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AND8394/D High Efficiency, Single Stage, Isolated Power Factor Corrected Power Supply Drivers Telecom Power
Prepared Frank Cathell
Introduction
This application note describes relatively novel simple produce off-line, power factor corrected higher output power supply using isolated, single stage conversion topology. power topology essentially buck-boost derived flyback converter operating continuous conduction mode (CCM) utilizing Semiconductor's NCP1652A controller which designed specifically this implementation. power supply described this application note Vdc, supply with universal input intended general purpose supplies, telecom distributed power "front-ends" constant voltage drivers such those used area lighting distributed lighting applications such refrigerator case lighting cove lighting. Efficiencies approaching were achieved with
power factor exceeding 0.95 most typical loads. supply includes overcurrent protection, overvoltage protection, brownout detection, input filter.
Background
Applications that require isolated, regulated output voltage along with input power factor correction typically involve stage conversion process depicted Figure This scheme composed input boost power factor corrector stage which converts pre-regulates input line into bus. This then provides voltage conventional dc-to-dc converter which appropriate topology. lower power applications less, this usually flyback converter.
input Filter Boost
Main Converter
output
Figure Conventional 2-Stage Conversion
With minor performance compromises, simpler technique used which power factor main converter sections combined into conversion stage. This significant advantages eliminates need bulky boost inductor, High Voltage MOSFET, power rectifier bulk capacitor. This illustrated Figure
input Filter Main Converter output
difference here that flyback conversion stage only handles voltage regulation input output isolation functions, provides power factor correction well. circuit essentially functions conventional converter with output being derived from secondary winding what would boost choke "normal" type non-isolated circuit. input converter 100/120 haversine instead pure voltage because normal input "bulk" capacitor following bridge rectifier reduced value microfarad less. full schematic single stage converter shown Figure
Figure Single Stage Conversion with NCP1652A
Semiconductor Components Industries, LLC, 2010
January, 2010 Rev.
Publication Order Number: AND8394/D
AND8394/D
100V
100,
102k
3.3uH
680uF,
(24V) MMSZ5252B
1/2W
3.3k
MSR860G
TL431A
100, 1/2W
2.7k
SFH615A-4
100V
5.6k
100nF 400V
MURS 160T
0.5W
2.2nF Notes: Crossed schematic lines connected. Heavy lines indicate power traces/planes. Z2/D9 optional (not used). Coilcraft BU10-1012R2B equivalent. Coilcraft P3221-AL equivalent. Coilcraft RFB0807-3R3L equivalent. will require small heatsinks. NCP1652A Power Supply Out, 90-265 Input (Rev MMSZ 5248B
MURS 160T
470uF
76.8k 0.1uF
MMSD 4148T
560k 0.5W
MRA4007T 22uF 450V 1/2W MMSD 4148T MMSZ 5252B 2.2k 30.1K 470pF 8.6k 4.7uF 7.32k 49.9k
MRA4007T
100uF
NCP1652
1.5KE440A 1N5406
365k
365k
0.1uF 600V
100k 33nF
0.47
365k
0.47
30.1k
332k
2.5A
0.5W
680pF
Figure Single Stage Converter Schematic
Single Stage Converter Characteristics
single stage, isolated converter derived from conventional buck-boost flyback topology. operational mode discontinuous conduction mode (DCM), critical conduction mode (CRM), continuous mode (CCM). While most common operational mode lower power circuits CRM, offers significant advantages applications that require fixed frequency operation with output voltages higher where synchronous rectification yields marginal efficiency improvements. CCM, peak MOSFET current significantly less than resulting lower switching losses, particularly power levels above
watts. also reduces high frequency output capacitor ripple current thus improving overall power supply reliability. NCP1652A controller designed particularly operation also provides second gate drive output implementation active clamp snubber higher power applications where voltage spikes caused flyback transformer's leakage inductance energy become significant issue. adapter circuit Figure achieved average efficiency approaching typical operation loads. flyback transformer designed effectively operate "deep" with relatively magnetizing current component (see Figure transformer design details).
10nF
AND8394/D
This resulted significantly reduced switching losses MOSFET over similar based design. single stage conversion process, regardless operational mode, several compromises over traditional 2-stage conversion scheme Figure They follows: with power factor corrector circuit, gain bandwidth control loop very low, typically range. This necessary, otherwise control loop would attempt regulate 100/120 line variations input this would result very poor power factor. consequence bandwidth, transient response load step changes will poor although regulation will excellent. most applications where point-of-load regulation (POL) utilized and/or load constant (e.g. load), slow transient response inconsequential. Figure shows output voltage profile supply turn-on with load with full load indicating controlled voltage rise with overshoot that sometimes typical with slow control loops. Because loop cannot regulate away 100/120 line ripple, will appear ripple component output. this circuit, output ripple order output voltage full load using with three output capacitors (see Figure Additional output capacitance will reduce this further. Again, most analog applications, this magnitude ripple should problem. lack large input bulk capacitor (C3), which would preclude high power factor, converter significant inherent hold-up time other than that provided stored energy output capacitors. Long hold time typically requirement power supply. power factor single stage converter tends degrade with increasing line decreasing load factors related D/(1-D) transfer function operation, however, most typical line load conditions will above 0.95. Despite these tradeoffs, single stage, isolated converter efficient very cost effective solution many applications where load relatively constant and/or point load (POL) regulators used downstream.
Circuit Technical Information
compensation operation adjusted depending primary inductance level transformer magnetizing ramp. switching frequency approximately with should adequate most applications. R16, R17, form simple circuit (optional) that monitors derived from T1's auxiliary winding. Since this voltage will track output voltage, provides simple primary side means sensing. form startup circuit NCP1652A which uses peak detector sample input haversine. This circuit, along with optional also doubles transient suppression circuit event short duration, high amplitude line transients that input capacitor would unable suppress. Input filter design: filter consists stages off-the-shelf common mode inductors which manufactured Coilcraft. common mode inductors have high leakage inductance single inductor used both common mode differential mode filtering. differential pass filter formed with leakage inductance capacitors from line-to-line. first stage filtering with second stage with leakage inductance leakage inductance
L3C18 L2C17 0.47 0.47
(eq.
59.97
(eq.
49.52
When testing accordance with 61000-4-6 limits (0.15 MHz) there should least attenuation switching frequency with these filter component values. input side filter fuse, safety. fuse rated amps continuous current, where average input current watts output
inLL 0.88 1.61 (eq.
NCP1652A components selection: logic level circuit components immediately associated with NCP1652A shown Figure schematic should work well with just about design implementation. Changes different output voltages involve modifying voltage sense divider TL431 (R29, R30. Zener resistor will required output voltages over value will determine peak limit MOSFET current sequential maximum output current. sets ramp
Where estimated efficiency (0.88) input line voltage full wave rectified there small bulk film capacitor (C3) across output bridge rectifiers (D1, D4). capacitor there decouple high frequency switching provide impedance source flyback converter. typical range capacitor this application, capacitor selected minimize residual power factor effects light load. Flyback Transformer Design: transformer design single stage converter more complex than standard flyback converter requires iterative process, especially when operation continuous conduction mode. There several ways mathematically approach this, however, treating transformer energy storage
AND8394/D
choke initially probably most straight forward way. Achieving correct design first largely matter experience with realizing what core volumes structures will support desired power level accommodate necessary coil turns. PQ3230 ferrite core chosen this design based previous experience following facts: core fairly large cross sectional area parameter (Ae) overall volume. This will minimize primary turns which contribute unwanted leakage inductance. shape core also good shielding effect radiated emissions, particularly required core entirely center pole. core window area good length width aspect ratio which helps minimize turn layers thus reduce leakage inductance magnetic flux proximity effects. minimal leakage inductance, this core will accommodate "sandwiched" secondary winding configuration where secondary between primary windings which connected series. Since peak primary current inductor will determine output power, peak magnitude current obtained from following relationship: Pout (min) ton( max) Where estimated efficiency, switching frequency, Vin(min) minimum average input voltage lowest line voltage, ton(max) maximum time. This results value W)/(0.88 70,000 (pk) Note that average line voltage used value Vac) line. This results from fact that input 100/120 haversine energy storage will function average voltage rms. Now, wire sizing purposes need know value this peak primary current. assume average duty cycle input assume almost rectangular waveform (the magnetizing component will actually about peak, this should give worst case estimate), value switching frequency component pure input would
0.707
(eq.
minimum primary inductance required given following: Lmin (min) ton( max) (120 ms)/ Where line value peak input voltage 1.414). make assumption: order most typical loading supply, let's double this inductance value minimum number primary turns required this core calculated:
(eq.
2800
must divide this 0.707 again account fact that input converter 100/120 haversine envelope pure This results primary current about Looking wire tables effectively choose magnet wire primary since will handle this current should have minimal skin effect loss kHz.
Where peak current rounded amps maximum flux density (Bmax) chosen kilogauss give saturation safety margin over-current conditions. Noting that PQ3230 bobbin winding width PQ3230 core about 0.73 inches, comfortably about turns number wire (dia. 0.022") layer bobbin total turns entire series primary, turns total good number with. next step will decide primary secondary turns ratio. This will determine reflected flyback voltage MOSFET also peak reverse voltage seen output rectifier Let's 2.5:1 where secondary will have turns (120 divided dc.) With this selection comfortably turns wound over layer with margins handle secondary current which will about worst case. reflected primary flyback voltage maximum output diode voltage will occur high line. Let's assume input voltage which translates peak voltage Vdc. reflected flyback voltage will peak secondary voltage plus output rectifier forward drop times turns ratio: Vflyback Adding this peak primary voltage gives plus leakage inductance spike which will probably order selected MOSFET should adequate this. primary bypassed with voltage clamping snubber network clamp residual spikes caused T1's leakage inductance. output rectifier's voltage will peak input voltage divided turns ratio plus output voltage output diode drop: Diode (378 2.5) (plus probable diode recovery spike) rated ultra-fast device more than sufficient handle this. Notice that small snubber composed across attenuate parasitic voltage spikes reduction. final transformer design detailed Figure
AND8394/D
Test Results
Power factor efficiency measurements were taken loads 25%, 50%, 100% both Euro
Load 100% 0.98 87.0 0.98 88.6 0.97 87.2 0.96 88.2
mains voltages. efficiencies were averaged results shown table below.
0.96 87.1 0.95 87.1
0.95 86.1 0.92
Overall Efficiency
87.2%
Output Ripple: output ripple with load 2000 output capacitance shown Figure input. ripple amplitude strictly function output capacity load power
supply since regulation loop bandwidth necessarily less than ripple frequency assure high power factor. Doubling amount output capacitance will halve ripple amplitude.
Figure Output Ripple
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Figure Drain Waveforms Full Load
Flyback Waveforms: waveforms Figures shows drain voltage profile MOSFET with full output load inputs.
leading edge voltage spike caused leakage inductance transformer largely damped snubber network
AND8394/D
Figure Drain Waveforms Load
waveforms Figures display Q1's drain waveform output load (1.25 Note that operation clearly this load both line input levels. Note that when flyback energy depleted, drain voltage will ring prior Q1's next turn-on resonant circuit formed transformer's primary inductance MOSFET's parasitic capacitance. This characteristic operation. drain waveforms prototype were typical relatively leakage inductance transformer. proper board layout techniques with minimal power loop
traces, liberal ground planes, clad "pours" where possible lower trace inductance will assure proper switching waveform profiles lowest generation. Very flyback transformer leakage inductance also extremely important previously mentioned. higher power applications cases were mechanical constraints limit optimum core structure and/or winding techniques, active clamp suppress primary voltage spikes necessary. optional auxiliary gate drive output NCP1652A provided this function.
AND8394/D
Figure Output Turn-on Profiles Load Full Load
output turn profiles Figures clearly indicate that output overshoot exists either load condition, particularly light load where uncommon exhibit overshoot with narrow bandwidth
control loops. full load throughput ripple clearly visible. selection component values will have significant impact turn profile response load changes.
AND8394/D
BILL MATERIALS NCP1652A ADAPTER DEMONSTRATION BOARD
Designator C24, Description Diode Diode Ultrafast Diode Signal Diode "soft" Diode Zener Diode Zener Diode MOSFET Controller Optocoupler Progam. Zener Caps Polyprop. Film Disc Ceramic Ceramic Ceramic Ceramic Disc Ceramic Ceramic Ceramic Ceramic Ceramic Electrolytic Electrolytic Electrolytic Electrolytic Electrolytic Electrolytic 0.25 Resistor Resistor Resistor 0.22 0.22 Input Transient Option Value Tolerance Footprint Axial Lead SOD123 TO-220AB Axial Lead SOD123 SOD123 TO-220 SOIC16 SOIC-8 1206 Semiconductor Semiconductor Infineon Semiconductor Vishay Semiconductor Rifa, Wima, Vishay,Epcos Rifa, Wima, Vishay Rifa, Wima, Vishay Vishay Anybody Manufacturer Semiconductor Semiconductor Semiconductor Semiconductor Semiconductor Manufacturer Part Number MRA4007T 1N5406 MURS160 MMSD4148A MSR860G 1.5KE440A MMSZ5248B MMSZ5252B SPP11N80C3 NCP1652A H11A817 SFH6156A-4 TL431A Disc Polypropylene Film Ceramic Disc Cap, Ceramic Ceramic Ceramic Ceramic Disc Ceramic Ceramic Ceramic Ceramic Ceramic Radial Lead, Radial Lead, Radial Lead Radial Lead Electrolytic Radial Lead, Radial Lead, Metal Film Resistor Metal Film Resistor Metal Film Resistor Substitution Allowed (Must Polyprop) High Quality Ceramic Pb-Free
1206/1210
Anybody
1206
Anybody
C10, C20,
1000 3.3k,
1206 1206 1206 1206 1206 Axial Lead Axial Lead Axial Lead
Anybody Anybody Anybody Anybody Anybody Anybody Rubycon, UCC, Nich. Rubycon, UCC, Nich. Rubycon, UCC, Nich. Rubycon, UCC, Nich. Rubycon, UCC, Nich. Rubycon, UCC, Nich. Anybody Anybody Anybody
Recommended Value
AND8394/D
BILL MATERIALS NCP1652A ADAPTER DEMONSTRATION BOARD
Designator Description Resistor Resistor Resistor Resistor Resistor 0.25 Resistor 0.25 Resistor 0.25 Resistor 0.25 Resistor 0.25 Resistor 0.25 Resistor 0.25 Resistor 0.25 Resistor 0.25 Resistor 0.25 Resistor 0.25 Resistor 0.25 Resistor 0.25 Resistor 0.25 Resistor 0.25 Resistor 0.25 Resistor 0.25 Resistor 0.25 Resistor 0.25 Resistor Fuse Inductor Inductor Choke Flyback xfmr Connectors Heatsink Value 560k Tolerance Footprint Axial Lead Axial Lead Axial Lead Manufacturer Anybody Anybody Anybody Anybody Ohmite Manufacturer Part Number Metal Film Resistor Metal Film Resistor Metal Film Resistor Axial Lead, Non-Inductive Axial Lead Metal Film Resistor 1206 Resistor 1206 Resistor 1206 Resistor 1206 Resistor 1206 Resistor 1206 Resistor 1206 Resistor 1206 Resistor 1206 Resistor 1206 Resistor 1206 Resistor 1206 Resistor 1206 Resistor 1206 Resistor 1206 Resistor 1206 Resistor 1206 Resistor 1206 Resistor 1206 Resistor Minifuse TR-5 Package BU10-1012R2B P3221-AL RFB0807-3R3L 13-1407 (600 Primary) 281-1435-ND 0.2") 531102B02500G Similar) Substitution Allowed Pb-Free
R21, (for
2.2k 2.7k 5.6k 102k 7.32k 8.6k 30.1k 49.9k 76.8k 100k 332k 365k
1206 1206 1206 1206 1206 1206 1206 1206 1206 1206 1206 1206 1206 1206 1206 1206 1206 1206 1206 TR-5 Core Toroid 0.2" Custom 25.4
Anybody Anybody Anybody Anybody Anybody Anybody Anybody Anybody Anybody Anybody Anybody Anybody Anybody Anybody Anybody Anybody Anybody Anybody Anybody Anybody Coilcraft Coilcraft Coilcraft Mesa Power Systems DigiKey Aavid
AND8394/D
MAGNETICS DESIGN DATA SHEET
Project: NCP1652A, Vout, isolated, single stage Part Description: Flyback transformer, kHz, Vout Schematic Core Type: PQ3230, 3C94 (Ferroxcube) material (Mag Inc.) Core Gap: core across pins Inductance: nominal measured across primary (pins Bobbin Type: mount (Mag PC-B3230-12 equivalent) Windings order): Winding type
Primary Secondary
Turns Material Gauge Insulation Data
turns #24HN over layer margins). Self-leads pins. Insulate next winding. turns #24HN close wound over layer centered with margins. Insulate with tape next winding. Same primary Insulate Vcc/Aux. turns #24HN spiral wound centered with margins. Insulate with tape terminate self-leads pins.
Primary Vcc/Aux
Hipot: from primary/Vcc secondary winding. Schematic
Lead Breakout Pinout
(bottom view)
Figure Flyback Transformer Design
AND8394/D
Conclusions
single stage, isolated converters where output voltage less, efficiency enhanced with synchronous output rectifiers instead convention Schottky diodes. Synchronous output rectifiers not, however, wholly compatible with continuous conduction mode (CCM) operation. This because operation will almost always transition into other depending load situation. light load oriented design will transition with operation, startup over-current mode usually operate CCM. result these modes operation, required gate drive signal synchronous MOSFET must based different sensing criteria each mode which causes additional circuit complexity. "problem mode" because there delayed timing sequence sync MOSFET prevent simultaneous conduction overlap with main primary side MOSFET. Even though necessary timing sequence achieved, critical issue still remains. When sync MOSFET turned just prior main primary MOSFET coming intrinsic body diode sync MOSFET must carry still flowing continuous flyback current. This parasitic body diode very poor recovery characteristics when main MOSFET turns this body diode force commutated significant reverse current will flow body diode during recovery process. This current along with associated circuit reactive parasitic components generates large voltage spikes
ringing sync MOSFET main MOSFET during this transition. This usually necessitates addition larger snubbers and/or clamping circuits avoid MOSFET failure. added circuit cost dissipative issues generally worth illustrated this application note, NCP1652A when optimized operation achieve high efficiency across wide load variation. single stage topology significantly reduces overall component bill material cost while still achieving high power factor compact form factor well behaved startup characteristics. Multiple protection schemes have been implemented this design address ensure robust reliable operation.
References
Data sheet NCP1652 Application note AND8124: Universal Input, Application note AND8147: Innovative Approach
Achieving Single Stage Step-Down Conversion Distributive Systems Application note AND8209: Single Stage, Notebook Adaptor Reference design TND317: Notebook AC-DC Adapter GreenPoint® Reference Design Single Stage, Converter
above documentation available download from Semiconductor's website (www.onsemi.com).
GreenPoint registered trademark Semiconductor Components Industries, (SCILLC).
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AND8394/D
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