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These years, light-emittingdiodes (LEDs) are widely usedfor various applications, suchas lighting and backlights of

thin TVs, because of their improvedperformance and the growing concernfor energy conservation. They are alsoexpected to be used as light sources for

various devices in the future, amongwhich include a high-brightness LEDas light source for camera shooting.At present, extremely bright LEDs areassembled in portable battery-operateddevices, including smartphones, digitalcameras, and digital camcorders as lightsources for shooting pictures. TheseLEDs are used as torch light during

video recording and asfl

ash during stillphoto shooting. The potential for LEDsto be used in wide variety of shootingscenes in the future is very high as theirperformance is improved.

LED Flash, Surrounding IssuesLEDs are characterized by their

brightness, which can be adjusted bycontrolling the amount and duration of

video recording.Fig. 1 (left)

shows a standardLED flash circuitc o n f i g u r a t i o ndiagram. A batteryis used as the powersource of the LED

and the amountof electric currentpassing through theLED depends on thebattery performance. For that reason,brightness is also controlled dependingon the battery performance. To lightthe LED brighter in accordance with itsimproved performance and the shooting

condition, it is necessary to pass alarger electric current to the LED. Fig.1 (right) shows the circuit configurationdiagram where an electrical double layercapacitor (EDLC) is used as an auxiliarypower source. This circuit enables theEDLC to supply larger electric current,which cannot be supplied from thebattery. Therefore, this circuit lightsthe LED brighter regardless of battery

Optimal EDLC for LED FlashSystem

To supply large electric currentto an LED within a short period oftime, the charging device used as an

auxiliary power source must have largecapacitance and low internal resistancecharacteristics. Another requirementis that, in order to supply a stablelarge electric current under variousenvironmental conditions, the internalresistance must be steadily low over awide temperature range.

It is known that the EDLC has a largecapacitance In addition because of

As LEDs move their way to flash and torch light systems of camera-employeddevices, high-capacitance and low-resistance EDLCs play a key role.

Optimal EDLC by MurataPowers LED Flash Systems

1400

Illuminationat1m(

lux)

0.000 0.002 0.004 0.006 0.008

Time (sec)

0.010 0.012 0.014 0.016 0.018

1200

1000

800

600

400

200

0

Fig. 2: Illumination characteristic when an LED is operated with alarge current (8A) using EDLC

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SPECIAL REPORT

LED & Lighting Technologies

Table 1 shows the lineup of EDLCsoffered by Murata Manufacturing. Photo

1 shows the LED flash demonstrationboard using Muratas EDLC. Thissystem can supply large electric currentof up to 8A to an LED for 33msec. Itallows current to be controlled between2A and 8A and 10 to 60msec.

Future ProspectsMore and more LEDs are being

assembled in smartphones and digitalcamcorders as lighting for shootingpictures. These devices can make theflash even brighter by using an EDLC asan auxiliary power source for the LEDs.On the other hand, digital still camerasuse a flash system consisting of a xenonflash tube. As LEDs are more easilycontrolled and have power saving and

space saving features, they are expectedto replace the xenonflash tube. Such LEDapplications require a circuit system thatcan pass larger electric current, an LED

with high luminous efficiency, and anEDLC with large capacitance and lowresistance.

Devices equipped with a cameraare expected to play even more

important roles in peoples lives astheir applications expand. Murata willcontinue to improve the features of itsproducts and introduce to the marketEDLCs with large capacitance and lowresistance in a compact, low-profileand lightweight package that is idealfor operating LEDs. Through theseactivities, the company will continue to

contribute to enhancing the convenienceof devices equipped with a camera.

About This Article:

The author, Kunio Nomura, is from thePlanning/Sales Promotion Section, HighPerformance Power Device Departmentat Murata Manufacturing Co., Ltd.

2.9

&DSDFLWRU9ROWDJH9 2.7

2.52.32.11.91.71.51.31.10.90.70.5

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&DSDFLWRU9ROWDJH9 2.7

2.52.32.11.91.71.51.31.10.90.70.5

0 0.2 0.4 0.6 0.8

'LVFKDUJH7LPHVHF 'LVFKDUJH7LPHVHF

Discharge characteristics (room temperature: 25C) Discharge characteristics (room temperature: -20C)

1 1.2 1.4

1A

2A

4A

8A

1A

2A

4A

8A

0 0.2 0.4 0.6 0.8 1 1.2 1.4

Fig. 3: Discharge characteristics (2.7V/700mF/30m product)

Instantaneous maximumallowable voltage (V)

ESR (TYP)(m)

Nominalcapacitance (mF)

Dimensions (LWT)(mm)

Operatingtemperature range

2.7V 30 700 20.518.51.5 mm -30C to 70C

5.5V 60 350 20.518.53.0 mm -30C to 70C

Table 1: EDLC product lineup (DME Series)

LED flash demonstration board using an EDLC