CMR in a TRANSFORMER.

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palreddyanurag

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Above Figure Shows Standard Test Circuit to Test CMR of Transformer...

a) 'eCM'=Sine Wave,Is 'eo' also Sine Wave
b) If 'C' were grounded instead fo 'R';does 'eo' remain same?
c) Is CMR due to Asymmetry of Inter-winding Capacitance of Transformer.

Below Shows IEEE standardized equivalent circuit of a pulse transformer.
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Why is the Circuit Asymmetrical w.r.t Rcu1,2 ,L(sig)1,2 ,C12?
 

a) Do you see a way to get a non-sinusoidal output when applying a sine?
b) Not necessarily (due to asymmetrical capacitance)
c) No, also with symmetrical capacitance, due to asymmetrical circuit
 
CMR in pulse transformers is rated for MIL-PRF/21038/27E as 45dB min @ 1MHz

I believe coupling capacitance, C12 must be < 1/200 of C2 to achieve this CMR as C1 is shorted during the test.

Value of C2, n and Lmag dominates the upper frequency limit.
 

Thank You For Replying...
- So from b) and c) we can say the finite value of CMR is due to Asymmetry of Transformer as a whole i.e. due to Leakage Inductance, InterWinding Capacitance...
- So in CMR Calculation 'eo' = max('eo C' , 'eo R' ) where 'eo C' = Voltage on C when R is Grounded and Vice Versa
 


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