AND8132/D Performance Improvements to the NCP1012 Evaluation Board http://onsemi.com Prepared by: Bc. Jan Grulich EMEA Application Lab SCG CDC Roznov, Czech Republic APPLICATION NOTE application note describes modifications to the basic circuit to reduce standby power consumption, increase efficiency, and reduce EMI. This application note uses the standard NCP1012 evaluation board, referenced in the NCP1010–1014 data sheet. The board includes only the core components needed to demonstrate the operation of the NCP101x; the C1 2n2/Y 1N4007 1N4007 R2 150 k D1 D2 E1 10 /400 V R1 47 R 1 1 2 E2 J1 CEE7.5/2 1 TR1 8 7 D5 U160 E3 470 /25 V 4 2 GND 3 GND 7 GND HV FB GND 2 1 6 5 IC1 NCP1012 VCC D6 B150 ZD1 11 V 5 4 IC2 PC817 J2 CZM5/2 R3 100 R R4 180 R 8 D3 D4 1N4007 10 /63 V 1N4007 C2 2n2/Y Figure 1. Schematic Diagram of the Demo Board Figure 2. PCB Component Placement Semiconductor Components Industries, LLC, 2003 August, 2003 − Rev. 0 1 Publication Order Number: AND8132/D AND8132/D circuit, the feedback loop operating current and various transformer losses. Of these, only the feedback loop operating current and drain clamp circuit can easily be modified. The feedback loop operating current must be calculated properly to achieve good DC voltage stability, adequate dynamic response and acceptable noise immunity. For the simplest case – zener type feedback − a typical operating current is 4.0−6.0 mA. This method is used in the demo board, resulting in 695 mW of standby consumption at 325 VDC. By reducing the operating current of the loop, the standby consumption is reduced, but with negative effects on the noise immunity and accuracy. For example, when bias resistor R4 is removed, the operating current is as low as 335 A and standby consumption is reduced to 314 mW. In this case circuit operation is still in the non−burst mode, so although the voltage stability is not as good there is still low AC ripple at the output. A more complicated, but more accurate, solution is based on the TLV431 shunt regulator. This regulator operates correctly at an operating current as low as 100 A. When used for this design, at no load, due to the high gain, it operates in burst mode. In this mode the complete design has standby consumption as low as 100 mW, but the output voltage is unstable, with noise and AC ripple, as shown in Figure 4. Output voltage waveforms for both feedback solutions: The evaluation board demonstrates the NCP1012 in a 7.0 W SMPS with the universal input voltage range (85 VAC−265 VAC) and an output of 12 V. The schematic of the SMPS is shown in Figure 1, and the component placement in Figure 2. The tested performance of the unmodified board is shown below: Item Test 1 Test 2 Vin DC (V) 125 325 Iin DC (mA) 66 25.1 Pin (W) 8.25 8.15 Vout DC (V) 11.99 12.1 Iout DC (mA) 520 520 Pout (W) 6.24 6.29 Efficiency (%) 75.6 77.1 Standby (mW) 638.3 695.6 Feedback Stability: The regulation was tested for stability over the full input voltage range (85 VAC−265 VAC) with a load of 550 mA. No instability was found. Standby Consumption Standby power consumption is one of the most important parameters for an SMPS under low− or no−load conditions. In the demo board the main sources of standby power consumption are the NCP1012 Vcc supply, the drain clamp Figure 3. Zener Feedback Figure 4. TLV431 Feedback P6KE200A or SA170A, or the SMD versions of both − P6SMB200AT3 and 1SMB170AT3 respectively. This clamp consists of a high voltage zener diode, or a TVS with an ultrafast rectifier diode in series. The zener clamp voltage is usually set to around 200 V. Using this clamp, the power consumption is significantly reduced. With R4 connected, the consumption is 526 mW at 300 V DC input voltage versus 306 mW with R4 disconnected. The active clamp allows greater reduction of standby power, but is more expensive than the simple RDC clamp. There are various ways to design the drain clamp circuit. The RDC clamp, used in the evaluation board, is the cheapest and most widely used. This clamp dissipates the peak energy from the transformer and part of the transformed energy. The peak energy need to be dissipated, but the transformed energy not. In case of the demo board this clamp is used. With R4 connected the consumption at 325 V DC input voltage is 695 mW. When R4 is removed, the consumption is reduced to 314 mW. Another approach is to use a TVS (transient voltage suppressor) clamp. Recommended parts include ON’s http://onsemi.com 2 AND8132/D example, an EMI filter is not necessary for the basic function of the SMPS, but it is mandatory for a real−world design. Figure 5 shows the EMI performance for the basic demo board before any modification; conducted emissions at the input are well above the maximum allowed by EN50081−1. When a 47 nF suppression capacitor X2 is added at the input, the magnitude of the EMI is dramatically reduced. The result is shown in Figure 6. This solution may be usable if X2 is increased to 100 nF or more. This TVS clamp solution has positive results not only on the standby consumption, but also on the efficiency both under normal operation and light load conditions. At 100 mA output current and 325 V DC input voltage, the input power drops from 2.94 W with the RDC clamp to 2.83 W with the TVS clamp. For higher output powers the benefit is not so significant. If the demo board design is intended for production, improvements in EMI performance are needed. For Figure 5. No EMI Filter Figure 6. X2 47 n Capacitor at Input Further improvement results from adding an LC filter L1 and E2 between the rectifier bridge and the bulk capacitor E1, as shown in Figure 7. PCB layout guidelines are followed. Figure 8 shows the improvement in conducted emissions as a result of adding capacitor X2 and coil L1 only; Figure 9 shows the result of implementing the complete EMI filter. 1N4007 1N4007 D2 D4 J1 CEE7.5/2 E1 10 /400 V E2 10 /400 V X2 47 n D3 1 2 D1 R1 47 R L1 2, 2 mH 1N4007 1N4007 Figure 7. Complete EMI Filter With L1 and E2, EMI radiation is reduced by more than 20 dBV. This design is acceptable for production if good Figure 8. Coil + X2 Capacitor http://onsemi.com 3 AND8132/D Figure 9. Complete EMI Filter Bills of material used for the standard and TVS versions of the demo board: Standard Version Part Value TVS Version Package Manuf. Part MMM Value Package Manuf. MMM C1 2n2/Y2 R41 Arcotronics C1 NU C2 2n2/Y2 R41 Arcotronics C2 2n2/Y2 R41 Arcotronics D1 1N4007 DO−41 ON Semiconductor D1 1N4007 DO−41 ON Semiconductor D2 1N4007 DO−41 ON Semiconductor D2 1N4007 DO−41 ON Semiconductor D3 1N4007 DO−41 ON Semiconductor D3 1N4007 DO−41 ON Semiconductor D4 1N4007 DO−41 ON Semiconductor D4 1N4007 DO−41 ON Semiconductor D5 MUR160 59−04 ON Semiconductor D5 MUR160 59−04 ON Semiconductor D6 MBR150 59−04 ON Semiconductor D6 MBR150 59−04 ON Semiconductor E1 10 /400 V NHG Panasonic E1 10 /400 V NHG Panasonic E2 10 /63 V KMG Nippon E2 10 /63 V KMG Nippon E3 470 /25 V KMF Nippon E3 470 /25 V KMF Nippon IC1 NCP1012 DIP 7 ON Semiconductor IC1 NCP1012 DIP 7 ON Semiconductor IC2 PC817 DIP 4 Sharp IC2 PC817 DIP 4 Sharp J1 CEE7.5/2 CEE7,5/2 Various J1 CEE7.5/2 CEE7,5/2 Various J2 CZM5/2 CZM5/2 Various J2 CZM5/2 CZM5/2 Various R1 47 R RM10 Vishay R1 47 R RM10 Vishay R2 150 k RM12,5 Vishay R2 P6KE200A SURMETIC 40 ON Semiconductor R3 100 R RM6,35 Vishay R3 100 R RM6,35 Vishay R4 180 R RM6,35 Vishay R4 180 R RM6,35 Vishay TR1 TR−NCP1012 EF16 Hor. P&V Elektronic TR1 TR−NCP1012 EF16 Hor. P&V Elektronic ZD1 1N5241B DO−204AH ON Semiconductor ZD1 1N5241B DO−204AH ON Semiconductor http://onsemi.com 4 AND8132/D Notes http://onsemi.com 5 AND8132/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. 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] JAPAN: ON Semiconductor, Japan Customer Focus Center 2−9−1 Kamimeguro, Meguro−ku, Tokyo, Japan 153−0051 Phone: 81−3−5773−3850 ON Semiconductor Website: http://onsemi.com For additional information, please contact your local Sales Representative. N. American Technical Support: 800−282−9855 Toll Free USA/Canada http://onsemi.com 6 AND8132/D