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View Full Version : How many volts does the screen have?!?



STK
11th June 2007, 08:38 PM
Ok,
I was mucking around with a voltstick today and put it near the bottom right of my screen. It lit up. so how many volts are in my screen when my power supply is 85w??? (macbook pro)

Simo.

forgie
11th June 2007, 08:43 PM
85W = power, this will not determine the voltage.

There is a high-voltage inverter in a CCFL backlit LCD, and I would guess around 400 Volts AC....

The voltage going into the Macbook Pro is actually 16.5 Volts - the inverter ups that to 400 using a small transformer (which is usually found in the display enclosure itself).

edit: A quick google suggests that a CCFL inverter is more likely to put out about 1000V AC.

STK
11th June 2007, 08:47 PM
the 400v area is 2x2cm so what happened to the 400 volts?

forgie
11th June 2007, 08:53 PM
the 400v area is 2x2cm so what happened to the 400 volts?
The "400v area" is probably where the inverter is - the transformer will give off a large magnetic field, which will be what is detected by your voltstick (maybe I'm wrong here - does anyone know how a voltstick works?). That high voltage will be at a quite low current running to the backlight, so it won't have anywhere near as strong a magnetic field on the cables. The actual backlight itself, while it may have 1000 (or was it actually 400?) volts across it, would have a magnetic field that is spread out over a large area, and thus would be difficult to detect with a basic instrument like a voltstick. The transformer's magnetic field on the other hand is very concentrated.