T
Thanks, this is on the PCB now, which has been made, and we cant go back unfortunately.
Anyway, i think we will increase the base resistor to 3k3 (R172) to limit the base-emitter zener current (if it ever occurs)
I saw a video once where they show some electronics meters which actually use a base-emitter of an NPN as a zener diode for circuit protection...so it can't be that bad i am thinking, as Easy Peasy partially notes in his kind description above.
Dear std_match, assuming the junction remains below 115 deg C how EXACTLY does zener operation reduce the gain of the device? natural drift or osmosis of dopants is generally temp dependent not reverse bias dependent ... ?
surely in a BJT the metallisation goes straight onto the Si, then if you want to protect the Al metal, you form an oxide on that, any non metallised Si can be oxidised - on the surface - but is there is not much near the junction in a planar device - in fact most of the junction is buried ... ?
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