Proper Application of the 2N3055 Transistor

There are electically isolated yet thermally conductive heat sink fitting kits available for TO-3 packages. You could also use the PNP equivalent 2N2955. Or maybe you could use the MJE 3055(NPN) or MJE2955(PNP) which are the TO-220 Plastic package.

. It's not just history that the collector is connected to the plate - even were we designing an economic 2N3055 replacement today the result would be the same.
. 67model is correct about the processing, but inexplicit as to the consequences: that the emitter and base connections are on one side of the plate, and the collector can be connected to either face.
. So the best side for attaching to the heat sink is the collector.

. Of course we could leave oxide films on the silicon, and connect all three terminals using wire-bonds. But an adequate oxide thickness (say 1 μm?) would add about 0.2^OC/W to the thermal resistance. Plus it increases packaging complexity. Al2O3 film inside the package would be better, but processing and attachment less straightforward.
. If you are happy to burn money, you could consider diamond film for insulating the collector; or you could plate the emitter thickly so it connected directly to the heat sink - but then you would need a through-silicon via to connect the base. Yet another option is a sandwich heatsink to the package - but here again the external insulator is a satisfactory (and cheaper) option.

At a 60 volt rating I suspect the back emf and inductive spikes from the horn kill it rather quickly. Most likely shorting it out to a permanently one state.

Just an educated guess.

Quite true but a simple solution of adding a reverse biased diode across the horn will solve this problem.

Rather put the diode across the transistor. Car electrics are very noisy, and spikes come from many sources. Even the stop-light switch activated by the brake pedal..

The guest wants to use the transistor between the load and -com, so while placing the suppression diode across the transistor provides some protection for the transistor, it does little to keep the back EMF voltage spike from an inductive load from reaching other components.

The best noise suppression scheme is achieved by placing the reversed bias diode red fred suggests directly across and as close to the load (horn) as possible. In this way, the stored inductive energy which creates the voltage spike is dissipated at the load before it can affect other components.

OK. But the problem is the horn is only one source of destructive spikes in the system. Some others are: Winscreen wiper motor, starter motor and solenoid, stop-light switch, turn indicator unit, relays for fuel pump etc.

So to protect the transistor, put the diode as close to it as possible! Or use a mosfet instead...

The destructive spikes are caused by opening of contacts in series with an inductive load. The back emf will forward bias the base-collector junction, and the reverse voltage will destroy the emitter-base junction. If the current is high (as with starter solenoid) the base-collector junction is also destroyed, giving you a short-circuit instead of a 2N3055.

MJB, excellent, you've gotta love that 40mohm on resistance, and at about a buck a piece,, well...

Also, modern MOSFET's have a built in reverse diode, with Zener characteristics. I've built some electronic ignition circuits and to date none have failed. I used 3 IRF840's in parallel. They're easy to parallel because of the temperature coefficient. Not so with bipolar transistors!

Well is probably almost 40 years since I last used 3055's in anything (car ignition I think!), but the question was also in my mind then as to why the case was collector, now at long last I understand why!

Many thanks to all who posted.

No sarcasm intended by the way.....I am really grateful. A nice bit of electronic history.......

I have put holes through the cases more than once by misuse....! they make a satisfying bang if done correctly! But they were also a bit too expensive for me to lose at the time......modern power transistors are cheap in comparison!!

I had a quick look in an Elektor from 1976, but nobody was selling a 3055 in that issue.....sadly........but I bet they were over a UK pound each.....

It was for some years my (only) favourite power transistor......

You would lose the bet! [age has its merits].

"Wireless World" Jan 1970 - Advert by "ElectroValue". 2N3055 = 16 shillings and sixpence each! £0.825 for the historically challenged.

I must have got the 2N3055s for the "Capacitor Discharge Ignition" in that issue from L.S.T. for 15/- each, since I penned a ring around the entry. The capacitor crept up to 800 volts before starting and at idle. No problem starting - and it would idle with "choke in" as soon as it started!

2N3055 = 55p from CPC in Jan 1977 W.W.

Regards,

67model

Excellent. Thanks.

That was a good bit of money in those days, I could go out, drink 3 pints of rough Scrumpy and have a bag of fish and chips.......and have some change.......

The fish and chips would cost at least 5 pounds alone today......what 3 pints of rough Scrumpy cost now I have no idea.......lets say 3 pounds.......at least.

I would not want to pay 8 pounds for a transistor.....

The 2N3055 has a collector, base (not gate, it's not a MOSFET, but bipolar) and emitter. Use a heatsink, and mount it on insulating pillars.

The other terminal is the base, not the gate.

Do you what to control the A+ or the ground?

What is the input, a ground ?

This transistor is typically used as light dimmer in aircraft applications.

The Triac for household use. "Insulated gate"..

I'd rather be flying!

I understand. We need the heat fpr deicing the wings. Good idea!
Anyone want some used 2N3055's?

I also often used a Silicon diode junction for temperature sensing. From memory, about -4mV/deg.C increase. Fridge or A/C control. Need a bit of hysteresis in the loop!

The back side of the transistor die is the collector. It is attached to the TO-3 case, which makes the case body the collector connection. It is possible to place a dielectric isolator (BeO works well) between the transistor die and the case. When you do this, you can make the TO-3 package the emitter or the base of the transistor. You also have the option of using a 3 leaded TO-3 package and having the case float. Any of these options are specials and will be expensive in small quantities.

BeO (Beryllium Oxide) is extremely dangerous if inhaled. Don't ever cut open a transistor where this may be present (Usually RF products). It's worse than asbestos, and causes mesothelioma, lung cancer, from which Steve McQueen died!

The 2N3055 transistor not a switching transistor but a linear device.

If used as a switch you have to drive deep in saturation.

This will delay the switcg-off and a sophisticated circuit is required for it.

Other explainations are well defined by some friends.

Was mostly used as driver in linear mode power suplly regulators.

Super as a linear regulator. We had to use fans to cool them.

Also, used the MJE3055 and mil spec op amp with !N4148 as temp sensor to replace the on/off thermostatic control in "Colvern" crystal ovens. Superb control. no more up and down Hz..

Important points in summary

• 2N3055 & 2N2955 are transistors;
  Transistors are for amplifier applications -- A large current is controlled by a small current in the base -- So applications will be for "sound output", "dimmer control" etc.,
• The electrodes of a Junction transistors are collector, emitter & base;
  In a FET or MOSFET which is better suited for switching applications such as controlling the horn etc., the electordes are Collector, Emitter and the gate.
• An input at the gate allows a switched change in the current between the other electrodes.
• Refering to the particular question -- that "it makes sense to ground the body of the transistor"-- for that application there is the twin of 2N3055 which is 2N2955.
• Collector-Base junction is reverse biased and maximum heat production is at this junction, so the heat dissipation or removal has to be linked to the collector.
• Use 2N3055 for +ve earth system & use 2N2955 for -ve earth system. They both have similar characteristics, but are of opposite polarity - one is NPN & the other is PNP.

No, No, and get the terminals right, in a FET, Gate, Drain, Source...sheesh..

Yes You are right. Source, Gate & Drain.