Harvesting equivalent components in such an Industrial shortage period - Page 1
Forum section: electronics / projects

author: Houseman
author_rank: Regular Contributor
timestamp: December 23, 2021, 01:45:14 am
content: Hi Forum.No surprise / no breaking news everyone here in the electronic industry (from the designer all the way to the producer) is facing the worst component shortage and eternal wait list ever happened: can remember for example back in end of 1990 a series of tornado in Philippines flooding the electronic manufacturer and reduced, apart from life losses and human pain, the RAM/HDD industry for PC for a while. But maybe life was at a little more slower pace or I was younger who knows.. ( hope no flames surge..)Let's take for example the BJT from NXP BC857QASZ. 20 weeks of delivery time (5months!!). I mean it is a "general purpose" ok automotive BJT but not a fancy stuff.In the need of searching an equivalent part in the plethora of general purpose BJT's what do I have to search?I remember a video of Dave navigating through digikey site and making an advanced parametric search, but once I have found let's say 10 available equivalent parts how to choose the nearest that fits the original one?Dig inside the datasheet of each? perform some Spice simulations? What are your suggestion you can give me?Could You please give me some practical hints?Best regards, and happy Xmas coming!!

author: SuzyC
author_rank: Frequent Contributor
timestamp: December 23, 2021, 02:04:53 am
content: The device you mention is unusual only in its packaging, it has two rather mediocre pnp transistors in an unusual SMD package.What makes a part special is the special use, the circuit function of this device. Just what is the intentioned function of this bjt pair, Is this part needed for something that is mission critical? How matched of what characteristics must the two PNP BJT's be?There is nothing fancy or high performance about this PNP transistor pair other than its matching of the two BJT and the pinout of its packaging. The two PNP's share the same package ensuring thermal matching.The data sheet for this device pair gives no indication that any characteristic of the PNP BJT are matched.Your ideas of solving the problem are right on track to making a match for a replacement, but you might also find a need to match the price.Match it up.

author: Terry Bites
author_rank: Super Contributor
timestamp: December 24, 2021, 03:16:47 pm
content: BC847QAPNZ?Digikey has thousands of them.Mouser has 2500 as of today.There will be substitutes.

author: Siwastaja
author_rank: Super Contributor
timestamp: December 24, 2021, 06:33:31 pm
content: The answer to your question is dire: beyond trivial replacements (where manufacturers guarantee compatibility, or it's just minor packaging differences), replacing componentsisdesign. A different person can do this work, but only if they are up to the task of designing such circuit. Yes, in practice this work is looking at datasheets and doing Spice simulations, among other things.It's best done by the original designer. Because they know their design, it's least work and least surprises.If the designer has always worked with the premise they can just specify any component and purchasing department will get it, then this process must change. Co-operation between designers/purchasers, andfastactions are important now. Also some risk-taking; you need to order what you can get and make those parts work.

author: Houseman
author_rank: Regular Contributor
timestamp: December 28, 2021, 08:30:35 am
content: Quote from: Terry Bites on December 24, 2021, 03:16:47 pmNope. The item you pointed is a complementary NPN+PNPI am searching for the PNP+PNP and NPN+NPN ones.Anyhow thanks for the effort.

author: Houseman
author_rank: Regular Contributor
timestamp: December 28, 2021, 08:39:23 am
content: Quote from: SuzyC on December 23, 2021, 02:04:53 amThank You for your reply, SusyC.Well, the need for PNP+PNP in the same package is for a current mirror part of a fixed current source generator. As I have learned (and as You said) being the two BJT in the same package ensures theoretically same hFE also if temperature rises a little bit there is no critical mismatch rather than using two different single BJT.Regards

author: Houseman
author_rank: Regular Contributor
timestamp: December 28, 2021, 09:05:28 am
content: Quote from: Siwastaja on December 24, 2021, 06:33:31 pmThank You, Siwastaja.I agree also with Your thoughts: I think in such a case is more a "marketing/purchasing" decision rather than a specific design request. Since it's not such a critical-life saving circuit I think the designer has made a call to the upper floor and asked "What kind of available BJT do we have already? - OK thanks."