A mains AC power supply failure buzzer circuit is a simple electronic device that sounds an alarm (buzzer) when the AC mains power goes out.
This can be helpful for alerting you to a power outage, especially if you have critical equipment that needs to be protected or if the outage occurs at night.
An electromagnetic switch called a relay is used in this circuit.
The relay coil is activated and the relay contacts are linked in a way that prevents the buzzer from working when AC power is available.
The contacts flip, the buzzer sounds and the relay coil becomes de energized when the power is cut off.
Circuit Working:
Parts List:
| Component Type | Description | Quantity |
|---|---|---|
| Capacitors | Ceramic 0.1μF | 1 |
| Electrolytic 2200μF, 25V | 1 | |
| Semiconductors | Diode 1N4007 | 1 |
| Bridge Rectifier 1N4007 | 4 | |
| Other Components | 12V Relay | 1 |
| Buzzer | 1 | |
| Transformer | 12-0-12V Transformer | 1 |
After assembling the circuit according to the schematic diagram shown above, switch it on by plugging it in.
Turn off the power and wait for the buzzer to start beeping to test it.
Similar to an emergency light, which turns on when the power goes off this circuit works in a similar manner.
The circuit operates in a simple manner.
The transformer reduces the high voltage 220V AC to a lesser voltage 12V AC when the electricity is turned on.
The bridge rectifier subsequently changes this lower voltages alternating current AC to direct current DC.
The bridge rectifier permits current to flow in a single direction during each half cycle of the AC waveform by connecting four unique diodes in a certain manner.
The output current becomes DC but keeps its original polarity.
A bridge rectifier circuit is that it does not need a certain kind of transformer.
The current flows through a capacitor C2 following its conversion to DC.
By eliminating undesirable frequencies added during rectification, this capacitor functions as a filter.
Another name for it is a smoothing capacitor.
Another capacitor C1 starts to charge as soon as the current reaches the relay, which then activates.
The circuit between the buzzer and the capacitor is completed when the electricity runs out and the relay returns to its initial condition.
After that, the buzzer discharges via the capacitor beeping continuously until the capacitor is empty.
If you use a bigger capacitor, the beeping duration can be extended.
The buzzer is receiving 0.310 Amps of electricity in this particular arrangement.
You may eliminate the bridge rectifier and transformer completely if you choose to utilize this circuit with a DC power supply instead.
Formulas:
Transformer Turns Ratio:
Using the input voltage and the number of turns in the main and secondary coils as inputs, this formula assists in determining the transformers output voltage.
Vo/Vi = Ns/Np
Where:
- Vo = Output voltage 12V AC
- Vi = Input voltage 220V AC
- Ns = Number of turns in the secondary coil
- Np = Number of turns in the primary coil
If you want to know how the transformer impacts the output voltage or if you wish to design the circuit using a different transformer, this formula might be helpful.
Capacitor Charging Time:
The duration of capacitor C1s charging when the power is on may be calculated using this formula.
t = CV / I
where:
- t = Charging time in seconds
- C = Capacitance of C1 in farads
- V = Charging voltage 12V DC
- I = Charging current limited by the circuit resistance
If you want to know how long it takes for the buzzer to sound when the electricity is switched on, this formula might assist.
How to Build:
To build a Mains AC Power Supply Failure Buzzer Circuit follow the below mentioned steps for circuit connections:
- Assemble all the components as mentioned in the diagram above.
- Connect a common contact of relay to ground through capacitor C2.
- Connect a relay coils between positive and negative supply rails.
- Connect a buzzer to NC terminal of relay and ground.
- Connect a capacitor C1 from positive supply to ground.
- Connect D1 diode between positive supply and ground.
- Connect positive of the bridge rectifier to the positive supply line of circuit.
- Connect the negative of the bridge rectifier to the negative supply line of circuit.
- Connect the 12V AC secondary wires of the transformers to the AC inputs of the bridge rectifier.
Safety Measures:
- Work on these circuits only if you are knowledgeable about safe electrical procedures.
- If not handled correctly, mains AC electricity can be hazardous and result in fatalities or severe injuries.
- Before doing any work on the circuit, ensure that it is correctly separated from the main power supply.
- Make use of parts whose voltage ratings correspond to the local mains voltage.
- Electronics retailers now sell pre made mains AC power supply failure alerts if you are not comfortable dealing with electronics.
Conclusion:
the mains AC power supply A useful tool for notifying you of power disruptions is a buzzer circuit.
It turns on when the main power goes out, much like an emergency light.
The circuit itself is really simple, with a relay controlling the buzzer a transformer stepping down the voltage, a bridge rectifier converting AC to DC and capacitors filtering and storing energy.
References:
What is T1 in this circuit for ‘Mains power failure alarm’? [closed]