8/13/2019 MAX16820 HB-LED PWM Auto Dimming

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Used in industrial, architectural, and automotive applications, as well as for warning lamps and emergency lights, high-

brightness power LEDs ( HBLEDs are becoming more and more popular, due in part to their relatively high efficiency

and long life! However, to achieve optimal lighting when ambient light is not constant, the driver circuit should be

capable of varying the LED brightness automatically!

Fig. 1 shows a typical operating circuit for the "#$%&' )! # modification to this circuit yields a stand-alone brightness

regulator ( Fig. 2 , which re*uires no microprocessor or microcontroller!

http://powerelectronics.com/power_management/led_drivers/led-lighting-system-optimized-201101http://powerelectronics.com/images/Standalone-Brightness-fig-1-210.jpghttp://powerelectronics.com/images/Standalone-Brightness-fig-2-210.jpghttp://powerelectronics.com/power_management/led_drivers/led-lighting-system-optimized-201101http://powerelectronics.com/images/Standalone-Brightness-fig-1-210.jpghttp://powerelectronics.com/images/Standalone-Brightness-fig-2-210.jpg

8/13/2019 MAX16820 HB-LED PWM Auto Dimming

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+t increases LED brightness when the ambient-to-LED ratio rises, and reduces brightness when that ratio declines! he

circuit operates with a supply voltage of & (four %!.- ## cells in series , and consists of three main sections/

#mbient light sensor 0% (1sram 23H45%) for visible-light wavelengths in the 4.)- to 67)-nm range

LED driver ("a8im "#$%&' ) with 9:" dimming input #nalog-to-9:" signal converter that converts the measured analog signal (proportional to light to a 9:" signal

for use in regulating the LED driver

Because the constant-current driver ("#$%&' ) includes a step-down converter, the efficiency is high (typically 6); !+ts operating voltage range is 5!. to ' , and it delivers up to . : of output power! his output is proportional to thelight intensity, which can be ads Dim input, ma?ing LED brightness

proportional to the brightness of the environment! o achieve the inverse regulation, you can insert an inverter in front

of the 9:" converter circuit!