The simple short circuit and
overload protector design presented here can be used for protecting
valuable mains operated gadgets like amplifiers, TV sets, DVD players or any other similar appliance.Normally all sophisticated gadgets today incorporate an in built short
circuit protector arrangement, yet still adding a more comprehensive
external protection device could only benefit the connected system.
Moreover, for gadgets such as amplifiers which are home built this
protection device could prove to be very effective and useful. Also for
an hobbyist who prefers building electronic gadgets at home could be
greatly benefited with the present idea.
The presented short circuit protector design works on a very basic principle and costs not more than a couple of dollars.
Let's learn the functioning details of the proposed circuit.
On applying power, the high current from the 220V input is dropped
sufficiently by C1, rectified by D1 and filtered by C2 to feed the gate
of the triac T1.
The triac conducts and switches ON the connected transformer primary
thus switching ON the load which in this case is a power amplifier.
The transistor Q1 along with R1, R2 forms a current sensor stage.
R2 specifically is chosen such that it develops adequate voltage across
itself at the specified dangerous high current threshold.
As usual the formula for determining R2 = 0.6/current(A)
As soon as the triggering voltage accumulates across R2, Q1 activates
and sinks the gate voltage of the triac to ground making it switch off.
The regulation continues as long as the short or overload condition is not removed.
The above short circuit regulation ensures that the current level above
the specified dangerous level is restricted safeguarding the precious
devices associated with the connected amplifier.
If a latching feature is required for the above design, the emitter Q1
can be configured with an SCR and the SCR can be used for latching and
switching off the triac.
AC Mains Short-Circuit Protector Circuit Diagram
Parts List
R1 = 100 ohms
R2 = see text
R3 = 1k
R4 = 10k
C1 = 0.33/400V
C2 = 1uf/250V
Q1 = BC547
Z1 = 12V/1 watt zener diode
T1 = BT136 or as per current rating
TR1 = As per load requirement specs.
Source By Swagatam
