Electrical Engineering

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misk94555

3:48 AM

@Lundin Can you chime in on this one, please? electrical.codidact.com/posts/291367

2 hours later…

Lundin

6:18 AM

@misk94555 I haven't really worked with SD cards, since I mostly work with industrial stuff where such things are often considered too fragile.

As for FAT, I have done my share of PC programming and even MS DOS, but I'm super rusty at file table stuff :)

3 hours later…

Lundin

8:50 AM

Does anyone know why we have orcad and cadence? I thought they were the same tool?

And Eagle is supposedly called Fusion these days, or at least you need to subscribe to Fusion to get Eagle.

...and we also have allegro which I assumed to be the semiconductor company but apparently this is Cadence too.

allegromicro.com Quite well-known silicon vendor.

6 hours later…

Nick Alexeev

2:57 PM

@Lundin I'd guess that cadence is an umbrella tag for anything that Cadence Design Systems makes. They make Virtuoso (an IC design software). They make Allegro (a PCB design software on a tier above OrCAD and Altium).

Allegro MicroSystems and Cadence's PCB design software Allegro aren't related [other than shared appreciation of fast symphonic music, maybe].

John Rennie

Is there anyone around willing to help with a beginner's question about mosfets?

I don't understand how this circuit works because as far as I can see the gate is connected to ground and no current will be flowing through point G.

So isn't the mosfet just fully on?

Nick Alexeev

@JohnRennie You're right that no DC current flows into a MOSFET gate.

(It takes come current to charge a MOSFET gate capacitance, but that's not what this example is about.)

MOSFETs are controlled by the voltage between gate and source (V_GS). That's unlike BJTs which are controlled by current into the base.

John Rennie

3:12 PM

Thanks :-)
So the voltage at S is Vs = Id × 1k and the voltage at G is zero?

Nick Alexeev

@JohnRennie The MOSFET may be fully on, or it may be in the Ohmic region. Check out this question about load line analysis: electronics.stackexchange.com/questions/533444/…

John Rennie

Thanks :-)

Nick Alexeev

@JohnRennie By the way, you called it a MOSFET. The example doesn't mention "MOSFET", and the symbol looks like a JFET. Are you sure that it's a MOSFET and not a JFET ?

John Rennie

Oops, that was not a deliberate action. It's just a FET.
My nephew has asked me this on the grounds I'm a physicist and should know such things. Sadly no physics course I ever did covered FETs.

Nick Alexeev

3:45 PM

@JohnRennie This might help: kennethkuhn.com/students/ee351/jfet_basics.pdf

My own intuition on JFETs is rusty. I'll have to read that to refresh it.

John Rennie

Thanks, I worked it out :-)

Vs = Id × 1k
and Vgs = -Vs

Then we use the Schockley equation:
Id = Idss(1 - Vgs/Vp)²

That gives a quadratic in Id and we get Id = 2.6mA.

5 hours later…

Nick Alexeev

8:54 PM

Reading RTC registers with side effects. Peculiar but it has a purpose.

A: STM32 RTC with HAL libraries

The STM32 RTC locks (freezes) the RTC when you read the time register and un-freezes it when you read the date register. This is done to protect you from the situation where you read the time just before midnight (e.g. 23:59:59) and then the RTC date rolls over to the next day before you read it...