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Problems with a boost converter

  1. Sep 15, 2018 at 9:09 PM #1

    electricalguy

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    I have a DC to DC boost converter that I purchased. It is a DFrobot DFRO123. I tested the unit by putting a DC voltage supply of 6 volts in the Vin terminal and connected the negative of the supply to the ground terminal. Then I connected a volt meter to the Vout and ground terminal. The boost converter worked just fine. But when I connected the same setup to a 2.3 ohms load the voltage dropped below the supply voltage. So now the boost converter is not working. With the 6 volt supply across the load I typically get ~2.7 amps without the boost converter. My goal is to get roughly 8 volts and roughly 0.5 amps across the 2.3 ohm load. Does anyone have any suggestions on another type of boost converter to use, or can anyone let me know why the boost converter isn't working?
     
  2. jcsd
  3. Sep 15, 2018 at 10:28 PM #2

    davenn

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    please supply a link to it … I cant find anything in a quick search


    what is the no load voltage output measured at ?

    A significant voltage drop is indicative of a load that is too low in resistance and the regulator and or the main PSU cannot supply the required current and therefore the Vout drops

    Using Ohms Law I ( current) = V/R
    Assuming a required and set for 8V out
    8V / 2.3 Ohms = 3.48 Amps

    And that is the way it is. A 2.3 Ohm load MUST draw 3.48A from a 8V supply

    So, therein lies your problem, either your 6V supply cannot supply 3.48A and/or the regulator chip cannot supply 3+ Amps

    Time to tell us all the details of your setup

    1) The 6V supply ?
    2) The regulator chip ?
    3) What the load is ?


    Dave
     
  4. Sep 15, 2018 at 11:36 PM #3

    wirenut

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    @davenn if you go to dfrobot.com and search dfr0123 it will come up. One thing I did see while glancing at it was if the output drops below the input then damage may occur to the module. Also this is a 20watt 3.4 volt to 37 volt input dc to dc boost conveter. Here is a link to it. www.dfrobot.com/product-444.html
     
  5. Sep 16, 2018 at 3:20 AM #4

    davenn

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    Hi

    thanks for that link
    it's now obvious that it cannot supply the load that the OP has put on it !

    We now need the op to respond to my other questions
     
  6. Sep 16, 2018 at 7:51 AM #5

    electricalguy

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    Hi
    The power supply unit is a BK Precision 9110 100 watt multirange 60 volt/5 amp DC power supply.
    I will give you the number that is on the top of the mosfet JM34RP LM2577S -ADJ P+. On the board it says SY-DC3403
    The load is an inductor that is roughly 11.7 mH at 2.3 ohms DC resistance.
    The specs on the Dfrobot boost converter says it's max output power is 15 watts, and max input current is 3 amps.
     
  7. Sep 16, 2018 at 3:49 PM #6

    CWatters

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    If you are stepping up 6V to 8V at 3.5A the input current will be at least...

    3.5 * 8/6 = 4.6A

    Which is more than 3A.
     
  8. Sep 16, 2018 at 3:55 PM #7

    CWatters

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    You need to limit the input current to 3A by increasing the load resistor.

    The max output current is...

    3*6/8= 2.25A

    So the minimum load resistor on 8V is 8/2.25=3.6R and possibly higher because I ignored efficiency.

    I haven't checked if it will need cooling as well.
     
  9. Sep 16, 2018 at 4:01 PM #8

    CWatters

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    Actually 2.25A Is still too high because 2.25A*8V=18W which is >15W.

    The minimum resistor value is at least

    R=V^2/P
    = 64/15
    = 4.3R
     
  10. Sep 16, 2018 at 5:21 PM #9

    davenn

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    it's a switching voltage regulator IC, not a MOSFET

    so why are you sticking an inductor straight across the PSU ... what is the purpose, what are you trying to achieve ?

    As I said in my previous post .... the power supply CANNOT handle that low resistance load

    yes, so, again, you are overloading the regulator, and it is probably going into shut down mode

    and added to that CWatters comments that I quote ......


    cheers
    Dave
     
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