Offset ground for 4V-8V low current programmable circuit?

Discussion in 'Embedded Systems and Microcontrollers' started by rkuris, Mar 31, 2016.

  1. rkuris

    Thread Starter New Member

    Feb 27, 2012
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    Hi,

    I need a circuit that will pro grammatically provide between 4V and 8V of output. I have a 10.5V power supply already. What I was thinking of doing was to float the ground of an arduino to 3.3V using a regulator, then build a simple PWM circuit to generate between 0-5V, which should be between 3.3V and 8.3V when compared to the original 10.5V ground.

    Questions: Will this work? Can I use a simple voltage regulator and connect the arduino's ground to the positive side of the regulator? How much current should I expect to flow through the regulator (so I can select the right 3.3V regulator)? The arduino is sure to draw far less than 500ma, but can I get by with a 250ma regulator for this?
     
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Welcome to AAC!
    Might work, but wouldn't it be simpler just to have a common ground for the Arduino and PWM circuit? A potential divider could feed back a fraction of the output voltage for comparison with a programmable reference voltage generated by the Arduino.
     
  3. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Or even just something like this?
    http://www.robgray.com/temp/transistor-circuit.png
    Connect Vcc to 10.5V and just write your arduino code to get 4-8V instead of 0-10.5V

    Throw a low pass filter (resistor/cap) if you need a more "analog" output vs a PWM..
     
  4. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Do keep in mind that any and all ripple on the PWM output WILL be a part of the output of that supply.

    You can keep adding cap to the output to make it smaller but some will always be there.
     
  5. rkuris

    Thread Starter New Member

    Feb 27, 2012
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    It does seem like adding a simple NPN transistor is the way to go. Thanks guys!

    The reason why I was hesitant is because I really don't ever want the output to be 0V or close to 10.5V, which is what will happen if the arduino locks up.
     
  6. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    You could incorporate zener diodes to clamp the output voltage within a defined range in the event of Arduino error.
     
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