Need help with NEC power transistor data sheet. - Page 1
Forum section: electronics / beginners

author: rwgast_lowlevellogicdesin
author_rank: Frequent Contributor
timestamp: July 14, 2016, 12:34:56 am
content: Over the years I have collected a ton of circuit broads with interesting IC's, well I am trying to kind of clean up and buy that I mean taking a heat gun to a few boards a day and collecting all semi conductors, esoteric parts, and usefull easy to spot passives like trimmer caps power shunts etc.Anyway I tore apart a kind of cheap 2.4ghz RC helicopter a while back, there are some transistors on itNEC 2SC3572I thought maybe they were for the lithium circuit which they could be but the epitaxial and say hi speed switching. I cant find an FT on this data sheet, can someone tell me what im missing here to figure out switching speed there is tf or fall time which is .7us.Second there is an IC on the board labeled LOG RX1A 1233 im sure its part of the RF system I would really like to figure out what it is but google isnt being very helpfull, theres another higher pin count chip with Asian letters next to it im guessing is the transceiver.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 14, 2016, 02:02:18 am
content: Hmm, "some" BJTs? Likely, using a circuit similar tohttp://www.pavouk.org/hw/en_atxps.html?Switching transistors don't need to be rated for fT. Likely, fT would peak in the low 10s of MHz, at Ic = 0.5-1A and Vce = 20V, or something like that.Epitaxial means it's not diffused, but neither of those terms mean much to you unless you understand semiconductor design. And, honestly, neither really means much to me either, and Idounderstand..Epitaxy is an additive process, so you can get more abrupt junctions, and more doping/impurities/crystal defects, which tend to reduce reverse recovery (diodes) or storage time (BJTs), and considerably reduce breakdown voltage. Which is why Vebo is a measly 7V -- the B-E junction is made with epitaxy, whereas Vcbo is a whopping 500V, made by light doping (and probably a first diffusion) of the initial silicon wafer.Still, at hFE = 5, you have a whopping 2.5us of storage time, so you need to be careful using these. They don't turn off "instantly" like MOSFETs do. You need to provide a big gulp of turn-off current (that's "-I_B2"!) to even achieve that.(A reminder that BJTs are voltage-operated devices! Like MOSFETs, it takes some amount of charge to turn the device on or off. The basic difference is, in forward bias, the "gate" leaks -- DC base current, which can be a blessing or a curse depending on how you use it. The gain is much higher, and the impedance is much lower, which just means: less voltage swing, but more drive current, for about the same relative output power.)That should be about all you ever wanted to know about power switching BJTs. Oh, and don't forget they don't have body diodes, so add external diodes to use them in a bridge configuration, for example!Tim

author: rwgast_lowlevellogicdesin
author_rank: Frequent Contributor
timestamp: July 14, 2016, 02:21:21 am
content: Ok well here is a link to a fairly big picture of the small chips so you can zoom out and clearly read ithttps://dl.dropboxusercontent.com/u/27653605/chips.jpg

author: rwgast_lowlevellogicdesin
author_rank: Frequent Contributor
timestamp: July 14, 2016, 05:27:34 am
content: I wonder why its so hard to find data sheets for chips that arent from the big guys

author: Kappes Buur
author_rank: Regular Contributor
timestamp: July 14, 2016, 08:26:56 am
content: 2sc3572