Switching control circuit for fixed-on-time power conversion system

摘要

A switching-control circuit configured to keep a transistor on for a predetermined time to generate a target-level-output-voltage from an input voltage. The circuit is configured to generate, every switching period of the transistor, a slope voltage corresponding to that of a ripple voltage contained in an output voltage during a time period when the transistor is off, limit an amplitude of the slope voltage so as not to exceed a predetermined amplitude greater than the amplitude of the slope voltage when the target-level-output-voltage is generated, add the slope voltage to a reference voltage, indicating a reference of the target-level-output-voltage, or a feedback voltage corresponding to the output voltage, and keep the transistor on for a predetermined time and thereafter turn off the transistor, when a level of either one voltage, added with the slope voltage, of the reference voltage and the feedback voltage reaches a level of another voltage thereof.

主权项

1. A switching control circuit configured to control a switching operation of a transistor so that the transistor is turned on and kept on for a predetermined time in order to generate an output voltage of a target level from an input voltage, the transistor having an input electrode applied with the input voltage and an output electrode connected to a load via an inductor, the switching control circuit comprising:
a voltage generating circuit configured to generate a slope voltage in each switching period of the transistor, the slope voltage changing with a slope corresponding to a slope of a ripple voltage, the ripple voltage contained in the output voltage during a time period during which the transistor is off; an amplitude limiting circuit configured to limit an amplitude of the slope voltage so as not to exceed a predetermined amplitude, the predetermined amplitude being greater than the amplitude of the slope voltage when the output voltage of the target level is generated, wherein the amplitude limiting circuit is configured to limit the amplitude of the slope voltage so as not to exceed the predetermined amplitude, and wherein the predetermined amplitude increases with an increase in level of the output voltage; an adding circuit configured to add the slope voltage to a reference voltage or a feedback voltage, the reference voltage indicating a reference of the output voltage of the target level, the feedback voltage corresponding to the output voltage; and a drive circuit configured to turn on the transistor to be kept on for a predetermined time and thereafter turn off the transistor, when a level of either one voltage, added with the slope voltage, of the reference voltage and the feedback voltage reaches a level of an other voltage thereof.