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Old 4th December 2006, 09:03 AM   #21
Eva is offline Eva  Spain
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I don't want to sound silly, but that waveform looks really polluted with EMI. You have still a lot of work to do to clean things up. The amount of rubbish during switching transients (both unexpectedly picked up by oscilloscope probe and present where you are measuring) has to be reduced by at least an order of magnitude.
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Old 4th December 2006, 12:01 PM   #22
crissty is offline crissty  Greenland
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Eva
OK, please suggest further how do i proceed, what things do i rectify.
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Old 4th December 2006, 02:19 PM   #23
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Default Re: Good reference

Quote:
Originally posted by rt7085
You are asking very fundamental questions here! So, instead of explaining every detail I am going to recommened a book to you: "Switching Power Supply Design & Optimization ", by Sanjaya Maniktala.

Sanjaya has a new book out: "Switching Power Supplies A to Z" --and I believe that there is a webcast he did which is archived on National Semi's website.

Jack
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Old 4th December 2006, 05:09 PM   #24
crissty is offline crissty  Greenland
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dear jack,
right now i dont have access to the book, so please help with any suggestions what should i check.

Actually i have used ultra fast clamping diodes on source drain of mosfets, but did not use any snubber, should i use it, how do i calculate the cap res values.
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Old 4th December 2006, 06:10 PM   #25
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Talking Snubbed!

See Marty Brown's Book for calculating snubber component values.
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Old 4th December 2006, 06:15 PM   #26
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Also, OnSemi and Fairchild both have white papers on snubbers for SMPS.
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Old 4th December 2006, 06:33 PM   #27
Nordic is offline Nordic  South Africa
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http://books.google.com/books?vid=IS...#PRA1-PA257,M1
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Old 5th December 2006, 02:58 PM   #28
crissty is offline crissty  Greenland
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OK, now i get a perfect gate pulse, and now there is no heating on the mosfets too.
I added a Fan as a load & everything gets smooth, & did not attach a snubber.
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Old 5th December 2006, 03:01 PM   #29
crissty is offline crissty  Greenland
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Connected a load of 12V / 21W bulb.
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Old 6th December 2006, 12:45 PM   #30
crissty is offline crissty  Greenland
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Please Please reply GURUS,

I have a 15V tap on trafo, i wanna know what value of startup resistace from +320V to positive voltage for the circuit, so that it should be able to startup the circuit and be capable of initial full turn on of the Mosfets properly. Presently i am giving reg 12V from seperate transformer to the circuit.

One more thing is, when i attach the 12V 21W bulb to output, the input DC shows 290V, when AC is 230V, is that OK. Cause I have designed Trafo for 360 V input.
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