DETERMINING PEAK TEMPERATURES IN SHORT TERM OVERLOADS HELPS TO AVOID SYSTEM FAILURE

摘要

Many high power electronic systems are subjected to short-term power loads over and above their normal steady-state operating conditions. These conditions typically occur during start-up or during heavy usage periods. Elevators, escalators and other "people movers" are prime examples. The effect of these additional loads on the temperature of the power semiconductor junction can have serious affects on the life and reliability of the system. The mass of the heat sink, material type, overall heat transfer coefficient and the amount of cooling surface are all factors in the speed of response to sudden, low duty-cycle power inputs. In most design efforts additional heat loads can be anticipated and compensated for by knowing duty cycle and application. Knowing a system will have heavy, short term use periods requires that these heat loads must be controlled and dissipated without exceeding safe design levels for the semiconductors and the system as a whole. In most cases, due to it's thermal capacity and size, the heat sink will act as a thermal accumulator providing a reservoir into which energy can be placed quickly and dissipated slowly while maintaining acceptable temperature levels.