Backlight system of display device with printed circuit board separate from and mounted to LED substrate with support pillars

A backlight system, wherein the backlight system comprises:

• an LED (light emitting diode) light source, which comprises an LED lamp and an LED substrate carrying the LED lamp;
• a back frame, which is disposed below the LED substrate and comprises at least two primary assembling pieces, the at least two primary assembling pieces being joined to form a main frame structure of the back frame;
• and
• a printed circuit board (PCB), which is disposed below the back frame and securely fixed to the LED substrate through support pillars received through hollow areas of the main frame structure and each having opposite ends respectively mounted to the PCB and LED substrate;
• wherein the at least two primary assembling pieces comprise a first primary assembling piece and a second primary assembling piece, the first primary assembling piece having an end forming two spaced joint sections, each of the joint sections having a structure mating an end of the second primary assembling piece, the end of the second primary assembling piece being switchable jointed to a first one and a second one of the two spaced joint sections, with the other joint section of the first primary assembling piece being idle, so that the second primary assembling piece is connected to the first primary assembling piece in a position-adjustable manner to respectively define a first size and a second size of the back frame, the second size being different from the first size.