| Electronics > Projects, Designs, and Technical Stuff |
| DC to DC |
| << < (3/4) > >> |
| TimNJ:
In my experience, designing with un-gapped powder-core toroids is pretty straightforward. (Not always, of course.) The Here's a datasheet for a Chang Sung toroid: http://eu0707.cafe24.com/_eng/download/prod/OD127.pdf The effective permeability of the core drops with DC bias, and as a result, the AL value drops too. (You can see this in the datasheet plot.) The AL value, or "inductance factor" is the relationship between number of turns and inductance. So, if you know your max nominal current through the inductor, you can determine if your "inductor" will really be acting like an inductor at all. Gapped ferrite cores are a bit more tricky due to the geometry and addition of the gap. You can take a look at the attached images for a procedure I have used with success. It looks a bit obtuse, but it's not too bad. I usually make an Excel spreadsheet so I can play with the parameters and see how things change. |
| TimNJ:
For anyone's reference, here's an Excel design spreadsheet I made using this method. Note 1: This spreadsheet does not include Step 1 "Determine the Core Size", as the core size was already determined by the product footprint. But, you probably don't want to do this unless you have an "intuitive feel" for this. Note 2: This spreadsheet is for a boost converter. You will have to use different formulas for determining proper inductance and ripple current for other topologies. |
| james_s:
That toroid looks like powdered iron, which IIRC behaves like a gapped core. As has been mentioned already, two identical looking ferrite cores can have very different properties and these properties are important. |
| TimNJ:
Powdered iron cores are sometimes called "distributed gap" cores. Instead of a single gap, as used with ferrite cores, you can think of a powdered iron core has having thousands (millions? billions?) of little gaps between each iron powder particle in the core. Inductors wound on powdered iron cores will have a much "softer" saturation curve. That is, there isn't a single point at which the inductance drops off sharply. It's gradual. There are also many types of powdered cores. The cheapest is simply "powdered iron", but there are other types like MPP, Hi-flux, and Sendust. All have their tradeoffs, of course. |
| aju11:
Saturation |
| Navigation |
| Message Index |
| Next page |
| Previous page |