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| I higher is hfe in 2N3904? |
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| Jasonbit:
Maybe I don't see right the all spefectaion in this datasheet (https://www.onsemi.com/pub/Collateral/2N3903-D.PDF). Supposedly this transistor on model 2N3904 should be HFE=40 but when I measure with my multimeter (on function hfe) I get a value 212. Why? (see this table please: https://snag.gy/a9SM8T.jpg ) Thanks [UPDATE1] heyyy, after I posted my question I see which this list has two lines to 2N3904. Ok, but what line should I look? (I need a transistor with a hfe very lower. Which model do you suggest I use? And where and how can I search about transistor with hfe below 100? Thanks |
| rstofer:
The values in the table are mostly Minimums but the Maximum might be as high as 300. In other words, the gain could be all over the map. The manufacturer just isn't characterizing Typical and Maximum. That a safe thing to do because we would design with Minimum gain and provide feedback to control the amplifier if we had very high gain. |
| drussell:
A 2N3904 has an hFE of between about 25 and 400, depending on the operating conditions. It says so plainly in the data sheet characteristics charts. (The gain of any transistor will vary widely depending on the exact circuit conditions). Perhaps if you told us a bit about what you are trying to do, what your circuit is, etc. we can provide some more helpful guidance. :) |
| Jasonbit:
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? The purporse of the circuit is see three stage on transistor (cutting, active, saturation). For this I thought to use an transistor with hfe very lower. What do you think? Thanks |
| Zero999:
Why not design the circuit so it works with any transistor, with a gain higher than 40? Designing a circuit so it only works with transistors with a narrow Hfe range, is extremely bad practise and will only cause problems, later on. |
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