Download 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
 The lamps are much cooler than
incandescent lamps
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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
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Lamp structure
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http://home.howstuffworks.com/
How does it work?
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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
How does it work?

http://home.howstuffworks.com/
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
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http://home.howstuffworks.com/
Conventional starter switch
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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
Starter switch
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.htm
Basics of Electronic Ballasts
C1
L
C2
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Half bridge configuration
The resonant circuit strikes on the lamp
Lamp preheat & ignition
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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>
Run
i(R3)
V(C2)
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In the steady state the lamp resistance reduces greatly
 current is controlled by L & C1
Ref <steady>
Typical operating points
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
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Simple & low cost
IC driven Ballast
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Easy to design
CCC Ballast
Load101
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Low loss – zero voltage switching
Reliable – automatic power limiting
Look up references on the web
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Encyclopedia
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Books
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http://www.knovel.com/knovel2/default.jsp
Company web sites
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http://www.britannica.com/
http://www.irf.com/technical-info/
IEEE/ IEE papers
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http://ieeexplore.ieee.org/Xplore/DynWel.jsp
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.
2.
3.
4.
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.