AND8288/D NCP1351 Evaluation Board, a 12 V / 2 A Full DCM Adapter Prepared by Stéphanie Conseil http://onsemi.com This application note describes a 12 V / 2 A simple adapter operated by NCP1351, a fixed on- time / variable off-time controller. This adapter features a very low standby power (below 90 mW at 230 VAC input voltage) and shows a good EMI signature. can thus easily combine startup time and standby consumption requirement. Overload Protection Based on Fault Timer: Every designer knows the difficulty 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, 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 overvoltage (OVP) or overtemperature (OTP). 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 Startup Current: Built on a proprietary circuitry, the NCP1351 startup section does not consume more than 10 mA during the startup sequence. The designer © Semiconductor Components Industries, LLC, 2007 June, 2007 - Rev. 0 Schematic The design must fulfill the following specifications: Input Voltage: 90 VAC – 265 VAC Output Voltage: 12 V @ 2 A Auto-recovery Short-circuit Protection Standby Power: 90 mW or Lower Startup Duration: Less than 3 s The maximum switching frequency is selected to 65 kHz. The converter operates in DCM only which allows a smaller transformer compared to CCM mode. Also, the converter behaves as a first order system and is easier to stabilize. The transformer parameters have been calculated by using the design recommendations described in the NCP1351 datasheet: LP = 310 mH IP = 1.8 A NP:NS = 1:0.18 NP:NAUX = 1:0.22 The core is a PQ20*20 made of a N87 material and has been manufactured by Delta Electronics (reference: 86H-7071). The leakage inductance is very low (around 1% of LP) leading to a good efficiency and reduced losses in no load condition. Half-wave connection for the startup resistors ensures less power loss in the startup resistor network compared to a classical bulk connection. 1 Publication Order Number: AND8288/D AND8288/D Voltage regulation at the secondary is achieved through a TLV431, which requires very low bias current (> 100 mA). Thus no additional bias resistor is needed. NCP1351 features natural frequency dithering as the switching frequency varies with the bulk ripple. Additional frequency dithering can be provided to the controller by injecting some half-wave ripple in the CS pin through a 3.3 MW resistor connected to the input line. A jumper on the board allows to connect or to disconnect the dithering resistor. Header2 L4 RN114-0.8/02 + RN1121.2/02 ~ C12 47mF 400V R14 680 kW + C2 10 nF 400 V D2 MUR160 D1N4937 R7 560 kW T1 R20 2.2 MW D3 1 mF + C5a 35 V R2 120 kW opto_e C17 + opto_c 2 1 2 3 1 R15 U2 4 3.9 kW 8 7 6 0 R6a 1.2 W 1 W 2.5 kW J2 1 R12 47 kW 5 3A/600V opto_c 10 R16 1N4148 C10 220 nF C8 220 pF R5 R8 1 kW C14 47 pF C1 100 nF R18 47 kW + C3 10 mF 25 V 4 SFH6156-2 C5 U1 100 nF 3 opto_e 2 R6b 1.2 W 1 W 2 0 D1N4148 100 nF C4 L2 C7 + 150 mF 25 V Header2 M1 NCP1351 C15 22 pF + 1 mF C5b 35 V C13 2.2 nF 0 35 V D1N4148 D6 2.2 mH OUT R10 6.8 kW 1 R19 1 MW R3 100 kW MBR820 D5 2 2 C11 220 nF X2 R11 47 kW 2W 22RR17 3 J1 R13 47 kW 2W D61056 D10 ~ 1 D9 C6 100 nF TL431 R9 6.2 kW Figure 1. Board schematic Measurements We obtained maximum startup duration of 2.5 s with a startup resistor of 1.36 MW and half-wave connection for the resistor. (See Figures 2 and 7) VCC: 5 V / div VIN = 320 VDC STARTUP POUT VIN = 120 VDC VIN = 320 VDC Startup Time @ IOUT = 2 A 2.5 s 1s VIN = 120 V dc TIME: 400 ms / div Figure 2. VCC Startup at Low and High Input Voltage http://onsemi.com 2 AND8288/D The power measurements were performed with a WT210A from Yokogawa. Before doing the measurements we operated the board for 15 minutes at full power to allow some warm-up time. In the above arrays, we can see that we achieve a good efficiency despite the load variation. Also, thanks to the expansion of the switching frequency at light loads, the efficiency does not decrease too much. By optimizing power dissipation in startup resistor and feedback components, we achieve an outstanding standby power of 82 mW at 230 VAC input voltage. After operating the board during 15 mn at full load in order to warm it up, conducted electromagnetic emission measurements were made in average mode using a Rohde & Schwarz EMI Test Receiver following the CISPR22 standard. The measurement was made with and without frequency dithering option, and with two different inputs filter size: 2x15 mH and 2x27 mH. (See Figure 3, Figure 4, Figure 5 and Figure 6) EFFICIENCY POUT VIN = 90 VAC VIN = 230 VAC 24 W 83% 85% 12 W 82% 84% 6W 77% 83% 1W 69% 75% 0.5 W 63% 64% POUT VIN = 90 VAC VIN = 230 VAC No-load 78 mW 82 mW 70 65 60 55 50 45 40 35 30 25 20 15 10 5 0 QP AV Level in dBmV Level in dBmV STANDBY Watt-Meter Internal Clock 150k 3004005008001M 2M 3M 4M 5M 6 8 10M 20M 30M 70 65 60 55 50 45 40 35 30 25 20 15 10 5 0 QP AV Watt-Meter Internal Clock 150k 300400 5008001M 2M 3M4M5M6 8 10M 20M 30M Frequency in Hz Frequency in Hz Figure 4. Board Conducted Emission at 110 VAC, 1.4 A Load, 2x15 mH Input Filter and Frequency Dithering QP AV Level in dBmV Level in dBmV Figure 3. Board Conducted Emission at 110 VAC, 1.4 A Load, 2x27 mH Input Filter 70 65 60 55 50 45 40 35 30 25 20 15 10 5 0 Noise Watt-Meter Internal Clock 150k 300400500800 1M 2M3M4M 5M 6 8 10M 20M 30M 70 65 60 55 50 45 40 35 30 25 20 15 10 5 0 QP AV Watt-Meter Internal Clock 150k 300400500 8001M 2M 3M4M5M 6 8 10M 20M 30M Frequency in Hz Frequency in Hz Figure 5. Board Conducted Emission at 220 VAC, 1.4 A Load, 2x27 mH Input Filter Figure 6. Board Conducted Emission at 220 VAC, 1.4 A Load, 2x15 mH Input Filter and Frequency Dithering http://onsemi.com 3 AND8288/D The peak seen at 1.5 MHz on the graphs is the watt-meter internal clock. The graphs show that frequency dithering improves the EMI signature between 400 kHz and 25 MHz (emission level below 35 dBmV) The drawback of implementing frequency dithering on CS pin is that it increases the output voltage ripple at light output loads. The output voltage ripple is 50 mV at 16 W output power 10 mV at 1 W output power. (See Figure 8) VCC: 5 V / div VOUT: 10 mV / div SCOPE SHOOTS TIME: 20 ms / div TIME: 400 ms / div Figure 8. Output Voltage Ripple for Different Loads at VIN = 320 VDC IOUT: 0.5 A / div VOUT: 50 mV / div Figure 7. VCC Startup at No Load and 1.4 A Load TIME: 40 ms / div Figure 9. Load Step from 1.2 A to 0.1 A with a 0.1 A / ms Slew-Rate from a 230 VAC Source Conclusion Asia The 24 W adapter built with NCP1351 shows excellent results on several parameters like the standby power (82 mW at VIN = 230 VAC), the efficiency, the EMI signature. The board features an option to inject frequency dithering in the design allowing to improve the EMI signature and to use a smaller input filter at the cost of the output ripple at light load. 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] Delta Electronics Transformer contact Americas Europe Delta Electronics Europe Wegalaan 16 2132JC Hoofddorp The Netherlands Coleman Liu Phone: (31) 23 566 8950 Fax: (31) 23 566 8910 Email: [email protected] Delta Products Corporation 4405 Cushing Parkway Fremont, CA 94538 U.S.A. Gordon Kuo Phone: (1) 510-668-5166 email: [email protected] http://onsemi.com 4 AND8288/D BILL OF MATERIAL Desig‐ nator Qty Description Value Tolerance Footprint Manufacturer Manufacturer Part Number Substitution Allowed Pb- ‐ Free C1,C4, C5,C10 4 SMD Capacitor 100nF/50V 5% SMD 1206 Phycomp 2238 581 15649 Yes Yes C2 1 Capacitor 10nF/630V 10% Radial Vishay MKT1822310635 Yes Yes C3 1 Electrolytic Capaci‐ tor 10mF/50V 20% Radial Panasonic ECA1HM100 Yes Yes C5b,C5a 2 Electrolytic Capaci‐ tor 1000mF/35V 20% Radial Panasonic EEUFC1V102 no Yes C6 1 Capacitor 100nF/50V 10% Radial Murata RPER71H104K2M 1A05U Yes Yes C7 1 Electrolytic Capaci‐ tor 150mF/35V 20% Radial Panasonic EEUFC1V151 Yes Yes C8 1 SMD Capacitor 220pF/50V 5% SMD 1206 Phycomp 2238 863 15221 Yes Yes C11 1 x2 Capacitor 220nF/630V 20% Radial Evox Rifa PHE840MD6220M Yes Yes C12 1 Electrolytic Capacitor 47mF/400V 20% Radial Panasonic ECA2GM470 Yes Yes C13 1 y1 Capacitor 2.2nF/250V 20% Radial Ceramite 440LD22 Yes Yes C14 1 SMD Capacitor 47pF/50V 5% SMD 1206 Phycomp 2238 863 15479 Yes Yes C15 1 SMD Capacitor 22pF/50V 5% SMD 1206 Phycomp 2238 863 15229 Yes Yes C17 1 Electrolytic Capacitor 100mF/35V 20% Radial Panasonic ECA1VM101 Yes Yes D2 1 Ultrafast Rectifier 1A/600V 0% Axial ON Semiconductor MUR160G Yes Yes D3 1 Rectifier Diode 1A/600V 0% Axial ON Semiconductor 1N4937G Yes Yes D5 1 Schottky Diode 8A/100V 0% TO-22 ON Semiconductor MUR820G Yes Yes D6 1 High-speed Diode 0.2A/75V 0% Axial Philips Semiconductor 1N4148 Yes Yes D8 1 High-speed Diode 0.2A/100V 0% SMD ON Semiconductor MMSD4148T1G Yes Yes D9 1 Shunt Regulator 2.5-36V/1100mA 2% TO-92 ON Semiconductor TLV431ILPG Yes Yes D10 1 Diode Bridge 1A/600V 0% Radial TAIWAN Semiconductor DB105G Yes Yes HS2 1 Heatsink 6.2°C/W 0% Radial Seifert KL194/25.4/SWI Yes Yes J1 1 Connector 230VAC/ 0% Radial Multicomp JR-201S(PCB) Yes Yes J2 1 Connector 2/” 0% RAD5.08 mm Weidmuller PM5.08/2/90 Yes Yes L4 1 Inductor 2*27mH /0.8A 0% Radial Schaffner RN114-0.8/02 Yes Yes M1 1 Power MOSFET N-Channel 3A/600V 0% T0-220 Fairchild FQP3N60 Yes Yes R2 1 Resistor 120kR /0.25W 5% SMD 1206 Vishay CRCW12061203F Yes Yes R3 1 Resistor 100kR /0.25W 5% SMD 1206 Vishay CRCW12061003F Yes Yes R5 1 SMD Resistor 2.4kR /0.25W 1% SMD 1206 Welwyn WCR 1206 2K4 2% Yes Yes R6b,R6a 2 SMD Resistor 1.2R/1W 5% SMD 1218 Phycomp 232273571208 Yes Yes R7 1 SMD Resistor 560kR /0.25W 1% SMD 1206 Vishay CRCW12065603F Yes Yes R8 1 Resistor 1kR/0.33W 5% Axial Neohm CFR25J1K0 Yes Yes R9 1 SMD Resistor 6.2kR /0.25W 1% SMD 1206 Phycomp 232272466202 Yes Yes http://onsemi.com 5 AND8288/D BILL OF MATERIAL Desig‐ nator Qty Description Value Tolerance Footprint Manufacturer Manufacturer Part Number Substitution Allowed Pb- ‐ Free R10 1 SMD Resistor 6.8kR /0.25W 1% SMD 1206 Vishay CRCW12066801F Yes Yes R11,R13 2 Resistor 47kR/2W 5% Axial Neohm CFR200J47K Yes Yes R12,R18 2 SMD Resistor 47kR /0.25W 1% SMD 1206 Vishay CRCW12064702F Yes Yes R14 1 SMD Resistor 680kR /0.25W 1% SMD 1206 Vishay CRCW12066803F Yes Yes R15 1 SMD Resistor 3.9kR/0.2W 1% SMD 1206 Vishay CRCW12063901F Yes Yes R16 1 SMD Resistor 10R/0.25W 1% SMD 1206 Vishay CRCW120610R0F Yes Yes R17 1 SMD Resistor 22R/0.25W 1% SMD 1206 Vishay CRCW120622R0F Yes Yes R19 1 Resistor 1MR/0.25W 5% SMD 1206 Vishay CRCW12061004F Yes Yes R20 1 SMD Resistor 2.2MR /0.25W 1% SMD 1206 Phycomp 232272462205 Yes Yes T1 1 Transformer 86H-7071 Radial Delta Electronics 86H-7071 No Yes U1 1 Optocoupler SFH6156/ U2 1 CMOS IC NCP1351 0% SMD Vishay SFH6156-2T No Yes SOIC-8H ON Semiconductor NCP1351B No Yes http://onsemi.com 6 AND8288/D PCB LAYOUT Figure 10. Top Side Components Figure 11. Copper Traces Figure 12. SMD Components http://onsemi.com 7 AND8288/D Figure 13. Adapter 12 V/24 W Picture (Top Side) 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 operat‐ ing parameters, including “Typicals” must be validated for each customer application by customer's technical experts. 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