AN4164 Application note STEVAL-ISA113V1: 12 V/4 W, 115 kHz non-isolated flyback By Mirko Sciortino Introduction This document describes a 12 V-350 mA power supply set in non-isolated flyback topology with the new VIPer06 offline high voltage converter by STMicroelectronics. The features of the device are: ■ 800 V avalanche rugged power section ■ PWM operation at 115 kHz with frequency jittering for lower EMI ■ Limiting current with adjustable set point ■ Onboard soft-start ■ Safe auto-restart after a fault condition (overload, short-circuit) ■ SSO-10 package Moreover, the VIPER06 does not require a biasing circuit to operate because the IC can be supplied by an internal current generator, therefore saving the cost of the transformers auxiliary winding (self-biasing). If the device is biased through an auxiliary winding or through a diode connected to the output (external biasing), it can reach very low standby consumption (< 50 mW at 265 VAC). Both cases are treated in the present document. The available protection features are: thermal shutdown with hysteresis, delayed overload protection, and open loop failure protection (the last is available only if the IC is externally biased). Figure 1. February 2013 Demonstration board image Doc ID 023660 Rev 1 1/38 www.st.com Contents AN4164 Contents 1 Adapter features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2 Circuit description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 3 Schematic and bill of material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 4 Transformer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 5 Testing the board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 6 7 5.1 Typical waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 5.2 Line/load regulation and output voltage ripple . . . . . . . . . . . . . . . . . . . . . 13 5.3 Burst mode and output voltage ripple . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 5.4 Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 5.5 Light load performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Functional check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 6.1 Soft-start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 6.2 Overload protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 6.3 Feedback loop failure protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Feedback loop calculation guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . 23 7.1 Transfer function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 7.2 Compensation procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 8 Thermal measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 9 EMI measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 10 Board layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 11 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 2/38 Doc ID 023660 Rev 1 AN4164 Contents Appendix A Test equipment and measurement of efficiency and light load performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 A.1 Measuring input power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 12 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 13 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 Doc ID 023660 Rev 1 3/38 List of tables AN4164 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. 4/38 Electrical specifications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Bill of material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Transformer characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Output voltage line-load regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Output voltage ripple at no/light load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 No load input power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Energy consumption criteria for no load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Light load performance POUT=25 mW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Light load performance POUT=50 mW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 POUT @ PIN=1 W . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 Doc ID 023660 Rev 1 AN4164 List of figures 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. Figure 44. Figure 45. Figure 46. Figure 47. Demonstration board image. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Application schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 VDD waveforms IC externally biased (J1 selected) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 VDD waveforms IC self-biased (J1 not selected) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Transformer, pin distances. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Transformer, electrical diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Transformer side view 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Transformer side view 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Drain current/voltage at 115 Vac, max. load. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Drain current/voltage at 230 Vac, max. load. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Drain current/voltage at 90 Vac, max. load. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Drain current/voltage at 265 Vac, max. load. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Line regulation, IC externally biased (J1 selected) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Line regulation, IC self-biased (J1 not selected) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Load regulation, IC externally biased (J1 selected) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Load regulation, IC self-biased (J1 not selected). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Output voltage ripple at 115 VAC no load. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Output voltage ripple at 230 VAC no load. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Output voltage ripple at 115 VAC 25 mA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Output voltage ripple at 230 VAC 25 mA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Active mode efficiency of the demonstration board and comparison with energy efficiency standards (IC externally biased) . . . . . . . . . . . . . . . . . . . . . . . . . . 15 PIN vs. VIN at no load and light load; IC externally biased (J1 selected) . . . . . . . . . . . . . . 17 PIN vs. VIN at no load and light load, IC self-biased (J1 not selected) . . . . . . . . . . . . . . . . 17 Efficiency at PIN = 1 W; IC externally biased (J1 selected) . . . . . . . . . . . . . . . . . . . . . . . . 18 Efficiency at PIN = 1 W; IC self biased (J1 not selected) . . . . . . . . . . . . . . . . . . . . . . . . . . 18 PIN at POUT = 250 mW; IC externally biased (J1 selected) . . . . . . . . . . . . . . . . . . . . . . . . 19 PIN at POUT = 250 mW; IC self biased (J1 not selected) . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Soft-start @ startup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Soft-start @ startup (zoom) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 OLP short-circuit applied: OLP tripping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Output short-circuit maintained: OLP steady-state . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Output short-circuit maintained: OLP steady-state (zoom) . . . . . . . . . . . . . . . . . . . . . . . . 21 Output short-circuit removal and converter restart. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Feedback loop failure protection: tripping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Feedback loop failure protection: steady-state . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Feedback loop failure protection: steady-state, zoom . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Feedback loop failure protection: converter restart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Control loop block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Thermal measurement at VIN = 90 VAC, full load, IC externally biased . . . . . . . . . . . . . . . 26 Thermal measurement at VIN = 115 VAC, full load, IC externally biased . . . . . . . . . . . . . . 26 Thermal measurement at VIN = 230 VAC, full load, IC externally biased . . . . . . . . . . . . . . 27 Thermal measurement at VIN = 265 VAC, full load, IC externally biased . . . . . . . . . . . . . . 27 Thermal measurement at VIN = 90 VAC, Iout = 310 mA, IC self biased . . . . . . . . . . . . . . . 27 Thermal measurement at VIN = 115 VAC, Iout = 310 mA, IC self biased . . . . . . . . . . . . . . 28 Thermal measurement at VIN = 230 VAC, full load, IC self biased . . . . . . . . . . . . . . . . . . . 28 Thermal measurement at VIN = 265 VAC, full load, IC self biased . . . . . . . . . . . . . . . . . . . 28 Average measurements at full load, TAMB=25 ×C, 115 VAC, IC externally biased . . . . . . 29 Doc ID 023660 Rev 1 5/38 List of figures Figure 48. Figure 49. Figure 50. Figure 51. Figure 52. Figure 53. Figure 54. 6/38 AN4164 Average measurements at full load, TAMB=25 ×C, 230 VAC, IC externally biased . . . . . . . 29 Board layout - complete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Board layout - top layer + top overlay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Board layout - bottom layer + top overlay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 Connection of the UUT to the wattmeter for power measurements . . . . . . . . . . . . . . . . . . 33 Switch in position 1 - setting for standby measurements . . . . . . . . . . . . . . . . . . . . . . . . . . 34 Switch in position 2 - setting for efficiency measurements . . . . . . . . . . . . . . . . . . . . . . . . . 34 Doc ID 023660 Rev 1 AN4164 1 Adapter features Adapter features The electrical specifications of the demonstration board are listed in Table 1. Table 1. Electrical specifications Parameter Symbol Value VIN [90 VAC; 265 VAC] Output voltage VOUT 12 V Max. output current IOUT 0.35 A Precision of output regulation ΔVOUT_LF ± 5% High frequency output voltage ripple ΔVOUT_HF 50 mV Max. ambient operating temperature TAMB(1) Input voltage range 30 ° C (self biasing) 60 ° C (external biasing) 1. see Section 2: Circuit description Doc ID 023660 Rev 1 7/38 Circuit description 2 AN4164 Circuit description The power supply is set in flyback topology. The schematic is given in Figure 2, and the bill of material in Table 2. The input section includes a resistor R0 for inrush current limiting, a diode bridge (D0) and a Pi filter for EMC suppression (Cin1, Lin, Cin2). The transformer core is a standard E13. The output voltage value is set in a simple way through the RfbH-RfbL voltage divider between the output terminal and the FB pin, according to the following formula: Equation 1 ⎛ RfbH ⎞ ⎟ V OUT = 3 .3V ⋅ ⎜⎜1 + RfbL ⎟⎠ ⎝ In fact, the FB pin is the input of an error amplifier and is an accurate 3.3 V voltage reference. In the schematic the upper resistor RfbH has been split into RfbH1 and RfbH2; and the lower resistor RfbL into RfbL1 and RfbL2 in order to allow a better tuning of the output voltage value. The compensation network is connected between the COMP pin (which is the output of the error amplifier) and the GND pin, and is made up of Cp, Cc and Rc. The resistor RLIM, placed between the LIM and GND pins, has the purpose of reducing the drain current limitation, from IDLIM to about 250 mA in order to limit the deliverable output power of the converter and keep safe the power components. At power-up, as the rectified input voltage rises over the VDRAINSTART threshold, the high voltage current generator starts charging the VDD capacitor, CVDD, from 0 V up to VDDon. At this point the Power MOSFET starts switching, the HV current generator is turned off and the IC is biased by the energy stored in CVDD. In this demonstration board, if the jumper J1 is not selected, the IC is biased through the internal high-voltage startup current generator, which is automatically turned on as the VDD voltage drops down to VDDCSon and switched off as VDD is charged up to VDDon (selfbiasing). Self-biasing is excluded by keeping the VDD pin voltage always above the VDDCSon threshold. In this board, since the output voltage is higher than VDDCSon, this is obtained by just selecting the jumper J1, which connects the output terminal to the VDD pin through a small signal diode. If the output voltage is lower than VDDCSon, the self-biasing can be excluded only using an auxiliary winding. The IC biasing through auxiliary winding or through the output is referred to as external biasing. In Figure 3 the VDD waveforms for both cases (IC external biased and self-biased) are shown. The use of self-biasing means higher power dissipation across the IC (which must be avoided if low standby consumption and/or high efficiency is required) and higher IC temperature respect to external biasing (at given ambient temperature, the maximum deliverable output power is lower; or, a lower maximum ambient temperature is required to deliver the same power throughput). For this reason, two different maximum TAMB values, in full load condition, are indicated in Table 1, depending on the selection of weather self biasing or external biasing. These values are confirmed by the thermal measurements reported in Section 8. 8/38 Doc ID 023660 Rev 1 - D0 + Cin1 + Cin2 + Lin Doc ID 023660 Rev 1 CVDD + GND Cf ilt1 VDD Cf b RLIM LIM VIper06SH FB Cp COMP DRAIN DRAIN DRAIN DRAIN DRAIN J1 Cc Rc T1 + Daux Cout D2 Cf ilt2 Rf bL2 Rf bL1 Rf bH2 Rf bH1 - VOUT Figure 2. AC IN R0 3 AC IN AN4164 Schematic and bill of material Schematic and bill of material Application schematic AM13328v1 9/38 Schematic and bill of material Table 2. AN4164 Bill of material Ref. Part Description Package Cin1 2.2 µF, 400 V NHG series electrolytic capacitor Cin2 4. 7 µF, 400 V AX series electrolytic capacitor Saxon CVDD 1 µF, 50 V electrolytic capacitor 1206 Cfilt1 100 nF, 50 V ceramic capacitor 0805 Cc 10 nF, 50 V ceramic capacitor 1206 Cp 1 nF, 50 V ceramic capacitor 1206 Cfb 1 nF, 50 V ceramic capacitor 0805 Cout 330 µF, 16 V ZL series ultra-low ESR electrolytic cap. Cfilt2 MB6S D2 STPS2H100 Daux 1N4148W 600 V 1 A diode bridge Rubycon TO-269AA Vishay 100 V, 2 A, power schottky rectifier SMA ST Surface mount fast switching diode SOD-123 Zetex 4.7 Ω 3/4 W resistor R0 RLIM 15 kΩ 5% 1/4 W resistor 0805 Rc 47 kΩ 5% 1/4 W resistor 0805 RfbH1 33 kΩ 1% 1/4 W resistor 0805 RfbH2 0Ω 1206 RfbL1 12 kΩ 1% 1/4 W resistor 1206 RfbL2 0.47 kΩ 1% 1/4 W resistor 0805 IC1 VIPer06HS Offline high-voltage PWM controller T1 1921.0040 Transformer SSO-10 ST Magnetica B82144A2105J 1 mH inductor LBC series Figure 3. VDD waveforms IC externally biased Figure 4. (J1 selected) AM13329v1 10/38 Murata Not mounted D0 Lin Manufacturer Doc ID 023660 Rev 1 Epcos VDD waveforms IC self-biased (J1 not selected) AM13330v1 AN4164 4 Transformer Transformer The characteristics of the transformer are listed in the table below. Table 3. Transformer characteristics Parameter Value Manufacturer Magnetica Part number 1921.0040 Primary inductance (pins 3 - 4) Leakage inductance Primary to secondary turn ratio (3 - 4)/(5 - 8) Primary to auxiliary turn ratio (3 - 4)/(2 - 1) Test conditions 1.2 mH ± 15% Measured at 1 kHz 0.1 V 2.8% Measured at 10 kHz 0.1 V 6.11 ± 5% Measured at 10 kHz 0.1 V 5 ± 5% Measured at 10 kHz 0.1 V The following figures show the electrical diagram, size and pin distances (in mm) of the transformer. Figure 5. Transformer, pin distances Figure 6. Transformer, electrical diagram AM13331v1 Figure 7. Transformer side view 1 AM13332v1 Figure 8. AM13333v1 Doc ID 023660 Rev 1 Transformer side view 2 AM13334v1 11/38 Testing the board AN4164 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 9 and 10, and for minimum and maximum input voltage in Figure 11 and 12 respectively. Figure 9. Drain current/voltage at 115 Vac, max. load Figure 10. Drain current/voltage at 230 Vac, max. load AM13335v1 Figure 11. Drain current/voltage at 90 Vac, max. load AM13336v1 Figure 12. Drain current/voltage at 265 Vac, max. load AM13337v1 12/38 Doc ID 023660 Rev 1 AM13338v1 AN4164 Testing the board 5.2 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 not affected by the line condition and by the IC biasing (self-biasing or external biasing). Table 4. Output voltage line-load regulation VOUT[V] No load VIN [VAC] 50% load 75% load 100% load IC externally biased IC self biased IC externally biased IC self biased IC externally biased IC self biased IC externally biased IC self biased 90 12.04 12.05 12.00 11.98 12.00 11.98 11.99 11.97 115 12.05 12.05 12.00 11.99 12.00 11.98 11.99 11.97 150 12.05 12.05 12.00 11.98 12.00 11.98 11.99 11.97 180 12.05 12.04 12.00 11.98 12.00 11.98 11.99 11.97 230 12.05 12.04 12.00 11.98 12.00 11.98 11.99 11.97 265 12.05 12.04 12.00 11.98 12.00 11.98 11.99 11.97 Figure 14. Line regulation, IC self-biased (J1 not selected) 12.2 12.2 12.1 12.1 12 12 VOUT [V] VOUT [V] Figure 13. Line regulation, IC externally biased (J1 selected) 0 11.9 25% 0 11.9 25% 50% 11.8 50% 11.8 75% 75% 100% 100% 11.7 11.7 80 105 130 155 180 205 230 VIN[V AC ] 80 255 Figure 15. Load regulation, IC externally biased (J1 selected) 130 180 205 230 12.2 12.1 12.1 12 90 12 90 11.9 115 115 230 11.8 255 AM11689v1 Figure 16. Load regulation, IC self-biased (J1 not selected) 12.2 11.9 155 VIN [V AC ] VOUT [V] VOUT [V] 105 AM11688v1 11.8 230 265 265 11.7 11.7 0 0.05 0.1 0.15 0.2 0.25 IOUT [A] 0.3 0.35 0.4 0 AM11690v1 Doc ID 023660 Rev 1 0.05 0.1 0.15 0.2 0.25 IOUT [A] 0.3 0.35 0.4 AM11691v1 13/38 Testing the board 5.3 AN4164 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 the energy is not transferred to the secondary side anymore. At this point, the feedback reaction to the stop of the energy delivery makes the COMP pin voltage increase again. As it rises 40 mV above the VCOMPL threshold, the normal switching operation is resumed. This results in a controlled on/off operation which is referred to as “burst mode”. This mode of operation keeps the frequency-related losses low when the load is very light or disconnected, making it easier to comply with energy saving regulations. The figures below show the output voltage ripple when the converter is no/lightly loaded and supplied with 115 VAC and with 230 VAC respectively. Figure 17. Output voltage ripple at 115 VAC no load Figure 18. Output voltage ripple at 230 VAC no load AM11692v1 Figure 19. Output voltage ripple at 115 VAC 25 mA AM11693v1 Figure 20. Output voltage ripple at 230 VAC 25 mA AM11694v1 14/38 Doc ID 023660 Rev 1 AM11695v1 AN4164 Testing the board Table 5 shows the measured value of the burst mode frequency ripple measured in different operating conditions. The ripple in burst mode operation is very low. Table 5. Output voltage ripple at no/light load VOUT [mV] VIN [VAC] 25 mA load 90 2 7 115 2 7 230 4 8 265 4 9 Efficiency The 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 are contained in a separate housing from the end-use devices they are powering) need to comply with the Code of Conduct (version 4.0) “active mode efficiency” criterion, which states an active mode efficiency higher than 71.18% for a power throughput of 4.2 W. Another standard to be applied to external power supplies in the coming years is the DOE (Department of energy) recommendation, whose active mode efficiency requirement for the same power throughput is 76.6%. If the IC is externally biased, the presented demonstration board is compliant with both standards, as can be seen from Figure 21, where the average efficiencies of the board at 115 VAC (81.6%) and at 230 VAC (77.2%) are plotted with dotted lines, together with the above limits. In the same figure the efficiency at 25%, 50%, 75% and 100% of output load for both input voltages is also shown. Figure 21. Active mode efficiency of the demonstration board and comparison with energy efficiency standards (IC externally biased) 85 83 81 79 eff [%] 5.4 No load 77 DOE limit 75 73 71 CoC4 limit 69 115 230 av @ 115 Vac av @ 230 Vac 67 65 0.2 0.4 0.6 0.8 Iout [% I OUT ] Doc ID 023660 Rev 1 1 AM13342v1 15/38 Testing the board 5.5 AN4164 Light load performance The input power of the converter has been measured in no load condition for different input voltages and the results are reported in Table 6. Table 6. No load input power PIN [mW] VIN [VAC] IC externally biased IC self-biased 90 17.6 108 115 18.9 138 150 20.9 179 180 23.1 214 230 26.9 275 265 30.2 317 In version 4 of the Code of Conduct, also the power consumption of the power supply when it is no loaded is considered. The criteria to be compliant with are reported in the table below: Table 7. Energy consumption criteria for no load Nameplate output power (Pno) Maximum power in no load for AC-DC EPS 0 W ≤ Pno ≤ 50 W < 0.3 W 50 W < Pno < 250 W < 0.5 W The performance of the presented board (when the self-biasing function is not used) is much better than required; the power consumption is more than ten times lower than the limit fixed by version 4 of the Code of Conduct. Even though the performance seems to be disproportionally better than requirements, it is worth noting that often AC-DC adapter or battery charger manufacturers have very strict requirements about no load consumption and if the converter is used as an auxiliary power supply, the line filter is often the big line filter of the entire power supply that increases greatly the standby consumption. Even though version 4 of the Code of Conduct does not have other requirements regarding light load performance, in order to give a more complete overview we report the input power and efficiency of the demonstration board also in two other light load cases. Table 8 and Table 9 show the performance when the output load is 25 mW and 50 mW respectively. 16/38 Doc ID 023660 Rev 1 AN4164 Testing the board Table 8. Light load performance POUT=25 mW PIN [mW] VIN [VAC] POUT [mW] Efficiency (%) IC externally biased IC self-biased IC externally biased IC self-biased 90 25 49.7 128 50.30 19.6 115 25 51.5 157 48.54 15.9 150 25 54.7 200 45.70 12.5 180 25 57.3 236 43.63 10.6 230 25 61.7 296 40.52 8.4 265 25 64.8 337 38.58 7.4 Table 9. Light load performance POUT=50 mW PIN [mW] VIN [VAC] POUT [mW] Efficiency (%) IC externally biased IC self-biased IC externally biased IC self-biased 90 50 82.4 167 60.71 29.94 115 50 85.0 198 58.82 25.25 150 50 89.3 242 55.99 20.66 180 50 93.0 280 53.76 17.86 230 50 98.0 341 51.02 14.66 265 50 101.1 384 49.46 13.02 The input power vs. input voltage for no load and light load condition (Table 6, 8 and 9) is shown in the figures below. Figure 22. PIN vs. VIN at no load and light load; IC externally biased (J1 selected) 200 Figure 23. PIN vs. VIN at no load and light load, IC self-biased (J1 not selected) 400 0 25mW 150 PIN [mW] 50mW 350 300 PIN [mW] 250 100 200 150 50 0 100 25mW 50 0 50mW 0 80 105 130 155 180 VIN [V AC ] 205 230 255 80 AM11543v1 Doc ID 023660 Rev 1 105 130 155 180 VIN [V AC ] 205 230 255 AM11544v1 17/38 Testing the board AN4164 Depending on the equipment supplied, it’s possible to have several criteria to measure the standby or light load performance of a converter. One criterion is the measurement of the output power when the input power is equal to one watt. In Table 10 the output power needed to have 1 W of input power in a different line conditions is given. Figure 24 and 25 show the diagram of the output powers corresponding to PIN = 1 W for different values of the input voltage. Table 10. POUT @ PIN=1 W POUT [W] VIN [VAC] PIN [W] Efficiency (%) IC externally biased IC self-biased IC externally biased IC self-biased 90 1 0.78 0.64 78 64 115 1 0.77 0.60 77 60 150 1 0.73 0.55 73 55 180 1 0.70 0.49 70 49 230 1 0.68 0.43 68 43 265 1 0.65 0.40 65 40 Figure 24. Efficiency at PIN = 1 W; IC externally Figure 25. Efficiency at PIN = 1 W; IC biased (J1 selected) self biased (J1 not selected) 80 80 75 75 70 70 65 eff [%] eff [%] 65 60 55 60 55 50 50 45 45 40 35 40 80 110 140 170 VIN [V AC ] 200 230 260 80 AM11545v1 110 140 170 200 VIN [VAC] 230 260 AM11546v1 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 performances are shown in Figure 26 for external biasing and in Figure 27 for self biasing. In the former case the converter can satisfy even this requirement. 18/38 Doc ID 023660 Rev 1 AN4164 Testing the board Figure 26. PIN at POUT = 250 mW; IC externally Figure 27. PIN at POUT = 250 mW; biased (J1 selected) IC self biased (J1 not selected) 0.8 0.5 0.75 0.7 0.45 0.6 0.4 PIN [W] PIN [W] 0.65 0.35 0.55 0.5 0.45 0.4 0.3 0.35 0.25 0.25 0.3 80 110 140 170 VIN [V AC ] 200 230 260 80 AM13108v1 Doc ID 023660 Rev 1 110 140 170 200 VIN [V AC ] 230 260 AM13109v1 19/38 Functional check 6 Functional check 6.1 Soft-start AN4164 At startup, the current limitation value reaches IDLIM after an internally fixed 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 soft-start phase is shown in Figure 28 and 29. Figure 28. Soft-start @ startup Figure 29. Soft-start @ startup (zoom) AM13094v1 6.2 AM13095v1 Overload protection In the case of overload or short-circuit (see Figure 30), the drain current reaches the IDLIM value (or the one set by the user through the RLIM resistor). In every cycle where this condition is met, a counter is incremented; if it is maintained continuously for the time tOVL (50 msec typical, internally fixed), the overload protection is tripped, the power section is turned off and the converter is disabled for a tRESTART time (1 second typ.). After this time has elapsed, the IC resumes switching and, if the short is still present, the protection occurs indefinitely in the same way (Figure 31). This ensures restart attempts of the converter with low repetition rate, so that it works safely with extremely low power throughput and avoids the IC overheating in the case of repeated overload events. Furthermore, every time the protection is tripped, the internal soft-startup function is invoked (Figure 32), in order to reduce the stress on the secondary diode. After the short removal, the IC resumes normal working. If the short is removed during tSS or tOVL, i.e. before the protection tripping, the counter is decremented on a cycle-by-cycle basis down to zero and the protection is not tripped. If the short-circuit is removed during tRESTART, the IC must wait for the tRESTART period to elapse before switching is resumed (Figure 33). 20/38 Doc ID 023660 Rev 1 AN4164 Functional check Figure 30. OLP short-circuit applied: OLP tripping Figure 31. Output short-circuit maintained: OLP steady-state Output is shorted here Normal operation tRESTART AM13096v1 Figure 32. Output short-circuit maintained: OLP steady-state (zoom) tSS AM13097v1 Figure 33. Output short-circuit removal and converter restart tOVL tRESTART Normal operation tRESTART Output short is removed here AM13098v1 6.3 AM13099v1 Feedback loop failure protection This protection is available any time the IC is not self-biased. As the loop is broken (RfbL shorted or RfbH open), the output voltage VOUT increases and the VIPER06 runs at its maximum current limitation. The VDD pin voltage increases as well, because it is linked to the VOUT voltage either directly or through the auxiliary winding, depending on the cases. If the VDD voltage reaches the VDDclamp threshold (23.5 V min.) in less than 50 msec, the IC is shut down by open loop failure protection (see Figure 34 and 35), otherwise by OLP, as described in the previous section. The breaking of the loop has been simulated by shorting the low-side resistor of the output voltage divider, RfbL = RfbL1+RfbL2. The same behavior can be induced opening the high-side resistor, RfbH = RfbH1+RfbH2. Doc ID 023660 Rev 1 21/38 Functional check AN4164 The protection acts in auto-restart mode with tRESTART = 1sec (Figure 35). As the fault is removed, normal operation is restored after the last tRESTART interval has been completed (Figure 37). Figure 34. Feedback loop failure protection: tripping Figure 35. Feedback loop failure protection: steady-state Fault is applied here tRESTART VDD reaches VDDCLAMP Normal operation < tOVL Normal operation Output short is removed here tRESTART AM13204v1 AM13203v1 Figure 36. Feedback loop failure protection: steady-state, zoom Figure 37. Feedback loop failure protection: converter restart Fault is removed here tRESTART < tOVL AM13205v1 22/38 Doc ID 023660 Rev 1 Normal operation AM13206v1 AN4164 Feedback loop calculation guidelines 7 Feedback loop calculation guidelines 7.1 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 to ensure the stability of the system. Figure 38. Control loop block diagram AM11582v1 The mathematical expression of the power plant G1(f) is the following: Equation 2 ΔVOUT G1 (f) = = ΔI pk j ⋅ 2 ⋅π ⋅ f j⋅ f ) VOUT ⋅ (1 + ) z fz = j ⋅2 ⋅π ⋅ f j⋅ f ) Ipkp( fsw, Vdc) ⋅ (1 + ) Ipkp( fsw, Vdc ) ⋅ (1 + p fp VOUT ⋅ (1 + where VOUT is the output voltage, Ipkp is the primary peak current, fp is the frequency of the pole due to the output load and fz the frequency of the zero due to the ESR of the output capacitor: Equation 3 fp = 1 π ⋅ C OUT ·(R OUT + 2ESR) Equation 4 fz = 1 2 ⋅ π ⋅ C OUT ·ESR Doc ID 023660 Rev 1 23/38 Feedback loop calculation guidelines AN4164 The mathematical expression of the compensator C(f) is: Equation 5 C( f ) = ΔI pk ΔVOUT C0 = ⋅ HCOMP f⋅j fZc ⎛ f ⋅ j⎞ 2 ⋅ π ⋅ f ⋅ j ⋅ ⎜⎜1 + ⎟ fPc ⎟⎠ ⎝ 1+ where: Equation 6 Co = − Gm RfbL ⋅ Cc + Cp RfbL + RfbH Equation 7 fZc = 1 2 ⋅ π ⋅ Rc ⋅ Cc Equation 8 fPc = Cc + Cp 2 ⋅ π ⋅ Rc ⋅ Cc ⋅ Cp are chosen in order to censure the stability of the overall system. Gm = 2 mA/V (typical) is the VIPER06 transconductance. 7.2 Compensation procedure The first step is to choose the pole and zero of the compensator and the crossing frequency, for instance: – fZc = fp/2 – fPc = fz – fcross = fcross_sel ≤fsw/10 G1(fcross_sel) can be calculated from equation (2) and, since by definition it is | C(fcross_sel)*G1(fcross_sel)| = 1, C0, can be calculated as follows: Equation 9 2 ⋅ π ⋅ fcross _ sel ⋅ j ⋅ 1 + C0 = 1+ 24/38 fcross _ sel ⋅ j fPc fcross _ sel ⋅ j fZc Doc ID 023660 Rev 1 ⋅ HCOMP G1( fcross _ sel ) AN4164 Feedback loop calculation guidelines 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 for fZc, fPc and fcross_sel should be made, and the procedure repeated. When the stability is ensured, the next step is to find the values of the schematic components, which can be calculated, using the above formulas, as follows: Equation 10 RfbL = RfbH Vout −1 3. 3V Equation 11 Cp = fZc Gm RfbL ⋅ ⋅ fPc C 0 RfbL+ RfbH Equation 12 ⎛ fPc ⎞ Cc = Cp ⋅ ⎜⎜ − 1⎟⎟ ⎝ fZc ⎠ Equation 13 Rc = Cc + Cp 2 ⋅ π ⋅ fPc ⋅ Cc ⋅ Cp Doc ID 023660 Rev 1 25/38 Thermal measurements 8 AN4164 Thermal measurements A thermal analysis of the demonstration board in full load condition at TAMB = 25 °C, both with and without the self-biasing function, has been performed using an IR camera. The results are shown in the following figures. When the self-biasing function is used the VIPER06 temperature is higher, due to the power dissipated by the HVstartup generator. Figure 39. Thermal measurement at VIN = 90 VAC, full load, IC externally biased AM13343v1 Figure 40. Thermal measurement at VIN = 115 VAC, full load, IC externally biased AM13344v1 26/38 Doc ID 023660 Rev 1 AN4164 Thermal measurements Figure 41. Thermal measurement at VIN = 230 VAC, full load, IC externally biased AM13345v1 Figure 42. Thermal measurement at VIN = 265 VAC, full load, IC externally biased AM13346v1 Figure 43. Thermal measurement at VIN = 90 VAC, Iout = 310 mA, IC self biased AM13347v1 Doc ID 023660 Rev 1 27/38 Thermal measurements AN4164 Figure 44. Thermal measurement at VIN = 115 VAC, Iout = 310 mA, IC self biased AM13348v1 Figure 45. Thermal measurement at VIN = 230 VAC, full load, IC self biased AM13349v1 Figure 46. Thermal measurement at VIN = 265 VAC, full load, IC self biased AM13350v1 28/38 Doc ID 023660 Rev 1 AN4164 9 EMI measurements EMI measurements A pre-compliance test to the EN55022 (class B) european normative has been performed using an EMC analyzer and an LISN. Average measurements are reported in the following figures. Figure 47. Average measurements at full load, TAMB=25 ° C, 115 VAC, IC externally biased AM13351v1 Figure 48. Average measurements at full load, TAMB=25 ° C, 230 VAC, IC externally biased AM13352v1 Doc ID 023660 Rev 1 29/38 Board layout 10 AN4164 Board layout Figure 49. Board layout - complete AM13339v1 Figure 50. Board layout - top layer + top overlay AM13340v1 30/38 Doc ID 023660 Rev 1 AN4164 Board layout Figure 51. Board layout - bottom layer + top overlay AM13341v1 Doc ID 023660 Rev 1 31/38 Conclusions 11 AN4164 Conclusions The VIPER06 allows a non-isolated converter to be designed in a simple way and with few external components. In this document a flyback has been described and characterized. Special attention has been given to light load performance. The efficiency performance has been compared to the requirements of the Code of Conduct (version 4) for an external ACDC adapter with very good results, the measured active mode efficiency is always higher with respect to the minimum required. 32/38 Doc ID 023660 Rev 1 AN4164 Test equipment and measurement of efficiency and light load performance Appendix A 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 form. The digital samples are then multiplied giving the instantaneous measured power. The sampling frequency is in the range of 20 kHz (or higher depending on the instrument used). The display provides the average measured power, averaging the instantaneous measured power in a short period of time (1 second typ.). Figure 52 shows how the wattmeter is connected to the UUT (unit under test) and to the AC source and the wattmeter internal block diagram. Figure 52. Connection of the UUT to the wattmeter for power measurements Switch 1 WATT METER 2 U.U.T (Unit Under test) Voltmeter AC SOURCE + V Multiplier A X Ammeter INPUT OUTPUT AVG DISPLAY AM13105v1 An electronic load has been connected to the output of the power converter (UUT), allowing to set and measure the converter's load current, while the output voltage has been measured by a voltmeter. The output power is the product between load current and output voltage. The ratio between the output power, calculated as previously stated, and the input power, measured by the wattmeter, is the converter's efficiency, which has been measured in different input/output conditions. A.1 Measuring input power With reference to Figure 52, the UUT input current causes a voltage drop across the ammeter's internal shunt resistance (the ammeter is not ideal as it has an internal resistance higher than zero) and across the cables connecting the wattmeter to the UUT. If the switch of Figure 52 is in position 1 (see also the simplified scheme of Figure 53), this voltage drop causes an input measured voltage higher than the input voltage at the UUT input that, of course, affects the measured power. The voltage drop is generally negligible if the UUT input current is low (for example when measuring the input power of UUT in light load condition). Doc ID 023660 Rev 1 33/38 Test equipment and measurement of efficiency and light load performance AN4164 Figure 53. Switch in position 1 - setting for standby measurements Wattmeter Ammeter AC SOURCE ~ A + U.U.T. AC INPUT V - UUT Voltmeter AM13106v1 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. If this is the case, the switch in Figure 52 can be changed to position 2 (see simplified scheme of Figure 54) where the UUT input voltage is measured directly at the UUT input terminal and the input current does not affect the measured input voltage. Figure 54. Switch in position 2 - setting for efficiency measurements Wattmeter Ammeter A AC SOURCE + ~ V - U.U.T. AC INPUT UUT Voltmeter AM13107v1 On the other hand, the position of Figure 54 may introduce a relevant error during light load measurements, when the UUT input current is low and the leakage current inside the voltmeter itself (which is not an ideal instrument and doesn't have infinite input resistance) is not negligible. This is the reason why it is recommended to use the setting of Figure 53 for light load measurements and Figure 54 for heavy load measurements. If it is not clear which measurement scheme has the lesser effect on the result, try with both and register the lower input power value. As noted in IEC 62301, instantaneous measurements are appropriate when power readings are stable. The UUT is operated at 100% of nameplate output current for at least 30 minutes (warm-up period) immediately prior to conducting efficiency measurements. After this warmup period, the AC input power is monitored for a period of 5 minutes to assess the stability of the UUT. If the power level does not drift by more than 5% from the maximum value 34/38 Doc ID 023660 Rev 1 AN4164 Test equipment and measurement of efficiency and light load performance observed, the UUT can be considered stable and the measurements can be recorded at the end of the 5-minute period. If AC input power is not stable over a 5-minute period, the average power or accumulated energy is measured over time for both AC input and DC output. Some wattmeter models allow the measured input power to be integrated in a time range and then the energy absorbed by the UUT to be measured during the integration time. The average input power is calculated by dividing it by the integration time itself. Doc ID 023660 Rev 1 35/38 References 12 36/38 AN4164 References 1. Code of conduct on energy efficiency of external power supplies, version 4 2. VIPER06 datasheet Doc ID 023660 Rev 1 AN4164 13 Revision history Revision history Table 11. Document revision history Date Revision 08-Feb-2013 1 Changes Initial release. Doc ID 023660 Rev 1 37/38 AN4164 Please Read Carefully: Information in this document is provided solely in connection with ST products. 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