This article is contributed by Arrow Electronics Co., Ltd.
Compared with traditional halogen low-voltage lighting, the use of high-brightness LEDs as interior decorative lights, landscape lighting, street lighting has many advantages. High-brightness LEDs provide greater brightness with less power consumption, and are energy-efficient, environmentally friendly, and low-cost to use. For example, Cree's XLamp XR-E LEDs provide 100 lumens of brightness with only 1W of power, and less than 80 XR-E LEDs can achieve general street lighting requirements. In addition, because XLampLEDs have a long life, LED lamps do not require expensive lamp replacement, which can reduce the total cost of street lighting.
The biggest challenge in high-brightness LED lighting design is heat dissipation. General lighting applications require placing several or a large number of LEDs in a single module to achieve the desired brightness. Concentrating multiple LEDs in a limited space will cause heat dissipation difficulties. Thermal issues can be solved by choosing a high quality solution with reasonable electronic design and thermal control. Arrow provides a comprehensive, high-quality, high-brightness LED lighting application solution. This article will focus on the application of MCUs, LED drivers and protection components in high-brightness LED lighting.
The MCU provides intelligent control of dimming LED illumination, eliminating low frequency flicker, and maintaining constant current. In general, LEDs have non-linear VI characteristics that require current limiting to prevent power consumption from exceeding the maximum budget, so a stable current source is the ideal power source for driving LEDs. Arrow's LED stable constant current source solution based on Freescale's 8-bit microcontroller MC9RS08KA2 (shown in Figure a) enables a small LED source with light-dark control through different current settings. . The implementation of the entire solution is very simple, its main features include: high-luminosity LED driver with 350mA current drive capability; control of the power supply voltage by controlling the buck converter to match the pre-voltage requirements of different LEDs; up to 80% efficiency Internally generate PWM switching frequency; realize feedback control on LED through current sense resistor; single-button light and dark control.
Figure: (a) LED constant current drive circuit based on Freescale's MCU MC9RS08KA2; (b) Typical application schematic of IR's IRS2540.
The buck converter can drive a high-brightness LED driver with three Ni-NH batteries and one lithium-ion battery. It can provide 3~4V output voltage and up to 1A output current. Most of the LED driver circuits based on buck converters require only 3 to 6 external components, and the circuit is very simple. Medium voltage LED drivers have flexible input voltages and output voltages. These drivers can drive more than one high-brightness LED string or array due to the very large output current. The high-voltage LED driver can be connected directly to a normal offline input (85~265V), which provides very high current and voltage. Most designs based on high voltage LED drivers use non-isolated connections that are more efficient than isolated designs.
International Rectifier (IR)'s IRS2540 and IRS2541 are high-voltage, high-frequency buck regulator control ICs that are ideal for AC/DC off-line non-isolated applications that require multiple LED circuits or DC/DC color mixing capabilities. The IRS2540 and IRS2541 are rated at 200V or 600V, and they feature a continuous-mode time-delay hysteretic buck regulator that uses an accurate on-chip bandgap reference to keep the average load current error within 5%. An external high-side bootstrap circuit drives the buck components up to 500kHz. Figure b shows a typical application schematic of the IRS2540.
When the LED lamp is connected incorrectly and misused, it will cause a large overload current and short circuit, and isolate the critical circuit to avoid damage to expensive components. PPTC devices are often used to protect circuits that have large inrush currents at startup. Fuse is suitable for use in circuit designs that do not require recovery, or where failure occurs only when the system fails. Tyco Electronics' nanoSMD and nanoSMD Series PolySwitch recoverable devices protect against excessive current damage. They are unaffected by the startup current and operate from 0.005 to 2.6 A. They operate very fast and have low mounting resistance on the board.
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Eversatis International Co., Ltd , http://www.eversatislight.com