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Topic: Questions about transistors, capacitors and diodes (Read 1 time) previous topic - next topic


I'm putting together a shopping list of components for general purpose use. Some of them from a post I made in this forum, some from Tom Igoes "Making Things Talk" and some from tutorials I've found online describing different stuff.

However I have some questions....

Capacitors: My retailer only carries electrolyte 0.1 uF. Can I buy that instead of ceramic?

Transistors: I'm only trying to buy some generic stuff in a batch not for any specific projects. And to me the first three on the list look pretty much the same. Can I exclude two of them or could there be other differences I need to consider? If I can, could I do without any of the others aswell?

  1. 2N3904 TO-92 NPN 50V 100mA
  2. 2N2222A TO-92 NPN 40V 800mA 300MHz
  3. BC547B TO-92 NPN 45V 0.1A
  4. TIP120 TO-220 NPN Darlington 60V 5A
  5. IRF540 TO-220 N-ch MOSFET 100V 28A
  6. 2N3906 TO-92 PNP 40V 200mA

Diodes: Same question as above...
  1. 1N4004 DO-41 400V 1A
  2. 1N4007 DO-41 1000V 1A
  3. Zener BZX55C3V3 DO-35 3.3V

Best regards


Very strange that your supplier only has electrolytic 0.1uF capacitors.  They're just about the commonest type to find in ceramic!  But you can use electrolytic (probably tantalum) as long as you connect them with the correct polarity.

The first three types of transistor are all very similar, as you noticed.  Maybe just buy the cheapest type!  There may be a similar situation with the 2N3906 and other small PNP types.

As for diodes, just get the 1N4007 and the Zener, although you are unlikely to need that 1000V rating!  1N4004 or even 1N4001 might be cheaper!



The BC547 is the cheapest of the bunch but since it's got a 100mA rating I'll go with the 2N2222A since I might need more juice driving multiple leds and whatnot.


... or I should just learn math better. Turns out they were labeled 100 nF instead of 0.1 uF.


100nF is the same value as 0.1uF (100 nano Farads equals 0.1 micro Farads).  Are you saying that your supplier has got 100nF parts in ceramic form?


The 3904 and 3906 are a NPN/PNP pair  with similar characteristics.

If you go with the 2N2222A, you should get a 2907 for the PNP.  I use the 2222/2907 type for my "generic" transistors.  You dont seem to have a higher current PNP on your list.  

You dont want to find out that your NPN and your PNP take different base resistors (different base current).  That will make substitution that much harder...


Yes I am...

Great tip... Btw how about a good PNP equivalend to BC547B (I realized a mix of transistors would be cheaper than buying just the high current ones).


While I'm not certain, since the 2N series are easier for me to get, the BC557 is considered to be the PNP equivalent to the BC547.


thank you...

I have yet another question. Since my first thought was to buy the more capable transistor of the three and also the most expensive one, not that price really matters since I'll be buying only 5 pcs, however I just want to get my head around this. In my list I already have a higher current capable darlington transistor. I could use this one for whatever might need more than 100 mA and go with any of the cheaper transistors under 100 mA.

This is the first time I'm buying transistors and using them, hence the many questions.


There are subtle differences between an ordinary (bipolar) transistor and a darlington.  One difference is that the base-emitter voltage of a darlington is about 1.4V, against 0.7V in a standard part.  So, a darlington might not be a good "universal substitute" for a standard transistor.


You can use two bipolars to make a pseudo darlington.  But I dont think you can easily substutue a darlington for a bipolar.  


Thanks alot...

I realize I have alot to learn about electronics and I want you guys to know that I appreciate the time and effort you put in answering my questions here.. even though this is mainly an arduino forum.

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