None whatsoever.
Liquid helium would freeze out all the carriers.
. Bipolar transistors: Ordinary Si bipolars (Si BJTs) suffer a rapid . decline in gain with cooling and are unusable below about 100 K
-- Jasen.
With tactics like that you can get 200W from a TO220 package (people do that and write it in their data sheet), so maybe 300W from the larger 2N3055 if it was built with the same care, but I don't think it is.
-- Jasen.
Cryo-diodes are neat. A PN diode's Vf goes up radically below 20K, and they get ohmic. Instead of mV/K, you get volts/K at the low end. The usual current is 10 uA.
Lakeshore makes nicely calibrated cryo-diodes. I did the cryo instrumentation for Jlabs and the helium plant for SSC.
-- John Larkin Highland Technology, Inc Science teaches us to doubt. Claude Bernard
The heat sinks in LT Spice are sort of cartoons. They are OK if you assume lumped models. Real life gets a lot more complex. As usual, the HELP isn't much help.
I'm liquid cooling some SiC fets in my Pockels Cell driver. To make things fast, it helps to use a small part and push it hard.
I recall an infamous PWM X10 power amplifier designed in 1964 by idiosyncratic but brilliant Ivor Catt for Clive Sinclair that was class D using seriously under rated germanium transistors in hard saturation. The thin bond out wires eventually failed due to vibration from the high currents interacting with the Earth's magnetic field. The power rating of the transistors was not actually exceeded but their tolerance of brutal currents flowing in them was. It wasn't a commercial success but it put him on the map. I thought I had imagined it until I found this OU document where the X10 gains honourable mention on p13 although being a marketing course it doesn't mention the technical cause of failure.
It actually worked pretty well for the price but died soon enough if used at anything more than 25% of rated power output that they had a lot of very unhappy customers. The later X20 did OK and they went on to develop quite a hobby following with various kits and very early cheap calculators and digital watches the size of a matchbox!
Top left of page 13 describes the thing. Later on Catt was better known for advocating wafer scale integration and railing against relativity.
The QL was doomed by Sir Clive's insistence that it used his own tape microdrives (so prone to jamming) rather than floppy disks. The rather tacky keyboard didn't help but was much better than a ZX80 one! Apart from that it was a good machine with a 68008 CPU and a Basic dialect that was well ahead of its time. Sadly it never became very popular.
Amstrad kit launched at about the same time took the most market share in the small business arena and the rest is history.
-- Regards, Martin Brown
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** Really ? That IS interesting.Bet he keeps real quiet about it.
** Not credible.** Has was also know for Wireless World articles about capacitors and transmission lines being the same.
Until " Ouida Dogg" came along and took a few bites out of him.
( Get it " I've a cat / " we'd a dog " ? )
Hysterical stuff, for conservative WW mag.
...... Phil
Yeah, a Hindenburg device. Send some to China in exchange for their virus.
The highest dissipation I have ever seen for a transistor was 625 watts. Made by Westinghouse and slow as hell. I am sure it it no longer available. To even find the part number would take me days in my ancient spec book.
If you can directly cool the die you can get quite a bit. The limiting factor other than current ad voltage is the thermal resistance to the case. So maybe you could take a 2N3055 and drill two holes in it and pump coolant right inside of it.
Of course there are no guarantees.
The big one is IXFH400N075T2. We tested a lot of mosfets for survival as linear amps, in a 17 KW NMR gradient amp, used for micro-imaging. It was the best n-channel we could find.
That design taught us to be skeptical of SOAR curves on data sheets.
-- John Larkin Highland Technology, Inc Science teaches us to doubt. Claude Bernard
I have used snow,ice, a toaster, a power diode and 120Vac to start my car in the dead of winter at -30'C in the 80's
I would connect Neutral to Vbat Gnd and Line thru the toaster to the diode in a jar of water with ice in it to start the car in few minutes when the battery was in poor condition. The peak current was enough to charge the battery.
It might have been fun to have Catt here, on s.e.d.
Jeroen Belleman
A diode and an incandescent bulb would work too.
I have charged a dead car battery with an ancient 18-volt modem wall-wart. It got too hot, so I added a heat gun in series as a ballast resistor.
Now I keep a bench power supply at home, and a few diodes and resistors. And a DVM of course. That's useful for all sorts of stuff, now and then.
There is a theory promoted by car-parts stores that a dead battery is permanently ruined. They sell chargers that won't put any current into a zero-volts battery, just to make their point.
-- John Larkin Highland Technology, Inc Science teaches us to doubt. Claude Bernard
Well, maybe it is. The technology of the day was weak on switchmode circuitry, and I've seen exploded-wire failures (in metal cases, just file off the lid and aim a microscope at the problem).
The dI/dt limit on a few millimeters of wire was due to magnetic forces, skin effect, and shockwve (ultrasonic) stresses. Not the terrestrial field, the current-induced field. Unlike thermal failure, there's no blob of melt at the end of the exploded wire... it's just GONE.
I have an 3A/10A Craftsman charger from the late '80s--just a transformer, slide switch for tap selection, and a bridge rectifier. WDNNS smart chargers for cars.
(Well, I also have a battery minder for my electric-start generator, which is comforting.)
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Heike Kamerlingh Onnes used a three-stage glass dewar for his helium liquification experiments. The first stage had LN2, the third stage had LHe, but the second stage had (iirc) about three litres of LH2, all in a glass flask.
Brr.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Did you prepare breakfast (toast) at the same time?
I recently tested some pcb mounted fuses to see how well they would survive the startup surge of a dc input power supply where a large capacitor was charged up very fast. After around 100,000 startups the fuse would fail from metal fatigue at the points where the fuse wire is welded to the connection wires. The peak current was around 30 to 50 times the rated current of the fuse for a few tens of microseconds. I also repeated the test with a powerful magnet on top of the fuse to see whether this made any difference. It did not.
I think the fuse wire "instantaneously" lengthened, thereby changing the angle of the wire at the terminations, effectively bending it backwards and forwards slightly each time. The geometry is probably very similar to that of bond wires in a power transistor.
John
We don't use surface-mount fuses. We tested some that would fail at currents within their hold ratings. They depend too much on PCB thermals and maybe on luck.
Ditto surface-mount polyfuses. We use leaded ones successfully.
"Silicon fuses", "E-fuses", have their own problems.
In general, protecting gear from wall-warts is tricky.
-- John Larkin Highland Technology, Inc Science teaches us to doubt. Claude Bernard
The fuses I tested were wire leaded, not surface mount. Surface mount had already been rejected for that project.
John
Indeed... I got into a tad of a barney with the dude in WW :-)
-- Kevin Aylward
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