zeners

[t.man]

what's the main purpose of connecting two zeners facing each other?

 

[Hero999]

It's for over voltage transient suppression.

The breakdown voltage is equal to the Vf plus the reverse breakdown voltage.

You can buy transient suppressors which are just two zeners connected back-to-back. The advantage is that it can be used for AC.

 

[Warpspeed]

The usual application for this is for use in ac circuits to clamp an ac voltage equally on both positive and negative halves of each cycle.

 

[Styx]

bipolarity clamp ±(Vz + Vd)
It is also used across the capacitor in OPAMP integrator circuit to clamp the output to a know level and stop the OPAMP driving itself into saturation (and thus cause issue and delays if/when it is winding out of saturation)

 

[electronspeed]

This back-back connection can also be used to clip the sinusoidal signal depending upon i/p and Vz of diode.This can be extended further to generate square wave.