However, there is still room for further improvement in terms of energy conversion efficiency, thermal management and production costs. For example, LED efficiency has been greatly improved. Many improvements in LEDs have resulted in better light generation within the chip and a better way to obtain light sources from the chip and its packaging. Similarly, the price of the 20mA white LED has been greatly reduced. When the LED was first introduced, the purchase price was $1. At present, it is possible to buy a 20 mA white LED at a purchase price of less than 30 cents.
LED lighting application needs analysis
Of course, all of these advancements have not only contributed to the use of LEDs as illumination sources in different applications, but have also spurred demand for LED driver ICs. To understand the obstacles to designing and manufacturing LED driver ICs, it is necessary to understand what conditions are required for white LEDs to emit light. The white LED must be driven with a constant current source so that the white spot does not change (ie the brightness must be the same). In addition, since the white LED is a diode, its internal forward voltage drop (Vf) must be overcome. Vf varies with the white LED current value and also with temperature. In general, the Vf of a 20 mA white LED varies from 2.5 V to 3.9 V over the entire operating temperature range. Most applications use multiple white LEDs, and it is also possible to configure these LEDs in parallel, series or series-parallel hybrids. This means that a white LED driver IC must be able to supply enough current and voltage for multiple LEDs in a particular configuration, and the voltage conversion topology used in this IC must meet both the input voltage range and the output voltage and current requirements.
Common applications for LEDs include display and indication of automotive and aircraft dashboards, traffic lights, cell phones, flat panel display backlights, miner lights, buildings and large stadium lighting, and the biggest driver of LED market growth in the coming and future years. Backlighting requirements from flat panel displays. These displays use LCD screens for televisions, navigation systems, portable media players, digital billboards and computer monitors. However, the adoption of LEDs faces the technical challenge of thermal management. Although LEDs do not radiate as much heat as other light sources, depending on the output power, some LEDs may require a suitable heat sink so that the light output is not reduced and the lifetime is not shortened. For example, a high brightness LED with a light output of 25 lm typically consumes more than 1 W of power. This means that the white LED driver IC must be converted with high efficiency so that it does not become a major cause of thermal problems. In addition, there are space constraints in many cases, and the LED driver solution must have a small footprint and a small form factor.
In the case of mobile phones, most mobile phones today have built-in digital cameras that can take high-resolution photos and videos. The increase in camera performance has also led to the need for high-power white light sources that need to be used indoors or in dimly lit environments. White LEDs have become the primary source of light for camera phones. Because white LEDs have many of the features that modern mobile phone designers want: small size, high light output, and the ability to provide "flash" and continuous illumination of "video" objects. High output power LEDs have been developed specifically for integrated camera lighting.
Portable product lighting solutions
Although it is easy to generate visible light with high-power LEDs, it is very difficult to form high-performance power and current control solutions without modifying existing designs. Linear Technology's LTC3454 is a new product designed to improve power conversion efficiency and accuracy in high current camera lighting applications and optimize LED current control.
Figure: High Power PWM LED Driver Circuit Based on LTC3783
The LTC3454 is a synchronous buck-boost DC/DC converter optimized for driving a single high-power LED with a single-cell Li-Ion battery input at currents up to 1A. The device automatically switches between synchronous buck, synchronous buck, and 4-switch buck-boost mode, depending on the relationship between VIN and LED forward voltage. PLED/PIN efficiency above 90% can be achieved over the entire available Li-Ion battery voltage range (2.7~4.2V).