[Amps] Zener Screen Regulators

[Jim Garland]

> One of life's great mysteries to me is why the professional electronics
> community continues to propagate the falsehood of "conventional" current
flow.
> It is as if civil engineers designed things based on water that flows
uphill.
> 
> Perhaps in the next life the creator can explain it to me. No one in this
life
> ever has.  :-)
> 
> 73, Bill W6WRT
> 
*************************
> By definition, current flow is the flow of charges.  The fact that
negative charges are
> embodied by a particle (an electron) is interesting, but irrelevant.
> 
> Negative charges flow in one direction; positive in another.  The use of
the direction of
> positive charges as the direction of positive current flow is entirely
arbitrary.  But it is the
> convention and is every bit as valid as the inverse.
> 
> Al
> AB2ZY
> 
*************************
I can remember hearing debates on this subject fifty years ago, so I doubt
it will be settled now. However, for what it's worth, Al is completely
correct. The confusion comes about because people equate the direction of
current flow with the direction of the charges that carry the current. The
oft-cited, old Navy manuals were wrong to equate the two concepts, and any
diagram that shows electric current flowing in the same direction as a
negatively charged electron beam is simply incorrect.

The sign convention embedded in the definition of electic current dates back
to the nineteenth century and is an integral part of Maxwell's equations of
electrodynamics. An electric field pushes on a positive charge and attracts
a negative charge. If a positively charged object loses its charge, the
current flow is away from the object. As Al observes, this is an arbitrary
convention, but it is a convention that predates the discovery of the
electron. We all need to get used to the convention, in part because it is
not going to change, and in part because anybody who insists on flouting it
will soon become hopelessly confused.

For starters, if you'll allow me to flog this horse a bit longer, the
universe is electrically neutral, which means that for every negative charge
there is a positive charge. Depending on the circumstances, an electric
current can be carried by either. The current flowing in the huge particle
accelerator in CERN (Switzerland) is carried by positively charged protons.
The current in a p-type semiconductor is carried by positively charge holes.
The current in a CRT is carried by negatively charged electrons (and the
direction of current is from the phospher to the electron gun!).
Anti-electrons (positrons) are identical to ordinary electrons, except they
have a positive charge. There are also negatively charged protons.
Obviously, there has to be some sort of sign convention, or we'd all go
crazy trying to sort all this out on a case-by-case basis.

The confusion over the sign convention is responsible for many common
misconceptions about current flow. For instance, the view of DC current in a
wire being analogous to water flowing in a pipe is one misconception. The
fact is that the conduction electrons in a copper wire are all moving at a
speed of about one percent of the speed of light, in all directions. This
speed is called the "Fermi velocity." The "drift velocity" of the electron
cloud, (which is analogous to the motion of the center of mass of all of
them) in a wire carrying a 1A current is typically only about 0.1 mm/sec. In
a wire carrying an AC or RF current, the center of mass of the electrons
doesn't go anywhere. It just jiggles back and forth about 1 micron or so.

So my advice, which you're free to ignore (but unwise to do so), is to get
used to the century-old sign convention. In an RF amplifier, the plate
current flows out of the positive terminal of the power supply, into the
plate of the tube, down to the cathode, and back into the negative terminal
of the power supply. Anything that sources current has current flowing out
of it. Anything that sinks current has current flowing into it. The sign of
the charge carriers is immaterial to this view.

End of sermon.

73,
Jim Garland W8ZR