Help needed with peak reverse voltage

Discussion in 'The Projects Forum' started by Manghameister, Feb 5, 2009.

  1. Manghameister

    Thread Starter New Member

    Jan 9, 2009
    3
    0
    I've made a seven segment adder circuit with decoders, however the 7 segments keep exceeding their peak reverse voltage by around 3 volts. I've tried everything in order to solve this problem and really need help. There are two switches on the circuit. The top is and on/off switch and the lower is a reset switch. Apart from this one problem the circuit should work completely. Any help would be greatly appreciated.

    P.S. I am pretty much a complete circuits novice and have very little knowledge about these things so please don't word it too complicated.
     
  2. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    As a start remove the 10K resistor near the battery and remove the wire going from the top of the reset button to ground.

    Where is the counter ?
     
  3. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Here is a link to Texas Instruments' CD74HC4511 datasheet:
    http://focus.ti.com/lit/ds/symlink/cd74hc4511.pdf

    What is not entirely obvious in the datasheet is that the IC is constructed to source current to the 7-segment display; therefore you either need a common cathode 7-segment display or you need another driver IC that will invert the outputs of the 74HC4511.

    Right now, you have the 7-segment common connected to +V via a 220 Ohm resistor. The display needs to be a common cathode type, and the common cathode connection needs to be connected straight to ground (-V).

    Mik3 already mentioned the 10k resistor needs to be removed.
    There is a more subtle problem in that you are shorting V+ to V- at the leftmost bottom junction. This will result in a non-functional circuit and a dead battery in very short order; they may even explode.

    The L inputs need to be held low.
    The RB and LT inputs need to be held high.
     
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