Design Of A Highly Accuracy AC-DC CC/CV Converter Based On A Cable Compensation Scheme Without Capacitor

In the increasingly severe global energy and environmental issues,low-power portable electronic products are favored.As the main power supply unit of portable electronic products,lithium-ion batteries have attracted more and more attention.Lithium-ion batteries have a high energy-to-weight ratio and energy-to-volume ratio,have no memory effect,can be recharged more frequently,have a longer service life,and are getting lower and lower prices.These features have facilitated the development of portable products in smaller and lighter directions,resulting in more and more products powered by single-cell Li-ion batteries.To meet the demand of high requirements of adapters and chargers for portable electronic products,this thesis thoroughly studied the aspect of improving the method of cable compensation,and proposed a highly accuracy ACDC constant voltage/constant(CV/CC)flyback converter,which is no need of external compensation capacitor.The proposed converter adopts primary side feedback(PSR)structure,which eliminates optocoupler and voltage regulator compared to the traditional secondary side feedback(SSR)structure,thus simplifies the system and reduces cost.The chip adopts pulse frequency modulation(PFM),detecting output voltage through the auxiliary winding and comparing it with the reference voltage through the error amplifier.Then the obtained error voltage is compared with a quasi-log wave to generate a control signal,which determines the switching frequency of the converter,thus achieving voltage output constant in CV mode.At the same time,cable compensation module of the chip processes the demagnetization time duty cycle.Firstly,the pre-filtering is performed,then the peak and valley values are sampled and averaged.Finally,being re-filtered by the switching capacitor,a compensation voltage is obtained,which increases with the demagnetization duty ratio.The compensation voltage adjusts the reference voltage to correct the output voltage,thus compensates the voltage loss on the charging cable.In CC mode,the chip detects the demagnetization time of the transformer from the auxiliary winding,and adjusts the switching frequency to make the switching period double of the demagnetization time,while the primary peak voltage stays constant.Therefore a constant output current is achieved.On the basis of theoretical analysis,the circuit and layout design of the system is presented.A control IC for the proposed CV/CC converter has been fabricated in NEC 1μm 5V HVCMOS process.Besides,a 5V/1A prototype is also fabricated.Experimental result under 85~265Vac input shows that the stand-by power is lower than 140 mW,and the highest efficiency can reach 78.2%.In CV mode,the output precision is within ±3%,the line regulation is ±0.5% and load regulation is ±0.9%.In CC mode,the output precision is ±2.5%,the line regulation is within ±2.1% and load regulation within ±1.2%.When the load increase from light to heavy,the output voltage also gradually increases by the function of the cable compensation inside the chip,thereby compensating the voltage lost on the cable.Therefore,it can be seen that the proposed control chip has a promising application in low power AC-DC CV/CC converter.