Schottky Diode Connection Problem

Discussion in 'General Electronics Chat' started by dripsys, May 16, 2018.

  1. dripsys

    Thread Starter New Member

    May 16, 2018
    2
    0
    Following is a schematic of the circuit I have which includes a Schottky diode.
    The general purpose of the circuit is to measure the battery voltage with a microprocessor analog input.

    When the switch SW1 is open and I measure the voltage at TP1 I get 5V. I checked the diode with an ohm meter and it is OK.

    Schottky-1.jpg
    To simplify the circuit I connected the Schottky diode with another regular diode (1N4001) in the following circuit:
    Schottky-2.jpg

    When I measure the voltage between TP-A and Ground, which is the regular diode, I get 100 mv. However, when I measure the voltage between TP-B and Ground, which is the Schottky diode, I get the full 5V.

    I thought that Schottky diodes are the same as regular diodes except that they have a low forward voltage drop. This low voltage drop is necessary for this circuit in order to use the full power of the battery.

    Any help will be greatly appreciated!

    Thanks,
    Eran Eckstein
     
  2. crutschow

    Expert

    Mar 14, 2008
    19,805
    5,543
    Schottky diodes have a higher reverse leakage.
    This is from the data sheet:
    upload_2018-5-16_15-45-0.png

    5V measured with a 10megΩ meter input impedance is 5μA, which near the nominal shown on the graph.

    Connect a 10kΩ load to ground and then measure the reverse voltage.

    So you likely will need to reduce the value of the 100kΩ resistors if you want a lower voltage when S1 is open.
     
    mcgyvr and dripsys like this.
  3. dripsys

    Thread Starter New Member

    May 16, 2018
    2
    0
    Perfect!
    Thanks for your help.
     
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