Abstract: A control circuit and a control method of a switching power supply, according to feedback signals on a pin FB and a pin CS, a constant current control module generates and outputs a control signal to control an output current of the switching power supply, thereby regulating duty cycle of a first transistor adaptively and controlling an output current Io of a power supply system to be constant; according to the feedback signals on the pin FB and on the pin CS, a constant current precision compensation module adaptively regulates circuit parameters of the constant current control module and a sample-and-hold module, preventing precision of constant current output from being influenced by change of a working mode and/or by variation of input conditions; when an output voltage changes, QR mode keeps unchanged or depth of a CCM keeps approximately constant.

Abstract: Disclosed is a high voltage power system with enable control, comprising a high voltage start-up circuit, a PWM control module, and a driving module; the high voltage start-up circuit comprises a first transistor, a third transistor, a fourth transistor, a resistor, a diode, a VDD detection unit and an I/O interface unit; the high voltage start-up circuit is controlled by an input of a pin EN; when the pin EN is set, the high voltage start-up circuit stops working; the power system is shut off and doesn't restart, and enters a zero standby state; when the pin EN is reset, the high voltage start-up circuit restores to work, and the power system restarts and enters a normal working state. The power system having the high voltage start-up circuit with enable control has characteristics that the standby input power consumption and standby input current are both close to zero.

Abstract: Disclosed is a short-circuit protection circuit for a voltage sampling resistor of a primary side converter, comprising a high voltage power transistor, a high voltage starting resistor, a first voltage dividing resistor of a port VDD, a second voltage dividing resistor of the port VDD, an NMOS transistor, a diode, a first comparator, a second comparator, a third comparator, a time delay circuit, a filter, a first logic circuit, a second logic circuit, a current supply, a first AND gate and a first inverter. The chip of the present disclosure is capable of correctly and effectively detecting whether the sampling resistor is shorted or not before the chip works normally, thereby avoiding the risk of damaging the chip by large current from the voltage feedback port FB due to turn-on of the switching transistor when the upper voltage sampling resistor is shorted, and greatly reducing the input power.

Abstract: The present disclosure relates to a circuit structure for enhancing EFT immunity of primary side converter, including a power ground and a feedback voltage detecting block, a feedback current detecting block, a controller, a PWM driving block, a high voltage starting block, a starting unit, a circuit for enhancing EFT immunity of primary side converter, a power MOS transistor, and an OR gate configured to perform a logical OR of an off-time calculated theoretically and an off-time output by an off-time control block. The present disclosure enhances EFT immunity effectively and improves the dynamic characteristics of the primary side converter.