Sure -- here's the core (aha, with reference!):
- Saturable Core Model, copied from:
- _SPICE Models For Power Electronics_, Meares and Hymowitz.
- .SUBCKT INDSAT 1 2 PARAMS: VSEC=1e-4 LMAG=1e-5 LSAT=1e-7 FEDDY=1e6 F1 1 2 VM1 1 G2 2 3 1 2 1 E1 4 2 3 2 1 VM1 4 5 0 RX 3 2 1E12 CB 3 2 {VSEC/500} IC=0 RB 5 2 {LMAG*500/VSEC} RS 5 6 {LSAT*500/VSEC} VP 7 2 250 VN 2 8 250 D1 6 7 DCLAMP D2 8 6 DCLAMP .MODEL DCLAMP D(CJO={3*VSEC/(6.28*FEDDY*500*LMAG)} VJ=25) .ENDS
A reasonable transformer model uses this saturable inductor as the primary inductance; a VCVS and CCCS "DC transformer" can do the ratio part, and you can add leakage in series, or use whatever model of mutual inductance you prefer. I'm leaving that stuff out, since it's personal preference how you might wish to construct it (in terms of k or LL, etc.). And "exercise for the student". ;)
The ratio between LMAG and LSAT is equal to the average permeability, so that a 10uH winding on a core of mu=100, when saturated, gives about
0.1uH, give or take leakage. Remember, more mu has almost no effect on leakage, but it increases k dramatically because it increases LMAG (the small signal inductance) dramatically. In practical terms, it changesFEDDY is the eddy current frequency; this is somewhere around the point where, in the ferrite core's datasheet, you see mu' starting to roll off and mu'' peaking. I think I got reasonable agreement between simulated core losses and actual test results, between a Ferroxcube 3F3 core and FEDDY = 4M. The mu'' peak on the datasheet is something like 1 or 2MHz I think. Probably depends on Bpk used for the test, so you'll get best results from actual tests.
Tim