LNK625 shield connection & diode
Goodmorning, I'm trying some applications with LNK625. I saw the DI-201 design idea. I'm trying also the applications for conducted emission. In my tests I saw that if I connect the shield (dot) to the +dc and I connect the diode (secondary side) in the positive line (like an45) I have a discrete behaviour. But, if I connect the diode (2nd) in the negative line (like di201) the performance is worst. Why? In an45 is shown to connect the shield (dot) to the 0V line and connect the diode (2nd) in the positive line. How is it possible? Thank you. Regards. Nicola.
Comments
Thank you. But, if I compare the DI-201 & AN-45 windings with the E-shiled transformer techniques (Primary, 1st page), I see differences from the functions of the windings and thier winding order. In DI-201 there are 4 windings, and the shield is between primary and secondary. You told me that it's called "cancellation winding", instead in E-shield slides it is called "balanced winding". In an45 there are 7 windings and the first one is called "cancelation", but you told me it is called "balanced". So, you told me, that the "cancelation winding" can be connected to the B+ and the "shield winding" can be connected to the primary RTN. Ok, what's the difference between the description in "E-shield techniques" and what you told me before? Another question is: do you use a Feedback winding as a shield winding? Thank you very much. Best regards. Nicola.
The cancellation winding is usually the first windinging layer and is commonly refernced to B+
The balanced shield is last primary layer (faces secondary) and may also function as feedback winding. If the output diode is in return leg then the function of balanced winding is changed to becoming a cancellation winding -- and I advised previously this particular arrangement is a little trickier to get right
The shield in DI-201 is called a cancellation winding which serves to neutralize
Emmissions from core of transformer. This type of shield should always be tied to B+. The AN45 shield is using a balanced winding technique which minimizes common mode noise generation by primary and secondary windings. This type is generally tied to primary return but sometimes can be tied to B+. It is a matter of experimentation.
The output diode connected to the minus end is another way to generate cancellation and can work well for some designs -- it is more touchy to get just right so it might be best to start with diode in + track.