Polarity Protection Circuit, does positive/negative ground matter?

[ericohman]

I read these two articles on polarity protection:
http://diyeffects.com/blog/archives/77
http://geofex.com/Article_Folders/mosswitch/mosswitch.htm

Images from diyeffects.com:


Will the diode be this way no matter if ground is + or -?
For example, PNP germanium circuits like Fuzz Face and Rangemaster, should I do like in the image above, if we pretend that the image above is showing a positive ground pedal.

Or is the example in the image only for - ground pedals, meaning I have to reverse the diode for + ground pedals? Quite confused. Electrons flow from - to + right?
Sorry for all the beginner questions, I have been googling but I honestly got more confused after reading articles about the way electrons flows...

[R.G.]

Electrons flow from - to + right?

Yes - but current flow is from + to -. Yep, this has confused people for a couple of centuries now. Blame it on the first experimenters. They could have guessed that the most fundamental charge carriers in electricity were "+" or "-" charges, and they guessed wrong. Bummer.

Will the diode be this way no matter if ground is + or -?

The arrow/point in the diode symbol always points the way the current flows (sorry - it's the reverse of the direction the electrons flow).
In the diagram, current flows out of the + end of the 9V battery, through the diode, and out to the pedal. It flows back from the pedal, into the "ground" symbol. Actually, none of this works unless the battery negative terminal is also connected to that "ground" symbol.  The ground symbol is just a label - it says "I'm always going to connect the reference probe of my voltmeter here. Everything more positive than this here voltage will show up as +, everything more negative will show up as minus." Ground means "reference voltage" because the original experimenters with electricity - yep, same guys who got the charge carriers wrong - thought that the ball of rock and dirt we stand on was the only good reference voltage, so it got called "ground", or "earth" in the UK.

For example, PNP germanium circuits like Fuzz Face and Rangemaster, should I do like in the image above, if we pretend that the image above is showing a positive ground pedal.

You would turn the diode around, and also the polarized caps, and also the battery. Now the battery positive terminal is tied to the reference point "ground", and all voltages are measured from there. The battery minus terminal connects to the bar end of the diode, and current can flow in the direction of the diode arrow from the + end of the battery through the effect, through the diode, and back to the battery minus. The capacitor has to be turned around because otherwise it's reverse biased and will leak and eventually die.

[ericohman]

Electrons flow from - to + right?

Yes - but current flow is from + to -

Thanks!

I re-read your post a few times, as well as re-read the article on diyeffects.com.
I hope I understood everything. I draw this, hopefully it's correct for a POSITIVE ground circuit.


EDIT: Or should the "diode parallel with the power supply" protection be the same way for both positive and negative ground circuits? If so, I guess I draw it wrong

[R.G.]

I re-read your post a few times, as well as re-read the article on diyeffects.com.
I hope I understood everything. I draw this, hopefully it's correct for a POSITIVE ground circuit.

I believe that's correct.

[ericohman]

Thank you!

When thinking electronics, is it true to say that I should think in terms of the way current flows (+ to -) rather than "hot to ground", in terms of diode orientation etc.

[R.G.]

Thank you!

When thinking electronics, is it true to say that I should think in terms of the way current flows (+ to -) rather than "hot to ground", in terms of diode orientation etc.

You're welcome. Yes; it helps in understanding the body of literature on electronics if you think of current as flowing from more positive voltages to more negative voltages.

This business of charge carriers flowing can get very confusing. In most conductors, it is the electrons which flow, because they are least-bound to the atoms and very light compared to the other charge carriers - protons. This is particularly true in vacuum tubes, where the flow is electrons from cathode to plate. Still, even in tube circuits, keep the idea that current is flowing from more positive (i.e. plate) to more negative (cathode).

In semiconductors, there is the concept of "hole flow". A semiconductor is a crystal lattice of atoms which have some electrons (but not all) that can move around. When you take a perfectly good neutral atom and move an electron away from it, the atom's charge becomes one electron's work *positive* because the number of protons and electrons are no longer balanced. This positive-charged atom becomes a "hole" that another electron can fall into.

However, where did the electron that fell into the hole come from? Yep, another atom. So with the electron moving into the hole, you could equivalently say that the hole has moved from this atom to the next atom that donated the electron. My reaction to this "revelation" in semiconductor physics class was "yeah, well, sure - an electron moving from one place to another is the same as the absence of an electron moving an equal and opposite amount. So what?".

The "so what" was that you can measure how much energy is needed to move a hole from place to place, and how much to move an electron, and that tells you the mass of the "hole" versus the electron, right? It turns out that a hole has a different mass than the electron. So a hole moving is NOT the same as an electron moving the other way. The subtleties get crazy from there.

By all means, don't go into the light... er, I mean, think of current as flowing from + places to - places and you'll be a step toward understanding all the normal schematics.