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Forum Index : Electronics : Another Saturation Tester Design

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Warpspeed
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Joined: 09/08/2007
Location: Australia
Posts: 4406
Posted: 12:14am 17 Jun 2019
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  nickskethisniks said  
I want to test an inductor for a buck converter.

First establish your choke requirements, and there are three main issues.

The absolute maximum dc current, which is straightforward.

The required inductance, which sets the ripple current which will always be at maximum at 50% duty cycle, and reduces to zero at both 100% and 0% duty cycle.
Consider how the peak to peak ripple current may force a buck converter go discontinuous at very light loading.

Thirdly, core loss, which is not usually a problem with chokes, but can be if you use an unsuitable material at both very high voltage swing, and high frequency, with far too few turns.

Its exactly like designing a transformer, you need both enough turns, and enough core cross sectional area to prevent ac magnetic saturation, and its the applied ac voltage that does that.
Dc ampere turns are a very different thing, and its the dc plus ac flux that gets you up to saturation. So if you use sufficient turns core loss usually becomes very low in a choke and can often just be ignored.

Anyhow, once you have established a max required dc current and required inductance, you can then turn to your inductor tester for some results.

The test conditions such as voltage, frequency, and duty cycle make no difference at all. If your choke measurement produces figures of xx microhenries and saturates at yy amps, that is what it is.

It may run under vastly different conditions in your buck regulator, but that choke will still have xx inductance, and saturate at yy current, which is all you really need to be sure of.

So no need to try and duplicate the running conditions in the actual buck regulator.
Just wind up the wick on your tester to get some nice results, and job done.
Cheers,  Tony.
 
Warpspeed
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Joined: 09/08/2007
Location: Australia
Posts: 4406
Posted: 12:21am 17 Jun 2019
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Very nice find there Poida
I knew it was out there somewhere.

That Billings book is an excellent read, and especially good for magnetics.
Cheers,  Tony.
 
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