Buck variable negative current

摘要

An active diode formed within a buck power regulator with an NMOS transistor is connected to a PMOS transistor at a node that is further connected to the regulator output through an inductor. The active diode combines the NMOS transistor with circuitry to prevent conduction once the active diode passes a threshold voltage. Additional circuitry compares the output voltage to the target input voltage and varies the threshold voltage of the active diode such that the active diode can discharge excess current from the regulator each cycle until the output voltage is less than the target voltage.

主权项

1. A switching mode power supply (SMPS), comprising:
a) a buck power regulator comprising a high-side PMOS pass transistor and a low side active diode; b) the low-side active diode capable of continuously varying a threshold voltage; c) a circuitry configured to control the threshold voltage of the active diode, comprising:
a first comparison circuit configured to compare a voltage representing an output voltage of the buck converter with a reference voltage, wherein an output of the first comparison circuit is connected to a first terminal of a circuit having resistance and to a first input of a second comparison circuit;said circuit having resistance, wherein a second terminal of the circuit having resistance is connected to ground, wherein a resistance of the circuit having resistance is capable of determining a threshold of the second comparison circuit permitting some of an excess current that has built up in the buck regulator to be conducted each cycle by the low-side active diode to Vss, or circuit ground; said second comparison circuit, configured to detect a zero crossing of a voltage of a node (LX) located between the PMOS pass transistor and the active diode, wherein a second input of the second comparison circuit is connected to the LX node and an output of the second comparison circuit is connected to a first input of a logic AND circuit; and
said logic AND circuit capable of turning off the low-side active diode if the high side PMOS pass transistor is not being driven by a signal and a voltage change across the low-side active diode is detected by the second comparison circuit, wherein an output of the AND circuit is connected to a gate of the low-side active diode; and d) said buck power regulator capable of discharging a portion of excess current to circuit ground when an overvoltage resulting from a high output voltage causes the threshold voltage to rise to allow discharge of said portion of the excess current.