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Automatic Power Off Circuit Diagram

It is an automatic power off circuit diagram.  If you need to shut-off any electronic device after a set amount of time then this circuit can do that automatically; when you are even sleeping!  For example this auto power off circuit can be used with garden/porch light, soldering iron/ glue gun or similar other devices to auto shut it off for saving electricity or save the device, or you can use it to suit your own needs.


Theory of operation of this automatic power off circuit

  • Here IC 555 is used as . It is a popular and very widely used timer IC. 
  • Input power for this timer circuit is provided using a transformer-less power supply which is made with a diode as a half wave rectifier, a voltage drop resistor, a filter capacitor and a zener diode.
  • In power supply section, diode D1 is used as a half wave rectifier 
  • And R1 used as a voltage drop resistor and C1 used as filter capacitor
  • S1, a push button switch is used to  trigger the timer IC
  • And the 555 timer output goes through a resistor (R4) to the ‘Gate’ of the TRIAC BT136
  • When timer output is high it triggers the TRIAC and turn on the load/output  device
  • When C2 (time delay capacitor) charge up to 2/3 of input voltage; then 555 output goes low (Pin-3 is the output pin of 555)
  • As timer output goes low, the TRIAC turn off the load/output  device
  • Here set time is around 20 minutes
  • Set time can be adjusted by changing the C2 value
  • A low leakage capacitor is recommended as C2


Parts List:

Parts Name Value
C1
Capacitor (Polarized)
220µF,12v
C2
Capacitor (Polarized)
1000µF,12v
C3
Capacitor (Non Polarized)
0.01µF
D1
Diode General
IN4007
D2
Zener Diode
8.2v,1w
R1
RESISTOR
10k,5w
R2
RESISTOR
1M, 0.5w
R3
RESISTOR
10k,0.5w
R4
RESISTOR
470Ω
S1
Normally Open
Push Button Switch
S2
FUSE
1A
T1
Triac
BT136
U1
IC
555


555 Pinout





Caution: It is an AC High Voltage Circuit, so do not touch any part off the circuit or parts when connected to Supply Voltage. As you know it is dangerous.

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