Pulse Discharge Characteristics of Surface Mount Capacitors

Transcription

1 Pulse Discharge Characerisics of Surface Moun Capaciors W.J. Carey, A.J. Wiebe, L.L Algilbers, and W.C. Nunnally 3 ARC Technology 376 NW h Sree, Whiewaer, KS, USA Tel: + ( ; carey@arc-ech.us, wiebe@arc-ech.us US Army Space and Missile Defense Command Hunsville, AL, USA Tel: + ( ; larry.algilbers@us.army.mil 3 Universiy of Missouri Columbia, MO, USA Tel: + ( ; nunnallyw@missouri.edu Absrac ARC Technology is developing pulse generaors for exremely compac geomeries requiring megawas of power and millijoule o Joule of oal energy. These devices are o be consruced wih surface moun componens and circui board fabricaion echniques o minimize volume, cos, and producion ime. Clearly, he componens in hese circuis are operaing well beyond heir design specificaions. Therefore, his paper examines he energy sorage and peak power capabiliies of various surface moun capacior echnologies and vendors o deermine heir applicabiliy in miniaure pulsed power circuis. I. INTRODUCTION ARC Technology is invesigaing surface moun ceramic capaciors for high curren, low volage applicaions. Capaciors were sudied over he range of 5 V o V and. µf o.5 µf, wih Type II X7R ceramics for high energy densiy. This paper presens he performance of a represenaive sample of capaciors from his sudy, using a simple Spice model o quickly selec he bes candidaes for deailed analysis. Communicaion wih capacior manufacurers demonsraed ha deailed Spice models are no available for high volage, high capaciance surface moun echnology (SMT devices over approximaely V. Therefore, a firspass circui model wih an inducor, resisor, and capacior in series (LRC was developed o calculae parasiic values for he capaciors from heir curren waveforms during pulse discharge, wih emphasis on predicing he riseime and peak curren. These values are verified in Spice and hen used o derive he energy and peak power densiies of each capacior. I should be noed ha he resuls of his sudy specifically arge single sho applicaions where riseime and peak curren are criical, bu he subsequen ail of he pulse is no of ineres. Therefore, he derived model reasonably predics he riseime and peak power of he capacior discharge while he volage is sill relaively high. However, he model does no mach he ail characerisics, which include srong effecs from he nonlinear capaciance of X7R wih respec o volage. II. EXPERIMENTAL ARRANGEMENT Characerizaion of a significan number of surface moun capaciors requires he developmen of rapid esing echniques. The es arrangemen shown in Fig. measures he capacior s pulse discharge characerisics wih a minimum of inducance. The curren viewing resisor (CVR mus have a resisance ha is approximaely less han or equal o he associaed SMT capacior impedance. The CVR chosen is a Caddock CC5FC surface moun. Ω high curren device, which is soldered direcly across he volage monioring SMA connecor. The capacior under es is soldered on one end o he ground erminal of he SMA connecor and in parallel wih he CVR. The high volage power supply is conneced hrough wo isolaion resisors o he ground side of he SMA connecor and o he remaining capacior erminal. HV connecion Capacior Fig.. Tes bed configuraion. Ground connecion CVR SMA connecor /6/$5. 6 IEEE 4

2 Repor Documenaion Page Form Approved OMB No Public reporing burden for he collecion of informaion is esimaed o average hour per response, including he ime for reviewing insrucions, searching exising daa sources, gahering and mainaining he daa needed, and compleing and reviewing he collecion of informaion. Send commens regarding his burden esimae or any oher aspec of his collecion of informaion, including suggesions for reducing his burden, o Washingon Headquarers Services, Direcorae for Informaion Operaions and Repors, 5 Jefferson Davis Highway, Suie 4, Arlingon VA -43. Respondens should be aware ha nowihsanding any oher provision of law, no person shall be subjec o a penaly for failing o comply wih a collecion of informaion if i does no display a currenly valid OMB conrol number.. REPORT DATE MAY 6. REPORT TYPE N/A 3. DATES COVERED - 4. TITLE AND SUBTITLE Pulse Discharge Characerisics of Surface Moun Capaciors 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S 5d. PROJECT NUMBER 5e. TASK NUMBER 5f. WORK UNIT NUMBER 7. PERFORMING ORGANIZATION NAME(S AND ADDRESS(ES ARC Technology 376 NW h Sree, Whiewaer, KS, USA 8. PERFORMING ORGANIZATION REPORT NUMBER 9. SPONSORING/MONITORING AGENCY NAME(S AND ADDRESS(ES. SPONSOR/MONITOR S ACRONYM(S. DISTRIBUTION/AVAILABILITY STATEMENT Approved for public release, disribuion unlimied. SPONSOR/MONITOR S REPORT NUMBER(S 3. SUPPLEMENTARY NOTES See also ADM963. IEEE Inernaional Power Modulaor Symposium (7h and High-Volage Workshop Held in Washingon, DC on May 4-8, 6 4. ABSTRACT 5. SUBJECT TERMS 6. SECURITY CLASSIFICATION OF: 7. LIMITATION OF ABSTRACT UU a. REPORT b. ABSTRACT c. THIS PAGE 8. NUMBER OF PAGES 4 9a. NAME OF RESPONSIBLE PERSON Sandard Form 98 (Rev Prescribed by ANSI Sd Z39-8

3 Each capacior in urn is soldered ino he es apparaus and charged o is raed volage. The pulse discharge is iniiaed by shoring he capacior high volage erminal direcly o he cener pin of he SMA. The resuling ransien even is measured wih a Tekronix TDS694C Digial Real- Time Oscilloscope. This arrangemen provides consisen measuremens wih variaions in he measured peak ampliudes and riseimes of only a few percen. III. EXPERIMENTAL RESULTS A wide range of high capaciance SMT capaciors have been esed for use in pulse discharge circuis. However, he available capaciance values and raed volages varied considerably beween vendors. waveforms for six represenaive SMT capacior pulse discharges are depiced in Fig.. IV. SIMULATION MODEL DEVELOPMENT Iniially i was anicipaed ha he capacior sudy would compare models for various high volage SMT packages o down-selec several viable candidaes for in-deph esing. However, communicaion wih various high volage SMT capacior manufacurers revealed ha exensive Spice models do no exis for high volage, high capaciance SMT devices because hey are ypically used in bypass and filer circuis. Therefore, a simple LRC circui model was developed based on he curren waveform from he pulse discharge waveforms of Fig.. An approximae soluion of he equaion for curren is derived in erms of he peak ampliude and is associaed ime. Assuming he capaciance is consan a is nominal value, a soluion for R and L is esablished. These parameers are hen compared wih measured values o deermine he SMT device values. Boh he underdamped and overdamped cases are considered, wih criical damping being a special case of each. The underdamped soluion is derived in deail. The overdamped soluion is mahemaically similar excep for he use of hyperbolic funcions. A. Underdamped LRC Circui τ = ( L R Muraa.uF V AVX.uF V Johanson.47uF 5V Vishay.33uF 5V Muraa.47uF 5V Novacap.56uF 5V Time(ns Fig.. Discharge measuremens for various SMT capaciors. ω ( τ = LC ( V τ I ( = e sin( ω (3 di ( d V τ V τ = e sin( ω + e cos( ω (4 A peak curren: = di ( d sin( ω cos( ω L τω = (6 τω = an( ω (7 For he case where ω < an( ω ω (8 This is valid for he parameers of ineres, where L ~ nh, C ~ nf, R ~ fracion of an Ohm, and ~ several nanoseconds a he curren imum. Therefore: τ a he poin of peak curren (9 Subsiuing (9 back ino (3: V I = e sin( ωτ (5 ( For he case where ω τ < sin( ωτ ωτ ( This is reasonable for he parameers above and τ ~ ns Therefore, V I (τ ( el From ( and (: R = (3 V ei L = R I (4 B. Overdamped LRC Circui The overdamped case closely follows he derivaion above, wih he excepion ha as he frequency becomes imaginary,ω becomes ϖ and he rigonomeric funcions become hyperbolic []. ϖ ( (5 = τ LC Equaion (7 hen becomes: anh( ϖ τω = (6 4

4 For he case where ϖ < anh( ϖ ϖ (7 which is sill valid over he parameers described. Equaion ( becomes: V I = e sinh( ϖ τ (8 For he case where ω τ < sinh( ϖ τ ϖ τ (9 which coninues o parallel he underdamped case. Therefore (3 and (4 are approximae soluions for L and R in boh he underdamped and overdamped cases for he parameer range described. These equaions describe he circui variables in erms of he measured peak curren and is associaed ime. The SMT package parameers are calculaed from hese values, knowing he resisance of he CVR and assuming ha he physical layou of he measuremen above is a minimum inducance for he package. R = R ( capacior R CVR L capacior = L ( The peak curren and is associaed ime are measured for each capacior from he waveforms in Fig.. Then (3, (4, (, and ( are used o calculae he capacior parameers. The resuls are abulaed in Table. V. COMPARISON OF RESULTS The calculaed parameers of Table are simulaed and ploed wih heir respecive measured waveforms in Fig. 3 hrough Fig. 8. The peak curren and peak imes are abulaed in Table along wih error calculaions. The model reasonably predics he peak curren, bu is less accurae a predicing he ime of he curren peak and he riseime Fig. 3. Muraa. µf, V measured and simulaed curren. Fig. 6. Vishay.33 µf, 5 V measured and simulaed curren Fig. 4. AVX. µf, V measured and simulaed curren. Fig. 7. Muraa.47 µf, 5 V measured and simulaed curren Fig. 5. Johanson.47 µf, 5 V measured and simulaed curren. Fig. 8. Novacap.56 µf, 5 V measured and simulaed curren. 43

5 Table Summary of capacior parameers. Vendor Capaciance Raed Calculaed Capacior Capacior Calculaed Calculaed P Package Volume Energy P Volage Ipeak TIpeak R R L Energy ino Mached Load Densiy Densiy (uf (V (A (ns (Ohms (Ohms (nh (mj (kw (cm^3 (mj/cm^3 (kw/cm^3 Muraa AVX Johanson Vishay Muraa Novacap Accuracy of he model ends o increase for he lower capaciance, higher volage devices. This is poenially aribued o he ransmission line behavior of MLC capaciors due o heir fabricaion geomery. Coninued SMT capacior sudy will address his observed effec. Power and energy densiy calculaions are included in Table. Energy is calculaed from he raed capaciance and volage. Peak power is calculaed assuming he capacior is discharging ino a resisive load ha maches he resisance of he capacior. VI. CONCLUSIONS This paper presens he pulse discharge characerisics of a represenaive sample of SMT capaciors esed in he. o.5 µf, 5 o V range. This work in progress will coninue o boh evaluae capaciors and increase he accuracy of he Spice model. Sandard SMT capaciors can be successfully used in pulse discharge applicaions for many shos. However, heir performance grealy varies beween package syles and vendors. For example, in Table, he power and energy densiies vary by a facor of 5 beween he capaciors shown. Also, a comparison of he 5 V capaciors shows ha hey delivered a similar oupu even hough one has less capaciance and a hird of he package size. Exensive Spice models do no exis for high volage, high capaciance surface moun capaciors because hey are ypically used in bypass and filer circuis. Techniques have been published which quanify he parasiic inducance and resisance wih measuremens ha rely solely on he wave shape, wih he diagnosic influence facored ou []. Table Comparison of measured and simulaed waveforms Vendor Capaciance % Error % Error Ipeak TIpeak Ipeak TIpeak Ipeak TIpeak (uf (A (ns (A (ns Muraa AVX Johanson Vishay Muraa Novacap However, hese mehods assume ha he capacior value remains consan during he discharge cycle, and ha he oupu will oscillae hrough zero for low load impedances. For his reason, hese mehods are no applicable for his ceramic capacior sudy due o he nonlineariies of he dielecric, hough hey work well for oher ypes of capaciors. Therefore, a firs-pass LRC circui model has been developed which reasonably predics he peak curren of acual measuremens o wihin approximaely 5% of heir measured values, which is he criical parameer of his sudy. The ime of peak curren and he wave shape of he rising edge of he pulse are prediced less accuraely. However, his simple model faciliaes quickly evaluaing many capaciors o selec he bes candidaes for more deailed analysis. A wide range of SMT capaciors have been esed for heir abiliy o be employed in pulse discharge applicaions. The resuls have been presened here for a represenaive sample of capaciors. Clearly, heir performance varies significanly and is no necessarily relaed o package size. Fuure direcions include employing SMT devices in pulse discharge circuis for specific applicaions and coninued model developmen. VII. REFERENCES [] Ness Engineering websie hp://home.san.rr.com/nessengr/echdaa/rlc/rlc.hml [] William C. Nunnally, M. Krisiansen, and Marion Hagler, Differenial Measuremen of fas energy discharge capacior, inducance, and resisance, IEEE Transacions on Insrumenaion and Measuremen, 4,, 975, pp. -4. [3] William J. Carey and William C. Nunnally, Generaion of Sub nanosecond Pulses using a Solid Sae Marx Circui wih TRAPATT Diodes as Swiches, presened a he s Inernaional Power Modulaor Symposium, Cosa Mesa, CA, June 994. [4] W. C. Nunnally and W. J. Carey, Compac, Megawa Sub-nanosecond Impulse Generaors using Convenional Elecronic Componens, presened a he SPIE Inernaional Symposium on Phoonics for Indusrial Applicaions, Boson, MA, Ocober