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Old 9th August 2012, 07:18 AM   #1
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Default About RCD snubber ckt

1) If snubber is to protect the switching transistor, then if the max voltage during turnoff of device is lesser than the Max VDS rating of mosfet, do we still need snubber?
2) If we implement snubber at primary winding of flyback transformer, do we need to add protection across the switching mosfet?
3) While designing snubber if we calculate peak voltage that would appear across switching mosfet.So after applying snubber ckt, Can we choose mosfet with lower voltage ?
4) how can leakage inductance be minimied? Or what factors influance leakage inductance of flyback transformer?
5) Wish to understand what is deltaVs (delta snubber voltage). (in application notes its said to be allowed ripple but cant get idea what do they mean by it.)
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Old 10th August 2012, 01:37 PM   #2
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Somebody pls, help
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Old 12th August 2012, 09:59 PM   #3
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1. The transient peaks can not be predicted accurately to be less than Vds Max. Also very fast, very difficult to measure.
2. The snubber across the transformer does not protect switch from its own stray inductance. ie. self inductance, pcb tracks, lead wires, etc.
3. if you accept 1 & 2 above.
4. transformer design, pcb design. search online for trafo design notes.
5. DeltaV is the rate of change of voltage. ie. rise/fall time. usually refers to snubber design, to prevent turn-on of the switch device by very fast transients.
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Old 19th August 2012, 11:42 AM   #4
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Whizgeek, thanks for your reply.

& sorry for the delay, its only today i checked this thread after 12th of aug, thinking its gone dead.
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Old 19th August 2012, 12:13 PM   #5
AndrewT is offline AndrewT  Scotland
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Au is obviously not interested in researching his new project !
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Old 19th August 2012, 02:09 PM   #6
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Dear Whizgeek, Vds is mentioned as voltage , its not a factor of time. although this is used in calculation of Csn( snubber capacitor) so i guess its about damping voltage. and its time relation. but not able to visualize it. Can I request you a figure (diagram) or a reference link. or may be even you can elaborate it to me.
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