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High(er) Voltage Power Supply OK Circuit for microcontroller

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by ADWSystems, Aug 3, 2017.

  1. ADWSystems

    ADWSystems Member

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    How about the MC34064 instead? Shipping costs are getting high to make another order from another vendor. Just sayin....

    Once you mentioned driving the opto, I can visualize the methodology.
     
  2. JonSea

    JonSea Well-Known Member

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    Looks like it should work. The supply current is about 10x what the MCP111 draws but it's still negligible for the voltage divider calculations.
     
  3. AnalogKid

    AnalogKid Well-Known Member

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    Neither did I in your first two posts.
     
  4. dave

    Dave New Member

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  5. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    You need a resistor to limit the LED current - but the zener removes 22V of the 24V supply, leaving only 2 volts for the LED and resistor.

    The whole point of using a zener is for it's voltage drop.
     
  6. AnalogKid

    AnalogKid Well-Known Member

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    A better choice would be something like 12 V or 15 V. This leaves plenty of headroom for the resistor so small inaccuracies in either part do not significantly alter the LED brightness and optocoupler output current.

    If a simple go/no-go signal is all that is required, use a 6.2 V zener for all three circuits, with different resistor values for each so all three LED currents are approx. equal. Commonality of parts usually is better, and three different zener values cost more than three different resistors.

    ak
     
  7. ADWSystems

    ADWSystems Member

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    I don't see the point of using 6.2V zener when trying to verify the 24V power supply is on. I don't see the 6.2V zener is any better than a straight resistor divider.
     
  8. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    I agree, an 18V zener would be more suitable.
     
  9. AnalogKid

    AnalogKid Well-Known Member

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  10. ADWSystems

    ADWSystems Member

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    Those sound like some good user requirements. A sharper break over point than a resistor divider in order provide an on-off signal to indicate if the power supply is online. The exact break over point should be somewhere relative to the supply voltage in order to provide an indication if the power supply is working. A 6.2V zener on a 24V power supply does not do this.
     
    Last edited: Aug 5, 2017

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