Hi,
Another newbie question…I have been reading schematics and seen a variety of transistors. Question is: Which ones to buy? (Of course, this depends on power and ampere ratings and a project’s needs.) But, in general which would be good for beginners.
I’ve got some 2N2222 ones.
Thx
Those are fine.
Leon
It depends on what you’re doing. Probably the one parameter that might be problematic is the beta value or the gain of the transistor. If a transistor has a beta of 200, it means that 1uA into the base lead will roughly translate to 200uA of current on the collector lead. In certain situations, you may run into a limitation where you want to control over an amp of current with an AVR, but the beta value of the transistor you have isn’t high enough to fully turn on the transistor given the output current limitations of the microcontroller. When that happens, I usually switch to using N-channel mosfets.
Otherwise, the 2N2222 is a very popular switching transistor that’s ideal for small signals/low current applications.
Thanks, all for the answers.
Just also a word of warning. \beta (or H_fe) in bipolars is usually not very tightly specified. Don’t make circuits that depend on exact values - expect some variance from part to part.
I find MOSFETs to be more suited for switching control for microcontrollers. Just look for one with a low voltage V_gs (close to 0, to cover both n and p channel), so they are fully based off of just your pin output.
MOSFETs tend to draw less current then BJTs. In their on state they theoretically draw nothing. But when they turn on you have to “fill up the charge well” just like charging a cap. That generally only matters when you have a very large FET. Of course you can use a small FET to drive a large one, similar idea (slightly different arrangement) to the BJT Darlington arrangement.
Back to the original question, the BJT you selected should work well for many applications, that is why they are so common. As you pointed out, it is all application specific.