AN2103 APPLICATION NOTE VIPower: VIPer12A ISOLATED FLYBACK CONVERTER REFERENCE BOARD

Transcription

1 AN203 APPLICATION NOTE VIPower: VIPer2A ISOLATED FLYBACK CONVERTER REFERENCE BOARD. ABSTRACT The presented circuit can be used to produce multiple isolated voltage outputs. It is dedicated to building an auxiliary power supply based on the VIPer2AS monolithic device. INTRODUCTION The aim of the presented reference boards is to propose a power supply solution based on an offline discontinuous current mode flyback converter with isolation between input and output. The flyback topology allows to fully exploit current and voltage capability of the incorporated monolithic device VIPer2AS when compared with buck converter based power supply. To ensure galvanic isolation between input and outputs, the secondary windings of the transformer are isolated from the primary ones. Also a feedback loop with isolation between the primary and secondary one is provided by means of an optocoupler in case of regulation from the secondary side or by means of an auxiliary winding in case of regulation from the primary side. The VIPer2AS incorporates the PWM controller with 60 khz internal oscillator and altogether with the vertical power MOSFET switch in a SO8 package. The presented power supply has three variants. All these variants have been incorporated in the presented reference board by different assembly options. 2. CIRCUIT DESCRIPTION 2. ISOLATED FLYBACK +5V/, +5V/ 500mA (VARIANT ) Table. Operating Conditions Input Voltage Range VAC Input Voltage Frequency Range 50/60Hz Main Output (regulated) 5V/500mA Second Output 5V/ Total Maximum Output power 5.5W 2..2 Circuit Operation The schematic of the power supply (Variant ) can be seen in Figure. The input capacitor C is charged from the mains through the diode bridge D. Capacitor C together with capacitor C2 and inductor L form an EMI filter. The DC voltage at C2 is applied to the primary winding of the transformer through the internal MOSFET switch of the VIPer2AS during ON time of the switching period. The snubber circuit consisting of resistor R3 and capacitor C6 reduces the voltage spike across the primary winding of the transformer due to the parasitic leakage inductance. It also slows down the dv/dt of the primary winding's voltage a little bit and thus improves EMI. The power supply provides two outputs from two secondary windings of the transformer through rectifiers D4, D5 and smoothing and storage capacitors C3 and C4. The VIPer2AS is supplied from 5V output voltage through transistor Q and diode D7. Start-up of the converter is achieved by internal start-up current source of the VIPer2AS which will charge the IC supply capacitor C5 to a specified start-up threshold voltage of about 6V. As soon as the C5 voltage reaches the start-up threshold, the internal 60kHz oscillator sets the internal flip-flop and turns-on the internal high voltage power MOSFET. The power MOSFET applies the bulk capacitor C and C2 high voltage to the transformer's primary winding and primary current will ramp-up. As soon as the primary current ramp reaches the VIPer's internal set-point defined by the feedback loop, the internal power switch turns off. The output capacitor C3 or C4 is charged by the energy stored in the transformer through rectifier diode D4 or D5. The current loop which charges the 5V output only flows through diode D5. Because of the D5 location, the 5V output is charged via both diodes D4 and D5. Beside the slight decrease of the converter power efficiency, it significantly improves the crossregulation of the outputs which was the main purpose of this arrangement. The voltage feedback loop senses the 5V output by resistor divider R5, R7. The control IC U2 compares the resistor divider output voltage with an internal reference voltage of 2.5V and changes the cathode voltage accordingly to keep the 5V output stable. If the 5V output voltage rises above it's nominal value, the cathode voltage of U2 goes down and cathode current will increase. The cathode current will flow through the optocoupler's March 2005 Rev. 2 /29

2 LED which emits light depending on the current. The emitted light opens the phototransistor of the optocoupler which will inject the current to FB pin 3 of the VIPer2AS accordingly. The FB pin current will decrease the peak primary current to reduce the power delivered to the outputs. Resistor R0 limits the U2 cathode current. Resistor R9 ensures minimum bias current of at least ma for U2 proper operation. Frequency compensation of the entire feedback loop is ensured by C9, C0 and R8. C0 improves EMI immunity, too. Resistor R5 limits the feedback current to a safe value, which is lower than specified by the maximum rating table in the data sheet. Capacitor C8 improves noise immunity of the FB input against noise. This variant has also incorporated an overload protection by means of transistor Q. In case of operation above the output current limit, no current flows to the FB pin and transistor Q is off. This interrupts the power supply of VIPer2AS from auxiliary winding TB, the VDD supply voltage will go below under-voltage threshold, VIPer2AS stops switching and resumes its operation from start-up. This process is repeated as long as an overload condition lasts. Resistor R8 and capacitor C2 ensures converter's proper start-up over the overload protection. Figure. Schematic Diagram of Isolated Flyback Converter (Variant ) D4 +5 V 5 STPR20A 200V A SFH67A-3 U5 A R9 TC 3u H 6 turns 0.2 TEX-E C3 20 uf 35V LXY + R4 22R 2 k 6 R V~ CO N L 2 N clamp R 0R 3W ~ + - ~ D S VAC 0.5A L BC 330uH 90mA + C 0u F 400 V KMG C3 nf 500V Y C6 4.7uF 500 V + C2 00 pf 400V KMG R3 00R EF6 AL = 20nH Gap = 0.22mm TA 3.mH 60 turns 0.8 CuL TD 0u H 9 turns 0.35 TEX-E 40V A C4 220uF 35V LXY D5 + D6 ZMM8 U2 TS243ILT 00R +5V R C9 0R 22nF R8 4.7k C 0 nf R5 4.7k R7 4.7k CO N2 2 3 clamp Layout Hints: C5, C8 have to be close to VIPer2A Assembly options: (): +5V/, +5V/500mA Drain4 8 Drain3 7 Drain2 6 Drain 5 R 6 0R Source2 Source 2 VDD U FB VIPer2AS 4 3 C5 22uF 50V KME C8 22nF + BC856B 4 U5 B SFH67A-3 R5 4.7k STPS L40A Q 3 R4 00R R 8 0k C2 00nF D7 BAV TB 39uH 34 turns 0.8 CuL 2/29

3 2..3 Bill of Materials The bill of materials presented in Table 2 covers all power supply variants; the schematic corresponding to the complete PCB is shown in Figure 2 and includes all assembly options. The components, which are specific for a particular variant, can be recognized by column named "Variant". Peak clamp D2 connected across the primary winding is optional instead of the RC snubber and it is not assembled on the board. For the case that a precise voltage regulation of the 5V output is required, resistor R6 connected from the 5V output to the control input of U2 can be assembled instead of R5. Table 2. Bill Of Materials for all Variants of the Isolated Flyback Converter Ref. Qty Variant Value Description CON Clamp, 2 pole, horizontal,.5mm 2, 380V, 5A CON2 Clamp, 3 pole, horizontal,.5mm 2, 380V, 5A C 0µF Electrolytic capacitor, KMG, 400V C2 4.7µF Electrolytic capacitor, KMG, 400V C3 20µF Electrolytic capacitor, LXY, 35V C4 (, 2) 220µF Electrolytic capacitor, LXY, 35V C5 () 22µF Electrolytic capacitor, KME, 50V (2, 3) 0µF C6 00pF Ceramic capacitor, X7R, 500V, C206 C7 (*) 20µF Electrolytic capacitor, LXY, 35V C8 22nF Ceramic capacitor, X7R, 50V, C0805 C9 () 00nF Ceramic capacitor, X7R, 50V, C0805 C0 () nf Ceramic capacitor, X7R, 50V, C0805 C (2) 2.2µF Tantalum capacitor, size A, B4596E, 0V, 7.0R (3) 00nF Ceramic capacitor, X7R, 50V, C206 C2 () 00nF Ceramic capacitor, X7R, 50V, C0805 C3 nf Ceramic capacitor, class Y, WKP, 500V D S250 Rectifier bridge, 250 Vac, 0.5A, TO-269AA D2 (*) PKC-36 STMicroelectronics, diode, peak clamp, 700V,.5W D3 (*) LL448 Diode, SMD, 75V, D4 STPR20A STMicroelectronics, diode, fast recovery, 200V, A D5 (, 2) STPSL40A STMicroelectronics, diode, schottky, 40V, A (3) OR Resistor D6 ZMM8 Diode, zener, 8V, 0.5W D7 BAV03 Diode, 250V, D8 (2, 3) ZMM8 Diode, zener, 8V, 0.5W L 330µH Inductor, bobbin core, B7808-S334-J, 90mA, 6.4R Q () BC856B Bipolar transistor, PNP, 65V, 00mA, 330mW R 0Ω Resistor, wirewound, fusible, TK20 CRF 254-4, 3W, 5% R2 (*) 22Ω Resistor, R0805, 00V, 0.25W, % R3 00Ω Resistor, 200V, 0.25W, R206, % R4 22Ω Resistor, 00V, 0.25W, R206, % R5 () 4.7KΩ Resistor, 00V, 0.25W, R0805, % 3/29

4 Table 2. Bill Of Materials for all Variants of the Isolated Flyback Converter (continued) Ref. Qty Variant Value Description R6 (*) 24KΩ Resistor, R0805, 00V, 0.25W, % R7, R8 2 () 4.7KΩ Resistor, R0805, 00V, 0.25W, % R9 () KΩ Resistor, R0805, 00V, 0.25W, % R0 () 00Ω Resistor, R0805, 00V, 0.25W, % R () 0Ω Resistor, R206 R4 00Ω Resistor, R0805, 00V, 0.25W, % R5 () 4.7KΩ Resistor, R0805, 00V, 0.25W, % (2, 3) KΩ R6 0Ω Resistor, R206 R7 (2, 3) 0Ω Resistor, R206 R8 () 0KΩ Resistor, R0805, 00V, 0.25W, % T Transformer, ferrite Fi324, EF6/4.7 U VIPer2AS STMicroelectronics, Offline SMPS Primary IC U2 () TS243ILT STMicroelectronics, Shut Reference IC, SMD, 2.5V, ma...00ma, 360mW U3 (2) L493CD50 STMicroelectronics, voltage regulator, low drop, with inhibit U4 (3) L78M05CDT STMicroelectronics, positive voltage regulator U5 () SFH67A-3 Optocoupler, TRIOS, 5.3KV 4/29

5 Figure 2. Complete Schematic Diagram of the Isolated Flyback Converter (all variants) D4 +5V U4 L78M05CDT (3) +5V V~ CON L 2 N clamp L N R 0R 3W ~ + - ~ D S VAC 0.5A + L BC 330uH 90mA C 0uF 400V KMG + C2 4.7uF 400V KMG C3 nf 500V Y C6 00pF 500V D2 PKC-36 (*) R3 00R EF6 AL = 20nH Gap = 0.22mm TA 3.mH 60 turns 0.8 CuL TC 3uH (, 3) 6 turns (, 3) 24uH (2) 4 turns (2) 0.2 TEX-E TD 0uH (, 3) 9 turns (, 3) 5uH (2) turns (2) 0.35 TEX-E STPR20A 200V A C4 220uF 35V LXY (, 2) D5 STPSL40A (, 2) 40V A 0R (3) C3 20uF 35V LXY + + R4 22R R2 22R (*) R0 00R () D6 ZMM8 2 U2 TS243ILT () U5A SFH67A-3 () R8 4.7k () C9 22nF () R9 k () C0 nf () R6 24k (*) R7 4. 7k () +5V R 0R () R5 4.7k () 2 3 CON2 clamp VIN VOUT GND U3 L493CD50 (2) 8 VIN VOUT 4 5 NC INH GND GND2 GND3 GND C 2. 2uF (2) 0V Ta 00nF (3) Layout Hints: C5, C8 have to be close to VIPer2A U R7 0R (2, 3) D3 LL448 (*) P V3+ R4 Transformer: core connected to V+ Assembly options: (): +5V/500mA, +5V/ (2): +5V/250mA, +5V/ (3): +5V/60mA, +5V/ (*): not assembled R6 0R 4 C5 22uF () 0uF (2, 3) 50V 3 KME Q () BC856B U5B () SFH67A-3 R8 0k () 00R + C7 20uF 35V LXY (*) TB 39uH 34 turns 0.8 CuL VDD D7 Drain4 Drain3 Drain2 Drain Source2 Source 2 VDD FB VIPer2AS C8 22nF D8 ZMM8 (2, 3) R5 4.7k () k (2, 3) C2 00nF () BAV P2 V Transformer Design Since an insulation is required between primary and secondary side, the transformer construction is made to fulfil the safety requirement of EN60950 by using a triple isolated wire for the secondary windings. The physical appearance, dimensions, windings and pin arrangement can be seen in Figure 3. The switched "hot" end of the primary winding is arranged towards the auxiliary winding to avoid capacitive coupling of noise from primary to the ferrite core and reduce EMI. A single layer of Mylar tape is placed between primary and auxiliary winding to improve isolation, but is not needed for safety reasons. The basic parameters of the ferrite core selected from Vogt's ferrite materials and shapes can be seen in Table 3. The gap size was optimized to ensure appropriate current capability and inductance to fully exploit switching frequency and switch's peak current limit of the VIPer2AS to achieve maximum output power. An overview of the most important parameters for each winding can be found in Table 3. The table is valid for all variants. The only differentiation between variants is the number of turns for the secondary windings. The difference is indicated in "number of turns" column. Figure 3. Transformer Dimensions, Windings and Bottom View Pin Arrangement 5/29

6 Table 3. Transformer's Core Parameters Shape EF 6/4.7 Material Vogt Fi 324 Gap Size 0.22 (mm) Inductance Factor A L 20 (nh) Table 4. Transformer's Windings Parameters Order Start Pin End Pin No. of Turns Wire Diameter Wire (mm) Material Inductance CuLL 3.mH Mylar Tape CuLL 39µH TEX-E 3µH TEX-E 0µH 2..5 PCB Layout The PCB is designed as a single sided board made of FR-4 material with 35µm copper plating with solder and silk screen mask. The assembled board contains both SMD and through hole components. The board incorporates all variants of the converter. The outline dimensions are 59x30mm. Assembly top side (through-hole components) and solder bottom (SMD components) side can be seen in Figure 4 and Figure 5. Figure 4. Assembly Top (not in scale) Figure 5. Assembly Solder Side (not in scale) 6/29

7 The PCB layout of the copper connections is depicted in Figure 6. The holes for through-hole components are not visible in the picture. The physical appearance of the converter can be observed in Figure 7. Figure 6. PCB Layout (not in scale) Figure 7. Picture of the Converter 7/29

8 2..6 Evaluation and Measurements The output regulation characteristics measured on 5V output can be seen in Figure 8. It shows the voltage variation of the 5V output with different load applied to the 5V output. Figure 9 shows the same characteristic as Figure 8, but measured at 375VDC input voltage. Figure 8. Output Regulation Characteristics of 5V Output at 25VDC Input Voltage (Parameter is Load Current on 5V Output) Output Voltage [V] mA 40mA 60mA 80mA 00mA 20mA 40mA 60mA 80mA Output Current [A] Figure 9. Output Regulation Characteristics of 5V output at 375VDC Input Voltage (Parameter is Load Current on 5V Output) Output Voltage [V] mA 40mA 60mA 80mA 00mA 20mA 40mA 60mA 80mA Output Current [A] 8/29

9 Similarly Figure 0 shows the output regulation characteristics measured on 5V output when a different load current is applied to the 5V output. Figu.shows the same characteristic as Figure 0, but measured at 375VDC input voltage. Figure 0. Output Regulation Characteristics of 5V Output at 25VDC Input Voltage (Parameter is Load Current on 5V Output) Output Voltage [V] mA 00mA 50mA 250mA 300mA 350mA 400mA 450mA 500mA Output Current [A] Figure. Output Regulation Characteristics of 5V Output at 375VDC Input Voltage (Parameter is Load Current on 5V Output) Output Voltage [V] mA 00mA 50mA 250mA 300mA 350mA 400mA 450mA 500mA Output Current [A] 9/29

10 One of the most observed parameters when judging the converter performance is power efficiency. Figure 2 depicts the dependency of the efficiency on load applied to the 5V output (parameter is load current on 5V output). Similarly Figure 3 shows the dependency on the 5V output current (parameter is load current on 5V output). Figure 4 and Figure 5 show the same characteristics as Figure 2 and Figure 3 but measured at an input voltage of 375 VDC. Figure 2. Efficiency Variation with 5V Output Current at 25VDC Input Voltage (Parameter is Load Current on 5V Output) Efficiency [%] mA 40mA 60mA 80mA 00mA 20mA 40mA 60mA 80mA Output Current [ma] Figure 3. Efficiency Variation with 5V Output Current at 25VDC Input Voltage (Parameter is Load Current on 5V Output) Effici ency [%] mA 00mA 50mA 250mA 300mA 350mA 400mA 450mA 500mA Output Current [ma] 0/29

11 Figure 4. Efficiency Variation with 5V Output Current at 375VDC Input Voltage (Parameter is Load Current on 5V Output) Efficiency [%] mA 40mA 60mA 80mA 00mA 20mA 40mA 60mA 80mA Output Current [ma] Figure 5. Efficiency Variation with 5V Output Current at 375VDC Input Voltage (Parameter is Load Current on 5V Output) Efficiency [%] mA 00mA 50mA 250mA 300mA 350mA 400mA 450mA 500mA Output Current [ma] /29

12 Following pictures (Figure 6 to 25) show the most important voltage or current waveforms at different input and output conditions. Channel is the power MOSFET drain terminal voltage of the VIPer2. Channel 2 shows the drain current of the VIPer2. The purpose of those pictures is to demonstrate the skipping cycle function at light or no-load condition and cycle-by-cycle primary current limitation at output shorted condition. Figure 8. V in = 25VDC, Nominal Load Figure 6. V in = 25VDC, NO-Load Figure 9. V in = 375VDC, Nominal Load Figure 7. V in = 375VDC, No-Load 2/29

13 Figure 20. V in = 25VDC, 50% Load on Both Outputs Figure 23. V in = 25VDC, 5V Output Shorted 5V Output No-load Figure 2. V in = 375VDC, 50% Load on Both Outputs Figure 24. V in = 375VDC, 5V output shorted, 5V Output No-Load Figure 22. V in = 25VDC, 5V Output Shorted, 5V Output No-Load Figure 25. V in = 375VDC, 5V Output Shorted, 5V Output No-Load 3/29

14 The feedback loop stability and response to a load change are demonstrated from Figure 26 to 29. Figure 28. Load Transient Response, 50mA to 0.5A on 5V Output, 5V Output Unloaded, V in = 375VDC Figure 26. Load Transient Response, 50mA to 0.5A on 5V Output, 5V Output Unloaded, V in = 25VDC Figure 29. Load Transient Response, 50mA to 0.5A on 5V Output, 5V Output Nominal Load, V in = 375VDC Figure 27. Load Transient Response, 50mA to 0.5A on 5V Output, 5V Output Nominal Load, V in = 25VDC 4/29

15 Furthermore conducted emissions were measured in neutral and line wire using a peak and average detector. The measurements were performed at 230VAC input voltage and both outputs were fully loaded. The results can be seen in Figure 30 to 33. Figure 30. Phase L, Average Detector Figure 3. Phase L, Peak Detector 5/29

16 Figure 32. Phase N, Average Detector Figure 33. Phase N, Peak Detector 6/29

17 2.2 ISOLATED FLYBACK +5V/200MA, +5V/ 250MA (VARIANT 2) Table 5. Operating Conditions Input Voltage Range VAC Input Voltage Frequency Range 50/60 Hz Main Output 5V/ Second Output 5V/250mA Total Maximum Output Power 4.25W 2.2. Circuit Operation The schematic of the power supply can be seen in Figure 34. The major difference, when compared to variant, is in the feedback loop. The output voltages are regulated from the primary side by a simple circuit consisting of zener diode D8 a resistor R5. Since the primary regulation is not as precise as the secondary regulation, the 5V output has a linear post regulator U3. The linear regulator requires some input-to-output voltage difference to assure a minimum dropout voltage. For this reason the number of turns of secondary windings is slightly different compares to the variant. Figure 34. Schematic Diagram of Isolated Flyback Converter (Variant 2) 200V A STPR20A +5V V~ CON L 2 N clamp R 0R 3W ~ + - ~ D S VAC 0.5A L BC 330uH 90mA + C 0uF 400V KMG C3 nf 500V Y 00pF 500V + C2 4.7uF R3 400V KMG 00R EF6 AL = 20nH Gap = 0.22mm C6 TA 3.mH 60 turns 0.8 CuL D4 TC 24uH 4 turns 0.2 TEX-E C4 TD 220uF 5uH 35V turns LXY 0.35 TEX-E D5 C3 20uF 35V LXY + + R4 22R U3 L493CD50 8 VIN VOUT 4 D6 5 NC INH ZMM8 GND GND2 GND3 GND V + C 2.2uF 0V Ta CON2 2 3 clamp Layout Hints: C5, C8 have to be close to VIPer2A Assembly options: (2): +5V/, +5V/250mA Drain4 8 Drain3 7 Drain2 6 Drain 5 R6 0R So urce2 So urce 2 U VDD 4 FB 3 VIPer2AS C8 22nF STPSL40A 40V A R7 R4 0R 00R C5 D8 0uF + 50V KME ZMM8 R5 k D7 BAV TB 39uH 34 turns 0.8 CuL 7/29

18 2.3 ISOLATED FLYBACK +5V/200MA, +5V/60MA (VARIANT 3) Table 6. Operating Conditions Input Voltage Range VAC Input Voltage Frequency Range 50/60 Hz Main Output (regulated) 5V/ Second Output 5V/60mA Total Maximum Output Power 3.3W 2.3. Circuit Operation The schematic diagram is depicted in Figure 35 and is very similar to the schematic of variant 2. It only has one output rectifier diode and one output electrolytic capacitor. The 5V linear regulator is directly supplied from 5V output. Figure 35. Schematic Diagram of Isolated Flyback Converter (Variant 3) 200V A STPR20A +5V 5 D V~ CON L 2 N clamp R 0R 3W ~ + - ~ D S VAC 0.5A L + C 0uF 400V KMG BC 330uH 90mA C2 4.7uF 400V KMG + 00pF 500V C3 nf 500V Y R3 00R EF6 AL = 20nH Gap = 0.22mm C6 TA 3.mH 60 turns 0.8 CuL TC 3uH 6 turns 0.2 TEX-E C3 + 20uF TD 35V 0uH LXY 9 turns 0.35 TEX-E D5 U4 L78M05CDT VIN VOUT GND R4 22R D6 ZMM8 +5V C 00nF CON2 2 3 clamp 0R Layout Hints: C5, C8 have to be close to VIPer2A Assembly options: (3): +5V/, +5V/60mA R6 0R Drain4 8 Drain3 7 Drain2 6 Drain 5 So urce2 So urce 2 U VDD 4 FB 3 VIPer2AS R7 0R C5 0uF + 50V KME R5 C8 k 22nF D8 ZMM8 R4 00R D7 BAV TB 39uH 34 turns 0.8 CuL 8/29

19 The output regulation characteristics measured on 5V output can be seen in Figure 36. It shows the voltage variation of the 5V output when different load is applied to 5V output. Figure 37 shows the same characteristic as Figure 36 but measured at 375VDC input voltage. Figure 36. Output Regulation Characteristics of 5V Output at 25VDC Input Voltage (Parameter is Load Current on 5V Output) Output Voltage [V] mA 40mA 60mA 80mA 00mA 20mA 40mA 60mA 80mA Output Current [A] Figure 37. Output Regulation Characteristics of 5V Output at 375VDC Input Voltage (Parameter is Load Current on 5V Output) Output Voltage [V] mA 40mA 60mA 80mA 00mA 20mA 40mA 60mA 80mA Output Current [A] 9/29

20 Similarly Figure 38 shows the output regulation characteristics measured on 5V output when different load current applied to 5V output. Figure 39 shows the same characteristic as Figure 38 but measured at 375VDC input voltage. Figure 38. Output Regulation Characteristics of 5V Output at 25VDC Input Voltage (Parameter is Load Current on 5V Output) 6.5 Output Voltage [V] mA 00mA 50mA 250mA 300mA 350mA 400mA 450mA 500mA Output Current [A] Figure 39. Output Regulation Characteristics of 5V Output at 375VDC Input Voltage (Parameter is Load Current on 5V Output) 6.5 Output Voltage [V] mA 2mA 8mA 24mA 30mA 36mA 42mA 48mA 54mA 60mA Output Current [A] 20/29

21 Figure 40 depicts the dependency of the efficiency on load applied to the 5V output (parameter is load current on 5V output). Similarly Figure 4 shows the dependency on the 5V output current (parameter is load current on 5V output). Figure 42 and Figure 43 show the same characteristics as Figure and Figure 4 but measured at input voltage of 375 VDC. Figure 40. Efficiency Variation with 5V Output Current at 25VDC Input Voltage (Parameter is Load Current on 5V Output Efficiency [%] mA 40mA 60mA 80mA 00mA 20mA 40mA 60mA 80mA Output Current [ma] Figure 4. Efficiency Variation with 5V Output Current at 25VDC Input Voltage (Parameter is Load Current on 5V Output) Efficiency [%] mA 00mA 50mA 250mA 300mA 350mA 400mA 450mA 500mA Output Current [ma] 2/29

22 Figure 42. Efficiency Variation with 5V Output Current at 375VDC Input Voltage (Parameter is Load Current on 5V Output) Efficiency [%] mA 40mA 60mA 80mA 00mA 20mA 40mA 60mA 80mA Output Current [ma] Figure 43. Efficiency Variation with 5V Output Current at 375VDC Input Voltage (Parameter is Load Current on 5V Output) Efficiency [%] mA 00mA 50mA 250mA 300mA 350mA 400mA 450mA 500mA Output Current [ma] 22/29

23 Following pictures (Figure 44 to Figure 53) show the most important voltage or current waveforms at different input and output conditions. Channel is the power MOSFET drain terminal voltage of the VIPer2. Channel 2 shows the drain current of the VIPer2. Figure 46. V in = 25VDC, Nominal Load Figure 44. V in = 25VDC, No-Load Figure 47. V in = 375VDC, Nominal Load Figure 45. V in = 375VDC, No-Load Figure 48. V in = 25VDC, 50% Load on Both Outputs The purpose of these pictures is to demonstrate the skipping cycle function at light or no-load condition and cycle-by-cycle primary current limitation at output shorted condition. 23/29

24 Figure 49. V in = 375VDC, 50% Load on Both Outputs Figure 52. V in = 375VDC, 5V Output Shorted, 5V Output No-Load Figure 50. V in = 25VDC, 5V Output Shorted, 5V Output No-Load Figure 53. V in = 375VDC, 5V Output Shorted, 5V Output No-Load Figure 5. V in = 25VDC, 5V Output Shorted, 5v Output No-Load The feedback loop stability and response to load transients are demonstrated in Figure 54 to Figure /29

25 Figure 54. Load Transient Response, 20ma to 0.2a on 5v Output, 5v Output Unloaded, V in = 25vdc Figure 56. Load Transient Response, 20mA to 0.2A on 5V Output, 5V Output Unloaded, V in = 375VDC Figure 55. Load Transient Response, 20mA to 0.2A on 5V Output, 5V Output Loaded by 60mA, V in = 25VDC Figure 57. Load Transient Response, 20mA to 0.2A on 5V Output, 5V Output Loaded by 60mA, V in = 375VDC 25/29

26 Conducted emissions were measured in neutral and line wire using a peak or average detector. The measurements were performed at 230VAC input voltage and both outputs were fully loaded. The results can be seen in Figure 58 to Figure 6. Figure 58. Phase L, Average Detector Figure 59. Phase L, Peak Detector 26/29

27 Figure 60. Phase N, Average Detector Figure 6. Phase N, Peak Detector 27/29

28 3. CONCLUSION Several variants of the reference board based on an isolated flyback converter built with monolithic switcher VIPer2AS were presented. It was demonstrated, how the reference board can be easily switched between variants or options. Depicted output regulation, waveforms, overall converter efficiency characteristics and transient responses measured at different working conditions show good performance of the reference boards. Also, thanks to the presented PCB layout and EMI input filter, boards are EMI compliant with regards to the emissions as it was validated by presented EMI measurements. All boards also passed EMI surge and burst tests for power supply immunity against incoming noise from mains. 28/29

29 Information furnished is believed to be accurate and reliable. However, STMicroelectronics assumes no responsibility for the consequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of STMicroelectronics. Specifications mentioned in this publication are subject to change without notice. This publication supersedes and replaces all information previously supplied. STMicroelectronics products are not authorized for use as critical components in life support devices or systems without express written approval of STMicroelectronics. The ST logo is a registered trademark of STMicroelectronics. All other names are the property of their respective owners 2005 STMicroelectronics - All rights reserved STMicroelectronics group of companies Australia - Belgium - Brazil - Canada - China - Czech Republic - Finland - France - Germany - Hong Kong - India - Israel - Italy - Japan - Malaysia - Malta - Morocco - Singapore - Spain - Sweden - Switzerland - United Kingdom - United States of America 29/29