NE555 forms an indirect feedback astable circuit, and a square wave is obtained at pin 3. R3 and C3 are coupling resistors and capacitors. The on-off of 9013 controls the switch of 13006 to make the high-frequency transformer work. The voltage of U2 is rectified by D3 and filtered by C4 and C5 to obtain DC power for the load. Different waveforms can be obtained on Ua, Ub, and Uc. D1 is for protecting 9013, D2, C3 and R5 are protection circuits.