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Old 10th September 2010, 01:45 PM   #1
frags is offline frags  Canada
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Default Heatsink at 2SJ109 in Aleph J

Does anybody use a heatsink at 2SJ109 in Aleph J. For me it looks like this device is getting pretty hot. In the closed case with ambient temperature inside 45C the transistor case temperature reaches 70C after 1 hour. I guess junction temperature is 75-80C. Or is it OK?
I'm using PCBs from Peter Daniel where 2SJ109 is pretty close to R5 which is getting quite hot.

Additionally what was the reason to connect R5 to negative rail? It could be connected to the ground with a value of 1.7K to get the same current through the zener but the power dissipation could be three timer lower at that resistor.

Last edited by frags; 10th September 2010 at 02:02 PM.
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Old 10th September 2010, 03:51 PM   #2
Zen Mod is offline Zen Mod  Serbia
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heatsink - if you think that's necessary

R5 - think about CMRR
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Old 10th September 2010, 04:06 PM   #3
frags is offline frags  Canada
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Zen Mod,

There is the capacitor across the zener anyway.
I'll check the behavior in a simulation software.

Thanks.
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Old 10th September 2010, 04:57 PM   #4
EUVL is offline EUVL  Europe
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Yes I have a 2SJ109 heatsink on my AX.

Patrick
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Old 10th September 2010, 05:06 PM   #5
frags is offline frags  Canada
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Patrick,

Could you post a picture how you've mounted heatsinks and what kind they are?

Thanks.
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Old 10th September 2010, 05:20 PM   #6
EUVL is offline EUVL  Europe
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Tomorrow.

Patrick
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Old 11th September 2010, 12:29 AM   #7
frags is offline frags  Canada
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I've changed R5 to 2.2k connected to the ground. As the result I got about 7C temperature drop on JFET case (from 70C to 63C in Peter Daniel's PCB) and C4 (before C4 could give a skin burn when touched). No any changes in the ripple of CCS and therefore in amplifier performance was discovered. So, highly recommended.
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Old 11th September 2010, 05:27 AM   #8
EUVL is offline EUVL  Europe
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TO92 has typically 80~100C/w junction to case, so you can calculate the junction temperature from power and case temperature.

I try to keep mine below 100C for reliability reasons.


Patrick
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Old 11th September 2010, 06:06 AM   #9
EUVL is offline EUVL  Europe
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As promised.

Patrick
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Old 11th September 2010, 06:02 PM   #10
frags is offline frags  Canada
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Very nice. Thank you, Patrick.
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