Patent ID: 8531851

Claim:
A start-up circuit, comprising: a) a delay circuit comprising a first resistor and a first capacitor, wherein said first capacitor is coupled between ground and a common node; and b) a control chip configured to receive a first reference voltage, wherein said control chip comprises an input pin coupled to an input voltage source, an output pin configured to supply power for a post device, and a multiplexed pin coupled to said first resistor at said common node to receive an external enable signal, c) wherein said start-up circuit is configured to output an electrical signal at said output pin in response to said external enable signal being activated, said electrical signal being output at said output pin based on a comparison of a voltage at said multiplexed pin against said first reference voltage, and after a delay time that is determined by a value of said first capacitor and said first reference voltage; d) wherein said voltage at said output pin is configured to increase continuously with a fixed rising slope that is determined by input current flowing through said multiplexed pin during a start-up process for said start-up circuit; e) a comparator having a first comparator terminal coupled to said multiplexed pin, a second comparator terminal coupled to said first reference voltage, and an output terminal configured to provide a comparator output to a logic and control module; f) a clamping module coupled to said multiplexed pin, wherein said clamping module is configured to clamp said voltage of said multiplexed pin to a second reference voltage; g) a driving module configured to receive current from both said logic and control module and said clamping module; h) a power switch having a first power switch terminal configured to receive an output of said driving module, a second power switch terminal configured to receive a voltage of said input voltage source, and a third power switch terminal coupled to said output pin to generate an output voltage signal with a fixed rising slope; and i) a current control module coupled to said third power switch terminal and said multiplexed pin, wherein said current control module is configured to compare a first current signal indicating an output current of said power switch against a second current signal indicating an input current of said multiplexed pin to control said output current of said power switch during said start-up process.