Switching power supply and controlling method thereof

Abstract

The invention discloses a switching power supply, which comprises a transformer primary side winding, a transformer auxiliary winding, a transformer secondary side winding, and a first control circuit coupled to the transformer primary side winding. The base electrode of a power transistor is connected with the output end of the first control circuit, the collector electrode is connected with the different end of the transformer primary side winding, and the emitter is earthed. The switching power supply further comprises a second control circuit coupled to the transformer secondary side winding, wherein the input end of the second control circuit is connected with the output end of the switching power supply, and the output end of the second control circuit is connected with the different end of the auxiliary winding. When the input voltage Vout of the switching power supply is lower than a first set voltage value, the second control circuit transmits a pulse signal to the first control circuit, and the first control circuit controls the power transistor to be conducted in order to transfer energy to the output end of the switching power supply through the transformer primary side winding. By the invention, the standby power consumption can be improved, and the output voltage precision in the light load and idle load range can be increased.

Description

A switching power supply and its control method technical field The present invention relates to the technical field of electronic circuits, and more specifically, to a switching power supply and a control method thereof. Background technique Due to the advantages of small size, high conversion efficiency and large output load capacity, switching power supply is widely used in many fields such as mobile phone chargers and power adapters. Output dynamic performance is a key indicator of switching power supply. In some mobile phone charger applications, the output voltage is required to not be lower than 4.2V when the load current is switched from 0mA to 700mA; in the application of notebook computers or LCD TVs, the system When switching from standby to normal working state, it is required that the undershoot peak of the output voltage cannot exceed + / -10% of the nominal value of the output voltage; the output voltage accuracy is another key indicator of the switching power...

AI Technical Summary

Problems solved by technology

Secondly, when the existing switching power supply is under light load, the output voltage Vout will have an overshoot problem because the output terminal cannot exhaust the energy supplied by the primary side (see Figure 4).

In this way, it will not only cause the output voltage to overshoot, but also cause unnecessary loss of energy, resulting in a decrease in efficiency

Figure 5 is a schematic diagram of the output voltage Vout and the load at the output end of the existing switching power supply. It can be seen from Figure 5 that the output voltage Vout overshoots significantly during the light-load to no-load stage.

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