Coupling factor of coupled inductor

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skn96

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Hello All
I'm trying to design a coupled inductors for the output stage of a 2.1kW, 400VDC input full bridge dc/dc converter with two complimentary output (+85 /-85). I'm using two 30 turns winding on a kool Mu (sendust) 26µ core to achieve two 25 uH inductor on the same core. So I will get a 50uH effective inductance on each output (+85 and -85) if the coupling factor is very close to 1. It's my first experience with coupled inductors and I wanna know if assuming the coupling factor very close to 1 is practical or not? If not how much coupling I can expect? What to do the maximize coupling?

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I would not use a coupled inductor if I were you, but it will work. You situation is just about ideal as you have identical output voltages (and currents I presume) and I assume the same type of output diodes. Problems start arising when you have two different output voltages, one with a Schottky diode and another with a fast recovery. Invariably the one voltage is not an integer multiple of the other so the turns ratio is not ideal. Under these conditions they should not be coupled too tightly.
In the interest of getting the product out the door in a reasonable time I would opt for separate output inductors and refine it if I have the time later. Depends on you situation I suppose. I try to minimise risk.
 
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