Suppose you have an inductor in a boost converter. The core gets hot. Why? What are the physical mechanisms that cause core loss? Eddy currents? Magnetic domains flipping? Coupling to materials outside the core? Others? How can these losses be minimized?
Answer
Most of the losses in a well-designed boost inductor are going to be:
- Resistive losses in the windings
- Hysteretic losses in the core
I won't attempt to trump Wikipedia's explanation of hysteresis losses:
When the magnetic field through the core changes, the magnetization of the core material changes by expansion and contraction of the tiny magnetic domains it is composed of, due to movement of the domain walls. This process causes losses, because the domain walls get "snagged" on defects in the crystal structure and then "snap" past them, dissipating energy as heat. This is called hysteresis loss. It can be seen in the graph of the B field versus the H field for the material, which has the form of a closed loop. The amount of energy lost in the material in one cycle of the applied field is proportional to the area inside the hysteresis loop. Since the energy lost in each cycle is constant, hysteresis power losses increase proportionally with frequency.
Essentially, the more you slosh around in the B-H loop, the more heat you make because sloshing around in the B-H loop generates heat. Higher frequency = more sloshing per unit time = more power loss. Also, since it's both the magnetizing current and the load current contributing to the B-H sloshing, higher power = more sloshing per unit time = more core loss.
I said "well-designed" for a reason. In my opinion, a well-designed boost inductor is going to use ferrite core material, which is essentially non-conductive and therefore practically immune to eddy current losses (i.e. there may be some, but they're insignificant compared with the hysteretic loss).
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