AND8486/D A 12 V / 40 W AC-DC Demonstrator with NCP1250 Prepared by: Christophe Basso ON Semiconductor http://onsemi.com APPLICATION NOTE Introduction The controller drives a 4 A/600 V power MOSFET whose turn-off is accelerated by the addition of a small PNP transistor, Q1. A 100 pF capacitor smoothes the drain-source signal at the switch opening and helps to soften the EMI signature. The transformer is built in a RM10 ferrite shape made of 3C90 material. The primary inductance is 700 mH and the turns ratio between the power secondary and the primary side is 1:0.15. This number is slightly increased to 1:0.17 on the auxiliary winding to maintain Vcc in no-load situations. The secondary side implements a classical TL431 whose bias current is automatically disconnected in a no-load situation through C5D7. This proprietary technique reduces the bias voltage applied to R19 left terminal when the converter enters standby mode. As this 1 mA burden disappears from the 19 V output in a no-load configuration, the input power greatly benefits from the situation. Furthermore, this architecture does not impact the transient response of the converter when transitioning from no-load to full-load. The converter has been laid out in a compact style as shown in Figure 2. The board can deliver a continuous current up to 3.5 A when operated in a 50°C ambient temperature. The overpower protection trips for a maximum current of 4.2 A. This value slightly varies between the boards and the line level but stays typically within a short range thanks to the proprietary non−dissipative OPP implemented in the NCP1250. Please see below the board performance in terms of efficiency in various loading conditions. The NCP1250 is implemented in a 40-W ac-dc adapter delivering a dc voltage of 12 V. The converter takes advantage of the NCP1250 high integration level to offer a very good performance in standby power and Over Power Protection. The Adapter Schematic The adopted schematic appears in Figure 1. You can see the NCP1250B (auto-recovery short-circuit protection, 65 kHz) driving a power MOSFET in a flyback current-mode configuration. The mains is applied on the rectifying diodes bridge through an EMI filter made of a 10-mH common-mode choke. Its leakage inductance is used together with C11 to form a differential mode filter. To further save power in standby mode (Pout = 0 W), we have combined the need to discharge the 0.47 mF X2 capacitor using resistors that will also be used to crank the controller at start-up. This is achieved by the set of four resistors (R15, R27, R17 and R20) that ensure the discharge of the capacitor when the power cord is un-plugged. For a 0.47 mF capacitor, a total of 2 MW is necessary to make the time constant less than 1 s, as recommended by the safety document IEC-950. As these resistors join at the NCP1250 Vcc pin where a 4.7 mF capacitor is connected, it offers a cheap charging means for the capacitor connected there. Experiments show that this solution supplies enough current to start the converter in less than 3 s at an input voltage of 85 V rms. Over Power Protection, Over Temperature Protection and Over Voltage Protection are implemented around pin 3. Please refer to the available application notes for design details regarding these parts. © Semiconductor Components Industries, LLC, 2011 February, 2011 − Rev. 0 1 Publication Order Number: AND8486/D + L1 R15 510k http://onsemi.com 2 250 V F1 2AT IN − R17 510k R20 510k 85−265 V rms C11 470n X2 2 x 10mH Wurth 744822120 IC4 KBU4K R27 510k 400 V C12 82uF R7 330k Vbulk C10 R5 22pF 1.8k C8 1nF D1 1N964 R3 330k R22 470k 1N4148 D10 C9 330pF C15 220p 4 5 2 3 6 1 NCP1250 R14 NTC R2 option 220k 22 1 C3 4.7uF C17 100uF R23 1k 3 T1 . 2 Np 11 R6a R6b R6c 1.3 1.3 1.3 R18 22k M1 D4 1N4937 10 Bridge Naux 12 . Q1 2N2907 1N4148 R16 D6 D3 1N4937 R24 220 R21 22 C2 10n R11 R13 47k 47k R25 47 R26 47 C5 10nF R19 1k D7 1N4937 L2 2.2uH IC2 TL431 C6 10nF R8 1k C18 22pF C5a C5b 680uF 680uF C13 2.2nF Type = Y1 1 kV C4 100pF Ns 5−6 .8−7 D5 NTST30100SG R9 10k R10 20k R12 18k C7 12 220uF V / 3.3 A AND8486/D Figure 1. The adapter uses all the features brought by the NCP1250 to implement a high-performance 40-W converter. AND8486/D Figure 2. The PCB layout and component arrangement offers a compact size. Light load efficiency: Efficiency Performance The NCP1250 excels in terms of efficiency and standby power. We have made a series of tests on the proposed adapter, carried at both high and low lines. The load is applied directly at the board terminals. The results appear below. Output Power Efficiency - Vin = 115 V rms (%) Efficiency - Vin = 230 V rms (%) 10.3 W - 25% 87.18 85.1 20.7 W - 50% 88.13 86.9 31.2 W - 75% 88.10 88.2 41.5 W - 100% 87.76 88.5 Average efficiency 87.8 87.2 Output Power Input power – Vin = 100 V rms (W) Input power – Vin = 230 V rms (W) 0.5 W 0.7 0.76 0.6 W 0.83 0.89 The performance is linked to the combined action of the frequency foldback and the skip cycle operation at constant peak current. Please note that the no-load standby power includes the 2 MW discharge resistors string placed across the X2 capacitor on the input filter. These numbers are excellent considering a low-voltage controller featuring a start-up network. Conclusion This application note describes how an ac-dc converter meeting all new efficiency challenges can be built with the new NCP1250. Despite a small TSOP-6 package and a limited amount of pins, the performance of the final board nicely competes against other more complex circuits by offering a similar set of options plus some unique features such as the non-dissipative OPP circuit. This makes the part the ideal candidate where space constraints, performance and cost sensitivity have to be combined. No-load standby power: Output Power Input power - Vin = 100 V rms (mW) Input power - Vin = 230 V rms (mW) 0 33 75 http://onsemi.com 3 AND8486/D Designator Quantity Description C2 1 high-voltage capacitor C3 1 electrolytic capacitor Manufacturer Manufacturer Part Number Vishay MKT1822310635 through-hole Panasonic ECA1VAD4R7X 100 pF/1000 V through-hole Value Footprint 10 nF/630 Vdc through-hole 4.7 uF/35 V C4 1 ceramic capacitor Panasonic ECKA3A101KBP C5a, C5b 2 electrolytic capacitor 680 uF/35 V through-hole Rubycon 35ZL680MEFC12.5X20 C5 1 ceramic capacitor 10 nF SMD1206 Multicomp MC1206B103K500CT C6 1 film capacitor 10 nF through-hole Multicomp MCRR50103X7RK0050 C7 1 electrolytic capacitor 220 uF/25 V through-hole Rubycon 25ML220M8X9 C8 1 ceramic capacitor 1 nF SMD1206 Multicomp MC1206B102K500CT C9 1 ceramic capacitor 330 pF SMD1206 Multicomp MC1206B220K500CT C10 1 ceramic capacitor 22 pF SMD1206 Multicomp MC1206B331K500CT C11 1 X2 capacitor Epcos B32922C3474M C12 1 high-voltage electrolytic capacitor through-hole Panasonic EEUED2G820 C13 1 EMI Y1 capacitor 2.2 nF/ 250 Vac through-hole CERAMITE 440LD22 C15 1 ceramic capacitor 220 pF SMD1206 Multicomp MC1206B221K500CT C17 1 electrolytic capacitor 100 uF/35 V through-hole Panasonic ECA1VM101 C18 1 ceramic capacitor 22pF through-hole Murata RPE5C2A220J2M1Z03A D1 1 Zener diode 18 V/ 0.5 W SOT23 ON Semiconductor BZX84C18LT3G D3, D4 2 fast diode 1N4937 D5 1 power diode NTST30100SG TO220 ON Semiconductor NTST30100SG D6 1 signal diode 1N4148 through-hole NXP 1N4148 470 nF/275 Vac through-hole 82 uF/400 V through-hole ON Semiconductor 1N4937G D7 1 fast diode MURA160 SMA ON Semiconductor MURA160T3G D10 1 signal diode 1N4148 SOD123 ON Semiconductor MMSD4148T3G F1 1 Fuse 250 V / 2 A T through-hole Multicomp MST 2A 250V HS1, HS2 2 heat sink IC2 1 shunt regulator TL431 through-hole ON Semiconductor IC4 1 diode bridge KBU4K through-hole J1 1 connector - through-hole Multicomp JR-201S J2 1 connector - through-hole WEIDMULLER PM5.08/2/90 L1 1 common mode inductor 2*10 mH/2 A through-hole Wurth Elektronik 744823210 L2 1 inductor 2.2 uH/6 A through-hole Wurth Elektronik 744772022 M1 1 high-voltage MOSFET 4 A/600 V TO220 ON Semiconductor NDF04N60ZG Q1 1 PNP transistor BC857 SOT23 ON Semiconductor BC857ALT1G Multicomp TL431CLPG KBU4K R5 1 resistor 1.8 k SMD1206 Vishay CRCW12061K80FKEA R6a, R6b, R6c 3 resistor 1.3 through-hole Multicomp MF251R3 R8, R19 2 resistor 1 k / 0.25 W through-hole Multicomp MF251K R9 1 resistor 10 k SMD1206 Vishay CRCW120610K0FKEA R10 1 resistor 20 k SMD1206 Vishay CRCW120620K0FKEA R11, R13 2 power resistor 47 k / 3 W through-hole Vishay PR03000204702JAC00 R12 1 resistor 18 k SMD1206 Vishay CRCW120618K0FKEA R14 1 NTC thermal sensor 100k@25°C through-hole Vishay NTCLE100E3104JB0 R15, R17, R20, R27 4 mains-connected resistor 510k SMD1206 Vishay CRCW1206510K00FKEA http://onsemi.com 4 AND8486/D Designator Quantity Description Value Footprint Manufacturer Manufacturer Part Number R16 1 resistor 10 SMD1206 Vishay CRCW120610R0FKEA R18 1 resistor 22 k through-hole Multicomp MF2522K R21 1 power resistor 22 /1 W through-hole Vishay PR01000102209JR500 R22 1 resistor 470 k SMD1206 Vishay CRCW1206470KFKEA R23 1 resistor 1k SMD1206 Vishay CRCW12061K00FKEA R24 1 resistor 220 through-hole Multicomp MF25220 R25, R26 2 resistor 47 / 1 W through-hole Vishay PR01000104709JA500 T1 1 RM10 flyback transformer through-hole CME France 17452/02 U1 1 optocoupler SFH615A-2 Vishay SFH615A-2 U3 1 65 kHz controler NCP1250B TSOP6 ON Semiconductor NCP1250A V1 1 countersunk head screws + nut M3x6mm V2 1 nylon screw + nut M3x6mm The transformer has been designed and manufactured by the following French company: CME transformateurs - 01160 – St Martin du Mont – France – Tel. : +33 (0)4 74 35 55 11 – Fax. : +33 (0)4 74 35 53 97 web: www.cmetransformateur.com e-mail: [email protected] ON Semiconductor and are registered trademarks of Semiconductor Components Industries, LLC (SCILLC). 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