what is a 150V matched pair BJT used for? - Page 1
Forum section: electronics / beginners

author: incf
author_rank: Frequent Contributor
timestamp: April 18, 2025, 10:45:19 am
content: One of the most stocked matched pair BJT transistors on digikey is a 150V 2x PNP matched array.Why would anyone need such a high breakdown voltage on a matched pair transistor?Perhaps high voltage "poor man's" op-amps? Or does that rating confer other advantages like reduced leakage current?

author: voltsandjolts
author_rank: Unknown
timestamp: April 18, 2025, 11:23:15 am
content: Presumably this:https://www.digikey.co.uk/en/products/detail/diodes-incorporated/DMMT5401-7-F/717761Useful in applications where matched pairs are useful, and require modestly high voltages I guess.

author: jwet
author_rank: Frequent Contributor
timestamp: April 19, 2025, 03:13:55 pm
content: There are two questions here, one asked and one implied.1. On the application question, they're used for current mirrors, high side drivers, amplifier internals and other general purpose apps. They are only matched to the extent that they are adjacent die on the same wafer- the spec is pretty vague- 2%- I don't even know what that means for offset? They're made in many voltages but 60 and 150V bipolars don't burn up much different area like MOSFET's would.2. The implied question is "Digikey has so many in stock- are these so popular in some way that only a few understand?". This is more interesting. The short answer is that they aren't very popular, they're very inexpensive parts and 600 thousand is only 200 standard reels. These parts are "blind built" (untested until packaged- no wafer level tests) and made in large lots just because of their size- imagine how many dual transistor die come out of a large wafer. If you launch say 3 wafers in the your fab, you'll have millions. Chip companies will keep wafer banks but these parts are really untested until packaged and your wafer bank could be duds. You have to package them just to see if they work. You end up with tons of them and they likely sell slowly. Its just the only way parts like this can make it to market. Diodes is happy to park them at Digikey and Digikey can honestly say that have 20 million parts in stock, etc.This is one of many funny things that IC companies and disties do. Disty's exist for the convenience of the manufacturers.

author: thermistor-guy
author_rank: Frequent Contributor
timestamp: April 20, 2025, 10:09:45 am
content: Quote from: incf on April 18, 2025, 10:45:19 amIn a past project I used a matched pnp pair to form a differential op-amp input stage, which sensed the current drawn on a 50V supply rail.

author: coppercone2
author_rank: Super Contributor
timestamp: April 20, 2025, 10:16:18 am
content: high voltage precise current sources mean measuring high resistances. Be happy that its cheap. While only partially related, I am amazed that we have high quality meggers now that go for as little as $40.Kind of insane to think about how hard it was to get a measurement instrument for measuring insulation (the main thing by which you can judge the ware on a inductor, transformer, motor, generator, etc) at a low price. It gives repair people such a big capability..https://www.amazon.com/Digital-Megohm-Meter-Tester-Insulation/dp/B0DDLBFFYP?gQT=1These might not even do constant current, but its still cool. The only reason why precision higher voltage technologies are not as popular is because the parts were never cheap... it does seem with hobby EE that when people see something above... 12V they have no clue about it lolThe interesting world of piezo / electric field technologies ....https://spectrum.ieee.org/electrostatic-motorI would like to see low cost piezomotor s and stuff too, their development might get helped by cheapie components. So you can get it without giving Apex Microtechnologies your hand... I know tons of people would be working on it if the drivers that were close to precise enough did not cost your soulI think your definition of poor man's is a bit off. This is what you are competing with. Try a term along the line of "not insane". Just how rich is the rich man you are talking about?https://www.mouser.com/ProductDetail/Apex-Microtechnology/PA83?qs=TiOZkKH1s2Q0CI4w1sWQCA%3D%3DNo one even wants to try working on them (let me tell you, its easy to fry em). The prices areelitist.

author: incf
author_rank: Frequent Contributor
timestamp: April 20, 2025, 10:26:46 am
content: Quote from: thermistor-guy on April 20, 2025, 10:09:45 amI suppose maybe it allowed you to sidestep common-mode input voltage range limitations, and possibly get better accuracy than one might achieve by using voltage dividers (which possess large tolerances when measuring high side current shunts)

author: David Hess
author_rank: Super Contributor
timestamp: April 20, 2025, 12:41:44 pm
content: Class-ab audio power amplifiers operate in that voltage range. A high voltage PNP matched pair is useful as the differential input stage.

author: TimFox
author_rank: Super Contributor
timestamp: April 20, 2025, 04:52:23 pm
content: Quote from: voltsandjolts on April 18, 2025, 11:23:15 amThis part is only 0.34 GBP in single quantity from a retail distributor, or 0.13 GBP at 100.That should not bother anyone.It’s not practicable to get 150 V in an IC, and we don’t use tubes anymore.