Re: QMX - smoke - another C107/Q108 failure
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Razvan said : "... the 5V rail would come alive before the 3,3V would do. But latch-ups are not harmfull, so if you do not have an answer to this question, just forget it: I will find it."
Dear Razvan,
The latch up phenomenon that CMOS components exhibit is much more dangerous than that and is to be avoided!
It's effects are unpredictable, ranging from the harmless and resettable condition that you mention to the full? destructive meltdown of the affected component, having made a massive short circuit between supply rail and ground!
Everything depends on the regenerative gain of the parasitic SCR that is intrinsic to the CMOS structure, and of the level of the current that is? being inappropriately injected into that SCR.
Modern CMOS circuits and processes have been engineered with latch up avoidance as an objective, and they have some forgiveness. Risks remain however. The processor in QMX for example has many pins that can "eat" an injection current of up to 5 mA without latch up or other damage. Some of the pins on that processor have zero tolerance for injected current!
Just an FYI, Razvan.
Wishing you well, JZ KJ4A?
On Thu, Aug 24, 2023, 5:38 PM DL2ARL < dl2arl@...> wrote: On Thu, Aug 24, 2023 at 01:46 AM, Rick Crowther wrote:
I meant only to rig up temporary linear supplies on my bench
hello Rick, Hello Hans,
this is exactly what I was aiming for myself: a temporary replacement of the smps boards until all other smoke tests have been succesfully passed.
Hans: really no offence intended! I am of an older school and do not trust these new-age gadgets piloted by software, not because of paranoia, but because of the fact that they do not belong to my trusted analog world. I find the ideas standing behind the SMPS concept of the QMX most refreshing and innovative: this is the main reason I am glad of having purchased a QMX, without having been in need of yet another qrp toy.
But now.. I am sort of discouraged by my own courage and would like to go one step behind into those quiet linear waters I am used to. Not for good, but at least for the first current intake of the fine rig. Afterwards, having thanks to Chris a test checklist for the SMPS boards outside the rig, without danger of damaging the main professor, I would maybe gain some courage and "replace the linear replacement" with it's new age microprofessor controlled switching PS.
This is what I meant. You might help by telling me if this is doable or if I am to expect some latch-up phenomena during power-up due to the fact that the 5V rail would come alive before the 3,3V would do. But latch-ups are not harmfull, so if you do not have an answer to this question, just forget it: I will find it out by myself.
Yours friendly, Razvan dl2arl?
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