This DC electronic fuse never needs to be replaced. It can be repaired with just a single press of the start/reset button S1. Once S1 is pressed, the thyristor T1 triggers and the current flows to the consumer load through T1 and resistor RS. Even after releasing the start button, the current continue to flow as long as the current’s value does not sink below a certain level.
The current flowing through the thyristor T1 will sink below the holding level when the current is rerouted through the transistor T2 2N3055. T2 and RS are built into the electronic fuse circuit for this purpose. If the voltage drop at RS exceeds above base-emitter-diode trigger voltage of the T2, the transistor conducts thereby bypassing the thyristor. The resistance value of RS must be at least 0.2 W. It must be dimensioned that the product of RS multiplied by the fuse current value equals to 0.7 volts.
Once T2 bypasses the T1, the current flowing through the thyristor sinks below the holding level and the T1 shuts off. This in turn causes the voltage drop at resistor RS to sink below the base-emitter trigger voltage of T2 and the transistor shuts off. The end result is the shutting off of the whole circuit. The DC fuse can be reactivated by pressing the start/reset button.
The value of resistor R1 is dependent on the supply voltage. Multiply the supply voltage with 1 KW to get the value of R1. Connect the dc electronic fuse circuit to the PLUS line of the consumer load. THe coltage drop at the circuit is less than 1 volt.