A voltage stabilizer is a common protecting device for our home, office, or industries. There are different types of voltage stabilizers in the market in a wide power capacity range. In this article, we will learn how we can design a voltage stabilizer and what is the working principle with other associated articles. So let’s start!

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What is voltage stabilizer?

A voltage stabilizer is a kind of regulator which regulates the output voltage and keeps it constant (or in a range). There is a difference in regulator and stabilizer. If you want to read more then you can read from here. The general thing that comes to our mind about voltage stabilizer is a machine like this:

voltage stabilizer

Which usually uses relays to switch the transformer taps to keep the output voltage in a range regardless of changes of input voltage. There are different types of voltage stabilizers in the market. Based on operation we can divide the voltage stabilizers into the following types:

  • Tap changing voltage stabilizer
  • Servo voltage stabilizer
  • Static voltage stabilizer

Tap Changing voltage stabilizer:

Here the common one is the TAP changing voltage stabilizer. This type of voltage stabilizer uses a transformer with multiple taps like this transformer:

voltage stabilizer transformer

An auxiliary power of around 12V is kept to drive the control circuitry of the voltage stabilizer. In this type of voltage stabilizer Relays or Thyristors are used to switch the input or output line with the transformer tap. Based on the configuration, this tap changing transformer type voltage stabilizers are three types;

  • Output switch type
  • Input switch type
  • Combined input & output switch type

What does it mean by Output switch type?

When the input line is injected into only one tap of the transformer and a set of relays (or other switches) is used to select different taps which carry the line to output, it is an output switch type voltage stabilizer. Let’s see this configuration below:

voltage stabilizer output switching transformer

Here the AC input is injected into the 220V tap of the transformer. And a rotary switch is selecting different taps which is carrying the voltage to the output. That means the input is fixed in position but the output is being switched between taps. Here the output voltage is calculated by:

Output voltage = (OUT TAP x INPUT VOLTAGE) / INPUT TAP

That means if the input voltage is 200V and the output is taken from 240V then the output is: 240*200/220 = 218.18V

Similarly, if the input voltage is 170V and the output is taken from 260V tap then output is: 260*170/220=200.9V

Pops & Cons of this method:

As the working principle of this type of voltage stabilizer is very simple so it is easy to make and troubleshoot. But the problem is you need extended tap voltages for a wide range which makes the transformer bulky as well as the material cost is higher. Besides, if the line voltage is high and as it is injected into a fixed tap the transformer may burn due to over-voltage injection. Also, the auxiliary voltage is varying a lot which impacts the circuit operation.

What does it mean by Input switch type?

When the output is taken from a fixed tap and the input is injected in different taps based on input voltage then it is called the input switch type voltage stabilizer. This configuration can be explained with this image:

voltage stabilizer input swithcing transformer

Here, the output is taken from a fixed tap and the input is injected into different taps based on the input voltage. Output voltage calculation is the same as output switch type.

If the input is 170V and injected into 180V and the output tap is 220V then, the output is: 220×170/180 = 207.7V

Similarly, if the input is 250V and injected into 260V then the output is: 220*250/260 = 211.5V

Pops & Cons of this method:

As the input is injected in different taps and output is taken from a single tap the transformer can be compressed in tap range. This makes the transformer price lower than the output switch type. Besides, the auxiliary supply is not much fluctuated. As the input is injected in different taps so transformer over voltage or under voltage injection is solved.

Combined switching type:

In the combined one, the injection and output switch both are changeable. It is a little bit complex but it helps to achieve a wide input voltage range and compressed transformer tap range. This configuration is like this:

voltage stabilizer combined switching transformer

Pops & Cons of this method:

The benefit of this method is a wide input voltage can be injected and at the same time, a narrow output can be achieved. Also, the transformer tap compression is good which reduces transformer tap as well as reduces material cost. Besides, the auxiliary output is also in a close range regardless of changes in input voltage.

Summary of tap changing voltage stabilizers:

As this type of voltage stabilizer changes the taps to keep the output in a range such as 220+/-10V so the output is not fixed. A wide change like 230 >> 210 or vice versa can happen. Also due to the tap changes an EMI can be generated which can impact sensitive equipment nearby.

You may find this helpful: How to design a voltage stabilizer using a micro-controller from A to Z

Servo Voltage Stabilizer:

The servo voltage stabilizer on the other hand uses a variable transformer with a carbon brash for selection. A gear motor is used to rotate the carbon brash position.

servo voltage stabilizer transformer

The input line is injected to a level and the output is taken from the transformer coil surface. As the connection is made by a moving carbon brash, so there are no sudden changes in output voltage. Usually, these transformers are designed in toroidal type to get maximum efficiency.

servo voltage stabilizer transformer
servo voltage stabilizer transformer

Pops & Cons of Servo voltage stabilizer:

The output is gradually corrected thus a smooth output voltage is obtained. But problem is, there is a correction delay. In any situation when the output was 220V for an input voltage, but if the input voltage changes suddenly, it takes time to correct the output voltage and meanwhile a high voltage spike can pass to the output loads.

Also as there is a mechanical operation, a lifetime of the carbon brash and motor is an issue. Proper maintenance is required otherwise carbon formation over the coil surface can create a loose connection.

Static Voltage Stabilizer:

A static voltage stabilizer is a combination of electronics and transformers. A buck-boost transformer is used with an inverter to add or subtract voltage from the line voltage. Digital Signal Processors (DSP) are used to monitor and control everything.

static voltage stabilizer

In a static voltage stabilizer, IGBTs are used in AC/AC converter. This AC is controlled by a DSP and injected with the input voltage either in phase or out phase with the input phase. That creates a voltage correction like this:

static voltage stabilizer

To know more, you can visit this site.

Pops & Cons of Static Voltage Stabilizer:

One of the most benefits of a static voltage stabilizer is the correction speed. Even if a welding machine is connected in the input line a small fluctuation can not pass to the output. Output is almost always constant regardless of input voltage fluctuation. Also as there is no mechanical moving part, a long life can be achieved. Only one disadvantage of Static Voltage Stabilizer is it is more complex than other types and more costly. But comparing with the result and performance, this cost is not an issue at all.


This article was an informative article before starting a design. In the next articles, we’ll make some voltage stabilizers practically. So you can read again to get the basic ideas clearly.

I hope you enjoyed this article and in the next articles, you’ll be with us. Thanks.


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I'm Mithun from Bangladesh. Electronics is my passion, love to work with electronics. This is my personal blog. Besides my regular works, I write some articles here. Most of them are open-source and everything is presented in the easiest way so that anyone can understand and learn it. Thanks.


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