Connect with us

Equivalent Transistor.

Discussion in 'Electronic Design' started by [email protected], Feb 16, 2007.

Scroll to continue with content
  1. Guest

    I am currently working on a project to regulate the speed of a
    computer's case fan using a momentary switch (see http://

    After working with one of the other users, I was able to come up with
    a workable circuit based on his reference design, located here:

    The problem is that I cannot find the specified transistors. I was
    able to aquire the rest of the components with minimal difficulty, but
    the Trans. are nowhere to be found.

    What I need is a short list (doesn't have to be complete, of course)
    of transistors that would be equivalent to a 2N4401 NPN switching
    transistor. It must take a 5-volt signal (<15mA) on the base from a
    TTL IC, and use this signal to control a twelve volt current not
    exceeding 250 mA (The higher this maximum, the better, but less than
    0.5A Max). As can be seen from the diagram mentioned above, a low
    input to the transistor disables the current, while a high (~5v)
    signal enables it.

    This is kind of an urgent matter as tommowow will be my last
    opportunity to pick them up; after which I will have to wait in agony
    until Monday-not a good experience.

  2. Guest

    *Correction: Ignore the statement about 0.5A max. I was looking at
    the datasheets for a 2N4401, and noticed that they themselves go up to
    600 mA. No ceiling on this one.
  3. Robert Baer

    Robert Baer Guest

    Cannot get the image.
    Use any medium-signal NPN; that is to say, not small signal like the
    infamous 2N2222 whic would be a POS in that application.
    BTW, one does not drive a transistor base with voltage...
  4. Robert Baer

    Robert Baer Guest

    So you found a transistor...
  5. Guest

    So you found a transistor...

    No, the schematic I am basing my design from calls for a few
    2N4401's. However, I am unable to aquire them, because the place I
    get components from does not carry any. The people who work there
    (think work-study undergrads), couldn't tell a diode from a toaster,
    so any querys as to what transistor would be a suitable replacement
    would go unanswered. I myself confuse electrical components with
    kitchen appliances from time to time as well, and I too don't know
    which transistors would work (hence this Usenet post directed at
    electronics experts/hobbyists). What I need is a list of parts
    numbers that you can say with complete certainty, "Yes, you can use
    this transitor instead of those for this application, and it will work
    as required". This way when I go to the stockroom with the
    elecrically illiterate, I can say "I need four 2Nxxx's. Do you carry
    those? No? How about 2Nyyyy's? 2Nzzzz's?". Get what I'm saying?

    If you look at the schematic, you'll see that I needed about a dozen
    pieces. I have every part but the transistors, and the miniboard /
    soldering equipment should be coming in the mail tommorow. I'd like
    to get it all done by tommorow night, but If I don't know which trans.
    to get, I'll have to wait until monday or later to get em'. Not good
    news, seeing as this (moderately) simple project is about a week in
    the making, and has taken varying amounts of effort from a dozen
    people or so.
  6. GPG

    GPG Guest
  7. Fred Bloggs

    Fred Bloggs Guest

    The 2N2222 will work in that application, they are cheap and abundant.
  8. Fred Bloggs

    Fred Bloggs Guest

    That's bull, even the PN2222A can handle 1A peak, and maintains a
    minimum HFE of 50 at 250mA with VCE,sat under 0.2V. It is a general
    purpose switching transistor, not small signal, and is competitive with
    the 2N4401 in most applications.
  9. Rich Grise

    Rich Grise Guest

    PN2222 is probably cheaper and easier to find. :)

    Then again, it's another number to hit the stockroom kids with. :)

  10. ehsjr

    ehsjr Guest

    BC337 is another substitute, besides 2N2222, that
    will work for you.

    It's best to look at the datsheets for the transistors
    the supplier can provide you. No one here has a
    crossreference list to what's in stock at your

  11. Rich Grise

    Rich Grise Guest

    That's the best idea - find out what they've GOT, then look up the
    data sheets and find one that will work.

    Just about any "general-purpose" NPN transistor should do.

    Good Luck!
  12. Robert Baer

    Robert Baer Guest

    Since the schamatic is inaccesable, i cannot help too much.
    NTE cross reference shows the 2N4401 as equivalent to their 123AP
    (TO-92 package, 600ma Ic max, 40Vce rating and 625mW max dissipation).
    Some other types that also cross to the 123AP are: 2N117, 2N118,
    2N118A, 2N119, 2N120, 2N148C, 2N148C/D, 2N148D, 2N160, 2N160A, 2N161,
    2N161A, 2N163, 2N263, 2N264, 2N385/46, 2N706/46, 2N706/51, 2N706A/46,
    2N706A/51, 2N706B/46, 2N706B/51, 2N708/46, 2N709A/46, 2N......., 2N4400,
    2N4401, 2N4420, 2N4421, 2N4422, 2N4432, 2N4432A, 2N4950, 2N4966, 2N4967,
    2N4968, 2N......, 2N5769, 2N5810, 2N5845, 2N5845A, 2N5851, 2N.... und so
    wieder ad nauseum.
  13. Robert Baer

    Robert Baer Guest

    I see, from figure 3, page 4 that a pissy 2N2222 is shown.
    Look at the data sheet curves for the 2N2222 and you will see that
    they are decent to about 100mA and after that, internal losses become
    Hell, a TIP50 would be better in its sleep!
  14. Robert Baer

    Robert Baer Guest

    ....and absolute shit above 100mA.
  15. Robert Baer

    Robert Baer Guest

    Excuse me! The original 2N2222 data sheet indicates "small signal"
    and the curves show that there are serious internal IR losses as one
    goes above 100mA; if one is crazy enough to attempt even 500mA, based on
    those specs, it would blow its cork!
    Now the PN2222A *might* be a little better due to a different die
    size and diffusion schedule.
    Looking at the Fairchild data sheet, please note there are no
    oerational specs or curves beyond 500mA, and those curves indicate that
    operation above 100mA can result in power dissipation tradeoffs that
    might not be acceptable.
    Furthemore operation at your vaunted one amp is certainly not
    recommended, as that is the *absolute maximum* rating!
  16. Robert Baer

    Robert Baer Guest

    That is about what i initially said..
  17. Fred Bloggs

    Fred Bloggs Guest

    That's not true, the transistor has been designed for maximal Hfe in
    that current range, and it is spec'd out to 500mA, which should give you
    a clue. You will be calling for a 2N3055 next.
  18. Rich Grise

    Rich Grise Guest

    Well, at least it wouldn't oscillate. ;-)

  19. Guest

    I mannaged to acquire a few 2N2222's, and they work fine; however,
    after building the final version of the circuit, I uncovered a
    separate problem which is best discussed in a separate post (IC
  20. Robert Baer

    Robert Baer Guest

    Lemme see now; Philips has a max spec of 800mA in the *metal* can,
    and both Fairchild and Philips indicate a VCE(sat) of 1.6V (!!!) at
    500mA - meaning an internal dissipation of 800mW nevermind the max
    dissipation spec is 500mW.
    I guess you love that loss and the smell of cooking silicon...
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day