This entry was posted on Saturday, June 14th, 2008 at 1:17 pm and is filed under Lighting.
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 toground. 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 LT1618â€™s constant-current loop regulates 50mV across the 2.49W sense resistor, setting the LED current to 20mA.