Magamp design with ferrite core saturable reactors

The authors explain the design tradeoffs that must be made in order to use ferrite core saturable reactors in magamp post regulators instead of the more common tape cores. In the past, ferrite core saturable reactors were rarely used above 30 kHz. A low loss, square loop ferrite material 3R1 is now available. The core losses for 3R1 in the 50 to 150 kHz range are significantly lower than those of other square loop ferrites. Thus, in many low current magamp designs 3R1 core can replace 1 mil square 80 cores with a significant reduction in the cost of the saturable reactor. However, the higher saturated permeability of 3R1 prevents it from competing in high-current low-headroom magamps. In those, 1/2 mil square 80 and 1-mil 2714A amorphous cores are much better choices. Minimum squareness ratios for these cores are 86% and 90% as compared to about 80% for 1 mil square 80 and 82% for a warm 3R1 core