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Sepic smps current transformer use

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Newbie level 2
Jun 26, 2014
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I build a Sepic converter around an UC3843 IC. The converter is suposed to work in continuous mode. The primary current, that passes through the Mosfet switch, is continuous. I try to use a current transformer because it is a high current and a sense resistor is unuseable, but current transformers are for AC currents so may be there is my problem. Can anyone give me a hint of how to use the CT. The Sepic is rated to be 500W.
The image depicts the whole circuit. I plan to use the circuit as a power converter for a wind turbine.


  • sepicompleto.jpg
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Its quite likely that the current transformer is saturating due to too high a voltage across the secondary.

It depends on the magnetics design of the current transformer, but many of them struggle to produce much more than 1 volt, and you are probably losing most of that across the series diode.
Check the specifications of your CT, and use a low voltage drop shottky diode.

Your best bet is either to design and wind your own current transformer, or use a Hall effect sensor instead.

The circuit should work, but only if the current transformer can generate enough usable peak output volts to satisfy your controller chip without saturation.

Thanks Tony, my scope broke two days ago. I will fix my problem and look at your suggestion. However, as you mention the difficulty of CT to produce the necessary voltage, I though to use a current sensor based on hall effect as those produced by allegro, like the ACS 712.

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