The working process of the power adapter

　　During the saturated conduction period of the switch tube VT, the DC voltage Ui of the positive pole of C1 is charged through L→VT→the positive pole of C2→the negative pole of C2. On the one hand, a DC voltage is established at both ends of C2, and on the other hand, the magnetic energy in the energy storage inductor L is continuously increased. When the switch tube VT is turned off, L induces left negative and right positive voltages, and the magnetic energy in L is released to C2 and the load through the freewheeling diode VD. The level of the voltage Uo at the output end of the power adapter is determined by the length of the saturated conduction time of VT, that is, the width of the base excitation pulse. The width of the base excitation pulse is determined by the error sampling and amplifying circuit.

　　If there is no freewheeling diode VD in the series power adapter, when the switch tube suddenly turns from saturated conduction to cut-off, because the magnetic energy in L cannot be released, a very high voltage will be induced. This voltage can easily lead to the breakdown of the switch VT. After the freewheeling diode VD is connected, when the switch is turned from saturated conduction to cut-off, the magnetic energy in L is released to C2 and the load circuit through VD. The extreme voltage drop is the input Ui value, and there is enough margin; on the other hand, during the off period of VT, L will release energy through the freewheeling diode VD, so that the load circuit can be supplemented by energy during the off period of the switch tube, which will Make the output voltage smoother and the power adapter more efficient.