AND8393 - Universal Input AC-DC Printer Adapter …

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4 Other names and brands may be claimed as the property of others. Semiconductor Components Industries, LLC, 2010 February, 2010 Rev. 21 Publication Order Number: AND8393 /DAND8393/D48 W, 24 V UniversalInput AC-DC PrinterAdapter Using the NCP1219 Prepared by: Dave BriggsON SemiconductorIntroductionThe NCP1219 is the newest part in the NCP12XX familyof current mode flyback controllers. The controller featuresdynamic self supply (DSS), eliminating the need forexternal startup circuitry, contributing to a cost effective,low parts count flyback controller design. The NCP1219also includes a user programmable skip cycle threshold,reducing power dissipation at light loads and in standbymode.

5 An externally provided latch signal delivered to theSkip/latch pin allows the realization of 48 W ac Adapter demonstration board targets a printeradapter application with a 24 V output, reconfigurable V in standby mode selectable with an external use of DSS mode is demonstrated for low inputvoltages, while an auxiliary winding is used for higher inputvoltages to maintain standby power below 1 W. TheNCP1219 demonstration board shows latched modeprotection function through the optional primary andsecondary overvoltage protection demonstration board is designed as an off line printeradapter power supply. The Adapter operates across universalinputs, 85 Vac to 265 Vac (47 Hz 63 Hz).

6 The adaptersupplies a regulated 24 V output. It can deliver a steady state30 W output with transient capability of 48 W, as defined inFigure 1. Transient Output Current Specificationtime (ms)Output Current (A) A700 ms300 msThe system has a low voltage standby mode enabled bypulling the MC node low. In standby mode the convertersupplies 70 mA of standby current at V whilemaintaining Input power below 1 W. The system isself contained, with the NCP1219 bias being provided bythe bulk voltage through an internal startup circuit. The ICbias is provided by either DSS for low Input voltages, or anauxiliary winding for higher Input voltages.

7 Thespecifications are summarized in Table 1. SUMMARY OF DEMONSTRATION BOARDSPECIFICATIONSR equirementUnitMinMaxInput VoltageVac85265 Line FrequencyHz4763 Output CurrentAdc ( transientpeak)Output PowerW 30 (48 transient peak)AverageEfficiency (EPAE nergy Star ) Standby VoltageVdc78 Standby PowerW 1 Output RippleVoltagemV 200 Output VoltageUnder/OvershootDuring TransientLoad Step A to AmV 200 DESIGN PROCEDUREThe converter design procedure is divided into severalsteps: Power Component Selection Loop Stability Analysis and Compensation IC Supply Circuits External Protection Circuits Standby Reconfiguration CircuitThroughout this application note, the minimum andmaximum Input voltages are referred as low and high line, demonstration board schematic is provided inFigure 2 for reference to component values throughout thedesign 2.

8 Demonstration Board SchematicF12A/250VT110u, Connector turns ratio, N, is chosen to minimize the voltagestresses placed on main switch, Q5, and the secondary diode,D12. N is calculated using Equation 1,N+NSNP+kC@ Vout)Vf 1)where NS is the number of turns on the secondary winding,NP is the number of turns on the primary winding, kc is theclamp voltage ratio, Vout is the regulated output voltage, Vfis the forward voltage drop of the secondary rectifyingdiode, BVDSS is the breakdown voltage of the main switch,kD is the derating factor of the main switch, Vos is the clampvoltage overshoot, and Vbulk(max) is the maximum DC bulkvoltage supplying the controller.

9 Using a 650 V MOSFET with a derating factor of and a clamp voltage ratio, kc, yields a turns ratio of This maintains sufficientmargin for the voltage rating of the power components for the flyback topology can beselected for operation in either discontinuous conductionmode (DCM) or continuous conduction mode (CCM).Measuring the tradeoffs of the two modes at the power levelrequired for this design, the transformer is designed to makea transition between DCM and CCM at low line and a loadcurrent of A. This ensures that the converter operates inDCM at nominal load. The critical primary inductance,LP(crit), to cause this transition is calculated usingEquation (crit)+h@Vbulk(min)2@ Vout)VfN 2@fOSC@Vout@Iout(crit)@ Vbulk(min))Vout)VfN @ Vout)VfN)h@Vbulk(min) (eq.

10 2)where fosc is the switching frequency of the controller, andIout(crit) is the load current at which the transition betweenDCM and CCM occurs. By operating in the transitionbetween DCM and CCM, the secondary RMS current isminimized, reducing the requirements on the transformerand output capacitor. For the demonstration board design,with a transition occurring at Iout = A, the primaryinductance is 350 RESISTORTo calculate the value of the current current sense resistor,Rsense, the peak current of the primary winding of thetransformer must first be calculated. The energy storagerelationship is used to determine the peak primary current,calculated using Equation +2@PoutLP(crit)@fOSC@h (eq.