Pre-bias control for switched mode power supplies

摘要

An embodiment of the invention provides a method of reducing a drop in voltage on a pre-biased output of a DC-DC step-down switching converter. A high side switch is activated to conduct a first current to the pre-biased output. After the high side switch is activated, a low side switch is activated to draw a second current from the pre-biased output such that the magnitude of the first current is greater than the magnitude of the second current for at least a portion of a time period T1. After the time period T1 ends, the magnitudes of the first and second currents are changed to maintain a predetermined voltage on the pre-biased output.

主权项

1. A method of reducing a drop in voltage on a pre-biased output of a DC-DC step-down switching converter comprising:
applying a pre—bias voltage to the output of the DC—DC step—down converter before activating the converter; activating a HS switch, the HS switch conducting a first current to the pre-biased output; activating a LS switch after the HS switch is activated, the LS switch drawing a second current from the pre-biased output wherein the second current is smaller in magnitude than the first current for at least a portion of a time period T1, changing the magnitudes of the first and second currents to maintain the predetermined voltage on the pre-biased output of the DC-DC step-down switching converter after the time period T1, wherein the second current drawn through the LS switch is controlled by the clock signal, a variable voltage reference and the feedback signal from the pre-biased output of the DC-DC step-down switching converter; delaying activating the LS switch until after the feedback signal exceeds the variable voltage reference whereby droop in output voltage is reduced, wherein the first current conducted through the HS switch is controlled by a clock signal, a fixed voltage reference, and a feedback signal from the pre-biased output of the DC-DC step-down switching converter.