A voltage stabilizer is a device used to detect fluctuating voltage levels and rectify them, ensuring a relatively stable output at the point where the load is connected. In this article, we will explore the design of a simple automatic mains AC voltage stabilizer that can serve this purpose. While there are many voltage stabilizers available on the market, building one yourself at home can be a rewarding experience. The Automatic Voltage Stabilizer (AVS) circuit described here is straightforward, reasonably accurate, and provides solid protection for any connected electronic device. It safeguards against dangerous high voltages and potential brownouts (low voltages). With an input range of 175 VAC to 280 VAC, the output will remain between 200 VAC and 255 VAC.

How Does a Voltage Stabilizer Work?

The circuit of a voltage stabilizer primarily consists of a voltage sensor. This sensor monitors AC mains voltage levels, detecting when they rise or fall to unsafe levels. When a dangerous input voltage is detected, it activates the relays, which switch the appropriate winding terminals of the auto transformer to adjust and stabilize the output voltage. This ensures the connected appliance receives a safe and stable voltage, allowing it to function properly even when the input voltage fluctuates.

Required Parts

For this circuit, you will need the following components:

  • Resistor ¼ watt, CFR R1 = 2K7
  • Preset P1 = 10K Linear
  • Transistor T1 = BC547
  • Zener Diode Z1 = 3V / 400mW
  • Diode D1, D2 = 1N4007
  • Capacitor = 220uF / 25V
  • Relay RL1 = 12V / DPDT mini (double pole, double throw)
  • Transformer T1 = 12-0-12V / 5A, T2 = 0-12V / 500mA (as per local specifications)
  • General-purpose board = 3” by 3”

Construction Steps

Using the provided circuit schematic, follow these steps to build the AVS:

  1. Insert and solder the transistor on the general-purpose board, trimming the leads afterward.
  2. Fix and solder the remaining components, including the relay, around the transistor.
  3. Interconnect the parts according to the circuit schematic.
  4. Connect the primary and secondary wires of the transformer to the relay contacts as shown in the diagram.

Circuit Description


The functioning of this simple voltage stabilizer circuit can be summarized as follows:

The primary active component of the circuit is the transistor T1. The smaller transformer’s output is rectified by D1 and filtered by C1 to provide the required operating power for the control circuit, which includes the transistor T1, preset P1, zener diode Z1, and the DPDT relay.

This voltage is also used as the reference or sensing voltage, varying proportionally with input voltage changes. For instance, if the normal DC operating voltage is 12V, a change in the input AC mains voltage by 25V would correspondingly alter the DC voltage to 14V or 10V.

The preset P1 is adjusted so that the transistor conducts and operates the relay when the AC mains voltage deviates beyond a preset limit (110V or 225V). If the input voltage exceeds this threshold, T1 conducts and activates the relay, which switches the transformer windings to subtract 25V from the input. This adjustment brings the output voltage down to about 205V. If the mains voltage increases further, the output voltage will remain 25V lower, ensuring protection even if the input reaches 260V, as the output will be limited to 235V.

Conversely, when the input AC voltage falls below normal, 25V is added to the output. If the input drops to 180V, the output will still be maintained at around 205V.

This basic design keeps the output within 200-250V for input ranges of 180-275V, though the stabilization may not be extremely precise. However, it offers reliable protection for connected appliances.

Testing the Circuit

To test the circuit:

  1. You will need a 0-12V universal DC variable power supply.
  2. Assume that 12V corresponds to an input of approximately 230VAC, which will be the trip voltage of the stabilizer.
  3. Connect the power supply to the circuit board’s supply terminals.
  4. Set the power supply to its maximum output of 12V.
  5. Adjust the preset so that the relay activates.
  6. Lower the power supply voltage to 11V, which should deactivate the relay.

With this adjustment, the stabilizer should keep the output voltage between 200V and 255V for input voltages ranging from 175V to 280V.

Conclusion

Building your own voltage stabilizer can be a fascinating project and offers the satisfaction of creating a useful tool that protects electronic appliances from voltage fluctuations. This basic design offers reliable protection by keeping the output voltage stable within a reasonable range. While it may not provide the most precise stabilization, it’s an effective solution for common household devices facing voltage fluctuations. By following the simple construction steps, you can build and test your own stabilizer to safeguard your electronic equipment from both high and low voltage levels.