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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


VOUT TYPICALLY 300V

DISTRIBUTEDTRIGGER

ELECTRODE

FLASHLAMP

HIGH CURRENTSWITCH

AN95 F04

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.

+


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

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