USB 5volts to 3.5volts

Discussion in 'The Projects Forum' started by noi, Nov 8, 2006.

  1. noi

    Thread Starter New Member

    Nov 8, 2006
    hi duds,
    how can i reduced a USB powered 5volts to 3.5volts with a atleast 500ma-800ma output? Please help. Thanks
  2. Gadget

    Distinguished Member

    Jan 10, 2006
    According to USB specs, a USB port will supply 100mA unless a request is made by the connected device to deliver more current..(up to a MAX of 500mA)
    2 USB ports can be used to get up to 1 Amp. Reducing to 3.5 Volts is a simple enough process, and would require a low dropout regulator.
    Hubs will only supply 100mA max.

    Looks like your main problem is going to be getting your USB port to supply more than 100mA and may require a dedicated USB interface chip.

    Might be a lot easier to use the 5 volt rail in your PC from a spare Disk drive power connector, and reduce that to 3.5 volt.
  3. Papabravo


    Feb 24, 2006
    You expect help after insulting us?! Sheesh....
  4. noi

    Thread Starter New Member

    Nov 8, 2006
    thanks GADGET, for the responsive reply... it really wants me to redured the voltage of the USB which is 5volts, yeah the problem is how can i maximized the current to 500mA?

    Is there any way of modifiying or adding of a certain ICs or transistors so that to meet the 3.5volts output?