Switchable const curr source

MikeML

Joined Oct 2, 2009
5,444
Here is how I would do it. Note that the emitter follower is a constant current source and switch in one. This will work provided the forward voltage drop of your Green LED is 3.2V or less.
 

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ScottWang

Joined Aug 23, 2012
7,397
2N7000 VGS = 4.5 V, ID = 75 mA,Rds typ=1.8Ω, max=5.3Ω
Vds = I * Rds_max
= 75mA*5.3Ω
= 0.4V
So if your Load is <75mA then using 2N7000 is ok.
Otherwise you have to find some other logic level mosfet and has a low Rds.
 
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