# A problem with zener limtting output voltage

1. Nov 15, 2013

### bibo_dvd

hello guys !!

i know that in zener diode limitting circuit
there are three types : 1-limitting Positive peak 2-limitting Negative peak 3-limtting both peaks

and i know that output voltage for
limitting positive peak =VZ+0.7v
limitting negative peak= -VZ-0.7v
but i don't know what will happen if the input voltage is changed ?!!
i mean is there a relationship between input voltage and VZ ??

in this photo i understand that in

(a) Positive peak output = 5.1v+0.7v=5.8v
Negative peak output =-3.3v-0.7=-4.0v
(b) Positive peak output =6.2v+0.7v=6.9v
Negative peak output = -15v-0.7v=-15.7v

but in related problem i don't know if the output voltage will change if the input voltage is changed ?!!
i think it will not change but iam not sure about that ..so help me guys !!!

Thank you :)

2. Nov 15, 2013

### Staff: Mentor

The zener characteristics are nearly independent of the input voltage. I say nearly because "real-life" zeners do have a small resistance value that will make the zener voltage vary a bit when its current changes (the same holds true for all diodes). Do a web search for zener characteristic curve and zener equivalent model.