Switching power supply for LEDs. Power supplies for LED lighting

Despite the wide selection of LED flashlights of various designs in stores, radio amateurs are developing their own versions of circuits for powering white super-bright LEDs. Basically, the task comes down to how to power an LED from just one battery or accumulator, and conduct practical research.

After a positive result is obtained, the circuit is disassembled, the parts are put into a box, the experiment is completed, and moral satisfaction sets in. Often research stops there, but sometimes the experience of assembling a specific unit on a breadboard turns into a real design, made according to all the rules of art. Below are several simple circuits, developed by radio amateurs.

In some cases, it is very difficult to determine who is the author of the scheme, since the same scheme appears on different sites and in different articles. Often the authors of articles honestly write that this article was found on the Internet, but it is unknown who published this diagram for the first time. Many circuits are simply copied from the boards of the same Chinese flashlights.

Why are converters needed?

The thing is that the direct voltage drop is, as a rule, no less than 2.4...3.4V, so it is simply impossible to light an LED from one battery with a voltage of 1.5V, and even more so from a battery with a voltage of 1.2V. There are two ways out here. Either use a battery of three or more galvanic cells, or build at least the simplest one.

It is the converter that will allow you to power the flashlight with just one battery. This solution reduces the cost of power supplies, and in addition allows for fuller use: many converters are operational with a deep battery discharge of up to 0.7V! Using a converter also allows you to reduce the size of the flashlight.

The circuit is a blocking oscillator. This is one of the classic electronic circuits, so if assembled correctly and in good working order, it starts working immediately. The main thing in this circuit is to wind transformer Tr1 correctly and not to confuse the phasing of the windings.

As a core for the transformer, you can use a ferrite ring from an unusable board. It is enough to wind several turns of insulated wire and connect the windings, as shown in the figure below.

The transformer can be wound with winding wire such as PEV or PEL with a diameter of no more than 0.3 mm, which will allow you to place a slightly larger number of turns on the ring, at least 10...15, which will somewhat improve the operation of the circuit.

The windings should be wound into two wires, then connect the ends of the windings as shown in the figure. The beginning of the windings in the diagram is shown by a dot. You can use any low-power npn transistor conductivity: KT315, KT503 and the like. Nowadays it is easier to find an imported transistor such as BC547.

If you don't have a transistor at hand n-p-n structures, then you can use, for example, KT361 or KT502. However, in this case you will have to change the polarity of the battery.

Resistor R1 is selected based on the best LED glow, although the circuit works even if it is simply replaced with a jumper. The above diagram is intended simply “for fun”, for conducting experiments. So after eight hours of continuous operation on one LED, the battery drops from 1.5V to 1.42V. We can say that it almost never discharges.

To study the load capacity of the circuit, you can try connecting several more LEDs in parallel. For example, with four LEDs the circuit continues to operate quite stably, with six LEDs the transistor begins to heat up, with eight LEDs the brightness drops noticeably and the transistor gets very hot. But the scheme still continues to work. But this is only for scientific research, since the transistor will not work for a long time in this mode.

If you plan to create a simple flashlight based on this circuit, you will have to add a couple more parts, which will ensure a brighter glow of the LED.

It is easy to see that in this circuit the LED is powered not by pulsating, but by direct current. Naturally, in this case the brightness of the glow will be slightly higher, and the level of pulsations of the emitted light will be much less. Any high-frequency diode, for example, KD521 (), will be suitable as a diode.

Converters with choke

Another simplest diagram is shown in the figure below. It is somewhat more complicated than the circuit in Figure 1, it contains 2 transistors, but instead of a transformer with two windings it only has inductor L1. Such a choke can be wound on a ring from the same energy saving lamp, for which you will need to wind only 15 turns of winding wire with a diameter of 0.3...0.5 mm.

With the specified inductor setting on the LED, you can get a voltage of up to 3.8V (forward voltage drop across the 5730 LED is 3.4V), which is enough to power a 1W LED. Setting up the circuit involves selecting the capacitance of capacitor C1 in the range of ±50% of the maximum brightness of the LED. The circuit is operational when the supply voltage is reduced to 0.7V, which ensures maximum use of battery capacity.

If the considered circuit is supplemented with a rectifier on diode D1, a filter on capacitor C1, and a zener diode D2, you will get a low-power power supply that can be used to power op-amp circuits or other electronic components. In this case, the inductance of the inductor is selected within the range of 200...350 μH, diode D1 with a Schottky barrier, zener diode D2 is selected according to the voltage of the supplied circuit.

With a successful combination of circumstances, using such a converter you can obtain an output voltage of 7...12V. If you plan to use the converter to power only LEDs, zener diode D2 can be excluded from the circuit.

All the considered circuits are the simplest voltage sources: limiting the current through the LED is carried out in much the same way as is done in various key fobs or in lighters with LEDs.

The LED, through the power button, without any limiting resistor, is powered by 3...4 small disk batteries, the internal resistance of which limits the current through the LED to a safe level.

Current Feedback Circuits

But an LED is, after all, a current device. It is not for nothing that the documentation for LEDs indicates direct current. Therefore, true LED power circuits contain current feedback: once the current through the LED reaches a certain value, the output stage is disconnected from the power supply.

Voltage stabilizers work exactly the same way, only there is voltage feedback. Below is a circuit for powering LEDs with current feedback.

Upon closer examination, you can see that the basis of the circuit is the same blocking oscillator assembled on transistor VT2. Transistor VT1 is the control one in the feedback circuit. Feedback in this scheme works as follows.

LEDs are powered by voltage that accumulates across an electrolytic capacitor. The capacitor is charged through a diode with pulsed voltage from the collector of transistor VT2. The rectified voltage is used to power the LEDs.

The current through the LEDs passes along the following path: the positive plate of the capacitor, LEDs with limiting resistors, the current feedback resistor (sensor) Roc, the negative plate of the electrolytic capacitor.

In this case, a voltage drop Uoc=I*Roc is created across the feedback resistor, where I is the current through the LEDs. As the voltage increases (the generator, after all, works and charges the capacitor), the current through the LEDs increases, and, consequently, the voltage across the feedback resistor Roc increases.

When Uoc reaches 0.6V, transistor VT1 opens, closing the base-emitter junction of transistor VT2. Transistor VT2 closes, the blocking generator stops, and stops charging the electrolytic capacitor. Under the influence of a load, the capacitor is discharged, and the voltage across the capacitor drops.

Reducing the voltage on the capacitor leads to a decrease in the current through the LEDs, and, as a result, a decrease in the feedback voltage Uoc. Therefore, transistor VT1 closes and does not interfere with the operation of the blocking generator. The generator starts up and the whole cycle repeats again and again.

By changing the resistance of the feedback resistor, you can vary the current through the LEDs within a wide range. Such circuits are called pulse current stabilizers.

Integral current stabilizers

Currently, current stabilizers for LEDs are produced in an integrated version. Examples include specialized microcircuits ZXLD381, ZXSC300. The circuits shown below are taken from the DataSheet of these chips.

The figure shows the design of the ZXLD381 chip. It contains a PWM generator (Pulse Control), a current sensor (Rsense) and an output transistor. There are only two hanging parts. These are LED and inductor L1. A typical connection diagram is shown in the following figure. The microcircuit is produced in the SOT23 package. The generation frequency of 350KHz is set by internal capacitors; it cannot be changed. The device efficiency is 85%, starting under load is possible even with a supply voltage of 0.8V.

The forward voltage of the LED should be no more than 3.5V, as indicated in the bottom line under the figure. The current through the LED is controlled by changing the inductance of the inductor, as shown in the table on the right side of the figure. The middle column shows the peak current, the last column shows the average current through the LED. To reduce the level of ripple and increase the brightness of the glow, it is possible to use a rectifier with a filter.

Here we use an LED with a forward voltage of 3.5V, a high-frequency diode D1 with a Schottky barrier, and a capacitor C1 preferably with a low equivalent series resistance (low ESR). These requirements are necessary in order to increase the overall efficiency of the device, heating the diode and capacitor as little as possible. The output current is selected by selecting the inductance of the inductor depending on the power of the LED.

It differs from the ZXLD381 in that it does not have an internal output transistor and a current sensor resistor. This solution allows you to significantly increase the output current of the device, and therefore use a higher power LED.

An external resistor R1 is used as a current sensor, by changing the value of which you can set the required current depending on the type of LED. This resistor is calculated using the formulas given in the datasheet for the ZXSC300 chip. We will not present these formulas here; if necessary, it is easy to find a datasheet and look up the formulas from there. The output current is limited only by the parameters of the output transistor.

When you turn on all the described circuits for the first time, it is advisable to connect the battery through a 10 Ohm resistor. This will help avoid the death of the transistor if, for example, the transformer windings are incorrectly connected. If the LED lights up with this resistor, then the resistor can be removed and further adjustments can be made.

Boris Aladyshkin

The steady trend in the development of portable electronics almost every day forces the average user to deal with charging the batteries of their mobile devices. Whether you are the owner of a mobile phone, tablet, laptop or even a car, one way or another you will repeatedly have to deal with charging the batteries of these devices. Today, the market for choosing chargers is so vast and large that it is quite difficult to make a competent and correct choice in this variety. charger, suitable for the type of battery used. In addition, today there are more than 20 types of batteries with different chemical compositions and bases. Each of them has its own specific charge and discharge operation. Due to economic benefits, modern production in this area is now concentrated primarily on the production of lead-acid (gel) (Pb), nickel-metal-hydride (NiMH), nickel-cadmium (NiCd) batteries and lithium-based batteries - lithium-ion ( Li-ion) and lithium-polymer (Li-polymer). The latter of these, by the way, are actively used in powering portable mobile devices. Mainly, lithium batteries have earned popularity due to the use of relatively inexpensive chemical components, a large number of recharge cycles (up to 1000), high specific energy, low degree of self-discharge, and the ability to hold capacity at negative temperatures.

The electrical circuit of the charger for lithium batteries used in mobile gadgets boils down to providing them with a constant voltage during charging, which exceeds the nominal voltage by 10–15%. For example, if a 3.7 V lithium-ion battery is used to power a mobile phone, then a stabilized power supply sufficient power to maintain the charging voltage no higher than 4.2V - 5V. That is why most portable chargers that come with the device are designed for a nominal voltage of 5V, determined by the maximum voltage of the processor and battery charge, taking into account the built-in stabilizer.

Of course, you shouldn’t forget about the charge controller, which takes care of the main algorithm for charging the battery, as well as polling its status. Modern lithium batteries produced for mobile devices with low current consumption already come with a built-in controller. The controller performs the function of limiting the charge current depending on the current battery capacity, turns off the voltage supply to the device in the event of a critical battery discharge, protects the battery in the event of a load short circuit (lithium batteries are very sensitive to high current loads and tend to get very hot and even explode). For the purpose of unification and interchangeability of lithium-ion batteries, back in 1997, Duracell and Intel developed a control bus for polling the status of the controller, its operation and charge, called SMBus. Drivers and protocols were written for this bus. Modern controllers still use the basics of the charging algorithm prescribed by this protocol. In terms of technical implementation, there are many microcircuits that can implement charge control of lithium batteries. Among them, the MCP738xx series, MAX1555 from MAXIM, STBC08 or STC4054 with a built-in protective n-channel MOSFET transistor, a charge current detection resistor and a controller supply voltage range from 4.25 to 6.5 Volts stand out. At the same time, in the latest microcircuits from STMicroelectronics, the battery charge voltage value of 4.2 V has a spread of only +/- 1%, and the charging current can reach 800 mA, which will allow charging batteries with a capacity of up to 5000 mAh.

Considering the charging algorithm for lithium-ion batteries, it is worth saying that this is one of the few types that provide the certified ability to charge with a current of up to 1C (100% of the battery capacity). Thus, a battery with a capacity of 3000 mAh can be charged with a current of up to 3A. However, frequent charging with a large “shock” current, although it will significantly reduce its time, will at the same time quite quickly reduce the battery capacity and render it unusable. From the experience of designing electrical circuits for chargers, we will say that the optimal charging value for a lithium-in (polymer) battery is 0.4C - 0.5C of its capacity.

A current value of 1C is allowed only at the moment of initial battery charging, when the battery capacity reaches approximately 70% of its maximum value. An example would be the charging of a smartphone or tablet, when the initial restoration of capacity occurs in a short time, and the remaining percentages accumulate slowly.

In practice, quite often the effect of deep discharge of a lithium battery occurs when its voltage drops below 5% of its capacity. In this case, the controller is not able to provide sufficient starting current to build up the initial charge capacity. (This is why it is not recommended to discharge such batteries below 10%). To solve such situations, you need to carefully disassemble the battery and turn off the built-in charge controller. Next, you need to connect an external charge source to the battery terminals, capable of delivering a current of at least 0.4C of the battery capacity and a voltage of no higher than 4.3V (for 3.7V batteries). The electrical circuit of the charger for the initial stage of charging such batteries can be used from the example below.

This circuit consists of a 1A current stabilizer. (set by resistor R5) on the parametric stabilizer LM317D2T and the switching voltage regulator LM2576S-adj. The stabilization voltage is determined by feedback to the 4th leg of the voltage stabilizer, that is, the ratio of resistances R6 and R7, which set the maximum battery charging voltage at idle. The transformer must produce 4.2 - 5.2 V on the secondary winding AC voltage. Then, after stabilization, we will receive 4.2 - 5V DC voltage, sufficient to charge the above-mentioned battery.

Nickel - metal - hydride batteries (NiMH) can most often be found in standard battery housings - this is the form factor AAA (R03), AA (R6), D, C, 6F22 9V. The electrical circuit of the charger for NiMH and NiCd batteries must include the following functionality related to the specific charging algorithm of this type of battery.

Different batteries (even with the same parameters) change their chemical and capacitive characteristics over time. As a result, it becomes necessary to organize the charging algorithm for each instance individually, since during the charging process (especially with high currents, which nickel batteries allow), excessive overcharging affects the rapid overheating of the battery. Temperatures during charging above 50 degrees due to chemically irreversible decomposition processes of nickel will completely destroy the battery. Thus, the electrical circuit of the charger must have the function of monitoring the temperature of the battery. To increase the service life and the number of recharge cycles of a nickel battery, it is advisable to discharge each cell to a voltage of at least 0.9V. current of about 0.3C from its capacity. For example, a battery with 2500 – 2700 mAh. Discharge the active load with a current of 1A. Also, the charger must support “training” charging, when a cyclic discharge to 0.9V occurs over several hours, followed by charging with a current of 0.3 - 0.4C. Based on practice, up to 30% of dead nickel batteries can be revived in this way, and nickel-cadmium batteries can be “reanimated” much more readily. According to the charging time, electrical circuits of chargers can be divided into “accelerated” (charge current up to 0.7 C with a full charge time of 2 – 2.5 hours), “medium duration” (0.3 – 0.4 C – charge in 5 – 6 hours .) and “classic” (current 0.1C – charging time 12 – 15 hours). When designing a charger for a NiMH or NiCd battery, you can also use the generally accepted formula for calculating charging time in hours:

T = (E/I) ∙ 1.5

where E is the battery capacity, mA/h,
I – charge current, mA,
1.5 – coefficient for compensation of efficiency during charging.
For example, the charging time of a battery with a capacity of 1200 mAh. a current of 120 mA (0.1C) will be:
(1200/120)*1.5 = 15 hours.

From the experience of operating chargers for nickel batteries, it is worth noting that the lower the charging current, the more recharge cycles the element will endure. As a rule, the manufacturer indicates the passport cycles when charging the battery with a current of 0.1 C with the longest charge time. The charger can determine the degree of charge of the cans by measuring the internal resistance due to the difference in voltage drop at the time of charging and discharging with a certain current (∆U method).

So, taking into account all of the above, one of the simplest solutions for self-assembly electrical diagram charger and at the same time highly efficient is Vitaly Sporysh’s circuit, a description of which can easily be found on the Internet.

The main advantages of this circuit are the ability to charge both one and two batteries connected in series, thermal control of the charge using a digital thermometer DS18B20, control and measurement of current during charging and discharging, automatic shutdown upon completion of charging, and the ability to charge the battery in an “accelerated” mode. In addition, with the help of specially written software and an additional board on the MAX232 TTL level converter chip, it is possible to control charging on a PC and further visualize it in the form of a graph. The disadvantages include the need for independent two-level power supply.

Lead-based (Pb) batteries can often be found in devices with high current consumption: cars, electric vehicles, uninterruptible power supplies, and as power sources for various power tools. There is no point in listing their advantages and disadvantages, which can be found on many sites on the Internet. In the process of implementing the electrical circuit of the charger for such batteries, two charging modes should be distinguished: buffer and cyclic.

Buffer charging mode involves simultaneously connecting both the charger and the load to the battery. This connection can be seen in uninterruptible power supplies, cars, wind and solar power systems. At the same time, during recharging, the device acts as a current limiter, and when the battery reaches its capacity, it switches to voltage limiting mode to compensate for self-discharge. In this mode, the battery acts as a supercapacitor. Cyclic mode involves turning off the charger when charging is complete and reconnecting it if the battery is low.

There are quite a lot of circuit solutions for charging these batteries on the Internet, so let’s look at some of them. For a novice radio amateur to implement a simple charger “on the knees,” the electrical circuit of the charger on the L200C chip from STMicroelectronics is perfect. The microcircuit is an ANALOG current regulator with the ability to stabilize voltage. Of all the advantages that this microcircuit has, it is the simplicity of the circuit design. Perhaps this is where all the advantages end. According to the datasheet for this chip, the maximum charge current can reach 2A, which theoretically will allow you to charge a battery with a capacity of up to 20 A/h with voltage

(adjustable) from 8 to 18V. However, as it turned out in practice, this microcircuit has much more disadvantages than advantages. Already when charging a 12-amp lead-gel SLA battery with a current of 1.2A, the microcircuit requires a radiator with an area of ​​at least 600 square meters. mm. A radiator with a fan from an old processor works well. According to the documentation for the microcircuit, voltages up to 40V can be applied to it. In fact, if you apply a voltage of more than 33V to the input. – the microcircuit burns out. This charger requires a fairly powerful power source capable of delivering a current of at least 2A. According to the above diagram secondary winding The transformer should produce no more than 15 - 17V. alternating voltage. The output voltage value at which the charger determines that the battery has reached its capacity is determined by the Uref value on the 4th leg of the microcircuit and is set by the resistive divider R7 and R1. Resistors R2 – R6 create feedback, determining the limit value of the battery charging current.

Resistor R2 at the same time determines its minimum value. When implementing a device, do not neglect the power value of the feedback resistances and it is better to use the ratings indicated in the circuit. To implement switching of the charging current, the best option would be to use a relay switch to which resistors R3 - R6 are connected. It is better to avoid using a low-resistance rheostat. This charger is capable of charging lead-based batteries with a capacity of up to 15 Ah. provided that the chip is well cooled.

The electrical circuit of a 3A pulse charger will help to significantly reduce the charging dimensions of small-capacity lead batteries (up to 20 A/h). current stabilizer with voltage regulation LM2576-ADJ.

For charging lead-acid or gel batteries with a capacity of up to 80A/h. (for example, automobiles). The impulse electrical circuit of a universal type charger presented below is perfect.

The circuit was successfully implemented by the author of this article in a case from an ATX computer power supply. Its elemental base is based on radioelements, mostly taken from a disassembled computer power supply. The charger works as a current stabilizer up to 8A. With adjustable voltage charge cutoff. Variable resistance R5 sets the value of the maximum charge current, and resistor R31 sets its limit voltage. A shunt on R33 is used as a current sensor. Relay K1 is necessary to protect the device from changing the polarity of the connection to the battery terminals. Pulse transformers T1 and T21 in finished form were also taken from a computer power supply. The electrical circuit of the charger works as follows:

1. turn on the charger with the battery disconnected (charging terminals folded back)

2. We set the charge voltage with variable resistance R31 (upper in the photo). For lead 12V. battery it should not exceed 13.8 - 14.0 V.

3. When the charging terminals are connected correctly, we hear the relay click, and on the lower indicator we see the value of the charging current, which we set with the lower variable resistance (R5 according to the diagram).

4. The charging algorithm is designed in such a way that the device charges the battery with a constant specified current. As the capacity accumulates, the charging current tends to a minimum value, and “recharging” occurs due to the previously set voltage.

A completely drained lead battery will not turn on the relay, nor will the charging itself. Therefore, it is important to provide a forced button for supplying instantaneous voltage from the internal power source of the charger to the control winding of relay K1. It should be remembered that when the button is pressed, the protection against polarity reversal will be disabled, so before a forced start, you need to pay special attention to the correct connection of the charger terminals to the battery. As an option, it is possible to start charging from a charged battery, and only then transfer the charging terminals to the required installed battery. The developer of the circuit can be found under the nickname Falconist on various radio-electronic forums.

To implement the voltage and current indicator, a circuit was used on the PIC16F690 pic controller and “super-available parts”, the firmware and operation description of which can be found on the Internet.

This electrical circuit of the charger, of course, does not claim to be a “reference”, but it is fully capable of replacing expensive industrial chargers, and can even significantly surpass many of them in functionality. In conclusion, it is worth saying that the latest universal charger circuit is designed mainly for a person trained in radio design. If you are just starting out, then it is better to use much simpler circuits in a powerful charger using an ordinary powerful transformer, a thyristor and its control system using several transistors. An example of the electrical circuit of such a charger is shown in the photo below.

See also diagrams.

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Main advantages LED lamps economical and long service life are considered. If you use them 10 hours a day, they will last 25 years. Again, these are the manufacturer's words. Perhaps they can last much longer? Let time answer this question. However, LED lamps, regardless of their type and scope of application, have one weak point - electric current.

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Power supply device

On any electrical appliance, 2 main parameters are indicated - power and input voltage. If the input voltage exceeds permissible norm– the device fails. Where is the current? Each device regulates this parameter independently. After all, with the same resistance and voltage, the current strength will never exceed the permissible values. Consequently, for the majority of household electrical appliances around us, a power supply is used, the task of which is to prevent exceeding the maximum permissible value voltage.

For LED lamps, a traditional power supply is not suitable, since the primary value in this case is the current value, exceeding the permissible threshold by at least 5% leads to rapid wear of the LED and a reduction in the service life of expensive equipment.

Using a power supply for lamps will lead to the following results.

Reduced service life of the lamp.
Reducing the brightness of the light.
Interference in the electrical network.
Power supply failure.

The way out of this situation is current sources for LED lamps (drivers). Unlike the power supply, the driver provides stable output power and current.

How does the driver work?

A lamp with a filament has an average luminous flux of 15 lumens/watt, and LED lamp 120 lumens/watt. Therefore, an LED lamp with a power of 10 W is equivalent to an “Ilyich light bulb” with a power of 80 W.

The driver allows you to connect the required number of lamps in series, while with each new element the voltage increases, but the current remains unchanged. For example, a current source for LED lamps with a power of 60 W allows you to connect 6 lamps of 10 W each in series, with a current of 500 mA and a total voltage of 120 V. This connection method increases the efficiency of lamps, and since the efficiency of drivers is 97-99% - there is virtually no loss.

How to choose the right driver

Current sources for LED lamps, which can be purchased in the online store “Vek LEDov” at one of the lowest prices in the Russian Federation, must be selected together with the lamp, while the number of lighting elements, connection method, the difference between the total power consumption of the elements and the output The driver power taking into account the efficiency indicated in the characteristics of the driver and LED lamps must match.

Despite objective problems with implementation LED lighting, more and more enterprises are engaged in the development and production of semiconductor lighting products. The research and production company Plazmainform entered this market in 2010 and currently positions itself as a developer and serial manufacturer of current sources for LED lamps.

LED power supplies (PS) are the most important part of a semiconductor lamp, largely determining the functional, lighting performance and reliability of the lighting device. For companies involved in the design and installation of lighting systems, in addition to luminous flux and color temperature, characteristics such as electrical safety, efficiency, power factor, luminous flux ripple factor, electromagnetic compatibility and cost are also important. As a result of cooperation between NPF Plazmainform and a number of enterprises that develop and produce lighting devices, open power sources were born and put into mass production, providing electrical powers of 15, 20, 30, 35, 50 and 100 W.

An analysis of the IP for LED lamps produced by a number of companies shows that the circuitry of the current sources is determined by the required output power of the lamp: if it is less than 60 W, then a flyback power factor corrector (PFC) with output current stabilization is usually selected. At higher output power, a separate PFC and a separate converter are used with output current stabilization and galvanic input/output isolation, performed using flyback, forward or resonant LLC type circuitry. Converters without galvanic isolation (step-down type, SEPIC, etc.) from the point of view of ensuring safety when operating LED lamps are not widespread.

During development, much attention was paid to parameters such as output current ripple, electromagnetic compatibility (EMC) and cost. The choice of output current pulsations is determined by the requirements for luminous flux pulsations, which are regulated by standards and amount to 10–20% for general-purpose lamps, and 5–10% for table lamps during prolonged use of a computer. For street lamps, luminous flux pulsations are not regulated and must be set for each specific application.

Considering that luminaires can be connected to electrical networks of sufficiently long length, to which high-current equipment can be connected, power supplies must withstand a test voltage of 1.5 kV wire-to-wire and wire-to-body, as well as nanosecond and microsecond pulse surges and dips with an amplitude of up to 1.0 kV. In addition, televisions, receivers and other equipment sensitive to interference can be connected to the same electrical networks. Therefore, it is necessary to ensure compliance of the IP with the following basic EMC standards: GOST R 51318.15-99, GOST R 51514-99, GOST R 51317.3.2.2006 (section 6, 7), GOST R 51317.3.3.2008, GOST R 51317.4.2.99, GOST R 51317.4 .4.2007, GOST R 51317.4.5.99, GOST R 51317.4.6.99, GOST R 51317.4.11.2007.

PSL (Power Supply Led) sources are made according to a flyback power factor corrector circuit with output current stabilization and voltage limitation. A typical block diagram is shown in Fig. 1. The basis of the converter is the PFC controller, which controls the power switch and provides a power factor above 0.9. Oscillograms of input voltage and current, as well as effective and limiting harmonic current values ​​of the PSL50 source are shown in Fig. 2 and 3. The EMC filter ensures electromagnetic compatibility in accordance with luminaire standards.

Rice. 1. Source block diagram

Rice. 2. PSL50 input voltage and current waveforms

Rice. 3. RMS and harmonic limits of PSL50 input current

As an example, Table 1 shows the level of radio interference at the PSL50 network terminals in the frequency range 0.009-30 MHz (quasi-peak values).

Table 1 . Radio interference level PSL50

The output filter provides the required level of output current ripple and, accordingly, light flux ripple. The level and shape of current and voltage ripples for two ratings of the PSL50 output filter are shown in Fig. 4–7.

The oscillograms show that increasing the output capacitance by 60% reduces the current ripple by half and, accordingly, reduces the ripple of the light flux, since the relationship between them is almost linear. When turned on, the sources provide a smooth voltage supply for 50 ms. The output voltage waveform at PSL50 startup is shown in Fig. 8.

Rice. 8. PSL50 output voltage when turned on

The current error signal amplifier (ESA) provides the formation of an error signal, maintaining the current through the LEDs at a given level. The voltage control unit limits the output voltage at idle. The galvanic isolation block is designed to transmit an error signal to the controller, to the primary circuit. The damper limits the voltage surge at the drain of the power switch, which allows the use of a lower voltage and cheaper transistor.

The power source is the network alternating current. Galvanic isolation of the input and output circuits between themselves and the housing can withstand 1.5 kV and ensures safe operation. The sources comply with domestic and international standards regarding EMC. There is built-in protection against short circuit at the output, ensuring no-load operation. The main technical characteristics of the sources are given in Table 2.

Table 2 . Power supply parameters

The appearance of PSL15, PSL35, PSL50 and PSL100 is shown in Fig. 9–12 respectively. The PSL20 and PSL30 sources have a design similar to the PSL35.

For special luminaire designs, an inexpensive networked non-isolated current source with a power of 9 W (PSL9) has been developed. It is a step-down converter with passive power factor correction. The source diagram is shown in Fig. 13, appearance - in Fig. 14. The basis of the source is the HV9910 driver chip. Chain C1–VD2–VD3–VD4–C2 is a passive PFC. The output current is set by resistors R4, R5, R6. C3 is the output filter capacitor. PSL9 source parameters are given in Table 3.

Rice. 13. PSL9 circuit

Rice. 14. Source PSL9

Table 3. PSL9 Source Options

Luminaires in the design of which PSL9, PSL15, PSL30, PSL100 are used are undergoing trial operation. Luminaires with PSL20, PSL35 and PSL50 are produced in series.

The selected circuit for constructing power supplies makes it possible to modify the design without great expense to obtain other values ​​of output voltage and current within the declared power, providing power to lamps with a different LED switching circuit.

In order to turn on the LED, you can use a familiar constant voltage source - a battery, a battery, a charger, etc.

To power LED lamps, as well as for other electrical appliances, a conventional electrical network, which is present in any apartment in the form of an outlet.
Everyone knows the phrase "220 volts". We don't need any more information. If it says 220V, it means you can plug it into the outlet.
For LEDs there are also 220V power supplies. Today there are a variety of LED designs that require different power supplies. For example, LED strips and modules require voltage direct current 12V, which means it can be used by any power supply that converts from AC 220V to constant pressure 12V. (like in a car). We often see such devices in everyday life. They power printers, scanners, phones, etc. they are also called network adapters.

But it is more convenient to power powerful plant LEDs with special sources not of voltage, but current sources - drivers. This name was invented by marketers, it is useful, it allows you to distinguish them from a simple power supply. Externally, they can be distinguished from power supplies only by markings (!)
Remember: driver- source of stable direct current. (precisely current, not voltage!)

LED current is its most important parameter and must be observed. Our one-watt LEDs usually have an indication in their passport of a rated current of 350mA, 700mA, etc. This does not mean that it cannot work at other currents - it can. But if you give it a current higher than the rated one, it will shine much brighter, but due to overheating its service life will be shortened.

Therefore, there is no need to exceed the rated current, but it would be better to even slightly lower it to 320mA. This will ensure the preservation of the resource for a long time (50,000 hours), due to the non-overheating of the crystal.
The simplest driver is a resistor that is connected in series with the LED, limits the current and “extinguishes” excess voltage, converting the passing current into heat.
It is possible to connect powerful LEDs this way, but it is very inconvenient - powerful resistors are needed. They need their own mounting location, etc. If you need a headache, use resistors and conventional stabilized voltage sources.
A working driver will under no circumstances produce more current than needed - no matter how you connect the diodes.

But there are already a lot of drivers, they look like electronic transformers for halogen lamps, and sellers are not always competent - so you need to carefully look at the label. The input and output voltage parameters should be indicated there.

Let's take a look at these labels.

The photo shows two drivers in waterproof housings. (There are some without a case at all - don’t take it if you don’t have enough experience). Both drivers provide 320mA current. Both operate on 220 V (100-240V). The upper driver allows you to connect 30-40 pieces of one-watt LEDs, and the lower one from 5 to 12 pieces. Information about the driver output voltage limits is the most important, it shows how many LEDs can be connected to the circuit (this is the total voltage drop for the entire circuit)

Why do we need this? This information is needed to preliminary check the driver’s ability to power a certain number of LEDs, taking into account the color of the crystal. The voltage drop across the LED depends on the type of crystal. Let me remind you that for red it is 1.8-2.1 Volts, and for blue, green and white it is 3-3.5 Volt.

For example, we want to light up 5 red LEDs. If we connect them in a circuit, we get the total voltage at the ends of the circuit 5 x 2 = 10 Volts. On the bottom driver it says 5-12 pieces, and the voltage is at least 15 Volts. You can't underload the driver! 5 pieces are not enough, you still need at least 3 pieces (8 pieces X 2V = 16V). If these were blue 5pcs, then the circuit voltage 5x3 = 15V is suitable.

Precisely because the lamp consists of LEDs of different colors, you must first calculate the total voltage drop across the entire circuit and only then select a driver. The voltage of our LED circuit must be within the output voltage specified on the driver label. If you do not fall within the specified limits, then you will have to add extra or reduce the previously calculated number of LEDs. This is the case when it is impossible to find another driver.

From practice: if you have calculated everything correctly, and the lamp “blinks” with LEDs, it means it lacks loads. We'll have to add another light. I add green ones - they greatly improve the perception of the eye, although it does not benefit the plants much.

Never load the driver to the upper power limit - this will lead to overheating and reduced reliability, because the external environment is unpredictable. Suddenly it gets hot in the kitchen from the pre-holiday frying and cooking and it overheats. kaput, however it may be.
If you come across a driver with a higher current, for example 700mA, you can use it for 350mA lights, but then you will have to make two parallel LED circuits, or turn on individual lights in pairs. In this case, troubles are possible - if one LED burns out (it has never happened), then the second circuit will be under double the current, but will continue to work with increased brightness until you intervene:

Be careful - there are drivers connected to low voltage sources 12V, 24V - this is indicated on the label. And their output voltages can be the same as those of the mains.

Addition. In addition to single-watt LEDs, there are other LEDs: 3,5,10 watts and more. The driver indicates the total power limits. For example, the top driver (30-40W) can power either 30 one-watt or 10 three-watt drivers, etc. The main thing is not to go beyond these parameters.
note LED drivers can be connected in parallel to one
load. This makes it possible to quickly increase the power of the luminous flux
LED lamp by increasing or decreasing the current. (Within reasonable limits, of course.)

For example, the seedlings began to stretch - we double the current through the blue
LEDs. At a rated current of 350mA (if the heat sink is good), this is possible however
this already reduces the durability resource.

You can use an additional lamp for this purpose, which
is powered by an additional driver only during intensive braking
tomato seedlings.

WARNINGS:

1. turning on and off the driver(s) should only be in the network cable
(220V), and not at the output to the LEDs.
You cannot switch the secondary circuit of the driver - the LEDs may fail.

2. Do not forget to increase the heat sink area for LEDs in advance, when
using additional current. And insulate it well
The range of available drivers is constantly expanding. Many
Russian factories began supplying “their” drivers assembled from Chinese
semi-finished products - this certainly pleases. But at the same time they began to come across
drivers at an attractive price, the characteristics of which do not indicate very
Important information for electrical safety. You and I don't need to know
electrical circuit of the driver, but the degree of protection against electrical shock
current depends on it. More about this.

If there is a transformer in the circuit (it has two windings or more), then
it galvanically separates the network from the LEDs (there is no electrical connection between
220V wires and wires for connecting LEDs!).
And if instead of a transformer (to save money), there is a choke with two
windings, then there is no galvanic separation of the input and output circuits
will not be! In fact, for professionals, there is nothing wrong with this.
Such drivers can be used for lamps hanging on inaccessible
height. Such designs provide for the impossibility of communication
LEDs with a housing and there is reliable grounding!

But using such drivers for homemade lamps is DANGEROUS for
LIFE!!! because the phase wire can be galvanically connected to
metal frame of the lamp.
Therefore, when purchasing drivers, be sure to inquire about the presence of galvanic isolation.