Hfe question

Knowing Hfe allows you to work out how much base current your driver circuit needs to provide to support a given collector current. Unfortunately, Hfe varies with collector current and manufacturers often only quote one data point. Sometimes you get a graph.

Hi

The answer is more commercial than technical. Fairchild is a low cost supplier. If you are designing a low cost bit of kit, look on the Fairchild website and chances are, their components will beat the competition. It is their way of buying their way into the market.

The gain will change as collector current changes and indeed the specs referred to in the table reflect those in the Fairchild datasheet. However, if you buy one component from 3 suppliers they should all perform the same. Regardless of the component (transistor, op amp etc) if they all have the same part number, they should all have very similar (if not identical) datasheets and can be interchanged accordingly.

To answer your question, they can all carry the same current and at that current, will all have (theoretically) the same gain

Rgds

--
Bill Naylor
www.electronworks.co.uk
Electronic Kits for Education and Fun

First off, kill the non-stock. The rest are similar packaging from essentially different manufacturers, which may have different processes they use with slightly different 'features' as a result. You'd need to look closer at each different datasheet to find out what differences are useful to you. Two are from the same manufacturer, Fairchild, and those are also (coincidentally?) the lowest two prices in the list. From Fairchild, the TIP41CTU appears to be packaged in rails while the TIP41C is in bulk, which probably accounts for slight differences in price.

Probably, the only reason that you see a difference in the listed hFE minimums on Digikey is that someone (filtering data from the manufacturers) chose to place those numbers into the database. If you look at the datasheet from Fairchild -- which is very easy to do, by way of using Digikey to get there -- you would see that the datasheet there specifies hFE for two values of Ic, 300mA and 3A. And that the minimum figures are 30 and 15, respectively. That hFE=15 at Ic=3A also matches the figures that Digikey shows.

All this goes to say that _you_ should learn to take a moment and go dig out the datasheets, themselves, and look them over a little on your own. You are way too focused on the numbers that Digikey decides to list. Once you learn a little more about how BJTs work, you'll find all of this being easier to get through, as well.

In short, they are all probably very close to each other on the usual, important parameters -- Vceo is 100V on all of them (which is what the 'C' on the TIP41 means), and all are also hFE=15 at Ic=3A. You don't see that until you go get the datasheets. But that is just something you have to learn to go do. When numbers in the columns on Digikey are spec'd differently (Ic=300mA for some, Ic=3A for others, for example), then that just means you need to go dig a little more.

Nothing new.

You would probably be just fine with any of them, if one of them works okay. Pick the cheapest, unless you know something specific that you care about and is different between them.

Keep in mind I'm a hobbyist, though. So if an expert rolls over my comments with a bludgeon, take their points to heart over mine.

Jon

If you buy one component from three different suppliers chances are they'll all three be similar in the main but remarkably different around the edges. I wouldn't change suppliers (or supplier part numbers) unless and until I had evaluated each part for suitability.

PITA? Yes. But it's a lot better than getting those calls from the manufacturing floor two weeks before the end of the quarter.

--
www.wescottdesign.com

"lerameur"

** You got some kind of aversion to looking at ACTUAL data sheets ???

Hfe is a VARIABLE - it varies with collector current level, temperature, Vce AND from sample to sample of a device type. Note that while the minimum value for Hfe at 3 amps in the table is 15, the max value is 75 !!!

The graph of Hfe ( figure 1) shows a typical sample tested at room temp and with Vce of 4 volts.

Different graphs would apply for higher and lower Vce values - generally Hfe rises with rising Vce and temp.

Capice ???

.... Phil

"Electronworks.co.uk"

** Huh - WTF does " theoretically the same gain " mean ??

The specs make it clear there is a range of Hfe values that varies from sample to sample.

..... Phil

Hi Phil

Glad to see you have surfaced from your hole. Take a selection of transistors from one manufacturer and a selection of transistors from another manufacture and stastically they should all have the same spread of gains.

Hope I have made my point clear. Keep taking the pills, crawl away and quietly die - please.

-- Bill Naylor

Electronic Kits for Education and Fun

"Electronworks.co.uk"

** Fuck off - you top posting fool.

Your "should" here is the one that means "is morally obliged to", of course, not the "can be reasonably expected".

Too bad this is the real world.

--
http://www.wescottdesign.com

"Tim Wescott" Electronworks.co.uk = Bill Naylor

world.

** Bill Naylor lives in his own little world ( planet Naylor) where things ARE as HE says they *SHOULD* be.

Note how he has a business selling simple kits to beginners - so no doubt HE likes to swap brands and suppliers about at whim to fill his kits.

Power BJTs are something I am very familiar with, particularly testing and matching them PLUS various ways to identify the fakes and sub-standard parts that have now flooded the hobby and spares trades.

In May of 1988, Electronics Australia magazine published my design for a " Power Transistor Tester " - it was then sold as a kit by several business here in Australia.

I can assure anyone here that the brand DOES matter and more importantly the chain of supply from factory to you must be uninterrupted.

..... Phil