hi,

i have a SCR which is 2N5062. From the datasheet i know that it is a 0.8Amp RMS 100V SCR.



From the picture above, my transformer rating is 12-0-12 1A. And the fuse rating is 1A. After the 7805 i put 1k resistor and a led as a load. SCR i'm using is 2N5062 and zenor diode is 1N5339B.

When i turn on the power the SCR will blow. But when i change the fuse rating to 500mA the fuse will not blow and the led will on.

Can someone explain this for me? thank you.

 

Your 7805 might be oscillating. It needs an output capacitor.

 

ya.sorry.forget to add in the picture.i have a 10uf/35v at the output part on my circuit.

 

What is the capacity of the filter capacitor? That cap in the schematic needs to be at least several hundred uF. The output needs a small value bypass capacitor, like .1 uF. The 10 uF cap won't work as well to suppress oscillations.