Thermal design power (TDP): Foundations — Hinglish deep dive

6.4.3 · D1 · Hardware › Power, Thermal & Reliability › Thermal design power (TDP)

Is page par kuch bhi assume nahi kiya gaya. Parent note Thermal design power (TDP) padhne se pehle, tumhe jaanna chahiye ki watt kya hota hai, heat ka matlab kya hai, chip garam kyun hoti hai, aur engineers ne temperature describe karne ke liye electricity ki language kaise borrow ki. Hum har symbol ground up se banate hain.

1. Power, energy, aur watt (woh unit jisme TDP measure hoti hai)

Shuru karte hain un do words se jo log constantly mix up karte hain.

Figure s01 — Tap analogy. Ek tap paani ko ek puddle mein daalta hai. Girte stream ki thickness (blue) power ko represent karti hai — energy kitni tezi se flow karti hai, watts mein. Floor par jama hota puddle (yellow) energy ko represent karta hai — total amount collected, joules mein. Wahi tap, do alag quantities: rate vs. total.

Tap picture dekho. Flow rate (stream ki thickness) power hai; puddle jo jama hoti hai woh energy hai. TDP ek power number hai, kyunki cooler ko rate ki parwah hoti hai jis par heat aati hai, na ki pure din ki total ki.

2. Heat aur temperature (do alag cheezein)

Hum baad mein teen temperatures se milenge. Abhi inhein naam dete hain:

$T_{j}$ — junction temperature, chip ke andar actual silicon ka temperature. "Junction" transistor ka purana slang hai chip ke kaam karne wale hisse ke liye.
$T_{ambient}$ — surrounding air ka temperature jisme cooler heat dump karta hai.
$T_{j,max}$ — highest junction temperature allowed chip ke khud ko protect karne se pehle. Isse cross karo aur chip slow ho jaati hai (dekho Thermal throttling) ya khatam ho jaati hai.

3. Electric charge, current, aur capacitance (electrical building blocks)

Isse pehle ki hum bol sakein kyun chip garam hoti hai, humein teen electrical words chahiye. Inhein order mein build karo.

Ab har electrical symbol jo humein chahiye — $Q$ , $I$ , $V$ , $C$ — ka ek plain meaning, ek unit, aur ek picture hai. Hum heat explain karne ke liye ready hain.

4. Chip heat kyun produce karti hai

Har chip millions of tiny switches se bani hoti hai jinhein transistors kehte hain. Jab ek transistor on aur off flip karta hai, toh woh electric charge ko move karta hai. Charge ko chip ke material se move karna resistance se milta hai, aur — bilkul light bulb filament ki tarah — woh electrical energy ko heat mein badal deta hai.

$P_{dyn} = α C V^{2} f$ kahan se aata hai

Formula accept karne se pehle, chaliye ise build karte hain, ek switching event at a time.

Ek capacitor of size $C$ ko voltage $V$ tak charge karne ki physics se stored energy milti hai $\frac{1}{2} C V^{2}$ . Lekin ise supply se charge karne par total $C V^{2}$ power source se bahar aata hai (aadha store hota hai, aadha andar aate waqt wires mein heat ban jaata hai), aur phir ise empty karne par stored aadha bhi heat ban jaata hai. Ek full charge-then-discharge cycle mein jo energy heat ban jaati hai woh hai:

$E_{sw} = C V^{2}$

Recall Textbook ka "½"

$\frac{1}{2} C V^{2}$ mein kahan gaya? $\frac{1}{2} C V^{2}$ capacitor mein stored energy hai ::: lekin ek complete charge aur discharge cycle mein dono halves eventually heat ban jaate hain, jisse ek full $C V^{2}$ per cycle milta hai — toh $P_{dyn}$ mein koi ½ nahi bachta. (Kuch textbooks factor ko $C$ ya $α$ mein fold karte hain; conventions vary hoti hain, toh check karo tumhara source kaun si energy mean karta hai.)

Total jo cooler ko handle karna hoga: $P_{total} = P_{dyn} + P_{static}$

Recall Dynamic power mein

$V$ squared kyun aata hai? Kyunki voltage double duty karta hai ::: yeh set karta hai ki kitna charge move hoga (bucket $Q = C V$ tak fill hoti hai) AUR kitni hard push hai, toh iska effect khud se multiply hota hai, giving $V^{2}$ .

5. Heat ke liye Ohm's-Law analogy (har TDP calculation ka core)

Yeh woh clever borrowing hai jo TDP math ko easy banata hai.

Electricity mein, Ohm's Law kehta hai ek voltage difference $Δ V$ ek resistance $R$ se current $I$ (charge per second, amperes mein — §3 mein define kiya) ko push karta hai: $Δ V = I \times R$

Engineers ne notice kiya ki heat bhi same tarah behave karti hai: ek temperature difference ek thermal resistance se heat flow ko push karta hai. Toh unhone equation ko symbol-for-symbol copy kar liya.

Figure s02 — Electrical–thermal analogy. Top (blue): "high V" se "low V" ka voltage difference ek current $I$ ko resistor $R$ se drive karta hai. Bottom (pink): hot junction $T_{j}$ se cool air $T_{ambient}$ ka temperature difference ek heat flow $P$ (watts) ko thermal resistance $R_{θ}$ se drive karta hai. Dono rows same equation hain bas labels swap hain.

Formula Thermal Ohm's Law

$Δ T = P \times R_{θ}$ Chip ke liye temperature difference define karna. General form hai $Δ T = T_{hot} - T_{cold}$ , jahan $T_{hot}$ simply "heat path ke hotter end ka temperature" hai aur $T_{cold}$ "cooler end ka temperature" hai. CPU ke liye hot end silicon junction hai aur cold end surrounding air hai, toh hum §2 se chip-specific names substitute karte hain: $T_{hot} = T_{j}, T_{cold} = T_{ambient}, Δ T = T_{j} - T_{ambient}$ (Hotter end) minus (cooler end) lene par, $Δ T > 0$ , aur heat hamesha hot se cold ki taraf flow karti hai.

$Δ T$ — temperature difference (°C), voltage ka role play karta hai.
$P$ — watts mein heat flow, current $I$ ka role play karta hai.
$R_{θ}$ — thermal resistance ("R-theta"), path heat flow ko kitna resist karta hai, °C/W mein measure hota hai. Kyunki yeh temperatures ka difference hai, ek degree Celsius ek kelvin ke barabar hota hai, toh °C/W aur K/W numerically identical hain — tum dono symbols dekhoge; inhein same unit treat karo.

Chhota $θ$ (Greek "theta") sirf ek subscript label hai jiska matlab "thermal" hai — yeh batata hai ki yeh R heat ke baare mein hai, electricity ke baare mein nahi.

Kyunki heat stages ki ek chain se travel karti hai, aur chain mein resistances simply add up ho jaate hain (bilkul series mein resistors ki tarah), parent note likhta hai: $R_{θ, total} = R_{θ, JC} + R_{θ, CS} + R_{θ, SA}$

Figure s03 — Heat teen series resistances cross karti hai. Boxes left to right: silicon junction ( $T_{j}$ ) → metal case → heatsink fins → ambient air ( $T_{ambient}$ ). Unke beech teen arrows hain labeled $R_{J C}$ (junction-to-case), $R_{C S}$ (case-to-sink, thermal paste), aur $R_{S A}$ (sink-to-ambient). Heat ek hiker hai jo teeno bridges cross karta hai row mein, toh resistances add hote hain: $R_{total} = R_{J C} + R_{C S} + R_{S A}$ .

Picture left to right padhlo — heat ek hiker hai jo teen bridges cross karta hai:

$R_{θ, JC}$ — Junction-to-Case: silicon se metal lid tak.
$R_{θ, CS}$ — Case-to-Sink: thermal paste ke across (dekho Heatsink design and thermal resistance).
$R_{θ, SA}$ — Sink-to-Ambient: heatsink fins se moving air mein.

6. Steady state vs. spikes — thermal capacitance (isliye TDP ek sustained number hai)

Upar wala thermal Ohm's Law ek steady-state picture hai: yeh assume karta hai ki heat itni der se flow kar rahi hai ki temperatures settle ho gayi hain. Lekin chips mein thermal mass bhi hoti hai, aur woh short bursts ke response ko change karti hai.

Figure s04 — Sudden load ke baad time ke saath junction temperature. Yellow curve: constant power apply karo aur $T_{j}$ gradually (instantly nahi) apni steady value ki taraf badhta hai, kyunki thermal capacitance ko pehle fill hona hota hai. Blue dashed line: final steady-state temperature jo thermal Ohm's Law predict karta hai. Pink arrow: ek brief power spike curve par sirf partway tak chadh paata hai load drop se pehle — exactly isliye ek chip momentarily TDP exceed kar sakti hai bina overheat hue.

7. Symbols ko saath mein rakhna

Pehle, is page ke dono halves ke beech missing link: TDP chip ki steady-state total heat flow ka sirf ek naam hai.

Ab thermal Ohm's Law ko rearrange karo dekho TDP kahan fit hota hai. Chip tab tak warm hoti hai jab tak heat removed heat made ke barabar na ho jaye. Us balance par heat flow $P$ TDP ke barabar hoti hai, toh: $TDP = \frac{T _{j} - T _{ambient}}{R _{θ, total}}$

Right side par har symbol tumhe ab pata hai. Chip ko safe rakhne ke liye hum demand karte hain $T_{j} \leq T_{j,max}$ , jo rearrange hoke cooling requirement deta hai: $R_{θ, total} \leq \frac{T _{j,max} - T _{ambient}}{TDP}$

Recall Agar garmi ke din

$T_{ambient}$ badhta hai, toh tumhare allowed $R_{θ, total}$ ka kya hoga? Numerator $T_{j,max} - T_{ambient}$ shrink ho jaata hai ::: toh allowed thermal resistance drop hoti hai — same cooler ab kafi nahi reh sakta, isliye servers ko Data center cooling ki parwah hoti hai.

Prerequisite map

Neeche diagram ek dependency map hai: ise top to bottom padhlo, arrows follow karo. Har box is page se ek idea hai, aur ek arrow $X \to Y$ matlab hai " $Y$ ke sense hone se pehle tumhe $X$ chahiye" — $X$ , $Y$ mein feed hota hai. Do independent roots (left par energy-in-joules, right par electrical Ohm law / $P = V I$ ) neeche flow karte hain aur dono bottom ke paas "cooling requirement" par milte hain, jo woh formula hai jis par parent note build hai. Figure s05 same map ko ek labelled picture ke roop mein draw karta hai agar neeche wala diagram render na ho.

Figure s05 — Prerequisite map ek picture ke roop mein draw kiya gaya. Left par yellow nodes energy/heat chain hain; right par blue nodes electrical chain hain ( $P = V I$ , charge, current, capacitance); bottom par pink nodes wahan hain jahan dono chains thermal Ohm's Law aur final cooling requirement mein merge hoti hain. Arrows har prerequisite se point karte hain us cheez ki taraf jo woh enable karta hai.

Equipment checklist

Khud ko test karo — agar tum har ek ka jawab de sako, toh tum parent note ke liye ready ho.

TDP kis unit mein measure hoti hai, aur kya yeh rate hai ya total?

Watts (W); yeh heat flow ki ek rate hai (joules per second), total amount of energy nahi.

Heat aur temperature mein kya difference hai?

Heat transit mein energy hai (joules mein measure, ya watts as a flow rate); temperature "kitna hot" hai — ek level, °C mein.

Electric charge aur current kya hain, aur unki units kya hain?

Charge coulombs mein electricity ki ek quantity hai; current woh rate hai jis par charge flow karti hai, amperes mein (1 A = 1 coulomb/s).

Master power relation aur uski units batao.

P = V \times I

— voltage (volts) times current (amperes) power deta hai (watts).

Capacitance kya hai, uski unit kya hai, aur uska defining equation kya hai?

Ek bucket per volt kitna charge hold karti hai; farads mein measure hota hai;

Q = C V

CPU mein essentially saari electrical power heat mein kyun badal jaati hai?

Chip koi mechanical work nahi karta, toh conservation of energy se har drawn joule heat ke roop mein bahar jaana chahiye.

P_{dyn} = α C V^{2} f

energy per switch se kaise follow karta hai?

Har full switch

E_{sw} = C V^{2}

heat dump karta hai; switching rate

α f

se multiply karo (fraction switching times ticks per second) power milta hai.

P_{static} = I_{leak} V

kahan se aata hai?

Yeh sirf master relation

P = V I

hai leakage current

I_{leak}

apply karke.

Thermal Ohm's Law aur uska sign convention batao.

Δ T = P \times R_{θ}

jahan

Δ T = T_{hot} - T_{cold} = T_{j} - T_{ambient}

, toh heat hotter end se cooler end ki taraf flow karti hai.

Thermal resistance

R_{θ}

ki units kya hain, aur low ya high better cooler mean karta hai?

°C/W, temperature differences ke liye K/W se identical; low better hai — har watt par thoda temperature rise.

TDP ka

P_{total}

se kya relation hai, aur yeh absolute worst case kyun nahi hai?

TDP maker ke chosen benchmark workload ke under steady state par

P_{total}

hai; stress tests, overclocks, aur turbo bursts isse exceed kar sakte hain.

Thermal capacitance kya hai aur yeh chip ko briefly TDP exceed karne kyun deti hai?

Woh heat jo mass ko 1 °C rise karne ke liye absorb karni hoti hai; yeh temperature rise delay karti hai, toh short spikes load drop se pehle sirf curve par partway tak chadh paate hain.

R_{θ, JC}

R_{θ, CS}

R_{θ, SA}

saath mein kyun add hote hain?

Heat unse series mein flow karti hai jaise ek chain mein resistors se, aur series resistances add hote hain.

T_{j}

T_{ambient}

, aur

T_{j,max}

mein se har ek kya refer karta hai?

Silicon junction temperature, surrounding air temperature, aur maximum junction temperature allowed throttling se pehle.