AN APPENDIX Diode Reverse Recovery Analysis [4] a typical reverse recovery waveform is shown in Figure A-1. The reverse recovery time trr has been traditionally defined as the time from diode current zero-crossing to where the current returns to within 10% of the peak recovery current IRM(rec). This does not give enough information to fully characterize the waveform shape abetter way to characterize the rectifier reverse recovery is to partition the reverse recovery time into two different regions ta and tb as shown in Figure A-1. The ta time is a function of the forward current and the applied di/dt. a charge can be assigned to this region denoted Qa, the area under the curve. The tb portion of the reverse recovery current is not very well understood Measured tb times vary greatly with the switch characteristic, circuit parasitics, load inductance and the applied reverse voltage. a relative softness can be defined as the ratio of tb to ta. General purpose rectifiers are very soft(softness factor of about 1.0), fast recovery diodes are fairly soft(softness factor of about 0.5)and ultrafast rectifiers are very abrupt (softness factor of about 0.2) tr total reverse recovery time [4] Source Controls. TMOs Power MOSFET ta fall time due to stored minority charge Transistor Data, Q4/92, DL135, Rev 4,(Phoenix: Motorola t= application and device dependent nc,1992),pp.2-922to2-9-23 RM(rec)=peak reverse recovery current Figure A-1. Reverse Recovery Waveform up AUEA al parameters can and do var ling"Typicals" must be validated for each customer application by customers not convey any license under its patent rights nor the rights of others. any other he Motorola product could create a situation w or use Motorola products for any suc tly or indirectly, any claim of personal injury or death such unintended or unauthorized use, even if such claim alleges that Motorola was negligent regarding the design or manufacture of the part. Motorola and (AA) are registered trademarks of Motorola, Inc. Motorola, Inc is an Equal Opportunity/Affirmative Action Employer. SA/EUROPE: Motorola Literature Distribution N: Nippon Motorola Ltd. Tatsum-SPD-JLDC, Toshikatsu O P.O. Box 20912: Phoenix, Arizona 85036. 1-800-441-2447 bu-Butsuryu-Center, 3-14-2 Tatsumi Koto-Ku, Tokyo 135, Japan. 03-3521-8315 MFAX:RMFAXO@email.sps.mot.com-TOUCHTONE(602)244-6609HONGKONG:MotorolaSemiconductorsHKLtd.8BTaiPingIndustrialPark, 51 Ting Kok Road, Tai Po, N.T., Hong Kong. 852-26629298 MTO-OLA AN1541

8 MOTOROLA APPENDIX Diode Reverse Recovery Analysis [4] Figure A–1. Reverse Recovery Waveform total reverse recovery time fall time due to stored minority charge application and device dependent peak reverse recovery current ÉÉÉ ÉÉÉ ÉÉÉ ÉÉÉ ÉÉÉ tb ta trr IRM(rec) IF di/dt Qa Qb trr = ta = tb = IRM(rec) = A typical reverse recovery waveform is shown in Figure A–1. The reverse recovery time trr has been traditionally defined as the time from diode current zero–crossing to where the current returns to within 10% of the peak recovery current IRM(rec). This does not give enough information to fully characterize the waveform shape. A better way to characterize the rectifier reverse recovery is to partition the reverse recovery time into two different regions, ta and tb, as shown in Figure A–1. The ta time is a function of the forward current and the applied di/dt. A charge can be assigned to this region denoted Qa, the area under the curve. The tb portion of the reverse recovery current is not very well understood. Measured tb times vary greatly with the switch characteristic, circuit parasitics, load inductance and the applied reverse voltage. A relative softness can be defined as the ratio of tb to ta. General purpose rectifiers are very soft (softness factor of about 1.0), fast recovery diodes are fairly soft (softness factor of about 0.5) and ultrafast rectifiers are very abrupt (softness factor of about 0.2). [4] Source: “Motor Controls,” TMOS Power MOSFET Transistor Data, Q4/92, DL135, Rev 4, (Phoenix: Motorola, Inc., 1992), pp. 2–9–22 to 2–9–23. Motorola reserves the right to make changes without further notice to any products herein. Motorola makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does Motorola assume any liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without limitation consequential or incidental damages. “Typical” parameters can and do vary in different applications. All operating parameters, including “Typicals” must be validated for each customer application by customer’s technical experts. Motorola does not convey any license under its patent rights nor the rights of others. Motorola products are not designed, intended, or authorized for use as components in systems intended for surgical implant into the body, or other applications intended to support or sustain life, or for any other application in which the failure of the Motorola product could create a situation where personal injury or death may occur. Should Buyer purchase or use Motorola products for any such unintended or unauthorized application, Buyer shall indemnify and hold Motorola and its officers, employees, subsidiaries, affiliates, and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized use, even if such claim alleges that Motorola was negligent regarding the design or manufacture of the part. Motorola and are registered trademarks of Motorola, Inc. Motorola, Inc. is an Equal Opportunity/Affirmative Action Employer. How to reach us: USA / EUROPE: Motorola Literature Distribution; JAPAN: Nippon Motorola Ltd.; Tatsumi–SPD–JLDC, Toshikatsu Otsuki, P.O. Box 20912; Phoenix, Arizona 85036. 1–800–441–2447 6F Seibu–Butsuryu–Center, 3–14–2 Tatsumi Koto–Ku, Tokyo 135, Japan. 03–3521–8315 MFAX: RMFAX0@email.sps.mot.com – TOUCHTONE (602) 244–6609 HONG KONG: Motorola Semiconductors H.K. Ltd.; 8B Tai Ping Industrial Park, INTERNET: http://Design–NET.com 51 Ting Kok Road, Tai Po, N.T., Hong Kong. 852–26629298 AN1541/D

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