Q:

DC buck Convertor

I want to power SIM800L which requires around 4v and 2amps(at peak only). If I attach DC buck converter to Arduino Uno 3.3V output, and power SIM800L, is it safe?

A:

Buck converters step down voltage.
Boost converters step up voltage.
The 3.3V of an arduino is limited by the arduinos regulator and is unlikely to support 4v * 2A or 8W stepped up, which would likely be 3.3V 2.4 Amps plus the efficiency penalty of the regulator (say 20% so 3.3V * 3A). It will burn out. Those on board arduino regulators are only good up to 1 amp in best conditions.

