In the field of AC/DC switching power supply applications, a starting circuit is needed to provide the required start-up voltage to the controller chip. In traditional application, The starting circuit is achieved by connecting a resistor with large resistance between the rectifier and the power terminal of the controller chip, the output terminal of the rectifier charges a bypass capacitor of the controller chip through the resistor with large resistance, when a starting voltage is reached, the controller starts, and the system begins to work properly. After the completion of the starting, the energy required by the power terminal of the controller chip is mainly provided by an auxiliary winding. In normal work period of the controller chip, the resistor in the starting circuit still consumes a certain amount of power, which seriously affects the overall efficiency of the system. One way to solve this problem is to reduce the starting current of the controller chip and increase the starting resistance. However, due to the large starting resistance, the starting current is correspondingly reduced, and the starting time is prolonged. Another way is to integrate the starting circuit into the controller chip, after the starting is completed and the system works normally, the starting circuit is closed to remove the effect on the overall efficiency of the switching power supply system from the starting circuit.
The controller chip integrates the starting circuit, the power can only be provided to the controller chip after the completion of the conversion from high voltage to low voltage, which inevitably increases the area of the chip, and how to effectively reduce the controller chip area without affecting the starting requirements of controller chip, is the key problem that the internal integrated starting circuit confronts and must be solved. To the power chip with the controller chip integrated high voltage power MOS, the problem becomes more prominent, the area of the chip is very big, which leads to an increasing cost of the chip.
In addition, the requirement of reducing power consumption for the modern switching power supply increases day by day, and a green switching power supply is necessary for all applications, which is not only referred to the handheld and battery power supply system in the past, therefore in the promise of protecting ecological environment, reducing the energy consumption of the electric power supply system and battery power supply system is indispensable. In China, it can bring more special advantages: reducing the load of coal-fired power stations. It not only requires that the control core of the power chip is with low power consumption characteristics, but also requires that the control core of the power chip has some features further reducing the power consumption of the system.
Therefore, it is necessary to put forward an effective technical solution to solve the problem existing in design of switching power supply chip in the prior art.