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Softrock Lite 6.2
Adventures in Electronics and Radio
Elecraft K2 and K3 Transceivers
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Matching 2N5109
Transistors
The Z10040B Norton amplifier kit ships with a matched pair
of 2N5109 transistors. I use an inexpensive digital multi-meter with a DC
transistor current gain matching function that measures the current gain hFE at
one (unknown) operating point.
I thought it would be interesting to see a dynamic
comparison of the 2N5109's, as measured with a Tektronix 575 curve tracer.
All curve traces are generated with 2 volts/division
horizontal axis, and 10 mA/division vertical axis. (100 ohm series resistance
selected). The base drive is 100uA/step.
First, let's look at the extreme—the two 2N5109's with the
highest and lowest DC current gain. The lowest gain of the 50 or so parts in my
stock is 44.
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The highest DC current gain of the stock in hand is 164.
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There's considerably difference in the dynamic characteristics of these two
transistors. (The loops seen in the higher gain transistor are a caused by
device heating and capacitance and are should be disregarded in the analysis.)
600uA base drive in the low gain device at 10V produces a collector current of
about 26mA. 600uA base drive to the high gain device produces 94mA at 10V, a
ratio of 3.16:1. The ratio of the multi-meter's value is 3.7:1, not too far from
the dynamic ratio.
I then plugged two transistors (Samples A and B) with
identical multi-meter DC gain readings of 68 into the curve tracer, with the
results seen below. The display parameters are identical to the two plots above,
but I've increased the number of base steps.
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Although not 100% congruent, it is apparent that the dynamic characteristics of
the matched transistors are quite close. For example, look at the 5th base step,
corresponding to 400uA base drive. At 10V, Sample A has a collector current of
28mA, whilst Sample B has a collector current of 29mA. Even at the maximum base
drive of 900uA, the collector currents are (at 10V) 65mA (Sample A) and 68mA
(Sample B).
Of course, the Z10040B has individual bias adjustment
trimmers so the individual transistor operating points can be adjusted based on
performance measurements, such as the 2nd order intercept. Still, it's
comforting to know that the transistors matched at one current setting with an
inexpensive multi-meter track quite well over a range of base and current
values. |
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