transistor matching - stupid newbee question
I did a search but couldnt find anything...sorry if I missed it.
So does anyone "match" the output transistors? Does it make a difference? How do I do this, just measure HFE?
Do I try to match each **pair** NPN/PNP or match all the NPN's and all the PNP's (like if I have parallel output transistors)??
Same with driver transistors - am I trying to match the NPN one with the PNP one? Or is this not necessary?
Current mirrors and input stage pairs are easy since they are the same kind (npn or pnp).
Finding matches within the NPNs or PNPs is pretty easy. I'm having difficulty finding matches of NPN with PNP though.
Hello there fellow Hoosier!
The only stupid question is the one not asked.
Not being an expert, this is what the forum has taught me.
You match PNP to PNP (not to NPN).
Same for NPN to NPN. basically You match like polarity devices.
While you do not match PNP to NPN, keeping them to within 50% hfe is a good idea.
Power devices are usually matched to 10% hfe, Drivers to 5% and inputs to 2%. These days manufacturer tolerances are such that usually same batch trannies are pretty well matched.
Matching is not as critical as it was in the 70's however that mind set still prevails and it's not a bad idea to go the extra yard of you have the time.
Hfe should be measured with the level of current that the device will be subjected to. No use measuring a power devices that will pump out 5-10A with a Multimeter that measures hfe @ 100ma.
Hope this helps,
PS Are you in Indy? Perhaps we could exchange notes/parts/projects etc. Cheers!
How to identify if the components are manufactured in the same lot. The retailers might mix new and old stocks. Mind to give me some ideas on that, Tks
Devices from the same lot have the same lot code number.
Matching tolerance depends on the use, i would like to add.
For preamp transistor matching can be stricter.
Hfe can be measured at different current level.
I measured 100s of 550C's once for a preamp circuit.
Mark Levinson had (one) of his girlfriends measure thousands of devices for his Cello components.
Probably not a good solution for you but I buy in 100's so I get it in a Tray (or rail) depending...
The problem is using them up... so here if you need MJ21193/4/5/6, I have em from same lots. ;-)
Jacco is right, you can see the batch numbers below the part number.
If matched components were so easy to do, why would we all have them. ;-)
Thanks k-amp! Just what I was looking for. So is using a curve tracer overboard? I found this neat little project at
http://www.fullnet.com/u/tomg/gooteect.htm (another hoosier!)
BTW - Im in South Bend, have done a few projects but still learning:
If you have the stash to pay for a curve tracer and your Mrs does not reach for kitchen hardware, nice apparatus !
Sweeping till 22 KHz is not impressive, think MHz and you are talking big money.
But do you think you will use it to its full use ?
Just a small powersupply (with a voltage regulator), a heatsink, a few power resistors, a DMM, and a few connectors do the matching trick too.
If you want more luxury: a variac and/or labsupply.
(building a labsupply yourself is easy and cheap)
I often wondered if someone will ever find it interesting to write some device matching software.
Should be even tempting Dollar wise, my guess.
Think of matching 20 devices simultaneously in a few seconds, a 1000 in an hour !!
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