ZXSC100

ISSUE 1 - JANUARY 2001

9

OTHER APPLICATIONS

Driving white LED’s in a flashlight application

The ZXSC100 solution is ideal for LED lamp driving

applications operating from a single cell. In principal

conversion from 1.2V to the 3.6V, typically required by

white LEDs, is necessary. Load currents in the region of

20mA to 50mA being required for a single LED element.

To minimise size, weight and cost, single cell operation

is an advantage. The ZXSC is well matched to single cell

NiCd and NiMH characteristics. The circuit will turn on at

1.06V, to maximise the life the battery can offer, the

converter does not turn off until the battery voltage falls

to 0.93V.

The circuit itself is very simple, a minimum number of

components are used and they are all small size. The

ZXSC uses the very small MSOP8 package, the pass

transistor is SOT23. No capacitors are required as

the circuit is stable under all conditions. The inductor

recommended is a low cost miniature component.

No compromise is made on efficiency however. In a

standard configuration efficiency well over 80% can

be achieved. With careful inductor selection

efficiency over 90% is possible.

The inherent flexibility of the ZXSC circuit means

that parallel or series LEDs can be driven depending

on application needs. A simple modification to the

application circuit means that the maximum pulse

current can b e programmed t o match the

characteristics of the chosen LED load, pulse current

in the range 10mA to 3A and beyond can be easily

achieved.

An application note (AN33) is available describing

various circuits for driving white LEDs. This

application note includes details of

circuits that

optimise battery life, maximise brightness and can

be constructed for minimal cost. Contact your local

Zetex office for further details.

Q1

ZXT13N15

R2

0.22R

L1

100µH

BAS

EM

RE

U1

ZXSC100

D1

WHITE LED

FB