USB LED Bulb Conversion

       I have these cheap USB powered LED bulbs which have a simple circuit - direct driven LEDs on 5V. It is a bit wasteful in power so I decided to mod them for longer runtime on camping trips.

I have a bunch of these tiny Marvell G47B based synchronous DC-DC converter modules and have not thought of a use for them as they are 5.5Vin max so usefulness is limited. But they are perfect for USB.

Basing on the datasheet, these are the purposes of the module pads.

For the output voltage setting, these are the resistors needed.

Simplified connection diagram

And a crude way of connecting it all to make a standalone DC-DC module.

Testing the proof of concept with a 3W LED.

Now we start with the LED Bulb. It draws about 3.3W as is unmodified, it drives the 10 LEDs at about 65mA each.

The LEDs use 18ohm resistors each. I desoldered them and used 1ohm resistors for each.

Since the LEDs need about 3.08V at 65mA, with 1 ohm resistors, would now need about 3.145V each. I programmed the module for 3.135V (closest) using the table above.

This is now the resulting power draw at 2.3W with about the same LED current!

Wrapped it in heatshrink for protection and some strain relief of the input cable.

More light for longer time on camping trips!

Page created and copyright R.Quan ©30 Jul 2017.