transistor 2n3055

the same

It's in the current datasheets. MOT always rated Tj @ 200C in metal can and 150C in plastic AFAIK and their power ratings with the notional Tc=25C reflect that.

I've always been curious about the point. I recall that there were once concerns about impurities in the epoxies at higher temps. Maybe they're much better now ?

Graham

the same

150C in

We usually design for around 130C peak Tj, so it's not really an issue. The TO-247 is thermally about the best you can do, short of something really exotic. There's a lot to be said for a larger number of smaller fets, given the choice, to avoid hot spots on the heatsink.

John

On the other hand, it's nice to chat on Usenet about stuff also. ::)))

4 eyes 3 grins

The answers posted so far regarding manufacturing methods are on target.

They make plastic wafers the shape of a TO-3 to insulate them, and little teflon washers that ensure the other leads are isoalted where the pass through a metal heatsink. I replaced all the 2N3055s in a power supply (one had internally shorted collector to the base) and they are built into an assembly of aluminum extrusion with insulators and a lot of thermal goo.

In fact, I should find some of those insulators for the 2N3055s I have left over from that project.

--
Ben Jackson AD7GD

http://www.ben.com/

Maplin used to do a 225w amplifier with 2*2n3055 and 2* mj2955 in the output stages. They are good beefy transistors for amps. For the amp they had to be on a beefy heatsink to get rid of heat. The transistors needed to be isolated from the heatsink as the collectors are connected to the transistor case. They dont have a lot of gain so tend to need a good driver transistor to the base. I think the 2n3055 has a gain of 40 if my memory serves me right.

"Marra" <

** At what load impedance ??

Certainly not 4 ohms, as that would way exceed the SOA of 2N3055s.

...... Phil

That would be pushing them way too far.

Graham

Can't be 8 ohms either as that would exceed Vce.

Graham

"Eeysore"

** So - I was alluding to maybe a 2 or 3 ohm load.

Whatever, the 225 watt figure is way over the top.

...... Phil

Yes, even 4 ohms would require a higher Vce.

I do have an ancient HH amp that uses 2N3055s IIRC to provide 80W into 8 ohms but that uses transformer drive so the bases are reverse driven when each device is non-conducting. It would be sailing very close to the wind otherwise.

For sure.

I recall an Orange 1kW amp, the 'killerwatt' IIRC, from the late 60s ? that had a 1 ohm load rating or therabouts.

Graham

Nah, these are "marketing" watts. ;-)

Cheers! Rich

Like the 'peak-to-peak' watts ?

Graham

Kinda - in Ham radio, you're limited to 1KW DC to the output stage, but when using SSB, they get away with 2 KW "PEP" - "Peak Envelope Power."

So, yeah, pretty much. :-)

Cheers! Rich

"Rich Grise"

** Shame you are such a f****ng moron you don't see he two ratings are in effect the same.

....... Phil