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Vbe matching without temperature drift
Vbe matching without temperature drift
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Old 12th January 2018, 02:35 PM   #1
classAchap is offline classAchap  United Kingdom
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Join Date: Oct 2008
Location: Yate Bristol
Default Vbe matching without temperature drift

Most Vbe matchers appear to be variations on a theme by Robert Moog, based on a current source, they share a troublesome Vbe temperature drift.

The matcher shown here consists of a simple circuit placing the transistors to be matched in series across the supply. The voltage is set to 2Vbe and may be changed to achieve a desired emitter current. A match is reached when the supply is bisected equally when the temperatures, emitter currents and Vbe are the same. Any environment temperature change is accommodated by an emitter current change but Vbe is unaffected. Measured Vbe(s) are also quite repeatable.

The photos show my matcher, the transistors are faced together and held in contact with clothes pin and clamp. This arrangement reaches stability in about 50 sec. The second 8 pin dil is a contact extension to facilitate measurements without disturbing the test transistors. Also note how the transistors are fitted to the dil socket - this gives better contact!

Matching pairs, of course, should be thermal greased and held in contact with heat-shrink as per usual.

Hope you like it.
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File Type: jpg IMG-0678.jpg (548.9 KB, 66 views)
File Type: jpg IMG-0679.jpg (541.8 KB, 61 views)
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File Type: asc Classachap Vbe Matching.asc (1.4 KB, 6 views)
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