# Can I drive (relatively) high power LEDs from a constant voltage supply?

I'm trying to tie together a single cell LiPo battery, an MPPT solar charger and a 3W LED

The problem is that the constant current supplies i'm seeing need 6V+ and the LiPo puts out a nominal 3.7

I understand that a big reason why constant current is preferred is because of the asymptotic nature of current draw as a function of voltage, but if i have a battery providing 3.7 (and let's say I run it through a linear voltage regulator), wouldn't this work just as well? If not - why?

• Lithium battery average voltage is 3.7V. Range is 4.2V down to, say, 3.5 or 3.4V, or even lower, depending on many things. If your LED is red or yellow, you can probably use the battery and a linear regulator, although the regulator will get very hot. If you are doing blue, green or white, it probably will not work well with a linear regulator because the battery voltage is not high enough in the lower part of the range. If you don't need to run the LED at full brightness, you may just get away with it. But at 750mA, probably not. Dec 5, 2017 at 18:46
• It is an awkward problem. If you really need full power out of a white, blue or green LED, you may need to boost then either linear regulate or buck regulate to drive the LED, or use a flyback topology of some sort. Dec 5, 2017 at 18:48
• @kolosy: See my answer to electronics.stackexchange.com/questions/342121/…. Dec 5, 2017 at 19:30
• If you can live with (say) 80% of the LiPo cell capacity, you should be able to come up with a constant current circuit that works down to about 3.3 or 3.4V and consider the cell "empty" at that point. (Bonus : the LiPo cell will probably last longer too)
– user16324
Dec 5, 2017 at 19:44