My rule of thumb is to keep a zener between 25% and 50% of its rated dissip= ation. I know that seems like a lot, but I believe that most zeners are at = their spec voltage at 50%. Zener diodes are why there are things like the LM385 and TL431 :) Another thing I'll do instead of a low voltage zener is use a few LEDs in s= eries. Reds are pretty solid. Cheerful regards, Bob ________________________________________ From: piclist-bounces@mit.edu on behalf of Jason = White=20 Sent: Monday, April 29, 2019 11:14 AM To: Microcontroller discussion list - Public. Subject: Re: [EE] Stability of Zener+Darlington BJT linear regulator? Thank you Dwayne, Bob, and Spehro for your input. I think I will opt for a base resistor in the 1k to 10k range to suppress oscillation. Any recommendations for the minimum correct zener current over a -40 to 85C operating range? I imagine that the minimum zener current is dependent on temperature. From the attached graph at 25C it looks like 500uA is as low as I could go. -- Jason White --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .