Method and apparatus to reduce audio frequencies in a switching power supply

摘要

An example power supply regulator includes an energy transfer element, a switch, and a controller. The controller includes a switch signal generator, a modulation circuit, and a multi-cycle modulator circuit. The modulation circuit modulates the period of a modulation switching signal when an equivalent switching frequency is greater than a reference frequency and fixes the switching period when the equivalent switching frequency is less than the reference frequency. The multi-cycle modulator circuit enables the switch signal generator to provide a switch signal uninterrupted if the equivalent switching frequency is greater than the reference frequency and disables the switch signal generator for a first time period and then enables the switch signal generator for a second time period when the equivalent frequency is less than the reference frequency. The multi-cycle modulator circuit varies the first time period to regulate the output.

主权项

1. A power supply regulator, comprising:
an energy transfer element to be coupled to receive an input voltage of the power supply regulator; a switch coupled to the energy transfer element, wherein the switch is opened and closed in response to a switch signal; and a controller coupled to provide the switch with the switch signal to regulate an output quantity at an output of the power supply regulator, wherein the controller comprises:
a switch signal generator coupled to generate the switch signal in response to a pulse width modulated (PWM) switching signal and in response to an enable/disable signal;a modulation circuit coupled to provide the switch signal generator with the PWM switching signal responsive to a feedback signal that indicates a load condition at the output of the power supply regulator, wherein the modulation circuit modulates a duty cycle of the PWM switching signal to provide a fixed peak switching current in the switch in response to the feedback signal indicating that the load condition is a light load condition, and wherein the modulation circuit modulates the duty cycle of the PWM switching signal to provide a variable peak switching current in the switch that is proportional to the feedback signal in response to the feedback signal indicating that the load condition is other than the light load condition; anda multi-cycle modulator circuit coupled to provide the switch signal generator with the enable/disable signal, wherein the enable/disable signal enables the switch signal generator to provide the switch signal uninterrupted in response to the feedback signal indicating that the load condition is other than the light load condition, and wherein the enable/disable signal disables the switch signal generator for a first time period and then enables the switch signal generator for a second time period in response to the feedback signal indicating that the load condition is the light load condition, wherein the first time period is adjusted to regulate the output.