NPN transistor used as zener diode and clipping diode .

[PimpMyTone]

I tried it in my LaVache and it sounds really interesting . Anybody use that kind of clipping ?

            The emitter-base junction of a bipolar NPN transistor behaves as a zener diode, with breakdown voltage at about 6.8 V for common bipolar processes and about 10 V for lightly doped base regions in BiCMOS processes. Older processes with poor control of doping characteristics had the variation of Zener voltage up to +-1 V, newer processes using ion implantation can achieve no more than +-0.25 V. The NPN transistor structure can be employed as a surface zener diode, with collector and emitter connected together as its cathode and base region as anode. In this approach the base doping profile usually narrows towards the surface, creating a region with intensified electric field where the avalanche breakdown occurs. The hot carriers produced by acceleration in the intense field sometime shoot into the oxide layer above the junction and become trapped there. The accumulation of trapped charges can then cause Zener walkout, a corresponding change of the Zener voltage of the junction. The same effect can be achieved by radiation damage.


              The emitter-base zener diodes can handle only smaller currents as the energy is dissipated in the base depletion region which is very small. Higher amount of dissipated energy (higher current for longer time, or a short very high current spike) will cause thermal damage to the junction and/or its contacts. Partial damage of the junction can shift its Zener voltage. Total destruction of the Zener junction by overheating it and causing migration of metallization across the junction ("spiking") can be used intentionally as a Zener zap antifuse .

[midwayfair]

I've played with transistors as clippers a bit. It's a good use for ones that I broke the legs off of desoldering and such...

I'm not certain you can get the Zener effect out of a transistor as a clipping diode in most stompbox applications (EDIT for clarity: the post reads like there wouldn't be enough voltage). But try it anyway! You might like it. Zeners sound really cool as clippers, not quite like silicon or LEDs.

[bigmufffuzzwizz]

I've never experimented with anything like that but sounds interesting. SO tied E and C for cathode and B becomes anode...hmm i'll try that when i get a chance..