In addition to providing an accurate input current limit, the
LT1618 can also be used to provide a regulated output
current for current-source applications. White LED drivers
are one such application for which the LT1618 is
ideally suited. With an input voltage range of 1.6V to 18V,
the LT1618 can provide LED drive from a variety of input
sources, including two or more alkaline cells, or one or
more Li-Ion cells. The circuit in Figure 7 is capable of
driving six white LEDs from a single Li-Ion cell. LED
brightness can be adjusted using a pulse width modulated
(PWM) signal, as shown, or by using a DC voltage to drive
the IADJ pin directly, without the R3/C3 lowpass filter. If
brightness control is not needed, simply tie the IADJ pin to
ground. Typical output voltage with the LEDs shown is
around 22V, and the R1, R2 output divider sets the
maximum output voltage to around 26V to protect the
LT1618 if the LEDs are disconnected. The LT1618’s
constant-current loop regulates 50mV across the 2.49W
sense resistor, setting the LED current to 20mA.
Read more original source:http://www.linear.com/pc/downloadDocument.do?
navId=H0,C1,C1003,C1042,C1031,C1061,P2079,D4452
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This entry was posted on Saturday, June 14th, 2008 at 1:17 pm and is filed under Lighting.
