Why CPU consumes dozens of watts and do not burnout? - Page 1
Forum section: electronics / general

author: Ivanko1
author_rank: Contributor
timestamp: February 05, 2017, 06:57:51 pm
content: Can somebody explain, why nowdays descktop processors consume so much power and do not blowout?I mean, so tiny transistors (dozens of nanometers!!!) can conduct so much amps - how they can not just burning out?Standart TDP is about from 10 to 100 watts, standart power voltage from 1 to 1,5 volts(!), it,s dozens amps for so tiny chip and transistors!Just how?

author: FrankBuss
author_rank: Unknown
timestamp: February 05, 2017, 07:02:36 pm
content: They don't conduct amps, it's millions of transistors, each conducting microamps. And maybe you have opened a PC once and saw the big heat sink to get the heat out.

author: wraper
author_rank: Unknown
timestamp: February 05, 2017, 07:02:59 pm
content: Quote from: Ivanko1 on February 05, 2017, 06:57:51 pmNow divide 100A current with a ~1 billion of transistors. And then look how big current it is through each of them in average.

author: wraper
author_rank: Unknown
timestamp: February 05, 2017, 07:07:01 pm
content: Quote from: FrankBuss on February 05, 2017, 07:02:36 pmLess than nanoamp per transistor in average. Current is consumed only during the moment of switching BTW. This is the reason why frequency CPU operates at has so much impact on power consumption.

author: Ivanko1
author_rank: Contributor
timestamp: February 05, 2017, 07:28:18 pm
content: Quote from: wraper on February 05, 2017, 07:07:01 pmHmm... I din't thought about that.)Quote from: wraper on February 05, 2017, 07:07:01 pmArent they must consume power to stay on-state to?P.s. Sorry for my english.)

author: rollatorwieltje
author_rank: Unknown
timestamp: February 05, 2017, 07:57:30 pm
content: Quote from: Ivanko1 on February 05, 2017, 07:28:18 pmThey are FET type transistors. The gate acts like a capacitor, once it is charged it will only draw leakage current, which is almost nothing. It is becoming a problem though, leakage current increases with smaller transistors.

author: Berni
author_rank: Super Contributor
timestamp: February 05, 2017, 08:19:08 pm
content: Yep all modern CPUs are built using FET transistors so they only need power to switch.And yes the amount of current feeding a modern CPU is just staggering. With a Vcore of 1.2V being pretty common it means that the CPU could be consuming 100A of current.

author: David Hess
author_rank: Super Contributor
timestamp: February 06, 2017, 12:48:30 am
content: Quote from: Berni on February 05, 2017, 08:19:08 pmGate and channel leakage in the last few generations of CMOS contribute greatly to power dissipation. This is especially the case at elevated temperatures. For a while, leakage in some CMOS high performance ICs contributed half or more of the power being dissipated and it has been a serious problem since at least the Pentium 4. This is why power gating exists.As far as the original question, all of the power has to be removed through the surface of the integrated circuit. The large area provides for a low junction to case thermal resistance on the order of 0.15C/W with the heat sink contributing another 0.15C/W to ambient so even 100 watts only raises the junction temperature about 30 degrees C above ambient.If you make a table showing power versus die area and temperature over the years of maximum performance Intel processors, you will find that the power per unit area is roughly constant. As the chips have gotten smaller, power has *had* to decrease to keep junction temperatures reasonable.

author: rsjsouza
author_rank: Super Contributor
timestamp: February 06, 2017, 01:21:47 am
content: One interesting aspect is that, despite there are billions of transistors switching very small currents, the interconnects are comparably small but can carry current densities (A/cm^2) higher than transmission lines, for example.