Research On The Output Controlling Key Techniques Of High Integration And Efficiency AC-DC Converter

AC-DC controller integrated circuit(IC)has been widely used in various adapters for portable devices,power supplies of household appliances,lighting and other applications.The technology trends of AC-DC controller IC focuses on efficiency improvement,integration improvement,control precision improvement and intelligence.Based on the characteristics of flyback AC-DC convertor,this thesis studies some key point on IC integration and efficiency improvement.Following parts are included in this thesis.A primary side integrated demagnetize time detection circuit is proposed to realize a fully integrated primary side controlled constant output current flyback controller.An on-chip high voltage capacitor communication method and related circuit are proposed to achieve high precision output voltage control and high integration.An adaptive zero crossing detection method is proposed for optimizing synchronized rectification in flyback converter.A flyback controller for constant output current is introduced,and then a fully integrated primary-side controlled flyback controller is proposed.To improve the integration of the controller,an on-chip high voltage power device,an on-chip integrated demagnetize time detection circuit and a control circuit without off-chip compensation are adopted.After an analysis of the characteristics of the flyback convertor and the parasitic factors in the circuit,a demagnetize time detection method based on parasitic capacitors on power device is proposed.Compared with conventional demagnetize time detection method,no off-chip resistor divider,auxiliary winding or opto-coupler is needed.The proposed controller has been designed and fabricated.The test results shows the design goals has been achieved.The size of the whole system is 1.6 cm × 2.4 cm × 1.4 cm.The error of the output current is less than ± 2.48%under 85-265V AC input.After the study of the flyback converter with constant current output,a flyback convertor with constant voltage output is.studied.To ensure high output control precision,fast response speed and high efficiency,a control method with dual-controller is adopted.A primary-side controller and a secondary-side controller are included in the system.The primary-side controller is integrated with high voltage power device and high voltage power supply circuit.The secondary-side controller is integrated with a synchronized rectification controller.The primary-side controller and the secondary-side controller communicates with each other via an isolated path to achieve close-loop control.To ensure the safety of the converter,a state machine with exception handling function is designed.In addition,to ensure the power up sequence of the converter,an additional power supply circuit is designed for secondary-side controller.The additional circuit can ensure the secondary-side controller a fast startup.Based on the dual-controller structure,to achieve reliable isolated communication,an isolated communication method based on an on-chip high voltage capacitor is proposed.The high voltage capacitor can be implemented on chip,therefore,no special package frame or extra component is need.The primary-side controller and the secondary-side controller can be integrated in to one single package.Several possible structures for on-chip high voltage capacitor are proposed.The parasitic parameters of the high voltage capacitor are analyzed.Then based on the analyses,a signal recovery circuit is designed for the communication.The proposed high voltage capacitor occupies only a size of a bounding pad,thus it will not increase the total cost of the system.To verify the proposed isolation communication method,the primary side IC and secondary side IC are designed and fabricated.A constant output voltage flyback convertor is built for test.The test results show that the proposed method can achieve stable close loop feedback.The error of the output voltage is less than 0.96%under 90-256 V AC input and 0-10 W load range.The response time is less than 200 μs when the load switches between empty load and full load.To further improve the efficiency of the system,based on the synchronized rectification method,non-ideal factors in synchronized rectification are analyzed.Based on the operation principle of flyback convertor,loop delay and non-ideal factor of comparator might reduce the effect of synchronized rectification.An adaptive zero crossing detection method for optimizing synchronized rectification is proposed.The loop can adaptively compensate the non-ideal factors in the circuit,then,achieve a precise synchronized rectification control.To verify the propose method,a circuit is designed and fabricated.The test results show that compared with conventional synchronized rectification method,the proposed method can effectively improve the efficiency of the flyback convertor.With the 85-220 V AC input,5 V 5 W output system,the best improvement of efficiency is 3%under 20-60%load.For heave load condition with load more than 80%,the best improvement of efficiency is 0.8%.