| Electronics > Beginners |
| I higher is hfe in 2N3904? |
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| rsjsouza:
Exactly. A transistor hfe changes too much with the bias, therefore you will always have to work with approximations. I strongly recommend you to search around on the internet about "bipolar transistor bias" or "transistor amplifier design" to get some useful references about the subject. I just found a practical guide online in the link below, with various sections that talk about fundamentals. http://www.learnabout-electronics.org/Amplifiers/amplifiers10.php |
| David Hess:
Hfe depends on diffusion during fabrication so it is not well controlled and it is very temperature sensitive. At best the manufacturer will grade parts into separate groups but even then, hfe varies considerably from unit to unit. For switching applications, hfe is what matters but for linear operation, transconductance which is very consistent is more important. If controlled switching is necessary, then there are various anti-saturation circuits like Baker clamps which can be used to handle a wide range of hfe. --- Quote from: Jasonbit on July 20, 2018, 02:45:09 pm ---But which line should I look? I repair ob "Note2". (2. Pulse Test: Pulse Width < 300us; Duty Cycle < 2%) This value are for when I will use transistor on this conditions? --- End quote --- The datasheet for the transistor will include hfe specifications at different collector currents. For transistors intended for switching applications this will be very brief but more specialized amplifiers may list hfe specifications at several collector currents. If necessary, pick a transistor intended to operate at the collector current you have chosen to get a better specification. If you want to explore cutoff, active, and saturation, then adjust the circuit to the transistor instead. |
| Jasonbit:
Thanks to your advice's ;D Exist any book or article where can I identify all parameters in datasheet? For example, the parameter Vebo - Emitter-Base Voltage and Vceo - Collector-Emitter Voltage I can't identify what means the last letter (o). I know this parameter means Voltages applied between emitter-base and between collector-emitter, respectively. But what means a last letter? Thanks |
| tggzzz:
--- Quote from: Jasonbit on July 21, 2018, 11:03:48 pm ---Exist any book or article where can I identify all parameters in datasheet? For example, the parameter Vebo - Emitter-Base Voltage and Vceo - Collector-Emitter Voltage I can't identify what means the last letter (o). I know this parameter means Voltages applied between emitter-base and between collector-emitter, respectively. But what means a last letter? --- End quote --- See http://lmgtfy.com/?q=Vceo |
| David Hess:
--- Quote from: Jasonbit on July 21, 2018, 11:03:48 pm ---I know this parameter means Voltages applied between emitter-base and between collector-emitter, respectively. But what means a last letter? --- End quote --- "o" in this case just means that the other terminal is open. Vce has several ratings depending on if the base is positive, negative, shorted to the emitter through a resistance, or open. Vceo is the lowest of these so the safest to design with. |
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