USB drivers for LED strings

[ju1ce]

Hi,

I recently opened my Tindie store to sell my first kits: dimmable constant current sources for LED strings. The idea is that one can use old phone chargers and other wall warts to power LED strings. There are two designs, a linear one ($8) and one built around a SMPS chip ($15). The latter can handle a bit more current and a wider supply voltage. The kits use SMD components, the smallest ones being 0603 and SOT-23 (even though having a SMD kit is a bit crazy, I think almost everyone can solder those).



I created these products because I wanted to power LED strings bought from eBay and there didn't seem to be a nice solution. Most existing solutions have poor connectors (screw terminals and no USB), support only a small subset of LED forward voltages and currents or have no dimming.




The designs are OSHW - the original CAD files are available on my blog. Viewers of this blog will get a 10% discount with code DEE6650. The code is valid until September 15th 2015. Thanks for everyone who have supported so far. I've sent one for Dave as well, I'm eager to find out what he thinks of them.



Here are the documentation PDFs with schematics and instructions:

• Linear supply documentation
• Switching supply documentation

-Jussi

[daveatol]

You could replace the driver IC with an ATTINY and have dimming controlled via USB as well as potentiometer

[sleemanj]

Charts of achievable output current at different forward voltages and efficiency thereof would be useful for the switcher.

Note that in your switcher doc you have the part number wrong (you have written SCT3926 instead of SCT2932)

Something this size which could actually push 10 watts into a 3x3 10w led (circa 10v forward) from a 12v input would be interesting.

[ju1ce]

You could replace the driver IC with an ATTINY and have dimming controlled via USB as well as potentiometer

I wouldn't trust a microcontroller in a control loop. Of course, the 555 could be replaced with a micro, but I like having a project without a microcontroller for a change - and 555 needs no code.

[ju1ce]

Charts of achievable output current at different forward voltages and efficiency thereof would be useful for the switcher.

Note that in your switcher doc you have the part number wrong (you have written SCT3926 instead of SCT2932)

Something this size which could actually push 10 watts into a 3x3 10w led (circa 10v forward) from a 12v input would be interesting.

Thanks for the tip, I fixed the document. I have a nice dummy load so I guess I could give more information about the characteristics of the supply. I checked how the thing performs with 12 V input and 10V load @ 955 mA. The board was drawing 876 mA of current, resulting in an efficiency of 91%. The IC does get a bit warm (so does the diode) but I guess it should survive prolonged use, especially if one manages to solder the thermal pad correctly.

Disclaimer: I never designed these products for this kind of a use case. The intended use for these is to drive LED strings with a few hundred milliamps so that they are pretty instead of blinding.

EDIT: Decided to go all the way. The efficiency figures for the switcher are now in the document.