A very simple electronic fuse can be built using electronic diagram below. These electronic fuse does not need to be replaced, can be "repaired" by simply pressing a button. By pressing S button current comes through Th thiristor and Rs resistor to the consumer .
After releasing button Th triac remains in conduction state, if the current passing through it does not fall below a certain value, holding current. To cancel the holding current is used resistor Rs and transistor T .
A simple electronic circuit that prevents incorrect connection of polarized sources in circuit can be made using electronic diagram below. Safety of polarity from the diagram below was dimensioned for a voltage of 12 volts. When connecting correctly voltage to terminals 1 and 2 through RE1 resting contact, diode D1 and the coil current flows once the switch closes the circuit (relay closing, established by contact or connection with device connected).