Hfe question

L

lerameur

Guest
Hello,

I was hoping for somebody to explain how to read the hfe column on the
specification sheet
if you look at digikey web site for the chip TIP41C, you will see the
column:
DC Current Gain (hFE) (Min) @ Ic, Vce
The same chip go between 0.60cents to 1.16dollar with just this
parameter different.
I read that Hfe is was the current gain, but can someone tell me why
it is more expensive, is it better?
the cheaper tip41c has: 30 @ 300mA, 4V TIP41CTU-ND
while the other at double the price is : 15 @ 3A, 4V TIP41CGOS-ND
I suppose the expensive one can carry more Ic, but the spec sheet are
identical and Ic is 6amp continuous
what does that 300mA or 3A stands for,

thanks
K
 
"lerameur" <lerameur@yahoo.com> wrote in message
news:d8945ea4-93cd-41a5-b977-861878446aaf@p5g2000pre.googlegroups.com...
Hello,

I was hoping for somebody to explain how to read the hfe column on the
specification sheet
if you look at digikey web site for the chip TIP41C, you will see the
column:
DC Current Gain (hFE) (Min) @ Ic, Vce
The same chip go between 0.60cents to 1.16dollar with just this
parameter different.
I read that Hfe is was the current gain, but can someone tell me why
it is more expensive, is it better?
the cheaper tip41c has: 30 @ 300mA, 4V TIP41CTU-ND
while the other at double the price is : 15 @ 3A, 4V TIP41CGOS-ND
I suppose the expensive one can carry more Ic, but the spec sheet are
identical and Ic is 6amp continuous
what does that 300mA or 3A stands for,
Click to expand...
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.
 
"lerameur" <lerameur@yahoo.com> wrote in message
news:d8945ea4-93cd-41a5-b977-861878446aaf@p5g2000pre.googlegroups.com...
Hello,

I was hoping for somebody to explain how to read the hfe column on the
specification sheet
if you look at digikey web site for the chip TIP41C, you will see the
column:
DC Current Gain (hFE) (Min) @ Ic, Vce
The same chip go between 0.60cents to 1.16dollar with just this
parameter different.
I read that Hfe is was the current gain, but can someone tell me why
it is more expensive, is it better?
the cheaper tip41c has: 30 @ 300mA, 4V TIP41CTU-ND
while the other at double the price is : 15 @ 3A, 4V TIP41CGOS-ND
I suppose the expensive one can carry more Ic, but the spec sheet are
identical and Ic is 6amp continuous
what does that 300mA or 3A stands for,

thanks
K
Click to expand...
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
 
On Fri, 12 Jun 2009 13:52:28 -0700 (PDT), lerameur
<lerameur@yahoo.com> wrote:

I was hoping for somebody to explain how to read the hfe column on the
specification sheet
if you look at digikey web site for the chip TIP41C, you will see the
column:
DC Current Gain (hFE) (Min) @ Ic, Vce
The same chip go between 0.60cents to 1.16dollar with just this
parameter different.
I read that Hfe is was the current gain, but can someone tell me why
it is more expensive, is it better?
the cheaper tip41c has: 30 @ 300mA, 4V TIP41CTU-ND
while the other at double the price is : 15 @ 3A, 4V TIP41CGOS-ND
I suppose the expensive one can carry more Ic, but the spec sheet are
identical and Ic is 6amp continuous
what does that 300mA or 3A stands for,
Click to expand...
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
 
On Fri, 12 Jun 2009 22:53:40 +0100, Electronworks.co.uk wrote:

"lerameur" <lerameur@yahoo.com> wrote in message
news:d8945ea4-93cd-41a5-b977-861878446aaf@p5g2000pre.googlegroups.com...
Hello,

I was hoping for somebody to explain how to read the hfe column on the
specification sheet
if you look at digikey web site for the chip TIP41C, you will see the
column:
DC Current Gain (hFE) (Min) @ Ic, Vce The same chip go between
0.60cents to 1.16dollar with just this parameter different.
I read that Hfe is was the current gain, but can someone tell me why it
is more expensive, is it better?
the cheaper tip41c has: 30 @ 300mA, 4V TIP41CTU-ND while the other at
double the price is : 15 @ 3A, 4V TIP41CGOS-ND I suppose the
expensive one can carry more Ic, but the spec sheet are identical and
Ic is 6amp continuous
what does that 300mA or 3A stands for,

thanks
K

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
Click to expand...
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"
Hello,

I was hoping for somebody to explain how to read the hfe column on the
specification sheet
if you look at digikey web site for the chip TIP41C, you will see the
column:
Click to expand...

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

http://www.fairchildsemi.com/ds/TI/TIP41.pdf

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"


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

** 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
www.electronworks.co.uk
Electronic Kits for Education and Fun


"Phil Allison" <phil_a@tpg.com.au> wrote in message
news:79ghmmF1qjt62U1@mid.individual.net...
"Electronworks.co.uk"


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


** 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
Click to expand...
 
"Electronworks.co.uk"


** Fuck off - you top posting fool.


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


"Phil Allison" <phil_a@tpg.com.au> wrote in message
news:79ghmmF1qjt62U1@mid.individual.net...

"Electronworks.co.uk"


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


** 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
Click to expand...
 
On Sat, 13 Jun 2009 22:15:19 +0100, Electronworks.co.uk wrote:

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.
Click to expand...
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
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.

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.
Click to expand...

** 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
 
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