Some info about transistors

Other Hardware General Electronics
1

Hi,
I don't understand transistors. I know they are PNP, NPN and have basic understanding what that mean, I think I roughly understand difference between monopolar and bipolar but that is all. When I use which type of transistor? What parameters are important? Do you know some good text about this? I didn't find anything general enough to get some basic insight.
Thanks

2

If you Google " transistor tutorial " it returns 558,000 entries, so you should find something you can follow ..

3

I don't understand transistors.

A regular bipolar transistor is a current-controlled switch or amplifier... For example, we can take the 5V output of the Arduino at low current and control a higher voltage and/or a higher current. ...

Think about how a small amount of force on your gas pedal in your car controls hundreds of horsepower.

I know they are PNP, NPN and have basic understanding what that mean

Since we're usually working with positive voltages we are almost always using NPN transistors.

What parameters are important?

Of course it depends on the circuit, but most of the time we're only concerned with current and power ratings. Current and power ratings are related and you have to be extra-careful about power dissipation in linear (non-switching) applications. And, be aware that the current & power ratings are defined with the transistor case at room temperature, so you normally need a heatsink and even with a heatsink you can rarely get away with dissipating the full rated power.

If you get into higher voltages, you may have to check the voltage rating and if you get into high frequencies you may have to check the high-frequency characteristics. With analog circuits, you may need to know the gain (Hfe), but with digital switching circuits you can usually assume an Hfe of about 100 and then you design your circuit to work with a gain of about 50 or more.

A big part of engineering is knowing what's important and what's not important. Usually, we are only interested in a few of the hundreds of pieces of information on a datasheet. But, there's no easy way to know what's important in a particular application... That only comes with study & understanding...