DIY protection circuit

Hi guys, we will take about the protection of devices such as fridges, Tv, water pump motor,s, etc.…

From my experience and technicians, there are two main problems:

First problem: high voltage in our country max voltage is 220v, sometimes voltage will reach 300v or 350v that will make catastrophic consequences for devices
Second problem: switching (turn on-off) that can generate reversed Emf in inductors, nowadays all of power supply based on SMPS there are a lot of inductors on SMPS :
I made this circuit to make 5 minutes delay or more before return the electricity & protect the device from high voltage :
تنزيل (1)
Bridge rectifier
dip switch
Transistors BC547 X 3
Resistors 10 K ohm X6,5Kohm,100 ohm, pot 100k ,
Zener 5v
تنزيل (1)
12 or5 or24 volt relay

Transformer 12v
2 – pole terminal block X3

Circuit explanation : power supply circuit

The transformer will convert 220 volts to 12v the benefit from transformer not only supply 12
volt but also monitor the input voltage when the voltage change from 220 to 300 the output will change too according to the ratio of turns.
Timing circuit (based on555):

We will generate one shoot pules for a particular time this time can be determined as we explained before in timers from the RC circuit, but here we make the capacitance constant at 1000u and we change time by adding parallel resistors between (pin2 and pin6) by using SW1 the Output in pin3 will trigger transistor
transistor circuit :slight_smile:
This transistor will take the signal from 555 then turn on the next circuit to make sure the following circuits will be turned after a particular delay
Comparator circuit

We will explain the comparator circuit later, comparator here will compare the voltage that came from the transformer to the voltage of Zener which act as 220 pot 100k to change the cut off level
After making sure the voltage is 220 it will pass the output to the next circuit
24-volt relay module circuit :

This is a modified relay module to be able to supply 24-volt relay
I attach the schematics and simulation down "all of circuits copy write belong to designer "
full circuit:

link of the circuit:
feel free to ask me any question:


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