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How to compute the Reset and Clamp circuitry ?

Posted by: Chris on Sat, 08/02/2008
I am designing a universal AC input 21V 3A output using a TOP247Y. This is the first time I design such a switching power supply and I'm not so sure how to design the Clamp and Reset circuitry for that power. I went thru the AN31 but I'm still unable to figure out the components value. Attached is my PIExpert design. Please help me. Regards.
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Submitted by PI-Spock on Wed, 08/06/2008
PI Expert version 7.0 now includes clamp circuit design. For example for your design it will recommend a RCD clamp circuit and will recommend initial values for the components based on the estimated leakage inductance and the peak primary current.
Submitted by prasun on Thu, 08/07/2008
hello, pls do not go with TOP 247Y because it may be a older part, a new version of series TOP-Hx is already out. Pls refer data book & select the device suitably based on power specification,enclosure & Operating line. Also, yes, PI-XLS software is available of PI web itself for better snubber design.
Submitted by sabahaddin babacan on Mon, 08/25/2008
It was a bit dificult if you have the correct diodes and a good transformer the circut will work but if you transformer is not good than it will never work and the diodes at the clamp will blow. You may contact Ep-Co elektronic for the correct transformer I buy from there. regards
Submitted by Renu_Bala on Fri, 06/18/2010

but how will calculate the value of these components?