AN2129 STMICROELECTRONICS | Alldatasheet
Document overview
- Manufacturer or author: Provided By ALLDATASHEET.COM(FREE DATASHEET DOWNLOAD SITE)
- PDF pages: 9
Technical content
1 Introduction
STMicroelectronics please refer to other application notes ([1] and [2]).
2 Dimming Concepts
sated by a very simple control circuit (usually a simple potentiometer is enough). Figure 1. Analog current control Figure 2. Average current control by PWM Figure 2. The current is switched between zero and the nominal current with a frequency high- "integrate" the light output and it will not be noticed as a blinking. cated control circuits (usually a microcontroller or another simple PWM generator).
3 L6902D DC/DC Converter
to work in a constant current mode, providing up to 1A output current with an accuracy of 5%. ence voltage or 2.5A (typical value) internal current limit for short circuit protection.
Figure 3. L6902D Block diagram (see [3] for details)
4 Application Board
R6) for modifying the current sense feedback. eter slider should be connected to the dimming pin (as it can be seen in Figure 4).
Figure 6. PCB layout Table 1. Bill of materials to receive precise output current. flowing through the LED is on its maximum (i.e. 350mA on this board).
cause it contains resistor values for the most common super high brightness LEDs. Table 2. Pre-calculated standard values for feedback loop
5 Measurement
Figure 9. PWM dimming (50%) Figure 10. Current ripple
efficiency was measured above 93%. Figure 11. Efficiency vs. input voltage (@ 350mA output current)
1 LED 2 LEDs 3 LEDs 4 LEDs 5 LEDs 6 LEDs
Figure 12. Efficiency vs. number of LEDs Figure 13. Output current variation
- Almost ideal dimming curve can be observed during digital control (Figure 15). On the an-
when maximum dimming voltage is applied. Figure 14. Output Current during analog Figure 15. Output current during digital
6 References and Related Materials
7 Revision History
Table 3. Revision History
Information furnished is believed to be accurate and reliable. However, STMicroelectronics assumes no responsibility for the consequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of STMicroelectronics. Specifications mentioned in this publicati on are subject to change without notice. This publication supersedes and replaces all information previously supplied. STMicroelectronics products are not authorized for use as critical components in life support devices or systems without express written approval of STMicroelectronics. The ST logo is a registered trademark of STMicroelectronics. All other names are the property of their respective owners © 2005 STMicroelectronics - All rights reserved STMicroelectronics group of companies Australia - Belgium - Brazil - Canada - China - Czech Republic - Finland - France - Germany - Hong Kong - India - Israel - Italy - Japan - Malaysia - Malta - Morocco - Singapore - Spain - Sweden - Switzerland - United Kingdom - United States of America AN2129 APPLICATION NOTE The present note which is for guidance onl y, aims at providing customers with information regarding their products in order for them to save time. As a result, STMicroelectr onics shall not be held liable for any direct, indirect or consequential damages with respect to any claims arising from the content of such a note and/or the use made by customers of the information contained herein in connection with their products.