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February 2013 Doc ID 023660 Rev 1 1/38

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 V

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. Demonstration board image

www.st.com

Summary of content (38 pages)

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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.
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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 . . . . . . . . . . . . .
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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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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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.
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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 . . . . . . . .
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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.
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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.
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- 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.
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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.
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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.
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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.
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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.
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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.
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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).
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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Board layout 10 AN4164 Board layout Figure 49. Board layout - complete AM13339v1 Figure 50.
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AN4164 Board layout Figure 51.
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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.
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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.
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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.
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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.
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References 12 36/38 AN4164 References 1. Code of conduct on energy efficiency of external power supplies, version 4 2.
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AN4164 13 Revision history Revision history Table 11. Document revision history Date Revision 08-Feb-2013 1 Changes Initial release.
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AN4164 Please Read Carefully: Information in this document is provided solely in connection with ST products. STMicroelectronics NV and its subsidiaries (“ST”) reserve the right to make changes, corrections, modifications or improvements, to this document, and the products and services described herein at any time, without notice. All ST products are sold pursuant to ST’s terms and conditions of sale.