In a control circuit and method for a high efficiency and low EMI switching amplifier, an input signal is compared with a reference signal to generate a comparison signal, and a control signal is generated in response to the comparison signal for a driver to generate an output signal. The output signal is fed back to control the slope of the reference signal in association with an initial level set for the reference signal to provide a minimum on-time period for the output signal. Alternatively, a reference value is provided to compare with the reference signal for setting a minimum on-time period for the output signal.