Hey Dr. K! Loved the video. Is there a textbook that talks about these considerations that you would suggest. Do not need detail, just a good source about power electronics and thermal considerations.
Thanks for the video Dr. k, I have a fundamental doubt, if by placing a heatsink we increase the thermal resistance of the final circuit (from the junction to the environment), according to the circuit model, why wouldn't it be better to leave it without that “additional resistance” of the heatsink? Clearly, it is better with the heatsink, but according to the model being used, it seems that it is not.
Hi Alvaro, great question. When you look at the datasheet for some devices there will be different listings for thermal resistance values. For example, you might find the thermal resistance from the junction-ambient and you might also see the thermal resistance from the junction-case. The latter will typically be a much lower value and this assumes that there is a heat-sink that will be attached to the case. The results is to find the total thermal resistance from the junction to the ambient and use that with the worst case ambient temp, power dissipation and junction temperature. Note that RJ-C + RCA(heatsink) is often less than RJC. Hope this helps. -Dr. K
Great video but if I may suggest a small correction, your thermal resistive circuit at @10:00, the 3rd resistance of R theta to heat sink is incorrect. It should be R case to ambiance. This way you can then calculate R theta to Ambiance by subtracting R1 (1.15) and R2 (0.5) giving you the required thermal resistance of the heat sink to "dissipate generate heat into the ambiance"
Actually, it should be "Film to Ambient" as the example assumes a thermal conductive film is placed between the case and the heatsink to improve thermal conductivity. The heatsink then has thermal resistance between the film and the ambient. Notice the film's thermal resistance is very low and could probably be ignored or included with the heatsink. The resulting analysis would just be the case-ambient resistance, which I am calling the heatsink. Typically, one would first use the junction-ambient thermal resistance found in the datasheet to check if a heatsink is even required. Sorry about any confusion. Thanks for watching. -Dr. K
Nice. However, for a more accurate analysis, the heatsink should be represented by a series connection of a resistor (K/W) and a capacitor for thermal capacitance (J/K).
EB1000, yes, absolutely. Also thermal capacitance should be added to the package as well. As mentioned in the intro this is a static model and a more complicated model would/should include the thermal capacitance. Thanks for watching. -Dr. K
I couldn't understand but when we will not use heat sink then junction temperature will be 85C + 2W*1.15C/W = 87.3C I know, i am wrong but can you please where i am doing mistake 😢😢😢?
Sir i have one question, why my İRF 530 N mosfet heat up when i gave 10volt between gate and source? The Output drain /source is not connect . I measure 40°C directly on the case.
Hi Monu, great question. Those datasheet specs assume you can keep the case at that exact temperature. Marinating the case at 25 degrees is no small feet and requires some type of cooling such as a heat-sink. If there is no heat-sink, then you will need to use the junction-ambient thermal resistance for calculations and that resistance is much, much greater than the junction to case resistance. Hope this helps answer your question. -Dr. K
Excellent presentation! Hope upload more vids!!
Yuchen, thank you for watching. -Dr. K
Hey Dr. K! Loved the video. Is there a textbook that talks about these considerations that you would suggest. Do not need detail, just a good source about power electronics and thermal considerations.
Thanks for the video Dr. k, I have a fundamental doubt, if by placing a heatsink we increase the thermal resistance of the final circuit (from the junction to the environment), according to the circuit model, why wouldn't it be better to leave it without that “additional resistance” of the heatsink?
Clearly, it is better with the heatsink, but according to the model being used, it seems that it is not.
Hi Alvaro, great question. When you look at the datasheet for some devices there will be different listings for thermal resistance values. For example, you might find the thermal resistance from the junction-ambient and you might also see the thermal resistance from the junction-case. The latter will typically be a much lower value and this assumes that there is a heat-sink that will be attached to the case. The results is to find the total thermal resistance from the junction to the ambient and use that with the worst case ambient temp, power dissipation and junction temperature. Note that RJ-C + RCA(heatsink) is often less than RJC. Hope this helps. -Dr. K
Very informative 👌
Great video but if I may suggest a small correction, your thermal resistive circuit at @10:00, the 3rd resistance of R theta to heat sink is incorrect. It should be R case to ambiance. This way you can then calculate R theta to Ambiance by subtracting R1 (1.15) and R2 (0.5) giving you the required thermal resistance of the heat sink to "dissipate generate heat into the ambiance"
Actually, it should be "Film to Ambient" as the example assumes a thermal conductive film is placed between the case and the heatsink to improve thermal conductivity. The heatsink then has thermal resistance between the film and the ambient. Notice the film's thermal resistance is very low and could probably be ignored or included with the heatsink. The resulting analysis would just be the case-ambient resistance, which I am calling the heatsink. Typically, one would first use the junction-ambient thermal resistance found in the datasheet to check if a heatsink is even required. Sorry about any confusion. Thanks for watching. -Dr. K
Awesome lecture! thanks a lot Dr.K.
You are welcome. Hope your design works well. -Dr. K
Nice. However, for a more accurate analysis, the heatsink should be represented by a series connection of a resistor (K/W) and a capacitor for thermal capacitance (J/K).
EB1000, yes, absolutely. Also thermal capacitance should be added to the package as well. As mentioned in the intro this is a static model and a more complicated model would/should include the thermal capacitance. Thanks for watching. -Dr. K
can you explain how to calculate the surfice aerea of an aluminium heat sink according to its thermal resistance to ambient. thanks in advance.
Thank you
Sir it's very good Work 👍, what's the
Song name of the beginning in your Video?
Serdar, thank you. The bumper music is "Drive In" by Track Tribe ruclips.net/video/CtiObueY_Zk/видео.html Thanks for watching. -Dr. K
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I couldn't understand but when we will not use heat sink then junction temperature will be 85C + 2W*1.15C/W = 87.3C
I know, i am wrong but can you please where i am doing mistake 😢😢😢?
You will need the following equation Tj - 85 = 2W*(1.15C/W + Rthermal_Heat_sink)
Sir i have one question, why my İRF 530 N mosfet heat up when i gave 10volt between gate and source? The Output drain /source is not connect . I measure 40°C directly on the case.
When the device is capable for 130W power dissipation for tc =25C
80W power dissipation for tc =85C
Then why we need of heatsink for 2W dissipation ?
Hi Monu, great question. Those datasheet specs assume you can keep the case at that exact temperature. Marinating the case at 25 degrees is no small feet and requires some type of cooling such as a heat-sink. If there is no heat-sink, then you will need to use the junction-ambient thermal resistance for calculations and that resistance is much, much greater than the junction to case resistance. Hope this helps answer your question. -Dr. K