Chapter 4 Experiments
4.4 Experimental Results and Discussion
4.4.2 Conversion Efficiency
To measure conversion efficiencies under different load conditions, we connect the
output of device under test to a DC electronic load. The testing setup is shown in Fig.
4.18. We calculate the conversion efficiency by dividing the power displayed on the DC
(a)
(b)
Fig. 4.19. Measured (a) conversion efficiencies and (b) currents flowing through the optocouplers when VIN = 110 2 V.
electronic load by the power read from the power analyzer. Two groups of experiment
with respectively VIN = 110 2 V and VIN = 220 2 V are conducted, and the results are portrayed in Fig. 4.19 and Fig. 4.20, respectively. In Fig. 4.19(a), we can observe
(a)
(b)
Fig. 4.20. Measured (a) conversion efficiencies and (b) currents flowing through the optocouplers when VIN = 220 2 V.
proposed counterpart does when the output power is larger than 7.2 W. But when the
load gets lighter, the converter with the proposed feedback circuit presents evidently
better efficiencies. For example, there is a 2.2% efficiency improvement under the
1.8-W output power (10% load) and a 3.6% improvement under the 0.9-W output (5%
load). Fig. 4.19(b) gives the measured currents of optocouplers in both of the converters.
Under light-loads conditions, ILED and IFBC in the conventional converter are larger than
ILED and IFBP in the proposed one, and their differences become even larger with the
decrease of the output power. This fact forms the basic reason for the light-load
efficiency improvement. Fig. 4.19(b) also indicates that the current transfer ratio CTR of
the optocoupler continuously degrades with the decrease of the conducting currents.
Therefore, the decrease of ILED is not as much as that of IFBP or IFBC.
Fig. 4.20 shows a very similar situation when a higher input voltage (VIN =
2
220 V) is applied. The conversion efficiencies of the proposed flyback converter shown in Fig. 4.20(a) are much better than that of the conventional one when the load is
lighter than 5.4 W. For instance, there is a 2.9% efficiency improvement under the
1.8-W output power and a 5.1% improvement under the 0.9-W output. Fig. 4.20(b) also
depicts the measured currents of optocouplers in both of the converters. Comparing Fig.
4.20(b) with Fig. 4.19(b), we can see that in Fig. 4.20(b), the two conventional curves
and the two proposed curves are separated even further. It is due to the higher input
voltage such that the inductor current level limit becomes lower under the same output
power condition. Therefore, VFBC becomes lower and VFBP becomes higher, leading to
this phenomenon. This outcome also explains why the proposed converter improves
more efficiency under the same light-load condition when a higher input voltage is
applied.
4.5 Conclusion
The PWM controller and the reverse-type shunt regulator are designed and
fabricated for implementing a flyback converter adopting the proposed feedback scheme.
By integrating both a proposed and a conventional feedback paths, the controller can be
adopted for the conventional feedback topology as well. Two flyback converters with
different feedback schemes are implemented using the fabricated chips for experiments.
The comparisons between the two converters are made as fair as possible by setting
their power stages and their resistor dividers identical, and even in their controllers, all
other building blocks except for the feedback circuits are the same. In the measurements
of the no-load power consumption, the converter adopting the proposed feedback
network is obviously superior to the conventional converter, and the currents of the
optocoupler in the proposed topology are proved to be almost zero under this condition.
Better light-load conversion efficiencies are observed in the converter with the proposed
feedback network, while at heavy loads, there is no significant distinction between the
efficiencies of the two converters.
Chapter 5
Dissertation Conclusion and Future Work
5.1 Dissertation Conclusion
Standby power has resulted in a huge amount of energy waste in recent years,
which makes both industry and academia gradually put concentration on this issue. The
conventional feedback network is widely adopted in isolated offline switch-mode power
supplies owing to the benefits of the simple circuit structure and low cost. However, the
power loss under very light/no-load conditions causes severe standby power problem
because the currents following through the optocoupler are increased with the decrease
of the output power. Previous literature offers some techniques to address the power loss
issue, while all of them bring about more or less disadvantages and are still not very
ideal solutions at all.
This dissertation proposes the phase reversal concept to address the power loss
issue of the feedback network. With this idea, the currents flowing through the
optocoupler and thus the generated power loss are both decreased with the output power.
Also, the supply current of the reverse-type shunt regulator is designed not to flow
through the optocoupler, making this part of power dissipation not reproduced on the
primary side. Following these thoughts, a complete isolated feedback network is
proposed. The power loss analysis of the proposed feedback network shows that the
optocoupler conducts averagely zero currents on both sides, which indicates that the
standby power of the feedback network is minimized.
The PWM controller and the reverse-type shunt regulator are designed and
fabricated for implementing a flyback converter adopting the proposed feedback scheme.
Two flyback converters with different feedback schemes are implemented using the
fabricated chips. Experiments demonstrate a significant improvement in the no-load
power loss over the conventional flyback converter. Better light-load efficiency is also
achieved. Although the experiments are carried out on the basis of flyback converter, we
do believe that it is also applicable to other transformer-isolated topologies. With the
above advantages, the proposed isolated feedback scheme proves to be a promising
solution for future low-standby-power converters.
5.2 Future Work
In this dissertation, we only examine the performance difference between two
converters adopting respectively the proposed and the conventional feedback topology.
It is encouraged to incorporate this proposed feedback method with other techniques,
such as the high voltage start-up, the low-standby-power EMI capacitor discharging
method, and a low-power controller, into a power supply unit to see how actually
low-standby-power it can achieve. For example, a low-power battery charger adopting
all aforementioned techniques would probably meet the strictest standard of 30-mW
standby power.
Another point that deserves improving is the error amplifier inside the reverse-type
shunt regulator. Originally designed with the two-stage operational amplifier structure
for simplicity and large output swing, it can be modified and implemented with an even
lower-quiescent-current circuit, such as a class AB amplifier. The lower quiescent
current is consumed, the lower standby power can be achieved.
Reference
[1] Energy Efficient Strategies Pty Ltd. (Dec. 2011). Third Survey of Residential
Standby Power Consumption of Australian Homes-2010. [Online]. Available:
http://www.energyrating.gov.au/resources/program-publications/?viewPublicationI
D=2405
[2] Market Transformation Programme (Feb. 2009). BNXS36: Estimated UK standby
electricity consumption in 2006. [Online]. Available: http://efficient-products.defra.
gov.uk/spm/download/document/id/784
[3] K. Ohkuni, “Standby power in Japan,” presented at the Int. Conf. on Standby
Power, 2008. [Online]. Available: http://www.sustainablebuildingscentre.org/
workshops/2008/int_standby/Ohkuni_ECCJ.pdf
[4] A. Meier and B. Nordman, “Low power mode energy use in California Homes,” in
Proc. ACEEE Summer Study Energy Efficiency in Buildings, 2008.
[5] P. Bertoldi and B. Atanasiu (2009). Electricity Consumption and Efficiency Trends
in European Union-Status Report 2009. [Online]. Available: http://publications.jrc.
ec.europa.eu/repository/handle/111111111/6260/
[6] The World Bank (Jul. 2008). Residential Consumption of Electricity in India.
[Online]. Available: http://moef.nic.in/downloads/public-information/Residentialp
owerconsumption.pdf
[7] A. Meier et al., “Standby power use in Chinese homes,” Energy and Buildings,
vol. 36, no. 12, pp. 1211-1216, Dec. 2004.
[8] M. Camilleri, N. Isaacs, and L. French, “Standby and baseload in New Zealand
houses: A nationwide statistically representative study,” in Proc. ACEEE Summer
Study Energy Efficiency in Buildings, 2006.
[9] A. Meier, “A worldwide review of standby power use in homes,” in Proc. Int.
Symp. Highly Efficient Use of Energy and Reduction of its Environmental Impact,
2002.
[10] Korean Ministry of Knowledge (Jun. 2010). Regulation on Energy Efficiency
Labeling and Standards. [Online]. Available: http://www.kemco.or.kr/nd_file/
kemco_eng/MKE_Notice_2010-124.pdf
[11] Ministry of Industry and Information Technology of PRC (Dec. 2009). YD/T
1591-2009: Technical requirements and test method for power adapter and
changing/data port of mobile telecommunication technical equipment.
[12] European Commission (Apr. 2009). Code of Conduct on Energy Efficiency of
External Power Supplies. [Online]. Available: http://re.jrc.ec.europa.eu/energyeffic
iency/pdf/CoC_Power_Supplies_Version4-March2009.pdf
[13] UL Environment (Jun. 2011). UL ISR 110-Interim Sustainability Requirements for
Mobile Phones. [Online]. Available: http://www.ulenvironment.com/ulenviron
ment/eng/pages/
[14] European Commission IPP Pilot Project on Mobile Phones. [Online]. Available:
http://ec.europa.eu/environment/ipp/mobile.htm
[15] A. Meier and B. Lebot, “One Watt Initiative: A global effort to reduce leaking
electricity,” May 1999. [Online]. Available: http://www.osti.gov/bridge/servlets/
purl/795944-XFu5mJ/native/795944.pdf
[16] B.-H. Lee et al., “No-load power reduction technique for AC/DC Adapters,” IEEE
Trans. Power Electron., vol. 27, no. 8, pp. 3685-3694, Aug. 2012.
[17] S.-Y. Cho et al., “A new standby structure based on a forward converter integrated
with a phase-shift full-bridge converter for server power supplies,” IEEE Trans.
Power Electron., vol. 28, no. 1, pp. 336-346, Jan. 2013.
[18] B.-Y. Chen and Y.-S. Lai, “Switching control technique of phase-shift controlled
full-bridge converter to improve efficiency under light-load and standby
conditions without additional auxiliary components,” IEEE Trans. Power
Electron., vol. 25, no. 4, pp. 1001-1012, Apr. 2010.
[19] B.-H. Lee and G.-W. Moon, “Zero no-load power AC/DC adapter for electronic
equipment with embedded battery,” IEEE Trans. Power Electron., vol. 28, no. 7,
pp. 3073-3076, Jul. 2013.
[20] Y.-K. Lo, S.-C. Yen, and C.-Y. Lin, “A high-efficiency AC-to-DC adaptor with low
standby power consumption,” IEEE Trans. Ind. Electron., vol. 55, no. 2, pp.
963-965, Feb. 2008.
[21] W.-R. Liou, M.-L. Yeh, and Y.-L. Kuo, “A high efficiency dual-mode buck
converter IC for portable applications,” IEEE Trans. Power Electron., vol. 23, no.
2, pp. 667-677, Mar. 2008.
[22] F.-F. Ma, W.-Z. Chen, and J.-C. Wu, “A monolithic current-mode buck converter
with advanced control and protection circuits,” IEEE Trans. Power Electron., vol.
22, no.5, pp. 1836-1846, Sep. 2007.
[23] H. Deng et al., “Monolithically integrated boost converter based on 0.5-μm
CMOS process,” IEEE Trans. Power Electron., vol. 20, no. 3, pp. 628-638, May
2005.
[24] B. Sahur and G. A. Rincon-Móra, “A high-efficiency, dual-mode, dynamic,
buck-boost power supply IC for portable applications,” in Proc. Int. Conf. VLSI
Design, 2005, pp. 858-861.
[25] Z. Bi and W. Xia, “A PWM/PFM switch technique of dual-mode buck converter,”
in Proc. IET Int. Commun. Conf. Wireless Mobile Computing, 2009, pp. 357-360.
[26] J. Xiao et al., “A 4-μA quiescent-current dual-mode digitally controlled buck
converter IC for cellular phone applications,” IEEE J. Solid-State Circuits, vol. 39,
no. 12, pp. 2342-2348, Dec. 2004.
[27] B. Sahur and G. A. Rincon-Móra, “An accurate, low-voltage, CMOS switching
power supply with adaptive on-time pulse-frequency modulation (PFM) control,”
IEEE Trans. Circuits Syst. I, Reg. Papers, vol. 54, no. 2, pp. 312-321, Feb. 2007.
[28] X. Zhang and D. Maksimovic, “Multimode digital controller for synchronous buck
converters operating over wide ranges of input voltages and load currents,” IEEE
Trans. Power Electron., vol. 25, no. 8, pp. 1958-1965, Aug. 2010.
[29] X. Duan and A. Q. Huang, “Current-mode variable-frequency control architecture
for high-current low-voltage dc-dc converters,” IEEE Trans. Power Electron., vol.
21, no. 4, pp. 1133-1137, Jul. 2006.
[30] K. Wang et al., “All-digital DPWM/DPFM controller for low-power DC-DC
converters,'' in Proc. IEEE Appl. Power Electron. Conf. Expo., 2006, pp. 719-723.
[31] M. Telefus et al., “Pulse train control technique for flyback converter,” IEEE
Trans. Power Electron., vol. 19, no. 3, pp. 757-764, May 2004.
[32] S. Kapat, A. Patra, and S. Banerjee, “Achieving monotonic variation of spectral
composition in DC-DC converters using pulse skipping modulation,” IEEE Trans.
Circuits Syst. I, Reg. Papers, vol. 58, no. 8, pp. 1958-1966, Aug. 2011.
[33] S. Kapat, S. Banerjee, and A. Patra, “Discontinuous map analysis of a DC-DC
converter governed by pulse skipping modulation,” IEEE Trans. Circuits Syst. I,
Reg. Papers, vol. 57, no. 7, pp. 1793-1801, Jul. 2010.
[34] Y. Ye et al., “PWM/PSM dual-mode controller for high efficiency DC-DC buck
converter,” in Proc. Power and Energy Eng. Conf., 2010, pp. 1-4.
[35] F. Li et al., “Design of an off-line AC/DC controller based on skip cycle
modulation,” in Proc. Int. Symp. Integrated Circuits, 2009, pp. 228-231.
[36] P. Luo et al., “Skip cycle modulation in switching DC-DC converter,” in Proc.
IEEE Int. Conf. Commun., Circuits Syst. West Sino Expo., 2002, pp. 1716-1719.
[37] P. Luo et al., “A high energy efficiency PSM/PWM dual mode for DC-DC
converter in portable applications,” in Proc. IEEE Int. Conf. Commun., Circuits
Syst., 2009, pp. 702-706.
[38] X. Gong et al., “A dual mode high efficiency buck DC-DC converter,” in Proc.
IEEE Int. Conf. ASIC, 2011, pp. 838-842.
[39] J.-H. Choi, D.-Y. Huh, and Y.-S. Kim, “The improved burst mode in the stand-by
operation of power supply,” in Proc. IEEE Appl. Power Electron. Conf. Expo.,
2004, pp. 426-432.
[40] B.-C. Kim, K.-B. Park, and G.-W. Moon, “Sawtooth burst mode control with
minimum peak current in stand-by operation of power supply,” in Proc. Int. Conf.
Power Electron.-ECCE Asia, 2011, pp. 474-479.
[41] H.-S. Choi and D.-Y. Huh, “Techniques to minimize power consumption of SMPS
in standby mode,” in Proc. IEEE Power Electron. Specialist Conf., 2005, pp.
2817-2822.
[42] D. M. Dwelley, “Voltage mode feedback burst mode circuit,” U.S. Patent 6 307
356, Oct. 23, 2001.
[43] J. Lei, “High voltage start-up circuit and method therefore,” U.S. Patent 5 640 317,
Jun. 17, 1997.
[44] W.-H. Huang, “Start-up circuit to discharge EMI filter of power supplies,” U.S.
Patent 0176341, Jul. 21, 2011.
[45] C.-L. Lin et al., “Safety capacitor discharging method and apparatus for ac-to-dc
converters,” U.S. Patent 0068751, Mar. 24, 2011.
[46] C. P. Basso, Switch-Mode Power Supplies: SPICE Simulations and Practical
Designs. New York: McGraw-Hill, 2008.
[47] C. P. Basso, “Eliminate the guesswork in crossover frequency selection,” Power
Electronics Technology, Aug. 2008. [Online]. Available: http://powerelectronics.
com/ac-dc-power-supplies/eliminate-guesswork-selecting-crossover-frequency
[48] C. P. Basso, “The TL431 in loop control.” [Online]. Available: http://cbasso.
pagesperso-orange.fr/Spice.htm
[49] Y. Li and J. Zheng, “A low-cost adaptive multi-mode digital control solution
maximizing AC/DC power supply efficiency,” in Proc. IEEE Appl. Power
Electron. Conf. Expo., 2010, pp. 349-354.
[50] Sharp Corporation, Osaka, Japan. High Density Mounting Type Photocoupler,
PC817 Series Data Sheet.
[51] R. Nalepa, N. Barry, and P. Meaney, “Primary side control circuit of a flyback
converter,” in Proc. IEEE Appl. Power Electron. Conf. Expo., 2001, pp. 542-547.
[52] C.-W. Chang, Y.-T. Lin, and Y.-Y. Tzou, “Digital primary-side sensing control for
flyback converters,” in Proc. Int. Conf. Power Electron. and Drive Syst., 2009, pp.
689-694.
[53] P.-L. Huang et al., “An adaptive high-precision over-power protection scheme for
primary-side controlled flyback converters,” IEEE Trans. Power Electron., vol. 26,
no. 10, pp. 2817-2824, Oct. 2011.
[54] Fairchild, Inc., South Portland, ME (2009). Primary-Side-Control PWM
Controller, FAN102 Data Sheet. [Online]. Available: http://www.fairchildsemi.
com/ds/FA/ FAN102.pdf
[55] T.-Y. Yang et al., “Output voltage control circuit of power converter for light-load
power saving,” U.S. Patent 0232187, Sep. 16, 2010.
[56] W.-H. Huang, “Feedback circuit with feedback impedance modulation for
improving power saving,” U.S. Patent 0133829, Jun. 9, 2011.
[57] Fairchild, Inc., South Portland, ME (2012). Highly Integrated Green-Mode PWM
Controller, SG6846A Data Sheet. [Online]. Available: http://www.fairchildsemi.
com/ds/SG/SG6846A.pdf
[58] A. P. Brokaw, “A simple three-terminal IC bandgap reference,” IEEE J.
Solid-State Circuits, vol. 9, no. 6, pp. 388-393, Dec. 1974.