Abstract. This application note describes basics powering high current
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AND8146/D High Current Capacitive Drop Drive Application Note
Abstract. This application note describes basics powering high current light emitting diodes (LEDs) utilizing capacitive divider circuit mains. linear regulator used control current order ensure optimal performance long life. characteristics explained, followed example design illustrate concept. INTRODUCTION Light emitting diodes, called LEDs, have existed many years. LEDs behave similarly normal diodes that they have forward voltage drop associated with forward current. Early LEDs emitted radiation only infrared (IR) spectrum. Later, visible LEDs emerged using various III-V compounds, such aluminum gallium arsenide (AlGaAs). Other colors, such yellow, amber green came shortly thereafter. breakthrough more colors came with blue LED; originally, this silicon carbide. applications these early LEDs were largely limited power displays, because output limited. breakthrough technology opening door wide variety higher power illuminating applications, which commercially available. This generation utilizes (AlInGaP) substrate emit significantly higher power amber light intensity. Additional colors, such green blue, built Indium-Gallium-Nitrogen (InGaN) substrate soon followed. full color spectrum, including white, possible using proper mixing filtering multiple colors. Today, colors amber, red-orange, typically from AlInGaP substrates, while royal blue, blue, cyan, green white from InGaN substrates. conversion efficiency electrical energy into light energy very important. Today's LEDs vary between efficiency. rest energy converted heat. This heat must effectively dissipated, operating junction temperature must maintained between -40°C +125°C. Incandescent lamps, including tungsten-halogen type, have efficiencies only about visible light. These emit broad, almost continuous spectrum energy, including only visible light, also ultraviolet (UV) infrared (IR) unusable heat. Technically, only incandescent lamp's energy converted directly into heat; surprisingly large amount heat generated them caused radiation being absorbed surrounding area. This heat reflected away from lamp, there lens filter front lamp heat trapped. only practical obtain different colors with incandescent lamps with light filter. This case with LEDs. LEDs produce rather narrow spectrum light therefore intrinsically more efficient converting electrical energy particular color than incandescent lamps with filter. There less electrical energy needed same lumen output, filter will attenuate light output substantially. Therefore color LEDs most efficient obtain colored light. White LEDs have same efficiency incandescent lamps, less efficient than fluorescent lamps. white LEDs have particular advantage over most known white light sources; this advantage longer lifetime. Many incandescent lamps rated between hours 2000 hours life. fluorescent lamp including like compact incandescent type offer between 8000 12,000 hours life. these lamps have filaments. greater number "on-off "cycles shorter lamp life filament breakage. White LEDs other hand have filaments thus have this failure mode. LEDs, regardless color, have extremely long lifetime, their current temperature limits exceeded. Lumileds Lighting LLC[1, published lifetime data stating that after 50,000 hours LEDs will have greater original light output. Using engineering rule thumb with data already collected, plotted, semi-log graph paper, LEDs projected have greater original light output after 100,000 hours. There 8736 hours normal year
Semiconductor Components Industries, LLC, 2004
February, 2004 Rev.
Publication Order Number: AND8146/D
AND8146/D
8760 hours during leap year, which equates 8742 hours year. This calculates over years months continuous service with light greater than initial output. Remember, order obtain maximum life, LEDs must operated within manufacturer's specified limits both current diode junction temperature. LEDs should used where extremely long life desired cost lamp replacement very high.
Characterization
maximum forward current varies with different type, style, manufacturer LEDs. Lumileds specified maximum forward currents mAdc, mAdc, mAdc, mAdc, mAdc, 1000 mAdc differently constructed LEDs. higher current devices have special thermally designed packages transfer heat from junction heat sink. This paper will concentrate circuits using Lumileds mAdc devices. same rules apply devices having other current ratings simply scaling current power designs. forward voltage drop varies between 2.50 4.00 rated forward current; Figure This variation material used, AlInGaP InGaN, operating junction temperature various manufacturing tolerances. This variation forward voltage drop must taken into account each lamp design. Lumileds sorts their devices according color, intensity, forward voltage drop maximum rated current. forward voltage characteristic provides better match maximum current than match lower current, Figure Wattage product forward voltage multiplied forward current. LEDs rated total wattage calculated taking minimum maximum forward voltage multiplied 0.35 0.350 2.50 0.88 minimum 0.350 4.00 1.40 maximum
FORWARD CURRENT (mA) Larger Variations Threshold Voltage Royal Blue, Blue, Cyan, Green, White (InGaN) Red, Reddish Orange, Amber (AllnGaP)
average, LEDs rated 0.350 (350 mA), considered devices. This makes calculation easy first order approximation. Because amount light limited from single LED, multiple LEDs used increase amount light. LEDs specified their rated current. easy advantageous place LEDs series because LEDs series have same current. Since LEDs current devices, current control technique must used ensure LEDs maintained within manufacturer's specifications. LEDs operated parallel. order operate LEDs parallel, devices must matched using forward voltage drop. This matching should occur manufacturer. process keeping proper voltage current through LEDs called ballasting. Ballasting techniques used extensively other lighting applications like fluorescent lamps.
Energy Supply Voltage Variation, Line Power
power line normally varies within five percent stated value. Like other source, variations much greater. line considered vary percent. United States Canada, normal line take values between Vac. There another condition called `brown out' where line voltage drops another percent Vac. `brown out' condition occurs when electrical utility company lowers value voltage generated. This happens under extreme high demand conditions; utility does this keep generating equipment operational within safe operating conditions while still providing some electrical energy customers. Under this condition incandescent lamps operate reduced light output reduce wattage. Most electric motors operate more economical fashion. line voltage variation from normal stated +10/-20 worst-case normal conditions.
Current Operating Point FORWARD CURRENT
0.01
0.001
Current Operating Point
0.0001 0.00001
FORWARD VOLTAGE
FORWARD VOLTAGE
Figure Typical Forward Voltage Different Colors
Figure Forward Voltage Matching LEDs
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Constant Current Design
easiest constant current approach voltage systems adjustable linear regulator such LM317 MC33269. circuit shown Figure
MC33269 Adjustable Linear Regulator Current
1.49 33e-6 1.24 33e-6
1.25
(eq.
Only half above current flows load, remaining current recirculated discharge coupling capacitor.
Half-Wave Capacitive Drop Circuit
1.25
Figure Half-Wave Capacitive Drop Supply Figure Constant Current Regulator
this scheme, adjustable regulator configured current regulator. regulator will maintain voltage 1.25 across series resistor. 1.25 reference voltage regulator. Consequently load current determined
ILED 1.25
(eq.
peak current mAdc required, sense resistor calculated
Capacitive Drop
Capacitive drop supplies have been used many consumer products, such smoke detectors. These types supplies accepted regulatory agencies, provided product sealed, consumer touch connections. concept schematic shown below Figure half-wave type capacitive drop circuit. capacitive drop supply essentially voltage divider such that series capacitor drops input voltage down more usable level. Each capacitive drop supply good narrow range line voltage line frequency applications. Vac, design different than Vac, circuit. Since front capacitor drops bulk line voltage, input current, Iac, defined Equation first order approximation. example, Equation shows amount current using capacitor line voltages: Vac, Vac.
IRMS 2pFCVAC (eq. AC_CAPACITOR 2pFC
half-wave circuit, Figure operates following fashion. During positive portion voltage, current flows through input resistor parallel combination When input voltage charged diode drop below Zener diode voltage, current will have another parallel path which flow. excess current flows through Zener diode, while capacitor remains charged voltage across load remains effectively constant. During this time, charges high voltage state. capacitor high voltage rated capacitor. Once charged must discharged order keep charge During negative half voltage, discharged through forward conduction Zener diode, engineering rule thumb, this approach provide load current mAdc each capacitance. This means that capacitor supply about mAdc current, capacitor needed supply 0.35 LED. following limit purpose each component. Fusible link metal film resistor additional current limit line transients rated capacitor Zener diode, device used output Diode; e.g. 1N4004 Electrolytic capacitor least times value Load Figure modified operation adding constant current circuit, such previously described
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AND8146/D
LM317 circuit. This shown Figure where value Zener defined device, 1N5934B. This circuit operate one, two, LEDs peak.
1N4004 1N5934B 1000 Neutral LM317
SPICE Simulation Half-Wave Capacitive Drop Circuit
half-wave capacitive drop circuit simulated IsSPICE from Intusoft with schematic shown Figure
Figure LED, Half-Wave, Capacitive Drop Circuit
Vreg
1N4004
LM317MOT Ifiltercap 1000 ADJUST
Vled
Blue Blue Iled
1N4004
1N4749
Figure Half-Wave Capacitor Drop Lumiled Circuit
Several points should noted. First, schematic shows diode parallel with Zener diode, reason forward voltage drop Zener diode higher than standard rectifier such 1N4004. parallel diode will shunt some current, causing Zener dissipate less power therefore cooler. Secondly, model LEDs, generic diode model modified match much larger forward voltage drop. this, fundamental diode equation evaluated:
Io(evD NVT-1)
(eq.
this equation diode current, forward drop diode, emission coefficient (usually between reverse saturation current, defined
(eq.
where Boltzmann's constant (1.38 10-23 J/K), absolute temperature (K), charge electron. forward drop blue from Lumileds about Letting Equation solved Modifying IsSpice model with these numbers yields simulation results shown Figure
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Figure Simulation Results Half-Wave Capacitive Drop Circuit
Figure shows current, input voltage LM317 regulator, input voltage. circuit shown Figure built tested. results actual waveforms shown Figure
simulation results shown Figure show good correlation with actual waveforms shown Figure model appears good first order model.
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AND8146/D
Figure Oscilloscope Measurements Half-Wave Capacitor Drop Lumiled Circuit
Notice that both actual simulated results, current clamped Equation During time input negative, energy source load 1000 capacitor. capacitor's energy depleted, LM317 comes regulation current decreases. Depending individual observer, light flicker line frequency rate noticeable under certain conditions. reduce eliminate possibility noticeable flicker larger electrolytic capacitor used. Another method reduce flicker effects full-wave version capacitive drop supply.
Full-Wave Capacitive Drop Circuit
three LED, full-wave, capacitive drop supply using LM317 current limiting element. full bridge version, coupling capacitor, charged discharged through full bridge. Depending upon load, value Zener vary needed except during high line conditions. resistor, mainly used filter, help maintain regulation.
full-wave version capacitive drop circuit shown Figure engineering rule thumb this approach mAdc load current possible each coupling capacitor. full bridge approach would only rated capacitor. Figure
Figure Full-Wave Capacitive Drop Supply
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1N5934 LM317
Making assumption, that IDC-AVERAGE used LED, equal 0.35 value coupling capacitor, calculated line, Vac, This shown Equation This value coupling capacitor used Figure
ILED 0.35 10.3e FVAC
(eq.
Figure Three LED, Full-Wave, Capacitive Drop
mentioned above, since there losses Zener diode, capacitor will used.
SPICE Simulation Full-Wave Capacitive Drop Circuit
current flowing through coupling capacitor determined using Equation full bridge version, this less than half value half-wave capacitive drop approach. value coupling capacitor able reduced there losses Zener diode. average value current flowing past bridge rectifiers calculated shown Equation
IDC-AVERAGE IRMS FCVAC FCVAC
(eq.
full-wave capacitive drop circuit also simulated using IsSPICE from Intusoft. LEDs were modeled before. simulation schematic shown Figure
Vreg
Vinpcap 1N4004 Vinpbrg
1N4004 1N5359A
Vfilt
LM317MOT ADJUST
Vout
Blue Blue Blue Iled Vled
1N4004 1N4004
Figure Simulation Schematic Full-Wave Capacitive Drop Circuit
results simulation shown Figure
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Figure Results Simulation Full-Wave Capacitive Drop Circuit
before, waveforms shown current, input voltage LM317 regulator, input
voltage. Again this shows good correlation with actual oscilloscope measurements Figure
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Figure Oscilloscope Measurements Full-Wave Capacitive Drop Circuit Demo Board Circuit
actual demo board circuit schematics shown below.
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AND8146/D
LM317BT w/Heatsink
3.6,
JMP1 LED1
Conn1
LED2
LED3
NOTE: denotes Parts List value/type
Figure Lumiled Demo Board Half/Full-Wave Capacitor Drop Circuit
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AND8146/D
HALF-WAVE PARTS LIST
Sch. Ref. Conn1 JMP1 LED1-LED2 LED3 ZD3-ZD4 Semiconductor Semiconductor Keystone Keystone Keystone Keystone Lumileds Littlefuse Semiconductor AAVID Panasonic Semiconductor Vendor Phoenix Contact Panasonic Part Number/Description 1715035 JSU23X106AQC Film Cap) EEU-FC1E102 (1000 1N4004 (1.0 Axial) Bare Wire Jumper (Prov. 1N4004) 224001 (1.0 Pigtail Fuse) LM317BT (1.5 Adj. Regulator) 566010B02800 (Heatsink) Insulated Stranded Wire approximately Bare Wire Jumper 5000 (Test Point Red) 5000 (Test Point Red) 5002 (Test Point White) 5001 (Test Point Black) LXHL-M*** indicates color) Bare Wire Jumper 1N5934B 1N5917 (4.7
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FULL-WAVE PARTS LIST
Sch. Ref. Conn1 JMP1 LED1, LED2, LED3 ZD3, ZD4, Semiconductor Semiconductor Keystone Keystone Keystone Keystone Lumileds Littlefuse Semiconductor AAVID Vendor Phoenix Contact Panasonic Panasonic Panasonic Panasonic Semiconductor Part Number/Description 1715035 ECH-A22405JX (4.0 Vac) ECH-A22405JX (4.0 Vac) EEU-FC1H101 (100 EEU-FC1E471 (470 1N4004 (1.0 Axial) 224001 (1.0 Pigtail Fuse) LM317BT (1.5 Adj. Regulator) 566010B02800 (Heatsink) Insulated Stranded Wire approximately 5000 (Test Point Red) 5000 (Test Point Red) 5002 (Test Point White) 5001 (Test Point Black) LXHL-M*** indicates color) 1N5934B 1N5917 (4.7
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Figure Side Foil Capacitive Drop Lumiled Demo Board
Figure Bottom Side Foil Capacitive Drop Lumiled Demo Board
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References Lumileds, www.lumiled.com. Luxeon, www.luxeon.com. Lumileds, www.lumileds.com/pdfs/DS45.PDF, October 2003. Lumileds, www.lumileds.com/pdfs/DS46.PDF, October 2003.
Semiconductor registered trademarks Semiconductor Components Industries, (SCILLC). SCILLC reserves right make changes without further notice products herein. SCILLC makes warranty, representation guarantee regarding suitability products particular purpose, does SCILLC assume liability arising application product circuit, specifically disclaims liability, including without limitation special, consequential incidental damages. "Typical" parameters which provided SCILLC data sheets and/or specifications vary different applications actual performance vary over time. operating parameters, including "Typicals" must validated each customer application customer's technical experts. SCILLC does convey license under patent rights rights others. SCILLC products designed, intended, authorized components systems intended surgical implant into body, other applications intended support sustain life, other application which failure SCILLC product could create situation where personal injury death occur. Should Buyer purchase SCILLC products such unintended unauthorized application, Buyer shall indemnify hold SCILLC officers, employees, subsidiaries, affiliates, distributors harmless against claims, costs, damages, expenses, reasonable attorney fees arising directly indirectly, claim personal injury death associated with such unintended unauthorized use, even such claim alleges that SCILLC negligent regarding design manufacture part. SCILLC Equal Opportunity/Affirmative Action Employer. This literature subject applicable copyright laws resale manner.
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