/diy/ - Do It Yourself

>>2738353
One of these led spotlights come with the next circuit,
If isn't too much bother , can explain me how does it works,please?
The varistor 07D271K is rated at 175V rms, so afaik, this would work as some kind of clipping diodes to hold the voltage between certain limits, the MB10F rectifier, the capacitor maintains the output level filling the possible gaps of the rectifier at the cycle change, I'm guessing the 150k resistor is to avoid any peak current, but this does work as I'm writing or not?
Also
Where is the DC-DC part to change the 120 to 5v? the led plate only has the pins to fit the output, but it does not have anything on it.
2nd also
is there a guide/book to recognize the circuit from the board? I have always failed to do so well, often got stuck with a resistor leading to nowhere or some track vanishing or invisible.
Thanks.