# Why does not all the current flows through Zener diode?

Let's assume the following circuit, where Zener diode is used as a voltage regulator. R16 (R18 later) is the load.

When the input voltage is sufficiently high for Zener diode to be reverse-biased, according to the current-voltage curve of the Zener diode, the current will flow through it. Also, I know that the resistance of the diode is very small (milliOhms) when it is opened.

Considering all of the above, I guess we can exchange the diode with the resistor of low resistance (R20 in the image below).

Now we can calculate the currents through R20

So, if the load has a small resistance, then most of the current will flow through Zener diode.

My questions are:

• Is it the correct interpretation of Zener diode's functioning?
• Do we use it for the loads, where only the voltage is important?
• – G36 Mar 2 '19 at 13:29