EVBUM2145 - 19 V, 3.0 A Universal Input AC
Contents
1. 19 V 16 V between the main output and the auxiliary winding Figure 7 shows the auxiliary supply circuit A resistor is included to provide the flexibility to redesign the circuit for higher output voltages Any extra bias voltage greater than 18 V is simply dissipated across the resistor NCP1271 Figure 7 Auxiliary Supply Soft Skip Adjustment When the load current drops the compensation network responds by reducing the peak current When the peak current reaches the skip peak current level the NCP1271 enters skip operation to reduce the power consumption The peak current level at which skip is entered should be set high for good standby power dissipation However it also needs to be set low enough that no audible noise occurs during each bunch of skip pulses To address this need the NCP1271 has a proprietary Soft Skip feature which ramps each bunch of pulses This dramatically lowers acoustic noise and allows a higher skip level to be set for greater power savings The NCP1271 also allows the designer to select the optimal level of the peak current during skip through a simple resistor from pin 1 to GND This skip resistor sets the skip level according to equation 4 Vskip Iskip X Rskip eq 4 where Iskip 43 uA typ The peak current when skip mode is activated can be calculated with equation 5 Vski skip 3V eq 5 Ipeak skip x Ipeak max For this evaluation board Vs ip was set to 1 3 V Rskip 30 12. Figure 17 shows the go to standby transition from full load operation The output voltage yellow trace does not consume current and remains at 19 V but the Vcc voltage drops from 16 V to 15 V because the Vcc auxiliary winding is not supplying current to the controller The minimum Vcc voltage in the transition can be as low as 12 V This is why the 16 V biasing voltage was selected to maintain Voc above Vcc off and prevent a Vcc reset x CITO UT 5 00 VION 5 00 WaN 500 miviciy 15 00 V oft 15 00 V otst 1 500 V ofst Figure 17 Operating to Standby Short Circuit Protection Measurements Figure 18 details the operation of the short circuit protection The load steps from 60 W to 100 W causing the peak current to increase to its maximum 1 V as shown by the blue CS voltage After approximately 130 ms the controller shuts the power supply down and enters double hiccup fault operation Figure 19 This provides very low power dissipation and protects the power components When the short circuit fault is removed the application recovers by executing a soft start and bringing the output back to 19 V PEONCH 40 53 x a mebasa 150 ma Tipper 50 0 medh f Stop 906 mv Oks Edge Positive Figure 18 Short Circuit Protection is Activated When the Output Load Increases to about 100 W Measure PIMEC P2auy C2 P3waINCH P4 6 21 ps hitp onsemi com NCP1271ADAPGEVB P6 top C2 P7 amc PO
3. Over Power Compensation input voltage is due to the propagation delay Tprop of the For this evaluation board the short circuit protection is NCP1271 This propagation delay has a more pronounced activated with an output load of 76 W at 85 Vac and 93 W effect on the power delivered at high line than at low line as at 265 Vac The variation in short circuit power level with shown in Figure 3 Peak Primary Current Additional Power Delivered due to Prop Delay lp max 230 Vac Slope Vpuk Lp gt gt lt l time Tprop Tprop Figure 3 Effect of Propagation Delay on the Maximum Power Delivered at High Line and Low Line This effect is called Over Power because it delivers NCP1271 more power than what is requested by the feedback loop Specifically for a DCM flyback system the total power delivered to the output including the prop delay effect is Pout 4 Lp Ip max Vbulk Lp Tprop Fsw n eq 3 The NCP1271 has been designed with a very low Tprop 50 ns typ This minimizes the over power effect However if reduced variation is required then over power compensation can be easily implemented by using one of the Figure 5 Over Power Compensation by Modifying circuits shown in Figures 4 and 5 the Auxiliary Winding Topology Vane The circuit in Figure 4 simply modifies the CS setpoint proportional to the HV bulk level This creates an offset which compensates for the propagation delay Ho
4. adapter s key flyback parameters were calculated to be Np Ns 5 1 Lp 180 uH Rcs 0 3 Q Ipeak full load 3 5 A Switch Rating 6 A 800 V Diode Rating 3 A 100 V Rsnubber 100 kQ Csnubber 10 nF Setting the Short Circuit Protection Level The current sense resistor Rcs or R8 provides two functions First it senses the primary current for current mode PWM operation Secondly it provides the maximum primary current limitation according to equation 1 _1V p max Res eq 1 The short circuit protection activates when the Ip max current is reached for more than 130 ms typ This also corresponds to Vpp being greater than or equal to 3 V for 130 ms Therefore Res must be set large enough to ensure that the required peak current can always be delivered but small enough to meet the short circuit protection requirements A DCM flyback converter has the following relationship Pout 1 2 x Lp x Ip x Fsw xn eq 2 Therefore for an assumed efficiency of 80 a peak current of 4 A should trigger the short circuit protection circuitry at 80 W This corresponds to an Rcs value of 0 25 Q This change in Rcs may also require that the snubber and transformer be re calculated to handle this level of peak current during the short circuit fault time A few iterations of the Excel based NCP1271 design spreadsheet should produce a good starting point for the application s design http onsemi com 2 NCP1271ADAPGEVB
5. duavC2 onan Timebase 160 ma Tri ea as Figure 19 The Controller Enters Double Hiccup Fault Operation during a Continuous Short Circuit Event Conclusion A 57 W flyback power supply featuring over voltage and short circuit protection using the NCP1271 was demonstrated to have excellent light load power dissipation and active mode efficiency The NCP1271 s proprietary Soft Skip operation offers low audible noise and excellent standby performance The NCP1271 design worksheet as well as other design aid resources are available at www onsemi com TEST PROCEDURE Required Equipment e gt 100VA 1 to 1 Isolated Transformer at AC line voltage e AC Power Supply with sinusoidal voltage output 50 to 60 Hz 85 to 264 Vac at least 80 W Digital Power Meter with low power range power consumption measurement capability Oscilloscope or Voltmeter NCP1271EVB Evaluation Board Electronic Load that can handle at least 6 4 A 19 V 57W Test Procedure 1 Connect the equipment as shown in Figure 20 2 The electronic load is will draw up to 3 A in constant current mode Make sure that the wires connecting between the electronic load and evaluation board can handle 3 A current 3 Set the AC Power Supply to 85 Vac Limit the maximum input current to 2 A 1 to 1 Isolated transformer gt 100 VA AC Power Supply gt 80W 85 to 265 Vac 50 or 60 Hz sinusoidal voltage VHigh Viow Yokogawa WT210 Digital Power Mete
6. logic due to strong magnetic fields from the high current 2 Locate the decoupling capacitors close to the device to improve noise immunity 3 Locate the Vcc capacitor very close to the device to prevent the circuit from entering a UVLO fault condition because of noise 4 Locate the output voltage sense resistor close to the output load points 5 Minimize the current sense trace It can become easily polluted with noise Minimize the distance between the feedback opto coupler and controller because this trace is also easily polluted 7 Minimize the distance between the MOSFET and controller because the PCB trace is high frequency and high current so it can easily pollute other parts of the circuit Additionally there are three pins in the NCP1271 that may need external decoupling capacitors 1 Skip latch pin Pin 1 If the voltage on this pin is above 8 0 V the circuit enters latch off protection mode Hence a decoupling capacitor on this pin is essential to improve noise immunity Additionally a resistor should always be placed from this pin to GND to prevent noise from causing the pin 1 level from exceeding the latch off level 2 Feedback pin Pin 2 A small capacitor may be necessary here for improved stability and noise immunity 3 Vcc pin Pin 6 The NCP1271 maintains normal operation when Vccis above Vcccort 9 1 V typical If Voc drops below Vcc off then the circuit enters UVLO protection and
7. restarts after a double hiccup Therefore if Vcc inadvertently drops below Vccvoff due to switching noise then the circuit will recognize it as a fault condition Hence it is important to locate the Vcc capacitor and a ceramic decoupling capacitor as close as possible to the NCP1271 an hitp onsemi com NCP1271ADAPGEVB MEASUREMENTS Standby Performance Thanks to the features in the NCP1271 the evaluation board power supply offers excellent no load and light load standby performance The 230 Vac power consumption of the 57 W circuit is only 83 mW And the input power at 230 Vac with 500 mW load is only 710 mW Figure 15 shows the efficiency with output loads from 500 mW to 60 W at 120 Vac and 230 Vac 95 90 120 Vac foe a 230 Vac O N oa EFFICIENCY I oO O oa 60 0 10 20 30 40 50 60 Pout W Figure 15 Efficiency of the NCP1271 Evaluation Board at Nominal Line Voltages Dynamic Study Figure 16 shows the startup transient waveforms of the circuit when the input is 110 Vac A 4 ms soft start is observed in the drain current The Vrp drops below 3 0 V after 32 ms Since this is shorter than the 130 ms fault validation time the circuit does not enter fault condition and starts up normally 5 00 Wie 500 mivicry 00 Viiv jsi 16 00 V ossi 1 500 V oft 3 000 V ofst Figure 16 Startup Transient CECIEL Trigger Stop 14 05 Edao Positive
8. source is needed That is usually the bias supply voltage Vcc Therefore to protect Pin 1 a resistor Riimit is connected to limit the current below the maximum allowed level In addition the internal ESD diode will limit the maximum voltage on Pin 1 to about 10 V This latch off feature can be configured in a variety of ways Some of the most popular include using the auxiliary winding to detect an overvoltage and using an NTC resistor to detect an overtemperature condition A few variations of these circuits are listed in Figures 9 to 12 F NCP1271 Figure 9 Simple Latchoff Circuit by Bipolar Transistors NTC resistor NCP1271 Figure 10 Overtemperature Protection Latch with a NTC Thermistor OVP NCP 1271 Figure 11 Output Overvoltage Protection Using the Auxiliary Winding Vout ppn LAN LLZ opto coupler T NCP1271 V Figure 12 Output Overvoltage Protection Using an Optocoupler http onsemi com 5 NCP1271ADAPGEVB It is important to note that when Pin 1 is open it sets the default skip level to 1 2 V However in this mode pin 1 is internally pulled high to the Vskip reset level 6 5 V typ This only leaves about 1 5 V of noise margin before the part latches off Therefore if a skip level of 1 2 V is desired then instead of leaving pin 1 open it is always recommended to place a 28 kQ resistor from pin 1 to GND Then the skip level becomes 1 2 V 28 KQ x 43 uA 1 2 V and the p
9. 1 C2 2 Ceramic X2 0 1 uF 275 V 10 N A Evox Rifa PHE840MA6100MA04 Yes Yes Capacitor C3 1 Electrolytic 82 uF 400 V 20 N A Panasonic ECOS2GP820BA or Yes Yes Capacitor EETED2G820BA C4 2 Electrolytic 100 uF 25 V 20 N A Panasonic ECA1EM101 Yes Yes C13 Capacitor C5 1 Polyester Film 10 nF 630 V 10 N A Newark DME6S1K Yes Yes Capacitor C6 2 Ceramic Chip 1 2 nF 25 V 10 1206 Vishay VJ1206Y122KXXA Yes Yes C7 Capacitor C8 3 Electrolytic 2200 uF 25 V 20 N A Rubycon 025YXG2200M12 5X30 Yes Yes C10 Capacitor C11 1 Ceramic Y2 1 nF 1 kV 20 N A Evox Rifa ERO610RJ4100M Yes Yes Capacitor hitp onsemi com 9 Table 2 BILL OF MATERIAL NCP1271ADAPGEVB Substi Desig Toler Manufacturer Part tution Lead nator QTY Description Value ance Footprint Manufacturer Number Allowed Free C12 1 Ceramic Chip 0 15 uF 25 V 10 1206 Vishay VJ1206Y154KXXA Yes Yes Capacitor Fuse 1 Time Delay Fuse 2A 250 V N A N A Cooper 1025TD2 R Yes Yes Heat 1 Heatsink for 11 2 C W N A N A Aavid 590302B03600 Yes N A sink TO 220 Package Heat 1 Mica Insulation for N A N A N A Keystone 4672 Yes N A sink TO 220 Package Insulati on Heat 1 Nylon 4 Shoulder N A N A N A Keystone 3049 Yes Yes sink Washer Washer AC 1 IEC60320 C8 2 5 A 250 Vac N A N A Qualtek 770W X2 10 Yes Yes Connec Connector 770W tor DC 1 3 terminal 3 96 mm N A N A N A Molex 26 60 4030 or Yes Yes Connec pitch male header 009652038 tor Stand 4 Standoff M F Hex
10. A SO 7 ON NCP1271D65R2 No Yes PWM Controller Semiconductor SO 7 IC3 1 Opto coupler CTR 50 600 N A SMD 4 Vishay SFH615AA X007 Yes Yes IC4 1 Voltage Reference 2 5V 1 SO 8 ON TL431AIDG No Yes Semiconductor Di 4 Standard Diode 3 A 600 V N A Axial ON 1N5406G No Yes D4 Semiconductor D5 1 Switching Diode 100 V N A SOD 123 ON MMSD914T1G No Yes Semiconductor D6 1 Standard Diode 1 A 600 V N A SMA ON MRA4005T3G No Yes Semiconductor D7 1 Ultrafast Diode 1 A 600 V N A SMB ON MURS160T3G No Yes Semiconductor D8 1 3A 100V Schottky 3 A 100 V N A Axial ON MBR3100G No Yes diode axial 267 05 Semiconductor D10 1 18V Zener Diode 18 V 14 mA 5 Axial ON MZP4746ARLG No Yes Semiconductor Q1 1 N Channel Mosfet 6 A 800 V N A TO 220A Infineon SPPO6N80C3 Yes Yes B R1 1 Leaded Resistor 100 KQ 2 W 5 Axial Digi key P100KW 2BK Yes Yes R2 1 Leaded Resistor 10 Q 1 4 W 5 Axial Yageo CFR 25JB 5210R Yes Yes R5 1 Ceramic Chip 30 1 KQ 1 4 W 1 1206 Vishay CRCW12063012FE3 Yes Yes Resistor R6 1 Ceramic Chip 10 Q 1 4 W 1 1206 Vishay CRCW120610ROFE3 Yes Yes Resistor R7 1 Ceramic Chip 511 Q 1 4W 1 1206 Vishay CRCW12065110FE3 Yes Yes Resistor R8 1 Ceramic Chip 0 25 Q 1 W 1 2512 Vishay WSL2512R2500FEA Yes Yes Resistor R9 2 Ceramic Chip 1 69 KQ 1 4 W 1 1206 Vishay CRCW12061691FE3 Yes Yes R10 Resistor R11 1 Ceramic Chip 15 8 KQ 1 4 W 1 1206 Vishay CRCW12061582FE3 Yes Yes Resistor R12 1 Ceramic Chip 2 37 KQ 1 4 W 1 1206 Vishay CRCW12062371FE3 Yes Yes Resistor C
11. ILLC does not convey any license under its patent rights nor the rights of others SCILLC products are not designed intended or authorized for use as components in systems intended for surgical implant into the body or other applications intended to support or sustain life or for any other application in which the failure of the SCILLC product could create a situation where personal injury or death may occur Should Buyer purchase or use SCILLC products for any such unintended or unauthorized application Buyer shall indemnify and hold SCILLC and its officers employees subsidiaries affiliates and distributors harmless against all claims costs damages and expenses and reasonable attorney fees arising out of directly or indirectly any claim of personal injury or death associated with such unintended or unauthorized use even if such claim alleges that SCILLC was negligent regarding the design or manufacture of the part SCILLC is an Equal Opportunity Affirmative Action Employer This literature is subject to all applicable copyright laws and is not for resale in any manner PUBLICATION ORDERING INFORMATION LITERATURE FULFILLMENT N American Technical Support 800 282 9855 Toll Free ON Semiconductor Website www onsemi com Literature Distribution Center for ON Semiconductor USA Canada P O Box 5163 Denver Colorado 80217 USA Europe Middle East and Africa Technical Support Order Literature http www onsemi com orderlit Phone 303 675 2175 o
12. KQ And Ipeak max s 1 V 0 25 Q 4 A Therefore Ipeak skip 1 7 A Minimum On Time Limitation The NCP1271 includes a current sense CS Leading Edge Blanking LEB filter The LEB filter blanks out the first 180 ns typ of the CS voltage at the beginning of each drive pulse This helps to prevent a premature reset of the output due to noise However this also results in a minimum on time of the device The duration is equal to the LEB time 180 ns typical and the propagation delay of logic 50 ns typical If the application circuit is configured for 0 skip by connecting Pin 1 to Ground then that minimum on time duration may result in an abnormally high output voltage during no load conditions Therefore it is recommended to set skip to some small value rather than disable it completely Ramp Compensation The NCP1271 also incorporates a feature called ramp compensation Ramp compensation is a known mean to cure subharmonic oscillations These oscillations take place at half the switching frequency and occur only during continuous conduction mode CCM with a duty cycle greater than 50 To prevent these oscillations one usually injects between 50 and 75 of the inductor down slope into the CS pin The NCP1271 generates an internal current ramp that is synchronized with the clock This current ramp is then routed to the CS pin Since the flyback design in this app note is well within DCM operation ramp compensation is
13. N A N A N A Digi key 4804K Yes N A off 4 40 Nyl 0 750 Access 1 4 40 1 4 inch screw N A N A N A Newark 30F698 Yes N A ories Access 5 4 40 screw nuts N A N A N A Newark 31F2106 Yes N A ories hitp onsemi com 10 NCP1271ADAPGEVB NCP1271 57 W Adaptor Layout Figure 22 Bottom View Soft Skip is a trademark of Semiconductor Components Industries LLC SCILLC ON Semiconductor and D are registered trademarks of Semiconductor Components Industries LLC SCILLC SCILLC owns the rights to a number of patents trademarks copyrights trade secrets and other Intellectual property A listing of SCILLC s product patent coverage may be accessed at www onsemi com site pdf Patent Marking pdf SCILLC reserves the right to make changes without further notice to any products herein SCILLC makes no warranty representation or guarantee regarding the suitability of its products for any particular purpose nor does SCILLC assume any liability arising out of the application or use of any product or circuit and specifically disclaims any and all liability including without limitation special consequential or incidental damages Typical parameters which may be provided in SCILLC data sheets and or specifications can and do vary in different applications and actual performance may vary over time All operating parameters including Typicals must be validated for each customer application by customer s technical experts SC
14. NCP1271ADAPGEVB 19 V 3 0 A Universal Input AC DC Adaptor Using NCP1271 Evaluation Board User s Manual ON Semiconductor hitp onsemi com Introduction The NCP1271 is one of the latest fixed frequency EVAL BOARD USER S MANUAL current mode PWM switching controllers with 1 adjustable Soft Skip standby operation for low level audible noise 2 integrated high voltage startup for saving standby power 3 timer based overload fault detection and 4 internal latch protection features Table 1 summarizes all the features of an NCP1271 based power supply This evaluation board user s manual presents an example circuit Figure 2 using the NCP1271 65 kHz version in a flyback topology The design steps and subsequent measurements are also included An Excel based design worksheet is available at www onsemi com The measurements show that the 19 V 3 0 A circuit Figure 1 Evaluation Board Photo delivers above 85 across a universal input 85 to 265 Vac The no load standby consumption is 83 mW at 230 Vac and the light load operation is greater than 75 efficient D1 D4 Fuse 2A 1N5406 x 4 C5 10nF 85 to 265 Vac 19V 3A Mode Choke D5 MMSz914 C9 2200 uF Common C10 2200 uF D8 MBR3100 D6 MRA4005T3 D7 MURS160 Caa R10 1 69 NNI Q1 SPPO6N80C3 IC3 SFH615AA X00 R9 1 69k R11 15 8k R5 30 1k C4 100uF D10 MZP4746A 18V PENEN R12 2 37k F
15. in 1 voltage is also 1 2 V This gives much better noise immunity and reduces the chance of falsely triggering the latch due to noise or leakage current from the external latch circuitry Additionally a small capacitor should be added to pin 1 to further increase the noise immunity HV Pin Protection Circuit When the main power is interrupted in the application the high voltage DC bus may potentially go negative in a short transient period Since this is directly connected to pin 8 it could create a reverse current out of the HV Pin and could potentially damage the device There are two easy solutions to this problem The first is demonstrated in Figure 13 The inserted diode turns on when the HV Pin voltage goes below the Vcc biasing voltage This eliminates the chance of negative voltage on the HV pin A second method is shown in Figure 14 Here the inserted resistor limits the negative current to a low level and protects the HV pin Either option works well but for this evaluation board a diode between Vcc and HV was used NCP1271 Figure 14 Protection Resistor on HV Pin Layout Consideration Figures 9 10 show the layout of the design It is a single layer PCB As with any power converter some care must be exercised with the design and layout The following are some important guidelines 1 Minimize the high current loop and locate the IC controller outside the high current loop to prevent malfunctioning of the IC internal
16. ing the AC input and allowing Vcc to drop below 4 V typ THE EVALUATION BOARD SPECIFICATION 85 to 265 Vac 50 Hz 19 Vdc 3 0 A Isolated e lt 100 mW Input Power at 230 Vac e Excellent Light Load Performance e No Audible Noise e gt 85 Full Load Efficiency e Short Circuit Protection Activates at lt 100W for Any Input Voltage Features A Discontinuous Conduction Mode DCM flyback was selected for this application DCM gives very good stability small inductor size lower leakage inductance and good transient response Flyback Calculations Several resources are available at www onsemi com to calculate the necessary component values for a flyback supply In particular an Excel based design spreadsheet can be found at www onsemi com collateral NCP1271SHEET xls Additionally most of the other NCP12xx application notes also apply to the NCP1271 For detailed information on designing a flyback power supply please visit AND8076 D Other app notes which may also aid in the design include AND8069 D Tips and Tricks to Build Efficient Circuits With the NCP1200 AND8205 D How to Choose a Switching Controller for Design AND8023 D Implementing the NCP1200 in Low Cost AC DC Converters AND8032 D Conducted EMI Filter Design for the NCP1200 AND8076 D A 70 W Low Standby Power Supply with the NCP12xx Series Based on the results from the NCP1271 design spreadsheet the final values for this
17. lyback transformer Cooper CTX22 17179 C11 1nF 1000V Lp 180uH leakage 2 5uH max np ns naux 30 6 5 Hi pot 3600Vac for 1 sec primary to secondary Hi pot 8500Vac for 1 sec winding to core Figure 2 Evaluation Board Schematic Semiconductor Components Industries LLC 2012 1 Publication Order Number October 2012 Rev 4 EVBUM2145 D NCP1271ADAPGEVB Table 1 FEATURES OF POWER SUPPLY USING NCP1271 Topology CCM DCM Flyback Standby Condition Soft Skip Operation Fault Condition Double Hiccup Restart Latch Protection Latch Off Activated Fixed frequency current mode control with inherent primary current limitation Frequency jittering to soften the EMI signature Built in soft start Output short circuit fault detection independent of the auxiliary winding Integrated high voltage startup that minimizes standby power loss Adjustable skip level for optimal standby power consumption Proprietary Soft Skip to reduce the risk of low frequency audible noise Soft Skip operation is automatically disabled if an abrupt transient load is applied from standby operation This improves the output response to a transient load Double Hiccup operation minimizes the power dissipation in a fault mode and allows the application to auto recover when the fault is removed An internal latch makes it easy to add overtemperature protection OTP or overvoltage protection OVP to any applications Latch is reset by unplugg
18. not necessary However for designs that do run in CCM with the NCP1271 ramp compensation is easy to implement It only requires one external resistor between Rcs and the CS pin The value of the ramp resistor to obtain 50 inductor down slope injection can be calculated with the following equation Vout V x XE 1 A Lp x Fsw x oA Rramp 0 50 x RCS x eq 6 hitp onsemi com 4 NCP1271ADAPGEVB Maximum Duty Cycle and Ramp Compensation If the ramp resistor is set too high the maximum duty cycle will be reduced But as a long as Rramp is below 10 KQ this will not be a problem A typical graph of the maximum duty cycle verses Rramp is shown in Figure 8 However it is not recommended to try to reduce the maximum duty cycle by the Ramp value because this relationship is not guaranteed by the production tests of the device 90 80 70 X60 50 Q 40 D 30 lt 20 10 0 0 5 10 15 20 25 30 35 40 Rramp RESISTOR KQ Figure 8 Maximum Duty Cycle Characteristics 45 50 Optional Output OVP Latch The NCP1271 includes a feature where if Pin 1 is brought above 8 0 V typ the part will safely latch off the controller The controller is reset by unplugging the AC input This allows for easy implementation of overvoltage OVP or overtemperature OTP protection In order to pull the Pin 1 voltage above the latch threshold a greater than 8 0 V
19. r 800 344 3860 Toll Free USA Canada Phone 421 33 790 2910 bs 3 Fax 303 675 2176 or 800 344 3867 Toll Free USA Canada Japan Customer Focus Center For additional information please contact your local Email orderlit onsemi com Phone 81 3 5817 1050 Sales Representative EVBUM2145 D
20. r IHigh lLow 4 Then turn on the system and apply an 85 Vac input to the Evaluation Board with no load on the output 5 Check if the output voltage is close to the nominal output 19 V and stable no bouncing around Note that there may be significant voltage drop across the output wire Increase the load to 3A and check that the output voltage is 19 V 7 Sweep the input voltage up to 264 Vac with 3A load on the output Ensure that the output is 19 V and there is no noise Decrease the output load to 0 5 A and sweep the input voltage from 264 Vac to 85 Vac Ensure that the output is 19 V and there is no noise an ioe NOTE High Voltage is dangerous Please be extra careful when dealing with high voltage NCP1271ADAPGEVB Evaluation Board Top view Electronic Load 19V 3A gt 80W Constant Current Mode such as KIKUSUI PLZ303W Voltmeter or Oscilloscope Figure 20 Test Setup hitp onsemi com Table 2 BILL OF MATERIAL NCP1271ADAPGEVB Substi Desig Toler Manufacturer Part tution Lead nator QTY Description Value ance Footprint Manufacturer Number Allowed Free T1 1 Common Mode 3 A 508 uH N A N A Coilcraft E3506 AL Yes Yes Line Choke T2 1 Custom 180 uH 30 6 5 10 N A Cooper CTX22 17179 Yes Yes Transformer 180 uH Coiltronics Primary inductance turn ratio 30 6 5 2 5 uH max leakage IC1 1 65kHz Flyback N A N
21. wever this does increase the standby power dissipation Figure 5 gives another option which results in much lower power dissipation By altering the position of the Aux winding diode a new point is created whose voltage is proportional to Vin The power dissipation is now reduced by a factor of Np Naux Values for Ropp are best found experimentally to give suitable precision for the activation of the short circuit protection NCP1271 Figure 4 Over Power Compensation by means of a Resistor to the Bulk Voltage hitp onsemi com 3 NCP1271ADAPGEVB Biasing the Controller The NCP1271 includes a high voltage HV startup pin Pin 8 which charges Vcc to its operating level This pin can be directly connected to the high voltage DC bus Once the device is powered up an auxiliary winding powers Vcc as shown in Figure 6 Rectified Input Output 19V 3A Figure 6 Vcc Biasing Scheme The range of Vcc is from 10 V min to 20 V max Therefore the auxiliary winding should be designed to give a level of Vcc within this range over all output loads When the circuit is in standby mode very few pulses are delivered and the auxiliary level decreases To provide enough voltage range a nominal Vcc level of 16 V was selected for this application Additionally an 18 V 45 Zener diode was added externally to protect the controller from abnormally high auxiliary levels The 16 V bias supply is constructed from a 6 5 turns ratio
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