Switching power supply with increased efficiency at light load

A switching power supply with increased efficiency at light load comprising:

• a switching power circuit comprising
• a rectifying unit to rectify input AC power;
• a power factor correction (PFC) unit connected to the rectifying unit for power factor corrections and outputting DC power with a high voltage level;
• and
• a first DC to DC converter connected to the PFC unit for bucking the DC power output from the PFC unit and outputting the bucked DC power to a load;
• a power monitoring circuit connected to the AC power and the first DC to DC converter to detect power of the AC power, determining whether the load is in a heavy, medium or light state, controlling the first DC to DC converter to operate when the load is in a heavy or medium state and bucking the DC power output from the PFC unit and outputting the bucked DC power to the load, or stopping the first DC to DC converter from outputting DC power to the load when the load is in a light state;
• and
• a light load power supplying circuit comprising
• a charging circuit connected to the PFC unit and the power monitoring circuit, controlled by the power monitoring circuit to convert the DC power output from the power factor correction unit to charge power when the load is in a heavy or medium state, and to stop operating when the load is in a light state;
• a battery connected to the charging circuit and charged by the charging circuit;
• and
• a second DC to DC converter connected to the power monitoring circuit, the battery and the load, and controlled by the power monitoring circuit to provide the DC power output from the battery to the load when the load is in a light state.