Questions about TDP


#1

TDP
Thermal Design Power (TDP) represents the average power, in watts, the processor dissipates when operating at Base Frequency with all cores active under an Intel-defined, high-complexity workload.

I am still confused about TDP for CPU, screen and other so I was wondering if somebody more knowledgeable could explain it very slowly.

The idea behind these questions is that people could CALCULATE how much battery life they can expect from V based on what they will be using V for.

Rather then on meaningless banchmarks like: “You can watch video for 13.5 hours”.

  1. Lets talk CPU first. Lets focus on M3 for simplicity (and because it seams to be the most popular).
    What does 4.5 Whr exactly means?
    What does “We have increased TDP to 7Whr” exactly means?.

Are these TDP when CPU is working in Turbo Boost?
Or when it is working in normal mode? If so what is Turbo Boost TDP?
What is the lowes frequency of M3 and what is TDP then?
What is frequency/TDP when I am watching offline word document or web page?

  1. And now about the screen.
    What are TDPs for specific brightness/nits?
    So if I know that in my room I can use it with 150 nits I could calculated screen TDP.

  2. What is TDP of other components?
    So if I know that I will be reading word documents offline I could calculate battery life.

Thanks


#2

There are quite some variables you need to calculate the battery life.

First, CPU can drain very little, or very much depending on the tasks it performs. If you are just letting your V stand there, doing nothing, it will sip power. As opposed running benchmarks or gaming, which will make it drain power.
Secondly, TDP stands for “Thermal Design Power”. this is NOT the same as power drain. This actually the amount of power that is being turned into heat, and essentially being wasted by the system. You’ll need the actual power drain of every component, internal and external. If there is USB stick in the V, it’ll last shorter then without it.

Technical

To be even more technical, TDP should be the amount of heat the chip can actually dissipate from itself. This means a “15W TDP” chip can remove 15W of heat from itself at each given moment. Any more then that and the chip will be designed to throttle, so it won’t damage itself. You can still increase the amount of heat the chip can generate by making it cool more quickly. Hard to do with the V, but in desktop’s it’s quite common to do this via an aftermarket cooler. CPU coolers let themselves get hotter by grabbing the heat away from the CPU and then radiate it out by their design. The continuous airflow usually accompanied with such coolers makes sure that cooler air always available for the coolers to radiate their heat away.

The amount of variables is, for the sake of argument, unlimited. Thus, you can’t calculate how much any battery powered computer will last.

The reason for the ‘meaningless’ benchmarks is so that there is a comparison table on which all similar devices can be tested. You can then compare your own device to the device that you might want to buy and see if it is increased, decreased, or the same. And make an educated guess as to how much longer/shorter the battery life is.

On top of that, battery life decreases with each use. That doesn’t make the calculations easier.

I hope this gives you some ease of mind.


#3

Thanks for the asnwer but it doesn’t really help as you might have guessed.

When you go to intel specs you will see something like: TDP: 4.5 W
So if your CPU is using 4.5 W (at some frequency) and you have 45 Wh battery and no other components are draining power then you would be able to use PC for 10h.
Or is there something wrong with my understanding and this calculation?
Since you are saying this is heat generation and not power draw from the battery.

Super easy calculation.

The other major power draw is screen depending on the brightness.

Everything else is negligalbe or if you want precision you can specify power draw of
Wi-Fi, SSD, Bluetoth, Keyboard

So I wouldn’t say that number of parameters is unlimited.
And depending on needed precisions these little aditional parameters can be neglected or some general number can be used to replace them.

But in any case you should get better estimate then Microsoft’s 13.5 hours in scenarion where CPU is not being used at all.


#4

Nop. TDP is not power drain. TDP is the amount of heat a CPU can remove from itself. For a CPU with a TDP of 4.5 W it can still even generate more heat then just 4.5W, it’ll just get hotter.
A 15 W CPU can still drain 45W if it’s cooled sufficiently. A 45W CPU can drain only 1 W if it’s not doing anything.

Most motherboards have some sort of wattage meter to measure it’s power drain, even that isn’t that accurate. On top of that, it fluctuates enormously depending on what you actually do.

So… You can’t calculate it.
It’s like you want to calculate the mileage of a car with only knowing it’s tank capacity.


#5

OK thanks.
So these are heat dissapation values which are important for choosing proper cooling.
So why specs don’t include any info on Power Draw?
This is supposed to be the main point of these CPUs and there is no info on it on official specs?

And if you know frequency can you calculate Power Draw (using some formula, graph).
Or this also doesn’t related in such a simple way?


#6

TDP can also be used as a vague guess about power draw. Obviously, because the efficiency of the processor comes into play too, that number doesn’t relate to the power consumption of the processor, only the residual heat after computations.

The heat released by the processor is a result of a processor that isn’t perfectly efficient. More energy goes in that is released through heat, and the rest of that energy goes into the computational tasks of the processor. The efficiency is most likely a giant mess of complicated equations, so trying to derive power consumption from heat expulsion would be rather difficult I assume (not exactly my specialty, but I do have some knowledge here).

Because a desktop processor may be rated at 60W, and the processor in the V is at 7W, we can see just how much more energy the desktop processor used compared to the V processor. These values (for heat) are easy to measure, give a good relative value for heat dissipation, computational ability, and power draw all in one number. But again, the number is relative to other processors.

Also, the number is just as average; as I’m sure you’re aware, the temperature of a processor fluctuates quite a bit, and power consumption fluctuates much much more. Finding a consistent, average value for power draw isn’t going to work very well, so TDP is used as a rough approximation.


#7

The maximum power draw is a whole bag of variables, it’s easier to just run benchmarks till the battery dies.
I’m also not a physicist, so I can’t really give you an exact formula or graph. I do know that ‘theoretically’ you can let a 4.5W CPU draw 1000W from the wall, if the cooling can dissipate the generated heat fast enough. So the efficiency of the cooling is a major factor in maximum power draw. CPU draws power so long it doesn’t reach it’s maximum temperature, after which it’s thermal throttled (slowed down to leat the heat escape).

The best way to test battery life is to have a consistent test (for example, use the playing of video at a certain brightness level) and use the same exact test on every device. That way you can compare devices, which has a better battery life, and which doesn’t. You should compare that to a device you know the battery life of. Then you can extract if the battery is better or worse.
This type of testing does have it’s drawbacks obviously, if a device was vastly optimized for video playback it would rate higher, which would be a faulty conclusion. But it’s the closest we got.