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Old 5th May 2012, 11:17 AM   #541
atupi is offline atupi  Romania
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I have installed the IRFP240 and is working fine but but the last 3 transistors close to output (the 2 sk170 and bipolar) are running very hot, almost impossible to touch. Maybe not all three of them are hot but is hard to say as they are very close on the pcb.
The negative rail seem to be much hotter than the other one. On the three 68ohm paraleled resistors i have 3.8v on the negative and 2v on the positive side.

Last edited by atupi; 5th May 2012 at 11:28 AM.
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Old 5th May 2012, 12:26 PM   #542
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I guess you have shorted one of the transistors. Are the IRF's isolated from chassis?

I wonder if the IRF's are shorted, and or bipolars.

Do you have any extra?
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Old 5th May 2012, 12:36 PM   #543
atupi is offline atupi  Romania
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I have some spare transistors. The IRF's are totally isolated from chassis as i dont have a chassis yet
Both regs are working but now i see one went a bit up to 12 v even if in the first minutes they where very close with less than 0,5v difference.

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Old 5th May 2012, 02:38 PM   #544
Salas is offline Salas  Greece
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With what kind of current and sinking are they running now?
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Old 5th May 2012, 08:17 PM   #545
atupi is offline atupi  Romania
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No sinking for the IRF's as they are slightly warm. I don't know to answer to the question regarding current. The strange thing is that acros leds i have a bigger voltage than theoretically they stabilize.
Across three leds string (ccs) i have 7.8v
The 100ohm resistors are also hot.

Last edited by atupi; 5th May 2012 at 08:43 PM.
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Old 5th May 2012, 08:57 PM   #546
Salas is offline Salas  Greece
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Better change the TO-92s related to the 100 Ohm path.
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Old 5th May 2012, 09:00 PM   #547
atupi is offline atupi  Romania
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Can you be more precise please?
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Old 5th May 2012, 09:02 PM   #548
Salas is offline Salas  Greece
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There is a Jfet connected to that 100 Ohm on your version right? Which board version and a photo would help too.
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Old 5th May 2012, 09:12 PM   #549
atupi is offline atupi  Romania
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For my build i have followed first posts of this thread: Building a symmetrical psu B1 buffer

Across Jfet close to 100ohm i have a voltage of 0.7V so seems to be ok i would say.
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Old 5th May 2012, 10:05 PM   #550
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Is Q5 cool? There are indications of over current by your findings in #545.
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