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Select core for Pure sine wave LC filter?

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arvinfx

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Hi,

I need a suitable O-ring core for 4.5A ( Peek) about 7.5mH, but I don`t have enough knowledge.

Witch size is suitable for my project?
 
You need to know the inductance required, the frequency, and the current carrying capacity.
The resistance of the winding will cause an I*I*R power loss. To reduce the power loss, use a larger conductor size. This will require a larger core to accomodate the amount of wire. So you will need to use a bigger core. You need to iterate these steps until you have a low enough power loss. Presumably there is NO DC current in the coil winding. If there is DC, you will need to have an air gap in the core.
 
Is air gap for Dc current only?

My project is this:

13752595801-jpg.75207


The frequency is 25Khz and SPWM is running on this H-bridge. for low THD I need to have a toroidal core that I said beside 30m inductor . I know about resistance loss , I need information about selecting suitable core for this project, 7-8mH and maximum peak of current is 5A.
 

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For this stuff I have the Philips Elcoma data book C5. This covers Philips range of Ferroxcube for power cores. The book includes a section on choke design. In your case, the operating frequency is 25 kHz but the waveform is presumably a square waveform which produces a sinewave with low THD (probably around 4 % or so.
the design requires judgement (intelligent guessing), and requires the I*I* Lmin value to be calculated (5*5*0.008) get an idea of the size of core to select. Then, the 'no. of turns per mH' is obtained based on the core size and the gap thickness. The core has to be sized in a way that keeps the peak induction below a certain value (based on the ferroxcube type). Losses consist of core eddy current loss plus skin effect loss in the conductors if the wire diameter is too large. Wire loss increases as d ** 4 whereas resistance increases by d**2
The Philips 'U' cores UU93/152/30 appear to be too small for this application. They would overheat by having too high a flux density (according to the I*I*L value).
Short of me doing the design for you, you can take this info and search what's available from core manufacturers.
Hope this helps.
 
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