Heat sink for TO-220F FQPF47P06-D - Page 1
Forum section: electronics / beginners

author: Vindhyachal.takniki
author_rank: Frequent Contributor
timestamp: December 25, 2020, 03:06:49 pm
content: I have ordered FQPF47P06-D, (my mistake) have 10Amps of current to pass.The mosfet is like this from back side. If i connect this type of heat sink behind will it be able to dissipate heat? and help to handle 10Amps?

author: wraper
author_rank: Unknown
timestamp: December 25, 2020, 03:15:14 pm
content: Current itself does not say anything about amount of dissipated heat. It's possible to pass 100A current and dissipate barely any heat, or pass 0.1A and dissipate tons of heat. It's all about power (V*I).

author: Siwastaja
author_rank: Super Contributor
timestamp: December 25, 2020, 03:41:05 pm
content: Assuming it's on/off switch (no fast PWM) so ignoring any potential switching losses, all loss is due to current flowing through Rds_on of the MOSFET.P = I^2 * RRds_on at 100 degC is approx. 1.5x headline figure (26mOhm per datasheet), soR = 26mOhm * 1.5 = 39mOhm (you can come back and iterate this assumption after you have calculated the actual Tj so have idea if it runs anywhere close this. Datasheets do have curves how Rds_on varies depending on Tj)P = (10A)^2 * 39 mOhm = 3.9WAssuming ambient temperature (this may be inside your case!) of 60 degC and maximum Tj=120 degC (don't try to operate it at Tj=175 degC even if datasheet says it's possible), so dT = (120-60) degC = 60 degC.So you need to get total Rth of the complete system to below 60 degC / 3.9W = 15.4 degC/W. Per datasheet, RthJ-A without heatsink is 62.5 degC/W, too much, so obviously youdoneed a heatsink.Total Rth is the sum of all thermal interfaces, from the junction, to finally ambient air.Then, per datasheet, RthJ-C - from juction to the MOSFET case - is 2.42 degC/W. Allowing another 2 degC/W of resistance for thermal interface material (going from MOSFET case, to the heatsink, use very thin pad, or thermal grease), your heatsink needs to be rated at15.4 degC/W - 2.42 degC/W - 2 degC/W = 11 degC/W or lower (better).If available, look up the datasheet for the heatsink you have, and you have your answer.Eyeballing it, Ithinkit is more than enough.Or you can open up Digikey/similar parametric searches and look heatsinks around 11 degC/W and look at their images and measurements and compare to what you have.Finally, try it out, measure the temperature. When in doubt, add extra margin.

author: Vindhyachal.takniki
author_rank: Frequent Contributor
timestamp: December 26, 2020, 02:59:34 pm
content: Issue is back side of mosfet, which is to be connected to heat sink is not metal, its some plastic type, so this I fear will that be able to transfer heat.this is mosfet:https://www.onsemi.com/products/discretes-drivers/mosfets/fqpf47p06

author: langwadt
author_rank: Super Contributor
timestamp: December 26, 2020, 03:16:39 pm
content: Quote from: Vindhyachal.takniki on December 26, 2020, 02:59:34 pmplastic just means it is isolated, so while it is a bit worse than metal you don't have to worry about needing to isolateit from the heatsink. 10A in 26mOhm in only 2.6W

author: wraper
author_rank: Unknown
timestamp: December 26, 2020, 03:18:16 pm
content: Quote from: Vindhyachal.takniki on December 26, 2020, 02:59:34 pmThe issue is you still did not say if it's acting like a switch or in linear mode, how large is gate voltage. As of thermal resistance, you have a datasheet for that. But again, you need to know power dissipated to calculate anything.

author: Siwastaja
author_rank: Super Contributor
timestamp: December 26, 2020, 03:49:18 pm
content: The datasheet RthJ-C takes the plastic case into account. If it was metal, it would be something like 0.5 degC/W or even lower. Just follow my calculation above.Indeed, I assumed the FET is driven properly on (so Vgs = -10V).

author: Benta
author_rank: Super Contributor
timestamp: December 26, 2020, 05:13:25 pm
content: Quote from: Siwastaja on December 26, 2020, 03:49:18 pmVery optimistic. TO-220 is normally 0.8...1 K/W, TO-220F around 2.5 K/W.

author: Siwastaja
author_rank: Super Contributor
timestamp: December 28, 2020, 07:45:24 am
content: Quote from: Benta on December 26, 2020, 05:13:25 pmRandom TO220 LM317 datasheet from TI pulled off the Interwebz says 0.1 K/W. Random TO220 IRFZ44 datasheet says 0.5 K/W typical.Always check the datasheets, of course.

author: wraper
author_rank: Unknown
timestamp: December 28, 2020, 07:51:13 am
content: Quote from: Siwastaja on December 28, 2020, 07:45:24 amIt's a typo. Figure is not real and 40 times smaller than for single gauge TO-220, and 10 times smaller than for TO-263

author: magic
author_rank: Super Contributor
timestamp: December 28, 2020, 08:34:23 am
content: LM317 has to be an error indeed, all manufacturers rate LM317 RthJC pretty poorly.Less than 1K/W is not uncommon for power MOSFETs in TO220, while the best BJTs tend to top out at 1K/W.

author: Siwastaja
author_rank: Super Contributor
timestamp: December 28, 2020, 07:17:24 pm
content: Maybe a bit OT, but for the record, the RthJ-C of a few non-isolated TO-220 MOSFETs, randomly picked from Digikey:IRF9Z34NPbF max 2.2 K/WPSMN027-100PS typ 0.8 max 1.46 K/WFQP30N06L max 1.90 K/WSPP17N80C3 max 0.6 K/W (note: isolated version max 3.6 K/W)CSD19533KCS max 0.8 K/WSo I agree it's likely a typo on the LM317 DS, maybe it's off by 10x and should read 1.0K/W, but OTOH, RthJ-C depends only on the die size and the process of bonding the die to the copper tab, so it's not completelyimpossibleto have 0.1K/W for a TO-220 device with a large die, for LM317 it is however unnecessary and unimportant to have such low thermal resistance because the real-world mounting resistance with thermal grease is around 0.5 K/W and it's damn hard to come up with heatsinks well below some 1 K/W so the external factors are dominating over the RthJ-C of an nonisolated TO220 device.For the OP, it's important to recognize that the package plastic isincludedin the RthJ-C number and doesn't need to be taken account again. If the same MOSFET would be produced in a non-isolated package, the number would be far less than the 2.42 K/W of this isolated part, correcting my earlier statement, likely between 0.5 and 1.5 K/W.BTW, 2.42 K/W is an exceptionally good number for an isolated package. If you need isolation, you won't get much better using nonisolated TO220 + isolated silpad/greased mica.