# Automatic Fuse Circuit

To restrict / security, electric current is usually used fuse
or patron is dissolved when going short will drop out and
must be replaced with a new one. Then, in order not to drop out of each
new change means that more money out to buy, then there fuse automatically work with the reset button. So there are problems with
each short, fuse will automatic decided flow then to return it
does not need to buy a new (if not broken) just press the reset the
equipment will live again.
This is one of the simplest electronic
fuse circuit one can make. The circuit uses only one transistor, one SCR, one push button switch and two resistors.
The value of R1 can be obtained from the equation; [Imax] X [R1] = 0.7V.
R2 can be obtained from the equation; R2 = [Vs] X [1K Ohms].
Wattage rating of R1 can be obtained from the equation; W = [Imax] X [Imax] X [R1].
For this circuit to work the current consumption of the load must be greater than the holding current of the SCR.
The
working of the circuit is very simple. Initially the load current
flows through SCR and resistor R1.The value of R1 is so selected that,
the maximum load current multiplied by the resistance of R1 is equal to
0.7 volts. When the load current exceeds the maximum value the voltage
drop across R1 becomes more than 0.7V and switches transistor Q1 ON.
Now the transistor completely bye passes the load current and the
current through triac falls below the holding current. This makes the
triac OFF. When SCR is OFF there will not be any current flow through
R1 and so the voltage across it falls to 0.This makes the transistor
OFF, completely isolating the load circuit.The fuse can be resetted by
pressing S1.When S1 is pressed the SCR is again triggered and remains
latched to conduct the load current.