Simplified schematic diagram of non-isolated switching power supply

In high-voltage switching power supplies, the power frequency transformer with isolation function is generally eliminated, as shown in the figure. It is a simplified schematic diagram of a switching power supply that is not isolated from the grid. The switching tube VTl is connected to the power grid through the rectifier diode VDl, and the switching tube is charged. The switching tube couples energy to the output end through the high-frequency transformer T. Because the output end and the input end have a common ground point and the error amplifier VT2 connected to the output end is directly connected to the switching tube VTl, the output end is connected to the power grid through VT2 and VTl.