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Automatic Voltage Stabilizer Circuit for TV sets and Refrigerator

Automatic Voltage Stabilizer Circuit for TV sets and Refrigerator

Here we will study the design of a simple automatic mains AC voltage stabilizer which can be applied for safeguarding appliances like TV and refrigerators from fluctuating voltages.

A voltage stabilizer is a device which is used to sense inappropriate voltage levels and correct them to produce a reasonably stable output at the output where the load is connected.

How the Circuit Functions

Referring to the figure we find that the proposed automatic voltage stabilizer circuit is configured with the single opamp IC 741. It becomes the control section of the whole design.The opamp is wired as a comparator, we all know how well this mode suits the IC 741 and other opamps. It's two inputs are suitable rigged for the said operations.

Pin #2 of the IC is clamped to a reference level, created by the resistor R1 and the zener diode, while pin #3 is applied with the sample voltage from the transformer or the supply source.

This voltage becomes the sensing voltage for the IC and is directly proportional to the varying AC input of our mains supply.

The preset is used to set the triggering point or the threshold point at which the voltage may be assumed to be dangerous or inappropriate. We will discuss this in the setting up procedure section.

The pin #6 which is the output of the IC, goes high as soon as pin #3 reaches the set point and activates the transistor/relay stage.

In case the the mains voltage crosses a predetermined threshold, the ICs non inverting detects it and its output immediately goes high, switching ON the transistor and the relay for the desired actions.

The relay, which is a DPDT type of relay, has its contacts wired up to a transformer, which is an ordinary transformer modified to perform the function of a stabilizer transformer.

It’s primary and secondary winding are interconnected in such a manner that through appropriate switching of its taps, the transformer is able to add or deduct a certain magnitude of AC mains voltage and produce the resultant to the output connected load.

The relay contacts are appropriately integrated to the transformer taps for executing the above actions as per the commands given by the opamp output.

So if the input AC voltage tends to increase a set threshold value, the transformer deducts some voltage and tries to stop the voltage from reaching dangerous levels and vice versa during low voltage situations.

Complete Circuit Diagram

simple TV fridge voltage stabilizer circuit

Opamp Calculations

If a resistor divider was used instead of a zener at pin#2, the relationship between the reference level at pin#2 of the opamp with the resistor divider and Vcc could be given as:

Vref = (R2 / R1 + R2) x Vcc

Where R2 is the resistor used instead of Z1.

Transformer Relay Wiring Diagram

stabilizer relay transformer wiring diagram

 Parts List

You will require the following components to make this homemade automatic mains voltage stabilizer circuit:

R1, R2 = 10K,

R3 = 470K or 1M, (lower values will enable faster voltage corrections)

C1 = 1000 uF / 25 V

D1, D2, D3 = 1N4007,

T1 = BC547,

TR1 = 0 – 12 V, 500 mA,

TR2 = 9 – 0 – 9 V, 5 Amp,IC1 = 741,
Z1, Z2 = 4.7V/400mW

Relay = DPDT, 12 V, 200 or more Ohms,Approximate Voltage Outputs for the Given Inputs

Stabilized Output Vs UnStabilized Input Voltage Proportions


200V -------- 212V
210V -------- 222V
220V -------- 232V
225V -------- 237V
230V -------- 218V
240V -------- 228V
250V -------- 238V

 How to Set Up the Circuit

The discussed simple automatic voltage stabilizer circuit may be set up with the following steps:

Initially do not connect the transformers to the circuit, also keep R3 disconnected.

Now, using a variable power supply, power the circuit across C1, the positive of the supply goes to the pin#7 line of the opamp while the negative goes to the negative pin#4 line of the opamp.

Set the voltage to about 12.5 voltage and adjust the preset so that the output of the IC just becomes high and triggers the relay.

Remember, here we have assumed that the DC output 12.5V from TR1 corresponds to around 225V AC input from mains....For your circuit be sure to confirm this before doing this set up procedure. Meaning, if suppose you find that your TR1 DC output corresponds to 13V for an input of 225V, then complete this procedure using 13V....and so on.

Now lowering the voltage to about 12 volts should make the opamp trip the relay to its original state or make it de-energized.

Repeat and check the relay action by altering the voltage from 12 to 13 volts, which should make the relay flip flop correspondingly.

Your setting up procedure is over.

Now you may connect both the transformer to its appropriate positions with the circuit, and also restore the R3 and the relay connections across their original points

Your simple home made mains voltage stabilizer circuit is ready.

When installed, the relay trips whenever the input voltage crosses 230 volts, bringing the output to 218 volts and keeps this distance continuously as the voltage reaches higher levels.

When the voltage drops back to 225, the relay gets de-energized pulling the voltage to 238 volts and maintains the difference as the voltage further goes down.

The above action keeps the output to the appliance well between 200 to 250 volts with fluctuations ranging from 180 to 265 volts.

Warning: A single wrong connection could lead to a fire hazard or explosion, therefore please proceed with caution. Always use a 100 watt protection bulb in series with the one of the mains line which goes to the stabilizer transformer initially. Once the operations are confirmed, you can remove this bulb.

2) The entire circuit is not isolated from mains, therefore users are advised to maintain extreme caution while testing the unit in an uncovered position and while powered ON, to avoid lethal electric shocks.


About the Author

I am an electronic engineer (dipIETE ), hobbyist, inventor, schematic/PCB designer, manufacturer. I am also the founder of the website: https://www.homemade-circuits.com/, where I love sharing my innovative circuit ideas and tutorials. If you have any circuit related query, you may interact through comments, I'll be most happy to help!

82 thoughts on “Automatic Voltage Stabilizer Circuit for TV sets and Refrigerator”

  1. How can the secondary and primary of the (second) auto-transformer be connected together to the mains AC input voltage. The specification says it’s a 12-0-12 volt and the primary is 220volt. Won’t it get burned does to insulation puncture. Thank you in advance for your reply.

    • The secondary and primary are added in series by the relay contact combinations, the secondary is never connected directly across the 220V mains.

      • Thank you for your quick reply. And will it be able to run a load of suppose a table fan i.e 150 watts because primary has high resistance and thinner wire than secondary so current will be limited to the primary’s rating.
        what is the workaround for this. Thank you in advance again.

        • To support a 150 watt load, the transformer should be also rated at 150 watts, otherwise it may become hot or even burn. A 12V 150 watt transformer would mean the secondary side having 150/12 = 12 amp rating, and the primary side 150/220 = 0.68 amps

  2. Hello good afternoon. I have a problem with 2 circuits the 2 are 9vcc. The problem is that when I feed them with separate sources they work well, but when I feed them with the same source they do not work well. The source voltage is correct. I really do not know what it can be. From already thank you very much.

  3. I did not understand the setting up procedure…you said that positive goes to the terminal of R1 …but which terminal of R1? and if i disconnect the relay then how will i understand that there is enough voltage to trigger the relay?

      • Thank you for your replay… Now If i disconnect the relay , how will i understand that the output is high enough to trigger the relay? is output will be 12v?

        • For the setting up procedure you will need an external variable power supply, once the set up procedure is complete after that you can connect TR1, TR2 and finalize the design.

        • Relay should not be disconnected, it seems to be a mistake, I’ll correct it soon…actually I meant to say keep the relay contacts disconnected with everything..anyway I’ll change it soon

  4. I have no problems assemblying the circuit so far as the diagram is correct i can follow everything and do the assembly… but my question is,
    Can this stabilizer carry the entire house, do the stabilizer have a wattage range? i intend to make it and stabilize my entire house and equipment… your help will be welcomed sir.

    • yes it can be used for whole house voltage regulation, by upgrading the the transformer and the relay according to your house’s maximum load specifications

      • Thanks for writing back sir.
        So how do i go about upgrading the transformer? at least i understand that i will need to upgrade the 5A transformer if i am not wrong, if i can recoil any transformer secondary to give me 15A, will that work? i look forward to be hearing from you.

          • Thank you very much sir.
            now if i may ask, how can i identify the amps of the equipments i have in the house? am i to just calculate all the amps and total it or how, Then what will be the effects if the amps is low? will it cause low voltage? the coils i fine in my area can deliver only 2amps so what if i twist it 5 in paralel, will that be able to give me 10amps or above.
            thanks for your help and understandings.

            • Hi Nkwenti,

              you can easily find the wattage of the appliances by referring to the back side labels of the respective appliances. You may note down the wattage specifications of the appliances from these labels, then add them up and divided this value with 220V or 120V as per the AC mains specs of your house. This will allow you to get the total maximum current requirement for your all house appliances.

              yes if the stabilizer transformer is not rated at twice the rating of your house’s total current consumption, then that might result in incorrect voltage stabilization from the unit…

            • Thank you sir for giving me your time and also teaching me the theory in details, youre trully a teacher, ok my problem is how to push the transformer to carry atleast 1500watts load so to be sure, now, please sir, have you any idea of the secondary coil guage of the transformer? i can do the coiling but dont know the exact guage, the coils i see that can be used for the secondary of the transformer which that is the important role can deliver only 2 to 3 amps, if i double the coils tho it will be in isolated mode, can that increase the amperes ratings that may be able to match my need? thanks for your help, youre not only an innovator but a teacher.

            • Thank you Nkwenti, I am sorry I do not have any expertise in the field of transformer winding, you may have to consult a professional transformer designer.
              Or you may open a 500 watt transformer and check the relevant wires gauges, and simply make it 3 times higher for your 1500 watt transformer.

  5. Please sir, can I get an op amp circuit for step down transformer which will have a fixed secondary voltage for input voltage range from 150v – 250v. Thanks

  6. Hello sir, long time. regards to you. I need a 5kva voltage stabilizer circuit with atleast 3 or 4 relays, using ic either Lm324 or 556 dual timer, with indicators of boost, buck and normal voltage. Pls send me the circuit diagram to my email.

    • It is the relay coil…D1 is the freewheeling diode for the relay coil which protects T1 from the back EMFs generated by the relay coil

  7. Dear Swagtam, please reply me as soon as possible I mailed you but got no reply. Kindly Sir help me what is N/C and N/O in diagram??and what is relation between stabilizer transformer and comparator circuit. and also what is suitable value for inductor placed parallel in D2. Sir please help me as soon as possible.

    • Dear Ali, it seems you are very new to electronics and therefore you seriously need to learn the basics first and then attempt this circuit or any other circuit, otherwise you may fail to succeed in building these circuits.

      The inductor with D2 is not a separate inductor, rather it is coil of the relay. The N/C and N/O are the twin contacts of a DPDT relay, in a DPDT relay the coil is single but the contacts are in pair.

      for more information about relays you an refer to the following post


    • No, TR1 can be a small 0-12V 500mA trafo, while TR2 is supposed to be the main stabilizer trafo and should be rated at 5 amps minimum, 12-0-12V

  8. sir i am having trouble connecting relay to the circuit.. i have dpdt 8pin relay and its pin configuration. sadly i cant get to wire it correctly can you please simplify by telling the connection scheme..like the collector of transistor is connected to COIL OF relay…
    2) how can i use 2 SPDT relays 5 terminals instead of 1 DPDT 8terminals

    • Asim, if you want to use 2 SPDT relays, then you just have to connect the relay coils of both the relays in parallel across the collector/positive line as shown in the diagram.

      as for the contacts, first identify the N/C, N/O and pole of the two relays, then simply join their N/C, N/C….N/O, N/O, and pole, pole together, and finally wire the common ends of these contacts to the transformer as indicated in the diagram.

    • when i am trying to calibrate the cicuit the relay is flickering even on 11-13v supply and the preset seems to be not doing anything at all
      please elaborate the callibration process please

    • keep the relay disconnected while calibrating, use an LED indication instead, for fixing the cut-off threshold, once the setting up is completed you can connect the relay back

      keep R3 disconnected while calibrating, reconnect it once the calibration is done.

  9. I have a stabilizer of 1KV of output Voltage Range of 220-240,but of late it produces output range of 250 -260…..why and how can i cure it…plz help

    • it could be happening due to any of the two reasons, either you have changed your battery with a new one and therefore the full charge of the battery is causing the extra voltage or the internal voltage correction setting is disturbed due to some reason…you can also check with a some kind of load connected and see if the voltage drops…

  10. HI Mr.Swagatam Majumdar how are you,
    You have good experience in electronics,I need hex cod pic 16f676, 5 step automatic voltage stabilizer with circuits diagram.I will be very thank full to you.

    • Muzamil, yes you can use the above shown circuit for safeguarding TV, fridge etc, but the transformer TR2 will need to be upgraded as per the load amp rating.

  11. Sir,
    can i use this stabilizer for 230-240V AC?? can i stabilize my refrigerator or tv or speaker system from it ???
    Plzz tell??

  12. hello my name is ariel of buenos aires Argentina. can you help me?
    in my area there are always low voltage 185 / 190vca .. I have a transformer 12v x 10 amps .. the question is: how I can connect to climb a little tansion …
    from already thank you very much.
    ATTE. ariel from Argentina.

    • hello ariel, your transformer will produce an increase of only 12V, meaning if the mains level is at 185, adding your trafo voltage will make it just 185 + 12 = 197V

      Buy a 12-0-12V/10amp trafo, this will boost the voltage to a useful level…i'll explain you how to do once you get it.

  13. hello mr swagatam, I'm looking to make a very high power voltage regulator, DC to DC. the required voltage is nearly 380 (moteur triphasé), any advices or simple shematic that could help. thank you

  14. How to Make a very Small Homemade Automatic Voltage Stabilizer that could be place along with led lights just before the LED drivers. it could be like pocket size compact .

  15. Hi sir i forgot something so the 2 relay have to switch same time when the circuit is power? (2nd)question please where is the relay coil i can only see 1 coil or its should be ignore (3rd)question can i set the circuit without variable power supply? thank you sir please don't ignore my question stay bless.

    • Hi zinnaboy, yes both the relays should operate together, preferably it should be a DPDT type meaning a relay having double sets of contacts but a single common coil. That's why you can see only one coil.

      If you want to use two separate relays then you can simply connect both the coils parallel with each other across D2

      You cannot set it without a variable power supply. It will be required.

  16. hi sir i build this circuit but it don't work sir i connected everything properly,sir you show T2 as a centertap 9-0-9 but in the circuit it don't connect to anywhere please i need your help sir thank you.How to Make a Small Homemade Automatic Voltage Stabilizer for TV sets and Refrigerator

    • Hi zinnaboy, T2 is a 0-18v trafo which can be achieved by using a 9-0-9 trafo with center tap shorted. the center tap does not connect anywhere.
      The circuit will definitely work if the settings are done correctly, and if the circuit is built without errors.

  17. Sir i have a voltage fluctuation problem at my house so my 18 watt tube gets blown off again and again in short period of time so i wanted to know is there any modification to be done in the Electronic ballast for protection such as a fuse or something like that?? Please suggest me sir….

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