Prior to that, how many existing boards do you need to use up, and how
many customers can you afford to loose when they do not work
About as many as he can afford to tighten, I suppose.
Prior to that, how many existing boards do you need to use up, and how
many customers can you afford to loose when they do not work
turbofans. I'll take the extra supplies as the lesser-of-two evils.
If Satan and Lucifer showed up at the inn, and the proprietor rented
them each a room, would he be the lessor of two evils? ;-)
Cheers!
Rich
About as many as he can afford to tighten, I suppose.
John Larkin said:The chances of this not working are nil; I'd be more worried about
meteor damage in shipping.
In fact I would think it is more likely that the "proper" LDO solution
will e.g. start oscillating, for some reason.
In fact I would think it is more likely that the "proper" LDO solution
will e.g. start oscillating, for some reason.
If the LDO starts oscillating "for some reason", it is either a faulty
(i.e. not meeting its specs) component, or the design was incorrect
(failing to take into account the entire range of operating
conditions, tolerances, tempcos, drift/aging, etc.) which is much more
common, particularly among advocates of using forward biased zener
diodes for power supplies.
The diode circuit cannot be designed correctly (because it is being
operated outside its specifications).
If you are saying it is easier to "get it working" for a diode circuit
than an LDO, you may be correct, under the right conditions (which
generally disappear the moment the product is shipped).
As mentioned earlier, continuously forward biasing a diode designed to
operate reverse-biased may cause long term problems.
Andy
^^^ anyWhat makes you think zeners should not be operated in forward bias?
The normal zener supply off line voltage switches between forward and
reverse bias at line frequency. Do you have any reason to suspect
there would be problem?
If the LDO starts oscillating "for some reason", it is either a faulty
(i.e. not meeting its specs) component, or the design was incorrect
(failing to take into account the entire range of operating
conditions, tolerances, tempcos, drift/aging, etc.) which is much more
common, particularly among advocates of using forward biased zener
diodes for power supplies.
The diode circuit cannot be designed correctly (because it is being
operated outside its specifications).
If you are saying it is easier to "get it working" for a diode circuit
than an LDO, you may be correct, under the right conditions (which
generally disappear the moment the product is shipped).
As mentioned earlier, continuously forward biasing a diode designed to
operate reverse-biased may cause long term problems.
John Larkin said:Dang, the power supplies are more trouble than the FPGAs.
The point is current spreading. Because they aren't intended for handling
large forward currents, their junctions aren't designed to handle the
thermal effects. Like an SCR's dI/dt rating, local heating can cause
failure not expected for that current level.
Tim
What a bizarre thing to say. I'm an electrical engineer, and I do
stuff like this all the time. The behavior of forward-biased PN
junctions is fairly well known by now.
You have a degree in Electrical Engineering. So do I.
When you design electronics that has to work right every time or the
wrong people will die, you learn to do it right.
The forward biased behavior of PN junctions designed to be operated
primarily (albeit not exclusively) in the negative biased mode is not
nearly so simple. I'm not an expert on forward biased zener diodes,
and I wouldn't use it that way unless I was. Apparently, from other
posts on this, there are potential problems that you and I are not
fully aware of. I won't design a product that way. I may design an
experiment that way, but I will specify additional analysis,
screening, and source control measures to ensure that, once proven to
be effective over the entire operating range, a product will continue
to operate correctly over its entire range of operating conditions,
over the duration of its production and useful life. Anything less is
hacking, not engineering. And the cost of those additional measures
nearly always exceeds the cost of doing it right in the first place.
Andy