Electronic Ballast Fundamentals

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

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Start up circuit

• http//home.howstuffworks.com/

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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

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Rapid start

• http//home.howstuffworks.com/fluorescent-lamp5.ht
  m

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Basics of Electronic Ballasts
C1
L
C2

• Half bridge configuration
• The resonant circuit strikes on the lamp

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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 ltstart1gt

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Run
i(R3) V(C2)

• In the steady state the lamp resistance reduces
  greatly
• current is controlled by L C1
• Ref ltsteadygt

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Typical operating points
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Types of Ballast circuits

• Self oscillating circuit
• IC driven circuit
• New Capacitor Couple Converter (CCC) circuit
  developed at the HKU Power Electronics Lab

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Self Oscillating Ballast

• Simple low cost

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IC driven Ballast

• Easy to design

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CCC Ballast
Load101

• Low loss zero voltage switching
• Reliable automatic power limiting

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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

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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

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References

1. http//home.howstuffworks.com/
2. http//www.repairfaq.org/sam/flamp.htmint0
3. HID Electronic Ballast Testing Public Interest
   Energy Research Program (PIER) Program,
   California, USA
4. T. Ribrarich A Systems Approach to Ballast IC
   Design IR Technical notes.