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How to match transistors?
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kjackman



Joined: Sep 05, 2010
Posts: 69
Location: Utah, USA

PostPosted: Thu Nov 11, 2010 11:11 pm    Post subject: Reply with quote  Mark this post and the followings unread

I just breadboarded the awesomely easy +/-15v circuit provided by Bill & Will at Dragonfly Alley. Thanks, guys!

Posted Image, might have been reduced in size. Click Image to view fullscreen.

So, does -0.689 volts sound about right for a 2N3904 NPN transistor? I think I must have made a mistake somewhere, because without the test transistor, the test points show -14.49 volts or thereabouts, with a current of zero mA.

Bill and Will said,

Quote:
"The Voltage across the test points is 7.5V and without a test transistor in the socket, there's .100 milliamps (that's 100 micro amps or 100µA) across them - perfect!"


...and that's not what I'm seeing Sad

I'm using half of a TL072 in place of the 741 I don't have, with the pins appropriately rearranged. Would the choice of op amp make a difference?

Here's a closeup:

Posted Image, might have been reduced in size. Click Image to view fullscreen.

EDIT: The layout above is incorrect. Building it this way will not work. Scroll down to see the corrected version.

It's a little hard to see, but there's a green wire hiding under that resistor in the middle of the three at top. It connects TL072 pin 4 to -15v. And the end of the 10k at left that's hiding under a white wire, is connected to the collector of the transistor on the right. And there's a teeny jumper wire hiding under that resistor, that ties the white +15 wire to the collector of the transistor under test.

Ehhh, screw it, my breadboard layout is a disaster waiting to happen. Embarassed I'll re-do the connections tomorrow with the right size wires and trimmed resistor leads, and go over it again. No wonder it takes me so long to troubleshoot these circuits. Neatness counts!

Last edited by kjackman on Sun Nov 14, 2010 5:27 pm; edited 1 time in total
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adambee7



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PostPosted: Fri Nov 12, 2010 12:14 am    Post subject: Reply with quote  Mark this post and the followings unread

yeah thats a bit high. they are usually around 600 mV. TL072 is ok but as your only using one of the opamps the unused one needs to have its + pin grounded and the output connected to - to stop unwanted interference with the other op amp. Very Happy Very Happy
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frijitz



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PostPosted: Fri Nov 12, 2010 2:50 am    Post subject: Reply with quote  Mark this post and the followings unread

kjackman wrote:
I just breadboarded the awesomely easy +/-15v circuit...

I've never been able to understand why such a complicated circuit is used. Here's a little doc on the simpler, easier and more accurate method I have been using. It's similar to Jim Patchell's method, except he grounds the collectors. Either way is fine. If you are going through a pile of devices, use the procedure under "multiple devices". Note that you do not need to swap the devices when you use this method.

Very Happy

Ian


transmat001.pdf
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Last edited by frijitz on Wed Mar 16, 2011 6:53 pm; edited 2 times in total
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frijitz



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PostPosted: Fri Nov 12, 2010 3:11 am    Post subject: Reply with quote  Mark this post and the followings unread

kjackman wrote:
Here's a closeup: ...

I can't tell, is the second resistor from the right connected to pin 3 or to pin 4?

Very Happy

Ian
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andrewF



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PostPosted: Fri Nov 12, 2010 3:20 am    Post subject: Reply with quote  Mark this post and the followings unread

thanks Ian
very succinct and easy to follow
I'll never buy another LM394/ssm2210 again!
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kjackman



Joined: Sep 05, 2010
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Location: Utah, USA

PostPosted: Fri Nov 12, 2010 6:40 am    Post subject: Reply with quote  Mark this post and the followings unread

frijitz wrote:

I can't tell, is the second resistor from the right connected to pin 3 or to pin 4?


Pin 3. Yeah, that's why I was saying I need to do this over. Way too hard to troubleshoot this mess.

I'll try your alternative method first though!
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mark_olson



Joined: Oct 26, 2006
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PostPosted: Fri Nov 12, 2010 7:24 am    Post subject: Reply with quote  Mark this post and the followings unread

frijitz wrote:
Here's a little doc on the simpler, easier and more accurate...


Really nice!

Thanks so much for posting this.

Now, do know of a circuit that will help me recover the hours and hours of my life that were lost searching for affordable/available matched pairs? Smile

Mark
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frijitz



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PostPosted: Fri Nov 12, 2010 10:24 am    Post subject: Reply with quote  Mark this post and the followings unread

mark_olson wrote:
Now, do know of a circuit that will help me recover the hours and hours of my life that were lost searching for affordable/available matched pairs? Smile

Unfortunately not, but if you find one, please let me know. Laughing
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kjackman



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PostPosted: Sun Nov 14, 2010 5:24 pm    Post subject: Reply with quote  Mark this post and the followings unread

OK folks, I discovered my error. Here's the corrected the breadboard layout:

Posted Image, might have been reduced in size. Click Image to view fullscreen.

The transistor on the left is the one under test. The white wires leading away from it to the left, go to the voltmeter: Top wire goes to (-), bottom wire goes to (+). IC is a TL072 dual op amp; transistors are both NPN (2N3904). Note the power supply labels on the right side: +, -, and ground reference. The 2K trimmer helps to calibrate to exactly 100 microAmps.

I haven't tried frijitz's method yet, but it looks much simpler. Normally I would have scrapped the Moog method and jumped right on this simpler one, but: a) I didn't want future generations of DIYers to copy my faulty breadboard layout above, and b) I really need the troubleshooting practice.
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adambee7



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PostPosted: Sun Nov 14, 2010 5:50 pm    Post subject: Reply with quote  Mark this post and the followings unread

its worth doing it both ways as a way of learning. i've done three different types of matching circuits on stripboard and bring them out when i need them. Very Happy Very Happy
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adambee7



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PostPosted: Sun Nov 14, 2010 6:09 pm    Post subject: Reply with quote  Mark this post and the followings unread

I built this npn matcher from Ray Wilson's schematic. this ones good for VCOs. i built the Moog NPN/PNP matcher aswell which i use for filters, etc.. Very Happy Very Happy


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emdot_ambient



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PostPosted: Mon Nov 15, 2010 1:31 pm    Post subject: Reply with quote  Mark this post and the followings unread

frijitz wrote:
Here's a little doc on the simpler, easier and more accurate method I have been using.

Would there need to be any adjustment to that circuit when using +/-15V power supplies?
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LektroiD



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PostPosted: Mon Nov 15, 2010 9:20 pm    Post subject: Reply with quote  Mark this post and the followings unread

kjackman wrote:
OK folks, I discovered my error. Here's the corrected the breadboard layout:

Posted Image, might have been reduced in size. Click Image to view fullscreen.

The transistor on the left is the one under test. The white wires leading away from it to the left, go to the voltmeter: Top wire goes to (-), bottom wire goes to (+). IC is a TL072 dual op amp; transistors are both NPN (2N3904). Note the power supply labels on the right side: +, -, and ground reference. The 2K trimmer helps to calibrate to exactly 100 microAmps.

I haven't tried frijitz's method yet, but it looks much simpler. Normally I would have scrapped the Moog method and jumped right on this simpler one, but: a) I didn't want future generations of DIYers to copy my faulty breadboard layout above, and b) I really need the troubleshooting practice.


Hi, and thanks for the layout, Confused about the 100mA though. I seem to be getting the 14V and 0mA too, that's with the new design (as I quoted)
Nothing I do seems to make the meter display even 0.0001mA

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kjackman



Joined: Sep 05, 2010
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PostPosted: Mon Nov 15, 2010 11:41 pm    Post subject: Reply with quote  Mark this post and the followings unread

LektroiD wrote:
Hi, and thanks for the layout, Confused about the 100mA though. I seem to be getting the 14V and 0mA too, that's with the new design (as I quoted). Nothing I do seems to make the meter display even 0.0001mA


I'm measuring current with both transistors in place. I break the connection at J20 on the board up there, and touch one meter probe to the resistor and the other to the transistor terminal at F20.

I first measured the current at zero, even after constructing the correct circuit above. It turned out my new meter has a different terminal post for measuring current than for measuring voltage. I just had to swap terminal posts! doh

If you've made any mistakes in the layout already, double-check all the connections and then try swapping out the TL072 and transistors. I'm pretty sure I fried the IC, or one or both transistors, somewhere along the way. I swapped all three out and things started working.

Which reminds me: How do I test a TL072? Rolling Eyes
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JRock



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PostPosted: Mon Nov 15, 2010 11:49 pm    Post subject: Reply with quote  Mark this post and the followings unread

This is a good coincidence cause I was just wondering where to ask this and I saw this Matching Transistors thread. Is there any reason this wouldn't work as a matched PNP pair? I know it's a quad and it probably won't fit on PCBs, But I'm building some stuff on Veroboard..

https://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_260734_-1
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JRock



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PostPosted: Tue Nov 16, 2010 12:02 am    Post subject: Reply with quote  Mark this post and the followings unread

Screw it. Frijitz! You rock! That's so simple even I can match my own transistors!
Awesome.
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reve



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PostPosted: Tue Jan 10, 2012 12:04 am    Post subject: Reply with quote  Mark this post and the followings unread

Sorry to resurrect a dead thread here... I'm curious if anyone could provide some guidance as to why constitutes an acceptable deviation from ground using Ian's method? I got this batch of 547c's from Mouser and I can't find a deviation beyond about 0.7mv. I'm not sure if I got a magic batch or if I should be looking for like... 0.01mv deviation.

Thanks!

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prgdeltablues



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PostPosted: Wed Jan 11, 2012 4:55 am    Post subject: Reply with quote  Mark this post and the followings unread

You may have struck lucky. I went through about 20 or so BC547's to find a pair that matched to within 1mV (actually I found two or three such pairs, but only two trannies in each bin as it were.) Ian's note says the CA3083 is specced at a 1mV match, though in practice some pairs are much better - but it seems as if for the usual expo converter usage, matching to 1mV is fine.

One thing did puzzle me a bit - you say 'deviation from ground' - these measurements are of the potential difference between two points, neither of which is ground (0V). Sorry if that's a misunderstanding of your post on my part, but it did look as if you might have been measuring the wrong thing?

Peter
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LektroiD



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PostPosted: Wed Jan 11, 2012 5:19 am    Post subject: Reply with quote  Mark this post and the followings unread

frijitz wrote:
kjackman wrote:
I just breadboarded the awesomely easy +/-15v circuit...

I've never been able to understand why such a complicated circuit is used. Here's a little doc on the simpler, easier and more accurate method I have been using. It's similar to Jim Patchell's method, except he grounds the collectors. Either way is fine. If you are going through a pile of devices, use the procedure under "multiple devices". Note that you do not need to swap the devices when you use this method.

Very Happy

Ian


I can't seem to download this PDF.. I had it on breadboard a while back, but after moving house, a few things have become unplugged.
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arnoid



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PostPosted: Thu Jan 12, 2012 8:07 am    Post subject: Reply with quote  Mark this post and the followings unread

frijitz wrote:
kjackman wrote:
I just breadboarded the awesomely easy +/-15v circuit...

I've never been able to understand why such a complicated circuit is used. Here's a little doc on the simpler, easier and more accurate method I have been using. It's similar to Jim Patchell's method, except he grounds the collectors. Either way is fine. If you are going through a pile of devices, use the procedure under "multiple devices". Note that you do not need to swap the devices when you use this method.

Very Happy

Ian


Hi

I build this little circuit and tryed to match two 2N3906 PNP transistors but I have problems with step 3:
(3) Plug in your transistors, power up, and write down the DVM voltage. (Make sure you wait until the voltage is stable.)

The voltage get's never stable it keeps moving from 0.062V to 0.074V.
I checked with 2 different DVM's.

Any suggestions ?

thx

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prgdeltablues



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PostPosted: Fri Jan 13, 2012 2:35 am    Post subject: Reply with quote  Mark this post and the followings unread

Does the rate at which the reading changes not slow down? It's to be expected that the dV changes as the transistors warm up as current flows through them, but it ought to level off after say 10-15 seconds. Maybe you're working in a slight draft? (If you blow on the transistors you'll see the reading change a fair bit, demonstrating this thermal sensitivity.)

Peter
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arnoid



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PostPosted: Fri Jan 13, 2012 3:34 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi there thx for your answer.

Yes the rate slows down but the value keeps changing.
I know transistors are temperature sensitve but its hard to decide wich value you should take/write down..

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funtykigs



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PostPosted: Sun May 06, 2012 7:52 am    Post subject: Reply with quote  Mark this post and the followings unread

Hey frijitz,

I know it's a while since you posted your transistor matching document.. but I wondered if a 1N4004 diode is suitable?

That's what I'm using anyway... it's the only thing I'm unsure about, I just stuck a pair of 2n3906's in your PNP testing rig and the mV reading is still fluctuating after a couple of minutes.. slowly floating between -0.2 mV to -0.7 mv and not staying still.

The transistors are very close... do they need to touch?

Thanks - I was very pleased to find this document!
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roborobert



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PostPosted: Thu Jun 06, 2013 5:01 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hey there,

thanks to frijitz 's very nice pdf i was able to build a transistor matcher within an hour Very Happy

i wrote because i didn't understand part of the calculation.
after i finished writing this post i understood it... so i edited/deleted the question and leave this post as a big thank you

best, rob
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fonik



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PostPosted: Fri Nov 15, 2013 2:18 am    Post subject: Reply with quote  Mark this post and the followings unread

arnoid wrote:
Hi there thx for your answer.

Yes the rate slows down but the value keeps changing.
I know transistors are temperature sensitve but its hard to decide wich value you should take/write down..

is there any solution to this?

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