The Design Of Adaptive Dead-time Control Circuit For GaN Driver ICs

The enhanced mode Gallium Nitride power devices have the characteristics of high switching speed.They are more suitable for high-frequency applications than silicon-based power devices,especially in switching power supply systems.However,it is well known that there are no parasitic diodes in GaN power devices,and the reverse conduction voltage drop is large.For GaN bridge system under high frequency operation,the reverse conduction loss will take up a large part of the overall loss if the dead-time is too long,and the risk of system power transistor shoot-through will increase if the dead-time is too short.Therefore,the tradeoff between loss and reliability must be considered in deadtime control technology.Therefore,it is of great significance to study the adaptive dead-time control circuit based on the GaN driver ICs.The characteristics of enhanced mode GaN power devices and the requirements of the adaptive dead-time control circuit for GaN driver ICs are introduced in this thesis firstly.Then the principle of traditional dead-time control circuits are given in detail.The limitations of prior art are analysed carefully in consideration of the 600 V high voltage application.On the basis of above analysis,an adaptive dead-time control circuit applied for GaN driver ICs is presented in this thesis.The circuit is composed of dv/dt detection circuit and delay regulating circuit.The dv/dt detection circuit converts the switch-node dv/dt corresponding to different load conditions into current signal.The current regulating delay circuit adjusts the delay of the gate control signal of the power transistors according to the current signal,achieving the goal that the dead-time varies with load conditions.Shoot-through between high and low power transistors is avoided and the reverse conduction loss is greatly reduced.Therefore,the bridge system based on GaN power devices can work efficiently under high frequency conditions.The proposed circuit was implemented in 600 V high-voltage BCD process.The Experimental results indicate that,under the condition of 600 V working voltage and 1MHz operating frequency,dead time varies adaptively with load conditions.When the load current varies from 6.8A to 1.1A,the high-side dead time error changes from 12.1ns to 11.7ns,and the low-side dead time error changes from 8.2ns to 8.0ns.The static current is 152.39 uA,all the above indexes meet the design requirements.