Lighting devices, where ultra-bright LEDs are used as light sources, will not surprise anyone. The demand for such devices is constantly growing, this is directly related to the low power consumption of these devices. Given that about 25-35% of the electricity consumed is spent on lighting, the savings will be very tangible.

But given the relatively high cost of ultra-bright LEDs, due to their design features, it is not yet time to talk about a complete transition to this type of lighting. According to experts, this process will take from 5 to 10 years, this is how long it will take to debug and introduce new technologies.

The efficiency of a lighting device is considered to be the ratio of the generated luminous flux (measured in lumens) to the electricity consumed (watts). A high-quality filament lamp has an efficiency of about 16 lumens per watt, a fluorescent (energy-saving) one four times more (64 lm / W), for long daylight lamps this figure is around 80 lm / W.

The efficiency of ultra-bright LEDs, which are currently mass-produced, is approximately the same as that of fluorescent lamps. Please note that we are talking about mass production. As for the theoretical limit for ultra-bright LED sources, it is defined by a threshold of 320 lm/W.

As many manufacturers promise, in the next few years, the efficiency can be increased to the level of 213 lm / W.

Influence of design features on cost

For the manufacture of ultra-bright LED light sources, one of two methods can be used:

• to obtain light close to white in spectrum, three crystals are used installed in one housing. One is red, the second is blue and the third is green;
• a crystal is used that emits in the blue or ultraviolet spectrum, it illuminates the lens coated with a phosphor, as a result, the radiation is converted into light that is close in spectrum to natural.

Despite the fact that the first option is more effective, its implementation is somewhat more expensive, which negatively affects the prevalence. In addition, the spectrum of light emitted by such a source differs from natural.

Devices made using the second technology have less efficiency. It should also be taken into account that the luminophor contains a complex composite based on cerium and yttrium, which are not cheap in themselves. Actually, this explains the relatively high cost of ultra-bright white light LEDs. The design of such a device is shown in the figure.

Designations:

• A - printed conductor;
• B - base with increased thermal conductivity;
• C - protective case of the device;
• D - solder paste;
• E - LED crystal emitting ultraviolet or blue light;
• F - phosphor coating;
• G - glue (can be replaced by a eutectic alloy);
• H - wire connecting the crystal and output;
• K - reflector;
• J - heat-removing base;
• L - power output;
• M is the dielectric layer.

Mounting Features

The operation of superbright LEDs is affected by the degree of heating of the crystal and the p-n junction itself. The service life of the device directly depends on the first, the level of the luminous flux depends on the second. Therefore, for a long service life of superbright LEDs, it is necessary to organize a reliable heat sink, this is done using a radiator.

It should be appreciated that the thermally conductive bases of these semiconductors generally conduct electricity. Therefore, when several elements are installed on one radiator, care should be taken to ensure reliable electrical insulation of the bases.

The rest of the installation rules are almost the same as for conventional diodes, that is, polarity must be observed, both when installing the part itself and when connecting the power.

Nutrition Features

Given the relatively high cost of ultra-bright LEDs, it is very important to use reliable and high-quality power supplies for their operation, since these semiconductor elements are critical to current overload.

After an emergency mode, the device may remain operational, but the power of the emitted light flux will be significantly reduced. In addition, such an element is likely to cause damage to other jointly connected LEDs.

Before talking about drivers for ultra-bright LEDs, let's briefly talk about the features of their power supply. First of all, you need to take into account the following factors:

• the power of the light flux emitted by these elements directly depends on the magnitude of the electric current flowing through them;
• superbright LEDs are characterized by a non-linear CVC (voltage-ampere characteristic);
• temperature has a strong influence on the IV characteristics of these semiconductor devices.

Below is the change in CVC at a temperature of a semiconductor element (superbright smd-LED) 20 ° C and 70 ° C.

As can be seen from the graph, when a stable voltage of 2 V is applied to the semiconductor, the electric current passing through it changes depending on temperature. When the crystal is heated to 20°C, it will be equal to 14 mA, when the temperature rises to 70°C, this parameter will correspond to 35 mA.

The result of such a difference will be a change in the power of the light flux at the same supply voltage. Based on this, it is necessary to stabilize not the voltage, but the electric current passing through the semiconductor.

Such power supplies are called LED drivers, they are ordinary current stabilizers. This device can be purchased ready-made or assembled by yourself, in the next section we will give some typical driver schemes.

Homemade LED Driver

Let's bring to your attention several options for drivers based on specialized microcircuits from the Monolithic Power System, the use of which greatly simplifies the design. The schemes are given as an example, a complete description of a typical inclusion can be found in the datasheet for the microcircuits.

The first option is based on the MP4688 step-down converter.

This driver can work with voltages from 4.5 to 80 V, the maximum output electric current threshold is 2 A, which allows you to power the lamp on high-power ultra-bright LEDs. The level of electric current passing through the LEDs is regulated by the resistance R FB. The implementation of PWM dimming with a frequency of 20 kHz allows you to smoothly change the current flowing through the LED.

The second version of the driver based on the MP2489 chip. Its compact housing (QFN8 or TSOT23-5) makes it possible to place the driver in the MR16 base used by halogen lamps, which allows replacing the latter with LED ones. A typical MP2489 connection diagram is shown in the figure.

The above circuit allows you to turn on two parallel LEDs, each with a working current of 350 mA.

The latest version of the driver based on the MP3412 chip, which can be used in portable flashlights. A distinctive feature of such a circuit is the ability to work from an AA battery.