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Complementary transistor matcher?
Complementary transistor matcher?
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Old 14th March 2015, 05:12 PM   #11
johngalt47 is offline johngalt47  United States
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Complementary transistor matcher?
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Originally Posted by gmphadte View Post
RNMarsh had posted this on some thread.

Gajanan Phadte
Ok, so I assembled this circuit but I didn't use the exact resistor values and I didn't have a 25-0-25 microammeter.

I put a 110 ohm resistor in place of the microammeter and measured the voltage across it.

I kept the same PNP transistor and used two different NPN transistors.

Both measured about the same. I guess I will have to use the exact resistor values and buy the analog ammeter.

Any ideas?
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Old 16th March 2015, 10:02 PM   #12
johngalt47 is offline johngalt47  United States
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Complementary transistor matcher?
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Originally Posted by jerluwoo View Post
A test jig to do small signal transistors. Scale would be 1uA per 1mV. Having a pair of transistors that are with in 10mV on all 3 settings would be a fairly good match. R4/R5 and R6/R7 should be closely matched to each other. Intended power supply is a 9 volt battery.
Ok, I think I have this one figured out.

With two nearly exact transistors, the differential is about .12 volts but it drifts up and down. It takes a while to settle down.
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Old 17th March 2015, 06:00 AM   #13
jerluwoo is offline jerluwoo  United States
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It may help to arrange the transistors so the flat sides touch and put a small piece of tape on to hold them together. The addition of a 1n4148 diode in the base circuit may also reduce variation.
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Old 17th March 2015, 08:32 AM   #14
Elvee is offline Elvee  Belgium
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Here is a circuit that will perform like the original one is supposed to, but better:

Without R4, one of the LEDs will practically always be lit (unless the beta's happen to match with extreme accuracy), and the brightness will indicate the degree of mismatch.

If this behavior is not desired, R4 can be added to introduce a threshold: if the mismatch is below a certain value, none of the LEDs will light.

The LEDs could be replaced by a milliameter (and the resistor values adapted)
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Old 18th March 2015, 08:52 PM   #15
AndrewT is offline AndrewT  Scotland
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This last looks good.
It seems to me that one could change the V1 supply voltage to vary the currents passing through the DUTs and see if the "matching" is good, or bad, over a range of currents.
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Old 18th March 2015, 09:07 PM   #16
Elvee is offline Elvee  Belgium
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Originally Posted by AndrewT View Post
It seems to me that one could change the V1 supply voltage to vary the currents passing through the DUTs and see if the "matching" is good, or bad, over a range of currents.
That could be an option, but varying R1 is probably simpler.
In this case, note that if R1 becomes too low combined with high Hfe transistors, there could be a risk of exceeding the Pmax of the transistors tested. Including limiting resistors in the collectors would be a wise precaution.
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Old 18th March 2015, 10:32 PM   #17
johngalt47 is offline johngalt47  United States
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Complementary transistor matcher?
What value would you choose forn the collector resistors?
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Old 18th March 2015, 11:27 PM   #18
benb is offline benb  United States
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I'm wondering, there are a lot of $20 or so DMM's that have a little socket to measure HFE/current gain of both PNPs and NPNs. Why not measure a bunch of each, sort each polarity by HFE, then it's easy pick the two that match best?
Quote:
Originally Posted by johngalt47 View Post
Ok, I think I have this one figured out.

With two nearly exact transistors, the differential is about .12 volts but it drifts up and down. It takes a while to settle down.
What's likely happening is your fingers heat up the transistor, increasing its gain (and some other parameters) slightly. Things change until it settles back to room temperature. Perhaps using tweezers to manipulate transistors will reduce this.
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Old 19th March 2015, 12:08 AM   #19
johngalt47 is offline johngalt47  United States
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Complementary transistor matcher?
I have one of those plus four other transistor testers. In any case, I just opened the latest Elektor magazine and on page 56 is .... wait for it ... a transistor tester!
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Old 19th March 2015, 07:51 AM   #20
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by johngalt47 View Post
What value would you choose forn the collector resistors?
Something like 27 ohm each will protect small transistors without interfering with a normal measurement.
They don't need to be matched (nor do the ones anyway).
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