A survey of the thermal stability of an active heat sink

In cases where forced convective cooling alone is inadequate, or where the size of the housing limits the heat sink's dimensions, ICs can be cooled using an active heat sink. Compared to a classical finned heat sink, it can benefit from a substantial size reduction or from an important enhancement of the heat transport from the IC to its surroundings. The active heat sink's function is based upon a Peltier-effect cooling system. The active heat sink controls the IC's thermal resistance to its surroundings. The Peltier-effect heat pump is a non-linear system. Therefore, surveys of the system's stability are far from evident. Thermo-electric models for both the Peltier-effect heat pump and a NTCR (Negative Temperature Coefficient Resistance) temperature sensor are presented. These are linked to thermal models for the IC packaging and a finned heat sink on one hand and to electronic models for the controlling circuit on the other hand. Simulation show non-linear thermal behaviour and system instabilities according to the power load on the IC, to the forward amplification of the circuit, but also to the ambient temperature change. The latter phenomenon occurs after power-on of the whole device of which the IC is a part. The theoretical results were confirmed by infrared thermographic measurements on a self constructed active heat sink.