Peak power rating of BC847

Interesting. So IKF is the corner when the beta fall of. So for a BC847 it would be around 50mA although the device is rated for max 200mA IC?

Thanks

Klaus

Yes. IKF is the current at which the emitter current "crowds", more current density at the emitter edge than available carriers, thus the beta collapses.

Max Ratings are an advertising gimmick ;-) Best applied for switching applications, not for good analog behavior. ...Jim Thompson

oduction. I have pointed out the over-rating high current to the original d esigner, but the response is that it works, no discussion about if we are o n the threshold robustness wise.

ent

it would be around 50mA although the device is rated for max 200mA IC?

Nice info.

So the internal derating specs for inhouse use should rarther specify "stay below IKF", than stay below 80% of ICmax?

Cheers

Klaus

Yep. And it occurred to my after my last post... an educational note... look up star and Christmas tree geometries (emitter periphery maximized relative to emitter area) to see how IKF is increased. ...Jim Thompson

Here's a link I had forgotten...

see pages 5 thru 8. ...Jim Thompson

Back at school we kept it under 200% :-)

No kidding, we had some 2N3055 where the top of the TO3 can turned blueish, like the exhaust pipes of a well-ridden motorcycle.

I blew a TO-3 version of an LM317 so dramatically that the die detached and left a square dent (from inside) on the lid ;-)

Then there's the alternator regulator that arc'd over and melted the controller chip into a bead of Silicon. ...Jim Thompson

yeah, sometimes people just have to learn by failing. Even with stubborn parties involved, being able to point at something and say "yeah, it's broken now" is easier than trying to argue about how something might fail.

As for skimkping out on already cheap parts, who knows what will happen when they try to save another $0.003 and try a new transistor vendor that was also just being cheap by running things at the edge.

Wasn't there also the switcher design where the boss came in, wiggled the power switch back and forth and ...? :-)

Pease talks about a boss testing his high-current power supply design by running a bastard file across the output terminals.

Cheers

Phil Hobbs

The Director of Engineering at my first employer could be more mean: He'd innocently stroll by, hold a little chat, quietly touched a cap or so on your prototype, yanked his hand back and exclaimed "Yikes! Why does this get so hot?". Upon which almost everyone would instantly pull the power cord.

I once was even more mean: A guy at a university lab had to go due to a nature call. It was in the days one could still smoke inside a lab. So I took a non-extinguished cigarette butt, carefully placed it into a beer cap (beer was also perfectly legal in the good old days), then shoved it into the guy's prototype with a ruler. He came back and saw smoke billowing from underneath his circuit, screamed and unplugged everything.

I had a coworker who'd lurk behind you in the lab and clap his cupped hands together when you turned on the power. The POP! sounded like some largish component letting go suddenly.

We explained the health issues of his actions (involving contusions matching various bits of lab equipment to his head and shoulders), and he desisted.

That company did all DC-powered stuff, but he also demonstrated a very convincing 60Hz roar that sounded just like some large piece of power electronics dying violently.

In Germany rolls were sold in thin paper bags. We had a habit of blowing these up, holding tight and then bursting them with the other hand. That sounded like a major electric kablouie.

I think I remember Bob Pease writing that. His boss tested out his switcher design by coming into the lab with a coarse "bastard" file, and running it across the power supply output terminals. This of course caused an amazing shower of sparks from the terminals.

Pease commented that the periodic-but-variable "make and break" timing of a coarse file was an excellent way to stimulate any lurking instabilities in the power supply's feedback regulating loops. If it was possible to throw the regulator into unstable oscillation, this sort of really horrid load behavior was an efficient way to find out.

Conversely, if the regulator didn't go kaboom when faced with this sort of abuse, it was a good sign that it might actually survive in the real world.

Yes, Pease did comment that his boss was exhibiting bastardly behavior!

Wasn't the boss, it was Ed Greenwood, my equivalent on the digital side of the aisle at OmniComp/GenRad.... but I outfoxed him with a simple patch. ...Jim Thompson

That's how I tested alternator regulators... rasp connection to battery >:-} ...Jim Thompson

In the mid '70s, one of the other new hires (a bumpkin fresh out of Clemson) was temperature testing his circuit in a box. While he was out, I stripped off the jacket from 6' or so of coax and piped it over to the bench backing his. When he came back, I started blowing smoke into the "pipe", just as the manager walked by.