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Complementary transistor matcher?
Complementary transistor matcher?
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Old 19th March 2015, 10:56 AM   #21
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by benb View Post
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?............
The usual DMM hFE function is OK for rough batching.

But it does not give the Ib, nor Ic of the test.
It does not control the Tj during the test, there is no control on the power dissipated in the device.
It does not give Vbe.
hFE and Vbe are very dependent on Tj and vary with Ic

For decent matching you need to monitor Ib and Ic and develop a method that somehow controls Tj, or at the least gives a consistent Tj between the DUTs during each test.
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Old 19th March 2015, 10:56 AM   #22
johngalt47 is offline johngalt47  United States
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Complementary transistor matcher?
On a side note, I am currently testing MPSA18 transistors. I am amazed at the wide disparity in Hfe!

So far they are varying between 600 and 1200! There are about 55 different values represented with 765 the most.
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Old 19th March 2015, 11:57 AM   #23
AndrewT is offline AndrewT  Scotland
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You are very lucky to get such high values of hFE.

Check a couple of samples at 1mA Ic, using a 100r collector resistor and a 10k base stopper.
You can measure hFE and Vbe during the test. See how they compare to the DMM results.

Try to arrange for a Vce to match what is stated in the datasheet.
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Old 24th March 2015, 10:46 PM   #24
johngalt47 is offline johngalt47  United States
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Complementary transistor matcher?
Ok, so I took two of the BC550C with nearly identical Vbe according to the DCA75 PN junction test which takes 34 measurements at different currents and tested them with Fritz' jig:

https://home.comcast.net/~ijfritz/Mi...ransmat001.pdf

At first I thought there was a problem and then I realized that my meter was reading 0.0003**, almost an order of magnitude less than the 0.002 volts which is considered to be a match.

So it validates the average Vbe measured by the DCA75. I'll post a spreadsheet showing what the graph looks like and also the spreadsheet exported out of the DCA75 software.
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Old 25th March 2015, 12:20 AM   #25
johngalt47 is offline johngalt47  United States
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Complementary transistor matcher?
As promised, here are some pics:
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Old 25th March 2015, 08:38 AM   #26
AndrewT is offline AndrewT  Scotland
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The Fritz jig is not much good.
It puts emitter resistors into the test circuit.
That use of Re swamps differences in the DUTs.

The current measuring resistor need to go into the collector leads.
The Re is very effective feedback. You must remove it, or at the very least minimise it.
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Old 25th March 2015, 09:13 AM   #27
johngalt47 is offline johngalt47  United States
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Complementary transistor matcher?
Good to know. In any case, after more testing, the measurement settled out at 0.0002 volts but when I swapped the transistors it measured 0.0006.

I don't understand this because the 100k resistors are 0.01% Caddock with a TC of 5.

On that same meter one resistor measures exactly 100,000 and the other measures 100,001 ohms using a 4 wire setup.

I'll go ahead and try the jig in message #14 to see what happens.
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Old 25th March 2015, 09:50 AM   #28
AndrewT is offline AndrewT  Scotland
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The post14 is a Wheatstone bridge.
It can be made very sensitive to small changes.
The jig is comparing half supply voltage (junction of the two resistors) to the output offset voltage at the junction of the two transistor collectors.

A small change in output offset ref. the 1/2Vsupply, is a measure of "unmatch" in the two DUTs.
If the DUTs match at one Ic, but move out of match as the Ic is changed, then the two transistors do not track each other over the range of tested Ic.
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Old 28th March 2015, 08:26 PM   #29
hahfran is offline hahfran  Germany
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Quote:
Originally Posted by Elvee View Post
Here is a circuit that will perform like the original one is supposed to, but better:

The LEDs could be replaced by a milliameter (and the resistor values adapted)
That is a well-known circuit. But unfortunately, not so good for matching complimentary power BJts.
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Old 29th March 2015, 12:51 PM   #30
johngalt47 is offline johngalt47  United States
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Complementary transistor matcher?
If I replaced the LEDs, what values should I use for the resistors?
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