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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
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
1N4007 1N4007 R2 150 k E1 10 m/400 V 1 E2 C1 2n2/Y
application note describes modifications to the basic circuit to reduce standby power consumption, increase efficiency, and reduce EMI.
1 TR1 8 7 D5 U160
D6 B150 E3 470 m/25 V
D1 D2 R1 47 R 1 2 J1 CEE7.5/2 D3 D4
4
6 5 ZD1 11 V
2 1 J2 CZM5/2
IC1 NCP1012 VCC HV FB GND 5 4 8 IC2 PC817
2 GND 3 GND 7 GND
R3 100 R R4 180 R
1N4007 10 m/63 V 1N4007
C2 2n2/Y
Figure 1. Schematic Diagram of the Demo Board
Figure 2. PCB Component Placement
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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 Vin DC (V) Iin DC (mA) Pin (W) Vout DC (V) Iout DC (mA) Pout (W) Efficiency (%) Standby (mW) Test 1 125 66 8.25 11.99 520 6.24 75.6 638.3 Test 2 325 25.1 8.15 12.1 520 6.29 77.1 695.6
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
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 mA 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 mA. 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:
Figure 3. Zener Feedback
Figure 4. TLV431 Feedback
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
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.
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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 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.
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.
1N4007 1N4007 L1 2, 2 mH D1 D2 E1 10 m/400 V E2 10 m/400 V D3 D4
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.
R1 47 R 1 2 J1 CEE7.5/2 X2 47 n
1N4007 1N4007
Figure 7. Complete EMI Filter
With L1 and E2, EMI radiation is reduced by more than 20 dBmV. This design is acceptable for production if good
Figure 8. Coil + X2 Capacitor
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Figure 9. Complete EMI Filter
Bills of material used for the standard and TVS versions of the demo board:
Standard Version
Part MMM C1 C2 D1 D2 D3 D4 D5 D6 E1 E2 E3 IC1 IC2 J1 J2 R1 R2 R3 R4 TR1 ZD1 2n2/Y2 2n2/Y2 1N4007 1N4007 1N4007 1N4007 MUR160 MBR150 10 m/400 V 10 m/63 V 470 m/25 V NCP1012 PC817 CEE7.5/2 CZM5/2 47 R 150 k 100 R 180 R TR-NCP1012 1N5241B R41 R41 DO-41 DO-41 DO-41 DO-41 59-04 59-04 NHG KMG KMF DIP 7 DIP 4 CEE7,5/2 CZM5/2 RM10 RM12,5 RM6,35 RM6,35 EF16 Hor. DO-204AH Arcotronics Arcotronics ON Semiconductor ON Semiconductor ON Semiconductor ON Semiconductor ON Semiconductor ON Semiconductor Panasonic Nippon Nippon ON Semiconductor Sharp Various Various Vishay Vishay Vishay Vishay P&V Elektronic ON Semiconductor Value Package Manuf.
TVS Version
Part MMM C1 C2 D1 D2 D3 D4 D5 D6 E1 E2 E3 IC1 IC2 J1 J2 R1 R2 R3 R4 TR1 ZD1 NU 2n2/Y2 1N4007 1N4007 1N4007 1N4007 MUR160 MBR150 10 m/400 V 10 m/63 V 470 m/25 V NCP1012 PC817 CEE7.5/2 CZM5/2 47 R P6KE200A 100 R 180 R TR-NCP1012 1N5241B R41 DO-41 DO-41 DO-41 DO-41 59-04 59-04 NHG KMG KMF DIP 7 DIP 4 CEE7,5/2 CZM5/2 RM10 SURMETIC 40 RM6,35 RM6,35 EF16 Hor. DO-204AH Arcotronics ON Semiconductor ON Semiconductor ON Semiconductor ON Semiconductor ON Semiconductor ON Semiconductor Panasonic Nippon Nippon ON Semiconductor Sharp Various Various Vishay ON Semiconductor Vishay Vishay P&V Elektronic ON Semiconductor Value Package Manuf.
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Notes
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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.
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