Voltage Stabilizer Circuit Diagram AC Voltage with Low Voltage Alarm

What is the use of voltage stabilizer? Voltage stabilizers are used to stabilize the input voltage to protect the rest of circuitry from unwanted electrical spikes, nowadays some devices have inbuilt stabilizer circuit. Due to the fluctuation of supply voltage devices may malfunction or damage permanently; to avoid these problems an ac voltage stabilizer is used. Now what is the voltage stabilizer price in local market? Is it reasonable?

Here we are gonna introduce a simple voltage regulator circuit diagram for low current devices. The main advantage of this circuit is that it will not use transformers of any kind.

Then how stabilizing is possible? Do you know resistor circuit can do stabilizing? Our voltage stabilizer circuit for ac uses only resistor to reduce the voltage, moreover the circuit embedded with buzzer alerts us while supply voltage turns below a preset level.

This low cost circuit is controlled by simple comparator IC LM324. Try this and build a home voltage stabilizer of your own.

Circuit of Voltage Stabilizer

Voltage Stabilizer Circuit Diagram

Components Required

  1. IC LM324
  2. Transistor (BC548x2)
  3. Zener diode (3.9V)
  4. Bridge
  5. Diode (1N4007x2)
  6. LED (Green, Red)
  7. Capacitor (100uFx2, 1000uF)
  8. Resistor (1Kx5,180/20 watts)
  9. POT (10Kx2)
  10. Buzzer (12V)
  11. Relay (12V/10A)
  12. Transformer (230V/0-12V; 500mA)
  13. 15 watt incandescent lamp

Working of Stabilizer Circuit

  • Circuit design of stabilizer is quite easy and compact. This is a relay type voltage stabilizer circuit diagram.
  • A 12V step down transformer is used to drive the stabilizer circuit and the same transformer is used to analyze the input line voltage.
  • Bridge rectifier is employed to convert AC to DC and 1000µF capacitor is used to filter AC ripples.
  • LM342 has four embedded comparators, among those we have used only two comparators for our stabilizer. First comparator compares low voltage level and other one for comparing high voltage level.
  • A 3.9V Zener diode is used to obtain reference voltage of 3.9V (can use any Zener diode of below 6V) and this reference voltage is used by both comparators.
  • Reference voltage is connected to the non-inverting terminal of the upper comparator and potentiometer is connected to inverting terminal. Then adjust the potentiometer value to get voltage greater than 3.9V (reference voltage) by keeping normal input voltage.
  • Inverting terminal of lower comparator is connected to reference voltage and the potentiometer corresponding to it is set to a voltage which is below the reference voltage (3.9 V) at non-inverting terminal.

Case 1: Normal supply voltage

  • In this situation both comparators are OFF (Output is low).
  • At normal supply voltage the lamp appears to be directly connected between phase and neutral. Same time the output of upper comparator is negative then LED_GREEN is ON, which indicates that input is normal. (Refer the following fig)

Circuit of Voltage Stabilizer normal

Case 2: Supply voltage Increases

  • When the AC input voltage is increased, corresponding output of DC also increases. When it exceeds preset level 3.9 V, obviously the voltage drop across both potentiometers will increase. When the voltage drop is greater than 3.9V then the output of lower comparator will become positive.
  • It leads to LED_RED and transistor to become ON, thus relay will switch and the connection to the lamp becomes through the resistor. So the voltage drop across lamp will reduce since resistor and lamp will come in series to the main supply. (LED_RED indicates the supply voltage increased).

Circuit of Voltage Stabilizer at low supply voltage

Case 3: Supply voltage decreases (Approximately below 180V AC)

  • When the line voltage is below a threshold level then voltage drop across both potentiometer will decrease, then the non-inverting terminal of upper comparator gets higher voltage than inverting terminal.
  • Then the output of upper comparator becomes positive and LED_GREEN turns OFF.
  • Transistor gets turned ON, accordingly relay ON which make disconnection of lamp from the supply. Same time buzzer is also turned ON to indicate the line voltage is below 180 volt.

In this way our stabilizer controls the output load.

Circuit of Voltage Stabilizer at over voltage

  • The value of the series resistor connected to lamp depends on the load power, for high power devices higher wattage resistors should be used.
  • We can build a high power stabilizer by little alteration in the circuit together with a step up transformer which can be used for refrigerator, TV, washing machines etc.

Now let me ask a question, weather the voltage stabilizer circuit for home is useful to you? Reply your suggestion via the comments.

23 thoughts on “Voltage Stabilizer Circuit Diagram AC Voltage with Low Voltage Alarm

  1. This is very helpful it has help me a lot ,but can i have a circuit that will step up the voltage when the power is down rather than cutoff ?

  2. Hi Yaseen,

    How to calibrate this circuit?
    if i use it with refrigerator what modification will it be?


  3. Hi dear Jaseem !
    I need to know about a circuit protector refrigerator with IC lm324.
    I mean the analysis of the circuit and the role of all diod, capacitors, resistances, and Op-Amps.
    I want to know how the circuit work in high voltage and low voltage.
    I know that in low voltage, the red LED start to blink and in normal voltage it is off an the green LED start to shin and in high voltage, green LED turns off and the red one turns on permanently.
    How can I send the picture of the circuit for you????????????
    I thank you so much if you answer my request.
    I need the answer immediately !!!

    • Those diodes are called flyback diodes/ free wheeling diodes. Those are used to protect the coil of the relay from high inrush current for rapid switching.

  4. hi Jaseem,
    I need the circuit for high power applications (i,e.. air conditioners,refridgerators..) so can u send me the circuits plsss..and i need it immediately plsss..and I will be thankful to u if u reply me immediately.

  5. Hi yaseen
    Your cct is very intresting but I need high power type from 5KVA voltage step up when the voltage is down to 100v it will step it up to 220v. Thanks in advance am expecting your reply.

  6. Pls in this case, there no diagram to illustrate the different windings of the main voltage regulator transformer that supplies different voltage and how the windings will be connected to d relays. can some one pls help with ds.

  7. Mr Masud. Function of capacitors across each relay is to bypass or short circuit the transient high voltage induced in the windings of the relays during its switching on or off ( Faraday’s Law of electromagnetic induction ). Because this voltage is detrimental for the transistors in series with the relays in the circuit.Otherwise this will destroy the transistors.

  8. Just wanted to know why both input and out in my ac stabiliser showing nil.I checked the supply line and its persfect.The display on plug socket is glowing and hence the supply line is ok.

  9. Good Day Sir, I thank you for this wonderful article; it is very helpful to me. I will like to have the circuit diagram for the type that can carry electronics like tv sets, cd audio player and even refrigerator, and can be able to keep the output voltage at an approximate value (like 220volts) when the input is low or high or normal. I will be happy if you will send it to me. Thanks!

  10. Sir, I would like to have a circuit diagram and construction to build a main line AVS maintaining voltage between 90 to 285 volts.

  11. PLS I want to know d main component dat will b burnt out if a thunder strike on a stabiizer when there is no light

  12. hello can please someone help me explain how to vary the potentiometer and at what conditions because mine adjusts but dont no how to set the upper and lower threshold

  13. Plis explain to me how i can make it increase the voltage output when voltage falls
    And why is the output not with in a given range say + or – [10] of da normal voltage.

  14. A very nice cct diagram.But pls i need i circuit diagram with upto 4 relays use to maintain the output voltage at 220v

  15. Nice circuit if the lamp used has a fixed rated power such as 60 watts or 40 watts. the series resistor has to be based on the power of this lamp and the current it takes.

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