Tutorial: What is the Thermal Design Power (TDP)?

Thermal Design Power



This is a value you meet often in CPU or graphics card reviews and tests. The Thermal Design Power or TDP in short, is the maximum power consumed by a device (graphics card for example) under normal / regular use. In other words, the TDP is the max power a device can dissipate when running real applications. What’s more the TDP is given for graphics card default clocks.

TDP is a manufacturer’s data and thanks to this value, VGA cooler makers can size their GPU coolers for example.

The TDP is not the maximum power consumed by processor. Under some special conditions, the device can consume more power than the TDP. In the world of GPU, this situation occurs when you run an application such as FurMark with an overclocked graphics card.

Funny thing, there even exists a term to describe applications like FurMark: power virus. Actually FurMark is not a virus but it has the same effect ;)

Here are some TDP values (from this source) as well as power values generated by FurMark:

  TDP (in Watts) FurMark (in Watts)
Radeon HD 4870 160 187
Radeon HD 4870 X2 286 373
Radeon HD 3870 105 123
GeForce GTX 295 289 316
GeForce GTX 280 236 226
GeForce 9800 GTX 156 186


And from some news, the upcoming NVIDIA GT300 GPU will have a TDP of 225 Watts (less than a GTX 280).

In place of TDP, you can also find the term Maximum Board Power or Max Power Draw or Power Envelope.

How to measure the max power consumption of a graphics card?
To get a good value of the max power consumption of a graphics card, just use a wattmeter (or a voltmeter and an amperometer and the formula P = U*I) plugged in the PSU (power supply unit). Measure the power in idle mode and measure the power under FurMark stability test mode:

Graphics card max power = (Power_FurMark - Power_Idle) 
                                     * PSU_Efficiency

Example:
GeForce 9800 GX2 (default clocks)
- TDP: 197 Watts
- IDLE: 191 Watts
- LOAD: 390 Watts
- PSU efficiency = 80%
- Max Power = (390 – 191) * 0.8 = 159 Watts

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