if any one know how to do this, please help me...

(Urgent............)


Thank u very much.............

 

You pretty much need a data sheet to answer that one, the curve of the zener will tell the tale. You have to calculate the current going through the zener, and match that with the data sheet to see what the predicted voltage is.

Basically the voltage across the load will be the zener voltage, give or take. Zeners are pretty flat (though not perfect).

The arrangement is a voltage divider, with the load being one resistor and R being the other. If the voltage divider drops below the zener voltage on the load the zener is effectively out of circuit.

If the voltage divider is above the zener voltage then you have the zener voltage on the load. Whatever the current going through R is being split between the load and the zener, calculate the current going through the load, and subtract that from the current going through R, what is left is going through the zener diode.

All About Circuits has a section on zeners, have you read it?

http://www.allaboutcircuits.com/vol_3/chpt_3/11.html

 

This certainly looks like a homework assignment by a teacher/professor/instructor.

Is it?

 

Yep. It started in the math forum though.

 

Well, it's really not that complicated.

There is a 10v Zener diode. If you take it to be a theoretically ideal Zener diode, that clamps at 10v no matter what the input current is, then figuring out what the voltage is across the 200 Ohm load is a piece of cake, right?

And after you figure out what the voltage is across the load, you then can figure out it's current, and what the voltage is across the 100 Ohm resistor, and what the current is through it, and the current through the Zener.

 

The datasheets for zener diodes shows their "dynamic impedance" which is used to calculate voltage regulation.

 

In a practical zener diode,the current through it must be greater than the keep-alive current for it to clamp the voltage across it for what it is rated for. By applying this and the basic circuit analysis theorems, the rest of the analysis is a piece of cake.........

 

It appears to me that the dynamic impedance of the zener is shown on the schematic: 10 ohms.

 

Thanks for every ones... But still i can't understand...... I'm sorry, My exam is 2maro.

Please if can any one solve this here with step by step...........
I'll be able to understand.

Thank you................