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

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

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

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

I LED = 0.1 / R

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

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

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

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

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

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

1. First way assumes that a constant voltage in the range from 0 to 6V is supplied to the DIM input. In this case, brightness adjustment from 0 to 100% is carried out at a voltage at the DIM pin from 0.5 to 2.5 volts. Increasing the voltage above 2.5 V (and up to 6 V) does not affect the current through the LEDs (the brightness does not change). On the contrary, reducing the voltage to a level of 0.3V or lower leads to the circuit turning off and putting it into standby mode (the current consumption drops to 95 μA). Thus, you can effectively control the operation of the driver without removing the supply voltage.
2. Second way involves supplying a signal from a pulse-width converter with an output frequency of 100-20000 Hz, the brightness will be determined by the duty cycle (pulse duty cycle). For example, if high level will remain for 1/4 of the period, and the low level, respectively, for 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 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 with increasing temperature p-n junction 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 wires PEL-0.35.

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).

Combining various ways switching on, 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 diagram LED lamp with driver for RT4515. Description of operation, signal levels, features of elements used and layout printed circuit board exactly the same as those, so there is no point in repeating them.

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

SN3350

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

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

R = 0.1 / I LED

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

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

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

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

Typical connection diagram:

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

ZXLD1350

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

Here are the main differences:

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

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

R = 0.1 / I LED

The minimum resistor resistance is 0.27 Ohm.

A typical connection diagram is no different from its counterparts:

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

More detailed characteristics 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 Chinese equivalent 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.

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In recent years, it has become increasingly popular. This is due to the fact that the LEDs used in the lamps, also called light-emitting diodes (LEDs), are quite bright, economical and durable. Using LED elements, interesting and original lighting effects are created that can be used in a wide variety of interiors. However, such lighting devices are very demanding on the parameters of electrical networks, especially on the current value. Therefore, for normal lighting operation, drivers for LEDs must be included in the circuit. In this article we will try to figure out what LED drivers are, what are their main characteristics, how not to make a mistake when choosing, and whether it is possible to make one yourself.

Without such a miniature device, the LEDs will not work

Since LEDs are current devices, they are accordingly very sensitive to this parameter. For normal lighting operation, a stabilized current with a nominal value must pass through the LED element. For these purposes, a driver for LED lamps was created.

Some readers, when they see the word driver, will be at a loss, since we are all accustomed to the fact that this term refers to some software that allows us to manage programs and devices. Translated from in English driver means: driver, driver, leash, mast, control program and more than 10 meanings, but they all have one function in common - control. This is the case with drivers for, only they control the current. So, we’ve sorted out the term, now let’s get to the point.

LED driver – electronic device, at the output of which, after stabilization, a direct current of the required magnitude is generated, ensuring normal operation of the LED elements. In this case, it is the current, not the voltage, that is stabilized. Devices that stabilize the output voltage are called, which are also used to power LED lighting elements.

As we already understood, the main parameter of the driver for LEDs is the output current, which the device can provide for a long time when the load is turned on. For normal and stable glow of LED elements, it is required that a current flow through the LED, the value of which must coincide with the values ​​​​specified in the technical data sheet of the semiconductor.

Where are LED drivers used?

As a rule, LED drivers are designed to operate with voltages of 10, 12, 24, 220 V and a constant current of 350 mA, 700 mA and 1 A. Current stabilizers for LEDs are produced mainly for specific products, but there are also universal devices that suitable for LED elements from leading manufacturers.

LED drivers in AC networks are mainly used for:

In electrical circuits with direct current, stabilizers are needed for the normal operation of on-board lighting and car headlights, portable lights, etc.

Current stabilizers are adapted to work with control systems and photocell sensors, and due to their compactness can be easily installed in distribution boxes. Also, using drivers, you can easily change the brightness and color of the LED elements, reducing the current through digital control.

How do stabilizing devices for LEDs work?

The principle of operation of the converter for and tapes is to maintain a given current value regardless of the output voltage. This is the difference between a power supply and an LED driver.

If we look at the diagram presented above, we will see that the current, thanks to resistor R1, is stabilized, and capacitor C1 sets the required frequency. Next, the diode bridge is switched on, as a result of which a stabilized current is supplied to the LEDs.

Device Features You Need to Pay Attention to

When choosing an LED driver for LED lamps, it is necessary to take into account the main parameters, namely: current, output voltage and power consumed by the connected load.

The output voltage of the current stabilizer depends on the following factors:

• number of LED elements;
• LED voltage drop;
• connection method.

The current at the output of the device is determined by the power and. The power of the load affects the current it consumes depending on the required glow intensity. It is the stabilizer that provides the LEDs with the required current.

Power LED lamp depends directly on:

• power of each LED element;
• total number of LEDs;
• colors.

The power consumed by the load can be calculated using the following formula:

P N = PLED × N , Where

• P N – total load power;
• P LED – power of an individual LED;
• N – number of LED elements connected to the load.

The maximum power of the current stabilizer should not be less than PH. For normal operation of the LED driver, it is recommended to provide a power reserve of at least 20÷30%.

In addition to the power and number of LEDs, the power of the load connected to the driver also depends on the color of the LED elements. The fact is that LEDs of different colors have different voltage drops when same value current So, for example, at CREE LED XP-E red, the voltage drop at a current of 350 mA is 1.9 ÷ 2.4 V, and the average power consumption will be about 750 mW. For a green LED element at the same current, the voltage drop will be 3.3÷3.9 V, and the average power will be almost 1.25 W. Accordingly, a current stabilizer designed for a power of 10 W can power 12÷13 red LEDs or 7-8 green LEDs.

Types of stabilizers by device type

Current stabilizers for light-emitting diodes are divided according to the type of device into pulsed and linear.

For a linear driver, the output is a current generator, which provides smooth stabilization of the output current when the input voltage is unstable, without creating high-frequency electromagnetic interference. Such devices have a simple design and low cost, but the not very high efficiency (up to 80%) narrows the scope of their use to low-power LED elements and strips.

Pulse-type devices allow you to create a series of current pulses at the output high frequency. Such drivers operate on the principle of pulse width modulation (PWM), that is, the average output current is determined by the ratio of the pulse width to their frequency. Such devices are more in demand due to their compactness and higher efficiency, which is about 95%. However, in comparison with linear PWM drivers, stabilizers have higher level electromagnetic interference.

How to choose a driver for LEDs

It should be immediately noted that a resistor cannot be a full replacement for a driver, since it is not able to protect the LEDs from power surges and impulse noise. Also not the best option will use a linear current source due to its low efficiency, limiting the capabilities of the stabilizer.

When choosing an LED driver for LEDs, you should adhere to the following basic recommendations:

• It is best to purchase a current stabilizer at the same time as the load;
• take into account the voltage drop across the LEDs;
• a high current rating reduces the efficiency of the LED and causes it to overheat;
• take into account the power of the load connected to the driver.

It is also necessary to pay attention that the stabilizer case indicates its power, operating ranges of input and output voltage, rated stabilized current and the degree of moisture and dust protection of the device.

Recommendation! How powerful and high-quality the driver for the LED strip or LED will be, of course, is up to you. However, it should be remembered that for normal operation of all created system lighting, it is best to buy a branded converter, especially when it comes to LED spotlights and other powerful lighting devices.

Connecting current converters for LEDs: driver circuit for a 220 V LED lamp

Most manufacturers produce drivers on integrated circuits (ICs), which allow them to be powered from a reduced voltage. All converters for LED lighting that currently exist are divided into simple ones, created on the basis of 1÷3 transistors, and more complex ones, made using PWM microcircuits.

The above is an IC based driver circuit, but as we mentioned, there are connection methods using resistors and transistors. In fact, there are many connection options and it is simply impossible to consider them all in detail in one review. On the Internet you can find almost any scheme suitable for your situation.

How to calculate a current stabilizer for LED lighting

To determine the output voltage of the converter, it is necessary to calculate the ratio of power and current. So, for example, with a power of 3 W and a current of 0.3 A, the maximum output voltage will be 10 V.Next, you need to decide on the connection method, parallel or serial, as well as the number of LEDs. The fact is that the rated power and voltage at the driver output depend on this. After calculating all these parameters, you can select the appropriate stabilizer.

It is worth noting that converters designed for a certain number of LED elements have protection against emergency situations. This type of device is characterized by incorrect operation when connecting a smaller number of LEDs - flickering is observed or does not work at all.

Dimmable driver for LED elements - what is it?

The latest models of converters for LEDs are adapted to work with dimmers of semiconductor crystals -. The use of these devices allows for more efficient use of electricity and increases the life of the LED element.

Dimmable converters come in two types. Some are included in the circuit between the stabilizer and LED lighting elements and operate via PWM control. Converters of this type are used to work with LED strips, ticker tape, etc.

In the second option, the dimmer is installed at the gap between the power source and the stabilizer, and the operating principle consists of both controlling the parameters of the current passing through the LEDs and using pulse-width modulation.

Features of Chinese current converters for LEDs

The high demand for drivers for LED lighting has led to their mass production in the Asian region, particularly in China. And this country is famous not only for high-quality electronics, but also for the mass production of all kinds of counterfeits. LED Drivers made in China They are pulse current converters, usually designed for 350÷700 mA and in an open-frame design.

The advantages of Chinese current converters are only low cost and the presence of galvanic isolation, but there are still more disadvantages and they consist of:

• high level of radio interference;
• unreliability caused by cheap circuit solutions;
• vulnerability to network fluctuations and overheating;
• high level of ripple at the output of the stabilizer;
• short service life.

Typically, Chinese-made components operate at the limit of their capabilities, without any reserve. Therefore, if you want to create a reliably operating lighting system, it is best to buy a converter for LEDs from a well-known, trusted manufacturer.

Service life of current converters

Like any electronic device, the driver for an LED current source has a certain service life, which depends on the following factors:

• network voltage stability;
• temperature changes;
• humidity level.

Well-known manufacturers guarantee their products for an average of 30,000 hours of operation. The cheapest, simplest stabilizers are designed to operate for 20,000 hours, average quality - 20,000 hours, and Japanese ones - up to 70,000 hours.

LED driver circuit based on RT 4115

Thanks to the emergence large quantity LED elements with a power of 1÷3 W and low price, most people prefer to make home and automotive lighting based on them. However, this requires a driver that will stabilize the current to the nominal value.

For correct operation of the converter, it is recommended to use tantalum capacitors. If you do not install a capacitor on the power supply, the integrated circuit (IC) will simply fail when the device is connected to the network. Above is a driver circuit for an LED on the PT4115 IC.

How to make your own LED driver

Using ready-made microcircuits, even a novice radio amateur can assemble a converter for LEDs of various powers. This requires the ability to read electrical diagrams and experience with a soldering iron.

You can assemble a current stabilizer for 3-watt stabilizers using a microcircuit from the Chinese manufacturer PowTech - PT4115. This IC can be used for LED elements with a power of more than 1 W and consists of control units with a fairly powerful transistor at the output. The converter, based on PT4115, has high efficiency and a minimum set of components.

As you can see, if you have experience, knowledge and desire, you can assemble an LED driver according to almost any scheme. Now let's consider step by step instructions creating a simple current converter for 3 LED elements with a power of 1 W each, from a charger for mobile phone. By the way, this will help you better understand the operation of the device and later move on to more complex circuits designed for large quantity LEDs and strips.

Instructions for assembling a driver for LEDs

Image	Description of the stage
	To assemble the stabilizer, you will not need an old mobile phone charger. We took them from Samsung, they are so reliable. Carefully disassemble the charger with parameters 5 V and 700 mA.
	We also need a 10 kOhm variable (tuning) resistor, 3 1 W LEDs and a cord with a plug.
	This is what the disassembled charger looks like, which we will redo.
	We unsolder the 5 kOhm output resistor and put a “tuner” in its place.
	Next, we find the output to the load and, having determined the polarity, solder the LEDs, pre-assembled in series.
	We unsolder the old contacts from the cord and connect the wire and plug in their place. Before checking the functionality of the driver for LEDs, you need to make sure that the connections are correct, that they are strong, and that nothing is created. short circuit. Only after this can you start testing.
	We start adjusting with a trimming resistor until the LEDs start to glow.
	As you can see, the LED elements are lit.
	Using a tester, we check the parameters we need: output voltage, current and power. If necessary, adjust with a resistor.
	That's all! The LEDs burn normally, nothing sparks or smokes anywhere, which means the conversion was successful, for which we congratulate you.

As you can see, making a simple driver for LEDs is very simple. Of course, experienced radio amateurs may not be interested in this scheme, but for a beginner it is perfect for practice.

Recently, a friend asked me to help with a problem. He is developing LED lamps, selling them along the way. He has accumulated a number of lamps that are not working correctly. Externally, this is expressed as follows: when turned on, the lamp flashes for a short time (less than a second), goes out for a second, and so repeats endlessly. He gave me three such lamps to study, I solved the problem, the fault turned out to be very interesting (just in the style of Hercule Poirot) and I want to tell you about the way to find the fault.

The LED lamp looks like this:

Fig 1. Appearance disassembled LED lamp

The developer has used an interesting solution - the heat from the operating LEDs is taken by a heat pipe and transferred to a classic aluminum radiator. According to the author, this solution allows for the correct thermal conditions for LEDs, minimizing thermal degradation and ensuring the longest possible service life of the diodes. At the same time, the service life of the diode power driver increases, since the driver board is removed from the thermal circuit and the board temperature does not exceed 50 degrees Celsius.

This solution - to separate the functional zones of light emission, heat removal and power current generation - made it possible to obtain high performance characteristics of the lamp in terms of reliability, durability and maintainability.
The disadvantage of such lamps, oddly enough, directly follows from its advantages - manufacturers do not need a durable lamp :). Does everyone remember the story about the conspiracy among incandescent lamp manufacturers about the maximum service life of 1000 hours?

Well, I can’t help but note the characteristic appearance of the product. My “state control” (wife) did not allow me to put these lamps in the chandelier where they are visible.

Let's return to the driver problems.

This is what the driver board looks like:

Fig 2. Appearance of the LED driver board from the surface mount side

And on the reverse side:

Fig 3. Appearance of the LED driver board from the power parts side

Studying it under a microscope made it possible to determine the type of control chip - it is MT7930. This is a flyback converter control chip (Fly Back), hung with various protections, like a Christmas tree with toys.

The MT7930 has built-in protection:

From excess current of the key element
supply voltage reduction
increasing supply voltage
short circuit in the load and load break.
from exceeding the temperature of the crystal

Declaring protection against short circuit in the load for a current source is rather of a marketing nature :)

It was not possible to obtain a schematic diagram for just such a driver, but a search on the Internet yielded several very similar diagrams. The closest one is shown in the figure:

Fig 4. LED Driver MT7930. Electrical circuit diagram

Analysis of this circuit and thoughtful reading of the manual for the microcircuit led me to the conclusion that the source of the blinking problem is the activation of the protection after the start. Those. the initial start-up procedure goes through (the lamp flashes - that’s what it is), but then the converter turns off due to one of the protections, the power capacitors are discharged and the cycle begins again.

Attention! The circuit contains life-threatening voltages! Do not repeat without proper understanding of what you are doing!

To study signals with an oscilloscope, you need to decouple the circuit from the network so that there is no galvanic contact. For this I used an isolation transformer. On the balcony, two Soviet-made TN36 transformers, dated 1975, were found in the reserves. Well, these are timeless devices, massive, covered in completely green varnish. I connected it according to the scheme 220 – 24 – 24 -220. Those. First I lowered the voltage to 24 volts (4 secondary windings of 6.3 volts each), and then increased it. Having multiple tapped primary windings gave me the opportunity to play with different supply voltages - from 110 volts to 238 volts. This solution is, of course, somewhat redundant, but quite suitable for one-time measurements.

Fig 5. Photo of an isolation transformer

From the description of the start in the manual it follows that when power is applied, capacitor C8 begins to charge through resistors R1 and R2 with a total resistance of about 600 kohms. Two resistors are used for safety reasons, so that if one breaks down, the current through this circuit does not exceed the safe value.

So, the power capacitor slowly charges (this time is about 300-400 ms) and when the voltage on it reaches 18.5 volts, the converter start procedure starts. The microcircuit begins to generate a sequence of pulses to the key field-effect transistor, which leads to the appearance of voltage on the Na winding. This voltage is used in two ways - to generate pulses feedback to control the output current (circuit R5 R6 C5) and to generate the operating supply voltage of the microcircuit (circuit D2 R9). At the same time, a current arises in the output circuit, which leads to the ignition of the lamp.

Why does the protection work and by what parameter?

First guess

Triggering of protection when output voltage is exceeded?

To test this assumption, I unsoldered and tested the resistors in the divider circuit (R5 10 kohm and R6 39 kohm). You can't check them without soldering them, since they are paralleled through the transformer winding. The elements turned out to be fine, but at some point the circuit started working!

I checked the shapes and voltages of the signals at all points of the converter with an oscilloscope and was surprised to see that they were all completely certified. No deviations from the norm...

I let the circuit run for an hour - everything was OK.

What if you let it cool? After 20 minutes in the off state it does not work.

Very good, apparently it’s a matter of heating some element?

But which one? And what element parameters can float away?

At this point I concluded that there was some kind of temperature sensitive element on the converter board. Heating this element completely normalizes the operation of the circuit.
What is this element?

Second guess

Suspicion fell on the transformer. The problem was thought of as follows: the transformer, due to manufacturing inaccuracies (say, the winding is under-wound by a couple of turns), operates in the saturation region, and due to a sharp drop in inductance and a sharp increase in current, the current protection of the field switch is triggered. This is a resistor R4 R8 R19 in the drain circuit, the signal from which is supplied to pin 8 (CS, apparently Current Sense) of the microcircuit and is used for the current feedback circuit and, when the setting of 2.4 volts is exceeded, turns off generation to protect the field-effect transistor and transformer from damage. On the board under study there are two resistors R15 R16 in parallel with an equivalent resistance of 2.3 ohms.

But as far as I know, the parameters of the transformer deteriorate when heated, i.e. The behavior of the system should be different - turn on, work for 5-10 minutes and turn off. The transformer on the board is quite massive and its thermal constant is no less than a few minutes.
Maybe, of course, there is a short-circuited turn in it that disappears when heated?

Resoldering the transformer to a guaranteed working one was impossible at that moment (they had not yet delivered a guaranteed working board), so I left this option for later, when there were no versions left at all :). Plus the intuitive feeling is not it. I trust my engineering intuition.

At this point, I tested the hypothesis about the operation of the current protection by reducing the current resistor by half by soldering the same one in parallel to it - this did not affect the blinking of the lamp in any way.

This means that everything is normal with the current of the field-effect transistor and there is no excess current. This was clearly visible from the signal shape on the oscilloscope screen. Peak sawtooth signal was 1.8 volts and clearly did not reach the value of 2.4 volts, at which the microcircuit turns off generation.

The circuit also turned out to be insensitive to changes in load - neither connecting the second head in parallel, nor switching a warm head to a cold one and back changed anything.

Third guess

I examined the supply voltage of the microcircuit. When operating in normal mode, all voltages were absolutely normal. In blinking mode too, as far as one could judge from the waveforms on the oscilloscope screen.

As before, the system blinked in a cold state and began to work normally when the transformer leg was warmed up with a soldering iron. Warm it up for 15 seconds and everything starts up fine.

Warming up the microcircuit with a soldering iron did nothing.

And the short heating time was very confusing... what could change in 15 seconds?

At some point, I sat down and methodically, logically cut off everything that was guaranteed to work. Once the lamp lights up, it means the starting circuits are working.
Once heating the board manages to start the system and it works for hours, it means the power systems are working properly.
It cools down and stops working - something depends on the temperature...
Is there a crack on the board in the feedback circuit? It cools and contracts, the contact is broken, it heats up, expands and the contact is restored?
I climbed a cold board with a tester - there are no breaks.

What else can interfere with the transition from startup mode to operating mode?!!!

Out of complete hopelessness, I intuitively soldered a 10 uF 35 volt electrolytic capacitor in parallel to power the same microcircuit.

And then happiness came. It's working!

Replacing the 10 uF capacitor with a 22 uF capacitor completely solved the problem.

Here it is, the culprit of the problem:

Figure 6. Capacitor with incorrect capacitance

Now the mechanism of the malfunction has become clear. The circuit has two power circuits for the microcircuit. The first, triggering, slowly charges capacitor C8 when 220 volts are supplied through a 600 kΩ resistor. After it is charged, the microcircuit begins to generate impulses for the field operator, starting the power part of the circuit. This leads to the generation of power for the microcircuit in operating mode on a separate winding, which is supplied to the capacitor through a diode with a resistor. The signal from this winding is also used to stabilize the output current.

Until the system reaches operating mode, the microcircuit is powered by the stored energy in the capacitor. And it was missing a little - literally a couple or three percent.
The voltage drop was enough for the microcircuit protection system to trigger due to low power and turn off everything. And the cycle began again.

It was not possible to detect this drop in the supply voltage with an oscilloscope - it was too rough an estimate. It seemed to me that everything was fine.

Warming up the board increased the capacitor capacity by the missing percentage - and there was already enough energy for a normal start-up.

It is clear why only some of the drivers failed despite the elements being fully functional. A bizarre combination of the following factors played a role:

Low power supply capacitance. The tolerance for the capacitance of electrolytic capacitors (-20% +80%) played a positive role, i.e. capacitances with a nominal value of 10 microfarads in 80% of cases have a real capacity of about 18 microfarads. Over time, the capacity decreases due to the drying out of the electrolyte.
Positive temperature dependence of the capacitance of electrolytic capacitors on temperature. Increased temperature at the output control point - just a couple of degrees is enough and the capacity is enough for normal startup. If we assume that at the exit control site it was not 20 degrees, but 25-27, then this turned out to be enough for almost 100% passing of the exit control.

The driver manufacturer saved money, of course, by using capacitors with a lower nominal value compared to the reference design from the manual (22 µF is indicated there), but fresh capacitors at elevated temperatures and taking into account the +80% spread allowed the batch of drivers to be delivered to the customer. The customer received seemingly working drivers, but over time they began to fail for some unknown reason. It would be interesting to know whether the manufacturer’s engineers took into account the peculiarities of the behavior of electrolytic capacitors with increasing temperature and the natural scatter, or did this happen by chance?

Today, probably, not a single apartment or private house can do without LED lighting. And street lighting is gradually changing to economical and durable LED elements. But looking at today’s topic of conversation, the question arises – what does the driver have to do with it (that’s how “driver” is translated from English)? This is the first question that comes to the mind of a person ignorant of LED lighting. In fact, without such a device, light diodes do not work with a voltage of 220 V. Today we will figure out what function the driver for LEDs performs, how to connect this device and whether it is possible to make it yourself.

Read in the article:

Why do we need drivers for LEDs and what are they?

The answer to the question of what is an LED driver is quite simple. This is a device that stabilizes the voltage and gives it the characteristics necessary for the operation of LED elements. To make it clearer, let's draw an analogy with a ballast fluorescent lamp, which also cannot work without additional equipment. The only difference is that the driver is compact in size and fits into the body of the light device. In essence, it can be called stabilizing starting device or frequency converter.

Where are stabilizing devices used for LED elements?

LED drivers for LEDs are used in various fields:

• street lighting lamps;
• household lighting lamps;
• LED strips and various lighting;
• office lamps with the form of fluorescent lamps.

Even daytime running lights of cars require the installation of such a device, but here everything is much simpler; you can get by with one resistor. And although the driver for an LED strip (for example) differs in characteristics from the voltage stabilizer of a light bulb, they perform the same function.

Operating principle of a 220V LED lamp driver circuit

The operating principle of the device is to maintain a given current at the output voltage (regardless of its value). This is the difference from a stabilizing power supply, which is responsible for voltage.

Looking at the circuit, we see that the current, passing through the resistance, is stabilized, and the capacitor gives it the desired frequency. Then the rectifying diode bridge comes into play. We get a stabilized forward current on the LEDs, which is again limited by resistors.

Driver Features Worth Considering

The characteristics of the converters required in a particular case are determined based on the parameters of the LED consumers. The main ones can be called:

1. Driver rated power– this parameter must exceed the total power consumed by the light diodes that will be in its circuit.
2. Output voltage– depends on the magnitude of the voltage drop across each of the light diodes.
3. Rated current, which depends on the brightness of the glow and the power consumption of the element.

It is important to know! The voltage drop across an LED depends on its color. For example, if you can connect 16 red LEDs to a 12 V power supply, then maximum amount green will already be 9.

Division of LED drivers by device type

Converters can be divided into two types - linear and pulse. Both types are applicable to light diodes, but the differences between them are noticeable in both cost and technical characteristics.

Linear converters are characterized by their simple design and low cost. But such drivers have a significant drawback - the ability to connect only low-power light elements. Part of the energy is spent on heat generation, which contributes to a decrease in efficiency.

Pulse converters are based on the principle of pulse width modulation (PWM) and during their operation, the values ​​of output currents are determined by such a parameter as the duty cycle. This means that there is no change in the pulse frequency, but the duty cycle can vary by values ​​from 10 to 80%. Such drivers allow you to extend the life of light diodes, but have one drawback. During their operation, it is possible to induce electromagnetic interference. Let's try to figure out what this threatens a person with simple example.

A person living in an apartment or house has a pacemaker. At the same time, in a small room there is a chandelier with many devices operating on pulsed ice drivers for. The pacemaker may begin to malfunction. Of course, this is exaggerated and to create such strong interference you need a lot of lamps that are located at a distance of less than a meter from the pacemaker, but there is still a risk.

How to choose a driver for an LED: some nuances

Before purchasing a converter, calculate the power consumed by the LEDs. The rated power of the device must exceed this figure by 25÷30%. Also, the stabilizer must match the output voltage.

If you plan to place it hidden, it is better to choose a converter without a housing - the cost will be lower with the same technical characteristics.

Important! Drivers made in China usually do not meet the stated specifications. You should not save money by purchasing a “made in” converter. It is better to give preference to a Russian manufacturer.

How to connect LED elements to the converter: methods and diagrams

LEDs are connected to the driver in two ways - in series or in parallel. For example, let's take 6 LED emitters with a voltage drop of 2 V. When serial connection you will need a 12 V and 300 mA driver. In this case, the glow will be even across all elements.

By connecting the emitters in parallel in a group of 3, we will be able to use a 6 V converter, but at 600 mA. The problem is that due to the uneven voltage drop, one line will glow brighter than the other.

We calculate the characteristics of the converter for LEDs

For an accurate calculation, we first determine the power consumption of the LEDs. Afterwards, the issue with the connection diagram is decided - will it be parallel or serial. The output voltage and rated power of the required converter will depend on this. That's all the work that needs to be done. Now, in an electrical store or on an online resource, we select a driver according to the calculated indicators.

Good to know! When purchasing a converter, ask the seller for a certificate of conformity for the product. If it is missing, it is better to refrain from purchasing.

What is a dimmable LED driver?

Dimmable is a driver for an LED lamp that supports changing input current parameters and is capable of changing output current parameters depending on this. This is achieved by changing the glow intensity of LED emitters. An example would be a controller for an LED strip with remote control. If desired, it becomes possible to “dim” the lighting in the room and give your eyes a rest. This is also appropriate if a child is sleeping in the room.

Dimming is performed from the remote control, or from a standard mechanical stepless switch.

Chinese converters - what's special about them

Chinese friends are famous for their ability to counterfeit equipment so that it becomes impossible to use. The same can be said for drivers. When purchasing a Chinese device, be prepared for inflated declared characteristics, low quality and rapid failure of the converter. If you are going to build your first LED lamp, practice and gain skills in radio electronics, such products are indispensable due to their low cost and ease of execution.

What affects the service life of converters

The causes of converter failure are:

1. Sudden power surges in the network.
2. Increased humidity if the device does not meet the degree of protection.
3. Temperature changes.
4. Insufficient ventilation.
5. Increased dustiness.
6. Incorrect calculation of consumer power.

Any of these reasons can be prevented or corrected. This means that it is within the power of a home craftsman to extend the service life of the stabilizing device.

PT4115 LED driver circuit with dimmer

It's about Chinese manufacturer, which is an exception to the rule. A microcircuit on the basis of which you can assemble a simple converter made by him. The PT4115 microprocessor has good characteristics and is gaining popularity in Russia.

Related article:

If LED lighting and conventional regulators are not suitable, then they are installed, which are slightly different structurally and technically. Today we’ll figure out what they are, how to choose and even make them. similar device on one's own.

The figure shows simplest scheme PT4115 driver for LEDs, which can be assembled by a novice home DIYer with no experience in working with radio electronics. An interesting feature of the microcircuit is an additional output (DIM) that allows the connection of a dimmer.

How to make a driver for LEDs with your own hands

Any novice craftsman can assemble an LED lamp driver circuit. But this will require accuracy and patience. The stabilizing device may not work the first time. To make it clearer to the reader how the work is done, we offer several simple diagrams.

As you can see, there is nothing complicated in the driver circuits for LEDs from a 220 V network. Let's try to look at all stages of work step by step.

Step-by-step instructions for making a DIY LED driver

Photo example	Action to be performed
	To work, we need a regular power supply for the phone. With its help, everything is done quickly and easily.
	After disassembling the charger in our hands, we already have an almost complete driver for three one-watt LEDs, but it needs a little modification.
	We solder a 5 kOhm limiting resistor, which is located near the output channel. It is he who does not give charger Apply too much voltage to the cell phone.
	Instead of a limiting resistor, we solder in a tuning resistor, setting it to the same 5 kOhm. Subsequently, we will add voltage to the required level.
	3 LEDs of 1 W each are soldered onto the output channel, connected in series, which gives us a total of 3 W.
	We find the input contacts and unsolder them from the printed circuit board. We don't need them anymore...
	...and in their place we solder a power cord through which 220 V power will be supplied.
	If desired, you can put a 1 Ohm resistor in the gap and set all the indicators with an ammeter. In this case, the attenuation range of the LEDs will be wider.
	After complete assembly, we check the functionality. The output voltage is 5 V, the LEDs are not lit yet.
	By turning the knob on the resistor, we see how the LED elements begin to “flare up”.

Be careful. From such a converter you can get a shock not only of 220 V (from the power cord), but also a shock of about 450 V, which is quite unpleasant (tested on myself).

Very important! Before you check the LED driver for functionality and connect it to a power source, you should once again visually check the correctness of the assembled circuit. Defeat electric shock It is dangerous to life, and the flash from a short circuit can cause damage to the eyes.

Current converters for light diodes: where to buy and what is the cost

Such devices can be purchased at electrical stores or online resources. The second option is more affordable. In addition, many manufacturers offer free shipping. Let's consider some models with an input voltage of 220 Vs technical characteristics and cost as of December 2017.

Photo	Model	Protection class, IP	Output voltage, V	Power, W	Cost, rub.
	DFT-I-40-LD64	20	60-130	45	400
	ZF-AC LD49	40	40-70	54	450
	XS0812-12W PS12	20	24-44	12	200
	PS100 (open)	20	30-36	100	1100
	PF4050A PS50	65	27-36	50	500
	PF100W LD100	65	23-36	100	1000

Looking at the prices, we can say that making a current converter yourself is more suitable for those for whom this is just a hobby. You can purchase such a device quite inexpensively.

Summarize

When choosing a current converter for LED lamps, you should carefully calculate everything. Any error may lead to a reduction in the service life of the purchased device. Despite the low cost of the stabilizer, it is quite unpleasant to constantly throw money away. Only in this case will the driver serve its intended duration. And when making it yourself, follow the electrical safety rules and be careful and attentive when assembling the circuit.

We hope that the information provided today was useful to our reader. Any questions you may have can be asked in the discussion – we will definitely answer them. Write, ask, share your experience with other readers.

And finally, a short video on today's topic:

The driver for an LED lamp is the most important element of the circuit, ensuring good brightness, efficiency and long-term operation of light sources. With its help, the alternating current of an industrial network with a voltage of 220 V is transformed into direct current of the desired value (12/24/48 V). We will understand all the functions of an electrical element and indicate important criteria for selecting devices.

The concept of a network driver and its purpose

Driver - electronic component, to which AC voltage is supplied, stabilization occurs and DC voltage is output. It is important to understand here that we are talking about receiving current. To convert voltage, conventional power supplies are used (the value of the output voltage is indicated on the case). Power supplies are operated in diode strips.

Main characteristics of the converter for LED lighting fixtures- output current. Auxiliary LED diodes or other semiconductors are used for the load. Almost always, the driver is powered from a 220 V industrial network, and the output voltage range starts from 2 - 3 and ends in tens of volts. To connect three 3 W LEDs, you need an electronic driver with an output voltage of 9 - 21 V and a current of 780 mA. At light load universal device characterized by a low coefficient of efficiency (efficiency).

To power vehicle headlights, a source with a constant voltage of 10 to 35 V is used. If the power is low, a driver is not necessary, but an appropriate resistor will be required. This component is an indispensable part of a household switch, but when switching an LED diode to a 220 V AC network, you cannot count on reliable and durable operation.

Principle of operation

The converter acts as a current source. Let's look at the differences between the product and the power supply - the voltage source.

At the output of each voltage converter we have a certain voltage that is not related to the load. For example, if you connect a 40 Ohm resistance to a 12 V power supply, a current of 300 mA will flow through it. If you install two resistors in parallel, the total current will be 600 mA, although the voltage will remain identical.

As for the driver, it gives the same current, despite the voltage changing up or down. Take a 30 ohm resistor and connect it to a 225 mA driver. The voltage will drop to 12 V. If you switch two parallel-connected resistors of 30 ohms each, the current will still remain equal to 225 mA, but the voltage will be halved - to 6 V.

Hence the conclusion: a high-quality driver guarantees the load a given output current, regardless of the changing voltage. As a result, the LED diode, when supplied with a voltage of 5 V, will shine equally brightly in comparison with a power source of 10 V, provided that the current remains the same.

Specifications

The need to purchase a driver arises if an interesting lamp without a current converter was found. Another option is to build the light source from scratch by purchasing each element separately.

Before purchasing a current converter, consider three main characteristics:

• output amperage;
• operating power;
• output voltage.

The output voltage is calculated based on the power connection diagram and the number of LEDs. The current value affects the power and glow level. The output current of the driver for LED diodes should be sufficient for a constant and bright glow.

The power of the product must be higher than the total value of all LEDs. The formula used for calculation is P = P (led) × X, where

• P (led) - diode power;
• X is the number of diodes.

To guarantee long-term operation of the driver, you need to focus on the power reserve - buy converters with a rated power 20 - 30% higher than the required value. Don't forget about the color factor, which is directly related to voltage drop. The latter value varies depending on different colors.

Best before date

The service life of the driver is somewhat shorter compared to the optical component of the LED lamp - about 30,000 hours.

This is due to a number of reasons: voltage surges, changes in temperature, humidity and load on the converter.

One of the vulnerable points is the smoothing capacitor, in which the electrolyte evaporates over time. In most cases, this happens when installed in rooms with high humidity or connected to a network that has voltage surges. This approach will lead to increased ripple at the output of the device, which negatively affects the LED diodes.

Often the driver lifespan is reduced due to partial load. If a 200W device is used with half the load (100W), half of the rated value will be returned to the grid, causing overload and more frequent power failures.

Types of drivers

The principle of operation of pulse drivers is more complicated - a series of high-frequency current pulses is formed at the output.

The frequency of occurrence of current pulses is always constant, but the duty cycle can vary in the range of 10 - 80%, which leads to a change in the value of the output current. Compact dimensions and high efficiency (90 – 95%) have led to the widespread use of pulse drivers. Their main drawback is the greater number of electromagnetic interferences (compared to linear ones).

The cost of the driver is affected by the presence or absence of galvanic isolation. In the latter case, the devices are usually cheaper, but the reliability is much lower due to the likelihood of electric shock.

Dimmable Driver

Dimmer is a device that allows you to adjust the brightness of light sources. Most drivers support this feature. With their help, the intensity of lighting during daylight hours is reduced, accents are placed on certain interior items, and the room is zoned. All this provides an opportunity to reduce energy costs and increase the service life of individual components.

Chinese drivers

Cheap and low-quality Chinese drivers are characterized by the absence of a housing. The output current usually does not exceed 700 mA. Against the background of minimal cost and (possibly) the presence of galvanic isolation, the disadvantages look much more serious:

• short service life;
• unreliability - cheap elements for circuits;
• large radio frequency interference;
• numerous pulsations;
• poor protection against high temperature and increase/decrease in mains voltage.

How to choose a driver

If you want to get a high-quality device that will last for several years and perform the required functions, we recommend avoiding purchasing cheap Chinese products. The physical parameters of such do not always coincide with the declared values. Do not buy devices that do not have warranty cards.

The simplest option, average in quality and price, is a current converter without a housing, connected to an industrial network with a voltage of 220 V. By choosing one or another modification of the device, you can use it for one or more LEDs. These are excellent elements used in laboratory research and experiments. For apartments and houses, it is advisable to buy drivers with a housing, since its absence reduces the reliability and safety of operation.

Ready-made current converter microcircuits for LED lamps

On the market you can find ready-made microcircuits for current conversion. Below we consider the most popular of all:

1. Supertex HV9910 is a pulse converter with a current of up to 10 mA that does not support decoupling.
2. ON Semiconductor UC3845 is a pulse-type device whose output current is 1 A.
3. Texas Instruments UCC28810 is a pulse-type driver with decoupling support and an output current of no more than 750 mA.
4. LM3404HV is a great option for powering LEDs high power. The work is based on the principle of a resonant type converter. To maintain the rated current, a resonant circuit consisting of a capacitor and a semiconductor Schottky diode is used. When selecting RON resistance, it is possible to set the required switching frequency.
5. Maxim MAX16800 - linear driver for low voltage (12 V). The output current is no more than 350 mA. This driver circuit for an LED lamp is an excellent option for a powerful LED diode or flashlight. Dimming supported.

Self-assembly of a converter for 220 V LEDs

The considered circuit resembles a switching type power supply. For example, let's take a simple switching type power supply that does not have galvanic isolation. The main advantages of such a scheme are simplicity and reliability.

Proceed with caution when choosing a method as there are no restrictions on output current. The LEDs will be powered by the 1.5 - 2 A they are assigned, but if you carelessly touch the bare wires with your hands, the current value will increase to tens of amperes and a strong shock will occur.

The simplest 220 V current converter circuit contains three stages:

• voltage divider with capacitive resistor;
• several diodes (bridge);
• Voltage regulator.

In the first stage, a capacitive resistor is used to independently recharge the capacitor and is not related to the operation of the circuit itself. The rating does not matter and is usually between 100 kOhm and 1 MOhm with a power of no more than 1 W. For these purposes, you cannot choose an electrolytic capacitor.

Current flows through the capacitor until it is fully charged. The lower the capacitor capacity, the faster the process will complete. A 0.3 µF capacitor will pass through itself a smaller portion of the total network voltage.

Diode bridge is used for transformation AC voltage to permanent. After the capacitor “cuts off” almost the entire voltage, the diode bridge will produce a direct current with a voltage of 20 - 22 V.

At the third stage, a smoothing filter is installed to stabilize the voltage. The capacitor and diode bridge reduce the voltage. Any changes in the voltage in the network affect the output amplitude of the diode bridge. To reduce ripple, an electrolytic capacitor is connected in parallel to the circuit.

Self-assembly of a 10 Watt converter

If you want to build a network driver with your own hands to power a powerful LED, use electronic boards from damaged housekeepers. Often, such lamps stop working precisely because of burnt-out lamps, although the electronic board continues to function. All components can be used to create a power supply, driver and other electrical devices. The process will require capacitors, diodes, transistors and chokes.

Disassemble a failed 20 W mercury lamp (suitable for a 10 W driver). In this case, it is guaranteed that the throttle will withstand the applied load. With increasing power requirements for network driver you will have to choose a more powerful economy unit or use an analogue with a huge core instead of a throttle.

Make 20 turns on the winding and use a soldering iron to connect it to the rectifier (diode bridge). Apply voltage from an industrial network of 220 V and use a multimeter to measure the resulting value at the output of the diode bridge. If you use the instructions, you will get a value in the region of 9 - 10 V. The LED source consumes 0.8 A at a nominal 900 mA. Since you will supply a reduced current, you can extend the life of the LED diode.

Conclusion

Despite their apparent simplicity and reliability, LEDs are more complex and demanding than other light sources.