[sdiy] Matched Transistors

[Jerry Gray-Eskue]

I thought I would share the results of one of my experiments.

I have built an "Adapt a Chip" board for the SOT666 to a 6 pin .1(inch) by
.3 dip package and successfully mounted a few of the PMP4501V NPN Matched
Transistor pairs. I then made a "Rube Goldberg" flying wire adapter to the
pin out of the CA3046 transistor pair used in the "Updated and Improved VCO"
http://www.musicfromouterspace.com/analogsynth/August2003VCO.html

I had previously constructed, replacing the unmatched 2N3904 pair I had
previously installed.

So far the transistor pair is operating normally and may suffice as a good
matched pair for general use in similar setups.

My main reservations is the physical size of the package (SOT666) and
possibly the die size will drastically limit the thermal mass and could lead
to temperature spike related failure when the power dissipation of the
transistors is high. Additionally DIY PCBs are pushing the limits to support
this footprint and additionally the package is so small that they may be
stolen by fleas or other small insects ;)

Ptot total power dissipation Tamb £ 25 °C
SOT666 [1][2] - 200 mW

The advantages are the PMP4501V NPN Matched Transistor pairs are inexpensive
(US $0.22) In Production and readily available from Mouser. Recommended
applications include Current Mirror and Differential Amplifier.

Table 2. Quick reference data - Per transistor
Symbol  Parameter                 Conditions    Min   Typ  Max   Unit

VCEO    collector-emitter voltage open base      -    -    45    V
IC      collector current                        -    -    100   mA
hFE     DC current gain           VCE = 5 V;    200  290   450
                                  IC = 2 mA

Table 2. Quick reference data 
continued
Symbol    Parameter      Conditions               Min       Typ     Max
Unit
hFE1/hFE2 hFE matching   VCE = 5 V;IC = 2 mA      [1] 0.95   1      -
VBE1-VBE2 VBE matching   VCE = 5 V;IC = 2 mA      [2] -      -      2    mV

[1] The smaller of the two values is taken as the numerator.
[2] The smaller of the two values is subtracted from the larger value.

- Jerry