back-to-back zener diode problem

[studystudystudy]

the back to back zener diode is used to limiter the voltage across. but i don't understand why resistor is needed here. please see the attachment.

the explaination i found is the resistor is served to impede the return charge drain current rate when one or both zener diode are operational.

please explain how the resistor can impede the return charge drain.

i try to understand it, but still don't understand

your help will be deeply appreciated. thank you

 

[IanP]

As far as the voltage source is concerned the Zeners are connected in series, not back-to-back ..
Reverse one of them and then you can remove the resistor from the equation ..


IanP

 

[studystudystudy]

dear IanP, isit the resistor is not necessary? just remove it only?

 

[karesz]

Hi,
I would say, a current limiter (your resistor) is (practically) overall needed!
You must see it on as a complex of 3 serial components, & not only the 2 x diodes, as a two pole element...
K.

 

[FvM]

Connecting an ideal (zero impedance) voltage source to the zener diodes will not give any limiting effect, but possibly damage the diodes.

 

[studystudystudy]

Connecting an ideal (zero impedance) voltage source to the zener diodes will not give any limiting effect, but possibly damage the diodes

so what should i do to limiting the voltage

 

[FvM]

Depends on the purpose of voltage limiting. My comment was related to the shown circuit, a real voltage source hasn't zero impedance of course. But if it's able to source a lot of current, you should add a series resistor between voltage source and limiting diodes.