Low noise forward/flyback switching power supply

摘要

Low noise DC/DC switching power supply employs a transformer, a main switch and an auxiliary switch. The auxiliary switch merely reflects the switching of the main switch and has lower voltage ratings. A maximum noise suppression is accomplished when both switches have the same current ratings. The power supply takes advantage of some resonant properties but operates in forward and/or flyback square wave modes. When the main switch is turned off, a leakage energy stored in the transformer is delivered to a capacitor. Subsequently, both switches are turned on, wherein the capacitor voltage is applied across the primary winding of the transformer. When the capacitor voltage is reduced to a desired value, the auxiliary switch turns off, wherein the primary voltage is reduced to the input voltage. The difference between both primary voltages is thus regulated. The EMI/RFI performance of the power supply is dramatically improved. A discontinuous mode allows uninterrupted input current at any time.