[ 13 ]lab · simulations

Thermal: temperature rise and heatsinks

A steady-state chain from power through junction-case, case-sink and sink-ambient resistance to the junction temperature and its margin to the part's rated maximum, plus a one-pole thermal-RC warm-up curve.

lab · sims · thermal

Gear train →Ratio, direction, planetary. Stepper torque/speed →Pull-out torque curve. Battery / power budget →Duty cycle to runtime. Circuit basics →Ohm's law, dividers, LEDs, RC.

The chain [ live ]

warm-up transient, T_j(max) dashed

—junction temperature

—margin to T_j(max)

—temperature rise

—total thermal resistance

—thermal time constant

Power & ambient

power dissipated (W) ambient temperature (°C) T_j(max) (°C)

Thermal resistance chain (°C/W)

θ junction-case θ case-sink θ sink-ambient

Thermal mass

thermal capacitance (J/°C)

Assumptions and limits. The three θ values are typical or assumed for the small QFN driver and clip-on heatsink in the presets, not measured on this owner's own hardware - see AGENTS.md's stance on labelling what is unverified. Steady state is linear (temperature rise is directly proportional to power - no derating of θ with temperature, no radiative or forced-air effects beyond what is baked into the assumed sink-ambient number). The transient is a single-pole RC warm-up, which is a fair approximation for a lumped thermal mass but ignores the separate, much faster time constant of the junction-to-case path. The driver's own dissipation (0.6/1.2 A presets) comes from 2 × I² × R_DS(on) with an illustrative 0.3Ω per half-bridge; the linear-regulator preset's power is the exact (V_in-V_out)×I instead.