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The LM3485 design is a buck regulator derived controlled current source designed to drive high power, high brightness LEDs (HBLEDs) at a constant current of 1.4A. The design can accept an input voltage ranging from 10V to 30V and can control the output current delivered to series and/or parallel arrays of HBLEDs as long as the forward voltage of all the LEDs in series is less than 0.9 x Vin. The accuracy of the output current is +-10%
Diode D2 provides an input for a pulse width modulation signal for dimming of the LED array. In order to fully enable and disable the LM3485 the PWM signal should have a maximum logic low level of 1.0V, a minimum logic high level of 2.0V, and minimum low and high periods of 40us. For example, at 100Hz, the minimum and maximum PWM duty cycles to which LM3485 can respond are 0.4% and 99.6%, respectively.
In the case that the input is powered but no LED array is connected to the output (output open circuit) the output voltage will rise to equal the input voltage. The output of the circuit is rated to 30V and will not suffer damage, however care should be taken not to connect an LED array if the output voltage is higher than the target forward voltage of the LED array in steady state.
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Example Schematic Showing Connection for all Components.
