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Power-on reset

Discussion in 'Electronic Basics' started by dbernat32, Sep 7, 2005.

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  1. dbernat32

    dbernat32 Guest

    Is there a relatively simple circuit which can assert a power-on reset.
    In other words, the line will go high briefly at power-on and then switch low and remain that way until power-off.

    Any ideas would be appreciated.

    --dbernat32
     
  2. Guest

    yes
    Searched all groups Results 1 - 10 of 552,000 for POWER ON RESET
    (0.36 seconds)

    GG
     
  3. Chris

    Chris Guest


    How does a spare inverter gate, plus an R, a C, and a diode sound?
    (View in fixed font or M$ Notepad):

    ` VCC VCC
    ` + +
    ` | |
    ` .-. |
    ` R| | - D
    ` | | ^ 1/6 74HC14
    ` '-' |
    ` | | |\ Reset Pulse
    ` o----o-----|H>O----o
    ` | |/
    ` C---
    ` ---
    ` |
    ` |
    ` ===
    ` GND
    created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

    Positive going pulse width (one and only one pulse at turn-on) will be
    a little less than R*C seconds. The schottky diode is actually
    optional if you have a linear supply that discharges slowly at
    turn-off.

    This is just about the simplest reset pulse you can get. Remember that
    this requires a gate with schmitt trigger input hysteresis to get a
    clean reset pulse at turn-on. If you've got a spare NAND gate on
    board, try using a 4093 schmitt trigger NAND gate instead of a standard
    NAND gate IC. But if a reset pulse with slow fall time is OK, you can
    just use any inverter gate (or a NAND or NOR set up as an inverter).

    If this doesn't do the job, describe your requirements. There are many
    power watchdog/monitor ICs that can do the job for you with equal
    simplicity (although they cost more). Do you need brownout protection,
    too (reset asserted if power supply goes below a certain voltage)? If
    so, one of these ICs or a comparator would be a better choice.

    Good luck
    Chris
     
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