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High Efficiency Single-Stage Multi-Fluorescent
Lamps Electronic Ballast
Hung-Ching Lu and Te-Lung Shih
Department of Electrical Engineering, Tatung University, Taiwan, R.O.C.
Abstract- A single-stage electronic ballast topology with the
properties of high efficiency and low stress is proposed in this
paper. The ballast consists of a voltage fed half-bridge
series-resonant series-parallel-load (SRSPL) inverter, playing the
role of lamp driver, and a voltage boost converter, which shares
low side switch device with half-bridge inverter and acts as
power-factor-correction (PFC). The inverter of the ballast is
loaded with resonant tanks which are designed and operated to be
capacitive and inductive to theoretically achieve both of
zero-voltage switching (ZVS) and zero-current switching (ZCS)
that eliminate the reactive current circulating through the switches
to prevent low switching and conduction losses. The boost
converter of the ballast provides sufficient high voltage to ignite the
lamp. In addition, prior to shaping the input current and reducing
harmonic currents to ignite the lamp, a power factor correction
stage is performed by the converter. The merit of a successive
ignition of the lamps can be attained with proposed operation
scheme so that current stress imposed on the switches can be
reduced. The simulation results and experimental measurements
are used to verify the theoretical prediction and analysis.
Index Terms:Single-Stage electronic ballast topology, Half-bridge
Series-resonant series-parallel-load (SRSPL) Inverter, Power Factor
Correction, Multi-Fluorescent Lamps Electronic Ballast
I. INTRODUCTIONIn recent years, electronic ballast has played a very important
role in lighting gears. In fluorescent lamp applications, the
electronic ballast is used widely because of its several
advantages. At high frequency operation, luminous efficacy of
fluorescent lamps is operated higher than 60Hz [1] and long
lamp life can be sustained. Most of the electronic ballast is
realized by resonant inverter operating at high frequency to
provide a sufficient high voltage to ignite the lamp and limit the
current. In conventional multiple fluorescent lamp lightingsystem, each lamp is equipped with its own LC network to
constitute a resonant tank. When all of the resonant tanks are
designed to operate at the same frequencies as the LC network,
the switching losses can be reduced; nevertheless, where
relatively large current will generated and flow through the
switches. This would also result in considerable conduction
losses and undesired current stress. In addition, a
power-factor-correction (PFC) circuit is attached to the ballast,
for the purpose of reducing the input line current harmonics.
The cost has increased when PFC stage cascade in front of
DC-AC inverter. In order to reduce the cost of the electronic
ballast, one single stage converter is used to perform both
function of the PFC and the DC-AC conversion simultaneously.
In this paper, a circuit operation scheme for multiple
fluorescent lamp lighting system is proposed. The scheme is to
operate all of the resonances for each resonant tank. By properly
selecting the component values of the overall tanks, an
equivalent resistive impedance of the overall tank can be derivedso as the switches can theoretically operate with both of
zero-voltage switching (ZVS) and zero-current-switching
(ZCS). Furthermore, conduction losses and current stress on the
switches can be reduced significantly since no reactive current
flows through switches. During startup transition, the lamps are
subsequently ignited because of switching frequency is
controlled to decrease monotonically. Hence, a small transition
peak current, as compared to that in the conventional ballast
system, will follow through switches during the glow-to-arc
transition.
The electronic ballast can be categorized systemically as dual
stage and single stage. The dual stage electronic ballastcompresses three switches and two controllers to consist of
AC-DC boost converter as PFC stage in front and DC-AC
half-bridge Inverter. However, dual stage electronic ballast has
better performance of power factor and current factor, where
cost increased by result of more complex circuitry. Therefore,
single stage electronic ballast was introduced to prevent the cost
drawback of dual stage electronic ballast, which has one switch
and one PFC controller of the boost converter can be omitted
[2-5]. Where the integrated boost converter and half-bridge
resonant inverter as shown in Fig. 1, in which boost converter is
operating in both of discontinue/continue modes with fixed
frequency and fixed duty cycle. The operating behavior is boostinductance current follow phase of input voltage to archive high
power factor [6, 7].
II. CIRCUIT OPERATIONIn this paper, work has been selected with four lamps in the
ballast; however, it could be three, five, six, etc. Next, the basic
multi-lamp requirements can be simply stated as follows:
(1) While a lamp is added; it should be ignited and kept in
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operation independently and should not disturb the operation of
other working lamps.
(2) While a lamp is removed from the light system; other
lamps should be kept in operation without interruption.
Fig 1. The proposed topology of Single-Stage Multi-Fluorescent Lamps
Electronic Ballast
With the above assumptions, that simplified electronic ballast,
explained as a half-bridge inverter, is used to supply the four
lamps, the connections between the lamps and the converter
have to be determined. But, before this discussion, it is
necessary to review the characteristics of the fluorescent lamp
firstly.
These lamps have a negative dynamic resistance behavior
which makes it necessary as the use of a ballast to limit the
current. A lamp modeling development which can predict the
fluorescent lamp electrical characteristics is necessary to do the
simulation of electronic ballasts due to the fluorescent lamp
nonlinear behavior. The lamp equivalent resistance of a
fluorescent can be expressed as
O SH
lamp S
O O H
V RVR R
I V V
= + =
(1)
where VOas well asIO are the rms lamp voltage and current,RS
and VHare defined as the parameters in the plasma model of
lamp.
The resonant tank design basin in [8] the method consists of
choosing the correct phase angle of the LCC resonant circuit that
will concern the lamp starting and the correct lamp power in
steady state. This analysis has just done for one of the lamps, and
the found values are repeated for all other ballast lamps.
Then, the phase angle is determined by
( ) ( )1 1 1 2 2 2 2 2tan 1lamp S P lamp lamp P R L C C R R C = +
(2)
where 2S
f = is the angular switching frequency, is
resonant tank impedance phase angle.
The half-bridge series-resonant series-parallel load resonant
circuits take account of resonant frequency operating characters
have both of capacitance and inductance, where parallel load
being capacitance are provided voltage gain and generated high
voltage with high equivalent lamp resistance to ignite the lamp.
However, the series load has well current regulation with
inductance characteristic, in which the voltage gain is reduced to
decrease the output voltage. When the lamp has beensuccessively ignited; the resonant frequency will be decreased
monotonically. Thus, the current stress imposed on the switches
can be reduced.
The voltage transfer function of the resonant circuit is given
as
2
( ) 1
( ) 1
1
11
1
lamp
lamp P lamp
lampin
S P lamp
PP
S lamp S lamp
R
V j j C R
RV jj L
j C j C R
C LLC j
C R C R
+
=
+ +
+
=
+ +
(3)
The series resonant frequency and CPmore then CSderived as
1S
SLC = (4)
The quality factor with (1) is
lamp
LCQR
= (5)
Take absolute value of (3) can be obtained as
22 2
2
( ) 1
( )
1
lamp
in
SP P
S S S S
V j
V jC C
QC C
=
+ +
(6)
During lamp igniting with character of series parallel resonant,
the lamp equivalent resistor can be considered as open circuit, (3)is used and the quality factor is close to zero, where ignite
voltage can be determined as
2
2 1
1
dc
strike
PP
S
VV
CLC
C
=
+
(7)
And the lamp stable voltage has been ignited can be derived
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as
,22
2
2 1
11
in
lamp rms
PP
S lamp S lamp
VV
C LLC
C R C R
=
+ +
(8)
Since operating frequency is 4 times of resonant frequency [5],
the resonant tank series inductorL and isolation capacitor CS
with operating frequency is expressed as
2S
S
fLC
= (9)
The capacitorCPon the resonant circuit is sustained the lamp
voltage during the lamp ignition,
1P
lamp
CR
= (10)
Therefore, with given stable lamp voltage Vlapm,rms, input DC
voltage Vdc and lamp equivalent resisterRlamp; the equations as
mention above can be solved to obtain resonator inductorL,
capacitorCSand ignition capacitorCP.
The ballast is obtained from the integration of the boost
converter design which considers output voltage is higher than
input voltage, which provides minimum ignition voltage and
operating voltage after lamp has ignited. The boost inductance
current into switch device on each switching cycle can be
obtained as of the boost converter and the half-bridge series
resonant parallel-loaded inverter. The operation of the boost
converter is in discontinued-current mode (DCM) providesunity power factor with constant frequency. In case of operating
partial lamps, a high power factor at the line input terminal will
be always retained. Thus, once the boost PFC stage is designed
to operate at DCM with fixed switching frequency, the input
current naturally follows the sinusoidal waveform of the ac line
source, that switching current of each cycle on the switch device
can be derived as
2
( ) sin(2 )2
m S
in
V D TI t ft
L= (11)
Furthermore, the input current and input voltage are operating
in same phase, which not only accomplish high input power
factor but also constraint total harmonic distortion of input
current, where the input power can be determined as
2
0
2 2
1sin(2 ) ( ) (2 )
2
4
in m in
m
P V ft I t d ft
V D
fL
=
=
(12)
With (11) the inductance of boost inductor can be derived as
2 2
4
m
in
V DL
fP L= (13)
III. SIMULATIONSome simulations have been done in order to verify the
multi-lamp arrangement behavior. To simulate, the fluorescent
lamp have been assumed same as the equivalent resistance
obtained from (1), the lamp as a resistor considered.
Additionally, the AC line voltage, rectifier bridge, and filter
capacitor have been used as a DC source, once that our aim is to
verify the multi-lamp arrangement behavior.
Simulation results are shown in Fig. 2, voltage in the lamps 1,
2, 3, and 4, in relation to Fig. 1. We can see that the lamp voltage
and switch voltage operation.
Fig 2. Thelamp voltage and one of switch voltage operation.
IV. EXPERIMENTAL RESULTSTo verify the predicted operation principles and theoretical
analysis of the proposed high efficiency single-stage ballast for
multiple fluorescent lamps, a laboratory electronic ballast of Fig.
1 is designed and built. The input voltage is 110Vat 60Hz, and
this circuit uses a dedicated integrated circuit TL494 to do the
high-frequency command, which switching frequency is fixed at
63kHz, and fixed duty 49.9%. Thus, the ballast can supply any
number of lamps and its frequency will not suffer variation. The
design parameters of circuit are shown in Table I.
Some experimental results have been done in order to verify
the experimental prototype behavior. The measured results are
presented the input voltage and current waveforms under
different operating conditions from single lamp, dual lamps and
triple lamps to quad lamps are shown in Fig. 3. Experimental
results are presented in Table. II. It is a prototype comparative
table to the different lamp numbers (4, 3, 2, and 1). where results
are illustrated of the input current is approximately sinusoidal
and operating same phase with input voltage, the power factor
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measured shown in Table II, and conclude it over 0.95 for all
lamps of experimental.
TABLE I. PARAMETER OF CIRCUIT
Designed Parameters
Design Reference Designed Value
1. Boost Inductor 1.1mH
2. Isolate CapacitorCS 60nF
3. Resonant CapacitorCP 3.5nF
4. Resonant Inductor 2.1mH
5. DC-link Capacitor 120uF
6 TL Lamp T5 28W
(a)
(b)
(c)
(d)
Vin50 V/divIin1 A/div time5 ms/div
Fig. 3. The waveform of Input voltage and current, Driving (a) single lamp,
(b)dual lamps, (c)triple lamps, and (d)quad lamps
TABLE II. EXPERMINTAL RESULTS
Number
of lamps
Single
lamp
Dual
lamps
Triple
lamps
Quad
lamps
Power
Factor0.953 0.961 0.968 0.973
The total ignition current ia for all lamps is 2.7A which is
shown in Fig. 4; with this current we can determine the
minimum rating of semiconductor switch device is 2.7A. In
order to prevent from destroying the device, the safe operation
rating of the MOSFET should be 5A or above. Next, Fig. 5
shows voltage over one lamp during its ignition process, which
maximum voltage is 827V. From these figures, it is possible to
verify the correct operation of the proposed electronic ballast,
during ignition and dimming control of the fluorescent lamps.Finally, Fig. 6.illustrates single lamp maximum start up current
is 390mA.
Iin1A/div time1 s/div
Fig. 4. Four Lamps ignited current waveform
0
0
Iin
Vin
Iin
0
Vin
Iin
Vin
0
Vin
Iin
0
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Vin200 V/div time5 ms/div
Fig 5. Lamp ignited voltage waveform
Iin100 mA/div time1 s/div
Fig 6. Single Lamp ignited current waveform
Fig. 7 shows the voltage and current waveforms through one
fluorescent lamp during operation at the maximum lighting
output condition. And Fig. 8 is shown the lamp 1, 2 and 3, 4 are
operating symmetrically and in 180o
opposite phase.
Fig. 9 is illustrates the voltage cross of the switches and
current waveform of boost inductor and resonant tanks which is
shown that the switching and conducting losses of the switches
in the proposed system are less than those in the conventional
system. In addition, the current stress imposed on the switches
in the proposed system is reduced significantly as compared to
that in the conventional one.
Vin100 V/div Iin200 mA/div time5 us/div
Fig 7. Lamp current and voltage are same phase driving
Vin100 V/div time5 us/div
Fig 8. Lamp current and voltage are same phase driving
Vin50 V/divIin200mA/div time2 us/div
Fig 9. Waveform driving signal and lamp current and boost inductor voltage
zero current switching and zero voltage switching
The solution to this problem is to determine an estimate of the
overall efficiency, measuring the input active power and the
active power of each lamp, one by one, using an oscilloscope. In
the maximum lighting condition, the total active power
processed through the lamps is approximately 112W, whereas
input active power is about 122W. Thus, the overall efficiency
of the proposed ballast is 91.8 0%, at the maximum lighting
condition.
V. CONCLUSIONA circuit operation scheme for a multiple fluorescent lamp
lighting system is proposed in this paper. The ballast is obtained
from the integration of a boost dc-to-dc converter and single
half-bridge series-resonant series-parallel loaded inverter. This
inverter circuit operation scheme is implemented with the
resonant tanks of the electronic ballast being capacitive andinductive, which can achieve lower switching losses, lower
conduction losses and lower current stresses over conventional
ballast with all inductive resonant tanks. The boost converter is
operated in discontinuous conduction mode and at constant
frequency providing an input power factor high enough to
satisfy present standard requirements. The operation of the
proposed ballast has also been investigated in detail in this paper.
A prototype of the ballast with proposed circuit operation
scheme for a four-lamp lighting system is implemented with
0
Vlamp1,2
Vlamp3,4
Vlamp
Ilamp
Low side switchHigh side switch
Lamp current ia
Boost inductor voltage
0
0
0
0
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practical considerations. In comparison with the conventional
electronic ballast for multiple fluorescent lamps, the proposed
electronic ballast for multiple fluorescent lamps presents a
significant reduction of cost. This reduction becomes even more
meaningful with larger number of lamps. The proposed
topology works as a good solution to implement low-cost
single-stage high efficiency electronic ballast for multiple
fluorescent lamps.
VI. ACKNOWLEDGMENTFinancial support of this research by the National Science
Council, Republic of China, under Grant NSC
97-2221-E-036-025 and Tatung University, Taipei, Taiwan,
under the grant B97-E04-040 is gratefully acknowledged.
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operation at high frequency, J. Illum. Eng. Soc., vol. 15, no. 1, 1985, pp.
63-74.
[2] L. Huber and M. M. Jovanovic, Single-Stage Single-SwitchInput-Current-Shaping Technique with Fast-Output-Voltage Regulation,IEEE Transactions on Power Electronics, Vol. 13, No. 3, May 1998, pp.
476-486.
[3] E. Deng, and S. Cuk, Single Stage, High Power Factor, Lamp Ballast,Proc IEEE Applied Power Electronics Conference, 1994, pp. 441-449.
[4] C. S. Moo, S. Y. Chan, and C. R. Lee, A Single-Stage High Power FactorElectronic Ballast with Duty-Ratio Controlled Series Resonant Inverter,
IEEE Transactions on Industrial Electronics, Vol. 46, No. 4, Aug. 1999, pp.
830-832.[5] J. A. Alves ,A. J. Perin, and I. Barbi,An electronic ballast with high power
factor for compact fluorescent lamps, Proc in Conf. Rec. IEEE-IAS Annu.Meeting, 1996, pp.2129-2135.
[6] M. A. Co, D. S. L. Simonetti and J. L. F. Vieira, High Power FactorElectronic Ballast Operating at Critical Conduction Mode, Proc PESC 96Record. Power Electronics Specialists Conference, 1996 27th Annual
IEEE, Vol. 2, June 1996, pp.962-968,.[7] J. Spangler and A. K. Behera, Power Factor Correction Techniques Used
For Fluorescent Lamp Ballast, Proc Conference Record of the 1991 IEEE
at Industry Applications Society Annual Meeting, Vol.2, , Oct. 1991, pp.1836-1841.
[8] R. N. Prado, A. R. Seidel, F. E. Bisogno, and R. K. Pavo, Self-OscillatingElectronic Ballast Design based on Point of View of Control System,
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