting value must be multiplied by two to improve the reliability of the circuit.
Selecting the rest of the circuit elements
Capacitor C3 installed in the power circuit of the microcircuit must have a capacity of 0.1 μF with a low ESR value, similar to C1 and C2. The unused PWMD and LD pins are also connected through C3 to the common wire.
Transistor Q1 and diode D1 are pulsed. Therefore, the choice should be made taking into account their frequency properties. Only elements with a short recovery time will be able to contain the negative influence of transients at the moment of switching at a frequency of about 100 kHz. The maximum current through Q1 and D1 is equal to the peak value of the LED current, taking into account the selected duty cycle: I Q1 \u003d I D1 \u003d D * I LED, A.
The voltage applied to Q1 and D1 is impulse in nature, but no more than the rectified voltage taking into account the capacitive filter, that is, 280V. The choice of power elements Q1 and D1 should be made with a margin, multiplying the calculated data by two.
The fuse (fuse) protects the circuit from an emergency short circuit and must withstand the maximum load current, including impulse noise, for a long time.
I FUSE \u003d 5 * I AC, A.
The RTH thermistor is installed to limit the driver inrush current when the filter capacitor is discharged. With its resistance RTH should protect the diodes of the bridge rectifier from breakdown in the initial seconds of operation.
R TH \u003d (√2 * 220) / 5 * I AC, Ohm.
Other options for enabling CPC9909
Soft start and analog dimming
If desired, the CPC9909 can provide a soft turn on of the LED when its brightness gradually increases. Soft start is realized with two fixed resistors connected to the LD pin, as shown in the figure. This solution extends the life of the LED.
Also, the LD pin allows you to implement the analog dimming function. To do this, the 2.2 kΩ resistor is replaced with a 5.1 kΩ variable resistor, thereby smoothly changing the potential at the LD pin.
Pulse dimming
You can control the glow of the LED by applying rectangular pulses to the PWMD (pulse width modulation dimming) pin. To do this, use a microcontroller or a pulse generator with mandatory separation through an optocoupler.
In addition to the considered driver option for LED lamps, there are similar circuit solutions from other manufacturers: HV9910, HV9961, PT4115, NE555, RCD-24, etc. Each of them has its own strengths and weaknesses, but in general, they successfully cope with the assigned load when assembling by hand.
Read the same
We worked as brightly and efficiently as possible, using special modules - drivers. Everyone can assemble a driver circuit for LEDs on their own, if, of course, there is knowledge in electrical engineering. The meaning of the device is to convert the alternating voltage flowing in the network into a constant (reduced) voltage. But before proceeding with the assembly, you need to decide what requirements are imposed on the device - analyze the characteristics and types of devices.
What are drivers for?
The main purpose of the drivers is to stabilize the current that flows through the LED. Moreover, it should be taken into account that the strength of the current that passes through the semiconductor crystal must be exactly the same as that of the LED according to the passport. This ensures stable lighting. The crystal in the LED will last much longer. To find out the voltage required to power the LEDs, you need to use the current-voltage characteristic. This is a graph showing the relationship between supply voltage and current.
If you plan to illuminate a residential or office space with LED lamps, then the driver must be powered from a 220 V AC household network. In some cases (if the LED lamp is of low power and is powered from a 220 V network), it is allowed to remove the LED driver circuit. From the network, if the device is powered, it is enough to include a constant resistor in the circuit.
Driver options
Before purchasing a device or making it yourself, you need to familiarize yourself with what its main characteristics are:
- Rated current consumption.
- Power.
- Output voltage.
The voltage at the output of the converter directly depends on the selected method of connecting the light source, the number of LEDs. The current is directly dependent on the brightness and power of the elements.
The converter must provide a current at which the LEDs will operate at the same brightness. On PT4115, the LED driver circuit is quite simple to implement - it is the most common voltage converter for use with LED elements. You can literally make a device based on it on your knee.
Driver power
The power of the device is the most important characteristic. The more powerful the driver is, the more LEDs can be connected to it (of course, simple calculations will have to be done). A prerequisite is that the driver power must be greater than that of all LEDs in total. This is expressed by the following formula:
P \u003d P (sv) x N,
where P, W is the driver power;
P (sv), W - power of one LED;
N is the number of LEDs.
For example, when assembling a driver circuit for a 10W LED, you can safely connect LED elements up to 10W as a load. It is imperative to have a small power reserve - about 25%. Therefore, if you plan to connect a 10 W LED, the driver must provide a power of at least 12.5-13 W.
LED colors
Be sure to consider what color the LED emits. It depends on what kind of voltage drop they will have at the same current strength. For example, with a supply current of 0.35 A, the voltage drop for red LED elements is approximately 1.9-2.4 V. The average power is 0.75 W. A similar model with green color will already have a drop in the range of 3.3-3.9 V, and a power of 1.25 W. Therefore, if you use a 220V LED driver circuit with conversion to 12V, a maximum of 9 elements with green or 16 elements with red can be connected to it.
Driver types
In total, there are two types of LED drivers:
- Pulse. With the help of such devices, high-frequency pulses are created in the output part of the device. The operation is based on the principles of PWM modulation. The average current value depends on the duty cycle (the ratio of the duration of one pulse to its repetition rate). The output current changes due to the fact that the duty cycle fluctuates in the range of 10-80%, and the frequency remains constant.
- Linear - a typical circuit and structure are made in the form of a current generator on transistors with a p-channel. With their help, it is possible to ensure the most smooth stabilization of the supply current if the input voltage is unstable. They are cheap, but they have low efficiency. It generates a lot of heat during operation, so it can only be used for low power LEDs.
Pulsed ones are more widespread, since their efficiency is much higher (can reach 95%). The devices are compact, the input voltage range is wide enough. But there is one big drawback - the high influence of various kinds of electromagnetic interference.
What to look for when buying?
The purchase of a driver must be done when choosing LEDs. On the PT4115, the LED driver circuitry allows for normal operation. Devices using PWM modulators, built on a single chip circuit, are used mostly in automotive engineering. In particular, for connecting backlights and headlights. But the quality of such simple devices is rather low - they are not suitable for use in household systems.
Dimmable driver
Almost all designs of converters allow you to adjust the brightness of the LED elements. With these devices, you can do the following:
- Reduce light intensity during the day.
- Hide or emphasize certain elements of the interior.
- Zoning the room.
Thanks to these qualities, you can significantly save on electricity, increase the resource of elements.
Varieties of dimmable drivers
Dimmable driver types:
- They are connected between the PSU and the light source. They allow you to control the energy that goes to the LED elements. The design is based on PWM modulators with microcontroller control. All energy goes to the LEDs in pulses. The energy that goes to the LEDs directly depends on the length of the pulses. Such driver designs are mainly used to operate power-stabilized modules. For example, for tapes or creeping lines.
- The second type of devices allows you to control the power supply. The control is carried out using a PWM modulator. The amount of current that flows through the LEDs also changes. As a rule, such designs are used to power those devices that require a stabilized current.
It is imperative to take into account the fact that PWM control has a bad effect on vision. It is best to use driver circuits to power the LEDs, in which the amperage is regulated. But here's one caveat - depending on the magnitude of the current, the glow will be different. At a low value, the elements will emit light with a yellow tint, while at a higher value, they will emit bluish light.
Which microcircuit to choose?
If you don't want to look for a finished device, you can make it yourself. And to make a calculation for specific LEDs. There are quite a lot of microcircuits for making drivers. You only need to be able to read electrical circuits and work with a soldering iron. For the simplest devices (up to 3 W), you can use the PT4115 chip. It's cheap and easy to get. The characteristics of the element are as follows:
- Supply voltage - 6-30 V.
- Output current - 1.2 A.
- Permissible error during current stabilization - no more than 5%.
- Load disconnection protection.
- Dimming pins.
- The efficiency is 97%.
Designation of microcircuit pins:
- SW - connection of the output switch.
- GND is the negative terminal of power and signal sources.
- DIM - brightness control.
- CSN - input current sensor.
- VIN is the positive terminal connected to the power supply.
Driver circuit options
Device options:
- If you have a 6-30V DC power supply.
- Powered by an alternating voltage of 12-18 V. A diode bridge and an electrolytic capacitor are introduced into the circuit. In fact, a "classic" bridge rectifier circuit with AC clipping.
It should be noted that the electrolytic capacitor does not smooth out the voltage ripple, but allows you to get rid of the variable component in it. In equivalent circuits (according to Kirchhoff's theorem), an electrolytic capacitor in an alternating current circuit is a conductor. But in the DC circuit, it is replaced by a break (there is no element).
It is possible to assemble the 220 LED driver circuit with your own hands only if you use an additional power supply. It necessarily involves a transformer that lowers the voltage to the required value of 12-18 V. Please note that you cannot connect drivers to LEDs without an electrolytic capacitor in the power supply. If it is necessary to install the inductance, it is necessary to calculate it. Typically the value is 70-220 μH.
Build process
All elements that are used in the circuit must be selected based on the datasheet (technical documentation). It usually even provides practical diagrams for using the devices. Be sure to use low impedance capacitors in the rectifier circuit (ESR should be low). The use of other analogs reduces the efficiency of the regulator. The capacitance must be at least 4.7 μF (in the case of using a direct current circuit) and from 100 μF (for operation in an alternating current circuit).
You can assemble a driver for LEDs according to the scheme with your own hands in just a few minutes, you only need the presence of elements. But you need to know the features of the installation. It is advisable to place the inductor near the output of the SW microcircuit. You can make it yourself, for this you only need a few elements:
- Ferrite bead - can be used with old computer power supplies.
- PEL-0.35 type wire in varnish insulation.
Try to place all elements as close to the microcircuit as possible, this will eliminate the appearance of interference. Never connect elements with long wires. They not only create a lot of interference, but are also able to receive them. As a result, a microcircuit that is unstable to these interference will not work correctly, and the current regulation will be disrupted.
Layout option
You can place all the elements in the body of an old fluorescent lamp. It already has everything - the case, the cartridge, the board (which can be reused). Inside, all the elements of the power supply and the microcircuit can be placed without much difficulty. And from the outside, install the LED that you plan to power from the device. Almost any driver circuit for 220 V LEDs can be used, the main thing is to lower the voltage. This can be easily done with the simplest transformer.
It is advisable to use a new mounting plate. Better to do without it altogether. The design is very simple, it is permissible to use a hinged installation. Be sure to make sure that the voltage at the output of the rectifier is within acceptable limits, otherwise the microcircuit will burn out. After assembly and connection, measure the current consumption. Please note that in case of a decrease in the supply current, the life of the LED element will increase.
Carefully choose a driver circuit for powering LEDs, calculate each component of the structure - the service life and reliability depend on this. With the correct selection of drivers, the characteristics of the LEDs will remain as high as possible, and the resource will not suffer. Driver circuits for high-power LEDs differ in that they have a larger number of elements. PWM modulation is often used, but at home, as they say, "on the knee", such devices are already difficult to assemble.
LEDs have become very popular. The main role in this was played by the LED driver, which maintains a constant output current of a certain value. We can say that this device is a current source for LED devices. This current driver, working in conjunction with the LED, ensures long life and reliable brightness. An analysis of the characteristics and types of these devices allows you to understand what functions they perform and how to choose them correctly.
What is a driver and what is its purpose?
An LED driver is an electronic device whose output produces a constant current after stabilization. In this case, not a voltage is generated, but a current. Devices that stabilize the voltage are called power supplies. The output voltage is indicated on their case. 12V power supplies are used to power LED strips, LED strips and modules.
The main parameter of the LED driver, with which it can provide the consumer for a long time at a certain load, is the output current. Separate LEDs or assemblies of similar elements are used as a load.
The driver for the LED is usually powered from a 220 V network. In most cases, the operating output voltage range is from three volts and can reach several tens of volts. To connect 6 3W LEDs, a driver with an output voltage of 9 to 21 V, rated for 780 mA is required. With its versatility, it has a low efficiency if you turn on the minimum load on it.
When lighting in cars, in the headlights of bicycles, motorcycles, mopeds, etc., the equipment of portable lights uses a power supply with a constant voltage, the value of which varies from 9 to 36 V. You can not use a driver for LEDs with low power, but in such In some cases, it will be necessary to insert an appropriate resistor into the 220 V supply network. Despite the fact that this element is used in household switches, it is quite problematic to connect the LED to a 220 V network and rely on reliability.
Key Features
The power that these devices are capable of delivering under load is an important indicator. Don't overload it trying to get the best results. As a result of such actions, the drivers for the LEDs or the LED elements themselves may fail.
The electronic stuffing of the device is influenced by many reasons:
- device protection class;
- elemental component that is used for assembly;
- input and output parameters;
- manufacturer's brand.
The manufacture of modern drivers is carried out using microcircuits using pulse-width conversion technology, which include pulse converters and current stabilizing circuits. PWM converters are powered from 220 V, have a high class of protection against short circuits, overloads, as well as high efficiency.
Specifications
Before purchasing a converter for LEDs, you should study the characteristics of the device. These include the following parameters:
- output power;
- output voltage;
- rated current.
LED driver connection diagram The output voltage is affected by the connection to the power source, the number of LEDs in it. The current value proportionally depends on the power of the diodes and the brightness of their radiation. The LED driver must supply as much current to the LEDs as needed to maintain constant brightness. It is worth remembering that the power of the required device must be more consumed by all LEDs. You can calculate it using the following formula:
P(led) - power of one LED element;
n - the number of LED elements.
To ensure long-term and stable operation of the driver, the power reserve of the device of 20-30% of the nominal should be taken into account.
When performing the calculation, the consumer's color factor should be taken into account, as it affects the voltage drop. It will have different meanings for different colors.
Shelf life
LED drivers, like all electronics, have a certain lifespan, which is greatly influenced by operating conditions. LED elements made by well-known brands are designed to operate up to 100 thousand hours, which is much longer than power supplies. In terms of quality, the calculated driver can be classified into three types:
- low quality, with a working capacity of up to 20 thousand hours;
- with averaged parameters - up to 50 thousand hours;
- a converter consisting of components from well-known brands - up to 70 thousand hours.
Many do not even know why to pay attention to this parameter. This will be needed to select a device for long-term use and further payback. For use in domestic premises, the first category is suitable (up to 20 thousand hours).
How to choose a driver?
There are many types of drivers used for LED lighting. Most of the products presented are made in China and do not have the required quality, but at the same time they stand out for their low price range. If you need a good driver, it is better not to chase the cheapness of Chinese production, since their characteristics do not always coincide with the declared ones, and rarely a warranty is attached to them. There may be a defect on the microcircuit or a quick failure of the device, in which case it will not be possible to exchange for a better product or return the funds.
The most commonly chosen option is a 220 V or 12 V open-frame driver. Various modifications allow them to be used for one or more LEDs. These devices can be selected for organizing research in the laboratory or conducting experiments. For phyto-lamps and household use, the drivers for the LEDs located in the housing are chosen. Open-frame devices benefit from price, but lose from aesthetics, security and reliability.
Types of drivers
Devices supplying power to LEDs can be conditionally divided into:
- pulse;
- linear.
Pulse-type devices produce a lot of high-frequency current pulses at the output and operate on the PWM principle, their efficiency is up to 95%. Pulse converters have one significant drawback - during operation, strong electromagnetic interference occurs. To ensure a stable output current, a current generator is installed in the linear driver, which acts as an output. Such devices have low efficiency (up to 80%), but they are technically simple and inexpensive. Such devices cannot be used for high power consumers.
From the above, it can be concluded that the power supply for the LEDs should be chosen very carefully. An example would be a fluorescent lamp, which is supplied with a current exceeding the norm by 20%. There will be practically no changes in its characteristics, but the efficiency of the LED will decrease several times.