Most basic solution to power Arduino from 100V + supply

Discussion in 'General Electronics Chat' started by CasualKilla, Jan 14, 2016.

  1. CasualKilla

    Thread Starter New Member

    Dec 12, 2015
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    I am theorizing using an arduino uno for the controller of a 100V to 24V power supply, however I have come to the predicament where I first need to power the arduino from 100V before I can use the arduino to make the 24V supply. I have included this info for background, but it is not so relevent to the problem. My question is what is the simplest way to power the arduino in this case. Efficiency does not need to be high.

    I am thinking that perhaps a zener diode and resistor will do the trick? Perhaps hooking up another voltage regulator or capacitor to the diode may help too? One more thing, the power is generally low ripple, but it can vary slowly between 60V to 150V over time.
     
  2. dl324

    Distinguished Member

    Mar 30, 2015
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    Your zener idea is probably the simplest. For acceptable voltage regulation, you need the zener current to be at least 10X larger than the maximum current the microcontroller will draw. Use the lowest voltage you anticipate and insure maximum zener ratings aren't exceeded for the highest voltage.

    What voltage do you want to operate the Uno at?
     
  3. CasualKilla

    Thread Starter New Member

    Dec 12, 2015
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    I will aim for something between 7V to 10V for the arduino Vin pin, depending on what zeners I can find. Ok cool, thanks for the thumb-rule. I will assume 200mA max for the arduino, as I do not have much details on the arduino circuit design yet.
     
  4. dl324

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    200mA is too much current for a zener regulator. You'll need to add a transistor for current gain.
     
  5. tcmtech

    Well-Known Member

    Nov 4, 2013
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    Most any common SMPS from a wall wart power adapter will work just fine for what you are doing.
     
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  6. CasualKilla

    Thread Starter New Member

    Dec 12, 2015
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    Ok yeah mybad, that would equate to 2A @ ~10V through the zener XD. Guess I could shoot for lower consumption, but how does the transistor work? I am assuming I will require a high Vbe capability BJT?
     
  7. CasualKilla

    Thread Starter New Member

    Dec 12, 2015
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    This is a 100Vdc supply not AC.

    Or is there a DC-DC conversion after the AC-DC rectification. Forgive my ignorance
     
    Last edited: Jan 14, 2016
  8. dl324

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    You use the transistor current gain to reduce the load on the zener. But power dissipation is still going to be an issue (somewhere).
     
  9. tcmtech

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    Yep there is a AC - DC conversion in the unit before they step the voltage down so they will work just fine on a DC input.
     
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  10. RichardO

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    May 4, 2013
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    tcmtech is too quick for me. :)
    I will add that the 100 volts DC may be too low for a typical wall wart. For the wall wart to run on 100 volts DC implies that it is designed to run from as low as 70 volts RMS.
     
  11. dl324

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    It's even worse. Supported input range needs to be 60-150VDC.
     
  12. tcmtech

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    I wouldn't worry about the slightly lower input voltage if the load is well below the units rated capacity.

    I have used SMPS based power supplies at input voltages way below their spec values without problems. Most will actually work just fine down to well under 40 VAC at partial loads.
     
  13. CasualKilla

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    Dec 12, 2015
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    Wall wort idea is cool and all, but I was hoping to do a design from scratch. I am more interested in learning than making something that just works. Could somebody elaborate on the zener + transistor regulator/supply idea?
     
  14. Veracohr

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    Jan 3, 2011
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    Like this. The graph is the output voltage with an input going from 60V to 100V. 10V zener, and about 200mA going to the load.

    Screen Shot 2016-01-15 at 11.24.11 AM.png

    But the transistor power dissipation goes from 10W to 18W.
     
  15. #12

    Expert

    Nov 30, 2010
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    I think you were hoping WE could do a design from scratch, then you would build it.

    The basic thermodynamics of any analog regulator that changes 100 volts into 10 volts at 0.2 amps is 18 watts of waste heat. Either decide to dissipate 18 watts or abandon the analog methods in favor of switching supplies or Wall Warts.
     
  16. CasualKilla

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    Dec 12, 2015
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    Hmm, yes I see your point. To tell you the truth my end goal was to build a switching regulator with the arduino as the controller, this is why I am hesitant to use a switching reg to power the Arduino. Also there isn't really any low power switching regs that do 100V + to 5V.
     
  17. tcmtech

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    Most any cheap USB charger cube will do that just fine. :rolleyes:
     
  18. #12

    Expert

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    That's a false fear. Any correct size switching supply can power the arduino without causing any interference with what the arduino is doing. The worst case scenario means you have to add a capacitor where the power plugs into the processor board.
     
  19. CasualKilla

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    Dec 12, 2015
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    Just opened up an ACtoDC 5V @ 250mA power supply. It seems to use a transformer not a switching DC-to-DC
     
  20. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    What is the input voltage range of the cube?
    Can you post a picture of the cube?
    Most SMPS are using a rectifier at the input with a capacitor.
    Feeding it with DC would not give a problem.

    Bertus
     
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