Buck/Boost driver question

[Th232]

I've been looking at various driver circuits recently, and maybe I just haven't been looking in the right places, but while I've seen a fair number of buck or boost drivers with varying input and output voltages, I've seen very few buck/boost drivers, and those that I have seem to be centred around CR123As.

I've been playing around with building my own lights, and what I'm after is a buck/boost board that will be suitable for using either 2x CR123A or RCRs, or 1x 18650, but also 1x CR123A in case I want to use the driver for another light as well. If it was just 2x CR123As or 1x 18650, I'd just go with a buck regulator, but I guess I'm just attracted to the versatility of such a driver, if it exists (partly because of the AUD=>USD exchange rate).

At the moment the only solution I seem to have found is using a buck regulator and either let it go into direct drive for using 1x CR123A, or buy a different regulator for it (the GD comes to mind). If I go the DD route, is there anything in particular (heating issues?) that I should watch out for?

Reusing the board for another light (and with a different battery pack) is nothing but a thought at the moment, but I figured it'd be good to see what's out there (if anything). Is there anything inherently stupid with any of the above thoughts?

 

[HarryN]

Hi Will,

Your request is perfectly logical, but you are right, there are very few options out there - perhaps none that actually will work. At least I could not find any now or in the past.

The closest I could come up with is this one from the sandwich shoppe

http://theledguy.chainreactionweb.com/product_info.php?products_id=1106&language=

It basically covers the entire range of 1 cell, primary or R. I have either this one or a similar one in a light I own driving a r/o Lux III, but also it can drive various single die white as well.

At one point in time, I looked at having a custom board made which would deal with your exact request. The main problem is that the components that make sense to use in a buck / boost setup typically didn't come in the input voltage that also makes sense. (have not looked lately).

The EE I was working with suggested that we could take "any input voltage" - boost it up to a new "fixed voltage", then buck it back down for current control. While this would likely work, it also would have considerable losses (2 conversions) and be rather large - so it didn't happen.

It is possible to make a light which uses your battery configuration, but not exactly universal. The basic idea is that you buy an LED package that has 4 die and wire them in series 4S , making it a fairly high Vf - nominal 12 - 16 volts range.

At that point, just use a boost only configuration and underdrive them as needed to deal with real battery capability. (2 x C = 2 x capacity max)

In that case, you can get other drivers from the shoppe or taskled.com or other boost driver options like a boost puck from these guys.

http://www.ledsupply.com/boostpuck.php

I know it is not exactly what we all want, but it does work.

 

[Th232]

Thanks for the info Harry, maybe it's time to start looking at homebrew circuits again, perhaps things have changed then.

Failing that, I'll also take a look into running a 4 die LED, thanks for bringing up that option as well.