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LED Driving Fundamentals: Circuit Design & Power Optimization Lab

Learn the basics of LEDs, circuit design, and power optimization in this module. Understand LED structure, characteristics, and power equations. Engage in team exercises to build and analyze LED circuits with different power sources.

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LED Driving Fundamentals: Circuit Design & Power Optimization Lab

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  1. Smart Lighting Lab Module 3: Driving LEDs Instructor: Sara Grier

  2. What is an LED? • Light Emitting Diode • Semiconductor light source • Diode – conducts current in only one direction; forward biased • Light emitted at characteristic wavelength/color • Color determined by chemistry of diode • Come in various packages • Can be assembled into arrays

  3. Schematic of an LED 1 = Cathode 2 = Anode

  4. Structure of an LED

  5. Diode Junction – “I-V curve”

  6. Intensity vs. Wavelength

  7. Schematics vs. Pictures

  8. Useful Circuit Equations • V=IR • V  Voltage • I  Current • R  Resistance • P = IV • P = V2/R • P = I2R • P  Power

  9. Duty Cycle and Power • Duty cycle – On and Off ; Low duty cycle  Low Power • D = t/T • t duration function is high • T  period of the function • D  duty cycle • Pavg/Po = t/T • Po  Peak Power • Pavg  Average Power

  10. Lab Procedure • Team Exercise 1 • Build circuit to display a current-voltage characteristic for one of our LEDs • Setup the circuit as shown in schematic, connecting wires to the proper pins on the Rhett Board • Open the ‘Function Generator’ tab • Set channel 1 to a 1kHz sine wave with 7V p-p and 0V DC offset (the LED should come on) • Open the ‘Oscilloscope’ tab • Channel X Settings: • Volts/Div: 2V • Coupling: DC • Input: A1 SE • Channel Y Settings: • Volts/Div: 2V • Coupling: DC • Input: A2 SE • Horizontal Settings • Time/Div: 1ms • Mode: X-Y • What is Vf? • Record a screenshot • What are the characteristics of the LED we are using? • How about the white LED?

  11. Team Exercise 2 • Design circuit to power LED with DC input from fixed voltage (resistor in series) • Identify the anode and cathode of the LED. • What voltage and resistance do we need to achieve 30mA? • For the specs of the LEDs we use and a target power level of < 85mW . • What resistor will yield this LED power level.? • Build it. • How much power is wasted in this scheme?

  12. Team Exercise 3 • Design a circuit to power a LED with PWM • The Rhett Board current limits at 50mA. Power can be limited using a duty cycle. • What duty cycle can yield a power level of 17mW? • Implement your scheme using the PMW1 control.

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