|
|
PDF AND8109D Data sheet ( Hoja de datos )
| Número de pieza | AND8109D | |
| Descripción | LED Constant Current Source Scheme | |
| Fabricantes | On Semiconductor | |
| Logotipo |  |
|
Hay una vista previa y un enlace de descarga de AND8109D (archivo pdf) en la parte inferior de esta página. Total 2 Páginas | ||
|
No Preview Available !
AND8109/D
LED Constant Current
Source Scheme
Theory of Operation
Prepared by: Mark Scholten
Senior Applications Engineer
http://onsemi.com
The LM317L wants to see 1.25 V between its VOUT pin
and the Vadj pin, and it will do whatever it can to keep that
voltage differential between them. So if a resistor is put in
series with the output, and the Vadj pin is connected to the
load side of the sense resistor, a current source is set up
which follows Equation 1:
IOUT
+
1.25
Rsense
(Approximately)
(eq. 1)
VIN
LM317L
VOUT
IOUT
Rsense
Vadj
Rload
But what if a series/parallel combination of LEDs is
wanted? The following circuit works fine, assuming that
there are not large variations in the forward voltage drop of
the LEDs. There could be a problem however if one of the
strings opens up for some reason. The LEDs that remain
would have 50% more current flowing through them, which
could cause them to be driven too hard and fail. So how does
one get around this problem?
VIN VOUT
LM317L
Rsense
IOUT
LED1 LED4 LED7
Vadj
LED2 LED5 LED8
LED3 LED6 LED9
Figure 1.
In order to set up a constant current source for an LED
string, the same circuit can be used by simply substituting
Rload with an LED string, as shown below.
VIN LM317L VOUT
IOUT
Rsense
LED1
Vadj LED2
Figure 3.
The following circuit takes care of this issue by splitting
up the current sense resistor into three resistors, one for each
leg of the LED string. The current through any one of the
LED strings is set by Equation 2:
IOUT
+
1.25
V)
R1
Vsat
(Approximately)
(eq. 2)
LED3
Figure 2.
Semiconductor Components Industries, LLC, 2003
January, 2003 – Rev. 0
1
Publication Order Number:
http://www.Datasheet4U.com
AND8109/D
1 page | ||
| Páginas | Total 2 Páginas | |
| PDF Descargar | [ Datasheet AND8109D.PDF ] | |
Hoja de datos destacado
| Número de pieza | Descripción | Fabricantes |
| AND8109 | LED Constant Current Source Scheme | On Semiconductor |
| AND8109D | LED Constant Current Source Scheme | On Semiconductor |
| Número de pieza | Descripción | Fabricantes |
| SLA6805M | High Voltage 3 phase Motor Driver IC. |
 Sanken |
| SDC1742 | 12- and 14-Bit Hybrid Synchro / Resolver-to-Digital Converters. |
 Analog Devices |
|
DataSheet.es es una pagina web que funciona como un repositorio de manuales o hoja de datos de muchos de los productos más populares, |
| DataSheet.es | 2020 | Privacy Policy | Contacto | Buscar |