General > General Technical Chat
Measuring hfe of "P2N2222A" varies wildly
Zero999:
--- Quote from: Cerebus on November 08, 2021, 02:44:39 pm ---
--- Quote from: Zero999 on November 08, 2021, 02:37:32 pm ---That depends on the frequency and GBWP of the transistor. At higher frequencies, there will be a significant difference between the hFE and hfe.
--- End quote ---
If we're all going to get pedantic about it then the significant difference is between the hFE at DC and the hfe at higher frequencies. :)
--- End quote ---
Fair enough my wording could have been better, but I would have thought it would be obvious that hFE is nearly equal to hfe at low frequencies and there's only a big difference at higher frequencies. For the purpose of this exercise, what constitutes high and low frequencies, depends on the transistor. A big and slow 2N3055's hfe might drop significantly at the upper end of the audio band, whereas a PN2222A's hFE and hfe can be treated the same, up to a few MHz.
Cerebus:
--- Quote from: Zero999 on November 08, 2021, 02:58:35 pm ---A big and slow 2N3055's hfe might drop significantly at the upper end of the audio band, whereas a PN2222A's hFE and hfe can be treated the same, up to a few MHz.
--- End quote ---
"Plummet" is the word you're looking for:
Yes, a guaranteed minimum hfe of 10 at 1kHz. There's a reason nobody uses 2N3055s in audio any more (if they have any sense).
SeanB:
Only problem with that is that a part branded as 2N3055 might actually be a very fast part, not the original slower than paint drying planar device, but the modern part, while meeting or exceeding all the headline specs for a 2N3055, might actually have quite a bit of gain at 30MHz, and can bite you. After all, all you need to brand a device as 2N3055, is have a peak collector current of 15A, gain greater than 3 at that current, and low leakage at 60V, which is very easy today with most modern process plant. But the data sheet does not reflect this at all, as you do not get typical values for a lot of those parameters, just the minimum JEDEC spec for the part number.
Cerebus:
That snippet is actually from the datasheet of a modern 2N3055 from OnSemi. That second column is a "Max" column, it was just too much faff to screen grab the table headers and integrate them into the upload.
Nevertheless, your point is well made.
CatalinaWOW:
Just out of curiosity I went and looked at the current OnSemi 2N3055AG data sheet. No mention of hfe at all. Just a gain bandwdith product spec (.8 MHz min to 6 mHz max for base part, 2.2 MHz min and 18 MHz max for a select part)
As always parts and their data sheets are a moving target, with traps for the unwary in any on going production situation.
https://www.onsemi.com/pdf/datasheet/2n3055a-d.pdf
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