Hi. I want to find out if my understandings are right. So this is a voltage regulator with zener diode. Say Vz=5volts. Until the point that the voltage at the zener reaches 5V, the zener remains off. The current equarion is Is=Iz+IL, Is=IL(where IL is the load current). As soon as the voltage at the zener reaches the 5V treshold voltage, it turns on and some minimal zener current flows, determined by this equation Iz=Is-IL. It starts regulating. From now on, we can say that IL=Vz/RL=almost constant. As Vsupply increases, the zener current increases and keeps Vz at almost constant level.

 

To fully understand how this circuit works you have to apply a load to the output of the circuit.

 

Look at it this way:

When Vin > Vz (the point at which the Zener starts to conduct)

Ir = (Vin - Vz) / R
Iz = Ir - I load

 

I would put it differently.

R + Rload constitute a voltage divider.
When Vload > Vz the zener will conduct so that Vload = Iload x Rload = Vz.

 

Your reasoning in post #1 is correct, assuming Is is the current through the voltage supply.

 

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Hi. I want to find out if my understandings are right. So this is a voltage regulator with zener diode. Say Vz=5volts. Until the point that the voltage at the zener reaches 5V, the zener remains off. The current equarion is Is=Iz+IL, Is=IL(where IL is the load current). As soon as the voltage at the zener reaches the 5V treshold voltage, it turns on and some minimal zener current flows, determined by this equation Iz=Is-IL. It starts regulating. From now on, we can say that IL=Vz/RL=almost constant. As Vsupply increases, the zener current increases and keeps Vz at almost constant level.

Worth noting, Iz must be greater than IL to keep the output voltage steady as RL changes. Typically 5 to 10 times IL.If IZ max is 50 mA IL must be in the neighborhood of 5 mA to 10 mA. This is a low power scheme.