High-voltage starting circuit and method integrating zero-crossing detection and X capacitor discharging

Abstract

The invention relates to a high-voltage starting circuit and method integrating zero-crossing detection and X capacitor discharge, which can be integrated in a flyback switching power supply chip. Thecircuit comprises a high-voltage starting module which supplies power to the flyback switching power supply chip when the power is on, enables the flyback switching power supply chip to be started quickly, and stops supplying power after the flyback switching power supply chip works normally; an alternating current detection module which is connected with the high-voltage starting module and usedfor detecting an alternating current zero crossing point and detecting whether alternating current is disconnected or not, wherein if it is detected that the alternating current is disconnected, a T0control signal is output to enable the high-voltage starting module to be started again and perform electric energy discharging action on the X capacitor so as to charge an energy storage capacitor of a VCC pin of the flyback switching power supply chip; and a VCC clamping module which is used for keeping the working voltage VCC of the flyback switching power supply chip within a reference voltage value. According to the high-voltage starting circuit, the starting time of the switching power supply chip can be shortened, the zero-crossing detection and X capacitor discharging can be integrated, the system application is simplified, and the system cost is reduced.

Description

technical field [0001] The invention relates to a high-voltage starting circuit and method integrating zero-crossing detection and X capacitor discharge, belonging to the technical field of switching power supply control. Background technique [0002] In the field of switching power supply, the switching power supply will be equipped with a startup circuit to start the switching power supply control chip when the power supply is powered on, drive the transformer to convert the voltage, and realize the normal operation of the switching power supply. The power supply of the switching power supply control chip generally comes from the auxiliary winding, but when the power supply is just started, the output of the secondary side is not established, and the voltage of the auxiliary winding is low, so it cannot supply power to the switching power supply control chip. Therefore, when the power supply is powered on, the switching power supply control chip takes power from the input ...

AI Technical Summary

Problems solved by technology

This method can meet the start-up requirements, but there are also some problems: 1. The charging current is small, 2. The switching power supply control chip takes a long time to start, 3. After the switching power supply chip works normally, there is still current on the starting resistor, causing unnecessary waste of power

It is often necessary to use X capacitors to reduce the interference of the system to the power grid and the grid to the system. However, after the system is powered off, there will be residual voltage on the X capacitor, and the residual voltage will exceed the safe voltage, which may cause people to touch the power plug. There is a risk of electric shock. In order to avoid dangerous residual voltage, a discharge resistor is often connected in parallel with both ends of the X capacitor, but it will generate a large power consumption.

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