A heating apparatus includes: first and second heaters, first and second switches, first and second ramp signal generation circuits, a signal processor circuit, first and second comparison circuits, and a switch control circuit. The first and second ramp signal generation circuits generate first and second ramp signals according to first and second output currents, respectively. The signal processor circuit senses a temperature to generate a temperature-related signal. The first and second comparison circuits compare the first and second ramp signals with the temperature-related signal, to generate a first PWM signal and a second PWM signal for controlling the first and second switches respectively, to determine the first and second output currents so that there is a predetermined ratio between average powers of the first heater and the second heater.