I am hoping to power a single high power LED with a forward voltage of 1.4V and a forward current of 1.4A using a 5V lithium ion battery.
From what I understand, there are several approaches:
- using a simple resistor, in series
- use a step down switching regulator
- build a constant current source using transistors
As I require the design to be as efficient as possible, I have ruled out the simple resistor in series.
My research suggests that building a constant current source using transistors would still result in quite a poor efficiency, so I have ruled this out.
I have come to the conclusion that a step down switching regulator would be the best solution as it can cope with the variable input voltage that would result from the lithium battery discharging, and is capable of high efficiencies whilst supporting PWM from a micro-controller.
I have found that the LT3477 can support input voltages of between 2.5-25V, and can output up to 3A. The datasheet for this device contains the following diagram:
The above image shows that the LEDs experience a 300mA current; I was wondering how to modify the circuit to increase the current to 1.4A.
Any advice is greatly appreciated, as are any better ways of approaching this problem. I would preferably like to stick to using a 5V power brick, so I can easily power a Raspberry Pi at the same time. PWM is not essential. The LED has a wavelength of 940nm (infrared).