| 摘要 |
A switch mode voltage regulator with synchronous rectification that produces ripple cancellation with fast load response is described. The switch mode voltage regulator comprises a main step-down regulator with synchronous rectification with an auxiliary step-down regulator that produces an output ripple cancellation current that is equal but opposite to the output ripple of the main regulator during static load conditions. During changing load conditions a feedback control circuit changes the duty cycle of the main regulator while a time-delay circuit prevents a change of the duty cycle in the auxiliary regulator. Thus, the main regulator is allowed to change its average current while preventing a counteracting average current change in the auxiliary regulator. An embodiment is described in which the duty cycle in the auxiliary regulator is changed in phase with the duty cycle of main regulator to further improve the dynamic response to load changes. A sub-cycle circuit is also described that overrides the feedback control circuit to improve the dynamic response to load changes. Accordingly, a fast transient response can be achieved with a switch mode regulator that has a low ripple voltage.
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