INTRODUCTION Although xenon lamps dominate standard camera market, the

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AND8135/D Efficient High Power Flash Light
INTRODUCTION Although xenon lamps dominate standard camera market, they applicable portable phone. matter fact, large reservoir capacitor high voltage associated with xenon flash make such concept suitable cellular phone equipments. semiconductor based White devices provide right choice when limited flash light becomes necessary illuminate photographic scene. This paper depicts basics xenon concept details typical White flash application. XENON LAMP CONCEPT pressure rare mixture fills glass envelope with ends electrodes both sides. steady state, voltage across electrodes value well below trigger voltage depicted Figure this point, current flows system stable until trigger voltage applied third electrode. This high voltage pulse, range, comes from transformer built with small magnetic tore triggered abrupt discharge capacitor (see Figure
Depending upon type flash involved, amount energy stored into capacitor Joule (small camera) thousand Joule professional applications.
+260
TRIGGER
XENON TUBE
Figure Basic Xenon Flash
advantage such concept very short pulse, making easy snap shot photos capture moving stuffs. drawbacks large physical size reservoir capacitor recycle time needed recharge capacitor between shots range consumer applications). Clearly, these drawbacks make xenon based flash suitable hand held cellular phone, with limited size energy supply. WHITE FLASH overcome physical size limitation, flash concept make profit high efficiency, term light, coming from modern white LED. With forward drop voltage, such diodes need extra high voltage trigger pulse, they extremely fast turn ON/OFF associated electronic circuit housed inside standard portable phone. Since white have electrical characteristics similar standard (see Figure must provide constant forward current control device.
Vtrig
Figure Xenon Flash Breakdown Voltage
ignited plasma generates bright flash, typical duration being consumer applications.
Semiconductor Components Industries, LLC, 2003
October, 2003 Rev.
Publication Order Number: AND8135/D
AND8135/D
circuit, built around NCP5007, designed support both beam current high flash pulse requested during capture photo. DC/DC boost converter, associated sense resistor provides constant current load properly bias white LEDs. With internal voltage reference (Vref), chip minimizes drops along battery supply path.
Power Beam Operating Mode
Figure Typical White Characteristics
Generally speaking, this mode operation used pre-light scene capture order minimize red-eye effect. NMOS transistor biased provides feedback voltage regulate load current. value derived from Ohm's law:
Iout
Consequently, standard voltage source cannot used straightforward extra ballast necessary current. other hand, flash must capable operate over typical battery voltage spread (2.8 more suitable structure than simple linear voltage regulator mandatory. achieve such constraints, Semiconductor developed full family white drivers, among which NCP5007 fulfill flash application demands. TYPICAL FLASH APPLICATION Since battery voltage ranges from high simplest economic handle this span arrange white series depicted Figure Such layout avoid leakage current during stand mode operation (most time, flash activated!).
ENABLE
With typical operating bias during illumination scene, sense resistor current dynamically modulated, necessary, using signal digital control: such mode operation depicted NCP5007 data sheet. same used control DC/DC from external CPU. course, more powerful light provided setting sense resistor accordingly. From practical stand point, capacitor mandatory avoid large spikes during energy transfers from inductor white LEDs. Moreover, such capacitor smoothes current flowing into LEDs, yielding better light efficiency.
VBat
VBat
Vout MBR0530
NCP5007 FLASH LWT67C LWT67C
LWT67C
Figure Typical Portable White Flash Circuit
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AND8135/D
High Power Flash Mode
Once system ready take photo, flash activated forcing high current bias into white LEDs. Unlike silver film, electronic sensor digital camera cannot capture scene couple millisecond, much longer delay necessary save pixels. Typically, such delay ranges from depending upon type camera lens. Consequently, using reservoir capacitor supply large current during really feasible. fact, sustain during with three LEDs series, assuming voltage cannot drop more than during pulse, should have 40000 µF/16 electrolytic capacitor, value compatible with portable equipment. that, re-charge this capacitor reasonable time, typically second, DC/DC converter should provide around when loading capacitor from zero. Therefore, instead designing chip re-charge capacitor, better converter supply immediately current called application. activate flash, shall turn NMOS providing lower sense resistor feedback loop. NMOS selected with internal Rdson suitable expected current. Since Rdson NMOS varies largely with temperature spread from another relatively large, more predictable circuit using larger NMOS associated with
external resistor series depicted demo board schematic diagram. Table gives selection preferred product handle such function.
Table Preferred NMOS Products
Part MMBF0201NLT1 MMBF0201NLT1 MMBF2201NT1 NTA4001NT1 MMFT960T1 Icmax 0.24 Rdson Package SO-8 SOT-23 SC-70 SC-75 SOT-223 BVSS
bipolar device fulfill this function, saturation voltages (Vcesat) such devices close define internal reference, cannot easily implemented this type circuit. DEMO BOARD SCHEMATIC DIAGRAM demo board, depicted Figure supports beam high power flash, together with digital circuit LED. that, built-in clock provides capability generate multiple flash evaluation purpose. mode operation selected means switches associated potentiometers depicted Table third switch push button manually trig flash.
Table Switches Configurations Potentiometers Functions
Select NCP5007 mode operation: forced High, operation pulsed Select Power Flash mode operation: Single shot triggered Repetitive mode Manual switch trig power flash VCC, then light Adjust pulse width applied Adjust frequency VCC, then Adjust power flash repetitive frequency Adjust power flash duration
extra functions make possible operation demo board stand alone basis, without need from external control. However, order provide higher flexibility, provisions made connect demo board MPU: three pins connector shall connected appropriate port control dimming flash functions. stand alone operation, switches forced chip runs continuously. beam current sense resistor demo board comes with resistor, yielding current through white LED. this point, trig flash pushing switch flash pre-set provide during time adjusted potentiometer
system re-arranged either light when running beam current, generate pulsed flash pace. dimming function activated when switch High. this mode, clock built with gates associated with shot circuit controls thus modulation load current. pulsed flash activated when switch High. this mode, clock built with gates associated with second side shot provide rate trig flash. pulse width manually adjusted with potentiometer waveforms captured from demo board (see Figure Figure illustrate currents voltages across major points.
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AND8135/D
Figure Beam Inductor Current
Figure High Power Flash Inductor Current
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AND8135/D
Figure Input Supply Current
Figure Beam High Beam Output Current
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AND8135/D
Figure Combined Beam Power Flash Output Current Output Power
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AND8135/D
mF/16 mF/6 MBR0530 mF/16 LWT67C LWT67C NL27WZ32 LWT67C
RCCOM
Vout
ENVbat
MMBF0201NLT1
500kA
NL27WZ32
1mF/10V SNJ54HC132J (14)
M54HC123
RCCOM
SNJ54HC132
1N4148
Adjust
SNJ54HC132
1.5k NORMAL/PWM
100k
mF/16 MBR0530
TRIG 1.5k REPEAT SINGLE/ REPEAT EXTERNAL
Vbat
Figure Demo Board Schematic Diagram http://onsemi.com
EXTL_EN
EXTL_FLASH
SNJ54HC132
100k
NORMAL: Constant Current PWM: intensity
500kA
Adjust Flash Duty Cycle
100kA
NL27WZ14
100kA
mF/10
NL27WZ14
1N4148
3.3R
Adjust Flash Pulse Width M54HC123
NCP5007
AND8135/D
Figure Layout http://onsemi.com
AND8135/D
Table High Beam Demo Board Part List
Used 1N4148 µF/10 µF/10 µF/6 M54HC123 MBR0530 SNJ54HC132 MMBF0201NLT1 NCP5007 NL27WZ14 NL27WZ32 EXTERNAL NORMAL/PWM SINGLE/REPEAT TRIG Vbat Part Designator R13, R11, 0805 0805 0805 0805 0805 DIODE0.4 0805 1210 0805 0805 1210 LED_2 LED_2 1210 SO-16 1210 SO-14 SOT-23 TSSOP5 SOT_23B SIP3 GND_TEST SIP3 SIP3 PUSH_BUT_B TEST_POINT PLUG_4MM_DUAL Footprint Resistor Resistor Resistor Resistor Resistor Diode Potentiometer, Linear Potentiometer, Linear Potentiometer, Linear Ceramic Capacitor, MURATA Ceramic Capacitor, MURATA Ceramic Capacitor, MURATA Ceramic Capacitor, MURATA Ceramic Capacitor, MURATA LED: OSRAM LWT67SQ2-4 Inductor: CoilCraft 1008 Dual Retriggerable shot Schottky Diode Quadruple Positive-NAND Gate with Schmitt-Trigger Input MOSFET White driver Dual schmitt trigger inverter Dual gate Connector Connector Manual Switch Manual Switch Push Button Connector Connector Description
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AND8135/D
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INTRODUCTION Although xenon lamps dominate standard camera market, the

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