2n3055 question

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2n3055 question

Post by High4Volts » Thu Dec 29, 2005 1:46 pm

Hi all! I am building a dc to 12 dc supply and am using a 2N3055 in it. My problem is i don't know which pins are what on it. The casing is the base correct? I notice the pins are offset to one end of the case and not centered.

<small>[ December 29, 2005, 01:46 PM: Message edited by: High4Volts ]</small>

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Re: 2n3055 question

Post by mnboy » Thu Dec 29, 2005 1:56 pm

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Re: 2n3055 question

Post by JPKNHTP » Thu Dec 29, 2005 2:02 pm

-God Bless

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Re: 2n3055 question

Post by Gorgon » Thu Dec 29, 2005 4:36 pm

Gorgon the Caretaker - Character in a childrens TV-show from 1968. ;)

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Re: 2n3055 question

Post by High4Volts » Thu Dec 29, 2005 5:53 pm

Thanks all... :)

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Re: 2n3055 question

Post by Edd » Tue Jan 03, 2006 2:25 am

Looks like only JPKNHTP gave info that might stay with you, should you not always have a data sheet at hand to consult, IF you can remember the B, E differentiation.

My associative technique (initiated back in ’56) for terminal identification of either the TO-3 metal case or its little brother TO-66 was:
Fix the orientation of the case bottom such that the two off centered wire terminals will be positioned above the case centerline. Grip the top of the xstr with the thumb + forefinger, thereby masking off the case top hole and its shaping. That resultant case shape should then resemble the head of a small beady eyed alien/or/cartoon character with its lips pursed into an “oohh” profile.
Then one merely uses a familiar referencee bit of Shakespeare:
…………….....……..To be or not to be.
The be , being the definitive word, whereupon the b (base) is assigned to the left “eye” and the e (emitter) to the right “eye”, leaving the collector to be the transistors metal case.

Should it be housed in the TO-3 plastic casing or its little brother the TO-220, then that transistor bottom is faced away from you with the plastic square on top, towards you, with its three “legs” hanging down. Left leg is b (base), right leg is e (emitter) and the center leg is collector. ( Same B E positional referencing in this situation also.)
With time, all will be ensconced within your memory, even when being viewed from different angles.

73's de Edd
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Re: 2n3055 question

Post by rshayes » Tue Jan 03, 2006 4:15 am

If you can't remember the orientation, you can use a Digital Multimeter (set for diode test).

First, you know where the collector is. A TO-3 package has the collector connected to the case. In a TO-220 package, the collector is both the center lead and the mounting tab.

The base can be found with the multimrter. There are three possible combinations of two pins. Two of these combinations will appear as diodes. They will show a reading of .6 to .8 in one direction and an overrange indication if the leads are reversed. The common lead for these two diodes is the base. If the common lead is two anodes, it is an NPN transistor. If the common lead is two cathodes, it is a PNP transistor. The third pair of connections will probably show overrange in both directions. These connections are the collector and emitter.

Since the collector and base have been identified, the third connection is the emitter.

On most metal cased transistors, such as TO-18 and TO-39, the collector is connected to the case as well as one lead. The emitter and base can be found in the same way as before.

On TO-92 transistors, the center lead is commonly either the collector or the base. If it is not the base, which can be determined with the multimeter, it will probably be the collector, and the third lead will be the emitter. This was the original lead arrangement for this package. All three leads went entirely through the package and the die was mounted on a flat spot on the center wire.

A later arrangement put the collector on one end. The wire had a right angle bend with the die mounted at the end of the bend next to the base and emitter leads. This arrangement usually has the base in the middle, with the exception of a few RF devices that have the emitter in the center and the base and collector on the ends.

Remember that a TO-92 package may have other devices in it such as a junction FET. This will show a different pattern. Two leads will be connected by a moderate resistance and will read the same for both lead connections. These will be the source and drain. The third lead will be the gate, and will act like a diode with respect to both the source and drain leads.

And then there was the unmarked can with four leads that was similar to a TO-39 can. It had a pulse transformer in it. But it could have been an RF transistor with the collector insulated from the case. The fourth lead may be the case.

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