AND8474 Implementing a 310 W Power Supply with the NCP1027, NCP1910 and NCP4303 http://onsemi.com Prepared by: Patrick Wang and Thierry Sutto ON Semiconductor APPLICATION NOTE load and 230 Vac, this reference design achieves > 92% at 50% load and 115 Vac. This reference document provides a detailed view of the performance achieved with this design in terms of efficiency, performance, and other key parameters. In addition, a detailed list of the bill--off--materials (BOM) is also provided. The following document describes a switch mode power supply (SMPS) with 5 Vsb @ 2 A and 12 V @ 25 A output intended for use as part of an ATX power supply. The reference design circuit consists of a double sided 200 x 130 mm printed circuit board with a height of only 35 mm. An overview of the entire SMPS architecture is provided in Figure 1. Achieving a maximum efficiency of 94% at 50% EMI filtering + rectification Input 90 to 265 Vac L2 D1 M1 M3 L1 1 C3 M5 4 U5 C2 L3 M2 3 12Vout C6 C7 M4 C1 0 2 12V_RTN XFMR--TAP 2xNCP4303 Sync. Rect. 12V_FB NCP1910 CCM PFC + LLC ON/OFF 1 2 Aux_supply U4 0 SW1 Remote Control 2 0 D2 5Vstby C4 3 C5 5 Aux_supply 4 NCP1027 Flyback 1 5Vstby_RTN XFMR2 0 5Vstby_FB Figure 1. Demo Board Block Diagram Semiconductor Components Industries, LLC, 2010 November, 2010 -- Rev. 0 1 Publication Order Number: AND8474/D AND8474 Architecture Overview However, it is noted that it is not easy to determine at which bulk voltage to start up the LLC converter especially when the regulated bulk voltage is close to the peak of sinusoidal input. To ensure the operation of LLC converter, the start--up level of bulk voltage is usually designed at below the peak value of the sinusoidal input line. It has a risk that the bulk voltage at start--up phase might be too low to provide a smooth rising waveform on main output. Besides, if there is something wrong in the PFC stage, e.g. the driving resistor is broken; the LLC stage will still operate even when the input ac voltage is at high line. To avoid the above risk, NCP1910 uses an instinctive logic to control the operating of PFC stage and LLC stage: At start--up phase, LLC is inhibited until PFC regulates the bulk voltage. LLC can not work continuously if PFC does not regulate the bulk voltage. For the protections, there are two kinds of behavior: If the detected failure is not critical, the protection behavior of PFC or LLC does not influence or stop each other immediately. For example, when the brown--out block finds the bulk voltage is too low, it stops the LLC only, but does not stop PFC. Similarly, the line brown--out block stops the PFC and change the status of PGout signal as the ac input voltage is too low, but stops LLC only after a certain delay (tDEL2) instead of turning--off immediately, which ensures the correct turn--off sequence from falling of power good signal to loss of main output. If the failure is critical, then both PFC and LLC stop immediately. For example, when LLC faces a short circuit situation so that its current information is above latch--off level, both PFC and LLC stop together. Or in case that the PFC feedback loop is out of order so that bulk voltage is above the latch--off level, which is sensed on a dedicated pin (OVP2), then both PFC and LLC stop together. Let’s see an example mentioned above about what happens if PFC driver resistor is broken at high line, e.g. 265 Vac (Vpeak = 2 ⋅ 265 = 374 V). Usually the brown--out level of LLC converter is lower than 374 V, so the LLC will keep operating even when PFC driver resistor is broken. There is no critical concern in this situation but just lost of the PFC function. The electricity company may not be happy with this situation. To avoid this symptom, NCP1910 implements a so--called “PFC abnormal” feature by sensing the VCTRL (the output of PFC Operational Trans--conductance Amplifier). If VCTRL is out of its operating range for longer than 1.4 second typically, then PFC latches off. Because this situation is not critical to LLC, LLC doesn’t stop immediately. Instead, it stops after 5 ms typically (tDEL2). Thanks to the combination of the two control cells in NCP1910, the FB pin which represents the information of bulk voltage is also used as the input of comparators to adjust Most of today’s computing applications like ATX PC use 12 V as the main power rail. This voltage is then further decreased to 5 V and 3.3 V by dc--dc step down converters. Because nearly all power passes through the 12 V output, it is critical that the efficiency of the main power stage is optimized. Most designs today utilize an LLC topology for the power stage to provide high efficiency at a reasonable cost. The LLC power stage provides inherently high efficiency results thanks to zero voltage switching (ZVS) on the primary side and zero current switching (ZCS) on the secondary side. Efficiency however decreases for higher output currents as the secondary RMS current reaches a high level. The solution for these losses on the secondary side is to use synchronous rectification instead of conventional rectifiers (Schottky diode). The circuit utilizes a Continuous Conduction Mode (CCM) PFC to provide a well regulated PFC output voltage that allows optimization of the downstream converter, and also to minimize the input current ripple. The ATX kind of power supply needs a remote signal to enable/disable the main output and a power good signal to inform the system for start--up or shut--down. In this demo board, For the remote on/off, NCP1910 reserves a dedicated on/off pin to reduce the surrounding circuits. In the demo board, a switch is used to control the on/off pin and hence the operation of main power. A green LED (LED1) indicates the operation status. As for the power good signal in the ATX power supply, it is usually managed by a supervisory chip at the secondary side to control the power good timing and also the Over--Current Protection (OCP), Over--Voltage Protection (OVP), Under--Voltage Protection (UVP) on the outputs. It usually needs an enable signal from primary side or from the winding of transformer to start the timing processing and protection features. NCP1910 provides a power good output signal (PGout pin) to instruct this enable signal through opto--coupler. In the demo board, a green LED (LED2) is used to indicate the power good output pin status. Housed in a SO--24WB package, the NCP1910 combines not only the control core of CCM PFC and LLC, but also the handshakes among PFC, LLC, and the secondary side. These handshakes signals include the remote on/off and the PGout pin mentioned above; and also internal signals to monitor the status of PFC and LLC converter to have correct operation and protection procedures. Rather than jumping directly to the board description, it is interesting to enumerate the various features we have packed in this part. To have a correct start--up on LLC converter, it is preferred to let PFC operate and regulate the bulk voltage before LLC starts operation. The most popular method on the application with the discrete controllers is to use a high voltage sensing rail to monitor the bulk voltage, so--called brown--out feature, to enable or stop the operation of LLC. http://onsemi.com 2 AND8474 the secondary side. The NCP4303A SR controller is used to achieve accurate turn--on and turn--off of the SR MOSFETs. The standby power supply (5 Vsb) is requested to work alone without PFC operating, i.e. the PFC is off at remote off mode. A flyback converter driven by NCP1027 is chosen. In summary, the architecture selected on this demo board allows system optimization so that the maximum efficiency is achieved without significantly increasing the component cost and circuit complexity. bulk voltage level to deliver the power good output signal and brown--out of LLC. The benefit of this feature is that it saves the extra high voltage sensing rails and provides accurate control for power good and brown--out level for LLC. The efficiency requirement is more challenging at low line compared to high line because of the conduction losses on EMI and PFC stage, e.g. the current sense resistor on the PFC stage. To reduce the power losses on this PFC current sensing resistor, the easiest way is to reduce its resistance. However, it comes with a higher peak current limitation level. The current sense scheme of PFC section in NCP1910 solves this problem. It provides a possibility to reduce the conduction losses on the current sense resistor and also keeps the same wanted peak current limitation level. The current source inside the CS pin maintains the CS pin at zero voltage. One can reduce the offset resistor (R17 + R20 in Figure 2) to reduce the maximum voltage drop and hence the power losses on current sense resistor (R12 // R13) depending on the acceptable noise immunity level. At the 90 Vac input and 310 W application, 0.8 W on the sense resistor could be saved by changing the sense resistor from 0.1 to 0.05 , R17//R20 could be adjusted to keep the same current peak level. The most important is that the saving losses is free. PFC light load efficiency has been improved with the frequency foldback of the NCP1910. When the power decreases below an externally fixed power value, the switching frequency decreases to 38 kHz typically. The LLC cell of NCP1910 can operate to a frequency up to 500 kHz. To avoid any frequency runaway in light load conditions but also to improve the standby power consumption, the NCP1910B welcomes a skip input (Skip pin) which permanently observes the opto--coupler collector. If this pin senses a low voltage, it cuts the LLC output pulses until the collector goes up again. The NCP1910A does not offer the skip capability and routes the analog ground on pin 16 instead. NCP1910 combines plenty of protection features for the robustness, which is detailed in datasheet. Together with these built--in handshakes and protections, the surrounding components are saved. To maximize efficiency of the LLC power stage, Synchronous Rectification (SR) has been implemented on DEMO BOARD SPECIFICATION Description Value Unit 90 -- 265 Vrms 310 W Minimum Output Load Current(s) 0 Adc Number of Outputs 2 -- Input voltage Range Output Power Nominal Output Voltage Output1: 12 V Output2: 5 Vstby 12 5% 5 5% Vdc Output Current Output1 (min/max) Output2 (min/max) 0/25 0/2 Adc Maximum startup time < 300 ms Standby Power (NCP1910 disabled) < 0.3 W Efficiency (115 Vrms and 230 Vrms) 10% Load 20% load 50% load 100% load 80 88 92 88 % Maximum Transient Output Power 150 W Hold up time (50% of full load) 17 ms Let’s focus more on the design of NCP1910. An application note which details the design steps, equations and tips will be published later on. Before that, an Excel based worksheet for calculation of the surrounding components of NCP1910 is provided on the web site. The process is to fill in the needed information, such as the power supply specification, the wished brown out level, the minimum and maximum frequency of LLC converter etc. And then it is done. http://onsemi.com 3 R14 0.1 uF/X2 C23 R70 150k R66 150k R71 150k R81 150k T POINT A T POINT A T POINT A TP4 TP2 F1 T5A/250V T POINT A R77 150k R72 150k 0.47 uF/X2 C28 CMT1-2.1-4L L6 AC inlet J2 0.47uF/X2 CMT1-2.1-4L L4 TP3 2.2nF/Y 1 B72210P2301K101 C14 2.2nF/Y 1 C16 C8 2.2nF/Y 1 R1 1M8 R2 3M R3 3M SK573-100 HS1 C46 1nF R49 24k R11 2M2 R6 1M5 C9 NTCin R38 24k R10 2M2 R7 1M5 13k SK573-100 1uF C47 43k R40 C44 100nF Q7 BC858B D6 MMSD4148 S236-10R RT1 RL1 G6DS-1A-H 12VDC R46 DRV Rsense R13 0R1 R12 0R1 Heatsink for DB1, PFC & LLC: C38 1nF 100nF C33 R33 10R R32 10R 220nF C42 C40 100nF 100nF C45 R47 430R R37 22k R27 47k 120k R42 R41 33k 1 C39 NC Relay Vcc 12 11 10 9 8 7 6 5 4 3 2 Vref LBO VM Vctrl FB OVP2 GND_LLC DRV VCC ML Bridge MH Vboot R26 10R R29 47k Q1 R28 47k Q2 SK573-50 HS2 C35 100nF 8.2k R24 Fold CS CS/FF Skip/GND_PFC PG_adj Vref BO_adj ON/OFF PGout Rt SS U4 NCP1910B R25 10R C18 C11 Vref R34 10k 470nF D11 MMSD4148 R39 0R 18k R48 ON/OFF PGout NTCout C41 10nF NC C37 C5 R43 20k IPP50R250CP Q3 120uF/450V 650 uH 120uF/450V QH03TZ600 D7 R52 1nF C31 C29 SK573 - 50 mm 1nF 100nF C30 330R 10R R18 NC R45 1.8k 510R 24k R17 1k R19 24k R51 1k R53 R20 DRV C32 100nF L1 67uH R44 D1 MUR160 MMSD4148 D8 MMSD4148 220pF/630Vdc D9 Heatsink for sync rect: 1.2k C7 15nF/630V D10 C48 C6 15nF/630V MURS160 R22 13 14 15 16 17 18 19 20 22 23 24 STP12NM50FP 1N5408 D3 STP12NM50FP MURS160 L2 12 11 10 9 8 7 VCC C54 3.9nF R75 27R Rsense Q6 BC848B VCC C43 100nF ? 4.7uF/25V C1 3k R21 6 1 T2 R74 27R 1 L7 1 L8 Q5 Q4 Q8 BC848B ON/OFF PGout Vref ISO4 SFH6156-2 Relay C49 1nF R76 27R R73 27R IRFB3206 IRFB3206 C53 3.9nF R16 47k R15 47k NC C51 ISO3 SFH6156-2 R50 1k U3 TL431 5.6k R62 NC R69 R82 22R R80 22R 10k C57 R78 0R 1k 30k 24k C52 22nF C21 1k 30k 24k 100nF R54 R63 8.2k R89 R86 R85 R90 R84 R83 C56 100nF R79 0R C20 1uF 1 2 3 4 C55 1uF 1 2 3 4 C58 R60 1k G G 10R R68 C24 DRV GND COMP CS DRV GND COMP CS house-keeping 1k SW1 SW LED1 Green LED R57 LED2 Green LED 510R 5.1k C25 PGI for R65 8.2k R56 C22 Vcc MIN_TOFF MIN_TON TRIG U5 NCP4303A R87 0R Vcc MIN_TOFF MIN_TON TRIG U6 NCP4303A R88 0R R64 12k R67 ISO1 SFH6156-2 1000uF/16V C13 TP1 NTCin N1L 1000uF/16V NTCout N 1000uF/16V DB1 GBU8J 8A 600V G 1000uF/16V Vb 1000uF/16V V+ 3 C19 8 7 6 5 8 7 6 5 0.6u L5 (5V to turn on) ON/OFF Signal 1000uF/16V 1uF/275Vac 3 4 t Figure 2. Main Application Schematic PFC and LLC 2 http://onsemi.com 2 N C27 P Vout J4 12V_out 12V_RTN J3 12V @ 24A 5VSTBY _OUT 470u/16V D5 AND8474 AND8474 C26 2.2nF/Y 1 10 Vb R8 47R T1 2 1 sec C3 10nF 5VSTBY _OUT 2.2uH MBRD835L D2 D1N4937 R9 150k L3 D12 dr 6 C15 1500uF/10V 9 VCC J1 C12 1500uF/10V 2 1 C17 220uF/10V C4 100uF/16V D4 D1N4937 R4 3M aux 7 5Vstby @ 2A 5 4 XFMR2 R23 1k U1 NCP1027 R5 2M 1 2 3 4 C36 2.2uF R31 27k C2 10uF/10V R30 78k R36 560k Vcc GND R Comp OPP R59 100R 8 BO FB Drain R61 10k 7 5 R58 1k C50 ISO2 SFH6156-2 100nF C34 2.2nF R35 47k C10 1uF/10V U2 TL431 R55 10k Figure 3. Application Schematic Standby Power Supply Table 1. BILL OF MATERIAL Qty Ref Part 1 C1 4.7 uF / 25 V Part Number Manufacturer 1 C2 10 uF / 10 V 1 C3 10nF 1 C4 100 uF / 16 V 1 C5 470 nF 2 C6, C7 4 C8, C13, C16, C26 15 nF / 630 V B32602L http://www.epcos.com 2.2 nF / Y1 B32021 http://www.epcos.com 1 C9 1 uF / 275 Vac B32672L http://www.epcos.com 1 C10 1 uF / 10 V 2 C11, C18 120 uF / 450 V B43601 http://www.epcos.com 2 C12, C15 1500 uF / 10 V FM series http://www.panasonic.com/industrial/electronic --components/ 1 C14 0.47 uF / X2 B32923 http://www.epcos.com 1 C17 220 uF / 10 V FM series http://www.panasonic.com/industrial/electronic --components/ 6 C19, C20, C21, C22, C24, C25 1000 uF / 16 V FM series http://www.panasonic.com/industrial/electronic --components/ 1 C23 0.1 uF / X2 B32922 http://www.epcos.com 1 C27 470u / 16 V FM series http://www.panasonic.com/industrial/electronic --components/ 1 C28 0.47 uF / X2 B32922 http://www.epcos.com 5 C29, C31, C38, C46, C49 1 nF http://onsemi.com 5 AND8474 Table 1. BILL OF MATERIAL Qty Ref Part Part Number Manufacturer 11 C30, C32, C33, C35, C40, C43, C44, C45, C50, C56, C57 100 nF 1 C34 2.2 nF 1 C36 2.2 uF 5 C37, C39, R45, C51, R69 NC 1 C41 10 nF 1 C42 220 nF 3 C47, C55, C58 1 uF 1 C48 220 pF / 630 Vdc 1 C52 22 nF 2 C53, C54 3.9 nF 1 DB1 GBU8J 8A 600 V http://www.fairchildsemi.com/ 1 D1 MUR160 http://www.onsemi.com 2 D2, D4 D1N4937 http://www.onsemi.com 1 D3 QH03TZ600 http://www.qspeed.com/ 1 D5 1N5408 http://www.onsemi.com 4 D6, D8, D9, D11 MMSD4148 http://www.onsemi.com 2 D7, D10 MURS160 http://www.onsemi.com 1 D12 MBRD835L http://www.onsemi.com http://www.epcos.com 1 F1 T5A / 250V 1 HS1 SK573--100 SK573--100 http://www.fischerelektronik.de 1 HS2 SK573--50 SK573--50 http://www.fischerelektronik.de 4 ISO1, ISO2, ISO3, ISO4 SFH6156--2 1 J1 HEADER 2 1 J2 AC inlet 1 J3 12 V_RTN 1 J4 12 V_out 2 LED1, LED2 Green LED 1 L1 67 uH 17462--LLC4 http://cmetransformateur.com/index.html 1 L2 650 uH QP--3325V http://www.yujingtech.com.tw/ 1 L3 2.2 uH 2 L4, L6 CMT1--2.1--4L CMT1--2.1--4L http://www.coilcraft.com 1 L5 0.6u http://www.vishay.com/ 2 L7, L8 1 2 Q1, Q2 STP12NM50FP http://www.st.com/ 1 Q3 IPP50R250CP http://www.infineon.com 2 Q4, Q5 IRFB3206 http://www.irf.com 2 Q6, Q8 BC848B http://www.onsemi.com 1 Q7 BC858B http://www.onsemi.com http://onsemi.com 6 AND8474 Table 1. BILL OF MATERIAL Qty Ref Part Part Number Manufacturer 1 RL1 G6DS--1A--H 12 VDC G6DS--1A--H 12VDC http://www.omron.com/ 1 RT1 S236--10R S236 http://www.epcos.com 1 R1 1M8 3 R2, R3, R4 3M 1 R5 2M 2 R6, R7 1M5 1 R8 47R 1 R9 150k 2 R10, R11 2M2 2 R12, R13 0R1 LVR03R1000FE12 http://www.vishay.com/ 1 R14 B72210P2301K101 B72210 http://www.epcos.com 2 R15, R16 47k 1 R17 330R 6 R18, R25, R26, R32, R33, R68 10R 9 R19, R23, R50, R51, R57, R58, R60, R89, R90 1k 1 R20 1.8k 1 R21 3k 1 R22 1.2k 3 R24, R63, R64 8.2k 4 R27, R28, R29, R35 47k 1 R30 78k 1 R31 27k 4 R34, R54, R55, R61 10k 1 R36 560k 1 R37 22k 6 R38, R49, R52, R53, R83, R85 24k 5 R39, R78, R79, R87, R88 0R 1 R40 43k 1 R41 33k 1 R42 120k 1 R43 36k 1 R44 750R 1 R46 13k 1 R47 430R 1 R48 18k 1 R56 510R 1 R59 100R http://onsemi.com 7 AND8474 Table 1. BILL OF MATERIAL Qty Ref Part Part Number Manufacturer 1 R62 5.6k 1 R65 5.1k 6 R66, R70, R71, R72, R77, R81 150k 1 R67 12k 4 R73, R74, R75, R76 27R 2 R80, R82 22R 2 R84, R86 30k 1 SW1 SW 4 TP1, TP2, TP3, TP4 T POINT A 1 T1 17437B http://cmetransformateur.com/index.html 1 T2 17459--LLC4 http://cmetransformateur.com/index.html 1 U1 NCP1027 http://www.onsemi.com 2 U2, U3 TL431 http://www.onsemi.com 1 U4 NCP1910B http://www.onsemi.com 2 U5, U6 NCP4303A http://www.onsemi.com GENERAL BEHAVIOR Figure 4. Component Placement (Component Side) http://onsemi.com 8 AND8474 Figure 5. Component Placement (Solder Side) Figure 6. PCB Layout (Component Side) http://onsemi.com 9 AND8474 Figure 7. PCB Layout (Solder Side) http://onsemi.com 10 AND8474 Efficiency results: Figure 8 illustrates the efficiency of the demonstration board when the standby power supply is unloaded at different output loads and different input voltages. Also the Climate Savers Computing Initiative (CSC) Silver and Gold levels have been drawn for reference. The efficiency of the board should be above of the following Silver or Gold levels for the two inputs voltage: 115 Vrms and 130 Vrms. In order to validate the Gold level of the demonstration board, the input voltage has been lowered to 100 Vrms, even with this low input voltage the demo board still pass the Gold level. Figure 8. Efficiency vs. Output Power at Different Input Voltage Figure 9. Power Factor vs. Output Power at Different Input Voltage http://onsemi.com 11 AND8474 Typical Waveforms: PFC section: Input voltage and current waveforms The following figures illustrate the input current and voltage delivered to the power supply (Vac and Iac) at different output loads (full load, 50% and 20% load) and two different input mains (115 Vac and 230 Vac). Input voltage Vac (100 V/div) Input current Iac (2 A/div) Time (4 ms/div) Figure 10. Vac = 115 Vac, Pin = 332 W, Vout = 12 V, Iout = 25 A, PF = 0.982, THD = 9.96% Input voltage Vac (100 V/div) Input current Iac (2 A/div) Time (4 ms/div) Figure 11. Vac = 115 Vac, Pin = 163 W, Vout = 12 V, Iout = 12.5 A, PF = 0.978, THD = 11.59% http://onsemi.com 12 AND8474 Input voltage Vac (100 V/div) Input current Iac (2 A/div) Time (4 ms/div) Figure 12. Vac = 115 Vac, Pin = 65.5 W, Vout = 12 V, Iout = 5 A, PF = 0.972, THD = 12.8% Input voltage Vac (200 V/div) Input current Iac (1 A/div) Time (4 ms/div) Figure 13. Vac = 230 Vac, Pin = 324 W, Vout = 12 V, Iout = 25 A, PF = 0.979, THD = 10.06% http://onsemi.com 13 AND8474 Input voltage Vac (200 V/div) Input current Iac (1 A/div) Time (4 ms/div) Figure 14. Vac = 230 Vac, Pin = 160 W, Vout = 12 V, Iout = 12.5 A, PF = 0.957, THD = 10.75% Input voltage Vac (200 V/div) Input current Iac (0.5 A/div) Time (4 ms/div) Figure 15. Vac = 230 Vac, Pin = 64.9 W, Vout = 12 V, Iout = 5 A, PF = 0.858, THD = 14.45% http://onsemi.com 14 AND8474 Soft--Start The two following curves illustrate the PFC’s soft-start at 115 Vac and 230 Vac input line voltage. Bulk voltage (200 V/div) Input current Iac (5 A/div) Vctrl pin (2 V/div) PFC_DRV (10 V/div) Time (20 ms/div) Figure 16. Soft--Start @ 115 V & Iout = 25 A Bulk voltage (200 V/div) Input current Iac (5 A/div) Vctrl pin (2 V/div) PFC_DRV (10 V/div) Time (20 ms/div) Figure 17. Soft--Start @ 230 V & Iout = 25 A. http://onsemi.com 15 AND8474 Line Brown Out Test: Input line voltage has been increased then decreased in order to test the brown out level. Figue 18 illustrates the start--up and shut down of the power supply when the input line voltage is varying from 60 Vac to 115 Vac and respectively from 115 Vac to 60 Vac. Bulk voltage (200 V/div) Input current Iac (5 A/div) Input Voltage (100 V/div) Time (1 s/div) Figure 18. Line Brown Out Test http://onsemi.com 16 AND8474 As depicted by the following figure, a zoom-in of the previous figure allows to measure accurately the bulk on level of the brown-out. Bulk voltage (200 V/div) Input current Iac (5 A/div) Input Voltage (100 V/div) Vbulk_ON = 124 Vpk = 88 Vrms Time (100 ms/div) Figure 19. Line Brown Out Test: Vbulk_ON Here after is a zoom-in on the shut down when the bulk off level is reached. Vbulk_OFF = 110 Vpk = 78 Vrms Bulk voltage (200 V/div) Input current Iac (5 A/div) Input Voltage (100 V/div) Time (100 ms/div) Figure 20. Line Brown Out Test: Vbulk_OFF Figure 21 illustrates a 50% line sag @ 230 Vac, there is no disruption on 12 V output. The output drops only by 5.3% (640 mV). http://onsemi.com 17 AND8474 Bulk voltage (200 V/div) 12 V output (2 V/div) Input current Iac (5 A/div) Input Voltage (200 V/div) Time (40 ms/div) Figure 21. Input Voltage Changing from 230 Vac to 115 Vac Transient Load The following figures illustrate the power supply stability when a step load output of 50% is applied. The step load has been applied with the following conditions: Vac = 115 Vac @ 60 Hz. Step load from 12.5 A to 25 A, with a 1 A/ms slope and 2 ms period. Figure 22 shows a step load response of 435 mV, or 3.6% of the 12 V output voltage. 12 V output (200 mV/div, Ac coupling) ΔV = 870 mV ΔV = 350 mV Time (400 s/div) Figure 22. Step Load Response Between 50% & 100% http://onsemi.com 18 AND8474 Output step load response illustrated with Figure 22 shows the step load response due to the closed loop regulation of the LLC added by spike due to the LC output switching filter. If L5 from the output filter is shorted, in that case the spike when the step load is applied disappears: Figure 23 illustrates the step load response of the LLC converter itself. However as the LC output switching frequency filter is now shorted the ripple noise due to the LLC switching frequency is bigger than the one in Figure 22. Moreover a short calculation shows that the drop at the beginning of step load is mainly due to L5. The voltage drop across L5 can be expressed as follow (the drop due to its ESR is not taken into account in this calculation): VL = L5 5 ΔI Δt (eq. 1) Where: L5 = 0.6 mH, ΔI = 12.5 A, Δt = 12.5 ms (slope of step load 1 A/ms) V L = 0.6m 5 12.5 = 0.6 V 12.5m (eq. 2) The difference between the drop measured and the drop calculated can be explained as follow: The step load is partially filtered by the output capacitor of the LC, thus the slope and ΔI can be a little bit smaller compare to the calculation. As L5 = 0.6 mH with 20% L5-20%=0.48 mH, the new drop will be 480 mV, thus L5 should be probably closer to its minimum value than its typical value. 12 V output (200 mV/div, Ac coupling) ΔV = 350 mV Time (400 s/div) Figure 23. Step Load Response Between 50% & 100%, when L5 is Shorted ON Semiconductor and are registered trademarks of Semiconductor Components Industries, LLC (SCILLC). SCILLC reserves the right to make changes without further notice to any products herein. SCILLC makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does SCILLC assume any liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without limitation special, consequential or incidental damages. “Typical” parameters which may be provided in SCILLC data sheets and/or specifications can and do vary in different applications and actual performance may vary over time. All operating parameters, including “Typicals” must be validated for each customer application by customer’s technical experts. SCILLC does not convey any license under its patent rights nor the rights of others. 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