Method and apparatus for improving the drop-out voltage in a low drop out voltage regulator

Abstract

A low voltage drop out circuit (10) has a voltage regulating transistor (13) between a supply voltage (12) and an output terminal (28). An active feedback loop controls the voltage regulating transistor (13) according to a magnitude of the supply voltage (12) to control the voltage on the output terminal (28). A reference voltage source (25) produces a reference voltage, and a switch, which may be a second transistor (45) of similar type than the voltage regulating transistor (13), is connected in parallel with the voltage regulating transistor (13). A comparing circuit (42) detects when the supply voltage (12) falls below the reference voltage (25) to operate the second transistor (45), which may be sized to be much larger than the voltage regulating transistor (13) to effectively short across the voltage regulating transistor (13) when the supply voltage (12) falls below a predetermined level.

Dependencies are inferred from the claim text.