rbw wrote:
to begin basing their notebooks on lower voltage L7400 and L7200 as well as an ultra low voltage processor later this month. Currently Core 2 Duo notebook processors are the full voltage T-series that suck the life out of batteries...
Keep in mind that voltage and current are inversely proportionate and directly relate to how much power the chip consumes: a basic principle of electronics (Ohm's law) states that voltage equals current times resistance; that is, a flow of one ampere through a resistance of one ohm means that the electrical pressure is one volt. Power (wattage), and directly, battery life, is also proportionate to voltage and current in the relationship P=VI (P being power, V being voltage, I being current (amps)). Thus, reducing the voltage will increase the current draw, but not change the power dissipation at all if the in-circuit resistance does not change. Case-in-point: look at any switch-mode power supply and look at the current figures for 120 V (standard half-wave single-phase) and 240V (standard full-wave single-phase US home delivery). If it draws, say, 4A at 120V it will draw 2A at 240V, ceteris paribus. In both cases, the power dissipation is 480W.
so, decreasing the voltage won't improve battery life unless they also somehow decrease the amount of current the chip draws. Since, in modern machines, the CPU draws only about 20% of the overall current, they'd have to decrease it a considerable amount to actually have a noticeable impact on battery life anyways. That means decreasing the power consumption in the CPU by 50% would still only result in a net gain of 10% more battery life. In my laptop, that would equate to about an additional 15 minutes of battery life (assuming I have the extended battery installed).
LCD backlight, graphics chip, memory subsystem, and any mechanical parts (fan/hard disk) are the other main draws. Wireless transceivers shouldn't be discounted either, as they also dissipate a substantial amount of power when actually transmitting. If we worked to decrease the power consumption of these devices, we'd probably be better off.
cheers, -kelsey -- [email protected] http://www.kernel-panic.org/cgi-bin/mailman/listinfo/kplug-list
