Method, apparatus and system for soft startup of electric power

The embodiment of the invention discloses a method, a device and a system for soft start of a power supply, the method comprises the following steps: a clock signal is detected; a required duty cycle signal is generated; the duty cycle signal is output to a switch, the opening and the closing of the switch are controlled, the charge of a capacitor is controlled, and the soft start of the power supply is realized. The soft start time of a circuit is prolonged by the soft start, the soft start function with longer time can be realized under the same area of a chip; the soft start time of the power supply can be flexibly changed by the regulation of the size of the capacitor, the size of the duty cycle and the length of the clock period.