# How to replace a LED driver with a plug-able power adapter?

I'm trying to build a small table lamp with a 1 watt led inside. I've got this working with a matching LED driver, however, this driver is not nicely packaged and would require me to create some kind of additional housing:

I would like to replace this driver with a more typical power adapter. The one you plug into a wall to charge your cellphone.

The problem is, I don't really know how to make that work. I know enough to be dangerous, which is why I'm asking this here.

From what I read on the package, the LED driver is supplying a constant current (300mA). So you can connect up to 3 1 Watt LEDs in series.

A basic USB power adapter is, I think, supplying a constant voltage of 5V. So, using a LED calculator and assuming that the LED is 3.3V (see below). I would need to add a 6.8 Ohm resistor in series.

So my question:

• Is it as easy as adding a 6.8 Ohm resistor or is there something more I need to worry about?

This is the only info I currently have on the LED (I'm using the top one):

You're right in thinking you can just use a resistor, but I'm not sure how you get 6.8 Ohms. 5V supply with 3.3V across the LED means 1.7V across the resistor. Divide 1.7V by 0.3A and you get 5.6 Ohms.

The power dissipated by the resistor will be 1.7 x 0.3 = 0.51 Watts. It will get slightly warm so I'd observe it under load for a while to make sure this wasn't going to cause a problem.

• Instead of actually thinking about it, I mindlessly put the values in some random online LED resistor calculator. You're absolutely correct about the resistor value (1.7/0.3=5.6) Commented Mar 20, 2017 at 10:49

Like everyone else, I'm pretty sure you have, somewhere, a box full of old wall warts which have long been separated from the stuff they once powered.

Grab one of suitable size, open it, throw away the contents, and replace them with your current LED driver. You can get rid of its plastic enclosure and only use its PCB.