Approach to the study

AN2842

14/22

Doc ID 15110 Rev 1

the same heat-sink, it is important to know their thermal distribution. In fact, two devices

connected in parallel, but with different working temperatures, have different behaviors. The

different working temperatures could be caused by other factors (another device mounted to

the same heat-sink, different air flow by fan, etc.). Many PFC systems use the same heat-

sink for power device and diode. In this case, the power device close to the diode shows a

working temperature higher than the other. If the circuit does not have a feedback system,

an increase in the temperature could cause failure of the system. In

Figure 16, details of this

phenomenon are shown.

Figure 16. Instant of failure

In the introduction of this document, the study was divided into two areas: the first, which

has been explored in the previous paragraphs, is an analysis of current imbalances due to

the external parameters of a power device. The second is an analysis of the intrinsic

characteristics of a power MOSFET, which are predominant in the mismatching. In this

parameters.

2.6

The following analysis refers to a system with two devices connected in parallel based on

the schematic in

Figure 17.