AND8278/D NCP1351 Evaluation Board 16 V / 32 V – 40 W Printer Power Supply Prepared by: Nicolas Cyr ON Semiconductor http://onsemi.com APPLICATION NOTE 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 and starts a timer to countdown. At the end of its charge, the timer either triggers an auto−recovery sequence (auto−restart, B and D versions) or permanently latches−off (A and C). On C and D versions the fault timer is started at an output power corresponding to 60% of the maximum deliverable power; to allow transient peak power delivery. 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 present document describes a printer power supply operated by the NCP1351, a fixed ton / variable off time controller. The board can deliver 10 W average on a 16 V output and 30 W average on a 32 V output with a transient peak power capability of 80 W. It however exhibits a low standby power: below 150 mW at no load whatever the input voltage. Let us first review the benefit of using the NCP1351: 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 consume more than 10 mA during the startup sequence. The © Semiconductor Components Industries, LLC, 2007 March, 2007 − Rev. 0 The Schematic The design must fulfill the following specifications: Input voltage: 88 – 265 Vac Output voltage: 16 V @ 0.625 A and 32 V @ 1 A nominal (40 W); with transient 80 W peak power capability during 40 ms, and 62 W peak during 400 ms Over power protection below 100 W for the whole input voltage range (LPS) Latched short−circuit protection Latched Over voltage protection Latch recovery time below 3 s Brown−out protection Start−up time below 3 s In order to deliver the peak output power, the NCP1351 will increase its switching frequency up to the upper limit set by the CT capacitor. To not jeopardize the EMI test compliance, the switching frequency should be kept below 150 kHz. We will choose 100 kHz to have a good margin. As a result the switching frequency at nominal load will be around 50 kHz. Since we need to deliver 80 W of transient peak power while ensuring the power will never be above 100 W, we will use the C version of NCP1351, specially tailored for this kind of application. When the controller detects a need for a frequency higher than 60 kHz, implying 1 Publication Order Number: AND8278/D AND8278/D 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 latches off the controller. During the fault condition, the power supply will anyway deliver the output power while the switching frequency is below its maximum value of 100 kHz. The transformer has been derived using the Excel® spreadsheet available from the ON Semiconductor website which also gives transformer parameters. We came up to the following values: Lp = 270 mH Np:Ns = 1:0.2 Np:Naux = 1:0.2 Ipk = 3 A The transformer has been manufactured by Coilcraft (www.coilcraft.com). The leakage inductance is kept around 3% of the primary inductance, leading to a good efficiency and reduced losses in no−load conditions. The schematic appears on Figure 1. The converter operates in DCM at nominal power; and for peak power it goes CCM with close to 50% duty−cycle at low mains and stays CCM at high line. D5 L3 D13 + + C13 U1 C12 R5 R24 R6 R15 D7 D4 + C19 C18 32 V C20 L2 C15 + C16 + C17 GND 16 V X6 R23 R10 L1 C14 X4x Fuse R13 R14 R8 C4 D9 NCP1351C 1 2 3 4 C6 R20 D3 R2 Aux D10 8 7 6 5 X11 X4 R1 C1 + C3 C8 C10 R28 R18 D11 + C7 R30 C23 R11 R31 X10 R19 R21 C21 R22 Figure 1. The Simplified 40 W Printer Board Featuring the NCP1351 Controller controller is latched (a direct connection to the AC line would also work). Despite a small value for C3, the VCC still maintains in no−load conditions thanks to the split configuration: Two 330 kW resistors in series with a 60 V zener diode ensure a clean start−up sequence with the 4.7 mF capacitor (C3), not from the bulk capacitor as it is usually done; but from the fully rectified, unfiltered haversine. This configuration allows for a quick release time after the HV rail R5 330 k + Cbulk R6 330 k 1 8 2 7 3 6 4 5 D10 60 V VCC + C3 4.7 m NCP1351 + C7 22 m Aux Figure 2. The split VCC configuration helps to start−up in a small period of time (C3 to charge alone) but the addition of a second, larger capacitor (C7), ensures enough VCC in standby. http://onsemi.com 2 AND8278/D The primary−side feedback current is fixed to roughly 300 mA via R8 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 2.7 kW value for R19 has proven to do just well, without degrading the standby power. The overvoltage protection uses a 17 V zener diode (D9) connected to the auxiliary VCC. When the voltage on this rail exceeds 17 V plus the NCP1351 5 V latch trip point (total is thus 22 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 falls below a few mA, that is to say when the power supply is disconnected from the mains outlet. To speed−up this reset phase, a connection to the fully rectified haversine resets the system faster (Figure 2). To satisfy the maximum power limit, we don’t need to add a true Over Power Protection (OPP) circuit since our NCP1351C transiently authorizes higher power, but safely latches off if the overpower lasts too long. To ensure a fault timer duration of at least 500 ms (to be able to deliver the 62 W power peak during 400 ms), the timer capacitor C10 must be 1.5 mF. This value will be adjusted depending on the specification, according to the maximum peak power duration the adapter must sustain. If anyway a constant overpower protection is needed over the whole input voltage range, a simple arrangement can be used: 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 don’t want this compensation for short TON durations since standby power can be affected. For this reason, we can insert a small integrator made of C9−R26 (see Figure 3). To avoid charging C9 during the flyback stroke, D14 clamps the positive excursion and offers a stronger negative voltage during the on time. Rcomp R26 470 k 2.2 k −N.Vin OPP Adjust C9 220 p D14 1N4148 Rcs 1 8 2 7 3 6 4 5 VCC + + Vaux Rsense NCP1351 Figure 3. A Simple Arrangement Provides an Adjustable Overpower Power Compensation A simple resistor connected between the auxiliary winding (that swings negative during the ON time) and the CT capacitor ensure a stable operation in CCM despite the duty cycle above 50% at very low line, due to the ripple on the bulk capacitor. The unique features of NCP1351C allow using a 100 mF bulk capacitor while delivering the transient peak power and ensuring the output is still regulated during line drop−outs. 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 min 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. http://onsemi.com 3 AND8278/D Efficiency: VIN (POUT) 120 Vac 230 Vac 40 W 84.4% 85.4% 25 W 85.9% 85.9% 10 W 86.0% 85.1% 5W 85.5% 83.2% 2W 83.4% 79.5% 1W 77.7% 73.3% 0.5 W 70.0% 66.3% VIN (POUT) 120 Vac 230 Vac No−load 75 mW 140 mW No−load Power: Overpower Protection Level: The power supply is able to deliver a peak power of 85 W during 500 ms from 85 Vac to 270 Vac. It can deliver a constant output power of more than 40 W, but less than 80 W over the same input voltage range. Start−up Time: VIN (POUT = 40 W) 85 Vac 230 Vac Start−up Duration 2.7 s 0.5 s In the above tables, we can see the excellent efficiency, especially at light load conditions thanks to the natural frequency foldback of the NCP1351. The no−load standby power stays below 150 mW at high line, a good performance for a dual output power supply able to deliver 80 W. Please note that the high−voltage probe observing the drain was removed and the load totally disconnected to avoid leakage. Despite operation in the audible range, we did not notice any noise problems coming from either the transformer or the RCD clamp capacitor. 120 100 Vin(max) Vin(min) FSW 80 60 CCM Transition 40 20 0 0 20 40 60 80 100 120 140 Pout Figure 4. Switching Frequency Variations vs. Output Load Scope Shots Below are some oscilloscope shots gathered on the demoboard: http://onsemi.com 4 AND8278/D 2.7 s 32 V VOUT VDRAIN Figure 5. Startup Time, VIN = 85 Vac 538 V VDRAIN VDRAIN Figure 6. Maximum Output Power, VIN = 265 Vac Conclusion The printer power supply built with the NCP1351 exhibits an excellent performance on several parameters like the efficiency and the low−load standby. The transient switching frequency increase allows to deliver peak power during a limited time; but if the overpower lasts longer than the set fault timer, the controller safely latches off. 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 printer adapter designs. http://onsemi.com 5 AND8278/D Bill of Materials Designator Qty Description Value Tol. Footprint C1, C4, C15, C18, C21 5 SMD capacitor 100 nF / 50 V 5% SMD 1206 C3 1 electrolytic capacitor 4.7 mF / 50 V 20% radial C5 0 SMD capacitor − 5% SMD 1206 C6 1 SMD capacitor 180 pF / 50 V 5% SMD 1206 C7 1 electrolytic capacitor 47 mF / 50 V 20% radial C8 1 SMD capacitor 10 nF / 50 V 5% SMD 1206 C9 0 SMD capacitor − 5% SMD 1206 C10 1 SMD capacitor 1.5 mF C12 1 Film capacitor 10 nF / 630 V 10% radial C13 1 electrolytic capacitor 100 mF / 400 V 20% radial C14 1 x2 capacitor 330 nF / 250 Vac 20% radial C16 1 electrolytic capacitor 1000 mF / 50 V 20% radial C17 1 electrolytic capacitor 100 mF / 50 V 20% radial C19 1 electrolytic capacitor 1000 mF / 25 V 20% radial C20 1 electrolytic capacitor 100 mF / 25 V 20% radial C23 1 y1 capacitor 2.2 nF / 250 Vac 20% radial C101 0 SMD capacitor − 5% SMD 1206 D1 1 SMD resistor 0 W / 0.25 W 5% SMD 1206 D2 0 Zener diode − 5% SOD−123 D3 1 High−voltage switching diode BAS20 200 mA / 200 V − SOT−23 D4 1 Fast−recovery rectifier 1N4937 1 A / 600 V − axial D5, D7 2 Schottky rectifier MBR20100CT 20 A / 100 V − TO−220 D9 1 Zener diode 17 V / 0.5 W 5% SOD−123 D10 1 Zener diode 60 V / 0.5 W 5% SOD−123 D11 1 Switching diode 200 mA / 75 V − SOD−123 D12 1 Zener diode 6.2 V / 0.5 W 5% SOD−123 D13 1 Standard rectifier 1 A / 1000 V − axial SMD 1206 D14 0 Switching diode − − SOD−123 HS1 1 Heatsink 6.2°C / W − radial HS2, HS3 2 TO−220 heatsink 27°C / W − − U1 1 Rectifier bridge DB105 1A / 600 V − DIP−4 U2 1 CMOS IC NCP1351A − − SOIC−8 X4 1 Optocoupler SFH615 − − DIP−4 X6 1 Common−mode choke Panasonic ELF−25F108A 2 * 15 mH/ 1 A − radial X10 1 shunt regulator TL431 2.5 – 36 V 5% TO−92 X11 1 Power MOSFET N−Channel 3 A / 600 V − TO−220 http://onsemi.com 6 AND8278/D Bill of Materials Designator Qty Description Value Tol. Footprint Q1 0 PNP transistor − − TO−92 T1 1 Transformer Coilcraft GA0007−AL − − radial J1 1 connector 230 Vac F1 1 Fuse 2 A / 250 Vac L1 1 SMD inductor Coilcraft 10 mH L2, L3 1 inductor 4.7 mH / 10 A − radial R1 1 SMD resistor 15 W / 0.25 W 5% SMD 1206 R2 1 resistor 4.7 MW / 0.33 W 5% axial R5, R6 2 SMD resistor 330 kW / 0.25 W 1% SMD 1206 radial T radial SMD DO1605T R7 1 SMD resistor 0 W / 0.25 W 5% SMD 1206 R8, R19 2 SMD resistor 2.7 kW / 0.25 W 5% SMD 1206 R9, R12 2 SMD resistor 0 W / 0.25 W 5% SMD 1206 R10, R11, R18 3 SMD resistor 1 kW / 0.25 W 5% SMD 1206 R13 1 SMD resistor 3.4 kW / 0.25 W 1% SMD 1206 R14 1 SMD resistor 0.33 W / 0.5 W 1% SMD 2010 R15 1 resistor 150 kW / 2 W 5% axial R16 0 SMD resistor − − SMD 2010 R17 0 SMD resistor − − SMD 1206 R20 1 SMD resistor 100 kW / 0.25 W 1% SMD 1206 R21 1 SMD resistor 56 kW / 0.25 W 1% SMD 1206 R22 1 SMD resistor 10 kW / 0.25 W 1% SMD 1206 R23, R24 2 SMD resistor 3.3 MW / 0.25 W 5% SMD 1206 R25 0 SMD resistor − 1% SMD 1206 R26 1 SMD resistor 0 W / 0.25 W 1% SMD 1206 R28 1 SMD resistor 8.2 kW / 0.25 W 1% SMD 1206 R30 1 SMD resistor 47 kW / 0.25 W 1% SMD 1206 R31 1 SMD resistor 180 kW / 0.25 W 1% SMD 1206 RV1 1 NTC − − Radial http://onsemi.com 7 AND8278/D PCB Layout Figure 7. Top Side Components Figure 8. Copper Traces Figure 9. SMD Components http://onsemi.com 8 AND8278/D U1 Fuse DF05M 220 n 0.33 NC R13 3.3 M R23 3.3 M C9 R2 4.7 M OptoBase X4x C5 FB 1.5 m 2.7 k R8 C4 0 R9 Ct R26 0 D12 6V2 NC C101 4 3 2 1 5 6 7 8 NTC NCP1351A 100 n Timer 1k R10 C10 C1 100 n C8 D9 10 n R11 1 k D2 17 V VCC D10 60 V 1N4148 NC 0 R12 R5 330 k 330 k + + NC Q1 D1 NC 10 n 1N4007 0 R1 15 R17 R6 D11 R7 4.7 m C7 47 m R24 R25 OPP NC C6 C3 Jitter CS 180 p NC C13 100 m + 3.4 k D14 NC 1N4007 D13 ELF−25F108A R14 Rsense X6 C14 D4 BAS20 D3 10 m L1 Aux 0 C12 R15 150 k D7 R30 Vaux MBR20100 C15 C18 100 n 47 k D5 MBR20100 100 n X11 IRFIB6N60 C16 X4 1000 m + C23 1000 m C19 + 2.2 n 1 k R18 4.7 m TL431 C17 SFH615A C21 10 k R22 100 n R28 3.24 k 105 k R20 R21 3.65 k 200 k R31 + X10 C20 + 2.7 k R19 L3 4.7 m L2 100 m 32 V 16 V GND Figure 10. The 40 W Printer Board Featuring the NCP1351 Controller http://onsemi.com 9 100 m AND8278/D 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. 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: Literature Distribution Center for ON Semiconductor P.O. Box 5163, Denver, Colorado 80217 USA Phone: 303−675−2175 or 800−344−3860 Toll Free USA/Canada Fax: 303−675−2176 or 800−344−3867 Toll Free USA/Canada Email: [email protected] N. American Technical Support: 800−282−9855 Toll Free USA/Canada Europe, Middle East and Africa Technical Support: Phone: 421 33 790 2910 Japan Customer Focus Center Phone: 81−3−5773−3850 http://onsemi.com 10 ON Semiconductor Website: www.onsemi.com Order Literature: http://www.onsemi.com/orderlit For additional information, please contact your local Sales Representative AND8278/D