TP40 is a general-purpose low-loss MnZn power ferrite with an initial permeability (μi) of 2000, a saturation flux density (Bs) of 480 mT at 25 °C (390 mT at 100 °C) and a Curie temperature above 220 °C. Its loss minimum lies near 100 °C: Pcv at 100 kHz / 200 mT decreases from 720 kW/m³ at 25 °C to 480 kW/m³ at 100 °C, at 300 kHz / 100 mT from 660 to 400 kW/m³, and coercivity (Hc) from 12 A/m to 6.5 A/m, consistent with the core temperature of a switch-mode supply at full load. Typical applications are 100–300 kHz forward, flyback and half-bridge main transformers and industrial and high-power supplies, particularly on large EE/EC/PQ cores. Among the six mid-frequency grades TP40 is the general-purpose reference: TM80/TM81/TM83 are recommended where a wide-temperature loss profile is required, TP44 (330 kW/m³ at 100 °C) where the 100 kHz / 200 mT loss budget is tighter, and TP45 (μi 2500) where a higher μi is needed to reduce the number of turns. Because the internal hot-spot temperature of a large core exceeds its surface temperature, the loss curve should be evaluated at the internal core temperature.