How to use analog hall effect chip of 5v input supply with 24V input supply voltage

Discussion in 'Analog & Mixed-Signal Design' started by Sumit560, Jul 2, 2016.

  1. Sumit560

    Thread Starter New Member

    Nov 18, 2015
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    I have mlx90365 chip which gives 0-5v analog output but i want to use it with 24v supply voltage and output should be 0-10v. can any one tell whether i have to use 24v -5V dc-dc converter and amplify the output signal of the chip to 0-10V.
     
  2. AlbertHall

    Well-Known Member

    Jun 4, 2014
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    Yes , you do.
     
  3. Sumit560

    Thread Starter New Member

    Nov 18, 2015
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    I have done some circuit simulation.Circuits works fine in simulation but when i did these circuits practically below problems are observed
    1)7805 IC get hot.
    2)amplified voltage is not stable and voltage amplified upto only 9V.
    3)How to add protection to hall chip against high voltage ,reverse voltage and current.
    Circuit diagram is attached.
    ckt.jpg
     
  4. bertus

    Administrator

    Apr 5, 2008
    15,649
    2,348
    Hello,

    What opamp do you use?
    Did you use the recommended wiring of the MLX?
    This is the page from the datasheet:

    MLX90365_recommended_wiring.png

    Bertus
     
  5. Sumit560

    Thread Starter New Member

    Nov 18, 2015
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    LM324 opamp used. and for melexis MLX90365 Chip i used recommended wiring in datasheet.
    In circuit i shown potentiometer instead of hall chip MLX90365 because i don't have melexis library in Proteus software.
     
  6. AlbertHall

    Well-Known Member

    Jun 4, 2014
    1,968
    387
    Also from the datasheet:
    upload_2016-7-3_9-4-46.png
    So the maximum output you might get just 95% of the supply voltage and if the 5V is on the low side then your 9V becomes possible.
    I think the first thing to sort out is the hot regulator. The hall effect device needs something like 8mA and there will be 19V across it. That is 150mW so that needs fixing. A zener diode in the supply the regulator to share the dissipation, a heatsink, a bigger regulator (perhaps TO220), or a switch mode regulator, though I think the switch mode is probably undesirable in this application.
     
  7. bertus

    Administrator

    Apr 5, 2008
    15,649
    2,348
    Hello,

    Do you have the capacitors mounted at the regulator as in your schematic?
    Oscillations can happen without them.
    Raise the values of R1 and R2 to 100 K.

    Bertus
     
  8. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,809
    1,105
    If the MLX chip is drawing its maximum rated current (12mA) the 7805 will be dissipating ~230mW so will get fairly hot without a heatsink or forced cooling.
     
  9. Sumit560

    Thread Starter New Member

    Nov 18, 2015
    4
    0
    yes capacitors are also mounted with regulator.
    If i check chip without any amplification and regulator circuit i got the output from 0 to 5V. but when i used it with amplification circuit then output voltage ranges from 0 to 8.9 V or 8.95 V.
     
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