Tony,
Can you explain the
meaning of these numbers?? Does a lower number mean the hardware is
better able to dissipate heat or simply has more thermal mass for the active
device to heat?? Any idea why metal is lower for BS170 but not for
TN0110??
I'm also a bit confused by
your term "max heatsink". ?What is "max heatsink" if not the fiber or
metal hardware you tested...did you also test with some kind of custom
heatsink?? If so, it would seem that this heatsink is doing something
dramatically different than the typical hardware whether metal or
fiber.
?
?
Bill
W2EB
East
Syracuse, NY
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I ran tests with fiber washer/nylon screw and also with metal washer/metal
screw. I also ran the TN0110.
Some experimental noise is evident I think but it is too big of a pain to redo
everything. Hopefully some useful insight can be gained from this.
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| Temperature rise
at center of identical heatsinks in degrees C |
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| attached to the
respective location |
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Case |
Drain |
Source |
Gate |
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total |
| BS170 max
heatsink |
4.5 |
3.7 |
2.4 |
1.9 |
|
12.5 |
| BS170 Fiber
Washer |
3.8 |
2.4 |
2.1 |
1.4 |
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9.7 |
| BS170 Metal
Washer |
3.1 |
2.5 |
1.8 |
1.3 |
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8.7 |
| TN0110 max
heatsink |
4.1 |
3.2 |
1.6 |
1.4 |
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10.3 |
| TN0110 Fiber
washer |
3.3 |
3.3 |
1.6 |
1.4 |
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9.6 |
| TN0110 Metal
Washer |
4 |
3.6 |
1.8 |
1.5 |
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10.9 |
| TN0110 Reverse
metal washer* |
3 |
3.8 |
1.6 |
1.6 |
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10 |
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| *Flat side
against washer, round side against heatsink |
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Tony
AD0VC
Very nice experiment, Paul
Nice to see some real experimental
data.?
I agree with Paul AI7JR, it would perhaps be
interesting to measure with only the flat of the transistor face against the
copper, since practically in a transceiver the curved part of the body is not
touching the copper. I don't
think there's any problem with the?measurements though; all the copper
plates are the same size with the same dissipation to the environment so it's
a reasonable relative comparison.
73 Hans G0UPL
On Thu, Sep 12, 2024 at 7:47?AM Paul - AI7JR via
?<paul.hanchett=
[email protected]> wrote:
I wonder if it tells what we want to know...
"Wrap the BS170 case with copper tape and solder it to another copper
plate."
In the QMX, only the flat side is connected to the heat sink... (Assuming
the washer and screw aren't very significant!) If that were taken into
account, heat extraction via the case and via the drain lead might be more
comparable, maybe even swapped?
You're making the assumption that temperature at the measurement point is a
proxy for power flow on the path. But the actual temperature is a function of
the thermal resistance from the measurement point to the environment...
It seems to me that you'd need to standardize the thermal resistance of
what you attach the measurement points to, in order to measure relative power
flow.
This is giving me a headache! Am I making it harder than it has to be?
Paul -- AI7JR
On 9/11/24 20:42, Sandy via ?wrote:
Hey Tony - That is an interesting result. There is no substitute for actual
measurement. This suggests that case contact with the pad is important. I
always install the BS170s first with the screw and washer ensuring they are
all flat and only then solder
in place. Thanks for your efforts! Sandy KB3EOF
On 9/11/24 22:18, mux_folder2001 via ?wrote:
I have attached a PDF file that describes an experiment with the goal of
determine where the heat flows in a BS170. The PDF contains pictures of the
fixture and a graph of the results. The essence of it is that, given equal
opportunity, heat will flow as follows:
-
Best flow is through the case.
-
Second best flow is the drain lead.
-
A distant third is the source lead.
-
Last is the gate lead.
The graph will give you a sense of how much difference there is between
them.?
The transistor is configured in a DC circuit and is dissipating 767mw
continuously in the test. I should have put that in the PDF file but I forgot
to.
Tony
AD0VC
--
Paul -- AI7JR
