Switching power supplies, and switch controllers for switching power supplies

A switching power supply comprising:

• a power converter comprising a transformer and a switch controlled by a driving signal, said transformer comprising a primary winding operable for receiving an input power from an AC/DC (alternating current/direct current) converter and a secondary winding operable for providing an output power for a load;
• a current sensor, coupled between said switch and ground, operable for generating a current monitoring signal indicating a current through said primary winding;
• a switch controller, coupled between an optical-coupler and said primary winding, operable for receiving a feedback signal from said optical-coupler, generating said driving signal based on said feedback signal to control said input power and said output power, receiving a line voltage signal indicating an input voltage of said power converter, and generating a compensation current corresponding to a peak value of said line voltage signal, wherein said feedback signal indicates an output voltage of said power converter, and wherein said AC/DC converter is operable for converting an AC voltage to said input voltage and providing said input voltage to said power converter;
• a compensation resistor coupled between said current sensor and said switch controller, wherein a voltage of said current monitoring signal is inversely proportional to said input voltage under control of said compensation current and said compensation resistor, wherein said voltage of said current monitoring signal increases if said input voltage decreases, and wherein said voltage of said current monitoring signal decreases if said input voltage increases;
• a safety capacitor;
• at least one diode;
• and
• a discharging switch coupled to said safety capacitor,
• wherein said discharging switch is turned on to discharge said safety capacitor through said at least one diode if an AC power source which provides said AC voltage is disconnected from said switching power supply.

A switch controller operable for controlling a power converter comprising a transformer and a switch controlled by a driving signal, said transformer comprising a primary winding operable for receiving an input power from an AC/DC converter (alternating current/direct current) and a secondary winding operable for providing an output power for a load, said switch controller comprising:

• a feedback terminal operable for receiving a feedback signal from an optical-coupler, wherein said feedback signal indicates an output voltage of said power converter;
• a driving terminal operable for providing said driving signal to control said input power and said output power based on said feedback signal;
• a line voltage monitoring terminal operable for receiving a line voltage signal indicating an input voltage of said power converter, wherein said input voltage is provided to said power converter by said AC/DC converter;
• and
• a current monitoring terminal operable for receiving a current monitoring signal indicating a current through said primary winding, wherein a compensation current corresponding to a peak value of said line voltage signal flows through said current monitoring terminal, wherein said current monitoring terminal is coupled to a compensation resistor, wherein a voltage of said current monitoring signal is inversely proportional to said input voltage under control of said compensation current and said compensation resistor, wherein said voltage of said current monitoring signal increases if said input voltage decreases, and wherein said voltage of said current monitoring signal decreases if said input voltage increases,
• wherein said switch controller is operable for turning on a discharging switch to discharge a safety capacitor through at least one diode if an AC power source that provides an AC voltage to said AC/DC converter is disconnected from said AC/DC converter.