I decided to build EFFICIENT power supply for my EEEPC 900. The laptop takes about 60mA of current while powered down and about 70mA while in suspend mode. I must mention that i removed the battery from the laptop to avoid it being charged from car battery and drain it empty.
Car battery has voltage of 10 to 14 volts probably and the laptop uses 12V input voltage. Normal switchers use transformer to generate this sort of voltage. Transformers are not efficient though and i don’t want to drain the car battery to generate heat.
So I came up with this device from National Semiconductor. LM5118. With my USB TV and active antenna connected, laptop took less than 2 Amps at 12V … P = U*I = 12*2 = 24Watt
Asus EEEPC 900 for my car