transistor 2n3055

The transistor 2N3055 is packaged in a TO3 case. It has its collector "grounded" to the case, and the base and emitter to the two pins. NPN transistors are usually used with the emitter going directly to ground, and the collector somewhere far from ground. Can someone give me a typical application for this 2n3055 transistor, showing how it is typically used in a circuit? What am I missing? The MJ2955, it's mating PNP, is the same way, and this, in a PNP makes sense.

Thanks for the help.

Bob Clark

Reply to
Bob Clark
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Power amps, pass filter.

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Reply to
Meat Plow

There is no such thing as a typical use. Transistors are used in all sorts of applications. The collectors are connected to cases because of the way transistors are made from slices of silicon. The slice becomes the collector, and the base and emitter are formed as islands on one side by successive masking, doping, heat treatment and metalization steps. Then the slice is bonded to the metal part of the case for heat sinking, as well as electrical connection to the collector, and flying leads are bonded to the top surface to make connection to the emitter and base islands.

The leads are not connected to make sense, they are connected in the only way that is feasible from a manufacturing standpoint.

Reply to
John Popelish

Many/most power transistors are not common emitter.

For instance, in a power supply the power transistor is used to pass the voltage to the output, so the collector is connected to the "raw" voltage source, and the emitter is the output. The transistor needs to supply current, it doesn't need to do any real voltage amplification.

In power amplifiers, it is rare to see a common emitter configuration. (You'd see them in the early days of transistors, but not in decades.) Again, the collector goes to the positive supply, and the emitter is connected to the output (and usually there is a complementary PNP transistor doing the mirror image to the negative supply voltage). The power output transistors do not need to supply much voltage gain, earlier stages take care of that, but the output transistors do have to supply current, and with a low output impedance. You won't get that with a common emitter configuration.

Since in neither case neither the collector nor emitter are grounded, it doesn't particularly matter which is connected to the case. It may be convenient, in terms of internal arrangement, to have the collector connected to the case.

Michael

Reply to
Michael Black

Hey Bob, a Google search on 2N3055 gives

720,000 hits. There's a world of fascinating information out there on the web.

81,000 hits from a search on "2N3055 circuit"!

That's a skill you need to master.

Good luck.

Chuck

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Reply to
Chuck

When seeing an NPN transistor used in a circuit, as a switch, the load is usually connected to "VCC", the current goes from +, through the load resistance, then to the collector, through the NPN transistor, and out the emitter to ground. Wouldn't it be nice if the transistors in the TO3 case had the emitter connected to the TO3 case which we could ground to the apparatus case. But since the transistors in the TO3 case are the reverse of this, one has to isolate the TO3 case from ground so as to be able to use an NPN transistor in the TO3 case. Maybe John Popelish is right, this is the only way a transistor can be made in the TO3 case. Hard to believe!!!

Thanks, Bob Clark

Reply to
Bob Clark

The collector is the chip substrate, and they solder that to the can to let the heat out. The emitter and base leads are on the top of the chip, so are connected to the pins by wire bonds. That's how most planar silicon transistors (and mosfets) work.

GaAs fets are nice for RF, because the source is the substrate and is convenient to bolt to a big grounded heatsink. I think there are some silicon npn RF transistors that have grounded emitters soldered to the case.

John

Reply to
John Larkin

It's only grounded if the case is grounded. In any case (lol) you may very well not want the current to flow to chassis/frame. Most power devices are isolated from chassis.

No they're not.

How about a quasi-complementary audio output stage ? Google it.

Not especially.

What makes sense is that the back of the transistor die is the collector and when soldered to a heatsink, the heatsink tab or header also becomes the collector connection.

Graham

Reply to
Eeyore

As a switch and only as a switch. Think amplifier instead of switch.

No. To the negative supply (power return). Not ground.

It would be no more convenient at all. In fact case to collector is better since where multiple devices are used in parallel the collectors tend to be commoned and the heatsink does that for you.

It's true. Most of the bulk of the die (chip) is collector.

Graham

Reply to
Eeyore

Hey, back when the TO-3 case was first designed and planer transistors were something pretty new, They were just tickled to have a high power package with a big transistor in it.

But the difficulty of isolating and mounting it, especially with high voltage on the collector, or with low capacitance to a heat sink, it fairly quickly was realized that something better would have to be designed. The power tab TO-220 (pin compatible with the TO-66, the smaller version of the TO-3) and TO-218 (pin compatible with the TO-3) and all their variants, carry most of the trade, today, that isn't surface mount.

But all but very specialized devices still have the collector to the heat sink surface, because that is the way planer transistor die are still made.

Reply to
John Popelish

I have used this pair of transistors in a power amplifier for a disco. I used 2 of each in the output stage.

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Reply to
Marra

Unity gain amplifiers (current boosters), just about anything a large transistor can do..

The case style does not govern the electrical use of the part other than maybe physical placement and heat dissipation.

You use a mounting kit that gives you an insulated sheet etc..

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Reply to
Jamie

Ever hear of insulators? They make em all the time and can be used to isolate the transistor case from the heat sink. When you learn how to design transistor circuits you will also learn how to physically mount the devices.

Reply to
sparky

"John Popelish"

** Nonsense.

Plastic " flat pack " power devices are not " better " than TO3 - they are merely cheap and nasty substitutes.

TO3 pack devices are now mostly found in professional / industrial equipment, on grounds of their higher reliability and where low cost is not so crucial.

....... Phil

Reply to
Phil Allison

collector

ground, and

typical

used in

same

I'm not sure, but you seem to be labouring under the misconception that since the collector of the NPN die is connected directly to the case, this constitutes an electrical "grounding". If it were mounted directly to a metal heatsink without isolation washers and insulator pad, and depending upon the connections to the base and emitter, it might result in fatal destruction of the device or other associated circuitry. Provided that any heatsink is isolated from circuit "ground" then you can mount them directly to a heatsink without insulation and no problems will arise, but in most situations this is not the case. As long as the three terminals C - B - E are connected as per a well designed circuit there will be no deleterious interaction and the device will perform as intended.

As to applications - there are many and varied and you should do some Googling.

Reply to
Ross Herbert

Agreed. The single mounting hole is alone cause for concern since it is realtively tricky to ensure a good thermal path. I use a large diameter washer on top of the device to help with this.

The same die can be reliably run at a higher Tj in a metal can too. This gives extra power rating.

A guy I used to work with annoyed the f**k out of me by insisting that we had to use TO-3Ps because he said they were (a) cheaper and (b) because everyone uses them now (as if that was a reason).

When I actually checked On-Semi's site, the TO-3 device is *CHEAPER* !!!!

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$2.17 for 250W (0.87 cents/W)

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$2.40 for 200W (1.2 cents /W)

It's also easier to cool metal can devices since they can operate at higher temps.

Graham

Reply to
Eeyore

to

The 2n3055 was very common in audio amps in mid 80's- about 50w with two and about 100w with 4 on the output stage-quite rugged transistors really

Reply to
cdd

The really big die simply won't fit into the antique TO-3 can, and the wirebond situation is awkward. The clamp-mount (no hole) TO-247's are much better.

Off-center packages, like TO-220 and TO-3P, are pretty bad.

The chip is the limit, not the epoxy.

John

Reply to
John Larkin

Really ? Those must be damn big dies in that case !

to

uses

What do you prefer ?

That's not what On Semi says.

The TO-204AA (TO-3) MJ21193/4 and the plastic TO-3P (TO-264) MJL21193/4 use the same die but it's derated in the plastic package.

Tj max = 150C in plastic vs 200C in TO-3.

Graham

Reply to
Eeyore

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