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Electronic Ballast Fundamentals

Electronic Ballast Fundamentals. Dr. Bryan M.H. Pong Hong Kong University. Fluorescent tubes. Much more efficient than incandescent lamps : 2 to 4 times more efficient The lamps last a lot longer – 10k to 20k hours versus 0.75k to 1k hours for an incandescent lamp

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Electronic Ballast Fundamentals

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  1. Electronic Ballast Fundamentals Dr. Bryan M.H. Pong Hong Kong University

  2. Fluorescent tubes • Much more efficient than incandescent lamps : 2 to 4 times more efficient • The lamps last a lot longer – 10k to 20k hours versus 0.75k to 1k hours for an incandescent lamp • The lamps are much cooler than incandescent lamps

  3. Lamp structure • The lamp is a sealed tube containing mercury vapor and some inert gases such as argon at very pressure • The inside of the tube is coated with phosphor • At the ends of the tube there are filaments or electrodes

  4. Lamp structure • http://home.howstuffworks.com/

  5. How does it work? • When the tube is off it does not conduct • It is turned on by a high voltage which excites the gas inside the tube • Once the tube conducts on a lower voltage is sufficient to maintain conduction • The electric current passes through the gas and emits UV, the internal phosphor coating converters the UV to visible light • The color of the light cab be varied by different combinations of phosphors

  6. How does it work? • http://home.howstuffworks.com/

  7. Lamp starting • When the lamps is off the tube is non -conductive • The tube must be excited or started by a high voltage • After the lamps is started the lamp voltage drops • A current limiting “ballast” is needed in between the power source and the lamp

  8. Start up circuit • http://home.howstuffworks.com/

  9. Conventional starter switch • A mechanical starter switch together with an inductive ballast start up the lamp • The starter switch is a small discharge bulb containing a gas like neon. • When connect to a voltage source the gas breaks down and the switch glows • The heat generated bends the bimetallic switch and closes it • One the switch is closed the glow is turned off and the bimetallic switch cools down and opens • When the switch opens a series connected ballast provides a high voltage and strikes on the tube

  10. Starter switch

  11. High frequency ballast • Conventional ballast produces 100/120Hz flicker • High frequency ballast is more efficient than magnetic ballast [3] • High frequency ballast, like most power electronics products, has smaller size and weight • Integrates ballast and starting functions

  12. Rapid start http://home.howstuffworks.com/fluorescent-lamp5.htm

  13. Basics of Electronic Ballasts • Half bridge configuration • The resonant circuit strikes on the lamp C1 L C2

  14. Lamp preheat & ignition • Before strike on the tube has very high resistance and effectively it is an open circuit • Operation at a high frequency preheats the filaments • Operation near resonance produces high voltage across C2 and strikes on the lamp • Ref <start1>

  15. Run • In the steady state the lamp resistance reduces greatly • current is controlled by L & C1 Ref <steady> i(R3) V(C2)

  16. Typical operating points

  17. Types of Ballast circuits • Self oscillating circuit • IC driven circuit • New Capacitor Couple Converter (CCC) circuit developed at the HKU Power Electronics Lab

  18. Self Oscillating Ballast • Simple & low cost

  19. IC driven Ballast • Easy to design

  20. CCC Ballast • Low loss – zero voltage switching • Reliable – automatic power limiting Load101

  21. Look up references on the web • Encyclopedia • http://www.britannica.com/ • Books • http://www.knovel.com/knovel2/default.jsp • Company web sites • http://www.irf.com/technical-info/ • IEEE/ IEE papers • http://ieeexplore.ieee.org/Xplore/DynWel.jsp

  22. What to do • Understand the fundamentals • Design the circuit and fill in the component parameters • Start to build the circuit in September • Expect a working circuit in December • Further work on lamp characteristics, power factor correction, comparison of topologies & dimming

  23. References • http://home.howstuffworks.com/ • http://www.repairfaq.org/sam/flamp.htm#int0 • “HID Electronic Ballast Testing” Public Interest Energy Research Program (PIER) Program, California, USA • T. Ribrarich “A Systems Approach to Ballast IC Design” IR Technical notes.

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