Patent ID: 7948273

Claim:
A soft-start device, comprising: a current source; a first transistor, coupled to the current source, wherein an amount of current conducted by the first transistor is determined according to a first voltage; and a second transistor, coupled to the current source, wherein an amount of current conducted by the second transistor is determined according to a fixed bias; wherein an initial voltage value of the first voltage is smaller than a voltage value of the fixed bias, and the voltage value of the first voltage is increased gradually to be larger than the voltage value of the fixed bias when a soft start begins, wherein the first voltage generates a reference voltage through the soft-start device, and at an initial stage, when the first voltage is less than the fixed bias, the reference voltage rises with the first voltage and at a subsequent stage, when the first voltage is larger than the fixed bias, the reference voltage assumes a stable voltage value without rising with the first voltage; a first resistor, coupled between a voltage source and the first transistor, wherein a potential difference between both ends of the first resistor is determined according to the amount of current conducted by the first transistor; a second resistor, coupled between the voltage source and the second transistor, wherein a potential difference between both ends of the second resistor is determined according to the amount of current conducted by the second transistor; and a first capacitor, coupled in parallel to the second resistor, and adapted to generate the reference voltage according to the potential difference between both ends of the second resistor; wherein when the voltage value of the first voltage is larger than the voltage value of the fixed bias, and the reference voltage has the stable voltage value.