Zener diodes square measure special diodes that let current not solely within the forward direction sort of a traditional diode, however additionally within the reverse direction if the voltage is larger than the breakdown voltage. This voltage is understood because of the “Zener Breakdown Voltage”.Zener breakdown is ascertained in extremely doped PN junctions, with a tunneling mechanism and happens for voltages of concerning five V or less.In extremely doped p-n junctions, physical phenomenon and valence bands on opposite aspect of the junction, become therefore shut throughout the reverse-bias that the electrons on the p-side will tunnel.
Junction Breakdown or Reverse Breakdown:
- An applied reverse bias (voltage) can end in a little current to flow through the device.
- At a selected high voltage price, that is named as breakdown voltage VB, massive currents begin to flow. If there’s no current limiting electrical device that is connected asynchronous with the diode, the diode is destroyed.
Fig: Zener Equivalent Circuits
I-V Characteristics curve
A Zener diode may be a semiconductor PN junction that’s designed for operation in an exceedingly reverse-breakdown region.
When a diode reaches a reverse breakdown, its voltage remains nearly constant although this changes drastically, and this is often key to the Zener diode operation.
Zener Breakdown Characteristic
As the reverse voltage (VR) will increase, the reverse current(IR) remains very tiny up to the knee of the curve.
Reverse current is additionally known as Zener current(Iz).
At knee purpose the breakdown impact begins, the inner Zener resistance (ZZ) begins to decrease.
The reverse current increase chop-chop.
The Zener breakdown (VZ) voltage remains nearly constant.
Fig: Zener Breakdown Characteristic
The ability to stay the reverse voltage constant across its terminal is that the key feature of the Zener diode.
A minimum reverse current Izk should be maintained so as to stay diode in regulation mode. Voltage decreases drastically if the present is reduced below the knee of the curve.
Above Izm, soap current, the Zener might get broken for good.