Frequency Control Circuit for Switched Mode Power Supplies
Original Publication Date: 1988-Apr-01
Included in the Prior Art Database: 2005-Feb-15
This article describes a circuit arrangement for controlling a switch mode power supply. The circuit arrangement includes a frequency control circuit and a timing circuit that determine the frequency at which a main switching transistor turns on. With reference to the figure, the power supply is comprised of flyback converter 10, frequency control circuit 12 and timing circuit 14. The frequency control circuit sets the frequency of operation for the power supply. This is accomplished by turning Q6 on and off at the desired frequency. The feedback winding is designed such that a DC voltage (Vbias = 15 V) is obtained across capacitor C3. The time constant between R5 and C3 is large enough so that this voltage remains constant. R6 is designed to have a much smaller value of resistance than R7, R8 or R9.