The increasing performance and integration of electronic components has not only enabled greater equipment functionality, but often delivers this in smaller and smaller form factors. Associated with this trend is the expectation that power supplies will also become more compact. Initially this demand was addressed by the adoption of switch-mode technology, but the continuing trend has led to increased power densities. Part of the remedy for this is to use higher switching frequencies and more efficient designs. However, the inescapable conclusion is that there will always be a need for effective thermal management in power electronics. In an ideal world all the energy input to a power supply would be converted to useable electrical power at the output. Unfortunately real life systems incur losses, and in a power supply, some energy is consumed by the internal electronics and converted into heat. Key components that contribute to such losses are transformer cores and windings, power switches, current sense resistors, and filter capacitors with significant ripple current. Consequently power in equals the power out plus the power dissipated as heat. Often the power dissipated in a power supply is not directly stated but instead given indirectly in terms of its efficiency, which is the ratio of output power to input power where efficiency (η) equals the power output divided by the power input. Hence, knowing the efficiency of a given power supply design and the required output power the user can calculate the power loss, or power that must be dissipated as heat, as power dissipated equals power output multiplied by (1/η - 1). This calculation needs to be done under worst case load conditions, i.e., for the maximum anticipated load power. Clearly higher efficiencies equate to less heat that will need to be dissipated, easing the problem of removing this heat from the supply. Nevertheless, appropriate thermal management is still vital and can have a direct impact on the performance of a power supply. For example, electronic circuits often perform more efficiently at lower temperatures and will tend to dissipate less energy as wasted heat. The efficiency gains that can be obtained through effective cooling increase significantly as the power output of the overall system increases. Higher temperature operation can also have an effect on reliability. Systems that run cooler will have a lower probability of failing within a given time. These factors make it important to consider all possibilities when looking at the cooling options for power supply designs.