Designs of flyback power converters are described. According to one aspect of the designs, a power converter includes a primary side including a primary winding of a transformer coupled to an input voltage and a primary switch for switching on or off the primary winding, a secondary side including a secondary winding of the transformer for generating an output voltage, and a loop controller configured to sample a feedback voltage representative of the output voltage, generate a gate signal with a fixed falling edge and an adjustable rising edge to drive the primary switch, and adjust a duty cycle of the gate signal by adjusting the rising edge of the gate signal until the feedback voltage converges to a reference voltage.