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# Predicting the SMPS radiated EMI in the transformer level

## Predicting the SMPS radiated EMI in the transformer level

(OP)
Hello all,

For predicting the conducted interferences caused by an SMPS, there is the EMC box, which you can use in the transformer level, ie. to solely measure the transformer.

But is there any similar kind of quick method in the transformer level for predicting the final RADIATED interferences of an SMPS, say, by measuring something from the winding? I understand the unevenness or "messiness" of the winding is very crucial considering radiated EMI, so how to measure this?

Best regards,
Jaakko

### RE: Predicting the SMPS radiated EMI in the transformer level

Considering it would change (slightly?  greatly?) from unit to unit, you're only hope of determining actual radiated power is to measure over a 3D landscape.

Dan - Owner
http://www.Hi-TecDesigns.com

### RE: Predicting the SMPS radiated EMI in the transformer level

(OP)
Any idea of what kind of commercial equipment would be available for this kind of measurement? Perhaps eddy current testing instruments could be used?

-Jaakko

### RE: Predicting the SMPS radiated EMI in the transformer level

It will depend hugely on the voltage, current, frequency, and the geometry of the transformer. In other words is this transformer an open or closed design to limit magnetic flux leakage and/or surrounding stray electric fields.

Electromagnetic radiation in the near field can be predominantly in the E or H fields, but total radiated power should be measured with a calibrated antenna and the proper equipment.

It is also highly likely that much of the total radiated noise power will come from other parts of the circuit as well as just the transformer. No way to fudge this, you really need to  get the whole contraption tested by an EMC lab, and act on whatever advice they offer on how to fix it if it is outside the limit.

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