It seems strange that the author has not met a single one that understands that concept since it is quite basic. I am guessing he just is bad at interviewing and asks trick questions till he meet someone who know the interviewing game inside out.
Voltage regulators missing capacitors at input/output
Missing pull-up/pull-down resistors on digital buses
Missing decoupling capacitors"
I mean ... looking at a schematic how should you know that the voltage regulator doesn't have internal caps without seeing the specs? Missing pullups? How do you know those are not internal? It is stupid.
how should you know that the voltage regulator doesn't have internal caps without seeing the specs?
Can you name one voltage regulator that has them? Maybe you've worked with a few, but just off the top of my head, the 78xx, 317, and 1117 don't, and neither do all the other miscellaneous ones that I've seen in consumer electronics.
It's not my field and I had little clue what was happening at the EE level. Maybe you could argue they are not what is normally meant by saying voltage regulators.
Integrated Switched-Capacitor Voltage Regulators will definitely be a thing in a few years they have already been produced in research labs and quite likely reached even limited production for low power <10W applications.
In general I agree with the GP look at how many unpopulated areas exist on modern boards.
How should you know if the lack of input filtering is because of poor design vs the fact that the spec of the power supply changed and you no longer need it?
If it’s not universally true and obvious it’s not a good test.
Modern boards are super complex I’m not an EE but I would more likely flag lacking probe points, probe points which are too far or too close apart or too far from common ground as bad design choices than try to figure out if there are enough caps for the voltage regulator without knowing the full specs of the damn thing.
For all i know that voltage regulator isn’t even being used anymore because the IC or PSU specs have changed mid production but because it was wave soldered with a different soldering method than the other SMTs they already had them on a bunch of boards...
If you can’t reverse engineer the board or the relevant within a few min it shouldn’t be in an interview.
Not an EE but I do a lot of HW RE if anyone puts a modern multi layer doubled sided board on my lap and tells me to point out what’s wrong with it in an interview I would ask them what’s wrong with them.
>It seems strange that the author has not met a single one that understands that concept since it is quite basic.
That's exactly what everyone says when candidates fail FizzBuzz.
The best explanation I know is that good candidates get hired quickly, so at any given moment, the candidate pool is dominated by people who keep failing questions like this.
- Stress-levels of the candidate
- Tone / demeanor of interviewer
- Communication prior to interview
I mean, sure, if you fail fizzbuzz interviews 10 times in a row, there seems to be some pattern going. But you could might as well fail it the first time, and get blackballed as incompetent.
Lately, my company has been looking for folks who can, essentially, compute the sum of items in an array in JavaScript. Seniors continue to fail this.
It would be great if they'd stumble over conundrums like "what if there are non-numeric entries in the array." Most often, they just stare and don't even start on the problem.
I can't really elaborate, but it's only barely more complicated than I'm representing. I'm with you. I can't believe it. Boggles my mind every time. And no we're not expecting a complicated solution.
I think it makes sense depending on the nature of the role in question.
If the role's primary function is to do validation prior to manufacture this seems like reasonable. it assumes that new circuits will have some number of fairly common mistakes. in my experience this is very true, despite the skill of the engineer who designed the circuit. missing termination, pullup/downs missing, etc. if the role is applications engineering...well...its far less likely you would be troubleshooting common circuit design issues so much as you would be troubleshooting common system design issues. im sure you can extend this to other functional roles an EE may take on. if the job is to design a MCC and size breakers to minimize arc flash hazards i doubt the applicant will be up on a correctly build half-bridge rectifier.
in that list quoted i've encountered all of it in new designs, including missing stuff plainly stated in the part's application notes (like those regulator caps).
Decoupling capacitors need to be within a few mm of the integrated circuit consuming the power. It really doesn't matter if the voltage regulator has them or not.
This is different than for bulk capacitors, but even those should still be on the same PCB assembly because connectors have higher resistance and this will limit their ability to handle transient surges.
I've yet to see a voltage regulator IC with built-in caps. DC-DC modules sure, but author argues that this kind of info (module / ic) should be present in schematics. BTW, some linear regulators can't handle ceramic and low-ESR capacitors at output, and may be better with none if that's the choise.
I hate to maybe be proving his point by showing that I'm not into the EE field and thinking of a board mounted DCDC-converter as a voltage regulator (which it is but not what you usually call it in english?)
I would still argue that logic IC have alot of internal pull ups. Or that eg. "Reset sequence of digital component is wrong" is a bad whiteboard question.
I believe that without qualification "linear regulator" could be just anything that regulate voltage. Usually you can easily tell from schematics around it if it's some switching IC, an LDO or a module. And if you have layout or 3d render of the board it'd be almost certain.
Otherwise the person may just ask: "where are caps, or is this thing a module or what?"
In my experience, "linear regulator" refers specifically to voltage regulators which drop from a high voltage to a lower voltage by burning all of the power in between (e.g. the venerable 7805).
They're useful if the voltage drop isn't too large and/or if you need a particularly stable output voltage; contrast them with switching regulators, which are more efficient but have some amount of output ripple.
One design that I worked on used a switching regulator to generate 5V, then linear regulators to generate something like 3.7V and 2.9V for various sensitive analog circuits.
No, switchers aren't “linear.” And on a schematic the regulator isn't going to be a box labeled “regulator”! It will have a part number, probably a familiar one.
ICs with multiple power domains have a boot sequence that must be followed or the IC isn't in the proper state. Many interview questions fall into the "assumed assumptions" category. Simply saying, "lets reset to a known good state and modify one variable at time disqualifies many candidates". Because we don't teach science like we should. We should be teaching the scientific method before we teach the three Rs.
It's not that stupid. If a candidate asks the questions you are asking then you know they are on the right track. It isn't about getting the right answers but about having the knowledge to ask the right questions.
Examples he gives:
"Current limiting resistors missing (BJTs, diodes, etc.)
Shorting a potentiometer node to a rail
Voltage regulators missing capacitors at input/output
Missing pull-up/pull-down resistors on digital buses
Missing decoupling capacitors"
I mean ... looking at a schematic how should you know that the voltage regulator doesn't have internal caps without seeing the specs? Missing pullups? How do you know those are not internal? It is stupid.