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Old 22nd May 2004, 08:41 PM   #1
Wagener is offline Wagener  South Africa
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Default sequence of the 4 power transistors on heatsink

Does it matter in what sequence and arangement I place the power transistors?

There are four (2 x MJ15003 and 2 X MJ15004) on each heatsink.

Can I place 2 MJ15004 next to each other and so on or must I place one MJ15003 and then a MJ15004?
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Old 22nd May 2004, 08:46 PM   #2
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As to my knowledge, you can place them as you like....
These are output devices, and a small thermal difference shouldn't matter
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Old 23rd May 2004, 12:54 PM   #3
djk is offline djk
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Leach goes two and two with the four bias diodes between. Its not a big deal.

http://users.ece.gatech.edu/~mleach/...hics/htsnk.gif
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Old 23rd May 2004, 03:50 PM   #4
Eva is offline Eva  Spain
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For better current sharing and bias stability it's preferable to have all NPN devices together and all PNP devices together also. You may use two electrically isolated independent heatsinks, one for NPN and other for PNP, and then no isolation will be required between the transistors and the heat sink

Both sets of transistors will dissipate the same power and will tend to be at the same temperature [except when heat sinks are of different sizes or receive different air flows] so compensation diodes may be all placed in one of the heat sinks

If you have just a single piece of heatsink then you only have two options : Cut it in two smaller pieces or electrically isolate transistor cases and screws from the heatsink
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Old 23rd May 2004, 06:52 PM   #5
lucpes is offline lucpes  Europe
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To ensure better device temp matching place identical devices closer to each other - what Eva said
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Old 24th May 2004, 04:27 AM   #6
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Default Eva

Please tell me more about your concerns.....
I really can't see the problem, unless the output devices are placed far apart....

The most critical part is to have the bias transistor (or diodes) placed in the "middle" to be sure that this reaches the averige temp. of the heatsink....
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