AN4165 Application note STEVAL-ISA111V1: 12 V/12 W, 115 kHz non-isolated flyback based on the VIPER26 By Mirko Sciortino Introduction This document describes a 12 V - 1 A power supply set in non-isolated flyback topology based on the VIPER26, an offline high-voltage converter offered by STMicroelectronics.
Contents AN4165 Contents 1 Adapter features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2 Circuit description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3 Bill of material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 4 Transformer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 5 Testing the board . . . . . . .
AN4165 Contents Appendix A Test equipment and measurement of efficiency and light load performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 A.1 Measuring input power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 16 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 17 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
List of figures AN4165 List of figures Figure 1. Figure 2. Figure 3. Figure 4. Figure 5. Figure 6. Figure 7. Figure 8. Figure 9. Figure 10. Figure 11. Figure 12. Figure 13. Figure 14. Figure 15. Figure 16. Figure 17. Figure 18. Figure 19. Figure 20. Figure 21. Figure 22. Figure 23. Figure 24. Figure 25. Figure 26. Figure 27. Figure 28. Figure 29. Figure 30. Figure 31. Figure 32. Figure 33. Figure 34. Figure 35. Figure 36. Figure 37. Figure 38. Figure 39. Figure 40. Figure 41. Figure 42. Figure 43.
AN4165 List of tables List of tables Table 1. Table 2. Table 3. Table 4. Table 5. Table 6. Table 7. Table 8. Table 9. Table 10. Table 11. Table 12. Table 13. Electrical specifications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Bill of material (simplified schematic) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Transformer characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Adapter features 1 AN4165 Adapter features The electrical specifications of the demonstration board are listed in Table 1. Table 1. Electrical specifications Symbol VIN Parameter Value [ 90 VAC - 265 VAC] Input voltage range VOUT Output voltage 12 V IOUT Max. output current 1A Δ VOUT_LF Precision of output regulation ± 5% Δ VOUT_HF High-frequency output voltage ripple 50 mV TAMB Max.
AN4165 2 Circuit description Circuit description The power supply is set in flyback topology. The complete schematic is given in Figure 2. A simplified schematic for VOUT ≥12 V and the relevant BOM are given in Figure 3 and in Table 2 respectively. The input section includes a resistor R1 and an NTC for inrush current limiting, a diode bridge (D0) and a Pi filter for EMC suppression (C1, L2, C2). The transformer core is a standard E20.
Application schematic - complete NTC T1 L2 t AC IN Circuit description 8/37 Figure 2.
Application schematic - simplified for VOUT ≥ 12 V AN4165 Figure 3.
Bill of material AN4165 3 Bill of material Table 2. Bill of material (simplified schematic) Reference Part NTC 2.2 Ω NTC Thermistor, S236 series F T2A 250 V 2 A, 250 VAC fuse, TR5 series Wickmann C1 10 µF, 400 V NHG series electrolytic capacitor Panasonic C2 22 µF, 35 V SMG series electrolytic capacitor Panasonic C4 2.2 µF, 63 V electrolytic capacitor C5 100 nF, 50 V ceramic capacitor C6 2.2 nF, 50 V ceramic capacitor C7 100 nF, 50 V ceramic capacitor C8 2.
AN4165 4 Transformer Transformer The characteristics of the transformer are listed in the table below. Table 3. Transformer characteristics Parameter Value Test conditions Manufacturer Magnetica Part number 1335.0089 Primary inductance 1.8 mH ±15% Measured at 1 kHz, TAMB = 20 oC Leakage inductance 3.12% Measured at 10 kHz, TAMB = 20 oC Primary to secondary turn ratio (3 - 5)/(6,7- 8,9) 5.8 ± 5% Measured at 10 kHz, TAMB = 20 oC Primary to auxiliary turn ratio (3 - 5)/(1 - 2) 5.
Testing the board AN4165 5 Testing the board 5.1 Typical waveforms Drain voltage and current waveforms in full load condition are shown for the two nominal input voltages in Figure 8 and 9, and for minimum and maximum input voltage in Figure 10 and 11 respectively. Figure 8. Figure 9. Drain current and voltage at VIN = 115 VAC, full load Drain current and voltage at VIN = 230 VAC, full load AM13362v1 Figure 10. Drain current and voltage at VIN = 90 VAC, full load AM13363v1 Figure 11.
AN4165 Line/load regulation and output voltage ripple 6 Line/load regulation and output voltage ripple The output voltage of the board has been measured in different line and load conditions. The results are shown in Table 4. The output voltage is practically unaffected by the line condition. Table 4. Output voltage line-load regulation VOUT[V] VIN [VAC] No load 50% load 75% load 100% load 90 11.94 11.91 11.92 11.92 115 11.94 11.91 11.92 11.92 150 11.94 11.92 11.91 11.91 180 11.
Line/load regulation and output voltage ripple Figure 14. Output voltage ripple at VIN = 115 VAC, full load AN4165 Figure 15.
AN4165 7 Burst mode and output voltage ripple Burst mode and output voltage ripple When the converter is lightly loaded, the COMP pin voltage decreases. As it reaches the shutdown threshold, VCOMPL (1.1 V, typical), the switching is disabled and energy is no longer transferred to the secondary side. So, the output voltage decreases and the regulation loop makes the COMP pin voltage increase again. As it rises 40 mV above the VCOMPL threshold, the normal switching operation is resumed.
Burst mode and output voltage ripple AN4165 Table 6 shows the measured value of the burst mode frequency ripple measured under different operating conditions. The ripple in burst mode operation is very low. Table 6.
AN4165 Efficiency Active mode efficiency is defined as the average of the efficiencies measured at 25%, 50%, 75% and 100% of maximum load, at nominal input voltage (VIN = 115 VAC and VIN = 230 VAC). External power supplies (the power supplies which are housed separately from the end-use devices they are powering) need to comply with the Code of Conduct (version 4.0) "Active mode efficiency" criterion, which requires an active mode efficiency higher than 77.7% for a power throughput of 12 W.
Light-load performance 9 AN4165 Light-load performance The input power of the converter has been measured in no load condition for different input voltages and the results are given in Table 7. Table 7. No load input power VIN [VAC] PIN [mW] 90 13.4 115 14.4 150 16.1 180 18.0 230 22.2 265 24.9 In version 4.0 of the Code of Conduct the power consumption of the power supply when it is not loaded is also considered. The criteria for compliance are given in the table below: Table 8.
AN4165 Light-load performance Table 10. Light load performance at POUT = 50 mW VIN [VAC] POUT [mW] PIN [mW] Efficiency (%) 90 50 76.7 65.2 115 50 78.5 63.7 150 50 82.0 61.0 180 50 85.0 58.8 230 50 90.0 55.6 265 50 94.0 53.2 The input power vs. input voltage for no load and light load condition (Table 7, 9 and 10) are shown in the figure below. Figure 21. PIN vs.
Light-load performance AN4165 Figure 22. Efficiency vs. VIN at PIN = 1 W 90 85 80 eff [%] 75 70 65 60 55 50 80 110 140 170 200 VIN [V AC ] 230 260 AM13378v1 Another requirement (EuP lot 6 ) is that the input power should be less than 500 mW when the converter is loaded with 250 mW. The converter can satisfy even this requirement, as shown in Figure 23. Figure 23. PIN at POUT = 0.25 W 0.5 0.45 PIN [W] 0.4 0.35 0.3 0.
AN4165 Functional check 10 Functional check 10.1 Soft-start At startup the current limitation value reaches IDLIM after an internally set time, tSS, whose typical value is 8.5 msec. This time is divided into 16 time intervals, each corresponding to a current limitation step progressively increasing. In this way the drain current is limited during the output voltage increase, therefore reducing the stress on the secondary diode. The softstart phase is shown in Figure 24 and 25. Figure 24.
Functional check AN4165 Figure 26. Output short-circuit applied: OLP tripping Figure 27. Output short-circuit maintained: OLP steady-state Output is shorted here tRESTART Normal operation AM11574v1 Figure 28. Output short-circuit maintained: OLP steady-state, zoom tSS tSS AM11575v1 Figure 29. Output short-circuit removal and converter restart tOVL tOVL tRESTART Normal operation Output short is removed here AM13381v1 10.
AN4165 Functional check shorting the low-side resistor of the output voltage divider, R4 = R4a + R4b. The same behavior can be caused by opening the high-side resistor, R3. The protection acts in auto-restart mode with tRESTART = 1 s (Figure 31). When the fault is removed, normal operation is restored after the last tRESTART interval has been completed (Figure 33). Figure 30. Feedback loop failure protection: Figure 31.
Feedback loop calculation guidelines AN4165 11 Feedback loop calculation guidelines 11.1 Transfer function The set PWM modulator + power stage is indicated with G1(f), while C(f) is the “controller”, i.e. the network which is in charge of ensuring the stability of the system. Figure 34.
AN4165 Feedback loop calculation guidelines The mathematical expression of the compensator C(f) is: Equation 5 C(f )= ΔI pk ΔV OUT = C0 ⋅ H COMP 1+ f ⋅j fZc ⎛ f ⋅j⎞ 2 ⋅ π ⋅ f ⋅ j ⋅ ⎜⎜1 + ⎟ fPc ⎟⎠ ⎝ where (with reference to the schematic of Figure 2): Equation 6 C0 = − Gm R4 ⋅ C 7 + C 8 R3 + R 4 Equation 7 fZc = 1 2 ⋅ π ⋅ R7 ⋅ C7 Equation 8 fPc = C7 + C 8 2 ⋅ π ⋅ R7 ⋅ C7 ⋅ C8 are to be chosen with the purpose to ensure the stability of the overall system.
Feedback loop calculation guidelines AN4165 At this point the Bode diagram of G1(f)*C(f) can be plotted, in order to check the phase margin for the stability. If the margin is not high enough, another choice should be made for fZc, fPc and fcross_sel, and the procedure repeated.
AN4165 Thermal measurements 12 Thermal measurements A thermal analysis of the board at full load condition,@ TAMB = 25 ° C has been performed using an IR camera. The worst case is VIN = 85 VAC, but the nominal input voltage cases (VIN = 115 VAC and VIN = 230 VAC) have also been considered. The results are shown in Figure 35, 36, 37 and 38 and summarized in Table 12. Figure 35. Thermal map at TAMB = 25 ° C, VIN = 85 VAC, full load Figure 36.
EMI measurements 13 AN4165 EMI measurements A pre-compliance test to EN55022 (Class B) European normative has been performed using an EMC analyzer and an LISN. First of all, a measurement of the background noise (board disconnected from the mains) was performed and is shown in Figure 39. Then the peak and average EMC measurements at 115 VAC/full load and 230 VAC/full load were performed and the results are shown in Figure 40, 41, 42 and 43. Figure 39. Background noise measurement AM13386v1 Figure 40.
AN4165 EMI measurements Figure 41. Peak measurement at 230 VAC/full load AM13388v1 Figure 42. Average measurement at 115 VAC/full load AM13389v1 Figure 43.
Board layout 14 AN4165 Board layout The board layout is shown in the figure below. Figure 44.
AN4165 15 Conclusions Conclusions The VIPER26 allows a simple design of a non-isolated converter with few external components. In this document a non-isolated flyback has been described and characterized. Special attention has been given to light load performance, confirmed as very good by bench analysis. Efficiency has been compared to the requirements of the Code of Conduct (version 4) for external AC/DC power supplies with very good results.
Test equipment and measurement of efficiency and light load performance Appendix A AN4165 Test equipment and measurement of efficiency and light load performance The converter input power has been measured using a wattmeter. The wattmeter measures simultaneously the converter input current (using its internal ammeter) and voltage (using its internal voltmeter). The wattmeter is a digital instrument so it samples the current and voltage and converts them to digital forms.
AN4165 Test equipment and measurement of efficiency and light load performance Figure 46. Switch in position 1 - setting for standby measurements Wattmeter Ammeter AC SOURCE ~ V A + U.U.T. AC INPUT - UUT Voltmeter AM11591v1 In the case of high UUT input current (i.e. for measurements in heavy load conditions), the voltage drop can be relevant compared to the UUT real input voltage.
Test equipment and measurement of efficiency and light load performance AN4165 As noted in IEC 62301, instantaneous measurements are appropriate when power readings are stable. The UUT is operated at 100% of nameplate output current output for at least 30 minutes (warm-up period) immediately prior to conducting efficiency measurements. After this warm-up period, the AC input power is monitored for a period of 5 minutes to assess the stability of the UUT.
AN4165 16 References References – Code of Conduct on energy efficiency of external power supplies, version 4 – VIPER26 datasheet Doc ID 023661 Rev 1 35/37
Revision history 17 AN4165 Revision history Table 13. 36/37 Document revision history Date Revision 18-Feb-2013 1 Changes Initial release.
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