How to design an Analog voltage stabilizer using Relays and LM324 Op-Amp and NE555 Timer IC

Published by MKDas on

A very common configuration of voltage stabilizers is using Op-Amp like LM324 and NE555 Timer IC. Before using any micro-controller this circuit configuration was used the most. Even still now, some companies are using this circuit where there is no digital display required. As because this design is easy and low cost, so still this circuit is popular. In this article, we’ll discuss voltage stabilizers using analog circuits. So let’s start our Analog voltage stabilizer circuit.

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Before we start, we have to know how the voltage stabilizer works. To know about the working principle, you can read the previous article from here.

Block Diagram:

Here is the block diagram of our Analog voltage stabilizer circuit:

Analog voltage stabilizer block diagram

In an Analog voltage stabilizer, the line voltage is stepped down to 12V or 18V to make a power supply for the operating circuit as well as the voltage sensing loop. Sometimes, a separate voltage loop is kept of 12V for sensing purposes. Then a voltage sensing circuit is used which is later used in the comparator circuits. A delay timer is kept to make an initial delay which helps in-line stabilization.

A set of Op-Amp comparator circuits are used for switching of different relays. These relays are used to change the transformer taps. Finally, the output is switched to the load. The whole process is not so complex at all. Only some blocks working at a time. The next step of our Analog voltage stabilizer describes block by block.

Transformer design:

It is completely the designer’s choice that how many taps will be used for the voltage stabilizer. But a suitable range of the lowest taps is 5. For a 220V system, these 5 taps are usually kept as 150V, 180V, 220V, 280V,260V & 0V. 5 Relays are used for this type of voltage stabilizers. So based on the choice of taps, you should design your own transformer. The formula is very simple, practice is required for good performance. Here is a practical way to do the job.

These steps to follow:

  1. First, select the tap numbers then voltages
  2. Calculate the total power and wire size from the ampere rating keep a safety margin for wire size here.
  3. Calculate the core area from that power rating. Keep a safety margin here for overloading issue
  4. Find the bobbin size of the transformer
  5. Calculate the Turn per Voltage for your design
  6. Calculate total turns and mark each tap, like for first tap 150V, 405turns, then for the second tap of 180V 512 turns, and so on.
  7. Wind a sample transformer for testing. Check the voltages with and without load. A full load test should be run for several hours. This will generate heat and will help to remove the moisture inside the core and coils.
  8. Give a varnish bath in a container immediately, keep overnight [or at least 3hrs] and extract the excess varnish by hanging the transformer for hours.
  9. Once the transformer is dry again, fit the angles and other accessories. Then set the terminals and test again.
  10. Once it passes the whole process you can scale it up but if fails, calculate where the fault is, then correct it and remake.

Sounds easy? No? It depends on your practice. Those are the way to make a professional transformer. I’ll publish a different article on transformer calculation later.

Circuit diagram blocks:

There are several blocks in our circuit and you already know that. If each block is explained separately, it will be easier to understand. Let’s see in blocks.

The Transformer:

Let’s use the 5 tap transformer for our design:

automatic voltage stabilizer transformer

The voltage sensing and power supply circuit:

automatic voltage stabilizer circuit

Here, using two separate winding works the best. because if only one winding is used, the sensing voltage will be changed due to the relay switches.

In the power supply circuit, two voltage regulators are used for better heat dissipation and division of headroom voltage. Diode D1 and D2 are used to protect the voltage regulators from reverse discharge. Sometimes, Transistors are used also LM317 can be used. The alternative circuits are:

automatic voltage stabilizer circuit

Here LM317 voltage regulator is used. As the headroom voltage is high, so sufficient heatsink must be used for cooling. Another type of power supply is:

voltage regulator using transistor circuit

In this type, the Tip122 Darlington transistor is used with a Zener diode of 12V to form a voltage regulator. This type of voltage regulator is pretty common in voltage stabilizers or analog circuits.

Note: It’s totally the designer’s choice which type s/he will use. A combination of these circuits can be formed to get an optimum result.

Delay circuit:

An initial delay is a must for the voltage stabilizer. Otherwise, a spike can be pass to the load which is dangerous for the loads. NE555 IC is the first name that comes for this purpose. NE555 is configured in one shot or monostable mode for this timer purpose.

NE555 delay timer animation

After the delay circuit, we need to design the comparator circuit which will actually control our relays for different voltages.

Comparator Circuit:

The most common Op-Amp ICs are LM324 and LM339. Depending on the designer’s choice s/he can use any one of these. While using LM339, you must keep in mind that it is open-collector type output and you need a pull-up resistor for that.

Op-Amp comparator circuit for voltage comparison animation

Here, R1 works as the hysteresis control resistor. Hysteresis is important in our circuit to protect the relays from sharp switching. Without hysteresis, the relay can be turned on/off at the same point of line voltage which will kill the relay as well as other connected contacts.

Relays:

Relays are very common for isolated switching purposes. And for a voltage stabilizer, a relay is a common choice too. There are different types of relays in the market. We will use the very common one with one set of NO/COM/NC.

relay for voltage stabilizer

While using these types of relays, we must use a freewheeling diode across the coil. A transistor can be used for switching the relay coils. Also, a capacitor across the relay coil is preferable for good magnetic flux generation across the relay coil.

transistor based relay driver circuit animation

Now, we can combine all the parts into one to form the control circuit.

Complete circuit diagram:

The whole circuit diagram is pretty large. I tried to draw it all in a clear way. If I made any mistake kindly let me know, I’ll correct it later.

automatic voltage stabilizer circuit

Explanation:

All the blocks are described earlier. In this circuit, all those blocks are attached to each other where they should be. There is a diode in between two consecutive comparator circuits to make them working one by one sequentially. Another two Op-Amp comparators are used to set the low and high voltage limits.

There are no other changes I think except a RC filter in the sensing circuit.

Fittings:

Once the circuit is ready, you can fit this in a box like this with other accessories.

voltage stabilizer

Other accessories:

Besides the control circuit and transformer, you need some other accessories for a complete Analog voltage stabilizer. Although it is not unknown to you if you come this far, here is the list for help:

  1. A box with suitable cutting holes for fittings
  2. AC cord for supply input
  3. Input circuit breaker/FUSE
  4. Output circuit breaker/FUSE
  5. Handle fitted with the box for handle
  6. Screws and washers
  7. Plastic supports for circuit placement
  8. Cable ties.

Conclusion:

As you see, analog circuits are too complex and sometimes they become so hard to troubleshoot. But on the other hand, a micro-controller can solve many complexities in any circuit. Analog circuits are cheap and once it is designed finally, can be used for a long time. It’s totally up to you what you’ll use. But I hope this article will help you make your own product.

Yes! I always post articles that can be turned into products or assist somehow. I think if you stay with me, one day your work will be productive and your business will grow. Thank you again. If you need any help kindly comment below.


MKDas

I'm Mithun K. Das; B.Sc. in EEE from KUET, Bangladesh. Blog: https://labprojectsbd.com. "First, electronics was my passion, then it was my education, and finally, electronics is now my profession." I run my own electronics lab, M's Lab (https://mlabsbd.com). Where I work with the creation of new products from ideas to something in real life. Besides this is my personal blog where I write for hobbyists and newcomers in the electronics arena. I also have a YouTube channel where I publish other helpful videos, you can find the link inside the articles. I always try to keep it simple so that it becomes easy to understand. I hope these will help them to learn electronics and apply the knowledge in their real life.

7 Comments

Joy · April 17, 2021 at 7:08 am

Thank you for giving student learning purpose project.Those who have a knowledge of electronics can easily make it. But Sir PIC Microcontroller 16f73 output & input volt meter with five step relays It would be nice .

    MKDas · April 17, 2021 at 10:14 am

    It’s my pleasure.

    >> I’ll post soon.

Asimiyu · April 17, 2021 at 9:08 am

Thank you sir for the new updated project on Analog stabilizer. I can wait to learn another new project. May God Almighty Allah continue to enrich your knowledge, together with prosperty. It is not easy for someone to dedicate his time, resources, and knowledge to help others without expecting return.
Your blog is part of what I have learnt till today and it is a source of many things I have learnt on digital circuits and programming, using mikroc c compiler.
Through, your previous website, I have learnt and built many circuits such as power optimization circuit project, using PiC16F73, AC voltage parameters, DC Display with 7-segment, AC voltmeter, and so on and recently, from your new blog, I have been learning and building. I built Solar PWM battery charger for 12V/5AH and it is working till now. I planning to built it for 24V @ 200AH battery by modifying some components, I have already bought IRF1404 MOSFET, PC817, heatsink, and others components.
However sir, the issues I have facing right now is that, I am using it as hybrid PWM charger, which the Battery will be charging either through solar panels or A/C rectified voltage. Here I determined to use Ferrite core as AC to DC buck converter and this is where I am hanging, I have done research on internet and I come across 220vac to 15vdc @10A, AC/DC buck converter using UC3842 using Ferrite core in YouTube, the site is “ElectroBUFF”. He gave primary winding, secondary winding and auxillary winding details but no formula to further increase to 28V at 10A.
Please sir, I just want a guide or formula or if you have any similar AC to DC flyback converter because, I always trust anything you posted. I need it urgently, I have already bought electronics components, with aims to get ac/DC flyback converter with 28v using Ferrite core but I can’t find

    MKDas · April 17, 2021 at 10:13 am

    I’m glad to know that my effort helped you. It’s my pleasure.

    SMPS issue: I’ll suggest designing the SMPS in CC/CV mode. Without Constant Current mode, your SMPS will be able to be used as a battery charger. It will burn itself. So first gather knowledge to build CC/CV SMPS. If I get time, I’ll post something on SMPS. SMPS is a bit complex if you do not understand the basic concept. I’ll try to explain.

      Asimiyu · April 17, 2021 at 11:42 am

      Ok sir. Thank you.

PAPARAO · June 18, 2021 at 5:40 pm

Sir,I am interesting to learn the pcb design and pcb circuit analysis please tell me how much fee is taken.

    MKDas · June 19, 2021 at 5:52 am

    Soon I’ll start PCB design tutorials. I hope it will help you a lot.

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