Research Of Integrated Method Of PSR Flyback Converter With High Precision Constant Current Adaptive Valley Switching And Synchronous Rectifier

Over the decades,the number of electronic products such as notebooks,smart phones and tablets has continued to increase rapidly.As a result,demand for switched-mode power supplies,particularly AC/DC converters,is also increasing rapidly.Flyback topology is the most attractive architecture for these low power conversion applications especially for battery charger and LED driver.It has the advantages of simple structure,low cost,good electrical isolation,compactness and wide input-voltage range.In this dissertation,a complete system intergration plan is proposed baesd on PSR(primary-side Regulation)control method aiming at how to improve the system efficiency,how to decrease system standby power,how to improve system constant current accuracy,how to minimize the output voltage error caused by the sampler,and how to speed up system dynamic response.The study mainly containing:1.This dissertation proposes a self-compensating CC(Constant Current)circuit.These days,demand for LED drivers and battery chargers is increasing,so the requirement for constant current accuracy is growing ever higher.However,it is still a challenge for converters designed according to traditional CC circuit to meet the high precision constant current requirement.This paper proposes a self-compensating OCP circuit to achieve a high-precision constant current at different input voltages.It consists of a CS S/H circuit and a dynamic OCP voltage reference circuit.Compared with conventional OCP circuits,it does not need an extra compensation circuit and it has a much bet ter CC precision.To verify the feasibility and performance of the proposed circuit,an IC controller that uses the proposed OCP circuit has been designed and fabricated in 0.35 μm 5-V/40-V high-voltage CMOS technology.Since the proposed circuit can be added into an IC controller without adding any extra pins,it can replace conventional OCP circuits perfectly.Therefore,the combination of the proposed scheme and the flyback configuration will make the entire proposal a viable contender for many low power applications.Experimental results show that the constant output current precision of the prototype is within ±1% when the input line voltage changes from 85 Vac to 265 Vac.In the common line voltage range(110Vac~220Vac),the output current regulation accuracy can reach a level as high as ±0.3%.2.A CV(Constant C urrent)circuit named as Dynamic Valley Selector circuit is proposed in this dissertation.In order to improve the system efficiency and to decrease system standby power,a power loss model and breakdown of the quasi-resonant flyback converter is not only derived,but also analyzed with mathematic analysis software,MATLAB.Then,a CV control method of Dynamic Valley Selector circuit is proposed to improve the system efficiency especially at light loads to meet the requirement of green power.With the help of this circuit,the power switch can be turned on at different valley of voltage stress across its drain and source terminals when load changes.Experimental result shows that the average energy conversion efficiency of the proposed prototype can reach as high as 82.3%,and its standby power loss is less than 30 m W under different input voltages.3.A high precision sampling and hold circuit is proposed.Although PSR regulation can achieve low cost and low standby power consumption,it still has many limitations.Since the auxiliary winding voltage contains not only the output voltage but also the voltage of the secondary-side rectifier diode,it is hard to precisely extract the output information.This dissertation proposes a novel sample and hold circuit which can sample the feedback voltage on auxiliary winding at the point that nearly the knee point.Although its sampling precision is lower than the digital sampling circuit,it also performs much better than the traditional sampling circuit.Furthermore,it can be widely used in PSR flyback converters because of its low cost,simple structure and no extra pins.4.A novel Dynamic Response Speed-up circuit is proposed in this dissertation.Limited by traditional primary-side sensing technology,PSR flyback controller suffers from poor dynamic response.A Dynamic Response Speed-up circuit contains a novel feedback comparison and sampler combo controlling circuit has been presented in the dissertation.It can detect the station when the load changes dramatically,and changes the pulse width of sampling signal.So the output of EA(Error Amplifier)changes much more quickly which makes the performance of dynamic response much better than the traditional circ uit.Test results show that the output voltage of the proposed PSR controller becomes stable within 3.4ms when load current changes abruptly from 0 to 1.5A and from 1.5A to 0.5.A SR(Synchronous Rectifier)driving integration strate gy for PSR converter is proposed.With the increase of the battery storage,it is common for the battery charger with large output current.Traditional rectifier diode has become an important factor affecting the conversion efficiency.This dissertation proposes a SR driving integration strategy for PSR converter.It mainly consists of a fast comparer used to turn on and turn off the SR switch quickly and a spurious trigger detection and protection circuit which can avoid the spurious triggering of the self-driven signal.To verify the feasibility and performance of the proposed SR driving integration strategy,an IC controller that uses the proposed OCP circuit has been designed and fabricated in 0.35 μm 5-V/40-V high-voltage CMOS technology.According to the test results,the system conversion efficiency can reach as high as 85.8% which has an improvement of 3.5% comparing to the rectifier with Schottky diode in the same application system.