Method for reducing body diode conduction in NMOS synchronous rectifiers

摘要

A switching regulator that practices the current invention includes a high-side switch M1 connected between an input voltage and a node LX. A low-side switch is connected between the node LX and ground. An inductor L is connected between LX and an output node (VOUT). A filtering capacitor connects VOUT to ground. The switching regulator has two distinct operational phases. During the first operational phase, the high-side switch is OFF and the low-side switch is ON. During the second operational phase, the high-side switch is ON and the low-side switch acts as a current source. During transitions between the second and first operational phases, the low-side switch is controlled to momentarily decrease the regulated drain-to-source current.

主权项

1. A method for operating a switching regulator, the switching regulator comprising a high-side switch and a low-side switch, the method comprising:
controlling the high-side switch to be substantially depleted during a first operational phase and to be substantially enhanced during a second operational phase; controlling the low-side switch to be substantially enhanced during the first operational phase and to provide a regulated drain-to-source current during the second operational phase; enabling a current mirror to generate a gate voltage for the low-side switch during the second operational phase; using, a drain voltage of a diode-connected N-channel MOSFET as the gate voltage of the low-side switch, a current source supplying the gate and drain of the N-channel MOSFET; and during transitions between the second and first operational phases, controlling the low-side switch to momentarily decrease the regulated drain-to-source current and providing an AC coupling between a voltage used to drive the high-side switch and the gate of the N-channel MOSEFT to momentarily decrease the low-side voltage.