Is there a transistor comparison chart or database to be found?

Question

When picking a transistor, I usually start with my supplier's catalogue and search and refine according to the specs I am most interested in. However, I seem to often come out with odd choices. For example I recently needed an NPN for basic switching of a 200mA current using an MCU, and ended up picking a BC337. It seems to work, however it also seems to be categorised as an 'audio amplifier' rather than a 'general purpose' or 'switching' transistor and so I can't help think I could have made a better choice (or maybe it doesn't matter). Likewise, I have a big bag of BC548's that I use a lot, because I happened to have one in my first 'beginners' set, and as it usually worked I just stuck to that regardless of if it was the best choice.

I think I would find useful a simple chart with the most common types, and their characteristics, that I could print off and have to hand to simply look up a suitable type. Google searching has found a few charts from the 60s, a few books (at ridiculous prices, nearly as out of date) but not a simple 'picker' or 'comparison chart' that I can find.

Can anybody recommend one? Or is there a simpler method for picking? Or does it really matter what the 'type' is if I'm just using it for switching (as I always am at the moment, as I'm only doing digital circuits so far)?

Maybe a better simpler question is...how do YOU go about picking a transistor for a switching job?

Answer 1

There are way too many transistor types, even if limited to bipolar as you seem to be asking about, for any kind of simple chart. After a while you will converge on some favorite types for certain applications. For example, my knee jerk small bipolar transistors are the 2N4401/4403 (in reality MMBT4401/4403, but the 2N numbers are shorter and easier to say). Lots of people seem to like the 2N3906 or 2N2222A, but the '4401 is a bit more robust and still dirt cheap.

如果你是新到这s and are not looking for something out of the ordinary, go to a distributor site like Mouser and look around. Lots of parts will meet the specs, but the price and quantity on hand will be good indicators of how mainstream it is. This is a case where low price is good not only to save money, but a indicator of what volume the part is produced in. The number of companies making basically the same part is another indicator. Unless you have special requirements, don't get something special.

When I do have special requirements, for bipolar transistors I usually go to the Zetex (now On Semi?) site. You will find much less overlap within any one manufacturer's line. Most of them have pretty good selection guides that let you drill down to find the part that best fits your need. However, the manufacturer won't give you much guidance on how obscure a part is. If the manufacturer stocks and sells their own stuff, then this is less important. If not, check a few mainstream distributors to see how popular and available the part is. The less popular and available, the more you are putting future production at risk.

If you find yourself really needing a particular obscure part, the first thing you should do is go back to your circuit and see if a little rearranging can alleviate some of the requirements. Sometimes you really need it, but you should ask yourself carefully why you need it if it looks like few others have needed it before. If you still need the obscure part, look around at other manufacturers for other options. Ideally you can spec two or three unique manufacturer parts for the specialized requirement. That will give purchasing some options in a few years when one manufacturer discontinues your part. In some cases it might mean putting two different footprints on a board so that different parts can be substituted depending on availability and price. Don't be the engineer that painted the company into a corner.

Answer 2

when i use transistors,i used to look at various parameters of my design such as supply voltage,frequency,current gain,power.Then i choose the appropriate transistor,

a)DC i)Low voltage,low power,high beta -->BC547(NPN),BC548(NPN),2N222(NPN),BC557(PNP) Applications->per-regulator(with zener ref),LED driver(for microcontroller)

ii)Low voltage,medium power,medium beta -->SL100(NPN),CK100(PNP),BD139,BD140. Applications->Relay driver,Low power series pass regulator,H-bridge,DC motor driver

iii)low voltage,high power,low beta->2N3055,TIP127,TIP125.

Applications->High power series pass regulator,Square wave inverter,DC motor driver,H-bridge

b)Audio frequency(20Hz-20Khz)

i)Low voltage,low power,high beta -->BC547(NPN),BC548(NPN),BC557(PNP).

Applications-> Pre-amp,Tone control,equalizer.

ii)Low voltage,medium power,medium beta->SL100,CK100.

Application->Medium power audio amplifier.

in some circuit designs you cannot directly connect transistors like SL100,CK100,BD139,BD140 with some microcontrollers. for driving relays,DC motors,DC incandescent lamp, because the beta of these transistors would be small. so it would require current in few milliamperes the microcontroller mayn't source/sink that much current. so you have to use pre-driver stage(BC547), then it should be connected with transistor. if you don't want to waste the power to drive the power transistor you may choose MOSFET.

you can follow the above mentioned steps, if you design your circuit from scratch. but this mayn't help you to repair the circuits, by replacing the faulty transistor(obsolete) with new one. if you want to do so then you get the datasheet of the obsolete/hardly findable transistor.and look at various parameters, then summarize them and look at the the datasheet of widely us transistors datasheet(you can simply replace it as if changing a faulty resistor with new one). some times this may or mayn't work ( because it depends on various design parameters like noise immunity,voltage/current gain,stability of the Q point,type of biasing,etc.. )

i suggest you stock easily available transistors and make a chart of those transistor parameters and try to design the circuits.

Answer 3

Download the list of 888 transistors with its electrical characteristics as xlsx:https://www.diodes.com/productcollection/export/8417

Or use the online transistor selector tool:https://www.rohm.com/calculators/digital-transistor-selection-tool