Types and characteristics of drivers for LED light sources. Repair of LED lamps using examples How to choose a driver power supply for LEDs

LEDs continue to push new boundaries in the world of artificial lighting, confirming their superiority with a number of advantages. Much of the credit for the successful development of LED technology goes to power supplies. Working in tandem, the driver and LED open new horizons, guaranteeing the consumer stable brightness and the stated service life.

What is an LED driver, and what functional load is assigned to it? What to look for when choosing and is there an alternative? Let's try to figure it out.

What is an LED driver and what is it for?

Scientifically speaking, an LED driver is an electronic device whose main output parameter is a stabilized current. It is current, not voltage. A device with voltage stabilization is usually called a “power supply” with an indication of the rated output voltage. It is used to power LED strips, modules and LED lines. But this is not about him.

The main electrical parameter of an LED driver is the output current, which it can provide for a long time when an appropriate load is connected. The load is played by individual LEDs or assemblies based on them. For a stable glow, it is necessary that the current specified in the passport data flows through the LED crystal. In turn, the voltage across it will drop exactly as much as the p-n junction needs at a given current value. The exact values of the flowing current and forward voltage drop can be determined from the current-voltage characteristic (CV) of the semiconductor device. The driver receives power, as a rule, from a constant 12 V network or an alternating network 220 V. Its output voltage is indicated in the form of two extreme values, between which stable operation is guaranteed. Typically, the operating range can be from three volts to several tens of volts. For example, a driver with U out = 9-12 V, I out = 350 mA, as a rule, is designed for sequential connection of three white LEDs with a power of 1 W. Each element will drop approximately 3.3 V, for a total of 9.9 V, which means it falls within the specified range.

From three to six LEDs of 3 W each can be connected to a stabilizer with an output voltage range of 9-21 V and a current of 780 mA. Such a driver is considered more universal, but has lower efficiency when turned on with minimal load.

An important parameter of an LED driver is the power it can deliver to the load. Don't try to get the most out of it. This is especially true for radio amateurs who make series-parallel chains of LEDs with equalizing resistors, and then overload the output transistor of the stabilizer with this homemade matrix.

The electronic part of the driver for the LED depends on many factors:

input and output parameters;
protection class;
applied element base;
manufacturer.

Modern drivers for LEDs are manufactured using the PWM conversion principle and using specialized microcircuits. Pulse width converters consist of pulse transformer and current stabilization circuits. They are powered by 220 V, have high efficiency and protection against short circuit and overload.

Drivers based on a single chip are more compact, as they are designed for power from a low-voltage source direct current. They also have high efficiency, but their reliability is lower due to the simplified electronic circuit. Such devices are in great demand for LED car tuning. As an example, we can name the PT4115 IC; you can read about a ready-made circuit solution based on this microcircuit in.

Criterias of choice

I would like to immediately note that a resistor is not an alternative to a driver for an LED. It will never protect against impulse noise and surges in the power supply network. Any change in the input voltage will pass through the resistor and lead to an abrupt change in current due to the nonlinearity of the LED I-V characteristic. A driver assembled on the basis of a linear stabilizer is also not the best option. Low efficiency greatly limits its capabilities.

You need to select an LED driver only after you know exactly the number and power of the LEDs to be connected.

Remember! Chips of the same standard size may have different power consumption due to the large number of counterfeits. Therefore, try to purchase LEDs only from trusted stores.

Regarding technical parameters, the following must be indicated on the LED driver housing:

power;
operating input voltage range;
operating range of output voltage;
rated stabilized current;
degree of protection against moisture and dust.

Packless drivers powered by 12 V and 220 V are very attractive. Among them, there are various modifications in which you can connect one or several powerful LEDs. Such devices are convenient for laboratory research and experiments. For home use, you will still have to place the product in the case. As a result, monetary savings on an open-type driver board are achieved at the expense of reliability and aesthetics.

In addition to selecting a driver for an LED based on electrical parameters, a potential buyer must clearly understand the conditions of its future operation (location, temperature, humidity). After all, the reliability of the entire system depends on where and how the driver is installed.

What is the purpose of the drivers?

A driver (power supply) is a device that performs the functions of stabilizing the current flowing through the LED circuit and is responsible for ensuring that the device you purchased works for the number of hours guaranteed by the manufacturer. When selecting a power supply, you must first thoroughly study its output characteristics, including current, voltage, power, coefficient useful action(efficiency), as well as the degree of its protection from exposure to external factors.

For example, the brightness of the LED depends on the current flow characteristics. The digital voltage symbol reflects the range in which the driver operates during possible voltage surges. And of course, the higher the efficiency, the more efficiently the device will work, and its service life will be longer.

Where are LED drivers used?

An electronic device - a driver - is usually powered from a 220V electrical network, but is designed to operate with very low voltages of 10, 12 and 24V. The operating output voltage range, in most cases, is from 3V to several tens of volts. For example, you need to connect seven 3V LEDs. In this case, you will need a driver with an output voltage from 9 to 24V, which is rated at 780 mA. Please note that, despite its versatility, such a driver will have a low efficiency if you give it a minimum load.

If you need to install lighting in a car, insert a lamp into a bicycle or motorcycle headlight, into one or two small street lamps or into a hand lamp, a power supply from 9 to 36V will be enough for you.

More powerful LED drivers will need to be selected if you intend to connect an LED system consisting of three or more devices outdoors, have chosen it to decorate your interior, or if you have office table lamps that operate at least 8 hours a day .

How does the driver work?

As we have already said, the LED driver acts as a current source. The voltage source produces a certain voltage at its output, ideally independent of the load.

For example, let's connect a 40 Ohm resistor to a 12 V source. A current of 300mA will flow through it.

Now let's turn on two resistors at once. The total current will be already 600mA.

The power supply maintains the specified current at its output. The voltage may change in this case. Let's also connect a 40 Ohm resistor to the 300 mA driver.

The power supply will create a 12V voltage drop across the resistor.

If you connect two resistors in parallel, the current will also be 300mA, and the voltage will drop by half.

What are the main characteristics LED drivers?

When selecting a driver, be sure to pay attention to parameters such as output voltage, power consumed by the load (current).

— The output voltage depends on the voltage drop across the LED; number of LEDs; depending on the connection method.

— The current at the output of the power supply is determined by the characteristics of the LEDs and depends on their power and brightness, quantity and color scheme.

Let's dwell on the color characteristics of LED lamps. By the way, the load power depends on this. For example, the average power consumption of a red LED varies within 740 mW. For green, the average power will be about 1.20 W. Based on this data, you can calculate in advance how much driver power you will need.

P=Pled x N

where Pled is the LED power, N is the number of connected diodes.

Another important rule. D For stable operation of the power supply, the power reserve must be at least 25%. That is, the following relationship must be satisfied:

Pmax ≥ (1.2…1.3)xP

where Pmax is the maximum power of the power supply.

How to properly connect LEDs?

There are several ways to connect LEDs.

The first method is sequential administration. Here you will need a driver with a voltage of 12V and a current of 300mA. With this method, the LEDs in the lamp or on the strip burn equally brightly, but if you decide to connect more LEDs, you will need a driver with a very high voltage.

The second method is parallel connection. A 6V power supply is suitable for us, and the current will be consumed approximately twice as much as with a serial connection. There is also a drawback - one circuit may shine brighter than the other.

Series-parallel connection - found in floodlights and other powerful lamps operating on both direct and alternating voltage.

The fourth method is to connect the driver in series, two at a time. It is the least preferred.

There is also a hybrid option. It combines the advantages of serial and parallel connection of LEDs.

Experts advise choosing a driver before you buy LEDs, and it is also advisable to first determine their connection diagram. This way the power supply will work more efficiently for you.

Linear and pulse drivers. What are their operating principles?

Today, linear and pulse drivers are produced for LED lamps and strips.
The linear output is a current generator, which provides voltage stabilization without creating electromagnetic interference. Such drivers are easy to use and not expensive, but their low efficiency limits their scope of application.

Switching drivers, on the contrary, have a high efficiency (about 96%), and are also compact. A driver with such characteristics is preferable to use for portable lighting devices, which allows you to increase the operating time of the power source. But there is also a minus - due to the high level of electromagnetic interference, it is less attractive.

Do you need a 220V LED driver?

Linear and pulse drivers are produced for inclusion in a 220V network. Moreover, if power supplies have galvanic isolation (transfer of energy or signal between electrical circuits without electrical contact between them), they demonstrate high efficiency, reliability and safety in operation.

Without galvanic isolation, the power supply will cost you less, but will not be as reliable and will require caution when connecting due to the danger of electric shock.

When selecting power parameters, experts recommend choosing LED drivers with a power exceeding the required minimum by 25%. Such a power reserve will prevent the electronic device and power supply from quickly failing.

Is it worth buying Chinese drivers?

Made in China – today on the market you can find hundreds of drivers of various characteristics made in China. What are they? These are mainly devices with pulse source current at 350-700mA. Low price and the presence of galvanic isolation allow such drivers to be in demand among buyers. But there are also disadvantages to a Chinese-made device. They often do not have a housing, the use of cheap elements reduces the reliability of the driver, and there is also no protection against overheating and fluctuations in the power supply.

Chinese drivers, like many products produced in the Middle Kingdom, are short-lived. Therefore, if you want to install a high-quality lighting system that will serve you for years, it is best to buy an LED converter from a trusted manufacturer.

What is the service life of an LED driver?

Drivers, like any electronics, have their own lifespan. The guaranteed service life of the LED driver is 30,000 hours. But do not forget that the operating time of the device will also depend on the instability of the mains voltage, the level of humidity and temperature changes, and the influence of external factors on it.

Incomplete driver load also reduces the life of the device. For example, if an LED driver is designed for 200W, but operates at a load of 90W, half of its power is returned to the electrical network, causing it to overload. This provokes frequent power failures and the device may burn out after only serving you for a year.

Follow our tips and then you won’t have to change LED devices often.

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

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

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

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

I LED = 0.1 / R

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

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

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

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

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

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

First way assumes that a constant voltage in the range from 0 to 6V is supplied to the DIM input. In this case, brightness adjustment from 0 to 100% is carried out at a voltage at the DIM pin from 0.5 to 2.5 volts. Increasing the voltage above 2.5 V (and up to 6 V) does not affect the current through the LEDs (the brightness does not change). On the contrary, reducing the voltage to a level of 0.3V or lower leads to the circuit turning off and putting it into standby mode (the current consumption drops to 95 μA). Thus, you can effectively control the operation of the driver without removing the supply voltage.
Second way involves supplying a signal from a pulse-width converter with an output frequency of 100-20000 Hz, the brightness will be determined by the duty cycle (pulse duty cycle). For example, if the high level lasts 1/4 of the period, and the low level, respectively, 3/4, then this will correspond to a brightness level of 25% of the maximum. You must understand that the driver operating frequency is determined by the inductance of the inductor and in no way depends on the dimming frequency.

The PT4115 LED driver circuit with constant voltage dimmer is shown in the figure below:

This circuit for adjusting the brightness of the LEDs works great due to the fact that inside the chip the DIM pin is “pulled up” to the 5V bus through a 200 kOhm resistor. Therefore, when the potentiometer slider is in its lowest position, a voltage divider of 200 + 200 kOhm is formed and a potential of 5/2 = 2.5V is formed at the DIM pin, which corresponds to 100% brightness.

How the scheme works

At the first moment of time, when the input voltage is applied, the current through R and L is zero and the output switch built into the microcircuit is open. The current through the LEDs begins to gradually increase. The rate of current rise depends on the magnitude of the inductance and supply voltage. The in-circuit comparator compares the potentials before and after resistor R and, as soon as the difference is 115 mV, a low level appears at its output, which closes the output switch.

Thanks to the energy stored in the inductance, the current through the LEDs does not disappear instantly, but begins to gradually decrease. The voltage drop across the resistor R gradually decreases. As soon as it reaches a value of 85 mV, the comparator will again issue a signal to open the output switch. And the whole cycle repeats all over again.

If it is necessary to reduce the range of current ripples through the LEDs, it is possible to connect a capacitor in parallel with the LEDs. The larger its capacity, the more the triangular shape of the current through the LEDs will be smoothed out and the more similar it will become to a sinusoidal one. The capacitor does not affect the operating frequency or efficiency of the driver, but increases the time it takes for the specified current through the LED to settle.

Important assembly details

An important element of the circuit is capacitor C1. It not only smoothes out ripples, but also compensates for the energy accumulated in the inductor at the moment the output switch is closed. Without C1, the energy stored in the inductor will flow through the Schottky diode to the power bus and can cause a breakdown of the microcircuit. Therefore, if you turn on the driver without a capacitor shunting the power supply, the microcircuit is almost guaranteed to shut down. And the greater the inductance of the inductor, the greater the chance of burning the microcontroller.

The minimum capacitance of capacitor C1 is 4.7 µF (and when the circuit is powered with a pulsating voltage after the diode bridge - at least 100 µF).

The capacitor should be located as close to the chip as possible and have the lowest possible ESR value (i.e. tantalum capacitors are welcome).

It is also very important to take a responsible approach to choosing a diode. It must have a low forward voltage drop, short recovery time during switching, and stable parameters when increasing temperatures p-n transition to prevent an increase in leakage current.

In principle, you can take a regular diode, but Schottky diodes are best suited to these requirements. For example, STPS2H100A in SMD version (forward voltage 0.65V, reverse - 100V, pulse current up to 75A, operating temperature up to 156°C) or FR103 in DO-41 housing (reverse voltage up to 200V, current up to 30A, temperature up to 150 °C). The common SS34s performed very well, which you can pull out of old boards or buy a whole pack for 90 rubles.

The inductance of the inductor depends on the output current (see table below). An incorrectly selected inductance value can lead to an increase in the power dissipated on the microcircuit and exceeding the operating temperature limits.

If it overheats above 160°C, the microcircuit will automatically turn off and remain in the off state until it cools down to 140°C, after which it will start automatically.

Despite the available tabular data, it is permissible to install a coil with an inductance deviation greater than the nominal value. In this case, the efficiency of the entire circuit changes, but it remains operational.

You can take a factory choke, or you can make it yourself from a ferrite ring from a burnt motherboard and PEL-0.35 wire.

If maximum autonomy of the device is important (portable lamps, lanterns), then, in order to increase the efficiency of the circuit, it makes sense to spend time carefully selecting the inductor. At low currents, the inductance must be larger to minimize current control errors resulting from the delay in switching the transistor.

The inductor should be located as close as possible to the SW pin, ideally connected directly to it.

And finally, the most precision element of the LED driver circuit is resistor R. As already mentioned, its minimum value is 0.082 Ohms, which corresponds to a current of 1.2 A.

Unfortunately, it is not always possible to find a resistor of a suitable value, so it’s time to remember the formulas for calculating the equivalent resistance when resistors are connected in series and in parallel:

R last = R 1 +R 2 +…+R n;
R pairs = (R 1 xR 2) / (R 1 +R 2).

By combining different connection methods, you can obtain the required resistance from several resistors at hand.

It is important to route the board so that the Schottky diode current does not flow along the path between R and VIN, as this can lead to errors in measuring the load current.

The low cost, high reliability and stability of driver characteristics on the RT4115 contribute to its widespread use in LED lamps Oh. Almost every second 12-volt LED lamp with an MR16 base is assembled on PT4115 (or CL6808).

The resistance of the current-setting resistor (in Ohms) is calculated using exactly the same formula:

R = 0.1 / I LED[A]

A typical connection diagram looks like this:

As you can see, everything is very similar to the circuit of an LED lamp with a RT4515 driver. The description of the operation, signal levels, features of the elements used and the layout of the printed circuit board are exactly the same as those, so there is no point in repeating.

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

SN3350

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

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

R = 0.1 / I LED

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

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

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

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

Typical connection diagram:

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

ZXLD1350

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

Here are the main differences:

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

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

R = 0.1 / I LED

The minimum resistor resistance is 0.27 Ohm.

A typical connection diagram is no different from its counterparts:

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

More detailed characteristics ZXLD1350 can be found in the datasheet for this chip.

The cost of the microcircuit is unreasonably high (), despite the fact that the output current is quite small. In general, it’s very much for everyone. I wouldn't get involved.

QX5241

QX5241 is a Chinese analogue of MAX16819 (MAX16820), but in a more convenient package. Also available under the names KF5241, 5241B. It is marked "5241a" (see photo).

In one well-known store they are sold almost by weight (10 pieces for 90 rubles).

The driver operates on exactly the same principle as all those described above (continuous step-down converter), but does not contain an output switch, so operation requires the connection of an external field-effect transistor.

You can take any N-channel MOSFET with suitable drain current and drain-source voltage. For example, the following are suitable: SQ2310ES (up to 20V!!!), 40N06, IRF7413, IPD090N03L, IRF7201. In general, the lower the opening voltage, the better.

Here are some key features of the LED driver on the QX5241:

maximum output current - 2.5 A;
Efficiency up to 96%;
maximum dimming frequency - 5 kHz;
maximum operating frequency of the converter is 1 MHz;
accuracy of current stabilization through LEDs - 1%;
supply voltage - 5.5 - 36 Volts (works normally at 38!);
output current is calculated by the formula: R = 0.2 / I LED

Read the specification (in English) for more details.

The LED driver on the QX5241 contains few parts and is always assembled according to this scheme:

The 5241 chip comes only in the SOT23-6 package, so it’s best not to approach it with a soldering iron for soldering pans. After installation, the board should be thoroughly washed to remove flux; any unknown contamination can negatively affect the operation of the microcircuit.

The difference between the supply voltage and the total voltage drop across the diodes should be 4 volts (or more). If it is less, then some glitches in operation are observed (current instability and inductor whistling). So take it with reserve. Moreover, the greater the output current, the greater the voltage reserve. Although, perhaps I just came across a bad copy of the microcircuit.

If the input voltage is less than the total drop across the LEDs, then generation fails. In this case, the output field switch opens completely and the LEDs light up (of course, not at full power, since the voltage is not enough).

AL9910

Diodes Incorporated has created one very interesting LED driver IC: the AL9910. It is curious in that its operating voltage range allows it to be connected directly to a 220V network (via a simple diode rectifier).

Here are its main characteristics:

input voltage - up to 500V (up to 277V for alternating);
built-in voltage stabilizer for powering the microcircuit, which does not require a quenching resistor;
the ability to adjust brightness by changing the potential on the control leg from 0.045 to 0.25V;
built-in overheating protection (triggered at 150°C);
operating frequency (25-300 kHz) is set by an external resistor;
an external field-effect transistor is required for operation;
Available in eight-legged SO-8 and SO-8EP packages.

The driver assembled on the AL9910 chip does not have galvanic isolation from the network, so it should be used only where direct contact with the circuit elements is impossible.

Due to low energy consumption, theoretical durability and lower prices, incandescent and energy-saving lamps are rapidly replacing them. But, despite the declared service life of up to 25 years, they often burn out without even serving the warranty period.

Unlike incandescent lamps, 90% of burnt-out LED lamps can be successfully repaired with your own hands, even without special training. The examples presented will help you repair failed LED lamps.

Before you start repairing an LED lamp, you need to understand its structure. Regardless of the appearance and type of LEDs used, all LED lamps, including filament bulbs, are designed the same. If you remove the walls of the lamp housing, you can see the driver inside, which is a printed circuit board with radio elements installed on it.

Any LED lamp is designed and works as follows. The supply voltage from the contacts of the electric cartridge is supplied to the terminals of the base. Two wires are soldered to it, through which voltage is supplied to the driver input. From the driver, the DC supply voltage is supplied to the board on which the LEDs are soldered.

The driver is an electronic unit - a current generator that converts the supply voltage into the current required to light the LEDs.

Sometimes, to diffuse light or protect against human contact with unprotected conductors of a board with LEDs, it is covered with diffusing protective glass.

About filament lamps

By appearance A filament lamp is similar to an incandescent lamp. The design of filament lamps differs from LED lamps in that they do not use a board with LEDs as light emitters, but a sealed glass flask filled with gas, in which one or more filament rods are placed. The driver is located in the base.

The filament rod is a glass or sapphire tube with a diameter of about 2 mm and a length of about 30 mm, on which 28 miniature LEDs coated in series with a phosphor are attached and connected. One filament consumes about 1 W of power. My operating experience shows that filament lamps are much more reliable than those made on the basis of SMD LEDs. I believe that over time they will replace all other artificial light sources.

Examples of LED lamp repairs

Attention, the electrical circuits of LED lamp drivers are galvanically connected to the phase of the electrical network and therefore care should be taken. Touching exposed parts of a circuit connected to an electrical outlet may result in electric shock.

LED lamp repair
ASD LED-A60, 11 W on SM2082 chip

Currently, powerful LED light bulbs have appeared, the drivers of which are assembled on SM2082 type chips. One of them worked for less than a year and ended up being repaired. The light went out randomly and came on again. When you tapped it, it responded with light or extinguishing. It became obvious that the problem was poor contact.

To get to the electronic part of the lamp, you need to use a knife to pick up the diffuser glass at the point of contact with the body. Sometimes it is difficult to separate the glass, since when it is seated, silicone is applied to the fixing ring.

After removing the light-scattering glass, access to the LEDs and the SM2082 current generator microcircuit became available. In this lamp, one part of the driver was mounted on an aluminum LED printed circuit board, and the second on a separate one.

An external inspection did not reveal any defective soldering or broken tracks. I had to remove the board with LEDs. To do this, the silicone was first cut off and the board was pryed off by the edge with a screwdriver blade.

To get to the driver located in the lamp body, I had to unsolder it by heating two contacts with a soldering iron at the same time and moving it to the right.

On one side of the driver circuit board, only an electrolytic capacitor with a capacity of 6.8 μF for a voltage of 400 V was installed.

A diode bridge and two series-connected resistors with a nominal value of 510 kOhm were installed on the reverse side of the driver board.

In order to figure out which of the boards the contact was missing, we had to connect them, observing the polarity, using two wires. After tapping the boards with the handle of a screwdriver, it became obvious that the fault lies in the board with the capacitor or in the contacts of the wires coming from the base of the LED lamp.

Since the soldering did not raise any suspicions, I first checked the reliability of the contact in the central terminal of the base. It can be easily removed if you pry it over the edge with a knife blade. But the contact was reliable. Just in case, I tinned the wire with solder.

It is difficult to remove the screw part of the base, so I decided to use a soldering iron to solder the soldering wires coming from the base. When I touched one of the soldering joints, the wire became exposed. A “cold” solder was detected. Since there was no way to get to the wire to strip it, I had to lubricate it with FIM active flux and then solder it again.

Once assembled, the LED lamp consistently emitted light despite being hit with the handle of a screwdriver. Checking the light flux for pulsations showed that they are significant with a frequency of 100 Hz. Such an LED lamp can only be installed in luminaires for general lighting.

Driver circuit diagram
LED lamp ASD LED-A60 on SM2082 chip

The electrical circuit of the ASD LED-A60 lamp, thanks to the use of a specialized SM2082 microcircuit in the driver to stabilize the current, turned out to be quite simple.

The driver circuit works as follows. The AC supply voltage is supplied through fuse F to the rectifier diode bridge assembled on the MB6S microassembly. Electrolytic capacitor C1 smoothes out ripples, and R1 serves to discharge it when the power is turned off.

From the positive terminal of the capacitor, the supply voltage is supplied directly to the LEDs connected in series. From the output of the last LED, the voltage is supplied to the input (pin 1) of the SM2082 microcircuit, the current in the microcircuit is stabilized and then from its output (pin 2) goes to the negative terminal of capacitor C1.

Resistor R2 sets the amount of current flowing through the HL LEDs. The amount of current is inversely proportional to its rating. If the value of the resistor is decreased, the current will increase; if the value is increased, the current will decrease. The SM2082 microcircuit allows you to adjust the current value with a resistor from 5 to 60 mA.

LED lamp repair
ASD LED-A60, 11 W, 220 V, E27

The repair included another ASD LED-A60 LED lamp, similar in appearance and with the same technical characteristics as the one repaired above.

When turned on, the lamp came on for a moment and then did not shine. This behavior of LED lamps is usually associated with a driver failure. So I immediately started disassembling the lamp.

The light-diffusing glass was removed with great difficulty, since along the entire line of contact with the body it was, despite the presence of a retainer, generously lubricated with silicone. To separate the glass, I had to look for a pliable place along the entire line of contact with the body using a knife, but still there was a crack in the body.

To gain access to the lamp driver, the next step was to remove the LED printed circuit board, which was pressed along the contour into the aluminum insert. Despite the fact that the board was aluminum and could be removed without fear of cracks, all attempts were unsuccessful. The board held tight.

It was also not possible to remove the board together with the aluminum insert, since it fit tightly to the case and was seated with the outer surface on silicone.

I decided to try removing the driver board from the base side. To do this, first, a knife was pryed out of the base and the central contact was removed. To remove the threaded part of the base, it was necessary to slightly bend its upper flange so that the core points would disengage from the base.

The driver became accessible and was freely extended to a certain position, but it was not possible to remove it completely, although the conductors from the LED board were sealed off.

The LED board had a hole in the center. I decided to try to remove the driver board by hitting its end through a metal rod threaded through this hole. The board moved a few centimeters and hit something. After further blows, the lamp body cracked along the ring and the board with the base of the base separated.

As it turned out, the board had an extension whose shoulders rested against the lamp body. It looks like the board was shaped this way to limit movement, although it would have been enough to fix it with a drop of silicone. Then the driver would be removed from either side of the lamp.

The 220 V voltage from the lamp base is supplied through a resistor - fuse FU to the MB6F rectifier bridge and is then smoothed out by an electrolytic capacitor. Next, the voltage is supplied to the SIC9553 chip, which stabilizes the current. Parallel connected resistors R20 and R80 between pins 1 and 8 MS set the amount of LED supply current.

The photo shows a typical electrical circuit diagram, given by the manufacturer of the SIC9553 chip in the Chinese datasheet.

This photo shows the appearance of the LED lamp driver from the installation side of the output elements. Since space allowed, to reduce the pulsation coefficient of the light flux, the capacitor at the driver output was soldered to 6.8 μF instead of 4.7 μF.

If you have to remove the drivers from the body of this lamp model and cannot remove the LED board, you can use a jigsaw to cut the lamp body around the circumference just above the screw part of the base.

In the end, all my efforts to remove the driver turned out to be useful only for understanding the LED lamp structure. The driver turned out to be OK.

The flash of the LEDs at the moment of switching on was caused by a breakdown in the crystal of one of them as a result of a voltage surge when the driver was started, which misled me. It was necessary to ring the LEDs first.

An attempt to test the LEDs with a multimeter was unsuccessful. The LEDs did not light up. It turned out that two light-emitting crystals connected in series are installed in one case, and in order for the LED to start flowing current, it is necessary to apply a voltage of 8 V to it.

A multimeter or tester turned on in resistance measurement mode produces a voltage within 3-4 V. I had to check the LEDs using a power supply, supplying 12 V to each LED through a 1 kOhm current-limiting resistor.

There was no replacement LED available, so the pads were shorted with a drop of solder instead. This is safe for driver operation, and the power of the LED lamp will decrease by only 0.7 W, which is almost imperceptible.

After repairing the electrical part of the LED lamp, the cracked body was glued together with quick-drying “Moment” superglue, the seams were smoothed by melting the plastic with a soldering iron and smoothed with sandpaper.

Just for fun, I did some measurements and calculations. The current flowing through the LEDs was 58 mA, the voltage was 8 V. Therefore, the power supplied to one LED was 0.46 W. With 16 LEDs, the result is 7.36 W, instead of the declared 11 W. Perhaps the manufacturer has indicated the total power consumption of the lamp, taking into account losses in the driver.

The service life of the ASD LED-A60, 11 W, 220 V, E27 LED lamp declared by the manufacturer raises serious doubts in my mind. In the small volume of the plastic lamp body, with low thermal conductivity, significant power is released - 11 W. As a result, the LEDs and driver operate at the maximum permissible temperature, which leads to accelerated degradation of their crystals and, as a consequence, to a sharp reduction in their time between failures.

LED lamp repair
LED smd B35 827 ERA, 7 W on BP2831A chip

An acquaintance shared with me that he bought five light bulbs like in the photo below, and after a month they all stopped working. He managed to throw away three of them, and, at my request, brought two for repairs.

The light bulb worked, but instead of bright light it emitted a flickering weak light with a frequency of several times per second. I immediately assumed that the electrolytic capacitor had swollen; usually, if it fails, the lamp begins to emit light like a strobe.

The light-scattering glass came off easily and was not glued. It was fixed by a slot on its rim and a protrusion in the lamp body.

The driver was secured using two solders to a printed circuit board with LEDs, as in one of the lamps described above.

A typical driver circuit on the BP2831A chip taken from the datasheet is shown in the photograph. The driver board was removed and all simple radio elements were checked; they all turned out to be in good order. I had to start checking the LEDs.

The LEDs in the lamp were installed of an unknown type with two crystals in the housing and inspection did not reveal any defects. By connecting the leads of each LED in series, I quickly identified the faulty one and replaced it with a drop of solder, as in the photo.

The light bulb worked for a week and was repaired again. Shorted the next LED. A week later I had to short-circuit another LED, and after the fourth I threw out the light bulb because I was tired of repairing it.

The reason for the failure of light bulbs of this design is obvious. LEDs overheat due to insufficient heat sink surface, and their service life is reduced to hundreds of hours.

Why is it permissible to short-circuit the terminals of burnt-out LEDs in LED lamps?

The LED lamp driver, unlike a constant voltage power supply, produces a stabilized current value at the output, not a voltage. Therefore, regardless of the load resistance within the specified limits, the current will always be constant and, therefore, the voltage drop across each of the LEDs will remain the same.

Therefore, as the number of series-connected LEDs in the circuit decreases, the voltage at the driver output will also decrease proportionally.

For example, if 50 LEDs are connected in series to the driver, and each of them drops a voltage of 3 V, then the voltage at the driver output is 150 V, and if you short-circuit 5 of them, the voltage will drop to 135 V, and the current will not change.

But the efficiency of the driver assembled according to this scheme will be low and the power loss will be more than 50%. For example, for an LED light bulb MR-16-2835-F27 you will need a 6.1 kOhm resistor with a power of 4 watts. It turns out that the resistor driver will consume power that exceeds the power consumption of LEDs and placing it in a small LED lamp housing will be unacceptable due to the release of more heat.

But if there is no other way to repair an LED lamp and it is very necessary, then the resistor driver can be placed in a separate housing; anyway, the power consumption of such an LED lamp will be four times less than incandescent lamps. It should be noted that the more LEDs connected in series in a light bulb, the higher the efficiency will be. With 80 series-connected SMD3528 LEDs, you will need an 800 Ohm resistor with a power of only 0.5 W. The capacitance of capacitor C1 will need to be increased to 4.7 µF.

Finding faulty LEDs

After removing the protective glass, it becomes possible to check the LEDs without peeling off the printed circuit board. First of all, a careful inspection of each LED is carried out. If even the smallest black dot is detected, not to mention blackening of the entire surface of the LED, then it is definitely faulty.

When inspecting the appearance of the LEDs, you need to carefully examine the quality of the soldering of their terminals. One of the light bulbs being repaired turned out to have four LEDs that were poorly soldered.

The photo shows a light bulb that had very small black dots on its four LEDs. I immediately marked the faulty LEDs with crosses so that they were clearly visible.

Faulty LEDs may not have any changes in appearance. Therefore, it is necessary to check each LED with a multimeter or pointer tester turned on in resistance measurement mode.

There are LED lamps in which standard LEDs are installed in appearance, in the housing of which two crystals connected in series are mounted at once. For example, lamps of the ASD LED-A60 series. To test such LEDs, it is necessary to apply a voltage of more than 6 V to its terminals, and any multimeter produces no more than 4 V. Therefore, checking such LEDs can only be done by applying a voltage of more than 6 (recommended 9-12) V to them from the power source through a 1 kOhm resistor .

The LED is checked like a regular diode; in one direction the resistance should be equal to tens of megaohms, and if you swap the probes (this changes the polarity of the voltage supply to the LED), then it should be small, and the LED may glow dimly.

When checking and replacing LEDs, the lamp must be fixed. To do this, you can use a suitable sized round jar.

You can check the serviceability of the LED without an additional DC source. But this verification method is possible if the light bulb driver is working properly. To do this, it is necessary to apply supply voltage to the base of the LED light bulb and short-circuit the terminals of each LED in series with each other using a wire jumper or, for example, the jaws of metal tweezers.

If suddenly all the LEDs light up, it means that the shorted one is definitely faulty. This method is suitable if only one LED in the circuit is faulty. With this method of checking, it is necessary to take into account that if the driver does not provide galvanic isolation from the electrical network, as for example in the diagrams above, then touching the LED solders with your hand is unsafe.

If one or even several LEDs turn out to be faulty and there is nothing to replace them with, then you can simply short-circuit the contact pads to which the LEDs were soldered. The light bulb will work with the same success, only the luminous flux will decrease slightly.

Other malfunctions of LED lamps

If checking the LEDs showed their serviceability, then the reason for the light bulb’s inoperability lies in the driver or in the soldering areas of the current-carrying conductors.

For example, in this light bulb a cold solder connection was found on the conductor supplying power to the printed circuit board. The soot released due to poor soldering even settled on the conductive paths of the printed circuit board. The soot was easily removed by wiping with a rag soaked in alcohol. The wire was soldered, stripped, tinned and re-soldered into the board. I was lucky with the repair of this light bulb.

Of the ten failed bulbs, only one had a faulty driver and a broken diode bridge. The driver repair consisted of replacing the diode bridge with four IN4007 diodes, designed for a reverse voltage of 1000 V and a current of 1 A.

Soldering SMD LEDs

To replace a faulty LED, it must be desoldered without damaging the printed conductors. The LED from the donor board also needs to be desoldered for replacement without damage.

It is almost impossible to desolder SMD LEDs with a simple soldering iron without damaging their housing. But if you use a special tip for a soldering iron or put an attachment made of copper wire on a standard tip, then the problem can be easily solved.

LEDs have polarity and when replacing, you need to install it correctly on the printed circuit board. Typically, printed conductors follow the shape of the leads on the LED. Therefore, a mistake can only be made if you are inattentive. To seal an LED, it is enough to install it on a printed circuit board and heat its ends with the contact pads with a 10-15 W soldering iron.

If the LED burns out like carbon, and the printed circuit board underneath is charred, then before installing a new LED, you must clean this area of the printed circuit board from burning, since it is a current conductor. When cleaning, you may find that the LED solder pads are burnt or peeled off.

In this case, the LED can be installed by soldering it to adjacent LEDs if the printed traces lead to them. To do this, you can take a piece of thin wire, bend it in half or three times, depending on the distance between the LEDs, tin it and solder it to them.

Repair of LED lamp series "LL-CORN" (corn lamp)
E27 4.6W 36x5050SMD

The design of the lamp, which is popularly called a corn lamp, shown in the photo below is different from the lamp described above, therefore the repair technology is different.

The design of LED SMD lamps of this type is very convenient for repair, since there is access to test the LEDs and replace them without disassembling the lamp body. True, I still disassembled the light bulb for fun in order to study its structure.

Checking the LEDs of an LED corn lamp is no different from the technology described above, but it must be taken into account that the SMD5050 LED housing contains three LEDs at once, usually connected in parallel (three dark dots of the crystals are visible on the yellow circle), and during testing all three should glow.

A faulty LED can be replaced with a new one or short-circuited with a jumper. This will not affect the reliability of the lamp, only the luminous flux will decrease slightly, unnoticeably to the eye.

The driver of this lamp is assembled according to the simplest circuit, without an isolating transformer, so touching the LED terminals when the lamp is on is unacceptable. Lamps of this design must not be installed in lamps that can be reached by children.

If all the LEDs are working, it means the driver is faulty, and the lamp will have to be disassembled to get to it.

To do this, you need to remove the rim from the side opposite the base. Using a small screwdriver or a knife blade, try in a circle to find the weak spot where the rim is glued the worst. If the rim gives way, then using the tool as a lever, the rim will easily come off around the entire perimeter.

The driver was assembled according to the electrical circuit, like the MR-16 lamp, only C1 had a capacity of 1 µF, and C2 - 4.7 µF. Due to the fact that the wires going from the driver to the lamp base were long, the driver was easily removed from the lamp body. After studying its circuit diagram, the driver was inserted back into the housing, and the bezel was glued into place with transparent Moment glue. The failed LED was replaced with a working one.

Repair of LED lamp "LL-CORN" (corn lamp)
E27 12W 80x5050SMD

When repairing a more powerful lamp, 12 W, there were no failed LEDs of the same design and in order to get to the drivers, we had to open the lamp using the technology described above.

This lamp gave me a surprise. The wires leading from the driver to the socket were short, and it was impossible to remove the driver from the lamp body for repair. I had to remove the base.

The lamp base was made of aluminum, cored around the circumference and held tightly. I had to drill out the mounting points with a 1.5 mm drill. After this, the base, pryed off with a knife, was easily removed.

But you can do without drilling the base if you use the edge of a knife to pry it around the circumference and slightly bend its upper edge. You should first put a mark on the base and body so that the base can be conveniently installed in place. To securely fasten the base after repairing the lamp, it will be enough to put it on the lamp body in such a way that the punched points on the base fall into the old places. Next, press these points with a sharp object.

Two wires were connected to the thread with a clamp, and the other two were pressed into the central contact of the base. I had to cut these wires.

As expected, there were two identical drivers, feeding 43 diodes each. They were covered with heat shrink tubing and taped together. In order for the driver to be placed back into the tube, I usually carefully cut it along the printed circuit board from the side where the parts are installed.

After repair, the driver is wrapped in a tube, which is fixed with a plastic tie or wrapped with several turns of thread.

In the electrical circuit of the driver of this lamp, protection elements are already installed, C1 for protection against pulse surges and R2, R3 for protection against current surges. When checking the elements, resistors R2 were immediately found to be open on both drivers. It appears that the LED lamp was supplied with a voltage that exceeded the permissible voltage. After replacing the resistors, I didn’t have a 10 ohm one at hand, so I set it to 5.1 ohms, and the lamp started working.

Repair of LED lamp series "LLB" LR-EW5N-5

The appearance of this type of light bulb inspires confidence. Aluminum body, high quality workmanship, beautiful design.

The design of the light bulb is such that disassembling it without the use of significant physical effort is impossible. Since the repair of any LED lamp begins with checking the serviceability of the LEDs, the first thing we had to do was remove the plastic protective glass.

The glass was fixed without glue on a groove made in the radiator with a collar inside it. To remove the glass, you need to use the end of a screwdriver, which will go between the fins of the radiator, to lean on the end of the radiator and, like a lever, lift the glass up.

Checking the LEDs with a tester showed that they are working properly, therefore, the driver is faulty and we need to get to it. The aluminum board was secured with four screws, which I unscrewed.

But contrary to expectations, behind the board there was a radiator plane, lubricated with heat-conducting paste. The board had to be returned to its place and the lamp continued to be disassembled from the base side.

Due to the fact that the plastic part to which the radiator was attached was held very tightly, I decided to go the proven route, remove the base and remove the driver through the opened hole for repair. I drilled out the core points, but the base was not removed. It turned out that it was still attached to the plastic due to the threaded connection.

I had to separate the plastic adapter from the radiator. It held up just like the protective glass. To do this, a cut was made with a hacksaw for metal at the junction of the plastic with the radiator and by turning a screwdriver with a wide blade, the parts were separated from each other.

After unsoldering the leads from the LED printed circuit board, the driver became available for repair. The driver circuit turned out to be more complex than previous light bulbs, with an isolation transformer and a microcircuit. One of the 400 V 4.7 µF electrolytic capacitors was swollen. I had to replace it.

A check of all semiconductor elements revealed a faulty Schottky diode D4 (pictured below left). There was an SS110 Schottky diode on the board, which was replaced with an existing analog 10 BQ100 (100 V, 1 A). The forward resistance of Schottky diodes is two times less than that of ordinary diodes. The LED light came on. The second light bulb had the same problem.

Repair of LED lamp series "LLB" LR-EW5N-3

This LED lamp is very similar in appearance to the "LLB" LR-EW5N-5, but its design is slightly different.

If you look closely, you can see that at the junction between the aluminum radiator and the spherical glass, unlike the LR-EW5N-5, there is a ring in which the glass is secured. To remove the protective glass, use a small screwdriver to pry it at the junction with the ring.

Three nine crystal super-bright LEDs are installed on an aluminum printed circuit board. The board is screwed to the heatsink with three screws. Checking the LEDs showed their serviceability. Therefore, the driver needs to be repaired. Having experience in repairing a similar LED lamp "LLB" LR-EW5N-5, I did not unscrew the screws, but unsoldered the current-carrying wires coming from the driver and continued disassembling the lamp from the base side.

The plastic connecting ring between the base and the radiator was removed with great difficulty. At the same time, part of it broke off. As it turned out, it was screwed to the radiator with three self-tapping screws. The driver was easily removed from the lamp body.

The screws that fasten the plastic ring of the base are covered by the driver, and it is difficult to see them, but they are on the same axis with the thread to which the transition part of the radiator is screwed. Therefore, you can reach them with a thin Phillips screwdriver.

The driver turned out to be assembled according to a transformer circuit. Checking all elements except the microcircuit did not reveal any failures. Consequently, the microcircuit is faulty; I couldn’t even find a mention of its type on the Internet. The LED light bulb could not be repaired; it will be useful for spare parts. But I studied its structure.

Repair of LED lamp series "LL" GU10-3W

At first glance, it turned out to be impossible to disassemble a burnt-out GU10-3W LED light bulb with protective glass. An attempt to remove the glass resulted in its chipping. When great force was applied, the glass cracked.

By the way, in the lamp marking, the letter G means that the lamp has a pin base, the letter U means that the lamp belongs to the class of energy-saving light bulbs, and the number 10 means the distance between the pins in millimeters.

LED light bulbs with a GU10 base have special pins and are installed in a socket with a rotation. Thanks to the expanding pins, the LED lamp is pinched in the socket and held securely even when shaking.

In order to disassemble this LED light bulb, I had to drill a hole with a diameter of 2.5 mm in its aluminum case at the level of the surface of the printed circuit board. The drilling location must be chosen in such a way that the drill does not damage the LED when exiting. If you don’t have a drill at hand, you can make a hole with a thick awl.

Next, a small screwdriver is inserted into the hole and, acting like a lever, the glass is lifted. I removed the glass from two light bulbs without any problems. If checking the LEDs with a tester shows their serviceability, then the printed circuit board is removed.

After separating the board from the lamp body, it immediately became obvious that the current-limiting resistors had burned out in both one and the other lamp. The calculator determined their nominal value from the stripes, 160 Ohms. Since the resistors burned out in LED bulbs of different batches, it is obvious that their power, judging by the size of 0.25 W, does not correspond to the power released when the driver operates at the maximum ambient temperature.

The driver circuit board was well filled with silicone, and I did not disconnect it from the board with the LEDs. I cut off the leads of the burnt resistors at the base and soldered them to more powerful resistors that were on hand. In one lamp I soldered a 150 Ohm resistor with a power of 1 W, in the second two in parallel with 320 Ohms with a power of 0.5 W.

In order to prevent accidental contact of the resistor terminal, to which the mains voltage is connected, with the metal body of the lamp, it was insulated with a drop of hot-melt adhesive. It is waterproof and an excellent insulator. I often use it to seal, insulate and secure electrical wires and other parts.

Hot melt adhesive is available in the form of rods with a diameter of 7, 12, 15 and 24 mm in different colors, from transparent to black. It melts, depending on the brand, at a temperature of 80-150°, which allows it to be melted using an electric soldering iron. It is enough to cut a piece of the rod, place it in the right place and heat it. Hot-melt glue will acquire the consistency of May honey. After cooling it becomes hard again. When reheated it becomes liquid again.

After replacing the resistors, the functionality of both bulbs was restored. All that remains is to secure the printed circuit board and protective glass in the lamp body.

When repairing LED lamps, I used liquid nails “Mounting” to secure printed circuit boards and plastic parts. The glue is odorless, adheres well to the surfaces of any materials, remains plastic after drying, and has sufficient heat resistance.

It is enough to take a small amount of glue on the end of a screwdriver and apply it to the places where the parts come into contact. After 15 minutes the glue will already hold.

When gluing the printed circuit board, in order not to wait, holding the board in place, since the wires were pushing it out, I additionally fixed the board at several points using hot glue.

The LED lamp began to flash like a strobe light

I had to repair a couple of LED lamps with drivers assembled on a microcircuit, the malfunction of which was the light blinking at a frequency of about one hertz, like in a strobe light.

One instance of the LED lamp began to blink immediately after being turned on for the first few seconds and then the lamp began to shine normally. Over time, the duration of the lamp's blinking after switching on began to increase, and the lamp began to blink continuously. The second instance of the LED lamp suddenly began blinking continuously.

After disassembling the lamps, it turned out that the electrolytic capacitors installed immediately after the rectifier bridges in the drivers had failed. It was easy to determine the malfunction, since the capacitor housings were swollen. But even if the capacitor looks free of external defects in appearance, then the repair of an LED light bulb with a stroboscopic effect must still begin with its replacement.

After replacing the electrolytic capacitors with working ones, the stroboscopic effect disappeared and the lamps began to shine normally.

Online calculators for determining resistor values
by color marking

When repairing LED lamps, it becomes necessary to determine the resistor value. According to the standard, modern resistors are marked by applying colored rings to their bodies. 4 colored rings are applied to simple resistors, and 5 to high-precision resistors.

Author's note: “There is a fairly large amount of information on the Internet about the power supply of LED products, but when I was preparing material for this article, I found a large amount of absurd information on sites from the top search engine results. In this case, there is either a complete absence or incorrect perception of basic theoretical information and concepts.”

LEDs are the most efficient of all common light sources today. Behind the efficiency there are also problems, for example, a high requirement for the stability of the current that powers them, poor tolerance of complex thermal operating conditions (at elevated temperatures). Hence the task of solving these problems. Let's see how the concepts of power supply and driver differ. First, let's delve into the theory.

Current source and voltage source

power unit is a generalized name for a part of an electronic device or other electrical equipment that supplies and regulates electricity to power this equipment. It can be located both inside the device and outside, in a separate housing.

Driver- a generalized name for a specialized source, switch or power regulator for specific electrical equipment.

There are two main types of power supplies:

Voltage source.

Current source.

Let's look at their differences.

Voltage source- this is a power source whose output voltage does not change when the output current changes.

An ideal voltage source has zero internal resistance, but the output current can be infinitely large. In reality, the situation is different.

Any voltage source has internal resistance. In this regard, the voltage may deviate slightly from the nominal when connecting a powerful load (powerful - low resistance, high current consumption), and the output current is determined by its internal structure.

For a real voltage source, the emergency mode of operation is the short circuit mode. In this mode, the current increases sharply; it is limited only by the internal resistance of the power source. If the power supply does not have short circuit protection, it will fail

Current source- this is a power source whose current remains set regardless of the resistance of the connected load.

Since the purpose of a current source is to maintain a given current level. The emergency operating mode for it is idle mode.

To explain the reason in simple words, the situation is as follows: let’s say you connected a load with a resistance of 1 Ohm to a current source with a rated 1 Ampere, then the voltage at its output will be set to 1 Volt. A power of 1 W will be released.

If you increase the load resistance, say, to 10 Ohms, then the current will still be 1A, and the voltage will already be set at 10V. This means that 10W of power will be released. Conversely, if you reduce the resistance to 0.1 Ohm, the current will still be 1A, and the voltage will be 0.1V.

Idling is a state when nothing is connected to the terminals of the power source. Then we can say that at idle the load resistance is very large (infinite). The voltage will increase until a current of 1A flows. In practice, an example of such a situation is the ignition coil of a car.

The voltage on the electrodes of the spark plug, when the power circuit of the primary winding of the coil opens, increases until its value reaches the breakdown voltage of the spark gap, after which current flows through the resulting spark and the energy accumulated in the coil is dissipated.

A short circuit condition for a current source is not an emergency operation mode. During a short circuit, the load resistance of the power source tends to zero, i.e. it is infinitely small. Then the voltage at the output of the current source will be appropriate for the flow of a given current, and the released power will be negligible.

Let's move on to practice

If we talk about modern nomenclature or names that are given to power supplies more by marketers than by engineers, then power supply it is commonly called a voltage source.

These include:

Charger for a mobile phone (in them, the conversion of values until the required charging current and voltage is achieved is carried out by converters installed on the board of the device being charged.

Power supply for laptop.

Power supply for LED strip.

The driver is the current source. Its main use in everyday life is to power individual and both of them with ordinary high power from 0.5 W.

LED Power

At the beginning of the article it was mentioned that LEDs have very high power requirements. The fact is that the LED is powered by current. It's connected with . Look at her.

The picture shows the current-voltage characteristics of diodes of different colors:

This branch shape (close to a parabola) is due to the characteristics of semiconductors and the impurities that are introduced into them, as well as the features of the pn junction. The current, when the voltage applied to the diode is less than the threshold, almost does not increase, or rather its increase is negligible. When the voltage at the diode terminals reaches a threshold level, the current through the diode begins to increase sharply.

If the current through a resistor grows linearly and depends on its resistance and applied voltage, then the increase in current through a diode does not obey this law. And with an increase in voltage by 1%, the current can increase by 100% or more.

Plus to this: for metals, the resistance increases as its temperature increases, but for semiconductors, on the contrary, the resistance drops, and the current begins to increase.

To find out the reasons for this in more detail, you need to delve into the course “Physical Foundations of Electronics” and learn about the types of charge carriers, the band gap and other interesting things, but we will not do this, we briefly considered these issues.

In technical specifications, the threshold voltage is designated as the voltage drop in forward bias; for white LEDs it is usually about 3 volts.

At first glance, it may seem that at the stage of design and production of the lamp it is enough to set a stable voltage at the output of the power supply and everything will be fine. They do this on LED strips, but they are powered from stabilized power supplies, and besides, the power of the LEDs used in strips is often * small, tenths and hundredths of a watt.

If such an LED is powered by a driver with a stable output current, then when the LED heats up, the current through it will not increase, but will remain unchanged, and the voltage at its terminals will therefore decrease slightly.

And if from the power supply (voltage source), after heating the current will increase, which will make the heating even stronger.

There is one more factor - the characteristics of all LEDs (as well as other elements) are always different.

Driver selection: characteristics, connection

To choose the right driver, you need to familiarize yourself with its technical characteristics, the main ones are:

Rated output current;

Maximum power;

Minimum power. Not always indicated. The fact is that some drivers will not start if a load less than a certain power is connected to them.

Often in stores, instead of power, they indicate:

Rated output current;

Output voltage range in the form of (min.)V...(max.)V, for example 3-15V.

The number of connected LEDs depends on the voltage range, written in the form (min)...(max), for example 1-3 LEDs.

Since the current through all elements is the same when connected in series, therefore the LEDs are connected to the driver in series.

It is not advisable (or rather impossible) to connect LEDs in parallel to the driver, because the voltage drops on the LEDs may differ slightly and one will be overloaded, and the other, on the contrary, will operate in a mode below the nominal one.

It is not recommended to connect more LEDs than specified by the driver design. The fact is that any power source has a certain maximum permissible power, which cannot be exceeded. And for each LED connected to a source of stabilized current, the voltage at its outputs will increase by approximately 3V (if the LED is white), and the power will be equal to the product of current and voltage, as usual.

Based on this, we will draw conclusions: in order to buy the right driver for LEDs, you need to determine the current that the LEDs consume and the voltage that drops across them, and select the driver according to the parameters.

For example, this driver supports connecting up to 12 powerful 1W LEDs with a current consumption of 0.4A.

This one produces a current of 1.5A and a voltage from 20 to 39V, which means you can connect to it, for example, a 1.5A LED, 32-36V and a power of 50W.

Conclusion

A driver is one type of power supply designed to provide LEDs with a given current. In principle, it doesn’t matter what this power source is called. Power supplies are called power supplies for 12 or 24 Volt LED strips; they can supply any current below the maximum. Knowing the correct names, you are unlikely to make a mistake when purchasing a product in stores, and you will not have to change it.