Shield windings from AN-18
Thanks for the advice on shield windings in AN-18.
Have you got any DER's that have shield windings for flyback?
What do you say about which way round to wind shield windings...ie the polarity.
Also, is it ok to have a high induced voltage from one end of the shield winding to the other? (ie lots of turns)
Also, is the attached shield winding, with unfortunate gaps, still OK?
评论
Hi treez,
Shield winding minimize the magnitude of dv/dt on seen by the secondary winding from high primary voltage swing. Shield winding should cover the whole length of the bobbin to be more effective and it should be out of phase from the primary.
Hi,
As you say, i thought it (the shield) would be wound to minimize dv/dt with the secondary....so secondary dot and shield dot would need to be at the same end of the bobbin?
The following offers a more detailed view.....
https://www.ti.com/seclit/ml/slup338/slup338.pdf
Hi treez,
If you want to counter the primary voltage effect of dv/dt with turn-ON of the switch, the secondary dot and shield dot would neet to be at the same end of the bobbin. If you wanted to counter the flyback effect/turn-OFF of the switch which have higher voltage magnitude the dot between secondary and shield needs to be at the opposite end. Thank you.
surely secondary_dot and shield_dot should always be at the same end of the bobbin?....this will then always minimize dv/dt between shield and secondary
Hi,
If we have a offline flyback with shield windings as follows……
Pri1---Bias-----shield1---sec----shield2------pri2
Do you agree that Shield1 dot should be at same end of bobbin as pri1 dot, also Shield2 dot should be at same end of bobbin as pri2 dot?
This will reduce the voltage between the primary and shield windings and reduce dv/dt?