Fun / Projects / with my 1997 America Dream

GlennLever wrote:

DrewE wrote:

That is the symbol for a diode, though in this case they placed it inside a sort of rough representation of the physical package its in. The actual diode symbol is the black triangle with the line at its apex in the middle of the bigger symbol. Current flows when the triangle end (the anode) is more positive than the line end (the cathode) and does not flow the other way around. (Technically, the anode must be more positive than the cathode by whatever the forward voltage of the diode is, which depends on its exact design and materials. Somewhere in the vicinity of half a volt is typical.)

In this circuit, the diode is almost certainly being used as a snubber for the solenoid's coil, to keep the voltage and current spikes that it produces when it is switched off from propagating back to the switches in the sensors and other connected circuitry. You can pretty much ignore it in analyzing the circuitry. Note that it is oriented such that it only conducts when the red wire is negative with respect to chassis ground, so it's reverse biased (not conducting) in the normal steady-state modes of operation, assuming these are typical 12V circuits.

So in this diagram, red is positive? That would seem to be a short,
I do understand that electrons flow from negative to positive

I don't know offhand whether the red wire would typically be positive or ground. In order for the diode to conduct, it needs to have a voltage below ground—be negative with respect to ground—which of course you won't generally find with a typical 12V negative ground circuit. It would not be conducting in steady-state operation. (When it does conduct, it is intended to short circuit to ground the voltage from the power stored by the inductance of the coil, rather than for instance causing an arcing in the switch contacts or whatever that opened to turn off the solenoid.)

Which direction the electrons themselves flow is not all that important here. The symbol for the diode sort of suggests that the charge carriers flow from positive to negative, opposite actual electron flow. Within the diode itself, the physics are a bit more complicated than just electrons moving along, too; but one doesn't need to understand that to analyze the circuitry.