A source driver circuit can include: (i) a control transistor having a control terminal and first and second power terminals, where the control transistor is coupled between a power terminal of a main switching transistor and ground; (ii) a power supply capacitor coupled between the control terminal of the main switching transistor and ground, where the power supply capacitor is configured to receive a bias voltage that is substantially constant; (iii) a freewheeling diode having a cathode coupled to a control terminal of the main switching transistor, and an anode coupled to the second power terminal of the main switching transistor; and (iv) the control transistor being controllable to be periodically turned on and off to control the main switching transistor to correspondingly follow on and off states of the control transistor.