electronic fuse

7-34 elektor july/august 1980 The electronic fuse shown here is a high speed and easily repaired direct current fuse. The thyristor (Th) is triggered by depressing push- button S for a brief period. The value of resistor Rgmust be about 1 Id2 for every volt of supply voltage. The pushbutton may be released as soon as the thyristor has turned on. The anode current continues to flow — without further control voltage - until it drops below a certain "hold" value. This will take place, for instance, if the current is conducted around the thyristor! This purpose is served by transistor T and resistor Rs. The thyristor current passes through resistor Rs and as soon as the drop in voltage across it is greater than the threshold level of the transistor this will conduct. The value of R (minimum: 0.2 SZ) must therefore be chosen in such a Ub =- max. 60 V Th= TIC 106 A ... D 4 A/250 V 2N3055 T ** g 5 electronic fuse way that the product of the maxi- mum current and R s is greater than the...