Voltage Peltier Cell Driver with digital potentiometer

Discussion in 'The Projects Forum' started by Alberto Beghetto, Jan 16, 2016.

  1. Alberto Beghetto

    Thread Starter New Member

    Jan 16, 2016
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    Hi All,
    i'm working on a device with couple of peltier cell, power to these cells must be adjustable. Searching on the net and speaking about that with hardware designer o choose (and i want to do that) to control cell power with a voltage control, not pwm control.

    To do that i found the SI-8010Y switching regulator. Datasheet attached.

    I just bought a couple of 51W cell, specs attached (all what i have).

    Looking on regulator datasheet, on tipical connection diagram schematics, i tought to change R1 with a digital potentiometer.
    Problem is that a digital potentiometer admit max voltage on its pins equal to Vdd of the component (typical max 5v), this is my problem.

    Looking on AAC i found this thread
    http://forum.allaboutcircuits.com/threads/0-57v-voltage-control-using-a-digital-pot.26927/

    close to the end on the thread an user (in reply #8) post a schematics
    http://forum.allaboutcircuits.com/attachments/power-supply-0-57v-png.11741/
    that use an opamp to "create" a reference voltare to regulator, in that case lm317. And, that schematics use 3.3v supply for potentiometer that i'll change with digital one.

    Can you help me to edit that schematics to my purpose? I'm very good with digital electonics, but with analog... i can't find connection with it :(

    Thanks for reading.
    Alberto Beghetto
     
  2. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
    5,003
    745
    If you're using the SI801 chip, pin 6 sets the output voltage, it has an internal 1v reference, and it compares it to this pin, so your digital voltage control has to be controlling this pin.
     
  3. Alberto Beghetto

    Thread Starter New Member

    Jan 16, 2016
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    Tanks for reply Dodgydave.

    If i understand correctly i must set pin 6 of si8010 at 1v when i get desired output voltage.

    For example, like i see in datasheet, in typical application circuit, if i have 5v output r1 and r2 must be respect. at 8k and 2k.

    But, can i control pin6 indipendently of output? i try to explain myself with simple schematics attached.
    Supposing that R1 and R3 are digital potentiomer and on its pins voltage must be lower than 5v (in this case i use 7805 to have digital voltage for mcu).

    In sch_A i use only potentiometer to adjust voltage output but, if i undestand correctly, i have to take this pin to internal 1.0 to take output voltage stable, if i want higher voltage i have to lower reference 1.0 of some steps, and viceversa. But i think this is not optimal solution.
    In sch_B i use an optocoupler to keep closed loop adjust and also have lower voltage on digital potentiometer (R3). Is this a solution? (very easy and simple)

    Thanks again
    Alberto
     
  4. Little Ghostman

    Member

    Jan 1, 2014
    294
    97
    Have a look at linear technology, they have alot of regulators etc for energy harvesting, I have a dev board from them thats been excellent with Pettier cells and such, I would get you a link but they moved the page I had booked marked :D
     
  5. Alberto Beghetto

    Thread Starter New Member

    Jan 16, 2016
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    0
    Tanks for reply Little Ghostman. Can you write me name of your board?

    I just bought si8010 regulator (.. for price vs output current vs NOT smd components). I'm only designing hardware interface for digital potentiometer. For somone who is strong in analog design this is an easy task (i think).

    Obvoiusly not for me.

    Alberto
     
  6. Little Ghostman

    Member

    Jan 1, 2014
    294
    97
    I will see if I can fine a link, the board has different circuits for energy harvesting, there is piezo and peltier etc on it.

    Some circuits here http://www.linear.com/solutions/search.php?tid[]=5&aid=2010&fid=0&pid=

    Dont get this one http://www.linear.com/solutions/1834 its utter shite

    I cant find it at the moment!! I will dig out my board and get the part number, the LT site can be a nightmare to find things on.

    The site looks like its changed bit, here is a link to various boards. I dont remember it costing that much! but they do have samples of some of the chips and full schematics, so might be an idea to build one rather than buy from them

    http://www.linear.com/demo/?demo_board=&part_number=&category_id=1799&companion_board=&software_id=
     
    Last edited: Jan 17, 2016
  7. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
    5,003
    745
    Your control is pin 6 on your S8010 regulator, this needs to be set between 0 and 1V for for full voltage, ideally using the output from the ic, or a precision voltage, otherwise its going to fluctuate, dont need the opto its a waste of time.
     
  8. Alberto Beghetto

    Thread Starter New Member

    Jan 16, 2016
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    Are you sure that voltage on pin 6 between 0 and 1v is directly drive to 1-15v output?

    For example, if i want 5v on output i must give aprox 0.3v on pin6?

    Why closed loop is wast of time?
     
  9. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
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    745
    The chip uses negative feedback, so the higher the voltage on pin 6, the lower the output voltage and viceversa, for 15V output set pin 6 to zero,

    The use of the opto-coupler is a waste of time here, as your not using live mains.
     
  10. Alberto Beghetto

    Thread Starter New Member

    Jan 16, 2016
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    Hi Dodgydave,
    thanks for reply. Ok now i undestrand. I've last question.

    Looking in datasheet, on tytpical application circuit, it use 8k and 2k resistors to give regulation to pin 6 and got 5v output. But with this configuration, if i'm right, i will have 1v on pin 6. 1v for 5v output, is different from what you just said me.

    Which one is correct?

    Thanks again
    Alberto Beghetto
     
  11. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
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    745
    Pin 6 will always have 1V on it, if it uses the chips own output to regulate it, to increase the output voltage the feedback resistors need to be changed so the top resistor drops more voltage.
     
  12. Alberto Beghetto

    Thread Starter New Member

    Jan 16, 2016
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    Ok perfect! now, it's clear.

    I your prev reply you said "The use of the opto-coupler is a waste of time here, as your not using live mains." What you mean with this? with "live mains"?
     
  13. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
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    If you were using a direct mains input and wanted to isolate it from the output, then you would use an opto coupler in the feedback loop, like the Uc3845 chips.
     
    Last edited: Jan 19, 2016
  14. Alberto Beghetto

    Thread Starter New Member

    Jan 16, 2016
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    0
    Hi,
    I'm trying to design a feedback circuit but got a lot of trouble with opto. Because of CTR and beacuse of transistor side, where i have to get 1v for pin6 feedback.

    So, what if i use an opamp to get reference for regulator. I attach a sketch of mt idea. Can you help me to complete design?

    My main problem is to control output voltage of my regulator with R10 resistor, this resistor will be a digital resistor, ajdusted by a mcu. So at the pads of R10 resister i can't have more of 5v.

    I thik, with an opamp i can reach my objective?

    I copy concept of schematics by a sch in first post of this thread. Help me please!
     
  15. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
    5,003
    745
    Does your digital pot from the mcu give out a 0-5v supply, or does it use resistance steps?

    If it gves out a 0-5v supply, just feed it into pin6, using a resistor divider.
     
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