Pseudo-constant frequency control for voltage converter

摘要

A pseudo-constant portion of a switching cycle (ON time or OFF time) is constant over short periods of time but the pseudo-constant portion is controlled over longer periods of time in a slow frequency control loop to maintain a desired frequency. The average frequency is maintained at or near a desired frequency but when there is a transient, local disturbance, or load change, or other occurrence, then for a short period of time the frequency will vary as the non pseudo-constant portion of the switching cycle changes to address the transient or other occurrence. The frequency control loop will slowly adjust the pseudo-constant portion of the switching cycle to return to the desired frequency.

主权项

1. A voltage converter having a switching cycle with an ON portion and an OFF portion, the voltage converter comprising:
a current control loop to sense a current flowing through an inductor and to compare the sensed current to a threshold current value to determine when to end the ON portion by turning off a switch, wherein the current flows through the inductor and the switch during the ON portion; a voltage control loop to sense an output voltage of the voltage converter and to determine a difference between the sensed output voltage and a reference voltage and to supply an indication of the difference for use in determining the threshold current value; and a timing control loop to compare a switching frequency of the voltage converter with a target switching frequency and to adjust the OFF portion of the switching cycle based on the compare of the switching frequency with the target switching frequency; wherein a bandwidth of the timing control loop is lower than a bandwidth of the voltage control loop.