AND8263/D NCP1351 Evaluation Board, a 19 V − 3 A Adapter Prepared by: Nicolas Cyr, Christophe Basso ON Semiconductor http://onsemi.com APPLICATION NOTE The NCP1351 at a Glance Fixed ton, variable toff current−mode control: implementing a fixed peak current mode control (hence the more appropriate term “quasi−fixed” ton), the NCP1351 modulates the off time duration according to the output power demand. In high power conditions, the switching frequency increases until a maximum is hit. This upper limit depends on an external capacitor selected by the designer. In light load conditions, the off time expands and the NCP1351 operates at a lower frequency. As the frequency reduces, the contribution of all frequency−dependent losses accordingly goes down (driver current, drain capacitive losses, switching losses), naturally improving the efficiency at various load levels. Peak Current Compression at Light Loads: Reducing the frequency will certainly force the converter to operate into the audible region. To prevent the transformer mechanical resonance, the NCP1351 gradually reduces – compresses – the peak current setpoint as the load becomes lighter. When the current reaches 30% of the nominal value, the compression stops and the off duration keeps expanding towards low frequencies. Low Standby−power: the frequency reduction technique offers an excellent solution for designers looking for low standby power converters. Also, compared to the skip−cycle method, the smooth off time expansion does not bring additional ripple in no−load conditions: the output voltage remains quiet. Natural Frequency Dithering: the quasi−fixed ton mode of operation improves the EMI signature since the switching frequency varies with the natural bulk ripple voltage. Extremely Low Start−up Current: built on a proprietary circuitry, the NCP1351 startup section does not consumme more than 10 mA during the startup sequence. The designer can thus easily combine startup time and standby consumption. Overload Protection Based on Fault Timer: every designer knows the pain of building converters where a precise over current limit must be obtained. When the fault detection relies on the auxiliary VCC, the pain even increases. Here, the NCP1351 observes the lack of feedback current starts a timer to countdown. At the end of its charge, © Semiconductor Components Industries, LLC, 2006 October, 2006 − Rev. 1 the timer either triggers an auto−recovery sequence (auto−restart, B version) or permanently latches−off (A). Latch Fault Input: a dedicated input lets the designer externally trigger the latch to build additional protections such as over−voltage (OVP) or over−temperature (OTP). The Schematic The design must fullfil the following specifications: Input voltage: 90 – 265 Vac Output voltage: 19 V @ 3 A Over voltage protection Over power protection Auto−recovery short−circuit protection Offering a good EMI signature, the 65 kHz maximum switching frequency has become an industry standard for the vast majority of power supplies connected on the mains. With the NCP1351, selecting a Ct capacitor of 270 pF fixes the upper limit to 65 kHz. As a result, when the controller detects a need for a higher frequency, implying an overload condition, it will start to charge the timer capacitor: if the overload disappears, the timer capacitor goes back to zero. If the fault remains, the timer capacitor voltage reaches 5 V and starts the auto−recovery process. The transformer has been derived using the design recommendations described in the NCP1351 data−sheet. We came−up to the following values: Lp = 770 mH Np:Ns = 1:0.25 Np:Naux = 1:0.18 It is also possible to use the Excel® spreadsheet available from the ON Semiconductor website which also gives transformer parameters. The core is a PQ26x25 made of a 3F3 material and has been manufactured by Delta Electronics (reference 86H−6232). The leakage inductance is kept around 1%, leading to a good efficiency and reduced losses in no−load conditions. The schematic appears on Figure 2. The converter operates in CCM with a 40% duty−cycle at low mains and stays CCM at high line. Despite the frequency variation, it is possible to evaluate the input voltage point at which the converter leaves CCM: 1 Publication Order Number: AND8263/D AND8263/D Vin, crit + 2PoutVout + 2 IpeakVouth * 2NPout 19 2 57 19 0.9 * 2 0.25 Where: Ipeak is the selected peak current in the inductor Vout, the output voltage η, the converter efficiency Pout, the delivered power N, the transformer turn ratio, Np:Ns = 1:N Since we are limited to 265 Vac, we can see that the converter will always be in CCM at full power. To the opposite, we can also predict the power level at which the converter leaves CCM at low and high line conditions: Pout, crit + hIpeakVinVout Vout ) NVin 57 + 380 Vdc (eq. 1) bulk R1 Vcc R2 + CVcc + Cres Figure 1. (eq. 2) The split VCC configuration helps to start−up in a small period of time (CVCC to charge alone) but the addition of a second, larger capacitor (Cres), ensures enough VCC in standby. The primary−side feedback current is fixed to roughly 300ĂmA via R5 and an additional bias is provided for the TL431. 1 mA at least must flow in the TL431 in worse case conditions (full load). Failure to respect this will degrade the power supply output impedance and regulation will suffer. A 1.5 kW has proven to do just well, without degrading the standby power. For an input voltage of 120 Vdc, the converter enters DCM for an output power below 42 W. When the voltage increases to 330 Vdc, the power level at which CCM is excited is 55 W. Two 1 MW resistors ensure a clean start−up sequence with the 4.7 mF capacitor (C3), directly from the bulk capacitor. Despite a small value for C3, the VCC still maintains in no−load conditions thanks to the split configuration: L1 J1 1 2 ~ IC4 C11 220 nF X2 + − RN114− 0.8/02 ~ KBU4K J3 OPP or no OPP JUMPER 1 100 mF R15 3.9 kW C15 U2 1 2 3 4 22 pF R19 100 kW 100 nF C4 R6b1 W 1 W R6a 1 W 1 W R5 1N4148 C8 2.5 kW C14 D9 8 7 6 5 NCP1351 15 V MBR20100 T1 86H−6232 D5 out 1N4937 D3 C17 + 0 35 V D1 1N4148 D6 D8 150 kW C18 270 pF 100 V R1 100 nF C13 2.2 nF Y1 0 4 A / 600 V M1 SPP04N60C3 2.2 kW opto_c 4 C5 0.1 mF Q1 C10 220 nF + 4.7 mF C1 C3 35 V 100 nF R18 47 kW opto_e 3 U1 SFH6156−2 220 pF 47 pF Figure 2. The 57 W Adapter Board Featuring the NCP1351 Controller http://onsemi.com 2 2.2 mH 1 mF+ + 1 mF L2 C7+ C5b 220 mF C5a 25 V 25 V 25 V 10 1N4148 R16 BC857 R20 C9 D2 MUR160 opto_c 2 opto_e C2 10 nF 400 V R7 R13 1 MW R11 47 kW 47 kW + C12 100 mF 400 V R2 1 MW R8 1 kW R14 NC R17 1.5 kW 2 1 J2 R12 27 kW R10 39 kW C6 IC2 100 nF TL431 R9 10 kW AND8263/D outlet. To speed−up this reset phase, a connection via a diode to the half−wave point will reset the circuit faster (Figure 3). Please note that the half−wave resistor equals the original bulk start−up resistor divided by 3.14. This provides the same startup current, despite the half−wave signal. The power dissipation is also slightly reduced (by 30% roughly). The overvoltage protection uses a 15 V zener diode (D1) connected to the auxiliary VCC. When the voltage on this rail exceeds 15 V plus the NCP1351 5 V latch trip point (total is thus 20 V), the circuit latches−off and immediately pulls the VCC pin down to 6 V. The reset occurs when the injected current into the VCC pin passes below a few mA, that is to say when the power supply is deconnected from the mains D2 D3 D6 Rstartup + mains D1 Ist Ist Vbulk C1 Vcc D7 Rstartup/3.14 + mains + D4 D5 CVcc Vbulk C3 Vcc + D8 CVcc Figure 3. Connecting the startup resistor to the mains before the diode bridge helps to speed−up the NCP1351 reset time when latched. To satisfy the maximum power limit, we can install an Over Power Protection (OPP) circuit. Given the negative sensing technique, we can use a portion of the auxiliary signal during the on time, as it also swings negative. However, we need this compensation at high line only since standby power can be affected. For this reason, we have installed a small integrator made of C18−R20. To avoid charging C18 during the flyback stroke, D9 clamps the positive excursion and offers a stronger negative voltage during the on time. Finally, the clamping network maintains the drain voltage below 520 V at high−line (375 Vdc) which provides 85% derating for the 600 V BVdss device. Measurements Once assembled, the board has been operated during 15 mn at full power to allow some warm−up time. We used a WT210A from Yokogawa to perform all power related measurements coupled to an electronic ac source. Efficiency VIN (POUT) 110 Vac 230 Vac 57 W 89.8% 91.2% 30 W 90% 91% 10 W 89% 88.5% 1W 72% 68.3% 0.5 W 60.7% 58% 60 50 90 Vac 230 Vac Fsw (kHz) 40 30 20 10 0 0 10 20 30 40 50 Pout (W) Figure 4. Switching Frequency Fsw vs. Pout http://onsemi.com 3 60 AND8263/D VIN (POUT) 110 Vac 230 Vac 0.5 W 833 mW 865 mW No−load 112 mW 139 mW VIN (POUT) 90 Vac 265 Vac Overpower 3.2 A 4.1 A VIN (IOUT = 3 A) 90 Vac 230 Vac Start−up Duration 1.5 s 0.5 s 0.5 Output Power No−load Power Overpower Protection Level Start−up Time at 90 Vac, which could be obtained by slightly increasing R19 or, if necessary, by increasing R15. Despite operation in the audible range, we did not notice any noise problems coming from either the transformer or the RCD clamp capacitor. On the above arrays, we can see the excellent efficiency at different loading conditions. The first explanation is the low leakage inductance on the tested transformer (below 1% of the primary inductance). Also, the frequency reduction in lighter load configurations helps for the switching losses. The no−load standby power stays below 150 mW at high line, a good performance for a 60 W adapter. Please note that the high−voltage probe observing the drain was removed and the load totally disconnected to avoid leakage. The OPP proves to work ok. Perhaps an improved margin would help Scope shots Below are some oscilloscope shots gathered on the demoboard: Vcc Vcc Vout Vout Figure 5. Startup time, Vin = 90 Vac Figure 6. Startup time, Vin = 230 Vac http://onsemi.com 4 AND8263/D Vcc Vcc margin margin Vds Vpin8 Vpin8 Figure 8. Short−circuit, Vin = 265 Vac Figure 7. Startup Sequence to Test the Margin on the 100 ms Timer. Vin = 90 Vac Iout = 3 A On the above picture, a short−circuit has been made at the highest line voltage. During the burst operation, the input power was maintained to 6.3 W at 275 Vac. It dropped to 5.2 W at 230 Vac. 600 V 550 550VV Figure 9. Maximum Output Power, Vin = 265 Vac Note the good margin on the drain thanks to the low leakage term http://onsemi.com 5 AND8263/D Figure 10. The Drain−source Waveform at Different Output Currents (3 A, 2 A and 1 A). The Input Voltage is 230 Vac Vcc Vcc Vout V out 28 V 28 V Figure 11. Short−circuit on the Optocoupler LED The output voltage increases to 28 V and then the controller latches−off. Different levels can be obtained by changing D1. http://onsemi.com 6 AND8263/D Conclusion The adapter built with the NCP1351 exhibits an excellent performance on several parameters like the efficiency and the no−load standby. The OPP is made in a simple non−dissipative way and does not hamper the standby power. The limited number of surrounding components around the controller associated to useful features (timer−based protection, latch input…) makes the NCP1351 an excellent choice for cost−sensitive adapter designs. Vout Delta Electronics Transformer Contacts Americas Delta Products Corparation 4405 Cushing Parkway Fremont, CA 94538 U.S.A. Gordon Kuo Phone: (1) 510−668−5166 email: GKuo@delta−corp.com Figure 12. Load Step from 0.5 A to 3 A with a 1 A / ms Slew−rate from a 90 Vac Asia Delta Electronics, Inc. 252 Shangying Road, Guishan Industrial Zone Taoyuan County 33341 Taiwan, R.O.C. Jack Kuo Phone: (886)−3−3591968 #2342 Fax: (886)−3−3591991 E−mail: [email protected] Vout Europe Figure 13. Load Step from 0.5 A to 3 A with a 1 A / ms Slew−rate from a 230 Vac source Delta Electronics Europe Wegalaan 16 2132JC Hoofddorp The Netherlands Coleman Liu Phone: (31) 23 566 8950 Fax: (31) 23 566 8910 Email: [email protected]−corp.com http://onsemi.com 7 AND8263/D Bill of Materials for the NCP1351 ZADIG Desig− nator Qty Description Value Tolerance Footprint Manufacturer Manufacturer Part Number Substitution Allowed Lead Free C1, C4, C5, C9 3 SMD capacitor 100 nF/50 V 5% SMD 1206 PHYCOMP 2238 581 15649 yes yes C2 1 capacitor 10 nF/630 V 10% radial Vishay 2222 372 61103 yes yes C3 1 electrolytic capacitor 4.7 mF/50 V 20% radial Panasonic ECA1HM4R7 yes yes C5b, C5a 2 electrolytic capacitor 1000 mF/35 V 20% radial Panasonic EEUFC1V102 no yes C6 1 capacitor 100 nF/50 V 10% radial AVX SR215C104KTR yes yes C7 1 electrolytic capacitor 220 mF/25 V 20% radial Panasonic EEUFC1E221 yes yes C8 1 SMD capacitor 220 pF/50 V 5% SMD 1206 PHYCOMP 2238 863 15471 yes yes C10 1 SMD capacitor 220 nF/50 V 10% SMD 1206 AVX CM316X7R224K50AT yes yes C11 1 X2 capacitor 220 nF/630 V 20% radial Evox Rifa PHE840MD6220M yes yes C12 1 electrolytic capacitor 100 mF/400 V 20% radial Panasonic ECA2GM101 yes yes C13 1 Y1 capacitor 2.2 nF/250 V 20% radial Ceramite 440LD22 yes yes C14 1 SMD capacitor 47 pF/50 V 5% SMD 1206 PHYCOMP 2238 863 15479 yes yes C15 1 SMD capacitor 22 pF/50 V 5% SMD 1206 PHYCOMP 2238 863 15229 yes yes C17 1 electrolytic capacitor 100 mF/35 V 20% radial Panasonic ECA1VM101 yes yes C18 1 SMD capacitor 270 pF/50 V 5% SMD 0805 PHYCOMP 2238 861 15271 yes yes D1 1 zener diode 15 V/225 mW 5% SOT23 ON Semiconductor BZX84C15LT1G yes yes D2 1 ultrafast rectifier 1 A/600 V 0% axial ON Semiconductor MUR160G yes yes D3 1 hight−speed diode 1 A/600 V 0% axial ON Semiconductor 1N4937G yes yes D5 1 schottky diode 20 A/100 V 0% TO220 ON Semiconductor MBR20100CTG yes yes D6 1 hight−speed diode 0.2 A/75 V 0% axial Philips Semiconductor 1N4148 yes yes D8,D9 1 hight−speed diode 0.2 A/100 V 0% SOD−123 ON Semiconductor MMSD4148G yes yes HS1, HS2 2 heatsink 6.2 °C/W 0% radial Seifert KL195/25.4/SWI yes yes IC2 1 shunt regulator 2.5−36 V/ 1−100 mA 2% TO92 ON Semiconductor TL431ILPG yes yes IC4 1 diode bridge 4 A/800 V 0% radial Multicomp KBU4K yes yes J1 1 connector 230 Vac/ 0% radial Schurter 0721−PP yes yes J2 1 connector 2/” 0% rad5.08mm Weidmuller PM5.08/2/90 yes yes L1 1 Common mode 2*27 mH/0.8 A 0% radial Schaffner RN114−0.8/02 yes yes L2 1 Inductor 2.2 mH/10 A 0% radial Wurth Elektronik 744772022 yes yes M1 1 power MOSFET N− Channel 4 A/600 V 0% TO220 Infineon SPP04N60C3 yes yes Q1 1 PNP transistor −100 mA/−45 V 0% TO92 ON Semiconductor BC857 yes yes R1 1 SMD resistor 2.2 kW/0.25 W 1% SOT23 Welwyn WCR12062K22% yes yes R2, R7 2 resistor 1 MW/0.33 W 5% axial Vishay SFR2500001004JR500 yes yes R5 1 SMD resistor 2.5 kW/0.25 W 2% SMD 1206 Welwyn WCR12062K52% yes yes R6b, R6a 2 SMD resistor 1 W/1 W 5% SMD 2512 PHYCOMP 232276260108 yes yes R8 1 resistor 1 kW/0.4 W 5% axial Vishay SFR2500001001JR500 yes yes R9 1 SMD resistor 10 kW/0.25 W 2% SMD 1206 Welwyn WCR120610K2% yes yes R10 1 SMD resistor 39 kW/0.25 W 2% SMD 1206 Welwyn WCR120639K2% yes yes R11, R13 2 resistor 47 kW/2 W 5% axial Multicomp MCF2W47K yes yes R12 1 SMD resistor 27 kW/0.25 W 2% SMD 1206 Welwyn WCR120627K2% yes yes http://onsemi.com 8 AND8263/D Bill of Materials for the NCP1351 ZADIG Desig− nator Qty Description Value Tolerance Footprint Manufacturer R14 1 SMD resistor NC R15 1 SMD resistor 3.9 kW/0.25 W 2% SMD 1206 Welwyn R16 1 SMD resistor 10 W/0.25 W 2% SMD 1206 Welwyn R17 1 SMD resistor 1.5 kW/0.25 W 2% SMD 1206 Welwyn R18 1 SMD resistor 47 kW/0.25 W 2% SMD 1206 R19 1 SMD resistor 100 kW/0.25 W 2% SMD 1206 R20 1 SMD resistor 150 kW/0.25 W 2% SMD 1206 TP1, TP2, TP3, TP4 4 pcb foot T POINT A FIX 4 H T1 1 Transformer 86H−6232 U1 1 optocoupler U2 1 CMOS IC Manufacturer Part Number SMD 1206 Substitution Lead Allowed Free yes yes WCR12063K92% yes yes WCR120610R2% yes yes WCR12061K52% yes yes Welwyn WCR120647K2% yes yes Welwyn WCR1206100K2% yes yes Welwyn WCR1206150K2% yes yes Richco LCBS−TF−M4−8−01 yes yes radial Delta 86H−6232 no yes sfh6156/ SMD Vishay SFH6156−2T no yes NCP1351B SO−8 ON Semiconductor NCP1351B no yes http://onsemi.com 9 AND8263/D PCB layout Figure 14. Top Side Components Figure 15. Copper Traces Figure 16. SMD components ON Semiconductor and are registered trademarks of Semiconductor Components Industries, LLC (SCILLC). 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. 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