How do constant current loads work and how to make one

Discussion in 'General Electronics Chat' started by Alexsieg, Sep 30, 2016.

  1. Alexsieg

    Alexsieg

    Joined:
    Sep 30, 2016
    Messages:
    8
    Likes Received:
    0
    Hi, I'm not the best at understanding electronics, how does a constant current load work and how can i make one, and what makes them have limits before they get fried?
     
    Alexsieg, Sep 30, 2016
    #1
    1. Advertisements

  2. Alexsieg

    AnalogKid VIP Member

    Joined:
    Jun 10, 2015
    Messages:
    1,304
    Likes Received:
    385
    Location:
    Ohio - GMT-5
    There are several ways to make a constant current circuit, and searching for the term 'constant current schematic' will return many schematics. One way is to monitor the voltage across a resistor, and use an opamp to automatically adjust the conduction of a transistor such that the voltage is a constant value. A constant voltage across a fixed resistance means there is a constant current through the resistance.

    Depending on the voltage across the resistance vs. the voltage across the transistor, you can distribute the power dissipation between the two components. After that it's an issue of thermal management. If the parts exceed their rated power dissipation, they burn up. If they exceed their rated operating temperature, they burn up. Heatsinks help, but do not guarantee survival.

    ak
     
    AnalogKid, Sep 30, 2016
    #2
    1. Advertisements

  3. Alexsieg

    Alexsieg

    Joined:
    Sep 30, 2016
    Messages:
    8
    Likes Received:
    0
    Im not really sure how all that works, all I've really made with electronics is a power bank from a few laptop batteries and just mess around with stuff.
     
    Alexsieg, Sep 30, 2016
    #3
  4. Alexsieg

    hevans1944 Hop VIP Member

    Joined:
    Jun 21, 2012
    Messages:
    2,949
    Likes Received:
    1,419
    Location:
    Venice, Florida, USA
    So, why do you want a "constant current" circuit? What kind of load do you want to attach to it? Do you use any meters or math when you mess around with stuff?:rolleyes: Please tell us what you are trying to DO.
     
    hevans1944, Sep 30, 2016
    #4
    Arouse1973 and Harald Kapp like this.
  5. Alexsieg

    Ratch VIP Member

    Joined:
    Mar 10, 2013
    Messages:
    737
    Likes Received:
    236
    If you cannot understand the explanation of how to do it, and have minimum electronic construction skills, how do you expect to achieve the goal of building what you want. Perhaps a study of elementary electrical theory knowledge and hardware basics is in order first.

    Ratch
     
    Ratch, Sep 30, 2016
    #5
    Arouse1973 and hevans1944 like this.
  6. Alexsieg

    Miguel Lopez

    Joined:
    Jan 25, 2012
    Messages:
    209
    Likes Received:
    36
    Location:
    Mayabeque, Cuba
    Miguel Lopez, Sep 30, 2016
    #6
    (*steve*) likes this.
  7. Alexsieg

    Alexsieg

    Joined:
    Sep 30, 2016
    Messages:
    8
    Likes Received:
    0
    I just want to make a constant current load instead of buying one, and how powerful could i make one without it being ridiculously expensive.
     
    Alexsieg, Oct 1, 2016
    #7
  8. Alexsieg

    Alexsieg

    Joined:
    Sep 30, 2016
    Messages:
    8
    Likes Received:
    0
    I know most of the basics of electronics i just don't know how to make circuits that to crazy things.
     
    Alexsieg, Oct 1, 2016
    #8
  9. Alexsieg

    duke37 VIP Member

    Joined:
    Jan 9, 2011
    Messages:
    3,976
    Likes Received:
    404
    Location:
    Derbyshire. UK
    At a rough guess you should be able to make a 1000V 1A supply for under $10000. A bargain.:)
     
    duke37, Oct 1, 2016
    #9
  10. Alexsieg

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Joined:
    Jan 21, 2010
    Messages:
    21,281
    Likes Received:
    1,598
    Location:
    Mid way between Beijing and the Ronne Ice Shelf
    Are you wanting to produce a load for testing batteries?

    If so, what is the maximum and minimum voltage you would want applied to it, and the maximum and minimum current you'd like to set it to sink?
     
    (*steve*), Oct 1, 2016
    #10
  11. Alexsieg

    hevans1944 Hop VIP Member

    Joined:
    Jun 21, 2012
    Messages:
    2,949
    Likes Received:
    1,419
    Location:
    Venice, Florida, USA
    I bet I could do something for a dollar. My specs, of course.
     
    hevans1944, Oct 2, 2016
    #11
  12. Alexsieg

    Herschel Peeler VIP Member

    Joined:
    Feb 21, 2016
    Messages:
    341
    Likes Received:
    62
    Location:
    Las Vegas
    More specifics, please. Vague assistance is all we can give for vague requests.
    What schematics have you found so far that might be close to your needs?
     
    Herschel Peeler, Oct 2, 2016
    #12
  13. Alexsieg

    Herschel Peeler VIP Member

    Joined:
    Feb 21, 2016
    Messages:
    341
    Likes Received:
    62
    Location:
    Las Vegas
    Design 36 active load.PNG
    Something like this? Basically you use a transistor as the load. You turn it on and into conduction just enough to be the resistance you need. Instead of driving the load it is the load.
     

    Attached Files:

    Herschel Peeler, Oct 2, 2016
    #13
  14. Alexsieg

    Miguel Lopez

    Joined:
    Jan 25, 2012
    Messages:
    209
    Likes Received:
    36
    Location:
    Mayabeque, Cuba
    I can do it cheaper. Of course, my own specs :D
     
    Miguel Lopez, Oct 3, 2016
    #14
    (*steve*) likes this.
  15. Alexsieg

    hevans1944 Hop VIP Member

    Joined:
    Jun 21, 2012
    Messages:
    2,949
    Likes Received:
    1,419
    Location:
    Venice, Florida, USA
    Yeah, Miguel, no way I can compete with off-shore labor.:( I bet someone in Asia can make this for nothing, and make a profit on the volume sold.:p
     
    hevans1944, Oct 3, 2016
    #15
  16. Alexsieg

    Alexsieg

    Joined:
    Sep 30, 2016
    Messages:
    8
    Likes Received:
    0
    I only need it to go up to 25v and around 5 amps.
     
    Alexsieg, Oct 9, 2016
    #16
  17. Alexsieg

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Joined:
    Jan 21, 2010
    Messages:
    21,281
    Likes Received:
    1,598
    Location:
    Mid way between Beijing and the Ronne Ice Shelf
    Ok, so they are the maximum ratings, what is the minimum voltage across the input that should allow it to operate at maximum current? What are the typical current you'd want it to operate at -- especially the lowest?
     
    (*steve*), Oct 9, 2016
    #17
  18. Alexsieg

    Alexsieg

    Joined:
    Sep 30, 2016
    Messages:
    8
    Likes Received:
    0
    The lowest voltage i would want it to run would be 3v, and a external power supply to keep it running of course.
     
    Alexsieg, Oct 9, 2016
    #18
  19. Alexsieg

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Joined:
    Jan 21, 2010
    Messages:
    21,281
    Likes Received:
    1,598
    Location:
    Mid way between Beijing and the Ronne Ice Shelf
    And the smallest current? Would you want to be able to easily and accurately set it for 1mA, or would a couple of hundred mA be practically the smallest current you'd require?
     
    (*steve*), Oct 9, 2016
    #19
  20. Alexsieg

    Alexsieg

    Joined:
    Sep 30, 2016
    Messages:
    8
    Likes Received:
    0
    The lowest i think should be 200ma if not then 400ma
     
    Alexsieg, Oct 9, 2016
    #20
    1. Advertisements

Want to reply to this thread or ask your own question?

It takes just 2 minutes to sign up (and it's free!). Just click the sign up button to choose a username and then you can ask your own questions on the forum.
Similar Threads
  1. ITSME.ULTIMATE

    How do I make a constant current load?

    ITSME.ULTIMATE, Mar 19, 2006, in forum: Electronic Basics
    Replies:
    3
    Views:
    5,605
    Deefoo
    Mar 21, 2006
  2. Viatcheslav Riabov

    VCR JVC HR-A33U loads non-existent tape and re-loads existent

    Viatcheslav Riabov, Sep 29, 2004, in forum: Electronic Repair
    Replies:
    3
    Views:
    769
    Mark D. Zacharias
    Oct 1, 2004
  3. mansoor.naseer@gmail.com

    Difference between Constant Current Regulator and Constant SourceInverter

    mansoor.naseer@gmail.com, May 5, 2009, in forum: Electronic Design
    Replies:
    1
    Views:
    1,019
  4. Paul Saha

    How to work with SN65HVD1782

    Paul Saha, Jul 7, 2016, in forum: Datasheets, Schematics, Manuals and Parts
    Replies:
    3
    Views:
    159
    Harald Kapp
    Jul 7, 2016
  5. Paul Saha

    How to make a alarm car security system?

    Paul Saha, Jul 25, 2016, in forum: Electronic Projects
    Replies:
    2
    Views:
    219
    Paul Saha
    Jul 26, 2016
  6. alex_gomez
    Replies:
    4
    Views:
    269
    Martaine2005
    Aug 24, 2016
  7. hevans1944

    How to Interface to PT4303-S Superhet Receiver Chip

    hevans1944, Sep 3, 2016, in forum: General Electronics Chat
    Replies:
    0
    Views:
    418
    hevans1944
    Sep 3, 2016
  8. Name...
    Replies:
    28
    Views:
    670
Loading...