DN70 Datasheet, PDF (1/4 Pages) Zetex Semiconductors – ZXSC400 Driving 2 serial high power LEDs

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.
V_IN=1.8V to 3.6V
L1
D1
U1
Vcc Vdrive
Stdn Isense
C1
Gnd
V_FB
ZXSC400
Q1
C2
R1
R2
Ref. Value
U1
Q1
D1
2A
L1
22␮H
R1
18m⍀
R2
820m⍀
R3
1K⍀
C1
22uF/10V
C2
100uF/10V
C3
220nF/10V
Figure 1 Schematic diagram
Part number Manufacturer
ZXSC400E6
Zetex
ZXTN25012EFH Zetex
ZHCS2000
Zetex
Generic
Generic
Generic
Generic
Generic
Generic
Generic
Generic
Generic
Generic
Generic
Generic
Generic
Generic
Comments
LED driver in SOT23-6
Low sat. NPN transistor in SOT23
2A Schottky in SOT23
I_SAT = 2A
0805 size
0805 size
0805 size
0805 size
Table 1 Bill of materials
Issue 3 - July 2007
1
© Zetex Semiconductors plc 2007
www.zetex.com