Issue 3 - July 2007

1

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© Zetex Semiconductors plc 2007

DN70

ZXSC400 Driving 2 serial high power LEDs

Description

This design note shows the ZXSC400 driving 2 serial LEDs. The input voltage ranges from 2V to

3.6V with a maximum output current of 360mA from 2.6V input.

Figure 1 shows a typical constant current solution with the ZXSC400 driving two 1W LEDs in

series. The wide input voltage range allows the use of different battery cell combinations. This

could be dual alkaline cells with voltage starting from 3V down to 2V or triple NiCad/NiMH cells

with voltage starting from 3.6V down to 2.7V.

Figure 1

Schematic diagram

Ref.

Value

Part number

Manufacturer

Comments

U1

ZXSC400E6

Zetex

LED driver in SOT23-6

Q1

ZXTN25012EFH Zetex

Low sat. NPN transistor in SOT23

D1

2A

ZHCS2000

Zetex

2A Schottky in SOT23

L1

22 H

Generic

Generic

R1

18m

Generic

Generic

0805 size

R2

820m

Generic

Generic

0805 size

R3

1K

Generic

Generic

0805 size

C1

22uF/10V

Generic

Generic

C2

100uF/10V

Generic

Generic

C3

220nF/10V

Generic

Generic

0805 size

Table 1

Bill of materials

Vcc

Gnd

Isense

Vdrive

Stdn

U1

ZXSC400

C2

L1

C1

R1

R2

Q1

D1