suggestions for switcher IC for 120vac in, 1.5A out, non-isolated?

hi gang,

I'm in the mood to rig up a bit of lighting for the home. I've got 4 XP-G's and a few yellow LEDs that were scavanged. The plan is wire them in series (nominally), running at 1.5A and a total voltage for the string somewhere around 12 to 15 volts.

I'd like to keep the package compact and easy to retrofit into the volume of a normal fixture. I could make life easy and just use a large wall-wart transformer to produce roughly the correct voltage, but these tend to be bulky and heavy. My preference would be to use a switcher IC and put together a basic high voltage buck converter. No need for dimming or anything fancy. Just a simple converter that would use easily obtainable components, i.e. no special transformers.

I've been browsing through a few of the IC manufacturer's sites, but haven't found anything that seemed ideal just yet. I did find an app note for an OnSemi part, the NCP1216, where it was used for a 0.5A circuit. Seems like it could be modified to 1.5A.
http://www.onsemi.com/pub_link/Collateral/DN06050-D.PDF

What else is out there? Is there already a design worked out that is not too hard to build?

thanks much,

Steve K.

Power Integrations has some great IC's for AC-DC LED Drivers. They also have great Reference Design Reports that give PCB layout ideas and BOM.
Here is one Design report I found after doing a quick search.
If you're willing to lower the drive current to 700mA, the designs can get much simpler http://www.powerint.com/sites/default/files/PDFFiles/der215.pdf

I'm assuming that you understand the dangers / complexities of designing AC-DC drivers so I won't get into that.

I'll have to look at their stuff in more detail The design report is interesting... The complexity is significantly greater than I wanted to deal with, but I'm intrigued at the level of detail in the document. It's the first app note I've seen where they actually show you the details of how to wind the transformer!

The option of using a wall-wart is certainly looking more attractive, as it eliminates a whole range of issues (power factor correction, high voltage safety and grounding, and emissions (to a degree)). The downside is the considerable bulk of magnetics designed for 60Hz.

I'm tempted to just throw together a simple hysteretic current-mode buck regulator and call it good enough. There would still be issues related to either driving a high side mosfet quickly, or sensing voltage across a current-sense resistor and translating that voltage down to a safe level that can be used by the controller. Both of these can get complicated, though, when dealing with line voltages.

Maybe I'll see how far I get with a good wall-wart, or check the prices on the off-the-shelf AC led drivers??

thanks,

Steve K.