Optimizing Ultra-Fast POWERplanar Rectifier Diode Switching Power Supp
|
|
|
Top Searches for this datasheet
Optimizing Ultra-Fast POWERplanar Rectifier Diode Switching Power Supplies
Optimizing Ultra-Fast POWERplanar Rectifier Diode Switching Power Supplies
INTRODUCTION device high voltage AC-DC power supplies ultrafast reverse recovery rectifier diode These diodes Figure only play major role power supply efficiency also major contributors circuit electromagnetic interference (EMI) even cause transistor failure they selected correctly would assume that this rectifier diode should approximate behavior ideal switch zero on-state voltage reverse leakage current instanteous turnon first glance design this single pn-junction device would appear quite straight forward review device equations reveals that many compromises must made optimize performance understanding these tradeoffs will allow circuit designer select most appropriate rectifier diode
National Semiconductor Application Note Ralph Locher January 1989
10062
Consider non-ideal behavior rectifier affects circuit performance buck regulator Figure solid lines Figure depict switching behavior transistor switch rectifier comparison waveforms (dashed lines) that represent ideal rectifier There four differences between cases most significant difference that peak collector current transistor switch Figure turn-on (time been increased magnitude peak reverse recovery current rectifier (IR(REC)) Correspondingly peak power dissipation within transistor increased from shown Figure maximum transistor voltage turn-off Figure been increased dynamic voltage drop rectifier during turn-on Since buck regulators generally voltages this increase minimal effect However more significant forward converter circuit Figure bridge circuits operating from high voltages where voltage margins cannot generous Since rectifier ideal power dissipation consists following components Conduction loss during on-time Turn-off loss during time turn-on loss during time (Figure Reverse blocking loss during period rectifier regains reverse blocking capability time ``snappy'' rectifier that quickly turns IR(REC) will contribute much more than ``soft'' fast recovery rectifier better transistor switch will intensify rather than improve shortcomings fast recovery rectifier necessary consider more fully conduction switching behavior rectifier diode
FIGURE Buck Regulator Step-Down Input Voltage
10062
FIGURE Forward Converter
AN-557
POWERplanaris trademark National Semiconductor Corporation C1995 National Semiconductor Corporation
10062
RRD-B30M115 Printed
CONDUCTION LOSSES conduction on-state losses occur whenever rectifier conducting forward current consists simply integration during on-time Literature dealt extensively with computation many different rectifier structures (Reference National Semiconductor POWERplanarline fast recovery diodes planar passivated epitaxial type which cross-sectional view found Figure shown that inversely proportional minority carrier lifetime directly proportional epitaxial thickness Figure Figure plots theoretical curves normalized minority carrier lifetimes rectifiers with 250V 500V avalanche voltage breakdown Since approximately equal minority carrier lifetime apparent that high current pn-junction rectifiers limited reverse recovery times because dramatically increases minority carrier lifetimes less than these also apparent that curves have broad minima around that another reason select this value minority carrier lifetime that becomes independent small changes minority carrier lifetime manufacturing tolerances immediately obvious that maximizing current through rectifier minimize However reverse recovery losses will quadruple that increasing attention must paid this parameter operating frequency raised
10062-3
FIGURE Transistor Rectifier Voltage Current Waveforms Buck Regulator Figure Transistor Rectifier Voltage Waveforms Transistor Rectifier Current Waveforms Transistor Power Dissipation Rectifier Power Dissipation POWER LOSSES ULTRA-FAST RECTIFIER DIODE Consider idealized rectifier current voltage waveforms Figure buck regulator Power dissipation within rectifier duty factor P(conduction) P(blocking) P(reverse recovery) (VFIF VRIR) VRMIR(REC)tbf Typical values 200V rectifier (assuming IR(REC) 200V (8A) (50V) (200V) (2A) kHz) 025W 125W
10062
FIGURE Representative Current Voltage Waveforms Rectifier Buck Regulator Found Figure
10062
FIGURE Cross-Sectional View POWERplanarP Fast Recovery Rectifier REVERSE RECOVERY LOSSES pn-junction rectifiers operating forward direction store charge form excess minority carriers amount stored charge proportional magnitude forward current process which rectifier diode brought conduction returned block state called commutation Figure shows expanded view current commutation also called reverse recovery Starting time rectifier switched from forward conducting state specified current ramp rate (bdIF current ramp rate will determined external circuit turn-on time transistor switch During time store charge within rectifier able supply more current than circuit requires that rectifier behaves like short circuit Stored charge depleted both reverse recovery current recombination within rectifier Eventually stored charge dwindles point that depletion region around junction starts grow allowing rectifier regain reverse blocking voltage capability (t2) From circuit-design standpoint most important parameters peak reverse recovery current ``S'' softness factor ``snappy'' rectifier will produce large amplitude voltage transient contribute significantly electro-magnetic interference Figure illustrates actual reverse recovery rectifier diodes peak voltage snappy rectifier 175V compared 142V peak FRP820 higher voltage resulting from both higher IR(REC) fact that reverse recovery current decays zero shorter time
10062
FIGURE Normalized 250V 500V Rated Rectifiers Function Minority Carrier Lifetime REVERSE BLOCKING LOSSES Planar passivation techniques have reduced surface leakage currents (IR) negligible amount that principle reverse leakage current recombination current space charge region Some many methods control minority carrier lifetimes electron neutron irradiation gold platinum diffusion each with advantages disadvantages 200V ultrafast recovery rectifiers gold diffusion still represents best compromise between speed ``soft'' recovery drawback gold diffusion relatively high reverse leakage current should pointed that reliability gold-diffused product same other rectifiers (all other factors being equal) since this leakage current bulk surface phenomenon Figure illustrates dependency recombination current junction temperature minority carrier lifetime which inversely proportional amount gold depletion region Experimental leakage test results have been plotted Figure National Semiconductor series rectifiers (FRP820 FRP1620 respectively) These points indicate that current injection level lifetime ranges from ns-30 relatively independent Since reliability design guidelines specify that rectifiers operated one-half their voltage rating below their maximum junction temperature expected leakage currents well designed power supplies will less than
10062
FIGURE Regeneration Current Gold-Doped Rectifier Diodes
10062
FIGURE Expanded View Current Commutation Rectifier Diode relative snappiness rectifier defined quantitatively dividing reverse recovery time into subperiods shown Figure softness factor ``S'' simply ratio rectifier with value factor will more likely produce dangerous voltage transients will also dissipate less reverse recovery energy than high factor rectifier reasonable compromise between these conflicting constraints would design rectifier with factors FRP820 rectifier competitive device Figure respectively Only recently become possible model ramp recovery p-i-n rectifiers (References following equations have proved useful predicting reverse recovery parameters Wi0u 40Dau
10062
Test Conditions
10062
Test Conditions
IR(REC)
QR(REC) where
80Dau
FIGURE Comparison Reverse Recovery FRP820 Series Rectifier Snappy Rectifier REVERSE RECOVERY CHARACTERIZATION Figures 10-13 plot QR(REC) IR(REC) versus FRP1600 series rectifiers typical conditions 200V different junction temperatures Theory only predicts also been experimentally verified that these parameters relatively independent only value latter suffices three four Figures 10-13 completely specifies reverse recovery behavior rectifier Since vary least over plotting range convenient formulate reverse recovery energy loss microwatts terms circuit parameters
minority carrier lifetime epitaxial thickness ambipolar diffusion constant
blocking voltage rating rectifier primarily determines given note that short minority lifetime only decreases IR(REC) happily increases These parameters plotted function minority carrier lifetime Figure been noted before minority carrier lifetime been targetted ns-30 minimize this choice resulted typical value IR(REC)
where peak reverse voltage ramp rate operating frequency (kHz)
Strr
(mW)
10062
FIGURE Theoretical Plots IR(REC) Minority Carrier Lifetime
10062
FIGURE Reverse Recovery Time FRP1600 Series Rectifier Diodes
10062
10062
FIGURE Reverse Recovery Current FRP1620 Series Rectifiers
FIGURE Softness Factor FRP1600 Series Rectifier Diodes Example Calculate reverse recovery power loss FRP1620 rectifier running 100V From Figures Substituting these values above equation (100V) (100 ms)(75 kHz) 29)(56 (2)(0
10062
FIGURE Reverse Recovery Charge FRP1600 Series Rectifier Diodes
205W There ways shape reverse recovery voltage spike most simple still most popular snubber circuit connected across primary transformer Figure This serves dual purpose suppressing voltage ringing switching action both transistor rectifier William McMurray shown design snubber minimize voltage transients ramps just diode reverse recovery current (Reference also
Optimizing Ultra-Fast POWERplanar Rectifier Diode Switching Power Supplies
sign snubbers minimize transistor power dissipation (Reference date because snubber plays major role reducing design tends empirical rather than theoretical CONCLUSION This application note pointed major considerations designing ultrafast reverse recovery rectifier shown that control minority carrier lifetime arriving optimum device Because diode contributes reverse recovery behavior must carefully controlled characterized order guarantee similar performance from
REFERENCES Ghandhi Semiconductor Power Devices (NYC) John Wiley Sons Berz ``Ramp Recovery p-i-n Diodes'' Solid-State Electronics Private Communication McMurray ``Optimum Snubbers Power Semiconductors'' IEEE Trans Industry Applications Sept 1972 McMurray ``Selection Snubbers Clamps Optimize Design Transistor Switching Converters'' PESC 1979 Conference Record
LIFE SUPPORT POLICY NATIONAL'S PRODUCTS AUTHORIZED CRITICAL COMPONENTS LIFE SUPPORT DEVICES SYSTEMS WITHOUT EXPRESS WRITTEN APPROVAL PRESIDENT NATIONAL SEMICONDUCTOR CORPORATION used herein Life support devices systems devices systems which intended surgical implant into body support sustain life whose failure perform when properly used accordance with instructions provided labeling reasonably expected result significant injury user critical component component life support device system whose failure perform reasonably expected cause failure life support device system affect safety effectiveness
AN-557
National Semiconductor Corporation 1111 West Bardin Road Arlington 76017 1(800) 272-9959 1(800) 737-7018
National Semiconductor Europe (a49) 0-180-530 Email cnjwge tevm2 Deutsch (a49) 0-180-530 English (a49) 0-180-532 Fran (a49) 0-180-532 Italiano (a49) 0-180-534
National Semiconductor Hong Kong 13th Floor Straight Block Ocean Centre Canton Tsimshatsui Kowloon Hong Kong (852) 2737-1600 (852) 2736-9960
National Semiconductor Japan 81-043-299-2309 81-043-299-2408
National does assume responsibility circuitry described circuit patent licenses implied National reserves right time without notice change said circuitry specifications
Other recent searches
Si4505DY - Si4505DY Si4505DY Datasheet
MBN1200E33D - MBN1200E33D MBN1200E33D Datasheet
LTC3872 - LTC3872 LTC3872 Datasheet
ICS8421004I-01 - ICS8421004I-01 ICS8421004I-01 Datasheet
2SB1148 - 2SB1148 2SB1148 Datasheet
2SB1148A - 2SB1148A 2SB1148A Datasheet
Privacy Policy | Disclaimer
© 2012 Datasheet Archive
