220V Over Under Voltage Cut Off Circuit using Transistors

This 220V Over Under Voltage Cut Off Circuit using Transistors help to protect electric things from too high or too low voltage.

It uses two transistors and some easy parts.

When voltage goes too much high or too much low then circuit cuts the power.

It is good for home use and might surprise some people how simple it is build.

What is a 220V Over Under Voltage Cut Off Circuit:

A 220V over under voltage cut off circuit is a safety electronic circuit.

It checks the voltage of 220V power.

If voltage goes too high or too low it stops power to the device.

This circuit help to save electric machines and home appliances from damage when voltage is not stable.

This circuit is very useful and simple to use.

Circuit Working:

Parts List:

In this circuit T1 and T2 work like inverter.

It means when T1 is ON T2 is OFF and when T1 is OFF then T2 is ON.

This is very simple working.

Preset P1 gives sensing voltage to base of T1 from DC power.

This help circuit know when to turn ON or OFF by setting voltage level to trip point.

If we want to change auto cut-off level or want higher voltage limit then we can adjust P1.

When voltage is normal means not high or not low then T1 stay OFF.

Then power connects through P2 and turn ON T2 so relay is ON and load gets power.

But if main voltage goes too high then voltage at base of T1 also increases.

Then T1 turns ON and it ground the base of T2.

Now T2 turns OFF and relay goes OFF and load also is OFF then this protect the device from high voltage.

Same way if voltage drops too low, T1 is already OFF.

But now P2 make T2 turn OFF too so again relay goes OFF and load is safe from low voltage.

This circuit trip when voltage is above 260V or below 200V for 220V line or above 130V and below 100V for 120V line.

So it is not super accurate but the range is little wide.

If we want better accuracy and more control then we need to use op-amps instead of transistors.

Formulas:

To find the output voltage Vout from voltage divider we need to use this formula:

For T1 transistor:

Vout = (P1 / (R1 + P1)) × Vin

where:

• Vout is the output voltage from the divider.
• R1 is the resistor in the circuit.
• P1 is the preset or variable resistor.
• Vin is the main input voltage.

For T2 transistor:

Vout = (P2 / (R2 + P2)) × Vin

where:

• Vout means output voltage.
• R2 is the resistor.
• P2 is the preset.
• Vin is input voltage.

This formula help to find how much voltage goes to base of T1 or T2.

How to Build:

To build a 220V Over Under Voltage Cut Off Circuit using Transistors follow the below steps for connections and assembling:

Assemble the Parts:

• First collect all parts shown in the circuit diagram.

Check Transistor Pins:

• Find legs the pinouts of both NPN transistors T1 and T2.
• Each transistor has 3 pins: Emitter, Base and Collector.

Connect T1 and T2:

• Join T1 and T2 in inverter style.
• Connect T1s collector to T2s emitter and T2s collector to T1s emitter.
• Check the circuit diagram to do it right.

Connect Presets P1 and P2:

• Connect P1 to T1s base and set it to sense high voltage.
• Connect P2 so it gives voltage to T2 an it keep T2 ON when voltage is normal.

Add Relay:

• Relay goes to T2s collector.
• When T2 is ON relay also is ON.

Set Voltage Limits:

• Adjust P1 and P2 to set the high and low voltage trip points.

Add Protection:

• Use resistors, capacitors and diodes to protect circuit and make it work smooth.

Power Supply:

• Give power to the circuit using DC source.

Test the Circuit:

• Try with different voltages.
• Check if relay turn ON and OFF at correct voltage levels.

Fine Tune:

• If needed change P1 and P2 values to get better results.

Important Points:

• Always follow the circuit diagram.
• Use correct resistor, capacitor, diode values.
• Be careful while working with electricity.
• If not sure take help from expert.

Conclusion:

This 220V Over Under Voltage Cut Off Circuit using Transistors to stop damage to devices when voltage goes too high or too low.

This circuit is very helpful in places where power is not stable like at homes, offices and factories.

References:

Overvoltage