POWER-HANDLING CAPABILITY OF FERRITE TRANSFORMERS AND CHOKES FOR SWITCHED-MODE POWER SUPPLIES.

A single equation is evolved for the power-handling capability of nine classes of transformer and two classes of choke used in fixed-frequency push-pull forward and flyback converters in switched-mode power supplies. The equation consists of three principal terms. The first term describes the winding and the permissible dissipation in the winding for a given overall temperature rise. The second term is the product of frequency and peak flux under steady-state operating conditions. The third term is a number which is tabulated for the classes of transformer and choke. The equation is applicable to power supplies in which the output voltage is held constant by a feedback loop which controls the duty cycle of the output switching stage. Additional equations are given for the output current range for good regulation, and for the required turns-per-volt. An example of the use of the equations is included.