Here is the circuit diagram of a fuse that has an automatic status indicator. This circuit can be added to circuit that operates from 12V DC. As long as the fuse is intact, the LED D3 will glow continuously and when the fuse blows off the LED will start and continue blinking.
The first part of the circuit includes an astable multivibrator built around transistors Q1 and Q2.The output of the multivibrator is coupled to the base of Q3 via diode D2.When the fuse is intact the base of Q3 will be pulled to a positive voltage by the resistor R5. The transistor will be ON and the LED D3 remains glowing. When the fuse of blown off, the base of Q3 will no longer be pulled to positive voltage and now the only biasing available at the base of Q3 will be the output from the astable multivibrator.
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