Patent ID: 7218080

Claim:
A soft-start apparatus for a power supply outputting a compensation signal to a PWM controller at a start-up transient of said power supply, comprising: a start-up capacitor; a first power source, connected to said start-up capacitor for charging up said start-up capacitor; a voltage-regulating unit, having a first input, a second input and an output; said first input of said voltage-regulating unit being supplied with an internal reference voltage, said second input of said voltage-regulating unit being connected to said output of said voltage-regulating unit and said start-up capacitor; wherein said voltage-regulating unit is used to regulate a reference voltage across said start-up capacitor; an error amplifier, having a first input, a second input and an output; said first input of said error amplifier being connected to said output of said voltage-regulating unit for receiving said reference voltage, said second input of said error amplifier being connected to a feedback terminal of said power supply for receiving a feedback voltage; wherein said error amplifier generates said compensation signal in response to said reference voltage and said feedback voltage; and a clamping diode, connected between said second input and said output of said error amplifier, said clamping diode being used for clamping said compensation signal at said start-up transient of said power supply.