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LED and USB connection advice.

i am a serial restorer and upcycler have done many lamps previously but they’ve all been 240v (UK).

i now want to venture into LED lamps powered by USB. USB is 12V which means i need a transformer….or do i?

my question is the following: if i buy 12V G4 LED lightbulbs with their corresponding socket am i able to simply wire them up using a USB cable and that’s it? I am not an expert but i was thinking if the bulbs are already 12V i wouldn’t need a transformer from 240V to 12V? any advice is greatly received. I’d be looking to run these lights from normal power banks and/or laptop USB ports. (the reason i want to avoid a transformer as it’s a bulky item and the lamp i have in mind is small, the transformer will just ruin it)

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Caveat Emptor: You are trying to do or modify something that is connected to mains voltage. Please tread very carefully and do additional research.

A few notes on your question and assumptions.

  • USB is a 5V device, not a 12V device
  • A lamp that was designed to handle G4 bulbs will already have a 12V transformer built in.
  • If you just want to power the G4 LED bulb (in it’s accompanying socket), then you need a 12VDC, constant current power source. The current required will vary depending on the bulb so it would be best if you have the specs. If not, you can tinker a circuit in series with a multimeter and play around with different current levels. Higher current will give a brighter output but also shorten life.
  • If you want to stick with USB (5V), then you can find individual, high brightness LED’s and create a drive circuit with a series resistor to modulate the required curent.

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