Variable Frequency-Duty Cycle Slow Start Control for Switched-Mode Power Supplies
Original Publication Date: 1989-Mar-01
Included in the Prior Art Database: 2005-Jan-27
Disclosed is a circuit that eliminates damaging charging currents from a switched-mode power supply to its secondary filter capacitor4s during power on without using relays, large inductors, or very fast switching components. Referring to Figs. 1 and 2, switching supplies generally have a current sense circuit to limit the current charging capacitor C during power on by forcing the duty cycle of the switching frequency fo to a minimum Dmin. Dmin is a function of the feedback loop delay td divided by the period of fo or Dmin=(td x fo).