linear mobile flash
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Application Note 95
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Simple Circuitry for Cellular Telephone/Camera
Flash IlluminationA Practical Guide for Successfully Implementing Flashlamps
Jim Williams and Albert Wu
March 2004
INTRODUCTION
Next generation cellular telephones will include high qual-ity photographic capability. Improved image sensors andoptics are readily utilized, but high quality Flash illumi-nation requires special attention. Flash lighting is crucialfor obtaining good photographic performance and mustbe quite carefully considered.
FLASH ILLUMINATION ALTERNATIVES
Two practical choices exist for flash illuminationLEDs(Light Emitting Diode) and flashlamps. Figure 1 comparesvarious performance categories for LED and flashlampapproaches. LEDs feature continuous operating capabilityand low density support circuitry among other advan-tages. Flashlamps, however, have some particularly
important characteristics for high quality photography.
Their line source light output is hundreds of times greaterthan point source LEDs, resulting in dense, easily diffusedlight over a wide area. Additionally, the flashlamp colortemperature of 5500K to 6000K, quite close to naturallight, eliminates the color correction necessitated by awhite LEDs blue peaked output.
FLASHLAMP BASICS
Figure 2 shows a conceptual flashlamp. The cylindricalglass envelope is filled with Xenon gas. Anode and cathodeelectrodes directly contact the gas; the trigger electrode,distributed along the lamps outer surface, does not. Gasbreakdown potential is in the multikilovolt range; oncebreakdown occurs, lamp impedance drops to 1. High
PERFORMANCE CATEGORY FLASHLAMP LED
Light Output HighTypically 10 to 400 Higher Than LEDs. Line Source Low. Point Source Output Makes Even Light DistributionOutput Makes Even Light Distribution Relatively Simple Somewhat Difficult
Illumination vs Time PulsedGood for Sharp, Still Picture ContinuousGood for Video
Color Temperature 5500K to 6000KVery Close to Natural Light. No Color 8500KBlue Light Requires Color CorrectionCorrection Necessary
Solution Size Typically 3.5mm 8mm 4mm for Optical Assembly. Typically 7mm 7mm 2.4mm for Optical Assembly,27mm 6mm 5mm for CircuitryDominated by Flash 7mm 7mm 5mm for CircuitryCapacitor (6.6mm Diameter; May be Remotely Mounted)
Support Circuit Complexity Moderate LowCharge Time 1 to 5 Seconds, Dependant Upon Flash Energy NoneLight Always Available
Operating Voltage Kilovolts to Trigger, 300V to Flash. ISUPPLY to Charge 100mA Typically 3.4V to 4.2V at 30mA per LED Continuousand Currents to 300mA, Dependant Upon Flash Energy. Essentially Zero 100mA Peak. Essentially Zero Standby Current
Standby Current
Battery Power Consumption 200 to 800 Flashes per Battery Recharge, Dependent 120mW per LED (Continuous Light)Upon Flash Energy 400mW per LED (Pulsed Light)
Partial Source: Perkin Elmer Optoelectronics
Figure 1. Performance Characteristics for LED and Flashlamp-Based Illumination. LEDs Feature Small Size,No Charge Time and Continuous Operating Capability; Flashlamps are Much Brighter with Better Color Temperature
, LTC and LT are registered trademarks of Linear Technology Corporation.
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current flow in the broken down gas produces intensevisible light. Practically, the large current necessary re-quires that the lamp be put into its low impedance statebefore emitting light. The trigger electrode serves this
function. It transmits a high voltage pulse through theglass envelope, ionizing the Xenon gas along the lamplength. This ionization breaks down the gas, placing it intoa low impedance state. The low impedance permits largecurrent to flow between anode and cathode, producingintense light. The energy involved is so high that currentflow and light output are limited to pulsed operation.Continuous operation would quickly produce extremetemperatures, damaging the lamp. When the current pulsedecays, lamp voltage drops to a low point and the lampreverts to its high impedance state, necessitating another
trigger event to initiate conduction.
SUPPORT CIRCUITRY
Figure 3 diagrams conceptual support circuitry forflashlamp operation. The flashlamp is serviced by a triggercircuit and a storage capacitor that generates the high
transient current. In operation, the flash capacitor istypically charged to 300V. Initially, the capacitor cannotdischarge because the lamp is in its high impedance state.A command applied to the trigger circuit results in amultikilovolt trigger pulse at the lamp. The lamp breaksdown, allowing the capacitor to discharge1. Capacitor,wiring and lamp impedances typically total a few ohms,resulting in transient current flow in the 100A range. Thisheavy current pulse produces the intense flash of light.The ultimate limitation on flash repetition rate is the lampsability to safely dissipate heat. A secondary limitation is thetime required for the charging circuit to fully charge theflash capacitor. The large capacitor charging towards ahigh voltage combines with the charge circuits finiteoutput impedance, limiting how quickly charging canoccur. Charge times of 1 to 5 seconds are realizable,depending upon available input power, capacitor valueand charge circuit characteristics.
The scheme shown discharges the capacitor in responseto a trigger command. It is sometimes desirable to effectpartial discharge, resulting in less intense light flashes.Such operation permits red-eye reduction, where themain flash is immediately preceded by one or more re-duced intensity flashes2. Figure 4s modifications providethis operation. A driver and a high current switch havebeen added to Figure 3. These components permit
CLEAR GLASS
ENVELOPE
CATHODE(NEGATIVE)
XENON GASINSIDE LAMP
ANODE(POSITIVE)
TRIGGER CONNECTIONAND CONDUCTIVEMATERIAL ALONG LAMP
AN95 F02
Figure 2. Flashlamp Consists of Xenon Gas-Filled Glass Cylinderwith Anode, Cathode and Trigger Electrodes. High VoltageTrigger Ionizes Gas, Lowering Breakdown Potential to PermitLight Producing Current Flow Between Anode and Cathode.Distributed Trigger Connection Along Lamp Length EnsuresComplete Lamp Breakdown, Resulting in Optimal Illumination
FLASH CAPACITORCHARGE CIRCUIT
TRIGGERCIRCUIT
MULTIKILOVOLTTRIGGERPULSE
FLASH STORAGECAPACITOR
VOUT TYPICALLY 300V
DISTRIBUTEDTRIGGER
ELECTRODE
FLASHLAMP
AN95 F03
CAPACITOR CHARGE/SHUTDOWN
CAPACITOR STATUS
TRIGGER/FLASHCOMMAND
Figure 3. Conceptual Flashlamp Circuitry Includes Charge Circuit, Storage Capacitor, Trigger and Lamp.Trigger Command Ionizes Lamp Gas, Allowing Capacitor Discharge Through Flashlamp. Capacitor Must beRecharged Before Next Trigger Induced Lamp Flash Can Occur
Note 1. Strictly speaking, the capacitor does not fully discharge
because the lamp reverts to its high impedance state when the
potential across it decays to some low value, typically 50V.
Note 2. Red-eye in a photograph is caused by the human retina
reflecting the light flash with a distinct red color. It is eliminated by
causing the eyes iris to constrict in response to a low intensity f lash
immediately preceding the main flash.
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stopping flash capacitor discharge by opening the lamps
conductive path. This arrangement allows the trigger/flash command control line pulse width to set currentflow duration, and hence, flash energy. The low energy,partial capacitor discharge allows rapid recharge, permit-ting several low intensity flashes in rapid succession im-mediately preceeding the main flash without lamp damage.
FLASH CAPACITOR CHARGER CIRCUITCONSIDERATIONS
The flash capacitor charger (Figure 5) is basically a
transformer coupled step-up converter with some specialcapabilities3. When the charge control line goes high,the regulator clocks the power switch, allowing step-uptransformer T1 to produce high voltage pulses. Thesepulses are rectified and filtered, producing the 300V DCoutput. Conversion efficiency is about 80%. The circuitregulates by stopping drive to the power switch when thedesired output is reached. It also pulls the DONE linelow, indicating that the capacitor is fully charged. Anycapacitor leakage-induced loss is compensated by inter-mittent power switch cycling. Normally, feedback would
be provided by resistively dividing down the output volt-age. This approach is not acceptable because it wouldrequire excessive switch cycling to offset the feedbackresistors constant power drain. While this action wouldmaintain regulation, it would also drain excessive powerfrom the primary source, presumably a battery. Regula-
tion is instead obtained by monitoring T1s flyback pulsecharacteristic, which reflects T1s secondary amplitude.The output voltage is set by T1s turns ratio4. This featurepermits tight capacitor voltage regulation, necessary toensure consistent flash intensity without exceeding lampenergy or capacitor voltage ratings. Also, flashlamp en-
ergy is conveniently determined by the capacitor valuewithout any other circuit alterations.
FLASH CAPACITORCHARGE CIRCUIT
TRIGGERCIRCUIT
DRIVER
MULTIKILOVOLTTRIGGER
PULSE
FLASH STORAGECAPACITOR
VOUT TYPICALLY 300V
DISTRIBUTEDTRIGGER
ELECTRODE
FLASHLAMP
HIGH CURRENTSWITCH
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CAPACITOR CHARGE/SHUTDOWN
CAPACITOR STATUS
TRIGGER/FLASHCOMMAND
Figure 4. Driver/Power Switch Added to Figure 3 Permits Partial Capacitor Discharge, Resulting in Controllable Light Emission.Capability Allows Pulsed Low Level Light Before Main Flash, Minimizing Red-Eye Phenomena
+
REGULATEDV
OUT
TYPICALLY300V
REGULATOR
LT3468
SWITCH
GND
CHARGE
AN95 F05
DONE
VIN
T1VIN
Figure 5. Flash Capacitor Charger Circuit Includes IC Regulator,
Step-Up Transformer, Rectifier and Capacitor. RegulatorControls Capacitor Voltage by Monitoring T1s Flyback Pulse,Eliminating Conventional Feedback Resistor Dividers Loss Path.Control Pins Include Charge Command and Charging Complete(DONE) Indication
Note 3. Details on this devices operation appear in Appendix A,
A Monolithic Flash Capacitor Charger.
Note 4. See Appendix A for recommended transformers.
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DETAILED CIRCUIT DISCUSSION
BEFORE PROCEEDING ANY FURTHER, THE READER ISWARNED THAT CAUTION MUST BE USED IN THE CON-STRUCTION, TESTING AND USE OF THIS CIRCUIT.
HIGH VOLTAGE, LETHAL POTENTIALS ARE PRESENTIN THIS CIRCUIT. EXTREME CAUTION MUST BE USEDIN WORKING WITH, AND MAKING CONNECTIONS TO,THIS CIRCUIT. REPEAT: THIS CIRCUIT CONTAINS DAN-GEROUS, HIGH VOLTAGE POTENTIALS. USE CAUTION.
Figure 6 is a complete flashlamp circuit based on theprevious text discussion. The capacitor charging circuit,similar to Figure 5, appears at the upper left. D2 has beenadded to safely clamp T1-originated reverse transientvoltage events. Q1 and Q2 drive high current switch Q3.The high voltage trigger pulse is formed by step-uptransformer T2. Assuming C1 is fully charged, whenQ1-Q2 turns Q3 on, C2 deposits current into T2s
primary. T2s secondary delivers a high voltage triggerpulse to the lamp, ionizing it to permit conduction. C1discharges through the lamp, producing light.
Figure 7 details the capacitor charging sequence. Trace A,
the charge input, goes high. This initiates T1 switching,causing C1 to ramp up (trace B). When C1 arrives at theregulation point, switching ceases and the resistivelypulled-up DONE line drops low (trace C), indicating C1scharged state. The TRIGGER command (trace D), result-ing in C1s discharge via the lamp-Q3 path, may occur anytime (in this case 600ms) after DONE goes low. Notethat this figures trigger command is lengthened for pho-tographic clarity; it normally is 500s to 1000s in dura-tion for a complete C1 discharge. Low level flash events,such as for red-eye reduction, are facilitated by short
duration trigger input commands.
+
FLASH STORAGECAPACITOR
DANGER! Lethal Potentials Present See Text
LT3468-1
SW
GND
CHARGE
DONE
TRIGGER
CHARGE
AN95 F06
DONE
VIN
T1
+VIN
FLASHLAMP
C113F330V
R11M
CAPACITORCHARGER
44.7F
1
5
8
+VIN3V TO 6V
100
DRIVER
1k
TRIGGER
C20.047F600V
3
20k
Q3HIGH CURRENTSWITCH
T2
2
1
T
A
C
Q1
C1: RUBYCON 330FW13AK6325D1: TOSHIBA DUAL DIODE 1SS306,
CONNECT DIODES IN SERIESD2: PANASONIC MA2Z720Q1, Q2: SILICONIX Si1501DL DUAL
D2
D1
Q2
30
Q3: TOSHIBA GT5G131 IGBTT1: TDK LDT565630T-002T2: KIJIMA MUSEN KP-98FLASHLAMP: PERKIN ELMER BGDC0007PKI5700
Figure 6. Complete Flashlamp Circuit Includes Capacitor Charging Components (Figure Left), Flash Capacitor C1, Trigger(R1, C2, T2), Q1-Q2 Driver, Q3 Power Switch and Flashlamp. TRIGGER Command Simultaneously Biases Q3 and IonizesLamp via T2. Resultant C1 Discharge Through Lamp Produces Light
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Figure 8 shows high speed detail of the high voltage trigger
pulse (trace A) and resultant flashlamp current (trace B).Some amount of time is required for the lamp to ionize andbegin conduction after triggering. Here, 10s after the8kVP-P trigger pulse, flashlamp current begins its ascentto nearly 100A. The current rises smoothly in 5s to a welldefined peak before beginning its descent. The resultantlight produced (Figure 9) rises more slowly, peaking inabout 25s before decaying. Slowing the oscilloscopesweep permits capturing the entire current and lightevents. Figure 10 shows that light output (trace B) followslamp current (trace A) profile, although current peaking is
more abrupt. Total event duration is 500s with mostenergy expended in the first 200s. The leading edgesdiscontinuous presentation is due to oscilloscope choppeddisplay mode operation.
LAMP, LAYOUT, RFI AND RELATED ISSUES
Lamp Considerations
Several lamp related issues require attention. Lamptriggering requirements must be thoroughly understood
and adhered to. If this is not done, incomplete or no lampflash may occur. Most trigger related problems involvetrigger transformer selection, drive and physical locationwith respect to the lamp. Some lamp manufacturerssupply the trigger transformer, lamp and light diffuser asa single, integrated assembly5. This obviously impliestrigger transformer approval by the lamp vendor, assum-ing it is driven properly. In cases where the lamp is
A = 2kV/DIV
B = 20A/DIV
5s/DIV AN95 F08
Figure 8. High Speed Detail of Trigger Pulse (Trace A) andResultant Flashlamp Current (Trace B). Current Approaches100A After Trigger Pulse Ionizes Lamp
A = RELATIVELIGHT/DIV
5s/DIV AN95 F09
Figure 9. Smoothly Ascending FlashlampLight Output Peaks in 25s
A = 20A/DIV
B = RELATIVELIGHT/DIV
AN95 F10100s/DIV
Figure 10. Photograph Captures Entire Current (Trace A) andLight (Trace B) Events. Light Output Follows Current ProfileAlthough Peaking is Less Defined. Leading Edges DashedPresentation Derives from Oscilloscopes Chopped DisplayOperationNote 5. See Reference 1.
Figure 7. Capacitor Charging Waveforms Include Charge Input(Trace A), C1 (Trace B), DONE Output (Trace C) and TRIGGERInput (Trace D). C1s Charge Time Depends Upon Its Value andCharge Circuit Output Impedance. TRIGGER Input, Widened forFigure Clarity, May Occur any Time After DONE Goes Low
A = 5V/DIV
B = 200V/DIV
C = 5V/DIV
D = 5V/DIV(INVERTED)
400ms/DIV AN95 F07
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Application Note 95
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Radio Frequency Interference
The flash circuits pulsed high voltages and currents makeRFI a concern. The capacitors high energy discharge isactually far less offensive than might be supposed. Figure12 shows the discharges 90A current peak confined to a70kHz bandwidth by its 5s risetime. This means there is
little harmonic energy at radio frequencies, easing thisconcern. Conversely, Figure 13s T2 high voltage outputhas a 250ns risetime (BW 1.5MHz), qualifying it as apotential RFI source. Fortunately, the energy involved and
A = 20A/DIV
5s/DIV AN95 F12
1000V/DIV
2s/DIV AN95 F13
Note:This application note was derived from a manuscript originally
prepared for publication inEDN magazine.
Figure 12. 90A Current Peak is Confined Within 70kHzBandwidth by 5s Risetime, Minimizing Noise Concerns
Figure 13. Trigger Pulses High Amplitude and Fast RisetimePromote RFI, but Energy and Path Exposure are Small,Simplifying Radiation Management
the exposed path length (see layout comments) are small,making interference management possible.
The simplest interference management involves placingradiating components away from sensitive circuit nodesor employing shielding. Another option takes advantage ofthe predictable time when the flash circuit operates. Sen-
sitive circuitry within the telephone can be blanked duringflash events, which typically last well under 1ms.
+
1M
1
1
Q3
C1
0.047F600V
20k 30
= RETURNED TO INTERNAL GROUND PLANE
VIN = RETURNED TO INTERNAL VIN PLANE
1
1k
Q1
Q2
100
4.7F
VIN
VIN
1
LT3468-1
CATHODE ANODE
T2TRIGGER
TRANSFORMER
D2
1
PRIMARY
AN95 F11
SECONDARY
T1FLYBACK
TRANSFORMER
1 D1
Figure 11. Magnified Demonstration Layout for Figure 6. High Current Flows in Tight Loop from C1 Positive Terminal, Through Lamp,Into Q3 and Back to C1. Lamp Connections are Wires, Not Traces. Wide T1 Secondary Spacing Accommodates 300V Output
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APPENDIX A
A MONOLITHIC FLASH CAPACITOR CHARGER
The LT3468/LT3468-1/LT3468-2 charge photoflash ca-
pacitors quickly and efficiently. Operation is understoodby referring to Figure A1. When the CHARGE pin is drivenhigh, a one shot sets both SR latches in the correct state.Power NPN, Q1, turns on and current begins ramping upin T1s primary. Comparator A1 monitors switch currentand when peak current reaches 1.4A (LT3468), 1A(LT3468-2) or 0.7A (LT3468-1), Q1 is turned off. Since T1 is utilizedas a flyback transformer, the flyback pulse on the SW pincauses A3s output to be high. SW pin voltage must be atleast 36mV above VIN for this to happen.
During this phase, current is delivered to the photoflash
capacitor via T1s secondary and D1. As the secondarycurrent decreases to zero, the SW pin voltage begins tocollapse. When the SW pin voltage drops to 36mV aboveVIN or lower, A3s output goes low. This fires a one shotwhich turns Q1 back on. This cycle continues, deliveringpower to the output.
Output voltage detection is accomplished via R2, R1, Q2and comparator A2. Resistors R1 and R2 are sized so thatwhen the SW voltage is 31.5V above VIN, A2s output goeshigh, resetting the master latch. This disables Q1, halting
VIN SW +DONE
CHARGE
C1
T1
R260k
Q1ENABLE
COUTPHOTOFLASHCAPACITOR
36mV
20mV
TO BATTERY
D2
Q2
VOUT
D1
LT3468: RSENSE = 0.015LT3468-2: RSENSE = 0.022LT3468-1: RSENSE = 0.03
AN95 FA1
1
GND
53
4 2
+
+
+
+
+
ONE-
SHOT
ONE-SHOT
DRIVER
PRIMARY SECONDARY
MASTERLATCH
RSENSE
VOUT COMPARATOR
R12.5k
SR Q
1.25VREFERENCE
Q3
Q1Q Q
S R
A3
A1
A2
CHIP ENABLE
Figure A1. LT3468 Block Diagram. Charge Pin Controls Power Switching to T1. Photoflash Capacitor Voltageis Regulated by Monitoring T1s Flyback Pulse, Eliminating Conventional Feedback Resistors Loss Path
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power delivery. Q3 is turned on, pulling the DONE pin low,indicating the part has finished charging. Power deliverycan only be restarted by toggling the CHARGE pin.
The CHARGE pin gives the user full control of the part.
Charging can be halted at any time by bringing theCHARGE pin low. Only when the final output voltage isreached will the DONE pin go low. Figure A2 shows thesevarious modes in action. When CHARGE is first broughthigh, charging commences. When CHARGE is brought
low during charging, the part shuts down and VOUT nolonger rises. When CHARGE is brought high again, charg-ing resumes. When the target VOUT voltage is reached, theDONE pin goes low and charging stops. Finally, the CHARGEpin is brought low again, the part enters shutdown and theDONE pin goes high.
The only difference between the three LT3468 versions isthe peak current level. The LT3468 offers the fastestcharge time. The LT3468-1 has the lowest peak currentcapability, and is designed for applications requiring lim-ited battery drain. Due to the lower peak current, theLT3468-1 can use a physically smaller transformer. TheLT3468-2 has a current limit between the LT3468 and theLT3468-1. Comparative plots of the three versions chargetime, efficiency and output voltage tolerance appear in
Figures A3, A4 and A5.Standard off-the-shelf transformers, available for allLT3468 versions, are available and detailed in Figure A6.For transformer design considerations, as well as othersupplemental information, see the LT3468 data sheet.
LT3468-2VIN = 3.6VCOUT = 50FVOUT
100V/DIV
VCHARGE5V/DIV
VDONE5V/DIV
1s/DIV AN95 FA2
Figure A2. Halting the Charging Cycle with the CHARGE Pin
Figure A3. Typical LT3438 Charge Times. Charge Time Varies with IC Version, Capacitor Size and Input Voltage
VIN (V)
2 3 4 5 6 7 8 9
CHARGETIME(s)
10
9
8
76
5
4
3
2
1
0
COUT = 50F
COUT = 100F
TA = 25C
VIN (V)
2 3 4 5 6 7 8 9
CHARGETIME(s)
10
9
8
76
5
4
3
2
1
0
COUT = 20F
COUT = 50F
TA = 25C
VIN (V)
2
CHARGETIME(s)
10
9
8
76
5
4
3
2
1
04 6 7
AN95 FA3
3 5 8 9
COUT = 100F
COUT = 50F
TA = 25C
LT3468 Charge Times LT3468-1 Charge Times LT3468-2 Charge Times
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VOUT (V)
50 100 150 200 250 300
EFFICIENCY(%)
90
80
40
50
60
70
VIN = 2.8V
VIN = 4.2V
TA = 25C
VIN = 3.6V
VOUT (V)
50 100 150 200 250 300
EFFICIENCY(%)
90
80
40
50
60
70
VIN = 2.8V
VIN = 4.2V
VIN = 3.6V
TA = 25C
VOUT (V)
50
EFFICIENCY
(%)
90
80
70
60
50
40250
AN95 FA4
100 150 200 300
TA = 25C
VIN = 4.2V
VIN = 2.8V
VIN = 3.6V
LT3468 Efficiency LT3468-1 Efficiency LT3468-2 Efficiency
Figure A4. Efficiency for the Three LT3468 Versions Varies with Input and Output Voltages
VIN (V)
2 3 4 5 6 7 8
VOUT
(V)
324
323
322
318
319
320
321
TA = 40C
TA = 25C
TA = 85C
VIN (V)
2 3 4 5 6 7 8
VOUT
(V)
324
323
322
318
319
320
321
TA = 40C
TA = 25C
TA = 85C
VIN (V)
VOUT
(V)
319
318
317
316
315
314
313
312
AN95 FA5
2 3 4 5 6 7 8
TA = 25C
TA = 85C
TA = 40C
LT3468 Output Voltage LT3468-1 Output Voltage LT3468-2 Output Voltage
Figure A5. Typical Output Voltage Tolerance for the Three LT3468 Versions.Tight Voltage Tolerance Prevents Overcharging Capacitor, Controls Flash Energy
SIZE LPRI LPRI-LEAKAGE RPRI RSECFOR USE WITH TRANSFORMER NAME (W L H) mm (H) (nH) N (m) () VENDOR
LT3468/LT3468-2 SBL-5.6-1 5.6 8.5 4.0 10 200 Max 10.2 103 26 Kijima MusenLT3468-1 SBL-5.6S-1 5.6 8.5 3.0 24 400 Max 10.2 305 55 Hong Kong Office
852-2489-8266 (ph)[email protected] (email)
LT3468 LDT565630T-001 5.8 5.8 3.0 6 200 Max 10.4 100 Max 10 Max TDKLT3468-1 LDT565630T-002 5.8 5.8 3.0 14.5 500 Max 10.2 240 Max 16.5 Max Chicago Sales OfficeLT3468-2 LDT565630T-003 5.8 5.8 3.0 10.5 550 Max 10.2 210 Max 14 Max (847) 803-6100 (ph)
www.components.tdk.com
LT3468/LT3468-1 T-15-089 6.4 7.7 4.0 12 400 Max 10.2 211 Max 27 Max Tokyo Coil EngineeringLT3468-1 T-15-083 8.0 8.9 2.0 20 500 Max 10.2 675 Max 35 Max Japan Office
0426-56-6336 (ph)www.tokyo-coil.co.jp
Figure A6. Standard Transformers Available for LT3468 Circuits. Note Small Size Despite High Output Voltage
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
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LT/TP 0304 1K PRINTED IN USALinear Technology Corporation1630 M C th Bl d Mil it CA 95035 7417