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Vol 87, September 2006
61
Power Factor Correction in Electronic Ballasts for Compact Fluorescent
Lamps
Bhim Singh, Fellow
V Khadkikar, Non-member
This paper deals with the development and comparison of various types of high power factor electronic ballasts for compact fluorescent lamps
(CFL). Electronic ballasts using passive power-factor correction (PFC) techniques and active PFC technique are designed, developed and tested
for a 20W CFL. Self-oscillating circuits are used to provide cost effective electronic ballasts for CFL. A comparative study is made in terms
of ignition voltage and current, ac mains current waveforms, its rms value, total harmonic distortion (THD), crest factor, third harmonics,
input power, power-factor and output lumens for general low cost, passive PFC based valley fill and charge clamp topologies and active PFC
topology with and without EMC filter based ballasts. The proposed active PFC based ballast with EMC filter results in high level of
performance of CFL in terms of power-factor of order of 0.999, THD of ac mains current of 4.7% and its crest factor of 1.42.
Keywords :
Electronics ballast; Power-factor correction; Vally fill electronics ballast; Charge pump passive; IFC based electronic ballast
INTRODUCTION
Power engineers are becoming more concerned about the quality of
supply system due to massive use of semiconductor devices almost
in all application areas. Therefore, power quality standards are being
imposed worldwide in order to maximize the efficiency of the
electrical equipments in utilizing existing generated power. Adding
additional generating capacity of electrical equipment is becoming
difficult and expensive because of environmental constraints.
Therefore, the onus for improved efficiency of different electrical
gadgets falls on the power users rather than power suppliers. During
the last few years the cost of electric power is increasing considerably
and the problem of energy saving becomes important and relevant.
Artificial illumination consumes more than 25% of electricity
generated over the world. Therefore, any improvement in efficiency
in artificial illumination system is desirable. Case studies show that
proper designing of high frequency electronic ballast can save upto
40 % to 50 % energy
1
. However, existing fluorescent lamps with
electronic ballast have power quality problems in terms of high value
of total harmonic distortion (THD) of the supply current, high
crest factor and poor power factor
2, 3
.
Most incandescent lighting systems do not cause the power quality
problems in a distribution system because they have sinusoidal current
waveforms that are in phase with the voltage waveform. Fluorescent
and high intensity discharge (HID) and low voltage incandescent
lighting systems, which use ballasts or transformers, may have
distorted current waveforms
2-25
. Highly distorted current waveform
is typical of some electronic ballast for fluorescent lamps. Devices
with such distorted current waveform draw current in short bursts,
which creates distortion in ac voltage. Both lighting manufacturers
and building owners are seriously concerned to improve power
quality.
High frequency electronic ballast operates ranging from 20 kHz
to 60 kHz, which is achieved by ac-dc-ac converter
4
. The harmonics
produced by these ballasts are at correspondingly high frequencies
and can interfere with communication equipments including radio,
intercoms and cordless phones. The recent trend is to equip the
lighting system in such a way that it can provide the regular and clean
power to the loads without polluting the input power supply
6-25
.
High efficiency, high frequency electronic ballasts offer enhanced
lighting performance and energy savings. The Electric Power Research
Institute (EPRI) of US has estimated that lighting consumes 20 %
- 25 % of all electric power and that lighting energy accounts for 40%
of the average commercial electric bill. The retrofit of existing facilities
with modern lighting systems increases productivity and can save
over one-half the energy of the original system.
The problems associated with conventional lighting systems with
magnetic ballast are follows
6
.

Flickering with 50 Hz input power supply;

Low power factor (0.4 to 0.6);

High THD of the supply current;

High crest factor of the supply current;

Large size and weight; and

Audible noise.
Electronic ballasts for fluorescent lighting systems have become the
standard now-a-days in the industry and further advancements
continue to increase the benefits of using electronic ballast. Following
is a summary of the advantages of electronic ballast technology
6,7,9
.

Greater efficiency

For T8 lamps, the overall lamp / ballast system efficacy can be
as much as 15% to 20% higher than magnetic ballast systems.

Electronic ballasts do not generate as much internal heat,
thereby reducing losses within the ballast itself.

Electronic ballasts are available that provide continuous, flicker
free dimming for most fluorescent lamps.
Bhim Singh and V Khadkikar are with the Department of Electrical
Engineering, Indian Institute of Technology, Hauz Khas, New Delhi 110 016.
This paper was received on September 02, 2003. Written discussion on this
paper will be entertained till December 31, 2006. 62
IE(I) Journal-EL

Better control and design flexibility.

Ability to drive more lamps

Reduced lamp flicker

Lighter in weight: Electronic components are not as heavy as
the coil and core used in magnetic ballast.

Quieter operation: Electronic components do not hum as
the core and coil components of magnetic ballast do.

End of life sensing
As already mentioned, existing fluorescent lamps with electronic ballast
have power quality problems in terms of high value of total harmonic
distortion (THD) of the supply current, high crest factor and poor
power factor and a number of attempts have been made in the past
to improve the performance of electronic ballasts
4-25
. Various
topologies of passive PFC based, namely, valley filled
4,14,21
, charge
clamped
5,8,11,13,15,19,20, 22,23
and active PFC based ballasts for discharge
lamps have been reported
16,25
.
This paper presents the design, development, testing and comparison
of various power factor correction techniques used in electronic ballast
for CFL. Electronic ballasts using passive PFC and active PFC circuits
are developed and tested. In all cases the basic operating principle is
based upon self-oscillating technique. The final proposed active PFC
based ballast with EMC filter has a power factor of 0.999 and ac
current THD of 4.7 % and crest factor of 1.42.
ROLE OF BALLAST
In the normal operation mode, discharge lamps and fluorescent
lamps show a negative differential resistance. Fluorescent lamp
behaves as a V-I characteristic with negative dynamic resistance after
the avalanche phenomenon is initiated, where the gas becomes
plasma. At high frequency, since the plasma density does not change
appreciably with variation of lamp voltages during operation, the
lamp appears as a current controlled resistor. This resistance decreases
with the increase of lamp current and the decrease of lamp voltage.
In other words, it behaves like a negative dynamic resistance. Therefore
a means to limiting the lamp current is essential.
Thus, when an arc is initiated in a fluorescent lamp, the lamp exhibits
a negative resistance characteristic. The resistance to current flow
through the lamp decreases as the current increases. This runaway
current condition would destroy the lamp in a few seconds if allowed
to occur. An auxiliary device, ballast, is required to limit current and
prevent this condition. In addition to limiting current, the ballast
has to provide the proper voltage for the lamp starting and for
normal operation. Generally an ac inductor is used as ballast element,
which is called as magnetic ballast or choke. The impedance of the
choke determines the limit of lamp current.
Electronic ballast for a fluorescent lamp is a circuit that functions as
a high frequency current source. Before the lamp turns ON, lamp
impedance is very high and thus generates enough high voltage to
start the lamp. After the lamp turns ON, lamp current is stabilized at
a desired value by the ballast. Inductor size reduces with increase in
frequency, and noise produced by the inductor is also reduced beyond
human audible range.
CIRCUIT TOPOLOGIES AND DEVELOPMENT
Different topologies of PFC techniques used in electronic
ballasts
4-25
are studied in detail and it is decided to develop four
circuits of PFC based electronic ballasts along with generally used
low cost ballast. These ballasts are designed for 20W compact
fluorescent lamp (CFL) to operate at 230 V, 50 Hz supply. The
operating principle is based on self-oscillating half bridge series
resonant parallel loaded inverter topology. In this section the
description of developed electronic ballasts without any PFC, with
passive based PFC and active PFC based circuits are given. Following
ballasts are considered in this work.
1. General low cost electronic ballast.
2. Valley fill passive PFC based electronic ballast.
3. Charge pump passive PFC based electronic ballast.
4. Boost active PFC based electronic ballast.
5. Boost active PFC based electronic ballast with EMC filter.
General Low Cost Electronic Ballast
The overall configuration of low cost generally used ballast is shown
in the Figure 1. A single-phase 230V, 50 Hz ac supply is converted
into dc by using diode bridge rectifier D1-D4. The capacitor C1 charges
to peak value of supply voltage which is around 315V