Switching power supply for increasing transmission rate of asymmetrical digital subscriber loop modem (ADSL MODEM)

The invention provides a switching power supply for increasing the transmission rate of an asymmetrical digital subscriber loop modem (ADSL MODEM). An absorption resistor is added in a clamping circuit of the switching power supply and serially connected to the anode or the cathode of a diode in the clamping circuit; in addition, an input filtering inductor is added between an input rectifying circuit and the clamping circuit, and compared with an input common mode inductor in the prior art, the input filtering inductor has small size. The clamping circuit is not only used for restricting a voltage peak in the shutoff process of a power device due to the leakage inductance of a primary side high voltage main winding of a transformer, but also can reduce the change rate of high frequency current due to the added absorption resistor and input filtering inductor and improve the electromagnetic interference, thereby increasing the transmission rate of the ADSL MODEM. The switching power supply provided by the inv