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General => General Technical Chat => Topic started by: ocset on November 04, 2019, 07:51:39 pm

Title: Dave Jones tutorial on base-emitter of NPN being used as zener diode
Post by: ocset on November 04, 2019, 07:51:39 pm

Hi
Dave Jones has a tutorial on the above.....ive searched but cant find it....i watched it about a year back.
Does anyone know where it is?

Dave takes apart some kit that uses an NPN  base-emitter in reverse as a zener....i think it was for protection, and i think it was a  DMM

Title: Re: Dave Jones tutorial on base-emitter of NPN being used as zener diode
Post by: richnormand on November 04, 2019, 08:07:16 pm

https://www.youtube.com/watch?v=BGcKjy_UNQ4 (https://www.youtube.com/watch?v=BGcKjy_UNQ4)

Title: Re: Dave Jones tutorial on base-emitter of NPN being used as zener diode
Post by: Dr. Frank on November 04, 2019, 08:11:49 pm

Easy, that's Fundamental EEVblog #1157 - Transistor Zener Clamp Circuit from Dec. 2018.
That clamping circuit is used in a Fluke 8060A - successfully - to protect the symmetrical DCV input for no more than 5V.
Dave then wants to adapt that to the 121GW Ohm protection, which does not work at all, because that use case is asymmetric and up to 15V or more.
Frank