Nowadays, mobile terminals such as smart phones are increasingly favored by consumers. However, the mobile terminal consumes large power energy, and needs to be charged frequently.
Typically, the mobile terminal is charged by a power adapter. The power adapter generally includes a primary rectifier circuit, a primary filter circuit, a transformer, a secondary rectifier circuit, a secondary filter circuit and a control circuit, such that the power adapter converts an input alternating current of 220V into a stable and low voltage direct current (for example, 5V) suitable for requirements of the mobile terminal, and provides the direct current to a power management device and a battery of the mobile terminal, thereby realizing charging the mobile terminal.
However, as the power of the power adapter becomes larger, for example, upgrade from 5 W to 10 W, 15 W, 25 W and other larger power, more electronic elements capable of bearing large power and realizing better control are required for adaptation, which not only increases a size of the power adapter, but also increases a production cost and manufacture difficulties of the power adapter.
Further, a current detection in a related power adapter is usually realized by using a current detection resistor and an operational amplifier. Since the detected current increases as the power of the power adapter increases, there is a high requirement in a dynamic range of a current detection circuit and it is also required to prevent saturation of the operational amplifier. However, after the dynamic range of the operational amplifier is increased (for example, by selecting the current resistor with low resistance and/or decreasing an amplification factor of the amplifier), when the charging is performed with small current, it is impossible to ensure a current detection precision for the small current, thus influencing application of the power adapter.