High and Low Voltage Cutoff with Delay and Alarm

This circuit serves as a safeguard for valuable equipment like televisions, air conditioners, and refrigerators, offering protection against both high and low voltage fluctuations. Whenever the incoming voltage deviates from the normal range, whether it’s too high or too low, the circuit automatically deactivates the connected load. Additionally, this circuit generates an audible alert when the main power supply is restored.

In such applications, voltage stabilizers are typically employed to maintain a consistent AC voltage. However, within voltage stabilizers, relays often experience frequent ON and OFF switching due to the irregular AC supply. This constant activation and deactivation of relays can lead to a shortened lifespan for both appliances and the stabilizer itself. Consequently, instead of relying on costly stabilizers, this project provides a cost-effective alternative for managing household appliances.

Outline

• 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:

When the supply voltage rises, causing the DC voltage at zener diode D4’s cathode to exceed 5.6V, transistor Q1 becomes active while transistor Q2 switches off. Consequently, relay RL1 disengages, resulting in the load being powered down.

Conversely, when the supply voltage drops, triggering transistor Q1 to activate, transistor Q2 turns off, leading to the load being switched off.

In the presence of the standard AC supply voltage, the DC voltage at zener diode D4’s cathode remains below 5.6V, signifying that transistor Q1 is in the off state. Consequently, transistor Q2 becomes active, causing the load to power on, as indicated by the illuminated 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

Upon power restoration following an outage, the 555 timer IC experiences a drop in its signal, initiating the functioning of the 555 timer IC. The output from the 555 timer IC sets the sound IC in motion, concurrently, it is routed through transistor Q3. Simultaneously, the 555 timer’s output connects to the base of transistor Q1, prompting transistor Q1 to switch to the ON state, while transistor Q2 is turned off. Consequently, the load is deactivated 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:

In this circuit, the 555 timer is configured to operate in monostable mode. To prevent sudden resets, pins 4 and 8 are connected together. The output signal from the 555 timer has a pulse width of approximately 10 seconds and is responsible for driving the speaker.

Thanks to the UM66 IC, when power is reinstated, the speaker produces a delightful sound. The speaker’s volume can be adjusted using the POT RV3.

The normal AC supply voltage is indicated by the green LED, while the power status is displayed by a red LED.

A zener diode D4 and transistor Q1 are employed to compare the input voltage, and based on the output of transistor Q1, transistor Q2 controls the load. Diodes D1 and D2 are used for rectification, and capacitor C1 serves as a filtering component.

How to Operate this Circuit?

1. Give the connections according to the circuit Diagram
2. While giving the supply, make sure that there is no common connection between AC and DC supplies.
3. Switch ON the input AC supply.
4. Make the input supply voltage low or high. Now, you can observe that load is automatically switches off.
5. Apply normal supply voltage. Now, you can observe that load will run by indicating the green LED.
6. Now resume the power. You can listen melodious sound.
7. Switch off the supply.

High and Low Voltage Cutoff with Delay and Alarm Circuit Advantages and Applications:

1. Cost is less as compared to voltage stabilizers
2. Consumes less power.
3. This circuit is used in homes and offices to protect equipments from high voltages and low voltages.