Help required

justinesmithies · Aug 17, 2013

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

odinhg · Aug 17, 2013

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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justinesmithies Thread Starter New Member

odinhg Active Member

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