Simple Automatic Power Delay OFF Circuit

This Automatic Power Delay OFF Circuit is like a friendly reminder to turn things off.

You can set it up with your device, and after a certain amount of time has passed like 1 hour, 2 hours etc. the circuit automatically cuts the power.

This is useful for things like leaving a nightlight on for a while or turning off a fan after you fall asleep.

Circuit Working:

Parts List:

This circuit, constructed using the 555 IC is designed to automatically shut off power after 20 minutes.

It can be utilized, for example, to turn off the porch light once the house is locked.

The 555 functions as a monostable where a momentary push on S1 causes the output to go high, triggering the triac and supplying power to the socket.

The ICs output returns low when C2 charges up to 2/3 of the supply voltage which typically takes about 20 minutes.

It is important for C2 to have low leakage to ensure it charges efficiently excessive leakage could result in slow charging or failure to reach full capacity.

The timer is powered by a half wave rectifier D1 voltage dropping resistor R1 zener diode D2 and filter capacitor C1.

Formulas:

The best timer for producing a time delay is a 555 IC set to monostable mode.

It has a single stable state in this mode.

After being triggered, it goes into a quasi stable state and stays there for a set amount of time before going back to the stable state.

Formula for Monostable 555 IC for Automatic Power Delay OFF Circuit:

The following formula may be used to get the time delay T in seconds:

T = 1.1 * R1 * C1

where:

• There is a time delay of T seconds.
• In ohms R1 is the timing resistor.
• The farad timing capacitor is denoted as C1.

Additional information:

Consider connecting a trimmer capacitor in parallel with C1 for more accurate timing.

Use a transistor or more 555 IC stages to increase the delay period past R1 and C1s practical limitations.

Make that the 555 IC power supply voltage stays within the designated range at all times.

How to Build:

To build a Simple Automatic Power Delay OFF Circuit follow the below mentioned steps for connections:

• Connect the pin 2 of the 555 IC and to one terminal of the push button switch S1.
• Connect the other terminal of S1 to ground.
• Connect pin 4 and pin 8 positive supply.
• Connect pin 1 of the 555 IC to the ground.
• Connect pin 5 to ground through capacitor C3.
• Connect pins 6 and 7 of the 555 IC together and connect them to one end of resistor R2 and capacitor C2 to ground.
• Connect the pin 3 to the gate of triac BT136 through resistor R4.
• Connect the anode of diode D1 to the power supply +Vcc and the cathode to the junction of resistor R1.
• Connect the cathode of zener diode to the junction of R1 and anode to the ground.

Note:

• Ensure that the capacitor C2 has low leakage and is appropriately sized to achieve the desired delay around 20 minutes for the circuit.
• Adjust the value of R1 and C2 if necessary to achieve the desired timing.

Conclusion:

An Automatic Power Delay OFF Circuit is a useful electronic circuit that automatically turns off power to a device after a set period of time.

It is commonly used in various applications to save energy control the operation of devices, and enhance the functionality of systems.

This circuit is a practical and efficient solution for automating power control in a wide range of scenarios.

References:

What is a Delay Circuit? 6 Types of Delay Circuits Explained