A Power Quality Improved Bridgeless Converter Based Computer Power Supply



Poor power quality, slow dynamic response, reduced output voltage regulation, high device stress, harmonic rich, periodically dense, peaky, distorted input current are the major problems which are frequently encountered in conventional switched mode power supplies (SMPSs) used in computers. To mitigate these problems, it is proposed here to use a non-isolated bridgeless buck-boost single ended primary inductance converter (SEPIC) in discontinuous conduction mode (DCM) at the front end of an SMPS. The bridgeless SEPIC at the front end provides stiffly regulated output dc voltage even under frequent input voltage variations and loads. The output of the front end converter is connected to a half bridge dc-dc converter for isolation and also for obtaining different dc voltage levels at the output that are needed in a computer. Controlling a single output voltage is able to regulate all the other dc output voltages as well. The design and simulation of the proposed power supply is carried out for obtaining improved power quality which is verified through the experimental results.


  1. Bridgeless converter
  2. PFC
  3. Input current
  4. Computer power supply



Fig.1 Schematic diagram of PFC converter based SMPS


Fig.2a Performance of the computer power supply at rated condition

Fig. 2b Input current and its harmonic spectrum at full load condition

Fig. 2c Waveform of various components of bridgeless converter

Fig.3a Performance of the computer power supply at light load condition

Fig. 3b Input current and its harmonic spectrum at light load condition


A bridgeless non-isolated SEPIC based power supply has been proposed here to mitigate the power quality problems prevalent in any conventional computer power supply. The proposed power supply is able to operate satisfactorily under wide variations in input voltages and loads. The design and simulation of the proposed power supply is initially carried to demonstrate its improved performance. Further, a laboratory prototype is built and experiments are conducted on this prototype. Test results obtained are found to be in line with the simulated performance. They corroborate the fact that the power quality problems at the front end are mitigated and hence, the proposed circuit can be a recommended solution for computers and other similar appliances.


[1] D. O. Koval and C. Carter, “Power quality characteristics of computer loads,” IEEE Trans. on Industry Applications, vol. 33, no. 3, pp. 613- 621, May/June1997.

[2] Abraham I. Pressman, Keith Billings and Taylor Morey, “Switching Power Supply Design,” 3rd ed., McGraw Hill, New York, 2009.

[3] B. Singh, B.N. Singh, A. Chandra, K. Al-Haddad, A. Pandey and D.P. Kothari, “A review of single-phase improved power quality AC-DC converters” IEEE Trans. on Industrial Electronics, vol.50, no.5, pp.962- 981, Oct. 2003.

[4] K. Mino, H. Matsumoto, Y. Nemoto, S. Fujita, D. Kawasaki, Ryuji Yamada, and N. Tawada, “A front-end converter with high reliability and high efficiency,” in IEEE Conf. on Energy Conversion Congress and Exposition (ECCE),2010, pp. 3216-3223.

[5] Jih-Sheng Lai, D. Hurst and T. Key, Switch-mode supply power factor improvement via harmonic elimination methods,” in 6th Annual IEEE Proc. on Applied Power Electronics Conference and Exposition, APEC’91, 1991, pp. 415-422.



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