If it asks for 5v, is that 5v under load?

Discussion in 'General Electronics Chat' started by Grayham, May 25, 2010.

  1. Grayham

    Thread Starter Member

    May 18, 2010

    I have built my own regulated 5v power supply.

    I have noticed though when I run my device off it that asks for 5v.
    My power supply will drop down to around 4.85v due to 850ma being drawn from it.

    The stock power supply I noticed drops it voltage too when the unit is connected to it, but it is 5.25v and drops to 4.98v when the unit is plugged in and running.

    My question is when something asks for 5v, does that mean it wants 5v when under load, or does it want 5v when nothing is plugged (but meaning when in use it will actually get 4.85v)?
  2. Markd77

    Senior Member

    Sep 7, 2009
    There is probably no definative answer to that. As there is no such thing in practice as exactly 5V, everthing will work within a range. How small that range is depends on the device and there are too many factors to go into without a thorough investgation.
    Usually a voltage that is too low will mean the device won't work properly and a voltage too high may cause it to fail.
  3. Norfindel

    AAC Fanatic!

    Mar 6, 2008
    Post the schematic. If the voltage drops 150mV, and the supply is regulated, there could be some problem with the circuit.
  4. Dalaran

    Senior Member

    Dec 3, 2009
    If it asks for +5V then it wants to see +5V during operation. That means that you should measure +5V while the unit is connected.

    Norfindel is right though, post your schematic. It sounds like either your components are not rated for the 850mA being drawn or there is something wrong in the design.