LED lamp device: DIY repair and disassembly, the principle of operation of the circuits

Recently, lamps using LEDs as light sources have become popular lighting devices. These lamps are distinguished by their energy efficiency and environmental friendliness. An electronic circuit is used to control the diodes - a driver. If the illuminator fails, given its high cost, it is profitable to carry out the repair yourself, but for this you need to know the structure of the LED lamp and be able to disassemble it.

General information

The operation of the LED device is based on the invention of the electron-hole junction. In 1907, physicist Henry Round was discovered by electroluminescence, which served as the beginning in the creation of point sources of radiation. After the invention of the p-n junction in 1961, engineers at Texas Instruments patented the infrared LED technology. A year later, American scientist Nick Holonyak invented a light source that works in the red range.

Over the next decade, LEDs have been developed that operate in the yellow, green and blue spectrum. The manufacturing technology for such radiation sources was expensive. Therefore, they were practically not used as lighting. Until 1990, researchers from the Japanese concern Nichia Chemical Industries received a cheap blue LED, which, in combination with green and red colors, gave effective radiation in white spectrum.

LED working principle

An LED is an electronic device that emits light when an electric current passes through it. Its generally accepted abbreviation is LED (light emitting diode). Light emission occurs during the recombination of charge carriers in the pn junction region. This transition is formed at the interface between materials with different types of conductivity.

When materials come into contact, drift and diffusion currents arise between them, leading to dynamic equilibrium. If a potential difference is applied to such a transition, then the diffusion current will increase and an active process of transition of minority charge carriers through the contact zone of materials will begin. Meeting each other at the border, these opposite charges begin to recombine, that is, they are destroyed with the release of energy.

But not every electron-hole transition can emit light during charge recombination. This is due to the width of the active region, which should be close to the quantum energy of the visible spectrum. In this case, the larger the contact area of ​​the p-n junction, the more energy can be released. The process of obtaining a complete LED is technologically complex, because multilayer structures are used for its manufacture. Therefore, in the event of a source of light failure, repairing an LED light bulb with your own hands will consist in replacing it.

The color spectrum of the luminescence is determined by the width of the electron-hole transition zone, which depends on semiconductor materials and dopants. Getting a white glow is achieved in three ways:

1. A combination of three colors: red, blue, green (RGB). In addition to the emitter, the LED housing contains: a reflector, a diffuser, a screen and a light filter.
2. By applying on LEDs operating in the ultraviolet spectrum, a phosphor of three colors. When current flows, the phosphor glows in different colors, the radiation of which is mixed by means of a lens.
3. The use of a blue LED with a phosphor of green and red radiation applied to it.

Emitter characteristics

When repairing LED lamps with their own hands, the user is often faced with the burnout of one or a group of LEDs. In order not to disrupt the operation of the device balanced by the manufacturer and not to aggravate the breakdown, the burned-out semiconductor is changed to a similar copy.

Each type of LED is characterized by a number of parameters, knowing which you can easily choose a replacement for it.. Important characteristics include:

1. Current consumption. Its average value is 0.02 A. However, there are designs in which two or even four crystals can be integrated simultaneously, each with its own p-n junction. Accordingly, the current consumption will increase by two and four times. An increase in the current strength leads to a change in the color gamut of the radiation with the subsequent burnout of the crystal. Therefore, together with them, electronic drivers are used in LED illuminators that maintain the current in the desired range. Using an LED diode with other parameters will lead to overheating of the driver elements and its breakdown.
2. The magnitude of the voltage drop. It is determined by the potential difference across the LED when current flows through it. This value depends on the color of the radiation, for example, blue, green, white - three volts, yellow, red - from 1.8 to 2.4 volts.
3. Light output. Devices with a diameter of five millimeters emit directional light with an output of up to 5 lumens. Therefore, in the design of the LED, the scattering angle is important, which can range from 20 to 120 degrees.
4. Colour temperature. There are three grades of white: warm, daytime, and cold. Since the perception of radiation largely depends on the color temperature, it is very important to use an LED with the same value as the burned-out one when replacing it.
5. Standard size. This parameter characterizes the size of the LED emitter. The most commonly used values ​​are 3528, 5050, 5730, 2835, 3014, and 5630. These numbers show the width and length of the SMD matrix. For example, 5730 - the size of the matrix is ​​5.7 mm in width and 3 mm in length. This metric ultimately affects brightness, color temperature, and power.

Driver device

The LED lamp driver is actually a power supply that stabilizes the current through the diode crystal. With all the variety of schemes for 220 V LED lamps, their principle of operation is the same. It consists in lowering the AC input voltage to the desired value and maintaining it at the same level regardless of changes in the input.

A specialized controller, an adjustable integrated stabilizer, resistor circuits can be used as the main element. But the most commonly used chips are pulse width modulation (PWM). They have the most stable and reliable parameters, providing the required output voltage.

The controller-based driver works on the principle of pulse frequency modulation. The input mains voltage is rectified by means of a diode bridge and fed to a capacitor, which is a filter element. Further, the signal goes to the input of the microcircuit, inside which it is converted into a constant value burst of pulses. These pulses drive a key element of the circuit, which is a field-effect transistor (Mosfet).

The incoming pulse opens the transistor and current begins to flow through the LEDs, while the inductor accumulates energy. As soon as there is a pause between the pulses, the Mosfet closes, and the current is supplied by the stored energy from the inductor. This process repeats in a cycle with a high frequency, so a sawtooth current flows through the LED diode.

The following microcircuits are most often used:

• HV9910.
• HV9961.
• CC28810.
• UCC28810.
• PT4115.
• RCD-24.

The driver pulse frequency is determined by the microcircuit strapping, and its stabilization is determined by comparing the reference potential difference of the controller with the value on the current sensor. LEDs are more sensitive to power quality than other light sources. Exceeding the current parameters by 15% will shorten their service life several times. Therefore, you should be especially careful when repairing or replacing a driver.

Self repair

There are no specialized service centers for the repair of LED lamps. In the event of a guarantee, they are simply exchanged for new products, and the old ones are disposed of. Although there are some breakdowns that are easy to fix with your own hands. Therefore, if the warranty replacement is denied, you should try to repair the 220 V LED lamp yourself. But before that, you need to figure out why the bulbs burn out. The reasons may be:

1. Voltage surges in the 220V network. High voltage at the input can cause a breakdown in the LED lamp driver and lead to burnout of the emitting crystals. To prevent this from happening, you should use protective devices at the electricity input, for example, a protection relay.
2. Incorrectly selected lamp. As a result, the LED lamp will not be provided with the required cooling, which will lead to its overheating and combustion. Therefore, when installing a light bulb, you should always pay attention to the instructions for the luminaire, which indicates its maximum permissible power.
3. Low quality elements used in the manufacture of the light source. To avoid such a problem, it is necessary to purchase only products from well-known manufacturers that have a mandatory certificate.

Dismantling the LED illuminator

It will not work to fix the lamp without disassembling it. Although they differ in their forms, their constructs are very similar to each other. So, in the lower basement part, which is screwed into the cartridge, the device driver itself is located. Above it is a radiator plate on which the LEDs are located. From above, they are closed with a cap, which can be transparent or matte. Disassembly of any type of lamp begins with removing the protective cap, and after that the driver is removed.

Therefore, for example, knowing how to disassemble an e27 LED lamp, you can disassemble other types of socles by analogy. Moreover, the most common type is just the E27 and its smaller copy - E14 (minion).

The structure of the lamp includes the following parts:

• protective cap;
• base;
• radiator with a set of LEDs;
• power driver.

Normal manufacturers make the top cap made of plastic, which is then fastened to the basement base. But at the same time, there is one caveat - a sealant is used to fix the top cover.

In order to separate the halves, a sharp instrument should be prepared. It can be a knife or a point bent with the letter "G". A tool is inserted under the dome of the lamp and the glue applied to it is removed in a circular motion. As soon as the glue is removed, the dome is removed by light shaking and pulling upwards.

This will open access to the radiator with LEDs. This radiator is pushed on with the same sharp object and pushed onto itself. Two wires will go from it, going to the lamp driver. If their length is not enough to remove the electronics board and the LED plate, then the wires are unsoldered.

Trouble-shooting

The most common cause of damage is a burned-out LED. Its integrity can be easily checked with a multimeter by switching it to vertebra mode. The red probe touches the anode (plus), and the black one - the cathode (minus). The working LED should light up. If it does not light up or a black dot is visible on its body, it is faulty. It is impossible to fix it, so you should solder it out, and a worker should be soldered to this place.

When desoldering, you may be faced with the fact that the soldering iron will simply stick to the LED body. This indicates insufficient power of the soldering iron and well-organized heat removal from the crystal. Therefore, you will need to use an infrared station or a soldering iron with a higher power.

If the LEDs are OK, then the cause of the failure is in the driver. First of all, the presence of voltage is checked both at the input and at the output of the board. In their absence, a common problem is a burst soldering or a faulty electrolyte located in the circuit after the diode bridge. It is also the cause of the strobe effect. Further, in the continuity mode, the diode bridge and fuses are checked. It will be impossible to check the generation of the microcircuit and the key transistor without an oscilloscope. All defective parts are replaced with the same or their taxes. And then a test switch is made.