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On the Inductor

Given my hobbyist state of ignorance, inductor design by manufacturers can seem like rocket-science. I believe many important practical details go into designing a commercially competitive device. I'm merely a hobbyist, so I can only stand back and appreciate from some distance and with my sincere respect what a manufacturer applies in designing products.

But there are some basics, too. In the above case, we can work out the energy being stored in the inductor once equilibrium is reached (a second later, at the latest.) The inductor current is DC -- it's not varying much. The energy in the choke inductor is \$E_{_\text{L}}=\frac12\,I_{_\text{L}}^{\,2}\,L_1=\frac12\,I_{_\text{LOAD}}^{\,2}\,L_1\$. In this case, that's about \$540\:\text{mJ}\$.

Webers is the Joules per Amp, so in this case we can work that out as \$\Phi_1 = \frac{540\:\text{mJ}}{2\:\text{A}}=270\:\text{mWb}\$. If you know the \$B_{_\text{MAX}}\$ of the core material and the number of turns, \$N\$, wound on the core, you can work out the the cross-section area as \$A\gt \frac{\Phi_1}{N\cdot B_{_\text{MAX}}}\$. If we are using a good quality iron core with \$B_{_\text{MAX}}=1.1\:\text{T}\$ and if \$N=1000\$, for example, then: \$A\gt \frac{270\:\text{mWb}}{1000\,\cdot\, 1.1\:\text{T}}\$. This suggests that the cross-section area must be \$A\approx 2.5\:\text{cm}^2\$. The 1000 windings will take up some magnetic path length to achieve, so the resulting inductor will have some significant mass.

I may be wrong about the quantitative details. Inductor design is more a matter of dimensional analysis to me as a hobbyist and it's possible I've gotten a factor wrong. But that's how it looks to me. I'll take whatever criticism experts lodge, with appreciation.

Anyway, that's a way of doing it.

If you can accept a higher peak voltage and a higher peak inductor current, you can reduce its magnitude. Say, by half or so. If the peak voltage is critical and you cannot accept a high value, then you need to increase its magnitude. Matching up the current limit of the inductor with the current limit of the resistor usually gives the better response, though, and is a nice balance for the design.

Anyway, that's a way of doing it. The way it once was done.

Note: Now, pause. There will also be an increasing inductor current. And perhaps this limit isn't good enough. But in practice it will be. Th reason is that while the inductor's current is climbing, so also is the limit-resistor's current declining. Done right, these will just almost perfectly cancel each other out so that if we design each for the same current limit, then the sum of their currents will also be similarly limited.

Note: Now, pause. There will also be an increasing inductor current. And perhaps this limit isn't good enough. But in practice it will be. The reason is that while the inductor's current is climbing, so also is the limit-resistor's current declining. Done right, these will just almost perfectly cancel each other out so that if we design each for the same current limit, then the sum of their currents will also be similarly limited.