说明：  阐述开关电源充电器原理，输入电压220V，输出电压48V，单管式开关电源，基于UC3842和LM358，带短路保护
(Describes the principle of switching power charger, input voltage 220V, output voltage 48V, single tube switching power supply, based on UC3842 and LM358, with short circuit protection)