If you had a regular diode with a turn-on voltage of 5V (hypothetically), and a Zener diode with a reverse-bias of 5V, would the Zener diode still be preferred in a voltage regulator?
I'm trying to understand why a Zener diode would be used instead of a regular diode if you could achieve the same regulation with both. Do Zener diodes have a more constant breakdown voltage over a wide range of currents compared to the turn-on voltage of regular diodes?
You could make a 5.6 volt diode with 8 forward connected diodes that each have a forward voltage of 0.7 volts at 1 mA. Ok that's one point on the graph and at room temperature with 5.6 volts applied you would get 1 mA.
If you lowered the voltage to 0.6 volts across each diode (4.8 volts in total), the current would reduce approximately ten times to about 0.1 mA.
And this is where the comparison breaks down. The same percent reduction in applied voltage across a zener would result in a significantly lower current being taken.
In other words, a zener has a much sharper knee characteristic. Same story if increasing the voltage; the diodes wouldn't conduct as much as the zener.
So, the zener has a much sharper knee characteristic compared to a bunch of series connected diodes.
Zener can also be made to have a fairly neutral temperature stability whereas diodes have a recognized voltage-temperature gradient that is almost etched in stone (all due respect to Moses).
The forward voltage drop of a diode depends on the composition of the diode. For silicon diodes, the drop is about 0.7 volts. LEDs have higher forward voltages, depending on colour and composition, but the maximum is about 3.2 volts, I think.
Zener diodes can be made with reverse breakdown voltages over a wide range - much wider that you could get in a forward-biased diode of any composition.
