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Complementary transistor matcher?
Complementary transistor matcher?
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Old 6th December 2016, 05:53 PM   #91
johngalt47 is offline johngalt47  United States
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Complementary transistor matcher?
For a 2N3904, how big should the load resistors be?
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Old 7th December 2016, 08:28 AM   #92
AndrewT is offline AndrewT  Scotland
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I tend to use 1k0 ±0.1% as the collector loads.
That lets you measure upto 10mA if you don't let the resistors get too warm. Use 100r for higher currents and 10r for power devices.
Gives a resolution down to 0.1µA using the 199.9mVdc scale of a DMM voltmeter.
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Old 9th December 2016, 07:52 PM   #93
johngalt47 is offline johngalt47  United States
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Complementary transistor matcher?
I'm thinking that I need to maintain precise control over the ambient temperature when measuring many of them.
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Old 9th December 2016, 08:46 PM   #94
Elvee is offline Elvee  Belgium
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The way I do this kind of test is to insert the whole bunch into a breadboard, then put a cover (leaving the emitters or drain or whatever you are going to test accessible from outside), let things rest and stabilize for 15 minutes, and then proceed with the tests, noting the "address" (breadboards are indexed) in front of the measured parameter.
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Old 9th December 2016, 10:32 PM   #95
johngalt47 is offline johngalt47  United States
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Complementary transistor matcher?
After watching the transistor being tested drift up and down over time, I decided to tape a thermocouple to one and see if the temperature was changing. Sure enough, for no good reason that I can tell, the transistor itself is changing temperature both up and down over time. If it were self heating, I would think it would run away but it eventually cools back down again. It performs this cycle continuously....
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Old 10th December 2016, 08:00 AM   #96
AndrewT is offline AndrewT  Scotland
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If you use an LTP style jig with the two devices thermally coupled, you fairly effectively remove the temperature variation from the comparison of DUT to REF.

Comparison is one of the most useful measurements you can achieve.
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Old 10th December 2016, 01:04 PM   #97
johngalt47 is offline johngalt47  United States
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Complementary transistor matcher?
Does LTP mean Long Tail Pair?

I've thought about making some kind of jig to accomplish that feat but am not sure about how to actually accomplish it.
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Old 10th December 2016, 02:22 PM   #98
AndrewT is offline AndrewT  Scotland
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I started with a 8pin DIP socket.
But clamping the two To92 together with the wide gap between the two rows of pins in the socket was bending the leadout a lot. Some while layer I bought some SIL sockets. They too are 0.1" pin pitch.
Cut off 3 sockets from the strip, cut off a second row of three sockets.
Glue these together to form a 2row by 3 receptacles grid. Instant glue works OK.
You have six pins out of the bottom side.
point to point wire these to form an LTP test jig.

This jig can be wired emitter to emitter and take this to 0V (-ve of a lab supply)
Wire the two bases together. This is where you input a voltage of ~600mV to get the LTP to conduct.
Attach a 1k0 0.1% resistor to each collector.
Connect the two resistors. This can be fed by two methods.
Either a direct wire from the +ve of the lab supply, or
to the tail of a CCS that can be preset to the current you want to measure DUT and REF at. Then the top of the CCS goes to +ve of lab supply. You can add another resistor here if you want a bit of protection in case the lab supply is set too high for the current rating of the devices. Another 1% 1k0 would drop 10V if your devices drew 10mA (5mA each if balanced but max of 10mA to one if badly unbalanced).

You can plug in a To92 DUT and REF facing towards each other and clamp them together with a wooden clothes peg.
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Last edited by AndrewT; 10th December 2016 at 02:31 PM.
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Old 10th December 2016, 06:12 PM   #99
johngalt47 is offline johngalt47  United States
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Complementary transistor matcher?
Awesome! Thanks a lot. I didn't think about using the SIL.
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Old 25th January 2017, 07:39 PM   #100
johngalt47 is offline johngalt47  United States
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Complementary transistor matcher?
I am still having the problem of the transistors not settling down even with their "heads" clamped together. Even if the power supply I am using did not have good regulation, both transistors see the same voltage. The collector resistors are within 0.007% of each other and the bases are seeing a little over 700mv. The collector currents are about 3 ma.

Any ideas?
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