blown fuse indicator - for low voltage circuits

for low voltage circuits This circuit, as the name suggests, indicates when a fuse has blown. As long as the fuse is good the LED lights continuously, but when it blows the LED flashes. If the values given in the diagram are used the cir- cuit is suitable for 12 V operation but it can easily be made suitable for 6 or 24 V by simply halving or doub- 8-00 ling the values of all the resistors. The indicator consists of an astable multivibrator (T1 and T2) and a LED driver stage (T3). The whole circuit, with the exception of R5, is con- nected before the fuse in the supply. The output of the multivibrator, which is always active as long as the supply is present, is connected, via D2, to the input of the LED driver stage (the base of T3). As long as july/august 1984 the fuse is good (not blown) the base current for T3 is always pro- vided via R5 and D1, with the result that the LED lights continuously. When the fuse blows the base cur- rent is only provided by the AMV and, as this is...