How will you use you power supply with 350V output if voltage drop on Mosfet pass transistor is only a few volts ? How will you detect a shorted pass transistor ?
The tubes are not dead, there are many applications where the tubes could never be replaced .... You use every day a microwave oven with a magnetron tube and you do not complain .
Just because you do not know anything about this technology does not mean you have to neglect it.
I know everything about this technology, from the underlying physics to the electrical characteristics of many standard parts.
I know better than anyone why tubes are nearly forgotten today, and why solid state has surpassed it in all but a few (electron-wave physics) applications.
Magnetrons are one, I gave another example (TWT) which I guess you didn't pick up on. Particle accelerators use klystrons, and more broadly speaking, any particle accelerator is itself a large, very complicated tube filled with vacuum, a vacuum tube if you will.
They only remain useful in niche applications. Everything from DC to UHF has been superseded. I'm not sure if GaN FETs will ever be cheap enough to replace the microwave oven magnetron, but it'll be an interesting day if it comes.QuoteA tube failing shorted (NB: between anode and cathode) ? .... it is extremely rare, I have never seen one in my life .... And on the tubes with connection of the anode on the top of the tube it's just impossible.
Er, well... screen and grid, let's say. Not a healthy situation for any of the circuits in this thread.
Cracked or melted glass also lets in gas, which acts to increase leakage or short out (sparking) electrodes.
I don't get you, man. Just because you can't imagine it, it doesn't exist? What kind of thought process is that? That's an extremely narrow, unimaginative way to go through life.
Tim
The reality is that you are prejudiced against tubes simply because it is old technology.
You still have not posted any diagrams on your 0 to 350V 200mA power supply solution ..... you only criticize without bringing any practical solution.
I'd gladly draw up a proper design -- simulation and BOM included -- if sponsored for it.
The crowbar circuit protects against a pass element short or control circuit failure where the output voltage rises all the way to the input voltage.
How will you use you power supply with 350V output if voltage drop on Mosfet pass transistor is only a few volts? How will you detect a shorted pass transistor?
How will you use you power supply with 350V output if voltage drop on Mosfet pass transistor is only a few volts ? How will you detect a shorted pass transistor ?
Simple -- crowbar based on the error amplifier output.
If it's commanding a low output, yet the output is high, the pass device is cacked.
If the output is high, but it's commanding even higher, it's saturated. (It might still be failed, who knows -- you'll find out when it comes out of saturation.)
You'd also delay this decision, and add an exception for low command * low output, to avoid nuisance trips.
It's just a comparator or two, a couple transistors, and a handful of resistors and a capacitor.
Tim
...Just about any semiconductor will fail short circuit. I don't know about valves.
Why is that a safety hazard? If the bench power supply is capable of giving a lethal voltage, then the best safety practice is to assume the output voltage has the potential to be lethal, even if it's set to a non-hazardous voltage. Never touch the output of a bench linear power supply which is powered by a lethal voltage on the other side of the pass element!
The same principle applies to a mains circuit switched of with a TRIAC or thyristor.It's exactly the opposite ... The safety rules require that if a power supply is adjustable from 0 to 350V, it can be used with 12V output without any risk for the operator.
A well-designed 0 to 350V power supply meeting basic safety principles can not be more dangerous when set to 12V than a simple 12V power supply with 7812.
Yes a crowbar circuit could be added to the error amplifier, but that won't protect against the adjustment potentiometer failing open.
At first it's what I expect... the 2N3904 seeing 1.7Apk discharging the MOSFETs' gate capacitance, and IRFP460 seeing around 3-4Apk drain current (1.3kWpk) each, for nanoseconds.
But changing output capacitance C2 from 0.22pF to 0.22uF drastically changes those values; 2N3904 seeing 0.039Apk discharging the MOSFET's gate capacitance, and IRFP460 seeing around 0.2Apk drain current, at C2=0.22uF
So the my simulation bullshit detector went off and I stopped.
Perhaps someone can explain what is going on. Strange SPICE results, but I'm not expert-level with it.
Yes a crowbar circuit could be added to the error amplifier, but that won't protect against the adjustment potentiometer failing open.
Always wire the potentiometer so that an open causes a low voltage or current fault.
Yes a crowbar circuit could be added to the error amplifier, but that won't protect against the adjustment potentiometer failing open.
Always wire the potentiometer so that an open causes a low voltage or current fault.How? It's possible to connect a potentiometer like that, so it fails low, if the wiper contact fails, but not if there's a break in the track.
I suppose a good quality wire wound potentiometer could be used, which is extremely unlikely to go open circuit, if it's used at a fraction of its power rating.
I made it
It works
Thanx
Using PL509 instead of EL34 is nonsense for the following reasons:
- The PL509 was a flyback pentode for color tv, it is no longer manufactured and, at least in Europe, it is more expensive than an EL34.
EL34 is still manufactured for tube amplifiers and will continue to be manufactured for a long time.
Yes. I grabbed the Mullard 1962 EL34 datasheet, so I think we are on the same page at last.
What would you suggest for optimum Vg2-k bias? A nominal 110V RMS winding as you suggested earlier, would give peak 155V so around 140-150V after filtering it to smooth it.
What sort of G2 current is that likely to give?
Also how much headroom on Va-k does it need to prevent it going into G2 toaster mode?