| Electronics > Beginners |
| Jellybean hobbyist general purpose transistors.. |
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| floobydust:
1970's Tektronix tested and ranked all transistors and diodes; ranked by hFE, leakage current, avalanche voltage etc. Some manufacturers have crap datasheets and I buy from those that have good information, like On-Semi and NXP. Diodes Inc datasheets are terrible, missing tons of the usual specs. If a spec is absent, it's not tested so buyer beware. Example BC846A datasheet: Infineon 13 pages, 17 graphs Fairchild 7 pages, 17 graphs Taiwan Semi 6 pages, 12 graphs On-Semi 13 pages, 10 graphs ea. NXP 15 pages, 8 graphs Diodes Inc 7 pages, 3 graphs |
| Vtile:
Is there a general rule of thumb for high(ish) voltage (ie. 100V to 140V range), but low leakage (Vce and maybe Vbe) BJT transistor type. ...Or is the higher voltage the rule of thumb to find lower leakage type. ** Low leakage, <15nA ** **When searching that transistor model*** PS. If we still try to stay on "general purpose" category. |
| David Hess:
--- Quote from: Vtile on October 19, 2017, 09:35:03 am ---Is there a general rule of thumb for high(ish) voltage (ie. 100V to 140V range), but low leakage (Vce and maybe Vbe) BJT transistor type. ...Or is the higher voltage the rule of thumb to find lower leakage type. ** Low leakage, <15nA ** **When searching that transistor model*** PS. If we still try to stay on "general purpose" category. --- End quote --- Leakage depends more on area, construction, processing, and temperature than voltage rating. For small signal transistors, it is only tested down to a level of 10s of nanoamps because that covers almost all applications and a more sensitive test would take longer. Voltage rating has more of an effect on recovery time. A thorough search will turn up transistors tested down to 10 nanoamps but I think of low leakage as 10 picoamps and lower which I have had no trouble finding in common parts like the 2N3904. |
| exe:
--- Quote from: T3sl4co1l on October 19, 2017, 04:58:41 am ---If it meets the datasheet, and your application works based on datasheet information, then you're fine. --- End quote --- The problem is many parameters are not specified, or only "typical" values are specified. Or how this parameters change with temperature, supply voltage, etc. |
| Vtile:
--- Quote from: David Hess on October 19, 2017, 01:09:15 pm --- --- Quote from: Vtile on October 19, 2017, 09:35:03 am ---Is there a general rule of thumb for high(ish) voltage (ie. 100V to 140V range), but low leakage (Vce and maybe Vbe) BJT transistor type. ...Or is the higher voltage the rule of thumb to find lower leakage type. ** Low leakage, <15nA ** **When searching that transistor model*** PS. If we still try to stay on "general purpose" category. --- End quote --- Leakage depends more on area, construction, processing, and temperature than voltage rating. For small signal transistors, it is only tested down to a level of 10s of nanoamps because that covers almost all applications and a more sensitive test would take longer. Voltage rating has more of an effect on recovery time. A thorough search will turn up transistors tested down to 10 nanoamps but I think of low leakage as 10 picoamps and lower which I have had no trouble finding in common parts like the 2N3904. --- End quote --- Makes sense, thx. PS. I just noticed that at least some types of PN2222 are "rated" to 10nA Icbo max. at 25 deg.C. I'm more and more confident the bulk box of cheap as dirt (they are sand after all) parts (from reputable source) is right way to go for most all non-production hobbyist needs, most critical feature seems to be that you have the stock pile to pick from. :) It would be interesting to know if the garden variety actually do have different internals between models or are they actually just from one outcome from a machine and then sorted to meet different key specifications of garden variety part numbers. I wouldn't be too surprised (without having even general knowledge of semiconductor production) if this would be the case looking at how close the specks are in many parts. |
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