Apologies if this question is too vague. I have incomplete information and I'm asking because I'm not sufficiently knowledgeable to answer this myself!
I have ten USB LED units and I have a 12v power supply (that is the only power supply I have available, no mains). I also have a number of LM340T 5 volt regulators. Given the components I have to hand, I want to figure out the best way to wire them up, or whether there is no best way to wire them up and I should do it differently.
There is very little info on the LED units, except that they're rated 5 Volts. I don't know the current rating. Inside are two pairs of tiny J3 transistors and resistors. I can't see the tracks, but I could work it out the circuit with a continuity tester. I imagine we're talking a few tens of mA but I don't know.
Do you think it would be a good/bad idea to use one LM340T per LED to drop the power from 12v to 5?
Do you think that the LED units (and their internal regulator circuit) would behave nicely in series to form a potential divider, three to a circuit to give 4v each?
Should I just get a proper Buck converter?