Transformer winding practices for smps

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Many of us DIYers need to wind their own ferrite core transformers and when the need comes we all try to put our hands in it. Some of these cores will be just carrying low voltages and the insulation between windings will not have to be so important due to the low voltages involved and does not have to be so specific.

However problems will arise when we deal with off line SMPS and care must be taken into account when dealing with insulation between windings and mandatory spacing between windings and bobbin cheeks. The reason for all this is due to the high voltages involved ranging in the 350volt region these normally having DC content in them.

We must understand that DC voltage tends to arc more readily as opposed to AC sine waves and often DC square waves when powering inductive loads have also spikes in them and these tend to rise quite considerably thus adding with the switching voltage itself.

Keeping all this in mind we must ensure that NO ARCING between windings will occur as these tend to have a very high temperature and thus ruining the windings and hence also the transformer itself. The risk of electric shock is also dangerous with the primary winding arcing with secondary windings and is lethal.

We must also understand that these ferrite cores get hot during operation and care must be taken that we use heat resisting materials in them.

The risk of things catching fire is also likely when arcing happens and I must Stress that care must be taken at all times so these things will not happen. The EU regulation board have set a list of mandatory rules regarding spacing and also type of materials used in the manufacture of these off line smps cores. I am not going to state all the mandatory necessities here but will point out the most important ones. Illustrations and pictures will help us understand more these procedures.

The most important mandatory regulations are as follows:-

All insulation materials are to be heat resisting up to a minimum of 150C these are all tapes used during manufacture including tapes between windings and also margin tapes. These tapes have to be non shrinkable with with heat and maintain their properties during use and will not deteriorate or deform with time. These tapes have to withstand high voltages of at least 600volts. Multi layers may be applied to bring out the necessary thickness to achieve the necessary voltage pressure resistance applied to it.
Margin clearance at the end of the bobbin is to be not less than 4mm. This however can be divided in to two thus having 2mm at the ends of each winding sides. With minimum clearance of 2mm has to be put in every winding including primary and secondary windings. This will bring a total of 4mm to the end path with each winding

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  1. mustafash92's Avatar
    i love smps i,m study mechatronics engineering