This circuit is a Fuse status indicators for power supply 12V. If a fuse is normally, the LED is going to lights all the time. But when it lacks, the LED will be blinking. The value of this equipment in the circuit is suitable for a 12 volt power supply.
However able to change the power supply 6 volt or 24 volt, By reducing the value of the resistor to half or increasing.
The display section consists of a stable multivibrators (Q1-BC547, Q2-BC547). And the driver LED section (Q3), All circuits except for the R5 connect before the fuse.
The output of the multivibrators is going to work all times there are power supply, by passed through the diode D2 to the input of the driver LED section (Q3‘s PinB) If the fuse is intact , the base current of Q3 has still always, by passed through R5 and D1,the color LED shown constantly. But when fuse in blown condition,the driver current Q3 is going to get from only multivibrators, so the led is flashing.
The current rate of Power consumption about 30 mA, by almost all were used by the LED. If you are used this circuit with some circuit that uses a high quality LED and changed R6 values to suitably with the lower current of the LED.
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