Selecting input with Schottky diodes

Discussion in 'General Electronics Chat' started by dor, Jun 21, 2009.

  1. dor

    Thread Starter Active Member

    Feb 20, 2009
    62
    0
    Hi,

    I need to build a circuit where I can choose which power-supply would supply the power to the system.

    The power supplies are: Battery, AC (converted to DC via a regulator) and USB's 5v pin.

    I understand that there's a technique for choosing the wanted power supply with Schotkky diodes. But I don't know & can't find any circuit in the internet.

    If the USB cable is connected to the system, I wish it to give power to the system.
    Otherwise, if the AC is connected, I wish that it would give power to the system.
    Otherwise, if the USB & AC are not connected, then the battery would give power to the system.

    I need this circuit in order to save the battery's power.

    Can anyone help me with that?

    Thank you.

    Dor.
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Here you go:
    [​IMG]

    The ground must be common between the three voltage sources.

    The battery voltage must be less than 5v, or the USB port won't supply the current until the battery drains below 5v.
     
  3. dor

    Thread Starter Active Member

    Feb 20, 2009
    62
    0
    Thanks!

    Is there a method to use a battery of 9v in the above case?

    I need that my output voltage, from all the power supplies, would be 5v.

    And what did you mean by "To_Ckt"?

    About the C1 capacitor: why did you choose this value (100uF) ? I guess that the capacitor helps in reducing the ripple. Am I correct?

    About the AC power supply: you didn't mention it in the schema, but the AC actually should pass through a regulator, right? I just want to make sure.
     
Loading...