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I used the eDesign Suite set up a Flyback converter for the L6566.   I need help with the compensation

Question asked by Brandon Taylor on Mar 15, 2018

I used the eDesign Suite set up a Flyback converter for the L6566.   The compensation loop design looked unreasonable with "Ropto" being only 51Ohms (output is 26V).  It would need to be 9W while attempting to source ~>400mA to the shunt and optocoupler.

 

Its an AC/DC QR flyback with 110-120Vac in.; 26Vdc (2%ripple) out @ up to 9A;  Primary inductance is 90uH; shunt voltage is 2.5V. I need a compensation application for the L6566, I can't trust the tool and would like guidance on setting the proper Rfb and Cfb for stable compensation.

 

The compensation pin is pulled up by 25K to 5V+/-2%.  I'm using a CTR of ~1 and a parallel (opto collector to ground) cap of 680pF.  For cout i'll use either 2200uF or 3300uF.

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