Electrical Engineering Challenge

I don't think they recommend 10uf on the output.

Mikek

looks like you're right, for modern schematics.

The datasheet says it isn't necessary, though it improves transient response. Input bypassing isn't needed unless it's a long way from its source.

I generally use the version of the symbol that separates the power pins from the business pins. The power subsection, and any decoupling, goes in the corner of the schematic sheet somewhere where it won't get in the way. This works well for single, dual, or quads.

There are also symbol variants that have the package drawn physically. If anyone wants that crap they can redraw my schematics.

It's weird that they only use one ground symbol. It's not the normal earth symbol, either. Where does it connect. *WHAT* does it connect.

Yeah, that's what I do. My schematics have a lower section or page of power supply pins and bypass caps... and thermal pads.

George H.

We really don't know the AC voltage or frequency. It could be running at 50 kHz and the 10 uF cap would be fine.

The only small nit I see is the fuse is after the switch.

tm

I am a Polarity Baer from the North Pole and say "check again".

• Electrically speaking,that makes zero difference: the fuse is going to function the same way and give the _circuit_ the same protecton.

I agree that the diodes look right. The arrows point in the direction of conventional current flow (positive carriers) and point to the positive input on the regulator. They point away from the negative rail (ground) and the AC connections are connected to the common points so current can flow in both directions. Here are some references.

Can you point us to a reference that says these are wrong?

If you include the switch as part of the "circuit" then it won't protect a short from the other side of the AC input to the switch. That is all we are saying. Typically that would not be an important thing, but it greatly depends on how the circuit is constructed whether a short there is possible or not.

ains, in which case the switch is required to precede the fuse :-)

This is a new one on me. Got a specific reference? Seems that it would ru le out the use of power-entry modules with integrated fuseholders.

There are plenty of questionable things about that diagram but the only rea l "bug" I see is that the switch is the only part with no reference designa tor. They religiously used them on everything else, so we can infer that t hey were required by the boss.

The polarized capacitor symbols are arguably OK for the 0.1 uF parts. They could be tantalum electrolytics -- or they could be old-school paper caps, where the symbol indicated the outer foil for self-shielding purposes. Yo u don't see a lot of Black Beauties hanging off of 7805s, though. Fortunat ely.

-- john, KE5FX

I traditionally use the "one side curved" symbol. Not that it ever made much difference, nor is its purpose ever relevant anymore (outer foil), but the plus was always the explicit polarization mark, so why use two different symbols?

The traditional blocky symbol of British drawings (and, I forget if it's also DIN/ISO/whatever standard now) never made sense to me. Possibly a cultural thing, but a point against is the "modern" DIN/ISO standard symbols being utterly nonsensical, and typographically ugly.

Tim

The ANSI/IEC logic symbols are atrocities.

I think Leiberman might be right BUT, shouldn't the input filter be bigger than the output filter ? Looking at the intermal schematic, it does not show a backcurrent protection diode.

A little leakage in C1 or C2, feeding a load that has significant filtering of its own, and being turned off.

There is also no suppression cap across the switch.

I would also like to see what their answer is. Who says they're the top dog expert ?

In fact, now that I mentioned no cap across the switch, there are also none across the recifiers. Even one across the transformer secondary.

Turning that switch off might be hard on those rectifiers if it happens at the peak of the AC cycle.

Not good engineering.

In fact I got an interesting thing about two amps happened the other day. I will post it in a separate thread though. It relates to the issues I just mentioned, maybe. Maybe not.

I read that as blackcurrant!

NT

Why?

These diagrams are hybrid circuit-/wiring- diagrams. My best guess is that the "one" change made by the editors was to move the GND off the IC GND node, which ruins the implied "star grounding" of the wiring- diagram interpretation of the drawing.