Hi, I'm a complete noob so bare with me...I have 'some' understanding of the bare-knuckle basics but it is extremely limited.
Just so you know, because what's coming next may be a really stupid question, though I just want to understand better.
I have a usb desk lamp, and it has 36 (!!!) leds (in plain series as it seems). First off, I do know this is not a good idea to do since the provided voltage through usb is going to be too low. White led's have a forward voltage of about 3.4 (?) volts, so in series that would require 3.4x36= 122.4v
Despite this it used to shine pretty bright none the less. I tore it apart a while ago, and remember there was a small brown ceramic capacitor (I think ?) between the plus and the switch, but I didn't look at its values. I'm trying to make it work again, but haven't added a resistor yet and thus the leds all shine pretty weak. I may have broke them already perhaps and they're simply dying, that or they're running on way too low voltage.
My question:
a) how is it possible, if these leds need 3.4v each, that a usb 'low' voltage source could make these 36 leds shine bright (in SERIES ?) with just a tiny ceramic capacitor ? The voltage is always going to be too low, so I don't get it... they really seem to be mounted just in series. They're all on a round piece of pcb, and they seem to be all interconnected on the pcb. Nothing else on it except those leds, and a plus/minus wire connected to the plus/minus of the pcb...
b) How can I determine which resistor would make them shine brighter, perhaps figuring out how it was configured originally ?
There really was nothing in this lamp except the leds, a tiny wire connecting them to a switch and some tiny capacitor in between
plus wire and switch.