Research On Control Strategy Of GaN Active-Clamp Flyback Converter

Flyback circuit has many advantages,such as simple topology,electrical isolation between input and output,small number of components,high reliability,so it has been widely used in the field of switching power supply.However,when the main switch is turned off,the energy of transformer’s leakage inductance is released through parasitic capacitance of the switch,resulting in LC oscillation,voltage spike and high voltage stress on the switch,which increases the switching loss and reduces the overall efficiency.The usual solution is to add a clamping branch to the flyback circuit so that the energy of the transformer’s leakage inductance has a release path.Among them,the active clamping scheme overcomes the disadvantage of passive clamping.Leakage inductance energy can be transmitted to the load through clamping capacitor.At the same time,the zero-voltage switching-on of the switch can be realized,by controlling the dead-time and choosing the components reasonably,and the loss of the switch and EMI can be reduced.But this scheme adds active devices,and the control of the circuit is more complex.In addition,there are also some problems such as high cycle energy and low efficiency when the circuit is in light load or no load.The control strategies of the current active clamp chips are mostly complex,and the corresponding peripheral circuits are also complex,which makes the practical application inconvenient.The control strategy of active clamp flyback circuit is discussed in this dissertation,based on the research progress of active clamp flyback circuit.On the basis of summarizing the existing control strategies,this dissertation proposes a simple control method in implementation,taking into account other indicators such as efficiency,power density and so on,which has a certain reference value.The performance of the proposed scheme is verified by a prototype experiment.At the same time,GaN,as the representative of wide bandgap semiconductor,has excellent characteristics such as low on-resistance and high switching speed.It can be used in active clamp circuit to replace traditional silicon devices,which is expected to improve the performance of the circuit.This dissertation also focuses on the application of GaN devices in active clamp circuits.GaN devices are used as switches to verify their performance through prototype experiments.