An example of a high-power LED driver IC is Linear Technology’s LT3791 -- a rather sophisticated buck-boost LED controller. This device enables a fixed output voltage regardless whether the input voltage is above, below are equal to it. However, unlike a complicated and low-efficiency SEPIC converter, this 4-switch synchronous, single inductor topology not only simplifies the converter design, but also improves the operating efficiency, thereby reducing the power lost as heat.
Figure 1: 100W LED driver for high bay lighting with 98.5 percent peak efficiency using the LT3791
Click on image to enlarge
As can be seen from Figure 1
, a 100W high bay lighting driver schematic, delivering a 33.3V/ 3A output the conversion efficiency is close to 96 percent across the entire input voltage range.
Some of its key features include a very wide input and output operating voltage range of up to 60V. For optimum and uniform light output of the LEDs within the string, it also provides very tight output voltage accuracy of +/- 2 percent and +/-6 percent LED current accuracy and +/-6 percent input current accuracy (over line, load and temperature).
For ease of use, the LT3791 can use either PWM or analog dimming. Its 4-switch buck-boost topology not only supplies seamless transition between modes, but gives very low noises in all of these modes, including the pass through mode where VOUT
– something which is very difficult to do, especially is a load transient event occurs during this mode! Furthermore, it has both input and output current regulation for maximizing system performance and reliability. Since this device is expected to be used in environments that are subjected to wide ambient temperature variations, this part is available in H Grade, meaning that it has an operating junction temperature range of -40°C to +150°C.
LEDs' bright future
It is clear that the efficacy of LEDs, coupled with their commercial price points, have crossed the inflection point at which they can be embraced for many lighting applications. The two examples given at the beginning of this article are just a few among the myriad of deployments occurring around the world today. The day of the LED is upon us. So I feel justified in saying; “Go LEDs Go!”
Tony Armstrong, director of product marketing, Power Products, Linear Technology Corporation, firstname.lastname@example.org
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