Zener diode

A Zener diode differs from a conventional solid-state diode in that it is built more robustly in order to stand up to breakdown voltages. A non-Zener diode operated reverse-biased will normally overheat and fail.

A diode will have a zone wherein the P and N materials exchange electrons, producing a neutral region. This neutral region does not readily conduct.

When forward biased, any diode will conduct electricity as the electrical potential removes the excess electrons from the P-type material, returning both doped regions to a neutral state and allowing current to flow. In the reverse direction, they stop conducting.

However, when a negative bias is applied to a Zener diode, the neutral region grows as the electrical potential draws electrons further into the P doped region. But it still conducts. Thus, as the negative bias increases, resistance to electron flow also increases and with the proper design, these effects will be in proportion and current flow will remain fairly constant.

With near-constant current flow, voltage developed across a resistor in series is held constant. Thus, a voltage-regulated power supply circuit can be made.