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2N3055

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terry
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Username: terry

Post Number: 616
Registered: 05-2005

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Posted on Wednesday, 16 February, 2011 - 09:35 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Im using a TL431 to drive a 2N3055 at about 4A but the TL431 burns out at this current. It works fine at 2A but I have not checked the drive level on the base of the 2N3055 yet. Dose anyone know what drive level is required at 4A ?

Thanks Terry
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vlf
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Username: vlf

Post Number: 228
Registered: 10-2005


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Posted on Wednesday, 16 February, 2011 - 10:10 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Hi Terry... the TL431 shunt regulator max current is 100 mA. The 2N3055 depends on C/E pd voltage, however data state at saturation I/CE=4A then I/B=400mA, the curve starts around 200mA.

Not sure this helps you though.

Regards, Brian L.
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epithumia
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Username: epithumia

Post Number: 839
Registered: 06-2006

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Posted on Wednesday, 16 February, 2011 - 10:11 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

From the datasheet below, gain appears to be 35 at 4A, so 4/35 ~= 114mA.

http://www.datasheetcatalog.org/datasheet/motorola/2N3055.pdf

Although that's at 4Volts. As vlf pointed out, the Vce affects the gain.

Epi

(Message edited by Epithumia on 16 February, 2011)
If you need me, Neil and me will be hanging out with the Dream King. - Tori Amos
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terry
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Username: terry

Post Number: 617
Registered: 05-2005

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Posted on Thursday, 17 February, 2011 - 08:03 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Thanks Guys, Im using it to start shunting a 12v lead acid battery at 14v to stop it being overcharged by my solar panel. The panel can output about 4A max but most of the time will be much lower as it is mounted flat on the roof of my camper.

I thought the 100mW drive from the TL431 would be enough to fully drive the 2N3055 but testing shows it is not, Im not great at working out the maths so I thought I would ask here as I know there are some clever people here :-)

It seems I will need to add another stage to ensure it is reliable.


Terry
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alec_t
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Username: alec_t

Post Number: 521
Registered: 03-2009

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Posted on Thursday, 17 February, 2011 - 11:04 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

I work on the assumption that gain figures in datasheets are a tad optimistic, so as a rule of thumb I calculate necessary base current as around twice the theoretical value, to give a good safety margin. I agree another stage is needed to drive the 3055.

Alec
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zeitghost
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Username: zeitghost

Post Number: 1597
Registered: 01-2006

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Posted on Thursday, 17 February, 2011 - 03:12 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Where did you see hFE = 35 at 4A?

The way I read it, hFE is 20 (tested minimum) at 4A.

And it's 5 at 10A.
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epithumia
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Username: epithumia

Post Number: 840
Registered: 06-2006

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Posted on Thursday, 17 February, 2011 - 06:42 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

I read 35 from the graph, figure 3. I was EXPECTING it to be 20, but missed the line where it said that.

I guess figure 3 must be typical.

Epi
If you need me, Neil and me will be hanging out with the Dream King. - Tori Amos
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zeitghost
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Username: zeitghost

Post Number: 1599
Registered: 01-2006

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Posted on Friday, 18 February, 2011 - 09:08 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Ah.

I never read graphs.

They're mostly made up. (i.e. "typicals").

I made some fine ones up when I worked for a semiconductor company. :-)
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atferrari
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Username: atferrari

Post Number: 1026
Registered: 05-2005


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Posted on Friday, 18 February, 2011 - 11:16 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

In the past, 40y++, hydrostatic particulars of vessels (data that allowed you to calculate basically stability, displacement and trim of vessels) used to be read in BIG size (plans is the name?) where the curves were printed.

Few vessel had them on a wall at the ship's office, so when you needed to estimate something it was necessary to deploy it on a table where space was never enough.

Those graphs being just a visual representation of a list of numbers (tables, what else?) is a big question why they were used after all.

Japanese vessels came always with tables what made quite easy to work with.

Computers nowadays changed that (and many Chief Officers are unable to do any moment calculation by hand anymore!).

Now that I think of it, the basic book we used to study the basics showed all that data in tables. Tradition after all...
Agustín Tomás - Buenos Aires - Argentina
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terry
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Username: terry

Post Number: 619
Registered: 05-2005

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Posted on Friday, 18 February, 2011 - 05:36 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Just a quick update, added a BD139 in the middle and it works a treat now :-)

Terry

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