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Digital output coupled with a voltage regulator

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  • Digital output coupled with a voltage regulator

    Ok, so I just bought a fusion brain and it's been amazing thus far. But I'm running into a problem with a little circuit I made that has two LDO voltage regulators, one at 12v and the other at 5v. They have an input pin that turns on the regulator when a voltage is applied (from 3v to 16v). I thought that this would work well with the digital output on the FB but upon further inspection I found that the positive output pin is connected straight to the battery (input voltage for FB) whereas the ground pin is not connected to ground unless that output is switched in the software. But my circuit is using the same ground that powers the FB so with the ground from my circuit and the positive pin from the digital output there is always a constant voltage regardless of whether or not it is engaged in the software.

    Any way around this? If not I may just need to go to a relay to control it or just not be able to turn on and off regulated voltages.


  • #2
    Yes, you are correct the outputs are switched ground. With 500 mA max rated output, you probably need a relay anyway.


    • #3
      I measured the current draw for the regulators and they were only about 60mA. I'd rather just try to use the input pin rather than a relay but it what it is.


      • #4
        Since you don't need much current driving the reg you could use the output to drive a opto isolator/coupler then tie the 'C' (collector) of the output of the isolator to your drive voltage, and the 'E' (emmiter) to the regulator. You might also need a pulldown resistor if the reg doesn't like floating inputs.


        • #5
          For positive logic switching, you can do lots of things. What I usually do is use pull up resistors then tie it through a standard logic inverter such as a 74LS04. They are 30yr old chips with 6 inverters in each. The output will be VCC to the 74LS04 when the FB output is on meaning the ground is activated.
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          30 Digital Outputs -- Directly drive a relay
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