I got my RPI3 cooled by a 5v dc fan and it only activates when it reaches 55°C so everything is fine i control it with PWM.
Now i want to cool it with a bigger 12V DC fan the problem is i need 12V, either from external source or from the PI itself and in this case i need a dc-dc converter which i found here
the thing is i can't find on the internet a similar project and how to cable it that's why i'm asking for help.
tried to do it myself on fritzing but i really dont think its good.
update : assuming the fan is a 4 wires (12v/grd/pwm/rpm) i did this on fritzing:
yellow wire is connected to PWM gpio.