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Dummy load

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by Doctore, Aug 17, 2013.

  1. Doctore

    Doctore Member

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    I want to build dl like here http://www.electro-tech-online.com/...emp-control-fan-load-bank-pwm-circuit.128753/
    But I need help because my englisch and electronic skills are not the best.
    And I start with my questions here http://www.electro-tech-online.com/...emp-control-fan-load-bank-pwm-circuit.128753/
    But this is not my thread, so I create new one.
    First I draw schematic:

    View attachment 75382

    ronv suggest add 75R resistor between the output of each Op amp and the FETs.
    Like this?:

    View attachment 75400

    Mosfets, I use irf2805pbf.
    About cooling, I want to use 12pcs of 120mm pc fans and car radiator, this give me few °C less than room temperature.

    Thanks for the replies.
     
  2. ronv

    ronv Well-Known Member Most Helpful Member

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  3. Doctore

    Doctore Member

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    Last edited: Aug 18, 2013
  4. dave

    Dave New Member

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  5. ronv

    ronv Well-Known Member Most Helpful Member

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    Yes, I see that now.

    The problem is that if the part does not have a spec for safe operating area that includes DC (always on) you cannot be sure it will be safe to use. I'm not sure I looked at all the "big" ones but I didn't see any others that looked good. Maybe you can look again. If you look at the safe operating area curves you should find one good for about 10 amps at 20 volts drain to source on the DC curve.
     
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  6. Doctore

    Doctore Member

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    "safe operating area curves" - I'm newbie in electronics and this is unreadable for me :)
    But previosly you tell me IRF2805PBF and IRF1407PBF are good...
    Other mosfets I don't find.
    What is price of shipping from digikey to poland?
     
  7. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    SOA is a term that encompases a lot of stuff. It might mean if something, then something is permissable otherwise it's not. Example, Aa device might be able to handle 10 A at 10 V, but only 2 at 200 V. It might withstand 100 A, if for 100 uS or less. That info is spelled out in the datasheets.

    I belive, that digikey has various locations, but there may be closer options for you suh as RS Electronics and Farnell.

    Check: http://www.digikey.pl/
     
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  8. ronv

    ronv Well-Known Member Most Helpful Member

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    Good idea KISS! :D

    Farnell Poland has the STP80NF12 for 9 PLN which is not to bad a price.

    Doc, Maybe it would be a good idea to tell us what you are going to do. Sometimes it works better than just going with what is already there. For example are you making a power supply load or maybe a battery load? Why? How many volt/amps?
     
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  9. ()blivion

    ()blivion Active Member

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    You should put decoupling/stabilizing capacitors from ground to VO and from ground to +VS on IC7, as close to the part as possible.

    Linear regulators like to oscillate without stabilizing caps.
     
  10. Doctore

    Doctore Member

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    Last edited: Aug 19, 2013
  11. Doctore

    Doctore Member

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    Ok here is some what I can get:
    *http://www.tme.eu/pl/details/auirf3305/tranzystory-z-kanalem-n-tht/international-rectifier/#
    http://www.tme.eu/pl/details/irf1407pbf/tranzystory-z-kanalem-n-tht/international-rectifier/#
    http://www.tme.eu/pl/details/irf2204pbf/tranzystory-z-kanalem-n-tht/international-rectifier/#
    *http://www.tme.eu/pl/details/irf2804pbf/tranzystory-z-kanalem-n-tht/international-rectifier/#
    http://www.tme.eu/pl/details/irf2805pbf/tranzystory-z-kanalem-n-tht/international-rectifier/#
    *http://www.tme.eu/pl/details/irf2907zpbf/tranzystory-z-kanalem-n-tht/international-rectifier/#
    http://www.tme.eu/pl/details/irf3808pbf/tranzystory-z-kanalem-n-tht/international-rectifier/#
    http://www.tme.eu/pl/details/irfb260npbf/tranzystory-z-kanalem-n-tht/international-rectifier/#
    http://www.tme.eu/pl/details/irfb3206pbf/tranzystory-z-kanalem-n-tht/international-rectifier/#
    http://www.tme.eu/pl/details/irfb3207zpbf/tranzystory-z-kanalem-n-tht/international-rectifier/#
    http://www.tme.eu/pl/details/irfb38n20dpbf/tranzystory-z-kanalem-n-tht/international-rectifier/#
    http://www.tme.eu/pl/details/irfb42n20dpbf/tranzystory-z-kanalem-n-tht/international-rectifier/#
    *http://www.tme.eu/pl/details/irfb4310pbf/tranzystory-z-kanalem-n-tht/international-rectifier/#
    http://www.tme.eu/pl/details/irfb4321pbf/tranzystory-z-kanalem-n-tht/international-rectifier/#
    *http://www.tme.eu/pl/details/irfb4332pbf/tranzystory-z-kanalem-n-tht/international-rectifier/#
    http://www.tme.eu/pl/details/irfb61n15dpbf/tranzystory-z-kanalem-n-tht/international-rectifier/#
    http://www.tme.eu/pl/details/irfba1404ppbf/tranzystory-z-kanalem-n-tht/international-rectifier/#
    http://www.tme.eu/pl/details/irfp260mpbf/tranzystory-z-kanalem-n-tht/international-rectifier/#
    http://www.tme.eu/pl/details/irfp260npbf/tranzystory-z-kanalem-n-tht/international-rectifier/#
    http://www.tme.eu/pl/details/irfsl3206pbf/tranzystory-z-kanalem-n-tht/international-rectifier/#
    http://www.tme.eu/pl/details/irfsl3207zpbf/tranzystory-z-kanalem-n-tht/international-rectifier/#
    http://www.tme.eu/pl/details/stp80nf10/tranzystory-z-kanalem-n-tht/st-microelectronics/#
    http://www.tme.eu/pl/details/sup57n20-33/tranzystory-z-kanalem-n-tht/vishay/sup57n20-33-e3/#

    Uff...

    *- Bad price, If i don't must get this one only other I don't want buy this
     
    Last edited: Aug 19, 2013
  12. misterT

    misterT Well-Known Member Most Helpful Member

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    Shipping is 18 EUR to finland and if you order more that 65 EUR worth, then shipping is free.. I didn't find shipping info to Poland, but I think they are quite similar (both are members of EU).
     
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  13. ronv

    ronv Well-Known Member Most Helpful Member

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    I think I already looked at all of those from that supplier.
    Here is where the resistor goes.
    I would be surprised if you find a good FET for less than 9. Lets confirm the current and voltage.
     

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  14. ()blivion

    ()blivion Active Member

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    Strictly speaking, one does not have to get the best FET's money can buy to make this project work. You can use pretty much any FET. However, the better each individual FET is, the fewer you will need to reach your total combined wattage. Which means less soldering, less cost, and less chances to screw something up.

    When searching for a FET, the factor I would start filtering by is package type, then sort by highest wattage. A higher wattage should more or less be inline with a larger SOA, only wattage is more easy to sort by and work with. Confirm a workable SOA before purchasing of course. I would look for TO-220 FET's at 300 watts a piece or better, that was about what we did last time.
     
  15. Doctore

    Doctore Member

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    Now schematic is 100% complete and good?
    FinalDummy.png
    For mosfets, already I do not have ideas......
    From digikey shipping cost are too expensive, tme is ok, but no needed mosfets, farnell not for little projects, fuq....
     
  16. ()blivion

    ()blivion Active Member

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    Looks mostly good, though you should still put some decoupling capacitors from pins 1-3 and pins 2-3 for IC7.

    Start with a shop you know serves your area, then search by highest watts in the TO-220 package. Only pick parts over 300 watts.

    Most online shops have powerful searches that let you find parts by part specs very easily. Doing it this way, with the specs above, will turn a selection of 10,000+ parts into ~100 or so, and most of what's left will work fine for this project.

    It must be out of their way to serve your area or something, we will have to use someone else then.

    I don't even know what you are saying here, sorry.

    Farnell/Newark certainly does sell small volumes for little projects. Maybe not in your area though? They also have perfectly acceptable MOSFET's for this project.
     
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  17. Doctore

    Doctore Member

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    I mean, tme is ok but don't sold mosfets what we need.

    So why when I showed 23 mosfets, none is not good for this project...

    I mean this is not for low cost projects, I can buy in farnell with minimum 100$ - I do not want spend to much for this project.

    EDIT: Now is good?
    dsfs.png
     
    Last edited: Aug 20, 2013
  18. ronv

    ronv Well-Known Member Most Helpful Member

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    Soa

    Here are 2 graphs of safe operating area. One is the 1407 the other the AP92T12 that I posted. Since almost all the power is disapated in the FETs the voltage across them is almost the full supply voltage (25 volts) and about 5 amps. If you look at the curves there is no DC line for the 1407, but if you used your imagination and drew one it might be 1 amp at 25 volts, while the other is good for maybe 15 amps. Big difference. :p

    ()blivion the block in Doctor's schematic is the temperature sensor not a regulator, so doesn't need the capacitors.

    I'll look for some other suppliers or FETs tonight.
     

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  19. ronv

    ronv Well-Known Member Most Helpful Member

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  20. ()blivion

    ()blivion Active Member

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    Oh!!!! Temp sensor NOT regulator... i see... i see...

    Doctore, the capacitors I told you to add, yeah.............. I'm guna have to ask you to just go and remove those now please :eek:.
     
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  21. Doctore

    Doctore Member

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    :mad:

    Ok

    EDIT: Now is all good?:
    Final.png
    And SOA, I have explained a little bit, but language barrier...
     
    Last edited: Aug 21, 2013

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