Failure Rate Calculation of PC s SMPSs

Transcription

1 International Journal of Macine Learning and omputing, ol. 3, No. 4, August 03 Failure Rate alculation of P s MPs B. Abdi, R. Gasemi, and. M. M. Mirtalaei, Member, IAI Abstract oday reliability is one of te serious requirements of electronic s. e numbers of failures, repair cost, guarantee, etc are estimated by reliability estimation. In tis paper, te reliability of a switcing power supply, wic is used for personal computers, evaluates. It will sow tat te most of failure rates depends on power circuit because of more stresses and dissipations. Derating effect of devices on te failure rate will discuss. Part stress count utilizes for failure rate calculations and a prototype s waveforms uses for stress detection and calculation of dissipations. Index erms Failure rate, reliability, MP, P. I. INRODUION witc Mode Power upplies (MPs) are used in Personal omputers (Ps), because of teir ig efficiency and low volume and weigt. MPs are used in all Ps for convert te voltage to different levels and establis it against input voltage and load variations []. e efficiency of joinery MPs, are used in Ps, is about 70% and all te power consumption of P produced by sub. o tey are te most critical point of Ps from reliability lookout and almost 90% of P failures belong to teir MPs. Lifetime and failure rate of a can be predicted by reliability calculations. Recently, reliability became to a prevalent issue in power electronic s. e effect of transformer leakage inductance on MPs reliability discussed in [], and influence of electrolytic capacitors on MP s reliability is given in [3]. Reliability modification of power electronic converter for full cell and potovoltaic application are discussed [4]-[]. Dissertation of operating mode (continuous and discontinuous modes) wit aim of reliability, for MPs, presented in [7] and using a single integrated power module (IPM) instead of paralleling power electronic devices are given in [8]. In tis paper, te metod of reliability calculation is presented for a P s MP. e most critical point of tem is introduced and te contrivances for teir modifications are proposed. e reliability calculation are done according to MIL-HDBK-7 [9] and using te metod of stress manner. interval is referred to as its reliability. It is dependent on te type and quality of te s and materials used in te device, tension of eac endures and te ambient conditions wic te devices are working. e failure rate in most of te electronic s is constant, represented by λ; te reliability is expressed by: R() t e t () e matematical mean of R (t) occurs at: t () Wic is te amount of time tat sould elapses until te first failure occurs. is is called te Mean ime to Failure (MF). e mean time to repair (MR) of te is negligible compared to MF, so te mean time between failures (MBF) of a is expressed as: MBF MR MF (3) e total rate of te failure is te sum of te failure rates of all s of te : N (4) n Hence, te reliability of te will be te product of all te components reliabilities [9]: R R (5) III. RLIABILIY ALULAION OF P MP II. DFINIION OF RLIABILIY e probability of proper function of a after a time Manuscript received January 3, 03; revised May 8, 03. is work was supported in by Damavand Branc, Islamic Azad University. e Autors are wit Damavand Branc, Islamic Azad University, Damavand, eran, Iran ( babakabdi@ieee.org). Fig.. P s switc mode power supply. Power supply, used in P, convert input voltage (0, 50Hz or 5, 0Hz) to ±, +5 and +3.3D and regulate tem against input voltage and load variations. ey can provide up to 00 watts continuously and up to 00 watts instantaneously. A P s power supply is sown in Fig. and its Block diagram is given in Fig.. It is basically a alf DOI: 0.773/IJML

2 International Journal of Macine Learning and omputing, ol. 3, No. 4, August 03 bridge D-D converter wic stabilizes output voltages using Pulse Widt Modulation (PWM) control []. Half of input rectified voltage, 0, will be applied to eac capacitor. o, =0.8 (0/00) and 34. R is series resistance factor. o, te failure rate of two input electrolytic capacitors is: c b R F / 0 Fig.. Block diagram of a switc mode power supply. In reliability calculation, tere is a basic failure rate for eac device wic is sown by b. e basic failure rate is affected by quality factor of eac device ( ), stress factor ( ) wic is te ratio of operational to nominal parameters (like voltage and current), temperature factor ( ) and working ambient or environmental factor ( ). ere are anoter factors belong to specific devices. For example capacitance factor ( ) belongs to capacitors. c All relations, equations and coefficients are acieved from MIL-HDBK-7 [9] and will not repeat in te reliability evaluation below. According Fig., reliability evaluation can be calculated as follows: A. Failure Rate of Input Rectifier Input rectifier consist a PBU05 bridge (00, A) and two electrolytic capacitors (80uF, 00) in series. e bridge includes 4 diodes wic details of teir failure rate calculation are given in section (3-). Briefly, te failure rate for input bridge rectifier is: Di b F / 0 Half bridge D-D converters utilize two serried bulk capacitors in teir input (Fig. ). e failure rate of electrolytic capacitors calculates as: () c b R B. Failure of Power witces and ransformer Half bridge converter consist two power switces. Here two power BJs, 3009KA, are used for tis aim. e failure rate of BJs can be calculated by equation (9). A (9) t b A R is application factor, 0.7 for switcing applications. R is power rating factor. is voltage stress factor and depends on applied voltage to rated voltage ratio (s) by: ( 3. s ) is temperature factor determines by: e (0) exp 4 ( ) J () were J is junction temperature of transistor and calculates as follow: P () J J loss were is transistor case temperature, J is termal resistance between junction and case and P loss is transistor dissipation. In switcing application transistor as two kind of dissipation: static (.I ) and dynamic. Dynamic loss originated by voltage and current overlap and calculated by integral of teir multiplication during switcing transient. ransformer s leakage inductance cause ignorable overlap between voltage and current during on transient as well as ig dissipation during off transient. is capacitance factor depends to amount of capacitance,, by equation (7). 0.3 (7) For a 80uF capacitor, is 4.5. is voltage stress factor. It depends on te applied voltage to nominal voltage ratio,, by equation (8) (8) Fig. 3. oltage and current waveform of power switc. Fig. 3 illustrates te voltage and current wave forms of switces for a sample commercial power supply, and teir 338

3 International Journal of Macine Learning and omputing, ol. 3, No. 4, August 03 overlap during off transient is sown in Fig. 4. ransistors saturation voltage ( (sat) ) is.5 volts. o, According to current sape and duty cycle given in Fig. 3, te static loss is 0.5W ( (sat). I (Avg). D). according Fig. 4, dynamic loss is.7w. erefore te total loss is.3w (0.5+.7). ransistor case temperature is 0 and according to transistor s dataseet, termal resistance between junction and case is 0. /W. Fig. 4. oltage and current waveform of power switc. ubstituting above numbers in equations and results.. Nominal voltage of transistors is 400 and according Fig. 3, applied voltage is 30. ese results s=0.8 and Finally, te failure rate of power switces can be determined as: t b A R F / 0 ransformer s failure rate calculates as follow: (3) F / 0 b is contact construction factor. It is for metallurgically bonded construction. Fig. 5 illustrates voltage and current waveforms for +5 output. According to tis figure, applied voltage is 4 volts wic results 0.. o, te failure rate of eac diode in +5 rectifier is: D5 b F / 0 Applied voltage for + and - is 7 wic results 0.7 and D 0.05 F/0. D. Failure Rate of Output Filters ac output consist a filer including two capacitors and two inductors. e failure rate of electrolytic capacitor calculates by equation. wo 0, 00UF capacitor are used in +5 output. o, failure rate of capacitors for tis output calculates as: c5 b R F /0 wo, 000UF capacitor are used in + output. o, failure rate of capacitors for tis output calculates as: c b R F /0 wo, 470UF capacitor are used in - output. o, failure rate of capacitors for tis output calculates as: cm b R F / 0 Failure rate of inductance calculates as: (5) t b c It is te same for entire outputs and calculates as: t b c F / 0 f. Failure Rate of ontrol ircuit ontrol unit includes a control I, 0 resistors, 5 ceramic capacitors and 8 electrolytic types, 0 diodes (n448) and 5 transistors (N). ) Failure Rate of ontrol I It calculates as: ( ) () I L Fig. 5. oltage and current waveform of output diodes.. Failure Rate of Output Rectifiers Double scottky diodes, B3030P (30A-30), are used for ig frequency output rectifiers. e failure rate of eac diode calculates as: (4) D5 b were is a coefficient based on te number of transistor used in te I. is packaging failure rate and is leaming factor and depends on producer background. ese entire coefficients are given in [9]. erefore I's failure rate can be calculated as: ( )0 0.9 (7) I Failures per 0 ours (F/0) L 339

4 International Journal of Macine Learning and omputing, ol. 3, No. 4, August 03 ) Failure Rate of ontrol's Resistors ere are 0 resistors in te control circuit. Altoug tey ave different values, tey are te same in reliability calculation. e Failure rate of eac resistor can be calculated as: 3) Failure rate of control's capacitors eramic capacitor's failure rate calculates as: capacitor is: c b (8) is capacitance factor. Failure rate for eac ceramic c ( F/ 0 ) 5 ceramic capacitors are used in control circuit. o teir entire failure rate is: c ( F/ 0 ) ere are also 8 electrolytic capacitors (0uF, 50) in control circuit. e failure rate for tis kind of capacitors calculates as: (9) c b R F /0 4) Failure rate of control's diodes ere are 0, N448, diodes in control circuit. Detail of calculation process is given in section (4). Briefly, te failure rate for tese diodes is: D b F / 0 5) Failure rate of control's transistors ere are 5, N, transistors in control circuit. Detail of calculation process is given in section (9). Briefly, te failure rate for tese entire transistors is: b A R F / 0 I. DIUION Failure rate of different s of a case study switc mode power supply are given in able I. It is clear tat te power circuitry ave muc failure rate tan control circuit. Altoug te number of s in control is more tan power circuit, te failure rate of power circuit is more because of more stress and dissipation. In te power circuit electrolytic capacitors ave more failure rate because of voltage derating disobedience. In control circuit, electrolytic capacitors ave a little failure rate because of good voltage derating. eir nominal voltage is 50 and teir applied voltage. o, reliability can be modified by proper derate of capacitors. Power circuit ontrol circuit ABL I: H FAILUR RA OF DIFFRN PAR IN P' MP Input Rectifier Input ap. Power witc +5 Diode Diode +5 ap. + ap. - ap. Inductors Power rans. Power stage circuit I resistors eramic ap. lectrolytic ap. ransistors Diodes otal ontrol circuit Number of used power control ac failure rate eac N n.8 MBF 47( / f ). ONLUION z e reliability of a P s MP as been fully derived in tis paper. It is sown tat te elements of te power circuit, account for te largest portion of te failure rate in te converter, and to increase te reliability, te power circuit elements sould be focused on. alculations for a prototype power supply ave sown tat electrolytic capacitors are more vulnerable because of weak voltage derating. RFRN [] A. Pressman, witcing Power upply Design, nd ed. McGraw-Hill, 998. [] B. Abdi, M. B. Menaj, L. Yazdanparast, and J. Milimonfared, e effect of te transformer winding on te reliability of switcing power supplies, I, 00. [3] Y. M. en, H.. Wu, M. W. ou, and K. Y. Lee, Online failure prediction of te electrolytic capacitor for L filter of switcing-mode power converters, I ransactions on Industrial lectronics, vol. 55, no., January 008. [4]. Rodriguez and G. A. J. Amaratunga, Long-lifetime power inverter for potovoltaic A modules, I ransactions on Industrial lectronics, vol. 55, no. 7, July 008. [5] F. an and H. alleja, Design strategy to optimize te reliability of grid-connected P s, I ransactions on Industrial lectronics, vol. 5, no., November 009. [] A. H. Ranjbar, B. Abdi,. A. Nabavi Niak, G. B. Garepetian, and J Milimonfared, Reliability comparison of fuel-cell D-D converter in two cases of using IPM switc and paralleling MOFs, International ymposium on Power lectronics, lectrical Drives, Automation and Motion, PDAM, 008. [7] B. Abdi, A. H. Ranjbar, J Milimonfared, and G. B. Garepetian, Reliability comparison of boost PF converter in DM and M operating modes, International ymposium on Power lectronics, lectrical Drives, Automation and Motion, PDAM, 008. [8] B. Abdi, A. H. Ranjbar, G. B. Garepetian, and J. Milimonfared, Reliability considerations for parallel performance of semiconductor switces in ig power switcing power supplies, I ransactions on Industrial lectronics, vol. 5, no., June

5 International Journal of Macine Learning and omputing, ol. 3, No. 4, August 03 [9] Reliability prediction of electronic equipment, Military Handbook, MIL-HDBK-7, Dec., 99. Babak Abdi was born in eran in 97. He received is M.. and P.D. degree in electrical engineering in 005 and 009 from Amirkabir University of ecnology (eran Polytecnic), eran, Iran, respectively. He is currently a member of I and a faculty member of Damavand branc, Islamic Azad University, eran, Iran. His researc interests include power electronics, application of reliability in power electronics, lectromagnetic Interferences (MI), and electrical macines and drives. ayyed Moammad Medi Mirtalaei was born in areza-isfaan, Iran in 983. He received is B.. degree in electrical engineering from Isfan University of ecnology, Iran in 005. He received is M.. and P.D. in electrical engineering from Amirkabir University of ecnology, eran, Iran in 007 and 0 respectively. His researc interest are power electronics, MI/M and numerical metod in electromagnetic. Reza Gasemi was born in eran, Iran in 979. He received is B.c. degree in lectrical engineering from emnan University in 000. He received te M.c. and te P.D. degree in control engineering from Amirkabir University of ecnology, eran, Iran in 004 and 009, respectively. His researc interests include large-cale ystems, adaptive control, robust control, nonlinear control, and intelligent s. Reza Gasemi joined te Dement of lectrical ngineering, Damavand Branc, Islamic Azad University, eran, Iran, were e is currently an assistant professor of electrical engineering. 34