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Adjustable current souce 12Vin 400mA o/p 32W

Discussion in 'Power Electronics' started by peterdbennett, Apr 3, 2019.

  1. peterdbennett

    peterdbennett

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    Apr 3, 2019
    Hi i need to build an adjustable current source to range from 0-400mA adjustable in increments of 10mA.Supplied from a 6V battery supply. Needs to be able to source 400mA into a 200Ohm load for a couple of seconds. Im having serious issues can anyone point me to an off the shelf unit open frame as it needs to be mounted internally in a fixture to drive other equipment. Any help or advice would be greatly appreciated.
    Thanks
    Peter
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,158
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    Jan 21, 2010
    To pass 400mA through a 200Ω resistor you'll need to apply 80V. That's a bit more than 6V.

    If you use a boost converter to create 80V (practically you'll need a little more) then your 6V battery better be capable of a 6A current.

    Once you have a sufficient voltage, a simple 2 transistor constant current circuit should do the trick. Beware that the main pass transistor would need to dissipate about 32W at 400mA if the output is sorted.
     
    peterdbennett likes this.
  3. peterdbennett

    peterdbennett

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    Apr 3, 2019
    Hi Steve, thanks very much for the reply
     
  4. WHONOES

    WHONOES

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    May 20, 2017
    Bearing in mind *STEVE's* reply, it is feasible but you may well have to use something designed for purpose.
     
  5. peterdbennett

    peterdbennett

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    Apr 3, 2019
    Hi WHONOES I have contacted a number of power supply manufactures and they have nothing available off the shelf. The design and build costs they are quoting are ecessive to say the least. Hence the reason for starting from scratch. If there is anything you or others could recommend it would be great.
    Thanks
    Peter
     
  6. BobK

    BobK

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    Jan 5, 2010
    I think it is time you told us what you are trying to do.

    Bob
     
  7. WHONOES

    WHONOES

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    May 20, 2017
    Are you able to build circuits from supplied schematics?
     
  8. peterdbennett

    peterdbennett

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    Apr 3, 2019
    Hi Whonoes I sure can. Have you something you could recommend ?
     
  9. TCSC47

    TCSC47

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    Mar 7, 2016
    Many people are happy to design powers supplies thinking they are very simple. On the surface, they are but in reality there are many little pitfalls. I always remember trying to discuss secondary breakdown characteristics of a particular power transistor with an application engineer from the manufacturer. I was rather disconcerted when I discovered he did not appear to know what secondary breakdown characteristics were. Failure to take them into account will not show up in initial testing but could lead to failure some time in the future use as the semiconductor substrate burns away a little bit every time it is used.

    If you have an educational project, then fair enough. Go for it, particularly as modern ICs have made the job much simpler.. But always remember that the power supply is the most critical component of any piece of equipment capable of doing the most damage if it fails. If your reputation and money rely on your project, bite the bullet and purchase a commercial design (there will be one somewhere) which will have been manufactured in quantity and been tested properly.
     
  10. WHONOES

    WHONOES

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    May 20, 2017
    Possibly. I like using the venerable 555 for switching supplies. If indeed you need to drive 400mA into 200Ω then you will need 80V.
    I will have a bash at some simulations to see what may work. It might be a straight forward switching boost converter or something with a transformer in it. Either configuration will need some form of control circuit to maintain a reasonable stable O/P voltage.
    I don't want to get into building a physical circuit to test it out though.

    Edit:
    Just spotted that your original post said 12V in the title whereas the main text says 6V. Which is it that you want. Doing it from 12V would be easier.
     
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