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 Forum index » DIY Hardware and Software » YuSynth
VCA hFE matching
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isak



Joined: Dec 13, 2009
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PostPosted: Mon May 13, 2013 6:32 am    Post subject:  VCA hFE matching Reply with quote  Mark this post and the followings unread

i have this irritating issue with my multimeter, i cant get the right reading of the hFE of bc547c.
i did a table with all the readings i get and if i find a match i check again both of them and they show me different reading.
what do you think, do i have a faulty multimeter?

is there another way to match hFE?

cheers.

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yusynth



Joined: Nov 24, 2005
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PostPosted: Mon May 13, 2013 6:54 am    Post subject: Reply with quote  Mark this post and the followings unread

This must be done at constant temperature and the transistors must be handled with plier to avoid contact with body heat.
By the way the exact matching is not important since there is a trimmer (A1) dedicated to compensate the unbalance.

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isak



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PostPosted: Mon May 13, 2013 7:35 am    Post subject: Reply with quote  Mark this post and the followings unread

thanks Yves.

i measure in windless room, stable temperature (i think).
i do insert the transistor by hand but i wait for about a min or too for things to cool down.
i see the reading start lets say at 700 and go down and stop at 692.
each measurement i wait for ad list 5 min till the reading is stable and not going up or down any more.
i hope i'm doing ok with measuring.

Yves just to my general knowledge is there any other way to measure hFE?

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yusynth



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PostPosted: Mon May 13, 2013 11:58 pm    Post subject: Reply with quote  Mark this post and the followings unread

Looks like the right way to measure it.
Another way of determining Hfe would require to build a test circuit
Fig 4.6 of http://www.mikroe.com/old/books/keu/04.htm

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isak



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PostPosted: Fri May 17, 2013 1:17 pm    Post subject: Reply with quote  Mark this post and the followings unread

interesting, thanks Yves.
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