I'm in the process of compiling some notes on inductor design. I have good hands-on experience in the field (excuse the pun), but I feel this experience hasn't been totally systematic. I have been reading online literature including design procedures from core manufacturers, but I have a specific question related to the iterative process that typically takes place due to the intrinsic complexity of this design task. It goes like this:
Let's assume you have a working flyback which uses say a gapped ferrite RM8. This particular flyback has specific constant working conditions (input voltage, output voltage, on time, switching frequency, output power, etc.) Let's assume that:
- The transformer is reset to zero flux density every cycle.
- The transformer size is driven by temperature rise rather than peak energy storage. The flux density swing and operating frequency are such that the heat drives the size, not I^2*L. The ferrite operates at a comfortable flux density far away from saturation.
- The core losses in those conditions are whatever P_core.
Our transformer works well, but say we now replace it with an oversized transformer of the same effective permeability, say for example an RM12. As its A_L is higher, we wind it with less turns so that its primary inductance L_1 is preserved, keeping the basic oscilloscope waveforms unaltered, so to say. Naturally, the bigger component will heat up less. However, and this is my question, will that be at higher or lower total core loss?
My thoughts so far are that N decreases as A_L increases (so as to preserve L_1 as described above), l (magnetic path length) increases, peak H decreases as a consequence of all this, peak to peak B decreases consequently, P_V (specific core losses) decreases significantly as a result... but obviously the core volume is significantly higher and, since most of these relationships are non-linear, I'm not sure what happens.