This circuit protects expensive equipment such as televisions, air conditioners, and refrigerators from both high and low voltages. The circuit automatically turns off the load if the supplied voltage is anomalous (high or low) voltage. This circuit also produces sound when main power resumes.
In this type of application, voltage stabilisers are typically employed to maintain a consistent AC voltage. Relays in voltage stabilisers, on the other hand, are constantly switching ON and OFF due to the irregular AC supply. The frequent energization and de-energization of relays shortens the life of appliances as well as the stabiliser. As a result, rather of using expensive stabilisers, it is preferable to utilise this project to control the appliances.
- High and Low Cutoff with Delay and Alarm Principle:
- High and Low Cutoff with Delay and Alarm Circuit Diagram:
- High and Low Cutoff with Delay and Alarm Circuit Design:
- How to Operate this Circuit?
- High and Low Cutoff with Delay and Alarm Circuit Advantages and Applications:
High and Low Voltage Cutoff with Delay and Alarm Principle:
The DC voltage at the cathode of zener diode D4 exceeds 5.6V when the supply voltage is high. Transistor Q1 is thus turned on, whereas transistor Q2 is turned off. As a result, the relay RL1 de-energizes, and the load is turned off.
Transistor Q1 switches to ON when the supply voltage is low, and transistor Q2 switches off as a result, turning the load off.
When the standard AC supply voltage is provided, the DC voltage at the cathode of zener diode D4 is less than 5.6V, indicating that transistor Q1 is now in the off state. As a result, transistor Q2 is turned on, and the load turns on, as indicated by the green LED.
| SUPPLY VOLTAGE | Q1 STATE | Q2 STATE | RELAY | LOAD |
|---|---|---|---|---|
| High | ON | OFF | De-energises | OFF |
| Low | ON | OFF | De-energises | OFF |
| Normal | OFF | ON | Energises | ON |
| Resume | ON | OFF | De-energises | OFF |
When power is restored after a power outage, the 555 timer IC dips low, triggering the 555 timer IC. The output of the 555 timer IC causes the sound IC to run through transistor Q3, at the same time as the output of the 555 timer is connected to the base of transistor Q1, transistor Q1 flips to ON and transistor Q2 is turned off. As a result, the load is turned off via the relay.
High and Low Voltage Cutoff with Delay and Alarm Circuit Diagram:
Circuit Components:
- Center tapped Transformer (12-0-12V, 500mA)
- NE 555 timer
- UM66 IC
- Speaker
- 12V Relay
- 4 Transistors – SL100
- 2 Zener diodes – 5.6V
- Zener diode – 5V
- LED’s – red, green
- 5 Diodes – 1n4001
- 16V Electrolytic capacitors – 100uF, 10uF, 1uF
- Ceramic capacitor – 0.01uF
- Potentiometers – 4.7k, 4.7k, 10k
- 7 Resistors – 1k
- Resistors – 10k, 1M
High and Low Voltage Cutoff with Delay and Alarm Circuit Design:
The 555 timer in this circuit is set to operate in monostable mode. Pins 4 and 8 are shorted in this circuit to prevent abrupt resets. The 555 timer output signal has a pulse width of around 10 seconds. The speaker is driven by this output signal.
Because of the UM66 IC, when power is restored, the speaker produces a lovely sound. POT RV3 can be used to regulate the speaker’s volume.
The green LED shows that the AC supply voltage is normal. The power indicator is a red LED.
The input voltage is compared using a zener diode D4 and a transistor Q1. Based on the output of transistor Q1, transistor Q2 shifts the load. For rectification, diodes D1 and D2 are utilised. Capacitor C1 acts as a filter.
How to Operate this Circuit?
- Give the connections according to the circuit Diagram
- While giving the supply, make sure that there is no common connection between AC and DC supplies.
- Switch ON the input AC supply.
- Make the input supply voltage low or high. Now, you can observe that load is automatically switches off.
- Apply normal supply voltage. Now, you can observe that load will run by indicating the green LED.
- Now resume the power. You can listen melodious sound.
- Switch off the supply.
High and Low Voltage Cutoff with Delay and Alarm Circuit Advantages and Applications:
- Cost is less as compared to voltage stabilizers
- Consumes less power.
- This circuit is used in homes and offices to protect equipments from high voltages and low voltages.
