I have a circuit keep blowing fuse(0.4A) with slightly lower rating of my transformer (0.5A) without any load, so i think is the issue of in-rush current. ***Note : my transformer is toroidal, saw a lot of website saying they inhibit higher inrush voltage (80times. scary)***Will the in-rush current will do any harm or any changes to other things(component) ?If so, what type or rating of fuse should i get ? (best if easily get, market available)ORis there any way to de-energize the transformer when it is turned off/before switch on, or any circuit to use for protect over-current/voltage during inrush ONLY ***Note that i want to make my circuit fuse safe from short circuit and blow the fuse if it is really short circuit***
The inrush current here happens because of the large capacitor. Initially it has no charge and no voltage, so the initial current flow into it is only limited by the resistance and reactance of the transformer. If anything a toroidal transformer would increase the inrush current, because it has less reactance! but the difference will be negligible. The usual (cheap) solution is to use a 'slow blow fuse', which wont blow from ther brief transient. Sometimes, a resistance is connected initially in series with the capacitor to minimise the initial current, and then shorted out by a relay after a small time. The limitations of a transformer are mainly due to heating: the inrush current is only a short time, so it should not cause the transformer to heat beyond its rating. Also, the rectifier may be damaged by the inrush if it exceeds its maximum 'non-repetetive' peak current rating, but this is usually very large.
Assuming the transformer is well designed and you are operating it within it's rating, no problem. I'd change the fuse to 3/4 amps slo-blow. .
What is the rating of the transformer, Input voltage, output voltage and output current? By 0.5 amps do you mean the input current of the transformer, because this would be the loaded current of the transformer.The transformer should not be blowing a fuse unloaded, transformers have a magnetizing current not an inrush current The magnetizing current is due to the inductance of the primary winding. Transformers act as coupled inductors and since the secondary is open the only load on the input fuse should be the small magnetizing current. I am guessing you might have a shorted winding.
