I was wondering whether there is a difference between Zener effect and Avalanche effect? How do they differ?
Electronic – Zener effect and Avalanche effect
zener
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KVL rules here. The zener branch (R1 and D1) will be at the same voltage as the capacitor branch (D2, R2, and C1), which will be 9V.
If you want the zener to limit the cap voltage, you need to move D2 to the midpoint junction of R1 and D1.
simulate this circuit – Schematic created using CircuitLab
Don't forget that D2 will eat a few hundred millivolts, meaning your cap voltage could end up as 1.6V or so.
Once you get the basic idea of how the zener clamp works, you can start playing around with the resistor values (hint: is R2 really necessary?) and see how the performance is impacted.
Zener diodes are constructed in a way so that in reverse-bias the zener effect causes current to flow. This can be controlled (at time of manufacture) to a certain voltage. In forward bias the operation is identical.
Wikipedia page on Zener effect (tunneling)
Signal diodes also break down in reverse bias but that is due to avalanche breakdown which may appear similar but is caused by something completely different. It is also generally at a higher voltage.
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Best Answer
There are two entirely different effects exploited in zener diodes; at low voltages, the effect is tunnelling across the junction, and at higher voltages, the effect is identical to the avalanche diode. The temperature coefficient of each effect is different; I can't find my reference offhand but one (I think tunnelling) the zener voltage decreases with temperature and the other effect has an increasing voltage with temperature.
The importance of this detail is that zener diodes around 5.6 or 6.2 volts have close to zero temperature coefficient of voltage, since in that voltage range, both effects are equally important.
Edit : "zener breakdown" at low voltages may not be tunnelling as I (mis?-)remembered; however it is a separate effect from avalanche breakdown. I did get the temperature dependence right way round though.
Wikipedia suggests the difference is this : in the zener effect, the electric field across the junction breaks bonds to release carriers; while in the avalanche effect it is collisions which break bonds and release carriers.
On the other hand, this article does use the words "quantum tunnelling" to describe the Zener effect, so maybe I'm not completely senile yet...