EC-5.6 Thermal Behaviour, and Why Everything Drifts
You can predict which way a parameter moves when a circuit warms up, explain where thermal noise comes from, and size a heat path well enough to keep a part inside its rating.
Before:nothing requiredUnlocks:PE2-5. MEMSEC-6. Semiconductor Devices and Device Models
Nothing in electronics holds still. Resistance, gain, threshold voltage, oscillator frequency and offset all move with temperature, and a design that ignores it works on the bench and fails in a car. This topic collects the thermal behaviour that later subjects each assume separately: which way each parameter drifts and why, where the noise floor comes from, and how heat actually leaves a device. It is short because it is a habit rather than a body of theory.
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Temperature coefficient, and reading a datasheet line honestly
A coefficient says how much a parameter moves per degree, and multiplying it by the real temperature range is the only way to know whether that matters. A part specified at twenty-five degrees tells you very little on its own.
NPTEL: Physics of Materials · CourseWhich way things drift, and the two that move opposite ways
A metal's resistance rises with temperature and a semiconductor's falls, which is why a resistor and a diode drift against each other. Circuits are sometimes built to exploit that cancellation deliberately.
Thermal noise, and why it sets a floor nothing can go below
Charge carriers move randomly because they are warm, and that random motion appears across any resistance as a voltage. The floor it sets depends only on temperature, resistance and bandwidth, so the only ways down are cooling or narrowing.
NPTEL: Fundamentals of Electronic Materials and Devices · CourseShot noise, and how it differs from the thermal kind
Current across a junction arrives as discrete carriers at random moments, so it fluctuates in proportion to the current itself rather than to temperature. Knowing which noise dominates decides whether reducing current helps or hurts.
Thermal resistance, and treating a heat path as a circuit
Heat flow behaves like current, temperature difference like voltage, and each interface adds a resistance, so a heat sink is sized with the same arithmetic as a potential divider. Junction temperature is what the rating is really about.
Thermal runaway, and the loop that destroys a part
If warming a device increases the current through it, that current warms it further, and the loop can end in destruction. Recognising a positive thermal loop before building the circuit is the whole point of this topic.
NPTEL: Physics of Materials · Course
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