The two most popular kinds of transistors you might use for a project are either BJTs or MOSFETs. With so many options, it was tough to pick just a few.
We covered the 2n3904 in this video. What BJTs are your favorites and why? Leave a comment below.
Transistors are electronic switches that are used to control things that would kill an Arduino, Raspberry Pi, or Beaglebone. There are two major types known as a BJT and MOSFET. This is part 1 of a two part series, which looks at BJTs first.
Learn what they are and how to use them.
Don’t forget to subscribe to the AddOhms YouTube channel to know when Part 2 on MOSFETs is released!
Episode Notes
Suggested links for Ep10:
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The best four transistors to keep in your toolbox [baldengineer.com]
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Fairchild 2n3904 Datasheet (BJT NPN Transistor) [fairchild.com]
Inside a NPN BJT
Zeptobars.com has an awesome picture of the die inside of a Fairchild S9014 BJT NPN. Zeptobars.com has a ton of other great images, check out their bare die pictures.
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3 Comments
I James, this is Carlos, from Portugal, do you have any information about a Mosfet ref. CMU06N02N 1209? It’s a Mosfet to control a DC motor for an RC unit.Thanks in advance and congratulations for your excelent way of teaching.Regards.Carlos
Thanks for the video. I am confused though, it seemed you assumed HFE to be 100, even though the spec sheet had many values listed depending conditions. For example 100 HFE was for IC = 10mA and VCE = 10V.
From the video I don’t see calculations made for IC or VCE so how can you be so sure its 100HFE? I understand HFE is a bit of a moving target. However unless I am missing something (which I’m sure I am) HFE is critical to determining how much current you will get between ICE. I’m struggling with finding a way to find out what HFE is for a given input current and desired output current.
For example, if I have my Raspberry Pico which has 3.3 V GPIO lines and I connect one to the base and I want to have 20mA available to me at the collector so I can “max power” an LED how can do this, if I dont know what HFE is? if I guess 1000 say in this case the LED would be toasted.
Is there a way using a multimeter and/or bench top power supply to determine what R values I need to use to get to 20mA? HFE is spread from 35 to 500 depending on the BJT. So Without guessing HFE how can I find out. I’ve ordered a tool that will measure it but I want to know how it can be done using just a bread board, some wires and an LED or another device? I’ve been searching for a good answer on this all over and cannot find it. HFE is assumed in almost everything I read. There has to be a way to test this without blowing through LEDs until I find a combination that hits 20mA. I know my problem is mostly going to go away when I get my measuring device (Peak Atlas DCA) which will help with other devices as well. Thanks.
You can’t use the transistor to limit the current for an LED. You still need a current-limiting resistor.
When using a BJT as a switch, you really don’t care what its hFE is since you’re driving into saturation anyway.