An Adaptive Power Transistor Driver Circuit Design For Flyback Switching Power Supply

Fly-back switching power supply is widely used in small power supply and adapter, because of its high efficiency, simple external auxiliary and good reliability. With the digital power supply developing towards the green direction, in the circuit design process, switching speed and the power loss have been increasingly concerned. This article will do the research and optimization on it.The principle of the transistor as a switch is introduced in this article at first. Then, we are going to discuss the way how to determine the working status of the switching transistor, as well as further analysis of the factors which affect the speed and losses. Then the design of the transistor driver circuit on how to improve switching speed and reduce losses is presented:for different peak current that flows through the primary inductance, take adaptive segmentation driven strategy, so that we can achieve lower switching losses on low load conditions. The switching speed is increased by using large current-on and pre-off, based on conventional digital control algorithm. At last, the design and simulation of the circuit and layout is shown.Use CSMC1μm700V BCD process to design and simulate the circuit by Cadence Spectre. The results show that transistor driver circuit designed in this paper can be compatible with existing digital power control algorithm. The base drive current range is 9.8mA-31.3mA, current accuracy is ±0.3mA. Compared to conventional drive mode, at light load and half load, the base driver power consumption was reduced by 28.4% and 13.7%.