DC Electronic Fuse

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.

Electronic DC fuse circuit diagram

dc electronic fuse circuit

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.

DC fuse PCB layout

electronic dc fuse pcb

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  • rui10h

    Gd morning,
    i tried it following a PSU.
    Really, it does not work with direct current.
    If i’m not mistaken, it cannot because, i think
    current must be switched off across the SCR.
    The voltage between anode and cathod SCR is
    near 0 volt when switched on, so the 2n3055
    is unusefull.It’s only a shunt.
    Have the author built it?
    So, in future ,do not write it on internet
    if no test.
    Better chance for homebuilders,
    All my friendship.

  • dorance

    how do we know the circuit is working?

  • Pentaconto

    This circuit is not a DC electronic fuse, not work as electronic fuse if a short-circuit occurrs at the DC output.


    Construct the circuit on a dot type common PCB as per the instructions given in the write up.Definitely it will work.

  • MijovicNet

    I cant get this circuit working???
    What i am doing wrong?