Zener barrier

[Dave0098]

Hello, i just want to make sure that i am understanding correctly how a zener barrier works. if the voltage rises past the rated amount for the circuit the zener diode deflects the voltage down to earth creating enought current to blow the fuse protecting the IS area equipment. and the resistor in series is to limit the amount of current aload to flow in the IS circuit. also how does a galvanic isolator i understand the principle behind it to isolate the IS circuit from a potentially dangerous rise in current. if anyone can help thanks alot im just trying to refresh my memory as ive not touch on this for a while.

cheers Dave

 

[pmac10]

a zener barrier consists of three parts, a current limiting circuit which as you rightly said would be a resistive element, a voltage limiting circuit which consists of zener diodes, these direct excess voltage to ground but as this is a dc application, that will not blow a fuse, the zener diodes ensure the voltage supplied to the IS is maintained at a safe level. the third part is the fuse, this protects the zener diodes from overheating, cant help you with the galvanic isolator but hope the first part helps

 

[Dave0098]

so why would the fuses not blow?

thanks pmac10

 

[confused-fuse]

also known as a crowbar circuit my test bench psu as one built in and i have made them myself self-reseting and pressing a button to reset the thyristor part of the circuit ... zeners are wonderful saved me hours on repairs

 

[pmac10]

so why would the fuses not blow?

thanks pmac10

as im sure you know in an ac system an earth fault travels along earth path back to the transformer and returns down the live line where it will blow the fuse. earth as in the planet plays no part in a dc circuit, it is simply a zero volts reference point not a protective path for fault currents.