The invention relates to a high-
voltage input auxiliary power circuit which comprises a switching tube combinational circuit, a
control circuit, a
flyback transformer, an absorption circuit, a DC input circuit, a power supply circuit, a current detection circuit and at least one
secondary circuit. The switching tube combinational circuit is connected with the DC input circuit, the
flyback transformer, the
control circuit, the power supply circuit and the detection circuit respectively. The switching tube combinational circuit comprises an MOS
transistor Q1, an MOS
transistor Q2, a TVS
transistor Z1, a
diode D1, a
diode D2 and a current-limiting
resistor R1. The grid
electrode of the MOS transistor Q1 is connected with a PWM
control circuit, the source
electrode of the MOS transistor Q1 is connected with one end of a current detection
resistor R2, and the drain
electrode of the MOS transistor Q1 is connected with the source electrode of the MOS transistor Q2. The drain electrode of the MOS transistor Q2 is connected with one end of the
flyback transformer T1, and the grid electrode of the MOS transistor Q2 is connected with the positive electrode of a driving
resistor R1 and the positive electrode of the clamping
diode D1. The positive electrode of the TVS transistor Z1 is connected with the source electrode of an NMOS transistor Q1, and the negative electrode of the TVS transistor Z1 is connected with the grid electrode of the MOS transistor Q1. The negative electrode of the clamping diode D1 is connected with one end of a DC input
capacitor C1. The positive electrode of the diode D1 is connected with the power supply circuit Vcc, and the negative electrode of the diode D1 is connected with the driving resistor R1. The mode that the MOS transistor Q1 and the MOS transistor Q2 are in series connection is adopted in the switching tube combinational circuit, the turn-off
voltage stress of the MOS transistors is lowered, and the high-
voltage input auxiliary power circuit is suitable for
high input voltage auxiliary power supplies; the TVS transistor Z1 is connected with the driving circuits (R1 and D1) and a clamping circuit D1, the
driving circuit of the MOS transistor Q2 is simplified, and cost is lowered.