Fan control for a ceiling mount flat TV monitor

The thermal design of a fan control circuit for use in a ceiling mount Flat TV monitor is discussed. The objective of using the fan control is to lower the noise from the Flat TV monitor to a level that is suitable for living room use. Furthermore the circuit is used as a protective measure for over temperatures. From an analysis of the requirements it follows that the fan control circuit needs a certain amount of hysteresis to remain stable. Technical and end-customer requirements are translated into so-called robust design requirements for the fan control circuit. Robust requirements take the effect of component tolerances on the functioning of the circuit into account. The spread in several circuit designs is evaluated as a function of component tolerances, using "Monte Carlo" simulations. Finally, the best design is chosen and the circuit is tested in the climatic room. The final test shows that the design is successful: no oscillations occur.