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Created November 13, 2011
Last modified June 08, 2017
Tags voltage-regulator   zener-diode  


A Zener diode provides controlled reverse breakdown, and can act as a fixed voltage reference.


Zener diode D1 provides a fixed breakdown voltage of about 5.1 volts over a wide range of currents. R1 is necessary to prevent over-loading of voltage source V1.

Using a Zener diode like this isn't a particularly efficient way to generate a fixed voltage reference due to the high currents involved, but it's quite simple and reliable.

A few things to try in CircuitLab

This circuit highlights several cool features of CircuitLab simulations that you can quickly try. Load this circuit with the "Open in editor" button above, and then click the "Simulate" tab to get started.


You can see the output voltage (near 5.1V) as well as the DC current running through the Zener diode -- those things can get quite hot!

DC sweep

Use the DC sweep to simulate how the output voltage will be affected if the input voltage changes. As you can see, the output remains quite close to 5.1V over many volts of input voltage.


You can plot the frequency response of this voltage reference, which might be useful if you have a noisy power supply (V1), and are curious to know how much of that noise makes it into the "regulated" voltage V(out). As you can see, with the current parameters, there's about -40dB gain between V(in) and V(out). This means that a ripple at the input will cause a ripple about 1/100th as big at the output -- not a bad start for power supply noise rejection.


how can current pass through the anode of zener? the direction is from cathode to anode

by mohni
May 30, 2013

Try it! You will be impressed. A Zener in the reverse voltage mode will break down at the Vz value and start to conduct. Its current can vary but the voltage that is dropped across the zener will remain fairly constant at the Vz value. About 5% (not real good conpaired for todays advanced circuits) but as the auoher said, " this circuit works well and is very stable." That's how the zener works.

by GAR
June 16, 2013

Why is there a current source on this circuit?

by jbarry456
March 19, 2014

The current source is used as a load. With this arrangement the voltage on the output can vary with the Vz while maintaining a constant current. In this case a load of 10 ma. If your circuit is not pulling a constant load then remove the current source.

by GAR
May 06, 2014

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