An energy output circuit and its control method includes a switch device (2), a transformer (4) and a controller (1). The switch device (2) is connected between a primary of the transformer (4) and an input power source in series. The controller (1) calculates an energy output waveform and sends a command according to a request or a level to control the switch device (2), to control the on/off time of the primary of the transformer (4). The transformer (4) is an ordinary low-frequency transformer.