I am currently designing a heatsink to handle the heat from a diode and a MOSFET. I can pick either two or one heatsink, and my goal is to minimize the volume of the heatsink.
Intuitively I would think that one heatsink for both the MOSFET and the diode would lead to the least amount of volume, but my results show that two separate heatsinks (one for the diode and one for the MOSFET) results in the least amount of total volume, can this make sense? If so, I would appreciate it very much if someone could give an intuitive explanation of it.
To obtain my results I used the following procedure:
To obtain the R_ha=R_heatsink_to_ambient when MOSFET and diode share heatsink the following thermal equivalent circuit was used:
By calculating the heatsink temperature that guaranteed MOSFET and diode junction temperature lower than rated values R_ha was found.
When the diode and MOSFET did not share heatsink, the following thermal equivalent was used:
Then R_ha_diode and R_ha_mosfet was calculated to satisfy rated temperature of the diode and MOSFET. Here is where I think I am doing the procedure wrong, because the heat from the MOSFET does not influence the diode and vice versa.
By using heatsink data sheet I found the volume for different switching frequencies (the minimum feasible volumes were picked from the datasheet):
As you can see from the scatter plot in all cases where two heatsinks were used the total volume of the two heatsinks was smaller than using one heatsink. I am of course not asking if my numbers are correct what I am wondering about is:
- Is my result logical, does it make sense that the total volume is smaller with two heatsinks?
- Is the thermal modelling correct?