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IC to protect against voltage faults?

Discussion in 'Electronic Design' started by Mike V., Jun 29, 2004.

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  1. Mike V.

    Mike V. Guest

    I've heard somewhere of a circuit (or IC?) that will turn off your
    voltage source to a motor if the microcontroller that controls the
    system malfunctions (e.g. latches up). If a square wave is not
    continuously applied, then the voltage turns off. For example, in the
    case of a latched-up micro, then the voltage source supplying the
    motor will get switched off. Is there any commercial IC to accomplish
    this? If not, I think it was on Electronics Design magazine, but I
    have no idea which issue it is.
  2. The Dallas ds1232(?) comes to mind, but its a reset chip, uc supervisor.
    You can also use a retriggerable one shot (74123) and trigger it via an interrupt routine. This you can set the time-out to your

  3. Ban

    Ban Guest

    Do you mean a watchdog timer? Google for it, there are hundreds around. It
    will give out a reset signal, which you can route to any convenient points
    in your circuit.
  4. Mike V.

    Mike V. Guest

    Martin and Ban, it's not a voltage supervisor nor watchdog that I have
    in mind. I don't want to reset the microcontroller due to a low
    voltage or watchdog timeout. However, I want to do something similiar
    to hardware that controls whether a voltage source to the motor is
    turned on or off. If the micro latches up, and the motor is turned on
    at full speed, then I can cause physical damage with a runaway motor.
  5. Joerg

    Joerg Guest

    Hi Mike,

    If this is a cost sensitive application you could do it discrete. Use
    the square wave pulses to keep a capacitor charged which in turn keeps a
    FET conducting. Then when the signal disappears a bleeder resistor (or
    the uC port itself via the charge resistor) discharges the cap and the
    FET turns off. This would not be a very graceful turn-off but it might
    suffice in some applications. Turn on and turn off times can be chosen
    by the respective RC ratios. Sometimes a diode in the charge up path is
    needed depending on the duty cycle of the "uC alive" indicator signal.

    Regards, Joerg
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