Thermal Calculator

Calculate junction temperature, thermal resistance, and heatsink requirements for electronic components

Input Parameters

Power Dissipation Pd (W)

Ambient Temperature Ta (°C)

25°C40°C50°C70°C85°C

θJC (Junction-to-Case) (°C/W)

θCS (Case-to-Sink) (°C/W)

θSA (Sink-to-Ambient) (°C/W)

Max Junction Temperature Tj_max (°C)

125°C150°C175°C

Package Presets

SOT-23SOT-223TO-92TO-220TO-220 + HeatsinkTO-247QFN-32 (5x5)QFP-48BGA-256DIP-8

θJA (Total)

62.00 °C/W

θJC + θCS + θSA

Tj (Junction Temp)

87.0 °C

SAFE

Tc (Case Temp)

85.5 °C

Ts (Sink Temp)

85.0 °C

Maximum Allowable Power

2.016 W

Pd_max = (Tj_max - Ta) / θJA = (150 - 25) / 62.00

Temperature Rise ΔT

62.0 °C

ΔT = Pd x θJA = 1 x 62.00

Thermal Resistance Chain Diagram

  Junction          Case             Sink            Ambient
     Tj                Tc                Ts               Ta
  87.0°C            85.5°C            85.0°C           25.0°C
     │                 │                 │                │
     ├──── θJC ────────┤──── θCS ────────┤──── θSA ───────┤
     │  1.5 °C/W     │  0.5 °C/W     │  60.0 °C/W   │
     │                 │                 │                │
     ├─── ΔT: 1.5°C ──┤─── ΔT: 0.5°C ──┤─── ΔT: 60.0°C ─┤
     │                                                   │
     └────────── θJA = 62.00 °C/W ─────────────┘
                  ΔT(total) = 62.0°C

     Power: Pd = 1 W
     Tj = Ta + Pd x θJA = 25 + 1 x 62.00 = 87.0°C

Safe Operating Area

0°CSAFE (<105°C)WARN (<135°C)DANGER150°C

Current Tj: 87.0°C / 150°C (58.0%)

Package Thermal Resistance Comparison(Pd = 1 W, Ta = 25°C)

Package	θJC	θCS	θSA	θJA	Tj	Pd_max
SOT-23	80	50	100	230	255.0°C	0.543 W
SOT-223	15	5	40	60	85.0°C	2.083 W
TO-92	50	30	120	200	225.0°C	0.625 W
TO-220	1.5	0.5	60	62	87.0°C	2.016 W
TO-220 + Heatsink	1.5	0.5	8	10	35.0°C	12.500 W
TO-247	0.5	0.3	40	40.8	65.8°C	3.064 W
QFN-32 (5x5)	5	5	25	35	60.0°C	3.571 W
QFP-48	10	5	30	45	70.0°C	2.778 W
BGA-256	3	2	15	20	45.0°C	6.250 W
DIP-8	30	10	60	100	125.0°C	1.250 W