- Joined Apr 16, 2010
See attachment for an example of how much the voltage across a Zener changes with current through it. At that low a current you may only get about half the rated voltage. So about 0.5 mA out and only about 1 Volt (?).
Current regulator diodes are J-FET's with the gate tied to the source. Because of this the minimum voltage allowed across the "diode" is the gate-source threshold voltage of the FET. The 1ma diode in the link looks like it needs around 3 to 4 volts minimum.
As previously noted, the zener current is too low for the zener to regulate voltage.What are the pitfalls of the 1mA constant current source shown below?
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by Jake Hertz
by Jake Hertz