Abstract: The present disclosure provides a soft start circuit and a power supply circuit. The soft start circuit is disposed between a negative electrode of a direct current bus capacitor and a negative terminal of a direct current power supply, so as to control, after a start begins, according to the current input by the direct current bus capacitor in a constant current module, whether to electrically connect the direct current power supply and the direct current bus capacitor; one end of the soft start circuit is further connected to a filtering protection module, so as to control, at the beginning of the start, according to the voltage output by the filtering protection module, the direct current power supply to be electrically connected to the direct current bus capacitor.