low voltage 1ma Constant current circuit

Discussion in 'The Projects Forum' started by Karenzee, Jul 2, 2016.

  1. Karenzee

    Thread Starter New Member

    Mar 6, 2015
    15
    0
    Hi,


    i searched the forum for constant current circuits but didn't extactly found what i needed.

    the circuit should operate as low as 1v (max 5v) and the output current 1ma.

    Precision is important.

    Current regulator diodes are a possibility (are the j505 recommended?) but a cheaper alternative would be great.


    Thanks!
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,986
    745
    What about a J113 fet circuit?
     
  3. sailorjoe

    Member

    Jun 4, 2013
    361
    63
  4. crutschow

    Expert

    Mar 14, 2008
    13,013
    3,233
    What is your supply voltage?
    Does the load need to be grounded?
     
  5. RichardO

    Well-Known Member

    May 4, 2013
    1,235
    384
    How precise does the current have to be?
    The 1 volt minimum requirement is a tough one. The J505 needs as much as 2.1 volts to regulate. :(

    Even the amazing LM10 op-amp/reference needs about 1.2 volts to operate... And the LM10 is little pricey at $2 to $3 each. :(
     
  6. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,172
    397
    LM334, adjustable current source, max. out - 10 mA, input V - 2-20 V.
     
  7. Karenzee

    Thread Starter New Member

    Mar 6, 2015
    15
    0
    Thank you for all the suggestions so far!

    I thought that the j505 worked as low as 1v (need to check the datasheet again)

    isn't there current regulator diodes fit for this? (the gain of space is a big plus)

    supply voltage 3v to 6v

    precision is important but 1ma to 1.15ma is ok.

    note that i test soil and water so the output/electrodes are submerged/buried.
     
  8. dannyf

    Well-Known Member

    Sep 13, 2015
    1,810
    362
    jfets would be a good choice here. Setting precise current output is tough with those guys, however.
     
  9. Bordodynov

    Active Member

    May 20, 2015
    638
    188
    See

    Current_1mA.png
     
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  10. Karenzee

    Thread Starter New Member

    Mar 6, 2015
    15
    0
    Bordodynov,

    This looks good, thank you! (isn't there an alternative for the 2sd2704k?)

    I'll probably try this and also go for 2.5 - 3v with j505 (cheaper than the LM10).
     
  11. Bordodynov

    Active Member

    May 20, 2015
    638
    188
    alternative for the 2sd2704k (hfe=820-2700) is transistor with high gain (hfe>400). for example BC547C.
    alternative BCV61C - DMMT5551, BCV62C -DMMT5401
    Current_1mA_.png
     
    Last edited: Jul 7, 2016
    Karenzee likes this.
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