Help required

Discussion in 'The Projects Forum' started by justinesmithies, Aug 17, 2013.

  1. justinesmithies

    Thread Starter New Member

    Aug 4, 2013
    5
    0
    I am using an LM334z run from a 12vdc supply to fix the output current to a max of 2Ma . What value pot would i need to put in series with negative side to be able to vary the current from the regulated max of 2Ma to 0Ma ??

    Any help would be brilliant.

    Thanx in advance

    Justine
     
  2. odinhg

    Active Member

    Jul 22, 2009
    65
    15
    You will need to read the datasheet here:
    http://www.ti.com/lit/ds/symlink/lm134.pdf

    At page 6, it explains to you the relationship between I_{SET} and R_{SET}.

    We get the following equation from the datasheet:
    I_{SET}=\left(\frac{V_{R}}{R_{SET}}\right) * \left(\frac{n}{n-1}\right)


    V_{R} and the ratio n between I_{SET} and I_{BIAS} can be found in Figure 9 and Figure 12 respectively.

    Your I_{SET} is 2mA. So for 25°C and 2mA we get:

    V_{R} = 63mV
    n = 16

    I_{SET}=\left(\frac{0.063mV}{R_{SET}}\right) * \left(\frac{16}{16-1}\right)

    2mA=\left(\frac{0.063mV}{R_{SET}}\right) * \left(1.067\right)

    Now you just have to calculate your unknown value of R_{SET} :)
     
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