CHARGING CIRCUIT, POWER ADAPTER AND CHARGING SYSTEM

The present application relates to the technical field of charging, and discloses a charging circuit, a power adapter and a charging system. The charging circuit is applied to the power adapter, and comprises: a voltage conversion unit, which is used for processing inputted AC power so as to output a first pulsating DC voltage; a voltage sampling unit, which is used for sampling the pulsating DC voltage outputted by the voltage conversion unit to obtain a sampled voltage; a comparator unit, a negative input terminal of which is connected to an output terminal of the voltage sampling unit, a positive input terminal of which is connected to a reference voltage supply terminal, and the comparator unit being used for comparing the sampled voltage with a preset reference voltage and outputting a comparison signal; and a switch unit, which is used for turning on when the comparator unit outputs a low level so that the charging circuit outputs a voltage, and which is used for turning off when the comparator unit out