Power supply board

The power supply board takes alternating current (AC) from the wall, at 100 to 240 volts, and turns it into steady, low direct-current (DC) voltages for the rest of the TV. On most sets it also powers the LED backlight.

It is built on a printed circuit board, with parts fixed by solder and wired in and out through connectors. Power flows through it in stages:

• it enters through a fuse, and inductors and ceramic capacitors filter out noise
• diodes turn the AC into DC, and a large electrolytic capacitor stores it as a high, smooth voltage
• power transistors switch that voltage on and off tens of thousands of times a second into a small transformer, which steps it down and keeps the low side isolated from the mains
• more diodes and capacitors smooth the output, while resistors sense the current

Controller chips run each stage and the LED driver, and heat sinks keep the transistors cool.

This switching design is why the board is light and flat. The faster a transformer is fed, the smaller it can be, so it is far smaller than the heavy transformer an old-style supply needed.