Electronic – How to replace a LED driver with a plug-able power adapter

ledled-driverpower supply

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:
led driver

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):
enter image description here

Best Answer

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.