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Current transformer - RMS and Peak

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rms current

Hello!
In my SMPS I need to use a current transformer. My RMS current is < 15A, but the peak value is 33A (worst case).

My question is, would a 25A RMS current transformer be OK?

I would like to use the CST306-2A transfomer:
N: 1:100
Lm: 14mH
Irms: 25A

The problem is, the datasheet doesn't say anything about peak current. It has good N and Lm values. Chosing a 35A RMS would mean 1:50 and 3.5mH which is too low for my design.

Can anyone help me out?

Best regards,
George
 

calculate rms current duty cycle

Basically, only RMS current counts for a transformer. The core shouldn't saturate of course, which is a matter of the voltage integral and achieved by a sufficient low termination resistor for a current transformer.
 

rms to peak

Thanks!
One more thing. I'm having problems with the calculating Volt-uSec product for the current transformer.
I need to put a current transformer here:
2ii8kd5.png


How do I calculate it?


Thank you again!
George
 

transformer peak rms

The Volt-uSec product depends on the termination and can be most easily calculated related to the secondary. That's what most CT datasheets specify. As another remark, cause you have an unipolar current, it's important that the current is keeping a maximum duty cycle to allow the transformer to demagnetisize between pulses, otherwise it would saturate.
 

calculating rms & peak

FvM you're the man :D
After a few days I got a reply from Triad Magnetics regarding the CST306-2A (25A RMS) transformer:

As long as the RMS current is at or below the 25A rating, a 33A peak current is acceptable. You will also want to ensure that this peak does not exceed the maximum Volt * microseconds limit because great inaccuracies occur if this limit is exceeded; however, no damage is done to the current transformer if this does occur (for example, the peak current is not important to your current monitoring, in which case the inaccuracy is of no importance).
Click to expand...

...which is exactly what you said.

Best regards!
 

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