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Old 24th October 2012, 05:22 PM   #61
pdul is offline pdul  Denmark
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Thought so. Thank you.
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Old 24th October 2012, 05:54 PM   #62
studeb is offline studeb  United States
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Just remebered this thread, glad to see the assembly guide.
Well written, thanks.
Looking forward to the boards.
I do think that the "how much hfe for which grouping" is going to come up repeatedly unless some targets are given.
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Old 24th October 2012, 08:41 PM   #63
pdul is offline pdul  Denmark
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I have now succesfully mounted the powertrannies on the boards. It was fairly easy after all I did the following. First i mounted the heatsinks on the boards with 6 8*3mm screws, then i used a small amount of thermal goof, to glue the silicone pads to the transistors, then stuck them into the board one at a time, steering them in place by their legs from under the board with one hand and placing the clips with the other, then with one hand holding the transistor and clips in place and pressing it in with a little plier.
When all of them in place, turn the board around and solder.
Hope this will serve as inspiration to some of you who havent got to this point of assembly yet
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Old 24th October 2012, 09:07 PM   #64
hesener is offline hesener  Germany
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Quote:
Originally Posted by pdul View Post
I have now succesfully mounted the powertrannies on the boards. It was fairly easy after all I did the following. First i mounted the heatsinks on the boards with 6 8*3mm screws, then i used a small amount of thermal goof, to glue the silicone pads to the transistors, then stuck them into the board one at a time, steering them in place by their legs from under the board with one hand and placing the clips with the other, then with one hand holding the transistor and clips in place and pressing it in with a little plier.
When all of them in place, turn the board around and solder.
Hope this will serve as inspiration to some of you who havent got to this point of assembly yet
very good
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Old 24th October 2012, 09:37 PM   #65
pdul is offline pdul  Denmark
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Just one way out of many to do it, but it works
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Old 25th October 2012, 08:08 AM   #66
hesener is offline hesener  Germany
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Yes, I did notice (too late for my own build) that the clips come in two version: v1 needs to be pre-assembled, and v2 can be used afterwards like you describe.

GOOD NEWS is that all of you have v2 clips, facilitating the mounting. The assembly guide however kind of refers to v1 - not a problem as that way can be done with v2 clips just as well. So we are good...
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Old 25th October 2012, 08:25 AM   #67
hesener is offline hesener  Germany
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Default transistor matching

Hi all,

it seems that not everybody has a curve tracer or a DMM that can measure the current gain of the transistors. So here is a little circuit that can do that, see attached picture.

It works like this:
The battery has 9V, so the voltage across the 4.2M resistor is 8.3V, giving a base current of 2uA. If the transistor has a current gain of , say, 500, this translates into a collector current of 1mA. That will cause a voltage drop of 510mV at the collector resistor. Using a DMM to measure the voltage across that resistor, it should give you the current gain immediately (and if you would use a 500Ohm resistor, 1mV corresponds to a gain of 1).

As long as you do it quickly, the battery voltage will not change too much over the course of measuring a few hundred transistors, but you may want to check the voltage from time to time, and re-measure "known" transistors so you can compensate.

Best to use some socket or test fixture for the transistors,these are available from your favourite components supplier at little cost (e.g. TF183 from Fischer Elektronik)

Edit: "DUT" is of course the device under test.
Edit: For measuring the PNPs, simply reverse the battery
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File Type: jpg transistor matching.jpg (26.7 KB, 591 views)
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Old 25th October 2012, 10:40 AM   #68
Nick77 is offline Nick77  United States
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Join Date: Dec 2009
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Quote:
Originally Posted by pdul View Post
I have now succesfully mounted the powertrannies on the boards. It was fairly easy after all I did the following. First i mounted the heatsinks on the boards with 6 8*3mm screws, then i used a small amount of thermal goof, to glue the silicone pads to the transistors, then stuck them into the board one at a time, steering them in place by their legs from under the board with one hand and placing the clips with the other, then with one hand holding the transistor and clips in place and pressing it in with a little plier.
When all of them in place, turn the board around and solder.
Hope this will serve as inspiration to some of you who havent got to this point of assembly yet
Hoping a lot of build pics will start showing up.
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Old 25th October 2012, 11:42 AM   #69
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I have posted a circuit I have found on the intraweb on MPP a while ago
The circuit hesener has posted is perfectly fine (please don't get me wrong)
this is a different just different way...
Transistor_matching

It does look at VBE matching and as the DUT and reference are at same ambient themperature it takes same variables (temperature and suply voltagge) out of the equations.
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File Type: gif 1ma_VBEcomparison_fixture.gif (5.2 KB, 561 views)
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Old 25th October 2012, 11:55 AM   #70
hesener is offline hesener  Germany
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very nice!
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