Electronic Fuse for DC Circuit

Tired replacing your power supply fuses, or it cost too much because too often to blow? Use this electronic fuse and your life would be easier. It is good for your new power supply design, or you can just add it to your old power supply unit. This fuse has real fast response because it works based on solid state device, a thyristor. No need to wait something to get hot and melt, the thyristor almost done the job before your milisecond timer counting up.

The resistor R2 should be chosen as 1k? per Volt of source voltage, for example 12k? for 12 volt supply, or 33k? for 33 volt source. The R1 resistor should be chosen to set the current point which should be cut on overload condition. The current breaking mechanism is done when the voltage across R1 exceed the bias voltage of Q2, and it’s about 0.7 volt. When this voltage point is exceeded, the Q2 transistor will turn on and and the current flow through the thyristor Q1 will fall below a level needed to maintain the thyristor latching. Therefore the thyristor will cut the current, and now the transistor Q2 also stops conducting because the base voltage (the voltage across R1) now disappear. After a current shorts and this electronic fuse cut the power supply, If everything is OK then you can get back to normal operation by pressing the reset switch SW1 to turn on the Thyristor again.