Prepared Alejandro Lara Mike Girand Semiconductor ABSTRACT increa
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AND8156/D NUD4001 NUD4011 Cost Integrated Current Sources LEDS Lighting Applications High Voltage (6.0
Prepared Alejandro Lara Mike Girand Semiconductor
ABSTRACT increasing usage Light Emitting Diodes (LEDs) address different lighting applications such traffic signals, exit signs, backlighting general illumination have made them very popular point where they attractive choice those lighting applications that were once domain incandescent lamps. LEDs have several advantages when compared with incandescent lamps. They offer fast turn-on, lower heat generation, lower power consumption, higher operating life, high resistance shock/vibration. Nevertheless, LEDs need driven properly ensure optimal performance long life. Designing implementing effective driver obtain benefits LEDs. driver's implementation must cost effective, which usually achieved with discrete components with integrated solutions. INTRODUCTION LEDs created from various doped semiconductor materials form diode junction. When electrical current flows through junction forward direction, electrical carriers deliver energy proportional forward voltage drop across diode junction, which emitted form light. amount energy relatively current infrared LEDs. However, green blue LEDs which manufactured from higher forward voltage materials, amount energy greater. conversion efficiency electrical energy into light energy very important. Today's LEDs vary between percent efficiency. rest energy converted heat. This heat must effectively dissipated, operating junction temperature must maintained higher than +125°C. Since device being used forward biased mode, once voltage applied exceeds diode forward voltage; current through device rise exponentially. Very
high currents would damage LEDs, this electronic drivers must added when LEDs driven from voltage source. amount light emitted proportional amount average current flowing through device forward bias direction. current varied, output light will vary similar way. Therefore, Light-Emitting Diode (LED) essentially junction semiconductor diode that emits light when current applied. definition, solid-state device that controls current without heated filaments therefore very reliable. LEDs have special characteristics that assure high reliability compatibility with electronic drive circuits. LEDs have advantages disadvantages when compared with other light sources such incandescent fluorescent lamps. most significant advantages fast turn-on, lower heat generation, lower power consumption, longer operating life, high resistance shock/vibration. Some disadvantages narrow viewing angle, near monochromatic light, limited wavelength selection, they require electronic drive circuits operation. LEDs, regardless color, have extremely long lifetime, whenever their current temperature limits exceeded. LumiledsLighting published lifetime data stating that after 50,000 hours LEDs will have percent greater original light output. Using engineering rule thumb with data already collected plotted semi-log graph paper, LEDs projected have percent greater original light output after 100,000 hours. This approximately years months continuous service with light greater than percent initial output. Remember, order obtain maximum life, LEDs must operated within manufacturers specified limits both current diode junction temperature. LEDs should used where extremely long life desired cost lamp replacement very high.
Semiconductor Components Industries, LLC, 2004
July, 2004 Rev.
Publication Order Number: AND8156/D
AND8156/D
Figure shows typical curve. This graph particular makes reference high current technology recently introduced. maximum forward current varies with different type, style, manufacturer LEDs. manufacturers have specified maximum forward currents differently constructed LEDs. higher current devices have special thermally designed packages transfer heat heat sink. same rules apply devices having other current ratings simply scaling down current power designs. TRADITIONAL METHODS DRIVING LEDS USING DISCRETE COMPONENTS There several methods drive LEDs with discrete components. Figure illustrates simplest using resistor series with supply voltage limit current. This type methodology simple cheap several disadvantages. most significant that since there current control device, variations input voltage will change average current LEDs, which results poor illumination quality sometimes even degradation total damage LEDs high line voltage conditions. better illustrate problem, calculations current supplied LEDs will made based circuit shown Figure normal line fluctuate percent therefore transformer output vary between 10.8 13.2 whenever normal secondary voltage 12.0 Vac. Based this, LED's current calculation low, normal, high voltage line made through Formula Formula
VLED) ILEDs
Figure Typical Curve Different LED's Colors (Courtesy: Lumileds)
Assuming that characteristics LEDs used are: then resulting current calculation each voltage line conditions follows: line: ILEDs Normal line: ILEDs High line: ILEDs
Bridge1 LED3 LXHL-MW1D 1000 LED2 LXHL-MW1D LED1 LXHL-MW1D
Figure Discrete driver circuit using resistor series with supply voltage. Application circuit landscape lighting.
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seen, change LED's current higher than $25% $10% variation line. line case, causes LEDs while high line case potentially damage them overheating caused high current. This why, these type drive circuits recommended often used because they basically eliminate valuable features LEDs. Another common driver method using discrete components made through linear regulator (MC7805, MC7809 similar), series medium power resistor (usually bigger). Figure shows this concept.
Linear Regulator MC7809 Bridge1 LED2 LXHL-MW1D
1000 LED1 LXHL-MW1D
Figure Discrete driver circuit using linear regulator series resistor. Application circuit landscape lighting.
LED's current regulated output voltage linear regulator value resistor resistor value easily calculated through Formula Formula
(Vout VLEDs) ILEDs
INTEGRATED DRIVERS NUD4001 DEVICES' DESCRIPTION
NUD4001 Device Description
Assuming that characteristics LEDs used are: then resulting resistor calculation follows:
(9.0 0.350
This integrated current source designed replace discrete solutions driving LEDs high voltage applications (6.0 integrated design technology eliminates individual components combining them into single small surface mount package (SOIC-8), which results significant reduction both system cost board space. Figure illustrates pin-out NUD4001 driver device.
power dissipation given
(0.350)2
Rext Current Point Iout Iout Iout Iout
current regulation mostly dependent regulator's performance should expected good since most voltage regulators provide good percentage line load regulation, usually lower than $5%. Although this type concept provides good current regulation LEDs, optimum applications where cost critical, either those requiring enable electronic dimming functions.
SO-8 Package, Case
Figure NUD4001 Integrated Driver Pin-out Description
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This device provides regulated current array, from input. drive arrays series parallel-series LEDs wide range applications. voltage overhead (1.4 facilitate usage voltage applications. current regulating principle made through generation constant voltage drop (0.7 across external power sense resistor (Rext), which sets current independently input voltage supplied. This operating principle makes very simple design LED's circuits around NUD4001 device. Nevertheless, there certain design considerations such maximum device's power dissipation (1.13 operating ambient temperature range, device's voltage overhead LED's array configuration that have taken into account before implementing this integrated driver. general design guide explained next section illustrated Figure this case device utilized drive three high intensity white LEDs 0.350
NUD4001 Iout Iout Current Point Iout Iout
Rext
Define VLED ILED supplier's data sheet: Example Figure VLED 10.5 Calculate Vdrop across NUD4001: Vdrop VLED Vdrop 12.0 10.5 Vdrop (Vdrop must higher than device's overhead, Calculate Power Dissipation (PD): Vdrop Iout 0.330 0.495 1.13 derated value based ambient temperature. Refer Figure NUD4001 device's data sheet), then select most appropriate recourse repeat steps 1-6: Reduce Reconfigure array reduce Vdrop Reduce Iout increasing Rext parallel configuration more NUD4001 devices. typical current regulation performance NUD4001 device circuit Figure using Rext shown Figure
0.40 0.35 0.30
Iout,
0.25 0.20 0.15
25°C
85°C
Figure NUD4001 Device Driving Three White High Current LEDs
0.10 0.05 0.00 Vin,
steps calculate value external sense resistor (Rext), validate operation device within power dissipation capability explained following design guide:
NUD4001 Device's Design Guide:
Determine Iout LED's current: ILED Calculate Resistor Value Rext: Rext
Iout Rext 0.330
Figure NUD4001 Device Regulation Performance Three Different Ambient Temperatures (05C, 255C 855C)
Define Vin: Figure
25°C, change LED's current only increment input voltage. This regulation ratings obtained from data shown Figure Vdc, Iout 13.8 Vdc, Iout
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Similar regulation values obtained elevated temperatures. However, important note that temperature, LED's current shifted factor while elevated temperature lowered factor 11%. These values also obtained from data shown Figure 25°C 12.5 Vdc, Iout 12.5 Vdc, Iout 85°C 12.5 Vdc, Iout Even seems strange, this type behavior ideal usually desired manufacturers. because high ambient temperatures junction temperature LEDs would increase reduction current cancels this effect. temperatures current increased small percentage (usually higher than 10%) since LED's junction temperature colder.
NUD4001 Power Dissipation
power dissipation device different ambient temperatures, which reduced ambient temperature rises. Figure shows power derating graph different ambient temperatures NUD4001 device (mounted onto FR-4, inches copper pad, coverage double sided board):
1.200 POWER DISSIPATION, 1.000 0.800 0.600 0.400 0.200 0.000
Although basic design considerations NUD4001 device explained design guide, necessary emphasize special attention power dissipation (PD) thermal parameters (RqJA) device these main things consider designing around power dissipation SO-8 package function size. This vary from minimum size soldering size given maximum power dissipation. Power dissipation surface mount device determined maximum rated junction temperature (TJ), thermal resistance from device junction ambient (RqJA), operating ambient temperature (TA). Using values provided NUD4001 device's data sheet, calculated through Formula Formula
RqJA
AMBIENT TEMPERATURE (°C)
Figure NUD4001 Power Dissipation (PD) Ambient Temperature (TA)
Based this information, possible conclude that order optimize LED's driver circuit design using NUD4001 device, necessary keep ratio between VLEDs possible also higher than device's overhead value good design window this ratio should between application. NUD4001 DESIGN CONSIDERATIONS APPLICATION CIRCUITS Currently, most landscape lighting applications being designed with technology high intensity white LEDs. This technology needs supplied with currents between which makes driver's power dissipation main design consideration. Figure illustrates typical landscape lighting application circuit using NUD4001 device LED's driver.
Rext1 4001 NUD4001 LED1 Luxeon Emitter, LED2 Luxeon Emitter,
NUD4001 device rated 1.13 25°C whenever mounted onto FR-4, inches pad, coverage double side board. thermal resistance junction-to-ambient 110°C/W under same board conditions. From Formula possible calculate
From: Transformer Electronic Transformer
LED3 Luxeon Emitter,
Figure landscape lighting application circuit using NUD4001 device drive three LEDs.
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first design consideration circuit shown Figure type diodes needed rectification (D1, D4), because input supplied from transformer electronic switching transformer. Therefore, case where electronic transformer used, necessary rectifier devices with fast reverse recovery time (trr), otherwise problems will experienced. Semiconductor's MURA105T3 device ideal choice these purposes. Another design consideration voltage drop (Vdrop) across NUD4001 device (Q1) directly impacts power dissipation device. explained previously, Vdrop dependent average voltage (Vavg) supplied device voltage drop LED's array (Vdrop Vavg VLEDS). optimum design, this Vdrop should kept between application. value capacitor (C1) important factor consider Vavg strongly depends value capacitor farads determined using Formula developed Savant [3]. Formula
VMAX DVfRRL
cases where input voltage supplied through transformer. Therefore electronic transformer used then formula applicable selection capacitor most likely made through entirely work. final design steps circuit Figure calculate external sense resistor (Rext), NUD4001 device's power dissipation (PD), which made following steps design guide previously explained. resulting Rext LED's current power dissipation same current value Based these calculations, resulting Bill Materials (BOM) follows:
Part Code LED1 LED3 Vendor Semiconductor Semiconductor VISHAY VISHAY LUMILEDs Part Number MURA105T3 NUD4001 LXHL-MW1D
Value capacitor farad VMAX Peak line voltage Peak-peak capacitor voltage normal Vpeak Twice line frequency (120 system) Effective load resistance effective load resistance (elr) term used converting LEDs driver into equivalent resistance. value this resistance that used selecting electrolytic capacitor. input average voltage driver given line voltage value divided current. Using Formula possible theoretically calculate capacitor needed wanted Vavg. case Figure Vavg selected that Vdrop higher than each they series, then resulting Vavg (Vdrop V(avg) VLEDS). Based this using Formula capacitor calculated follows:
37.2
closest commercial capacitor value which gives first approximation capacitor (C1) needed. This value should taken final necessary additional analysis validate important notice that Formula only applicable
Figures show oscilloscope pictures waveforms generated across circuit shown Figure once previous implemented. Figure refers case where input voltage taken from transformer (Tamura 3FD-424 similar), Figure case switching transformer (Cooper LZR-404 similar). current regulation performance circuit shown Figure different average voltages values resulting from variations line, similar than shown Figure 25°C, change LED's current expected only increment input voltage. There some cases where application only requires light instead three, those cases necessary external power resistor reduce voltage drop (Vdrop) across NUD4001 device have operating within power dissipation (PD) capabilities. Figure illustrates this circuit concept Figures show circuit regulation performance, NUD4001 device's power dissipation, power dissipation power external resistor (Rext2) respectively. D1-D4, Rext1 similar defined circuit Figure only addition circuit Figure power resistor Rext2. Similar circuits made drive different arrays input voltage applications (6.0 main important consider exceed power dissipation NUD4001 device assure reliable operation.
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Vavg
Channels Definition Ch1- Ch1- 10V/div Ch1- 12Vrms Ch2- Vavg Ch2- 5V/div Ch2- 13Vavg
Channels Definition 10V/div 12Vrms Vavg 10V/div 12.8V Vavg Iavg 200mA/div 315mAavg
Iavg
Ch3- Iavg Ch3- 200mA/div Ch3- 320mAavg
Iavg
10V/div 200mA/div
5V/div
10V/div 200mA/div
10V/div
Figure Waveforms generated across circuit shown Figure when transformer used supply voltage.
Figure Waveforms generated across circuit shown Figure when electronic switching transformer used supply voltage.
Rext2 Rext1 From: Transformer Electronic Transformer 4001 NUD4001 LED1 Luxeon Emitter,
Figure landscape lighting application circuit using NUD4001 device drive LED.
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0.400 0.360 0.320 0.280 Iout, 0.240 0.200 0.160 0.120 0.080 0.040 0.000 Vin, 25°C POWER, WATTS 85°C 2.00 1.75 1.50 1.25 1.00 0.75 0.50 0.25 0.00 Vin, 25°C 85°C
Figure Current regulation performance circuit Figure different Vavg values.
Figure NUD4001 device's power dissipation when operating circuit Figure different Vavg values.
2.80 2.40 POWER, WATTS 2.00 1.60 1.20 0.80 0.40 0.00 Vin, 25°C 85°C
Figure Power dissipation Rext2 circuit Figure different Vavg values.
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NUD4011 DESIGN CONSIDERATIONS APPLICATION CIRCUITS addition already explained design considerations NUD4001 device, necessary consider power factor requirements transient voltage protection when designing circuits around there requirement power factor, then circuit becomes simpler does need have full bridge rectifier capacitor. Figure shows schematic diagram drive array white, current units application using NUD4011 device. This device similar than NUD4001 device with higher breakdown voltage.
NUD4011 Rext1 4011 LED1 Nichia, VARISTOR LED2 Nichia,
LED30 Nichia,
Figure application circuit using NUD4011 drive white current LEDs series. requirement power factor.
Figure current conduction occurs only after peak voltage positive cycle exceeds forward voltage array. total forward voltage given voltage specific device multiplied number LEDs connected series. Assuming that Nichia white LEDs with characteristics used, then resulting total forward voltage series LEDs array This indicates that current conduction only present during time that positive cycle input higher than This something very important consider determining value external resistor (Rext1) LED's current because dependent peak current value conduction time. better illustrate this, current peak calculation made circuit shown Figure Formula shows equation calculate instantaneous voltage over time sinusoidal waveform:
Formula
Vpeak
Using this formula other analogies, possible determine time current conduction during positive cycle input. known, Vpeak happens cycle, which translates 4.165 msec time frequency. Formula then used find
39.52°
then, since 4.165 msec, then 39.44° 1.82 msec. Based this, current conduction time calculated follows:
(4.165 msec 1.82 msec) 4.67 msec
Assuming that current waveform square shaped, possible that since 16.66 msec 100% duty cycle, 4.67 msec 28%, therefore:
I(avg) Ipeak duty cycle
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average current wanted
I(avg) Ipeak duty cycle Ipeak 0.28 Ipeak 89.2
procedure already explained. only variation frequency which increased because usage full bridge rectifier. frequency affects duty cycle therefore Ipeak calculation. NUD4001 DEVICE'S ENABLE FUNCTIONS addition current regulation function, NUD4001 device offers ability LEDs dimming applications using external small signal transistor connected between ground. This very important feature specially those applications where multicolor lighting required (swimming pools, bars, etc.). same small signal transistor used enable function conditioning applications. Figure illustrates circuit function application drive three high current (350 white LEDs.
NUD4001 Rext1 4001 LED1 LXHL-MW1D LED1 LXHL-MW1D LED1 LXHL-MW1D
Upon calculation Ipeak, possible calculate Rext:
Rext Ipeak Rext 7.84
This theoretical procedure provides have first approximation value Rext needed. However should taken final until validated through analysis. Figure shows expected current waveforms LED's array circuit shown Figure with Rext
0.09 0.08 AMPLITUDE, AMPS 0.07 0.06 0.05 0.04 0.03 0.02 0.01 0.00 0.05 0.15 TIME, SECS 0.25 I(avg) Iout
Rext2 2N2222
Figure Ipeak I(avg) waveforms through LED's array circuit shown Figure with Rext
Figure NUD4001 Device Configuration Function
observed, Ipeak I(avg) values exactly match with calculated ones. this why, important analysis achieve specific design targets. power dissipation NUD4011 device circuit shown Figure calculated follows:
[(Vpeak VLEDs) I(avg)] 0.28 0.464
order achieve lower power dissipation driver (NUD4011), necessary configure LED's array that total close enough voltage applied application power factor requirements, then necessary full bridge rectifier across input keep phase current voltage waveforms much possible. Rext calculation made through same
function Rext2 pull device when signal base transistor low. average current applied directly dependent duty cycle (Iavg Ipeak duty cycle). LED's light intensity directly dependent average current I(avg) applied. case Figure current 100% duty cycle therefore, proportionally decreases narrower duty cycles. circuit good frequencies between kHz. Most dimming applications frequencies within this range. same type configuration used enable function. only difference that base transistor driven. same concepts applied high voltage applications, only things consider select transistor with high enough breakdown voltage, external power resistor (1/4 between collector transistor.
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SUMMARY
Discrete Methods (resistors)
Discrete methods drive LEDs recommended often used because they basically eliminate valuable features LEDs, sometimes even cause total damage.
Linear Regulators
Although concept linear regulators provide good current regulation LED's circuits, still optimum applications where cost critical, either those applications requiring enable electronic dimming functions.
NUD4001 Device
LEDs driven from high voltage supply, then necessary external power resistor reduce voltage drop across device (see Figure 11). Selection proper copper area according application needs device's specifications achieving optimum device's operation. enable features well cost implementation what distinguishes NUD4001 NUD4011 devices from linear regulators discrete solutions (resistors) drive LEDs. REFERENCES Semiconductor site: www.onsemi.com Fitzgerald, A.E. Higginbotham, David Arvin Basic Electrical Engineering. Fifth edition. 1981. Lumiled: www.lumiled.com Nichia: www.nichia.com Boylestad, Robert Circuit Networks. Eighth edition. August, 1988. PSPICE release 9.1. Released notes February 2000. Semiconductor's data sheets NUD4001/D NUD4011/D.
NUD4001 device offers cost current regulation integrated solution different LED's circuits high ac/dc voltage (6.0 Design considerations such device's power dissipation, breakdown voltage maximum current capability have taken into account before implementation application circuits. Selection proper LED's configuration drop much possible supply voltage array achieve design optimization. quantity
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Lumiled trademark Lumileds Lighting, U.S. LLC.
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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