zener diode inuition machanism for regulation

another perspective 0 to 2.8A active NPN load from a DC-biased triangle generator.



The 1N4742A is a 1W, 12V Zener diode, is a a nominal Zener voltage of 12V 5% at a test current IZT=21 mA, in the datasheet has a 9Ω Zener impedance, 5 μA maximum reverse leakage current, etc.). A 1A diode was added to correct for the Vbe error in a 50W power transistor to obtain 12V out.

As the output goes towards no-load, Vbe drops rapidly with Ib as Iz rises but it does not raise Vz as much as the drop in Vbe so any design must ensure the error budget does not exceed the output tolerance for all ranges in bias current.

There is no attempt to say this is an efficient design, nor optimized for low Vo error, but to demonstrate the weakness of Zener linear regulators and starving Vbe of current for learning how to avoid pitfalls in regulation errors.