1. Don’t Be a Sunday (LED) Driver HDDG #0xF Jason Cerundolo

2. LEDs!

3. Throwie

4. Problem

5. Shunt Resistor I led = 2 mA V led = 1.8 V V R = V batt – 1.8 V I R = 2 mA R = (V batt – 1.8 V)/(2 mA) Vbatt = 3.0 V R = 1.2 V / 2 mA = 600 Ohm

6. Microcontroller Control LED power sourced by GPIO pin R = (5.0 V – 1.8 V)/(2 mA) R = 1.6 kOhm

7. Microcontroller Control LED power sunk by GPIO pin

8. Microcontroller Control Pros Different supplies for LED and MCU Sink more current than source Cons Watch your max rating on GPIO voltage

9. PWM Control Pros Cheap Easy Cons Possible strobing effect Max f PWM = f CLK / 2^n Ideally f PWM > 500 Hz

10. Current Control vs Voltage Control Maxim Application Note 3256

11. Why Current Control? Avoid max current Control brightness Control white balance

12. Linear Current Control I led = 200 mA V R2 = V BE = 0.6 V R = 3 Ohm V cc > V led + 1.5 V P waste = (V cc – V led ) * 200 mA PWM Control available

13. Switching Current Control More efficient But this is a voltage supply…

14. Switching Current Control V FB = 0.5 V I LED = V FB /R P waste = 0.5 V * I LED No output cap Be careful about using EN pin for PWM control

15. Buck Converter Details Methods for Dimming Control PWM on EN pin Override V REF Add to V FB

16. PWM Dimming P waste = 0.1 V * I LED Minimum on time 6 cycles 1.5 MHz switching frequency 8 bit control => f PWM = 1.5 MHz / (6 * 2^8) = 977 Hz Datasheet recommends 500 Hz

17. Analog Dimming Vctrl [V] V R1 [V]

18. Better PWM Control Pro FET provides a sharper turn-off Con Make sure you can switch the FET V TH_EFF = V TH + V FB

19. Multiple LEDs Maxim Application Note 3256

20. Multiple LEDs Only turn on one LED at a time LEDs can be different types (eg, red, green, and blue)

21. Multiple LEDs Turn on any number of LEDs, as long as D1 is active All LEDs must have similar I-V curve

22. Strings of LEDs Multiple LEDs in series All LEDs have same current Vcc > n*V f + V FB

23. Boost Converter Driver Multiple LEDs in series All LEDs have same current Output cap is back Vcc < n*V f + V FB V max > n*V f + V FB

24. Putting it all together https://github.com/ReclaimerLabs/Dronelight

25. Thank You Twitter: @AscendedDaniel Website: http://reclaimerlabs.comhttp://reclaimerlabs.com Github: https://github.com/ReclaimerLabs/https://github.com/ReclaimerLabs/

26. More Information https://www.maximintegrated.com/en/app-notes/index.mvp/id/3256 http://electronics.stackexchange.com/questions/55823/how-can-i- efficiently-drive-an-led http://electronics.stackexchange.com/questions/55823/how-can-i- efficiently-drive-an-led http://www.analog.com/library/analogdialogue/archives/47- 03/smart_led_driver.html http://www.analog.com/library/analogdialogue/archives/47- 03/smart_led_driver.html

28. RGB LED Matrix Panel

29. Integrated IC LEDs