Wanna know about smps design - Page 3

Eva · 4th December 2006, 08:03 AM

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.

crissty · 4th December 2006, 11:01 AM

Eva
OK, please suggest further how do i proceed, what things do i rectify.

jackinnj · 4th December 2006, 01:19 PM

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

crissty · 4th December 2006, 04:09 PM

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.

N-Channel · 4th December 2006, 05:10 PM

See Marty Brown's Book for calculating snubber component values.

jackinnj · 4th December 2006, 05:15 PM

Also, OnSemi and Fairchild both have white papers on snubbers for SMPS.

Nordic · 4th December 2006, 05:33 PM

http://books.google.com/books?vid=IS...#PRA1-PA257,M1

crissty · 5th December 2006, 01:58 PM

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.

crissty · 5th December 2006, 02:01 PM

Connected a load of 12V / 21W bulb.

crissty · 6th December 2006, 11:45 AM

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.

4th December 2006, 08:03 AM	#21
Eva diyAudio Member Join Date: Oct 2003 Location: Near the sea	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. __________________ I use to feel like the small child in The Emperor's New Clothes tale

4th December 2006, 05:10 PM	#25
N-Channel diyAudio Member Join Date: Mar 2003 Location: Sol System	Snubbed! See Marty Brown's Book for calculating snubber component values.

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4th December 2006, 11:01 AM	#22
crissty diyAudio Member Join Date: May 2005 Location: Greenland	Eva OK, please suggest further how do i proceed, what things do i rectify.

4th December 2006, 04:09 PM	#24
crissty diyAudio Member Join Date: May 2005 Location: Greenland	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.

4th December 2006, 05:15 PM	#26
jackinnj diyAudio Member Join Date: Apr 2002 Location: Llanddewi Brefi, NJ	Also, OnSemi and Fairchild both have white papers on snubbers for SMPS.

4th December 2006, 05:33 PM	#27
Nordic diyAudio Member Join Date: Sep 2005	http://books.google.com/books?vid=IS...#PRA1-PA257,M1

6th December 2006, 11:45 AM	#30
crissty diyAudio Member Join Date: May 2005 Location: Greenland	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.