Another choice is to simulate using SwitcherCAD


--- On Fri, 10/3/08, Jesse Lackey <jsl-ml@celestialaudio.com> wrote:

> From: Jesse Lackey <jsl-ml@celestialaudio.com>
> Subject: [EE] measuring current through an inductor
> To: "Microcontroller discussion list - Public." <piclist@mit.edu>
> Date: Friday, October 3, 2008, 8:34 PM
> Hello all, as time goes by I find myself doing more and more
> dc/dc work, 
> including things like switcher battery chargers and high
> power LED 
> drivers, mostly successfully but sometimes not.
> 
> In doing the design of such things, the inductor is often
> the biggest 
> question.  Datasheets for whatever IC is running the show
> of course give 
> guidance, but sometimes this is less than complete, and
> sometimes 
> they'll give typical but not corner-case information,
> and sometimes 
> they'll give info needed to run whatever it is at max
> power, and I'm 
> designing for 1/5 of that, and don't want to use a way
> overkill inductor.
> 
> Ok, all this leads up to the question: how do I measure
> current through 
> an inductor as it is operating under normal loads in such
> designs?  If I 
> put a 0.1R resistor in series, I can get some kind of
> measurement (with 
> a scope, 2 channel, in difference mode), but for some
> inductors adding 
> 0.1R to its resistance changes the overall operation
> considerably.
> 
> The goal of all this is twofold - firstly to check that the
> inductor 
> isn't saturating at corner cases, and secondly to see
> how predicted 
> operation compares with actual and maybe optimize the
> design to use 
> smaller/cheaper inductors.
> 
> Suggestions?
> 
> Thanks everyone!
> J
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