Hello all.
My name is jimmy and I like Hendrix gin, hence the username jimmiegin. Now, when I am not drinking gin, and sometimes when I am, I am learning all I can about my new hobby. So my question is a basic one but is confusing me all the same. I am currently learning about transistors and zener referenced regulated power supply. What I am not sure of is current flow direction and how a resistor in series with a zener, but not with output, can limit current to the load? or have I got something totally wrong?

 

Hi, If you have time try to read my old post (8 and 10) here
https://forum.allaboutcircuits.com/showthread.php?p=485066#post485066

 

Your diagram is correct. The Zener is being used as a Shunt Regulator. Current through the resistor will cause a voltage drop which will reduce the output voltage by that amount. The Zener diode starts conducting in the reverse bias direction at a value determined by the manufacturer. If the external load does not draw enough current (which is shouldn't) to cause sufficient voltage drop through the resistor, the current through the Zener makes up the difference. If you look at the data sheet for a Zener, you will see the current/voltage curve for the device which may help explain how it works

 

how a resistor in series with a zener, but not with output, can limit current to the load? or have I got something totally wrong?

The resistor will create an overall current limit. Say you have a 10V source and a 1kΩ resistor, there can't be more than 10mA total in the circuit. The zener requires a certain amount of current to attain its rated voltage, so that means there's a limited amount of current (less than the 10mA total), that is available for the load (with the zener voltage remaining constant). If the load attempts to draw too much current away from the zener, the zener voltage will drop, which will in turn reduce the current to the load.

 

Hello and welcome.

Please read my post#5 to another new starter, in this thread about current flow

http://forum.allaboutcircuits.com/showthread.php?t=96302

 

WoW thank you very much all.