Thermal design power (TDP) — Hinglish notes

6.4.3 · Hardware › Power, Thermal & Reliability

Overview

Thermal Design Power (TDP) woh maximum heat hai jo ek processor ya component realistic workloads ke dauran dissipate karne ke liye design kiya gaya hai, aur ise watts (W) mein measure karte hain. Yeh cooling system designers ko bata deta hai: "Tumhare heatsink aur fan ko kam se kam itni heat handle karni chahiye."

Core Concepts

TDP Ka Asli Matlab

Key Points:

Peak power nahi hai: TDP ≠ maximum instantaneous power draw. Modern CPUs briefly TDP se zyada ja sakte hain (Intel ka "Turbo Boost" kuch seconds ke liye 1.5× TDP pull kar sakta hai), lekin TDP thermal steady-state ko represent karta hai.
Realistic, synthetic nahi: Manufacturer ke expected workloads se calculate hota hai (jaise mixed compute tasks), na ki Prime95 jaisi artificial stress tests se.
Cooling requirement: Tumhare heatsink ki thermal resistance $R_{θ} \leq \frac{T _{j,max} - T _{ambient}}{TDP}$ honi chahiye, taaki throttling na ho.

Physics: Power Se Heat Tak

Electrical power heat kyun ban jaati hai?

CPU mein har transistor ek tiny switch ki tarah kaam karta hai. Jab woh switch karta hai:

Capacitance charge/discharge karta hai → dynamic power: $P_{dyn} = α C V^{2} f$
- $α$ = activity factor (fraction of transistors switching)
- $C$ = total capacitance
- $V$ = supply voltage
- $f$ = clock frequency
"Off" hone par bhi current leak karta hai → static power: $P_{static} = I_{leak} V$

Total power: $P_{total} = P_{dyn} + P_{static}$

Conservation of energy: Yeh saari electrical power heat ban jaati hai (koi mechanical work nahi hota). Chip junction temperature tab tak badhti hai jab tak heat removal aur heat generation balance nahi ho jaate:

TDP = \frac{T _{j} - T _{ambient}}{R _{θ, total}}

Jahaan:

$T_{j}$ = junction (chip die) temperature
$T_{ambient}$ = surrounding air temperature
$R_{θ, total}$ = total thermal resistance (chip → heatsink → air, in °C/W ya K/W)

Yeh kyun matter karta hai: Agar tumhare heatsink ka $R_{θ, SA}$ zyada high hai, toh chip $T_{j,max}$ tak pahunch jaata hai aur thermal throttling shuru ho jaati hai—CPU apni frequency reduce karta hai TDP kam karne ke liye, performance sacrifice karke.

Worked Examples

Worked example Example 1: Heatsink Selection

Problem: Ek Intel Core i7 ka TDP = 125 W hai, $T_{j,max} = 100° C$ hai. Room temperature 25°C hai. Chip package ka $R_{θ, JC} = 0.2° C / W$ hai, thermal paste se $R_{θ, CS} = 0.05° C / W$ milta hai. Heatsink thermal resistance maximum kitna ho sakta hai?

Solution:

Total temperature rise budget:
$Δ T_{max} = T_{j,max} - T_{ambient} = 100 - 25 = 75° C$ Kyun? Yeh temperature ka "room" hai jo humhare paas throttling se pehle hai.
Required total thermal resistance:
$R_{θ, total} = \frac{Δ T _{max}}{TDP} = \frac{75}{125} = 0.6 °C/W$

Kyun? Ohm's Law ka analogy: $Δ T = P \times R_{θ}$ , isliye $R_{θ} = Δ T / P$ .
Heatsink ke liye budget:
$R_{θ, SA} = R_{θ, total} - R_{θ, JC} - R_{θ, CS}$
$R_{θ, SA} = 0.6 - 0.2 - 0.05 = 0.35 °C/W$

Subtract kyun karte hain? Series resistances add hoti hain: $R_{θ, total} = R_{θ, JC} + R_{θ, CS} + R_{θ, SA}$ .

Answer: Tumhe ek aisa heatsink chahiye jiska $R_{θ, SA} \leq 0.35° C / W$ ho (ek decent tower cooler ya AIO liquid cooler).

Worked example Example 2: Overclocking aur TDP

Problem: Tum usi i7 ko 3.5 GHz se 4.2 GHz tak overclock karte ho aur voltage 1.2 V se 1.35 V tak badhate ho. New power consumption estimate karo (assume karo ki dynamic power dominate karti hai, activity unchanged hai).

Solution:

Dynamic power formula:
$P_{dyn} = α C V^{2} f$ ( $V^{2} f$ ke proportional)
New se old power ka ratio:
$\frac{P _{new}}{P _{old}} = \frac{V _{new}^{2} f _{new}}{V _{old}^{2} f _{old}} = \frac{( 1.35 ) ^{2} \times 4.2}{( 1.2 ) ^{2} \times 3.5}$

Kyun? Power $V^{2} f$ ke saath scale karti hai; capacitance aur activity factor constant rehte hain.
Calculate karo:
$\frac{P _{new}}{P _{old}} = \frac{1.8225 \times 4.2}{1.44 \times 3.5} = \frac{7.6545}{5.04} \approx 1.52$

$P_{new} \approx 1.52 \times 125 = 190 W$ Yeh step kyun? Baseline TDP ko scaling factor se multiply karo.

Answer: New power ≈ 190 W. Tumhara original cooler (125 W ke liye rated) ab inadequate hai—tum thermal throttling dekhoge ya tumhe ek zyada powerful cooler chahiye hoga.

Common Mistakes

Active Recall

Recall TDP ko 12-saal ke bachche ko explain karo

Socho tumhare laptop ka brain (CPU) computer ke andar ek chhote se heater ki tarah hai. Jab woh hard kaam kar raha hota hai—game khel raha ho ya video edit kar raha ho—toh woh bahut garam ho jaata hai, bilkul waise jaise tumhara phone garam ho jaata hai.

TDP ek warning label ki tarah hai jo kehta hai: "Hey, yeh brain full-speed kaam karte waqt 100-watt bulb jitna garam ho sakta hai!" Toh computer ki cooling system (fan aur metal fins) ko itni heat blow away karne ke liye kaafi strong hona chahiye, warna brain overheat ho jaayega aur khud ko protect karne ke liye slow ho jaayega.

Iska matlab yeh nahi ki brain hamesha 100 watts use karta hai—kabhi kabhi woh bas chill kar raha hota hai aur barely warm hota hai. Lekin jab woh hard kaam kar raha hota hai, fan ko woh 100 watts ki heat handle karni hoti hai. Agar fan bahut weak hai, toh brain bahut garam ho jaata hai aur kehta hai, "Okay, main cool hone tak slow ho jaata hoon," aur tumhara game lag karne lagta hai. Isliye gaming laptops ke bade, loud fans hote hain—zyada TDP ko zyada cooling chahiye!

Connections

Power consumption in CMOS circuits — TDP kahan se aata hai (dynamic + static power)
Thermal throttling — Kya hota hai jab cooling TDP ke saath keep up nahi kar paati
Overclocking and voltage scaling — V aur f badalne se power (aur TDP) kaise affect hoti hai
Heatsink design and thermal resistance — TDP meet karne ke liye cooling solution engineer karna
Process node scaling — Kyun newer chips ka same performance ke liye TDP kam hota hai (lower C, lower V)
Turbo Boost and power states — CPUs burst workloads ke dauran TDP briefly kyun exceed karte hain
Data center cooling — TDP × (hazaaron servers) = massive HVAC requirements
Laptop thermal design — Thin laptops kyun throttle karte hain: given TDP ke liye limited cooling

Flashcards

#flashcards/hardware

TDP ka full form kya hai aur yeh kya measure karta hai?

Thermal Design Power; woh maximum sustained heat output (watts mein) jo ek processor realistic high-intensity workloads ke dauran generate karta hai, cooling systems ke liye design target ke roop mein use hota hai.

TDP chip ki average power consumption hai—true ya false?

False. TDP woh thermal load (heat) hai jo cooler ko sustained load ke dauran handle karni hoti hai, na ki saare usage scenarios mein average power draw.

TDP aur thermal resistance mein kya relationship hai?

TDP = \frac{T _{j} - T _{ambient}}{R _{θ, total}}

. Chip ka temperature rise, TDP aur junction se ambient air tak ki total thermal resistance ke product ke barabar hota hai.

Agar ek CPU ka TDP = 100 W hai,

T_{j,max} = 100° C

hai, ambient = 25°C hai, aur package

R_{θ, JC} = 0.2° C / W

hai, toh maximum heatsink

R_{θ, SA}

kitna hoga agar thermal paste negligible hai?

Total budget:

R_{θ, total} = (100 - 25) /100 = 0.75° C / W

. Toh

R_{θ, SA} \leq 0.75 - 0.2 = 0.55° C / W

Overclocking TDP kyun badhata hai?

Dynamic power

P_{dyn} \propto V^{2} f

. Voltage (V) aur frequency (f) badhane se power (aur isliye heat) voltage ke saath quadratically aur frequency ke saath linearly badhti hai.

Ek laptop CPU ka TDP 15 W hai lekin system wall se 50 W draw karta hai. Explain karo.

TDP sirf CPU ki thermal output hai. Total system power mein GPU, display, SSD, motherboard, aur PSU inefficiency shamil hain—yeh sab CPU ke TDP se pare add ho jaate hain.

Agar ek heatsink ki thermal resistance kisi given TDP ke liye zyada high hai toh kya hota hai?

Chip ka junction temperature

T_{j,max}

se exceed ho jaata hai, jisse thermal throttling trigger hoti hai: CPU clock speed reduce karta hai power aur heat kam karne ke liye, performance sacrifice karke damage prevent karta hai.

Modern CPUs apni TDP rating briefly kyun exceed kar sakte hain?

Intel Turbo Boost jaisi technologies TDP se upar short bursts allow karti hain (jaise kuch seconds ke liye 1.5×) kyunki chip ka thermal mass transient heat spikes absorb kar sakta hai steady-state temperature tak pahunchne se pehle.