Provided are a power supply circuit, a power supply device and a control method. The power supply circuit includes a primary rectifier unit, a modulation unit, a transformer, a secondary rectifier and filtering unit, and a control unit. In the power supply circuit, a liquid electrolytic capacitor at a primary side is removed, such that a volume of the power supply circuit is smaller, and is safe to use. Moreover, an output current of the power supply circuit has a periodically changing current value, and the control unit can control the duration of the output current in which the current value is 0.