Need some Diode help Please

Discussion in 'General Electronics Chat' started by hightechredneck, Mar 29, 2012.

  1. hightechredneck

    Thread Starter New Member

    Mar 29, 2012
    Hello guys hope everyone is doing well. I am doing some projects with some friends and have arose at a problem and I need some assistance on how to deal with it. We make home made trail cameras by connecting wires to the trigger wires on the camera and connecting them to external power, and control boards. My question arises in the external power. With so many choices of batteries out there, and some cameras having internal rechargeable batteries that there is some backfeeding involved sometimes and the batteries leak. Here is the scenario: You have 2 to 4 external battery holders (3v) connected in parallel to maintain voltage, connected to the internal power leads that hook to the internal batteries. If the batteries in the camera are lithium, and the externals are alkaline, there seems to be some backfeeding and the batteries outside the camera leak. I suggested a diode and they told me that would not work, and that reduces the voltage from the externals. What we are attempting to do is prevent the internal batteries from feeding back into the external batteries, without reducing the voltage supplied. Can anyone suggest a solution?
    Thanks in advance,
  2. crutschow


    Mar 14, 2008
    The simplest would be to use a large Schottky diode. It will have a drop of only a few tenths of a volt at low currents.

    If you absolutely want zero drop then you will need something like a voltage comparator driving a MOSFET switch in series with the batteries. The comparator will turn the switch off when the camera voltage is higher than the external voltage.
  3. jimkeith

    Active Member

    Oct 26, 2011
    Yes, use schottky diode as crutschow said
    1N5817 Schottky Diode 1A, 20V
    Voltage drop @ 10mA = 0.25V
    Voltage drop @ 70mA = 0.30V