Instructables
Picture of Zener Diode Shunt Regulator
Every circuit needs a power source, but different circuits have different power requirements. For most small scale electronics, the power consumption is (is or at least could be with better design) very low. For those times when you don't need a lot of power, just a precise voltage level, the simplest means of regulating the supply voltage is by using a Zener diode.

In this Instructable, I will compare a typical voltage regulation circuit with the Zener diode shunt regulator circuit and show you the proper way of selecting the perfect components for your circuit needs. Correct usage of this circuit can save time and money, but it is not well suited for all designs. So grab those breadboards and let's gown to business!
 
Remove these adsRemove these ads by Signing Up

Step 1: Zener Diode Basics

In case you don't know, a diode is a special type of electrical component that lets current flow freely in one direction, but blocks it from flowing in reverse - in the water analogy, the diode would be a one-way valve, only allowing water to flow in a specific direction. A typical diode will have a voltage drop of around 0.7V when forward biased. 

All diodes have a "reverse breakdown voltage" which if applied to the diode in reverse will cause current to flow backwards through the component, typically destroying it in the process. This value is typically in the hundreds to thousands of volts. A Zener diode (similar to an "Avalanche Diode") is a special sub-class of diodes that will allow current to flow in the reverse direction if the applied voltage is above a certain level without damaging the component. Of course, there are limitations to the voltage level and/or current flow, but those are things that the design engineer must take into consideration. 

Some common Zener diode breakdown voltages are: 1.8, 3.3, 5.1, 7.5, and 12.6, making them ideal for use in many small circuits.
stevenarango5 months ago

great instruct able. lots of great info. thanks

benjamin7125 months ago

Thanks for the article. I am building a wind mill generator and have a charge controller rated for a maximum input of 15V. I want to protect the controller in the event of voltage spikes from the gerneator motor above 15V. Attached is a possible design I came up with using the information above. I was hoping you could tell me if it would work as desired. (Would all voltage above 15V short to ground?).

Note* I have not determined the total resistance equivalent of the load or measured current values. Hopefully above at least 1A. Thanks!

zener diode.jpg
Kurt E. Clothier (author)  benjamin7125 months ago

Your use of this type of diode is generall called an Avalance diode instead of Zener, but it's basically the same thing. Have a look at this page for more info:

http://en.wikipedia.org/wiki/Avalanche_diode


It looks to me like you have the diode "pointing" to ground. That means ALL current would short directly to ground. To use the diode as a clipper, it needs to "point" at the voltage. Remember, a diode only lets current flow in the direction it is pointing unless the voltage level exceeds its "breakdown voltage." We can exploit that by using Zeners with low breakdown levels to only allow higher voltages to pass.

I would recommend you post your circuit and questions on the following website.

http://electronics.stackexchange.com/


It's a community of Electrical Engineers and they will gladly offer you advice and direction. Just be warned, if you don't word it very well, they might seem a bit rude... its just to protect the integrity of the sight. Take a look at a few other questions (or read the about page) to see what I mean.

http://electronics.stackexchange.com/about

lam6 months ago

Dear Sir Kurt E.

Please help me to know in 2 circuit (photo) is same working (function) or not ??? Thank you so much

lam

zener.JPG
Kurt E. Clothier (author)  lam6 months ago

Iam,
No, the diodes in your circuit do not do the same thing as in mine. What you have is a type of "clipper circuit" that limits the amplitude of the output wave form:

http://en.wikipedia.org/wiki/Clipper_(electronics)

Dear Sir Kurt E.

Thank you so much for your reply.

Kind regards

lam,

jhorapalok7 months ago

Thanks for the write-up.... very informative indeed.

Kurt E. Clothier (author)  jhorapalok7 months ago

No problem, glad it helped!

franssoa1 year ago
Thank you. Clear instructable, very understandable even for my bad english.
vicdex1 year ago
You are a very good material, go on with your good instruction,
Phil B1 year ago
Thank you for this. It is very well done and helpful. I was familiar with the idea of using a zener diode as a shunt to clamp the voltage in a circuit at a desired level, but had given no thought to disapating surplus input power with a dropping resistor.

Once we had a wireless telephone that gave us a lot of crosstalk in the earpiece. I happened to check the output of the 12 volt wall transformer and found it was 13.4 volts. I clamped the voltage of the transformer with a 12 volt zener diode and the crosstalk problem disappeared. (Actually, to be certain the zener diode could handle the power, I placed to zeners in parallel. I know that is not the way to do it, and the zeners may not be closely enough matched so that one bears the larger part of the work, but it worked out fine for me.)
Kurt E. Clothier (author)  Phil B1 year ago
Thank you for the comments. I've found that pretty much anything in electronics that has a specified voltage level on it is really +-10% of that voltage. I've mostly always used Zener diodes for clamping purposes as well, but thought it might be helpful for some people to see how they could serve as an actual, stable power supply for small loads. The burn off resistor is very important, because that extra voltage is dropping somewhere, and the diode typically can't handle that kind of current flow.
Thank you. I have also seen regulator circuits that use a power transistor clamped at its base with a Zener diode, but I never attempted building one.
Phil B1 year ago
Thank you for this. It is very well done and helpful. I was familiar with the idea of using a zener diode as a shunt to clamp the voltage in a circuit at a desired level, but had given no thought to disapating surplus input power with a dropping resistor.

Once we had a wireless telephone that gave us a lot of crosstalk in the earpiece. I happened to check the output of the 12 volt wall transformer and found it was 13.4 volts. I clamped the voltage of the transformer with a 12 volt zener diode and the crosstalk problem disappeared. (Actually, to be certain the zener diode could handle the power, I placed two 12 volt zeners in parallel. I know that is not the way to do it, and the zeners may not be closely enough matched so that one bears the larger part of the work, but it worked out fine for me.)