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

 

[mneary]

Please re-check the diagram. For most problems you probably would have one side of the generator connected to 0V.

 

[ericgibbs]

hi,
Is that the full circuit.? whats connected to right side of the Vgen ?

 

[studystudystudy]

yes, mneary, my circuit is wrong, the polarity of zener diode D2 should parallel with D1, mean, the zener diode D2, -ve should face to left hand, while +ve should connect to Vgen -ve.

so that it can be back to back. to act as the voltage limiter. but isit the resistor not necessary?

 

[studystudystudy]

hi,
Is that the full circuit.? whats connected to right side of the Vgen ?

just assume is Vout