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Transcript
MODULE 4: LEDs SUMMER CHALLENGE Electrical Engineering: Smart Lighting Michael Rahaim, PhD Candidate Multimedia Communications Lab Boston University [email protected] Module 4: LEDs 07/09/2015 Overview Boston From “Lighting” to Here Smart Lighting University Slideshow Title Goes What is a Diode? LEDs! Electrical Power LED Drivers 2 Module 4: LEDs 07/09/2015 Lighting & Color Science Boston Visible Light is a form of electromagnetic radiation University Slideshow Title Goes Here mm Wave Spectrum 100km 10km 1km 3kHz 30kHz 300kHz 100m 10m 1m 100mm 3MHz 30MHz 300MHz 3GHz 10mm 1mm 100μm 30GHz 300GHz 3THz 10μm 1μm 100nm 10nm 1nm 3PHz 30PHz 300PHz 30THz 300THz microwave Spectrum 780nm 380THz Visible Light Spectrum 400nm 750THz The human eye responds to the visible light spectrum White light is the presence of all colors 3 Module 4: LEDs 07/09/2015 Smart Lighting Boston InUniversity what Slideshow waysTitle can light be better? Goes Here Energy Efficiency Healthy Lighting Productivity (Data access) 4 Module 4: LEDs 07/09/2015 What is a diode? Boston A University device that allows current to flow in one direction Slideshow Title Goes Here Forward Bias Voltage For current to flow, diodes require a forward bias voltage In an ideal diode, voltage drop remains constant Anode Cathode 5 Module 4: LEDs 07/09/2015 Kirchhoff’s Voltage Law Boston The algebraic sum of all voltages in a loop must equal 0 University Slideshow Title Goes Here I + R1 𝑉0 + −𝑉1 + −𝑉2 = 0 + A V0 V1 R2 V2 - Relationship to Diode circuits Once the diode reaches the turn on voltage, 𝑉𝑅 increases with 𝑉𝑆 Current through the circuit increases with 𝑉𝑅 + 𝑉𝐷 Decreasing 𝑅 also increases with 𝑉𝑅 + 𝑉𝑆 + −𝑉𝐷 + −𝑉𝑅 = 0 𝑉𝑆 - 𝑉𝑅 + 6 Module 4: LEDs 07/09/2015 LEDs Boston University Slideshow Title Goes Here David Miller Module 4: LEDs 07/09/2015 How Do LEDs Work? Boston LED Materials University Slideshow Title Goes Here Semiconducting materials Current can only flow in one direction Passing through the LED, electrons lose energy Lost energy creates photons Photons have discrete wavelength related to band-gap Band-gap width and energy The wider the band-gap, the greater the energy of the photon released Specialized materials & processes required to achieve wide band-gap Planck’s Relation: E= hc l Module 4: LEDs 07/09/2015 Small Band Gap: Low Energy Red Light Boston University Slideshow Title Goes Here Conduction Band Small Band Gap Valence Band 9 Module 4: LEDs 07/09/2015 Large Band Gap: High Energy Blue Light Boston University Slideshow Title Goes Here Conduction Band Large Band Gap Valence Band 10 Module 4: LEDs 07/09/2015 Experiment I Boston LED circuit University Slideshow Title Goes Here Determining the turn-on voltage 11 Module 4: LEDs 07/09/2015 Electrical Power Boston Power is the rate that energy is consumed. University Slideshow Title Goes Here 𝑃 = 𝑉𝐼 This is another one of those important equations… Power is measured in Watts [𝑊] or [J/s] Energy sources (such as batteries) produce power while the load of the circuit absorbs power. + 𝑉𝐷 𝑉𝑆 − 𝑉𝐷 𝑉𝑅 = 𝐼= 𝑅 𝑅 + 𝑉𝑆 - 𝑉𝑅 + 𝑉𝐷 𝑉𝑆 − 𝑉𝐷 𝑃𝐷 = 𝑉𝐷 𝐼 = 𝑅 12 Module 4: LEDs 07/09/2015 Electric Power 𝑉 = 𝐼𝑅 Boston Combining the previous equation with OHMS LAW: University Slideshow Title Goes Here 2 𝑉2 𝑃 = 𝑉𝐼 = 𝐼 𝑅 = 𝑅 Consider a 60𝑊 incandescent attached to a 120𝑉 source How does current change if you replace the 60W bulb with 120W bulb? 2 120 60 = 𝑅1 2 120 120 = 𝑅2 𝑅2 = 120 = 0.5𝑅1 𝑉 𝐼1 = 𝑅1 𝑉 𝑉 𝐼2 = = = 2𝐼1 𝑅2 0.5𝑅1 13 Module 4: LEDs 07/09/2015 Experiment II Boston LED Drivers University Slideshow Title Goes Here Power Consumption 14 Module 4: LEDs 07/09/2015 Recap Boston What did you University Slideshow Title Goes Here today? 15