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274 IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 13, NO. 2, MARCH 1998

Fig. 1. Series-resonant electronic ballast with the proposed PFC circuit.

Fig. 2. Simplified equivalent circuit of Fig. 1.

or into the load. The PFC circuit arranged in this way

can draw current from the ac line in every switching cycle

of the inverter. As a result, the input line current becomes a

high-frequency pulsating waveform with a sinusoidal envelope

which is in phase with the input voltage. The high-frequency

contents in the input current can be removed simply by a small

filter at input terminal. Consequently, a nearly unity powerfactor can be obtained.

III. CURRENT-SHAPING OPERATION

In order to facilitate the analysis of the current-shaping op-

eration, the electronic ballast circuit in Fig. 1 can be simplified

to a schematic circuit as shown in Fig. 2. The rectifier bridge

is represented by the diode and is the rectified line

voltage

(1)

where is the voltage amplitude and is the frequency

of the line source.

For a well-designed electronic ballast, as stated in [16] and

[17], the resonant circuit represents an inductive load and can

be equivalent to a sinusoidal current source with the inverter

switching frequency

(2)

where is the amplitude of the load current.

In fact, the inverter frequency is relatively high in compar-

ison with the line frequency so that the variation at the input

line voltage can be neglected during one switching cycle.

TABLE ICONDUCTING SWITCHES FOR EACH INTERVAL AT

TABLE IICONDUCTING SWITCHES FOR EACH INTERVAL AT

During the turn-on period of the transistor , a resonant

current flows from the line source through the boost inductor

and transistor charging

(3)

where and are the initial conditions with respect to

and and is the resonant frequency

(4)

The voltage across is

(5)

At the low voltages of the rectified line source, the peak

values of is less than the dc-link voltage . The inductor

current resonates over one-half cycle and stays at zero. Under

such a condition, the inductor current is discontinuous and

hence the input current.

At the high voltages of , the inductor current tends to

be continuous and can reach . Beyond this point,

turns on and is clamped at . Since is greater than

the peak value of , the inductor current charges the dc-link

capacitor and decreases linearly

(6)

Figs. 3 and 4 illustrate the simulated results at a low voltage

of and at the peak of the rectified line source

( ), respectively. The conducting switches in each

time interval are listed in Tables I and II. The simulations are

based on the circuit parameters given by the following design

example.

As shown in Fig. 3, the maximum voltage of is less

than , and the inductor current is discontinuous. The

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MOO et al.: POWER-FACTOR-CORRECTION CIRCUIT FOR ELECTRONIC BALLASTS 275

Fig. 3. Calculated waveforms at .

waveforms are depicted from the instant at which a positive

load current starts to flow. During Interval I, the bottom

transistor is turned on and carries both the load current

and the inductor current. The capacitor is charged by this

inductor current and the voltage of is clamped at zero. At

the end of this time interval, the inductor current resonates tozero, and the voltage across increases to its maximum. At

this instant, the rectifier and the diode turn off. During

Interval II, the load current flows through and the inductor

current stays at zero. At the beginning of interval III,

is switched off. Then, the energy stored in is transferred

to the load and declines. When the rectified line voltage

becomes greater than the rectifier diodes are forward

biased and the line source starts to charge and through

the inductor. This charging current, however, is always less

than the load current by which is discharged. Therefore,

decreases continuously during Interval IV and eventually falls

to zero. Then, turns on and carries the freewheeling current

which is equal to the difference between the load current andthe inductor current. At the end of interval V, the freewheeling

current comes to zero and the transistor is turned on. Since

the power switches are operated symmetrically and is equal

to , the operation of the next half cycle is similar.

At the peak voltage of , the inductor current is continu-

ous with very small ripple as shown in Fig. 4. During Interval

I, is switched on. Prior to this time, has been charged up

and clamped at . Since is very large as compared with

, most of the inductor current flows through . Therefore,

carries only the load current. At the beginning of Interval

II, is switched off and the energy stored in is discharged

Fig. 4. Calculated waveforms at .

to the load. Meanwhile, is charged by the inductor current.

At this operating voltage, the inductor current is at its peak, the

voltage of increases rapidly. In this case, the sum of

and may reach and then becomes forward biased.

As stated above, the inductor current mostly flows through

during Interval III and is continuously discharge bythe load current. When is completely discharged, turns

on and carries the freewheeling current. Since the discharging

period is much longer, only a short duration of freewheeling

is found and the freewheeling current is smaller as compared

with the operation at low voltages of . At the moment

when the freewheeling comes to an end, is switched on

and the next half cycle ensues.

Fig. 5 shows the calculated input current waveform over

half a cycle of the line source. In this figure, the inverter

frequency is made low and the high-frequency contents are

not filtered for the purpose of illustration. It can be found

that the input current is discontinuous over the lower range

of the ac-line voltage while becoming continuous over thehigher voltage range. The pulsating current dithers around

a sinusoidal fundamental wave, which is in phase with the

input voltage. Removing the high-frequency contents, a nearly

sinusoidal input current can be obtained.

IV. DESIGN CONSIDERATION

In order to achieve unity power factor, the average inductor

current should be made to follow its fundamental wave which

is in phase with input line voltage. The fundamental current

can be determined by the input power and the voltage speci-

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MOO et al.: POWER-FACTOR-CORRECTION CIRCUIT FOR ELECTRONIC BALLASTS 277

(a) (b)

Fig. 7. Measured waveforms of inductor current and capacitor voltage at (a)and (b) .

(a) (b)

Fig. 8. Current waveforms of transistor, antiparallel diode, and load currentat (a) and (b) .

Fig. 9. Experimental waveforms of input line voltage and current.

with the inverter load currents. In Fig. 8(a), it is found that the

transistor carries a current slightly larger than that without PFC

circuit. This is because that the transistor has been turned on to

flow a part of charging current before the load current becomes

positive. A larger transistor current results in more conduction

loss. However, at a high voltage of , the transistor carries

only the load current as shown in Fig. 8(b). On the other hand,

the freewheeling currents become much smaller for both cases.

Besides, the energy stored in the high-frequency capacitors

discharge directly into the load, but not through the powerswitches. This makes a merit of reducing the losses on the

switches.

The measured overall efficiency of the electronic ballast is

93.0%. It is only slightly less than that of the original design

(93.8%). The crest factor of the lamp current is 1.38, which is

the same as the original design without the PFC circuit. This

implies that the added PFC circuit does not affect the output

characteristics of the inverter stage.

The measured input line current of the electronic ballast is

shown in Fig. 9. The high-frequency pulsating currents have

been filtered out by a small capacitor at the input terminal.

The measured power factor is greater than 0.99 and the total

harmonic distortion is lower than 8%.

VI. CONCLUSIONS

A new PFC circuit designed for the high-frequency half-

bridge series-resonant electronic ballast has been presented.

The proposed approach employs additional small energy tanks

for shaping the input current into the desired sinusoidalwaveform by processing a part of power. The high-frequency

operation is described for designing circuit parameters. Ex-

perimental results prove that nearly unity power factor can

be achieved by properly choosing circuit parameters. The

PFC circuit involves virtually no loss since it consists of

only reactive components and the energy transfer diodes are

turned on and off softly. The added inductors and capacitors

are operated at the high frequency and thus can maintain

the attributes of small volume and light weight as those in

the active filters. More importantly, preventing the use of

additional active power switches and sophisticated control

circuit, the electronic ballasts incorporating the proposed PFC

scheme are obviously cost effective.

REFERENCES

[1] E. E. Hammer, High frequency characteristics of fluorescent lamps upto 500 kHz, J. Illum. Eng. Soc., pp. 5261, 1987.

[2] E. E. Hammer and T. K. McGowan, Characteristics of various F40fluorescent systems at 60 Hz and high frequency, IEEE Trans. Ind.

Applicat., vol. 21, no. 1, pp. 1116, 1985.[3] J. Spangler and A. K. Behera, Power factor correction techniques used

for fluorescent lamp ballast, in Proc. IEEE-IAS Annu. Meet., 1991, pp.18361841.

[4] S. B. Dewan, Optimum input and output filter for a single-phaserectifier power supply, IEEE Trans. Ind. Applicat., vol. 17, no. 3, pp.282288, 1981.

[5] F. C. Schwarz, A time-domain analysis of the power factor for arectifier filter system with over- and subcritical inductance, IEEE Trans.

Ind. Electron., vol. 20, no. 2, pp. 6168, 1973.[6] M. Kazerani, P. D. Ziogas, and G. Joos, A novel active current

waveshaping technique for solid-state input power factor conditioners,IEEE Trans. Ind. Electron., vol. 38, no. 1, pp. 7278, 1991.

[7] J. C. Salmon, Techniques for minimizing the input current distortionof current-controlled single-phase boost rectifiers, IEEE Trans. Power

Electron., vol. 8, no. 4, pp. 509520, 1993.[8] J. L. Freitas Vieira, M. A. Co, and L. D. Zorzal, High power factor

electronic ballast based on a single power processing stage, in IEEEPESC95, 1995, pp. 687693.

[9] M. Madigan, R. Erickson, and E. Ismail, Integrated high qualityrectifierregulator, in IEEE PESC92, 1992, pp. 10431051.

[10] H. Matsuo, N. Aoike, F. Kurokawa, and A. Hisako, A new combinedvoltageresonant inverter with high power factor and low distortionfactor, in IEEE PESC94, pp. 331335.

[11] C. S. Moo, Y. C. Chang, and J. C. Lee, A new dynamic filter forthe electronic ballast with the parallel-load resonant inverter, in Proc.

IEEE-IAS Annu. Meet., 1995, pp. 25972601.[12] C. Licitra, L. Malesani, G. Spiazzi, P. Tenti, and A. Testa, Single-ended

soft-switching electronic ballast with unity power factor, IEEE Trans.Ind. Applicat., vol. 29, no. 2, pp. 382387, 1993.

[13] E. Deng and S. Cuk, Single stage, high power factor, lamp ballast, inIEEE APEC94, pp. 441449.

[14] R. King, A normalized model for the half-bridge series resonantconverter, IEEE Trans. Aerosp. Electron. Syst., pp. 190198, Mar. 1981.

[15] W. J. Gu and K. Harada, Novel self-excited PWM converters with zero-voltage-switched resonant transition using a saturable core, in IEEE

APEC92, pp. 5865.[16] M. K. Kazimierczuk, Class D voltage-switching MOSFET power

amplifier, in IEEE Proc. B, Electron. Power Appl., Nov. 1991, pp.285296.

[17] M. K. Kazimierczuk and W. Szaraniec, Electronic ballast for fluores-cent lamps, IEEE Trans. Power Electron., vol. 8, no. 4, pp. 386395,1993.

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278 IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 13, NO. 2, MARCH 1998

Chin S. Moo was born in 1953. He received theB.S. degree in electrical engineering in 1976, theM.S. degree in 1984, and the Ph.D. degree in 1990,all from National Chen-Kung University, Taiwan,R.O.C.

He worked for eight years as an Electrical En-gineer with South-East Cement Co., Kaohsiung,Taiwan. Currently, he is an Associate Professor ofthe Department of Electrical Engineering, NationalSun Yat-Sen University, Kaohsiung, Taiwan. His re-

search interests include power electronic convertersand their applications.

Ying C. Chuang was born in Kaohsiung, Taiwan,R.O.C., in 1962. He received the B.S. degree inelectrical engineering in 1988 from National TaiwanInstitute of Technology, Taipei, Taiwan, and theM.S. degree in electrical engineering from NationalCheng Kung University, Tainan, Taiwan, in 1990.He is currently working towards the Ph.D. degreeat National Sun Yat-Sen University, Kaohsiung,Taiwan.

His fields of interests are electronic ballasts andpower electronic drive systems.

Ching R. Lee was born in Kimmen, Taiwan,R.O.C., on June 6, 1964. He received the B.S.E.E.and M.S.E.E. degrees from the National Sun Yat-Sen University, Kaohsiung, Taiwan, in 1986 and1991, respectively, and is currently working towardthe Ph.D. degree at the same university.

His main research interests include PFC andelectronic ballasts.