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Old 30th September 2012, 04:40 AM   #1001
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As arm as it should for being biased at 150mA. I didn't measure it. There as a time it got hot due to oscillation but not after I fixed it.

I didn't do the cap shield trick ith Fetzilla, in case you misunderstood.
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Old 30th September 2012, 09:03 AM   #1002
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Syk,
your FetZilla will run too hot because your heatsink is the wrong shape, the wrong size, in the wrong orientation and is far too thin.

Choose a proper heatsink for the duty !
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Old 30th September 2012, 09:23 AM   #1003
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Quote:
Originally Posted by AndrewT View Post
Syk,
your FetZilla will run too hot because your heatsink is the wrong shape, the wrong size, in the wrong orientation and is far too thin.

Choose a proper heatsink for the duty !
Hi Andrew,
Currently this is the largest heat sink available from the local store here in HK , it measures 12" x 4.5" x 1.25". I will order a set with case after the golden week holiday, will you kindly help to determine what will be the proper type and size ?

Thanks
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Old 30th September 2012, 09:27 AM   #1004
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assume a Ta and Ts for the dissipation you need.
From there you can determine the required Rth s-a to which you have applied the necessary deltaT de-rating.

But you must ensure that your de-rating takes account of the thickness of the backplate. This is not usually specified by the heatsink manufacturer due to the way they all assume isothermal conditions for the entire backplate area.
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Old 30th September 2012, 09:48 AM   #1005
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Mine runs after hours between 38 and 41 and can keeps my hands on the sinks the hole time.
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Old 30th September 2012, 10:15 AM   #1006
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Mine runs after hours between 38 and 41 and can keeps my hands on the sinks the hole time.
I can touch it butting is quite warm.
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Old 2nd October 2012, 09:34 AM   #1007
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Something bad just happened.
Click the image to open in full size.

Click the image to open in full size.

Both channels were working fine on the start-up test before I put them in a temporary case except being a little hot. Today I put them both in a case and connect to a power transformer. After I switch-on the power, a not too loud hum and spark came off from both PCB, it looks like R22 and R24 were blown but everything else looks ok, the fuse still ok. I examine the wiring and discovered that ( I am using only one transformer, a 2 x 26VAC 250VA R-Core) the V+ AC input from left channel and the V- AC input were connecting to the same secondary winding. Could this be the cause to the blown resistors ? What to do next?
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Old 2nd October 2012, 10:23 AM   #1008
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Pretty hard to get the magic smoke back in those little resistors.
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Old 2nd October 2012, 10:24 AM   #1009
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Am I wrong, or you were running out of solder when setting those elcos?
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Old 2nd October 2012, 10:32 AM   #1010
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I intentionally use less solder there so that I can replace those caps easy later on. R22 and R24 will be replaced.
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