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 Posted: Feb 22, 2012 - 06:26 PM |
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Joined: Aug 01, 2003
Posts: 256
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I need to choose the best thermal condition for a schottky diode. I have always believed that to220 has better thermal resistance junction to case than smd variant Dpak to252AA . But very suprisingly the TO220 component from multicom has(given in datasheet) Tjc 3.4 C/W . The other diode (vishay) with DPAK (to252AA) has only Tjc=2 C/W
is it a general rule or are there quality differences between manufactorers. (multicomp v.s vishay)
incal99 |
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We dream of a world where current does not need the voltage to flow.
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Posted: Feb 22, 2012 - 06:51 PM |
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Joined: Oct 05, 2006
Posts: 2297
Location: Poland
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| Why do you think a package outline standard has anything to do with thermal resistance? |
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No RSTDISBL, no fun!
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Posted: Feb 22, 2012 - 08:44 PM |
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Joined: Oct 30, 2002
Posts: 5727
Location: The Netherlands
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| You know the lower the number the better it is? The DPAK is a clear winner. |
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Posted: Feb 22, 2012 - 09:56 PM |
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Joined: Nov 22, 2002
Posts: 12193
Location: Tangent, OR, USA
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That is junction to case. You still have case to ambient. I'd (almost) bet that TO220 has better case to ambient. Often, that is the dominant component of the total thermal resistance.
Jim |
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Jim Wagner
Oregon Research Electronics, Consulting Div.
Tangent, OR, USA
"The only thing standing between us and victory is defeat" P.G.Wodhouse in Wooster & Jeeves series
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Posted: Feb 23, 2012 - 12:46 AM |
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Joined: Feb 19, 2010
Posts: 509
Location: Montreal, QC, CA
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| In the case of a DPAK package most of the heat is dissipated from the copper connected to the bottom pad. That is why they are more efficient than TO220 without heatsink. The board copper area acts as very large area heatsink and takes almost no extra space. If you do not connect the bottom pad thermally with the board, or if the copper area is too small, the TO220 will win out because it has more exposed metal to free air. |
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Posted: Feb 23, 2012 - 10:03 AM |
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Joined: May 01, 2003
Posts: 580
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| I always try to use DPaks with a couple of centimetres square copper underneath, on both sides, with a number of 1mm holes linking the 2 planes. Works well.... |
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Posted: Feb 23, 2012 - 07:13 PM |
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Joined: May 15, 2004
Posts: 62
Location: Dallas, Texas
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Case to ambient only takes into account the physical package in free air and could be dominated by proper heat sinking.
Randy |
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Posted: Feb 23, 2012 - 07:33 PM |
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Joined: Aug 01, 2003
Posts: 256
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ka7EHK: IMHO I agree with K5HJ Tjc is more important because I will never need to calculate or use the value Tja as I use such high power devices always with heat sink.
I am planning to use the diodes on a 1 layer aluminium PCB. internal layer is not FR4 but pure aluminium on top of aluminium there is a electric isolating but thermally efficient polymer. over this polymer copper is coated (which will be etched as pcb)
The aluminium layer is also directly connected to a very large heatsink.
According to this description , I plan to use dpak or to220, But evenif I use To220 i will clip the legs and use the TO220 as smd device because aluminium boards does not support vias or holes.
My final question is when i clip the legs and use both DPAK or TO220 on the alu pcb as quasi smd devices why should DPAK perform much far better (upto 2 times better) . Because the packages in this form (both smd converted) have nearly the same layout (both have a large base that is leaded to a large copper area that is also connected to an aluminim layer.
Is the internal base plate of DPAK physically different than TO220?
best regards.
incal99 |
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We dream of a world where current does not need the voltage to flow.
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Posted: Feb 23, 2012 - 10:03 PM |
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Joined: May 15, 2004
Posts: 62
Location: Dallas, Texas
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Usually the Tjc of the TO220 and Dpak packages are the same. There must be something else going on here between the two manufacturers such as die geometry. Are the electrical specs the same for both?
Randy |
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