EVBUM2144 - A 5.0 V/2.0 A Standby Power Supply for Intel
Contents
1. _ _ 9302 FBO 4 02 Meg On the board we purposely modified these values to further improve the standby power 27 mW Auxiliary Winding The auxiliary winding is set to deliver 13 V nominal when the converter is fully loaded To avoid any Vcc drops during transient loading e g sudden load removal the main Vcc capacitor C7 has been increased to 100 uF leading to a stable Vcc in no load conditions The resistor R7 sets the Overvoltage Protection OVP level by adjusting the injected current in pin 1 internal shunt in case of problems With 1 0 kQ the OVP level is set to VOVP 1 0k 7 0m 8 7 15 7V typical on the auxiliary winding Different values can be obtained by changing the resistor values or the ratio between the power and auxiliary windings Clamping Section The converter uses an RCD clamp to safely limit the voltage excursion on the MOSFET drain Failure to keep Vas t below 700 V will permanently damage the circuit In application where the input line can be subject to strong high voltage parasitic pulses we recommend the usage of a Transient Voltage Suppressor TVS that will hard clamp all potentially lethal spikes on the drain Figure 9 portrays the way to wire the TVS Finally the TVS offers superior performance in standby power compared to the RCD clamp Simply because the RCD clamp always activates since the capacitor discharges via the resistor R as soon the leakage inductance is reset Unfortunately even i2. 2 5 A with a 1 0 A us slew rate Vin 85 Vac http onsemi com 9 NCP1027ATXGEVB Qr Qi 50 reid 3 iil ole alal 10 0 ms div afa It In o TTE Figure 15 Load step where V is banged from 0 1 A to 2 5 A with a 1 0 A us slew rate Vin 230 Vac Figures 14 and 15 represent the step load response from on the waveforms comes from the current discontinuity the standby mode to the wake up mode featuring a indured by the LC filter inductor L7 variation from 100 mA up to 2 5 A The spike you can see JH ldiy I M l MW v MANDE n I TI i I i M j i m MA u m Ny l pi M Me I IN uli n wn Figure 16 Peak to peak ripple Pout 0 5 W Cable length 30 cm Vin 85 Vac http onsemi com 10 NCP1027ATXGEVB ejes Figure 17 Peak to peak ripple Pout 0 5 W Cable length 30 cm Vin 230 Vac Figures 16 and 17 display the ripple amplitude when the measurement has been carried at two line levels and using board enters skip cycle mainly at a 0 5 W output power The 30 cm long cables to mimic a real PSU cabling connector Lm uu I L a Foy E _ s I I I L L I I F 1 ve I I P t I I I I I I I I I I I I r1 I I IfI I I I I I I I I I I I I I I 1 I I I I I I I I I I I S aii j I I L I I I I I I I I I I I I rt 1 I I I I I I I ie ee a fi ey a ai i ES a r ae ae ee ae i Lp opm poc ea ee R a I I I I I I I tot I I I I
3. I I I I I I I I I I I I tot I I I I I I I I I I I I I I I I I l Il I I I I I I I I I I I I I I I I I l Il I I I I I I I I I I n ae esea 0 15 10 10 0 30 0 MHz Figure 18 EMI signature low line and high line in quasi peak Pout 10 W Figure 18 shows the advantage of EMI jittering offering successfully made in Quasi Peak QP it implies immediate a clean signature at both line levels As the sweep is compliance in average mode http onsemi com 11 NCP1027ATXGEVB High Line EEEE RR a mmm a INC pcr LENT I o ph 676 ms ms ole eE E 200 ms div Figure 20 Output Current Waveform in Short Circuit Some PC application specs require the output average and lpeak 6 4 A RMS currents in short circuit to stay within given limits e loutay 6 4 x 54 676 511 mA With this design we have obtained the following results at i un E 54 _ high line lout rms 6 4 676 18A http onsemi com 12 NCP1027ATXGEVB PCB Views The PCB routing includes large copper areas around the diode is placed on the copper side and due to its low Vy it integrated circuit to maximize its power dissipation The leads to good thermal performance Gr 10ftoubnodmsed HO xX amp HIHZM MAIO gH nkg c4 BRBIBS amp IIIM Figure 21 The PCB Copper Area of the Demonstration Board Figure 22 The SMD Positions on the Copper Side http onsemi com 13 NCP1027ATXGEVB MIC 2BIB 526 85 ph D2 r2 o gu
4. rer uu zi oa a a e es e R4 9 5v p 2 ele A tL Heese Al o n ul i ew a V9 ce el GND ON dii Semiconductor SOLAN NEP1BZ7 Figure 23 Component Side View BILL OF MATERIAL Substi Toler Manufacturer Part tution Value ance Number Allowed Table 1 BILL OF MATERIAL Semiconductor on 2 5 V 936V 296 TO 92 ON TLA31CLPRPG 1 mA 100 mA Semiconductor 70 V 60 mA NA DIP 4 Vishay SFH615A Semiconductors 800 V 1A NA DFM Vishay DFO8ME3 General El ld Edid Eb Ceramic ac 2 2 nF 2096 Leaded Vishay Draloric WKP222MCPR Yes Capacitor Class 500 Vac 50 Hz spacing Y1 12 5 mm 220 nF 275 2096 Leaded Evox Rifa PHE840MX6220M Yes Vac spacing 15 mm Multilayer 100 nF 50 V 1096 1206 Epcos B37872K5104K060 Ceramic Capacitor X7R Metallized 10 nF 630 V 1096 Lead Vishay MKT1822310635 Polyester Film spacing Roederstein Capacitor 10 mm C6 1 Multilayer Ceramic 10 nF 50V 1096 1206 Epcos B37872K5103K060 Capacitor X7R C7 1 Minature 10 EF 63 V 2096 Radial Panasonic ECA1JM100 Aluminum Electrolytic Capacitor http onsemi com 14 NCP1027ATXGEVB Table 1 BILL OF MATERIAL Substi Desig Toler Manufacturer Part tution nator Description Value ance Number Allowed Electrolytic 100 uF 10 V Radial Panasonic EEUFC1A101 Capacitor C Multilayer 1nF 50 V 10 1206 Epcos B37872K5102K060 Yes Yes Ceramic Capacitor X7R DPAK 4 ON MBRD835LG Semiconductor Axial 1N4937G Em duum Sc
5. NCP1027ATXGEVB A 5 0 V 2 0 A Standby Power Supply for Intel Compliant ATX Applications Evaluation Board User s Manual ATX power supply units PSU require a standby section who keeps alive some particular areas of the motherboard Among the live sections are the USB ports the Ethernet controller and so on The Intel ATX Power Supply Design Guide 2 01 rev June 04 describes the standby voltage rail needed for this purpose This is the 5 0 VSB section 3 3 3 e Output voltage 5 0 V 5 e Nominal load current 2 0 A e 500 ms pulses current USB wake up event 2 5 A e Input power less than 1 0 W at 230 Vac for an output power of 500 mW Power on time 2 0 s maximum e Short circuit protection with auto recovery On top of these requirements most of PSU designers use the standby power supply as an auxiliary rail to power the main controller This is an auxiliary 12 13 V rail or if an UC384X is implemented this rail can go up to 20 V When put in standby a small switch shuts down the controller by interrupting this rail To help designers quickly fulfilling the above needs the NCP1027 has been introduced This DIP 8 package hosts a high performance controller together with a low Rps on 700 V BVdss MOSFET On top of the standby needs we have packed other interesting goodies in this circuit They are summarized below e Brown out detection the controller will not allow operation in low mains conditions You can adjus
6. ON Semiconductor and OW 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 SCILLC 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 d
7. eak Figure 8 shows the results before and after OPP implementation The output current stays below 3 5 A in all cases which is well within specs 6 Without OPP O1 BA With OPP OUTPUT CURRENT A no CO me 1 0 240 INPUT VOLTAGE m Figure 8 Over Power Protection at work keeps the output current below 3 5 A Brown out Brown out BO detection offers a means to protect the converter in presence of low input voltages by stopping switching operation until the mains comes back to a normal value The circuit works by observing a fraction of the bulk level via a resistive divider routed to pin 2 When the level on pin 2 lies below 0 6 V the controller does not allow switching operation but the high voltage current source maintains the Vcc on pin 1 Then as soon as pin 2 voltage crosses 0 6 V the Vcc is ready to power the chip and switching can start As this occurs pin 2 injects around 12 uA Igo in the resistive bridge to create a hysteresis The designer must thus select the turn on and turn off voltages to further apply the following equations Vbulki VBO VBO Vgo bulkt Vbuik2 _ lower VBOTSo x Vpulk1 VBO Suppose we want to start at Vin 110 Vdc 77 Vac and stop operation at Vi 70 Vdc 50 Vac then applying Equations 12 and 13 leads to the following values 4 0 MQ 22 kQ Rupper Hlower eq 12 eq 13 Rupper Riower Total power dissipation at nominal line is then
8. eath 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 or 800 344 3860 Toll Free USA Canada Phone 421 33 790 2910 i f 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 EVBUM2144 D
9. g at both high and low line conditions The circuit can be slightly modified to add some more soft start in case designers would fear output overshoots Figure 11 shows how to connect a 1 0 uF 10 V capacitor to soften the start up Figure 9 A TVS must be used if the Input Voltage can be subject to High Voltage Spikes OPEN oF gF gF i oje agl 500 ns div WETEA Scales Figure 10 Always Check the Voltage on the Drain at the highest Line Condition 265 Vac sequence D1 L1 MBRD835L 2 2 uH 10 k 10 k Figure 11 A 1 0 uF Capacitor connected on the TL431 strengthens the Startup Sequence http onsemi com 7 NCP1027ATXGEVB The basic description being done let us have a look at the board performance Standby measurements were captured with a Yokogawa WT7210 on a board after it warmed up for 15 minutes Please make sure the WT210 volt mater is placed before the current shunt otherwise its input impedance will degrade the low power measurements by 30 mW at high line Static Measurements Vin 230 Vac Tambient 25 C Poit 0 Via 88 mW Maus 10 14 V Pout 0 55W P2779 mW Vaux 211 64 V 1 64 2 Pot 10W Ph 12 3 W Vaux 212 14 V y 81 3 Please note that replacing Rg by a 200 V TVS as mentioned in the text reduces the input power at 0 5 W 230 Vac down to 715 mW and 73 mW at no load Teige NCP1027 50 C at Post 10 W Short circuit temperature NCP1027 Tease 42 C Tdiode 52 C Maxi
10. hing frequency 65 kHz must be respected Various iterations have lead us to adopt the following characteristics Lp 3 4 mH Np Ns power 1 0 06 Vin the input voltage Vout the output voltage Calculations lead to the following mode transition load values noD pde Lowest line Vj 120 Vdc Re 4 56 Q or Iout 1 0 A The auxiliary winding in this case delivers 12 5 V but it Highest line Vn 370 Vdc R 24 Q or Iout 2 0 A can be set to any other value depending on the main controller Vcc The turn ratio limits the reflected value on the drain to less than 100 V without risks of biasing the MOSFET body diode at the lowest input voltage This transformer is available from Coilcraft under a reference detailed in the Bill Of Material BOM As we have seen our design operates in CCM at full load but obviously enters the Discontinuous Conduction Mode Please note that low line is actually 85 Vac but the ATX PSU including a large bulk capacitor we can neglect the ripple given the low output power of this converter hence a 120 V value At the highest line the design operates at the boundary between CCM and DCM The duty cycle at full load and lowest input line can be evaluated via the flyback static transfer function DCM at light loads The transition point can be evaluated 2 Vout eq 2 using the following formula NVin Vout NVin Vout 2 The highest duty cycle is found to be 41 However this Rc 2LpN2Fsw NV i P
11. hottky Barrier 35V 8A Rectifier Fast Recovery 600V 1A Rectifier Weidmuller 1760510000 PCB Connector PCB Connector 2096 T eet mm x Wurth 744772022 9 5mm Elektonic 22 5mm x Schaffner RN114 0 8 02 21 5 mm U D2 D4 lt Common Mode 27 mH 0 8A Inductor R1 Axial Lead 10 kQ 1 4 W 5 Axial Panasonic ERD S2TJ103V Yes Carbon Film Resistor R10 Metal Film 2 8 MQ 1 4 W 5 Axial Vishay Dale CCF072M80JKE36 Yes Resistor R11 Axial Lead 2 2 MQ 1 4 W Carbon Film Resistor R13 Axial Lead 47 KQ 1 4 W 5 Axial Panasonic ERD S2TJ473V Yes Carbon Film Resistor R14 Axial Lead 560 KQ 1 4 W Yes Carbon Film Resistor SMD Resistor 10 kQ 1 4 W SMD Resistor 100 Q 1 4 W l s 596 1206 Vishay Dale CRCW120610KOJNEA 5 1206 Vishay Dale CRCW1206100RJNEA zJ zy l MN id i Axial Lead 680 Q 1 4 W 596 Axial Panasonic ERD S2TJ681V Yes Carbon Film Resistor 5 Axial Lead 47 Q 1 4 W 596 Axial Panasonic ERD S2TJ470V Yes Carbon Film Resistor R6 Power Metal Film 150 kQ 1 W 5 Axial Vishay BC PR01000201503JAC00 Yes Resistor Components Axial Lead 1 kQ 1 4 W i Panasonic ERD S2TJ102V Carbon Film Resistor SMD Resistor 78 kQ 1 4 1206 Vishay Dale CRCW120678KJNEA SMD Resistor 27 kQ 1 4 1206 Vishay Dale CRCW120627KJNEA IS ui i NN X Hi http onsemi com 15 NCP1027ATXGEVB TEST PROCEDURE vout lout Electronic load Figure 24 Test Setup Required Equipment Test Procedure ac Power Suppl
12. l values VboukH 375 Vdc Voulk 200 Vdc lopp 31 UA V 2 45 V VbulkH VbulkL Vt 70 kQ eq 10 IOPP VbulkL Vf I ROPPL V V ROPPH RoPPL ye 5 6 MQ eq 11 Voc U3b Unfortunately despite the good behavior of the network its permanent presence on the bulk rail will affect the consumption in standby When you chase every hidden milli watt it can become a nasty problem To avoid this trouble a simple solution around the auxiliary winding can be worked out This is presented in Figure 7 During the on time where the power switch is turned on the input voltage appears across the primary transformer Given the auxiliary diode configuration N Vj V4 also appears on the cathode N being the primary to secondary turn ratio As this voltage moves up and down with the bulk level we can perfectly use it for our OPP purposes Due to its pulsating low voltage nature power consumption will be the smallest ROPPH 560 kQ ROPPL 47 k Figure 7 The Auxiliary Diode lends itself very well to a cheap and energy efficient OPP Implementation http onsemi com NCP1027ATXGEVB Hooking an oscilloscope probe on D4 cathode gives us the bulk image evolution between its minimum and maximum values We can then run the calculation again to obtain Roppgu and Roppr Voulk 55 Vdc Voull 37 Vdc lopp 31 pA Vy 2 45 V Roppu 580 KQ 560 kQ after tweak RoppL 41 KQ 47 KQ after tw
13. mum output current 3 0 A 265 Vac Vin 85 Vac Tambient 25 C Pout 0 P 54 mW Vaux 10 15 V Pout 0 5W Pin 704 mW Vax 11 6V n 71 Pot 10W Pph 12 6W Vaux 12 6V n2 79 596 Tossa NCP1027 60 C at Po t 10 W Short circuit temperature Tease NCP1027 44 C Tdiode 52 C Maximum output current 3 1 A Dynamic Measurements Some critical waveforms have been captured on the demonstration board and are reproduced below 0 Rim r T o O E E H 200 ms div Figure 12 Short Circuit Protection Drain Source Waveform In Figure 12 we can see the power supply operating in a below 896 keeping all component temperatures at a moderate so called hiccup mode trying to re start as soon as the level This is an auto recovery type of protection implying internal timer has elapsed The resulting duty burst stays a re start when the fault is removed Vi 230 Vac http onsemi com 8 NCP1027ATXGEVB o e g H 5 00 msz div Figure 13 Startup Sequence at Three Loading Conditions Figure 13 shows a typical startup sequence captured at waveform This waveform has been captured with the different output levels 0 0 5 W and 10 W for Vin 85 Vac 1 0 uF wired as suggested by Figure 11 Changing the input voltage does not modify the shape of the i m f Nh y p Tru Ih Mr i It oes H 10 0 m div E It IN o 83 D mV 2 t Figure 14 Load step where Vout is banged from 0 1 A to
14. n standby this mechanism generates light losses If you want to further save 50 mW a TVS is of good usage A 200 V TVS has shown to be a good solution here You can use the 1 5KE200A from ON Semiconductor for instance http onsemi com 6 NCP1027ATXGEVB Vbulk Secondary Side The secondary side uses a Schottky diode featuring an 8 0 A capability and a breakdown voltage of 35 V This is D2 enough since high line conditions imply a Peak Inverse 1 5KE220A 3 Voltage PIV of PIV NVin Vout 0 06 x 370 5 27 2 V eq 14 E i The forward voltage Vf goes down to 0 41 V Tj 125 1N4937 ZA i z which neglecting ohmic losses induces conduction losses of Pdiode IRMS Rd lavgVt 2 x 0 41 0 8 W eq 15 The output capacitor Cout is selected to a pass the adequate RMS current b limit the undershoot AV when the output is banged by a current step AI The undershoot depth of a closed loop converter having a bandwidth f can be evaluated via the following formula VS GT eq 16 Calculations gave us a value of 2 4 mF made of two low impedance 10 V 1200 uF capacitors A TL431 ensures a stable regulation at 5 0 V via a type 2 amplifier R3 and the NCP1027 internal pullup resistor set the midband gain whereas C4 sets the zero position The small capacitor Co filters out residual noise and adds a high frequency pole acting together with the optocoupler one The step load response is clean without any ringin
15. nnecting a resistive network to the bulk capacitor as Figure 3 depicts Bulk ROPPH Ut NCP1027 Cbulk z Ib1 2 7 E F 3 Ib3 Ib2 4 5 ROPPL Figure 3 A Possible Option to Reduce the Peak Excursion consists of Connecting a Resistive Divider to the Bulk Capacitor By injecting a current p3 proportional to Vp iz the maximum peak current limits reduces Analytically obtaining the right value for p3 might represent a complicated exercise as many parameters play a role To the opposite a simple experimental method can be setup to obtain the value of the needed current 1 Configure your working power supply as suggested by Figure 4 or 5 These figures are purposely simplified for ease of understanding of the added circuitry Figure 4 represents the safest way to run the measurement as the dc power supply injects current via an optoisolator without sharing the converter s ground An amp meter is inserted to read the current 55 Leave the dc bias to zero for now 2 Power the converter and set the input voltage to the highest of your specification Let us assume it is 375 Vdc http onsemi com 3 NCP1027ATXGEVB 3 Increase the output current to the point where the 5 At a certain time if you continue to increase the system should shut down per specification Let s current in pin 7 the converter enters in protection say 3 2 A for this design mode The current flowing in pin 7 and the voltage 4 Star
16. ns we evaluate the resistor value to be Rramp eee 91k eq 6 In case no ramp compensation is required pin 2 must be tied to Vcc the adjacent pin As experiments were carried at lower input voltages Cp is small on the demo board it was decided to slightly increase the amount of ramp compensation by reducing Ryamp to 78 KQ Over Power Protection OPP Power supply controllers sensing the primary current to check whether it goes over a certain limit often face propagation delay problems That is to say despite the current limit detection by a dedicated comparator the information takes a certain amount of time to propagate through the logic circuits and eventually reset the latch During this time the primary current keeps increasing by a rate given by the primary inductance and the input voltage Hence we can quickly see the effects of a 100 ns delay at high line or low line Vin Ifinal lpeak max m tprop eq 7 If the limit is set to 750 mA then we have 100 H A eq 8 Ifinal 50m 3 100n 53 m 3 A eq 9 Ifinal S0 M z 100 n 61m The difference looks small but it often leads to a significant different in output current capabilities especially with larger propagation delays Hence the need to act in high line conditions via a dedicated circuitry The NCP1027 hosts a special section used to reduce the maximum peak current limit as the mains increases The system works by co
17. nted turning the SMPS on around 80 Vac and turning it off at 60 Vac Different values can easily be selected by altering the dedicated resistive network Please note that this network impedance has a direct influence on the standby power To limit the amount of current the supply can deliver at high line it is necessary to limit the propagation delay effects The NCP1027 hosts an exclusive circuitry used to reduce the maximum peak current as the line increases We will see that once implemented around the auxiliary diode it does not affect the standby power and nicely harnesses the maximum power The electrical schematic of the board appears on Figure 2 Publication Order Number EVBUM 2144 D NCP1027ATXGEVB TR1 Lp 3 4 mH Np Ns 1 0 06 Bulk Np Naux 1 0 15 D1 L1 E MBRD835L 22uH 9V 2A gt C5 C1 Lt_L tC2 10 nF 1500 uF 1500 uF 0 13 V R6 e 150 k 0 5 W R5 TR R10 47 2 8 Me g D4 R3 100 R1 1N4937 R11 10 k 2 2 Meg U3 AS Y R14 560 kQ C10 NCP1027 C13 Lt 47 uF L 1 uF 400 V u R2 10k C6 R9 R13 10 nF 27 K 47 KQ C11 V 2 2 nF Type Y1 Figure 2 The Evaluation Board Electrical Schematic without the EMI Filter for Simpler Representation Let us start the review by the transformer description where Transformer Lp the primary inductance 3 4 mH The design of the transformer section represents the most N the turn ratio 0 06 difficult part as standby power in no load and 0 5 W output Fyy the switc
18. t the level at which the circuit starts or stops operation e Ramp compensation designing in Continuous Conduction Mode helps to reduce conduction losses However at low input voltage 85 Vac the duty cycle might exceed 50 and the risk exists to enter a subharmonic mode A simple resistor to ground injects the right compensation level e Over Power Protection a resistive network to the bulk reduces the peak current capability and accordingly harnesses the maximum power at high line As this is Semiconductor Components Industries LLC 2012 October 2012 Rev 1 ON Semiconductor http onsemi com EVAL BOARD USER S MANUAL done independently from the auxiliary Vcc the design gains in simplicity and execution speed e Latch off input some PC manufacturers require a complete latch off in presence of an external event e g overtemperature The controller offers this possibility via a dedicated input e Frequency dithering the switching frequency here 65 kHz is modulated during operation This naturally spreads the harmonic content and reduces the peak value when analyzing the signature Figure 1 Evaluation Board Photo Design Description A full CCM operation gave us an adequate performance in this particular case with good full load efficiency results as we will see The part switches at 65 kHz which represents a good trade off between switching losses and EMI control A brown out circuit was impleme
19. t to increase the variable power supply dc on it prior to the shutdown correspond to the voltage until the amp meter deviates Increase variables you look for In this example we measured carefully because you deal with hundred of uA only a Vr voltage of 2 45 V and a current of 31 uA R4 R2 10k 10k U1 NCP1027 t Variable Power Supply Figure 4 An Isolated Way to safely Inject Current into Pin 7 at High Line U1 NCP1027 L Variable T Power Supply Figure 5 A Non isolated Way to Inject Current into Pin 7 at High Line http onsemi com 4 NCP1027ATXGEVB The preliminary curve showing the relationship between the injected current and the maximum peak current setpoint appears in Figure 6 We can see that 31 uA corresponds to 90 096 80 0 70 0 60 0 50 0 40 0 30 0 20 0 10 0 0 0 IPEAK IPEAKOPP IPEAK a 20 reduction in the maximum peak current capability The V parameter specifies the voltage at which pin 7 starts to pump in current It is around 2 5 V as we can see it LOPP CURRENT uA Figure 6 Maximum Peak Current Setpoint Reduction vs Pin 7 Injected Current To compute the resistor values we need to define the range within which the OPP reduction should activate As we do not want any OPP action at low input voltages we will select resistors to start reducing at V 200 Vdc with a clamp at Vj 375 Vdc Using the following equations and our collected data leads us to the fina
20. u number is likely to increase a little given the presence of the leakage inductance http onsemi com 2 NCP1027ATXGEVB Ramp Compensation Being in CCM with a duty cycle close to 50 or above 50 in transient conditions we need ramp compensation Several ways exist to evaluate the amount of ramp compensation The quickest one evaluates the off slope of the secondary inductance and injects around 50 of this slope through a compensating ramp S4 into the controller With the NCP1027 the ramp compensation level is set via a simple resistor connected from pin 2 to the ground as shown in Figure 2 We can calculate the off slope the one actually needed to evaluate 4 by reflecting the output voltage over the primary inductance The slope is projected over a complete switching period _ Vout Vf NLp 6x 15u Soff Tsw 906 x 34m 441 mA 15 us eq 3 The NCP1027 features a current mode architecture using a SENSEFET device That is to say the controller does not directly sense the current via a resistor but through a Kelvin cell For this particular circuit the cell ratio can be modeled as an equivalent sense resistor of 350 mQ This current slope will thus become a voltage slope having a value of S off 0 441 x 0 375 165 mV 15us eq 4 If we chose 50 of this down slope then the final compensation ramp will present a slope of Sa S off 83 mV 15 us 5 53 kV s eq 5 Following the data sheet indicatio
21. y 85 Vac 265 Vac 1 A 1 Connect the test setup as shown in Figure 24 e Electronic Load 5 V up to3A 2 Apply an input voltage 85 Vac VIN 265 Vac 50 Hz or 60 Hz e Yokogawa Power Meter WT210 e NCP1027ATX Evaluation Board e Multimeter 3 Connect electronic load to output connector 4 Test the conditions given in Table 2 EE 2 DESIRED RESULTS Measurements Conditions Results Comments Output Voltage Vin 100 Vac Vout 5V 5 no load Input consumption at high line and no Vin 230 Vac Pin 0 09 W 15 No load measurment can load no load Vout 5 V fluctuate run WT210 in average mode 3 Input consumption at high line line and ViN 230 Vac Pin 0 83 W 10 low load load 0 1 A Vout 5 V Pout 0 5 W Output voltage at high line and full load Vin 230 Vac Vour 5V 5 5 Output voltage at low line and full load Vin 85 Vac Vout 5V 5 lload 2 5A Brownout detection Vin J until Vout 0 V Vin 56 Vac 15 Output voltage must collapse louT 2A under 56 Vac 7 Maximum output at low line Vin 85 Vac PouTmax 14W 15 Output voltage must collapse lout 1 above 14 W Maximum output at high line Vin 230 Vac PouTmax 18 W 15 Output voltage must collapse lout 1 above 18 W http onsemi com 16 NCP1027ATXGEVB SENSEFET is a registered trademark of Semiconductor Components Industries LLC SCILLC Intel is a registered trademark of Intel Corporation in the U S and or other countries
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