Zener diodes

D

delbert

Gawd
Joined
Jul 14, 2001
Messages
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I understand the basics including the use of diodes, and even thought I understood the basic principles of zener diodes, but I guess not. Forgive the crude ms paint artwork, but can somebody explain the use of the zener diode in the schematic below?
zener.gif

The symbol on the left is supposed to be a circuit breaker. It's power in at any rate.
 
Its providling a constant voltage for the circuit, whatever the value of the diode itself is.

Not sure what the rest of the picture shows, but thats what a zener diode does, allows a set value of voltage to cross through it.
 
If you exceed the zener's breakdown voltage, it'll begin shunting the current to ground. Thereby (I assume) protecting the switch.

Its providling a constant voltage for the circuit...
Click to expand...
No, a zener provides a maximum voltage. It acts as a cap.
 
Yea, what he said, I was backwards my appologies. I was thinking what he said, just wasn't typing it. It limits the voltage, I was thinking constant as if it goes over, it keeps it at the given.

ie. 13V gets cut to 12V if thats the zener thats installed.
 
Thanks for the quick replys.
The solenoid is energized by the switch (providing a ground). I’m just not understanding the function of the zener diode. A regular diode would be blocking the (second?) ground and therefore be useless in this case. Then there must be a reason for the “zener” part. I’m guessing, but I don’t understand it’s function. Could it simply be absorbing the collapsing current when the solenoid relaxes (switch opens)?
Link to actual (simplified) schematic.
 
Guessing here since I don't know the application, but it appears a standard zener barrier case; without it, when the solenoid collapses, you'd get sparking across the switch terminals, leading to eventual degredation and failure.
 
Yeah thanks. I was beginning to answer my own question as I typed my last reply. I’m just not used to seeing them installed in this manner. It must be a surge suppression circuit for the collapsing field. Thanks again.
 
It looks something like an overload protection.

Once the switch is closed, and the current is flowing the zener is probably ignored, no current flow through it, but when an overload is detected the zener saves the solonoid by dumping the excess current through itself, instead of through the switch.
 
The switches used are rather heavy duty so I wouldn’t necessarily say it’s for overload. This is airliner stuff I work on. I think preventing the sparking across the switch when the contacts open (kick back from the field collapse) as masher said is the key. I am use to seeing them parallel to the coil, not remote like this. It confused me for a bit. Thanks again for everyones help.
 
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