Suppressing sparks when attaching buck converter to battery
Is there any way to suppress these sparks when i attach the converter?


This is caused by inrush current and, for many devices like this can be several tens or even hundreds of amps i.e. much more than the normal full-load running input current. It can be particularly bad on on-line SMPS units and a lot of them use a negative temperature coefficient thermistor to reduce this transient effect.

The thermistor has an initially high resistance when cold thus lowering inrush current but, as it warms over the period of a few seconds, its resistance drops significantly. However, it represents a loss in efficiency even when warm so some circuits have evolved to use a MOSFET to control the inrush: -



Q1 initially does not switch on when power is applied due to the capacitor C1. That capacitor gradually (over a second or so) charges and as it does so the MOSFET is turned on gradually thus alleviating the inrush problem.

Here's another example with values: -



Image stolen from here and here's a version with a little more sophistication: -



The extra transistor guarantees that the current cannot rise above a certain value.