How do I find the right Transistor?

Discussion in 'General Electronics Chat' started by Mongrel_Shark, Jun 5, 2012.

  1. Mongrel_Shark

    Thread Starter New Member

    May 30, 2012
    So I'm pretty new to transistors. Used them in circuits drawn by others before. But now I need to find one (or even better a few I can play around with) which meets certain requirements.

    In this case I really need to know the low ranges, I need low base voltage. So I figure I need germanium. Ordered some big ones (ac141k, stop laughing please, they have shiny heatsink, and I love shiny things) because I thought they would be versatile as well as being useful in a later project I am planning. As I suspected, they don't work very well on my low power circuit. I can get light from .2v, but its not as good as the same circuit with a BC337, 347, 348,349, or even a 2n3904....

    Before you ask. I am making a joule thief to run on very low voltages. (in this example, a solar cell indoors) There are tons that go down to around .5v even with .6-.7v silicon transistors. Due to the boost from the induction coil increasing base volts.

    I've seen one go down to less than .2v and still light an LED (Dimly) using a bc107. With a specific coil winding.

    I don't need much help on the coils. I want to learn the maths there asap. I'll start a thread on my joule thief project if I feel I need serious help.

    I was just wondering if there is a search engine for transistors and other semis?

    Even a big chart?

    The local electronics store has a partly handy chart for all the parts they stock. but it's a very limited selection and mostly just has max ratings. never lowest operation figures.

    So my main Question is this.

    Once I know what characteristics are desirable. How do I find the right component?

    Trawling through data sheets in making my brain go numb...

    Especially with old germanium stuff that is out of production.

    How do I find the right Semi?
  2. BSomer


    Dec 28, 2011
    I do not think that I can provide much help in the way of which transistor you need. However, online stores such as Mouser and DigiKey have pretty good search engines of sorts. You get to the category you desire, i.e. transistors (discrete semiconductors), then pick through the parametric search bar for the characteristics that meet your requirements. Sometimes you can narrow your available selection to a dozen or less.

    I say that they are pretty good though there are some devices that can "fall through the cracks". The parameters for the devices are filled in by a person and sometimes they make mistakes or do not put everything in for a device.
    Mongrel_Shark likes this.
  3. Mongrel_Shark

    Thread Starter New Member

    May 30, 2012
    Thats a LOT better than going through all the data sheets at the data sheet archive....

    I hope they still sell germanium..

    If anyone does know of anything that would be good around .2v and under 40ma MAX, I can get light from 200 micro amps, (aiming for 4 micro amps, not holding my breath on that) That will work in a joule thief. Please let me know.

    Or if anyone knows of an online search that has datasheets in a database so I can search by characteristic, rater than model no. That is equal to or better than the suggestions above. Please let me know.
  4. absf

    AAC Fanatic!

    Dec 29, 2010
    Last edited: Jun 5, 2012
  5. Rbeckett


    Sep 3, 2010
    You can go to mouser and the other big components sellers and use the filter to select an appropriate transistor that way. Just keep adding one parameter at a time till you get a reasonable number of suitable options. Works fer me...
    Wheelchair Bob
  6. Wendy


    Mar 24, 2008
    Don't be afraid to "audition" components. This is done all the time by hobbyists, and transistors are cheap. Last time I bought PN2222A in bulk my cost was around 1.3¢ each.
  7. radiohead

    Distinguished Member

    May 28, 2009
    There are similar sheets out there like this one...

    I hope this helps.