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LED flashlight evaluation board based on the L6920DA
Data Brief
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Last Updated: 25/03/2008
Pages: 4
Related Application Notes
Low Voltage LED Driver Using L6920D, L4971 and L6902D
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STEVAL-ILL008V1
LED flashlight evaluation board based on the L6920DA
Data Brief
Features
High efficiency step-up converter Powered from two cell batteries Output voltage Vout = 3.5 V Minimum operating input voltage Vin = 1 V
Description
White LEDs are gaining popularity as sources of illumination due to their high efficiency and reliability. Typical forward voltage drop across a white LED is approximately 3.5 V. When these LEDs are powered from a single or two cell batteries, a boost converter is needed to boost the voltage to drive the LEDs. This evaluation board, based on the L6920DA, implements a high efficiency step-up converter which requires very few passive components to perform the conversion from the battery voltage to the selected output voltage or current. Startup is guaranteed at 1 V and the device operates down to 0.6 V. The device has a very low quiescent current of only 10 A. An internal synchronous rectifier is implemented with a 120 m P-channel MOSFET, replacing the conventional boost diode, to improve efficiency. This also could reduce the cost of the application since no external diode required. STEVAL-ILL008V1
March 2008
Rev 1
1/4
www.st.com 4
For further information contact your local STMicroelectronics sales office.
1
2 Vd d 3
C3 0 .1 u F 1
2
30k 1 /8 W 5%
1
2
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Circuit schematic
Figure 1. Schematic
J2 1 7 LX S H D N FB L BI R E F GN D L6920D 1 Ou t Vc c 5 U2 6 L BO 3
+
L1 12 OU T 1 C1 47uF 6 .3 V 6TPB47M S nyo Sany 8 5 2 4 C4 0 .1 u F 10uH DO1608C-103 Coilcraft
U1 1
J4 C ON 1
Circuit schematic
1 C2 47uF 6 .3 V
C ON 1
+
B T1 3V
D1 L ED 1 J5 C ON 1 R1 0 .3 3 1 /8 W 1%
J6
1
C ON 1
32 R5 1 51k 1 /8 W 5% 1 R3 2 1nF 2 C5
1
4 N o n In vIn v_ In TS 9 5 1 IL T_ S OT2 3 -5 L
SW1 SP S W SLIDE-SP D T Apem 5136N Apem 25136NH
R4 1k 1 /8 W 5%
STEVAL-ILL008V1
STEVAL-ILL008V1
Revision history
2
Revision history
Table 1.
Date 27-Feb-2008
Document revision history
Revision 1 Initial release. Changes
3/4
STEVAL-ILL008V1
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Document Number: 14501
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