When I meant a spike, I was meaning voltage spike, looking back you were on about one running alongside the main supply line with it cutting fuse if spike happened
Don't remember that (not surprising) but there is a device for that (Voltage spikes) called MOVs (metal oxide varistors) that a certain over-voltage level, short the mains power to ground (and then blow a fuse or trip a breaker). That's all a MOV can do. And, of course, it dies in the process, and must then be replaced.
When you say it (the zener, my edit) fails to maintain that constant, does it really matter if voltage low, wouldn't objects just shut down to lack of power
NOTE: A zener in never in a circuit without a resistor (R) (or resistance in some manner) in series with it.
If you were to put a voltmeter
across (that is, one lead of the meter on one side of the resistor [that is in series with the zener] and the other lead on the other side of that resistor) you'd see that as you increased the supply voltage, the voltage across the zener would stay essentially the same, while the voltage across the resistor would go up by the amount the supply voltage had gone up.
It is this resistor/zener circuit that "bleeds off" excess voltage by the increased current running through it, caused by the zener's automatically
decreasing it's internal resistance (R) to maintain a constant voltage (E) across itself. The excess current now runs through the fixed resistor
as well, thereby increasing the voltage across it, (bleeding it off).
Again, the zener (at least as far as I've ever used them) isn't really designed for supplying a constant voltage (as apposed to current) to anything other than another component/circuit in a larger array of components. It's used to maintain a constant voltage, most often as a bias on a component, like the base of a transistor, so that it will respond to other circuit stimuli in a predictable manner. Something else in the larger circuit (like the power supplying the entire circuit) might vary to some degree for some reason, and the zener counters that effect by maintaining a constant voltage.
And so, in a sense, with input voltages
too low, other "objects" (components in the circuit) will shut down or not perform as expected and the entire circuit would then fail to perform optimally or at all, depending. And, of course, with input voltage too high, the zener can (and will) fail, rendering the
entire circuit unusable and possibly damaging other components in the process.
I know all this is difficult. That's why the sims. By making changes to the circuit,
one at a time and then seeing the resulting values, you'll be able to grasp what the zener is doing.
Nobody said it ain't confusing. It is. But by being methodical with your testing, you'll get it. An if not, we'll just keep plugggin' till you do.
CBB
