ZENER DIODES

Zener diode is designed to operate in reverse conduction. Zener breakdown occurs at a precisely defined voltage, allowing the diode to be used as a voltage reference or clipper. While Zener diodes are usually operated in reverse conduction, they may also be operated in cutoff and forward conduction. The device was named after Clarence Zener, who discovered this electrical property. Strictly speaking, a Zener diode is one in which the reverse breakdown is due to electron quantum tunnelling under high electric field strength—the Zener effect. However, many diodes described as "Zener" diodes rely instead on avalanche breakdown as the mechanism. Both types are used with the Zener effect predominating under 5.6 V and avalanche breakdown above. Common applications include providing a reference voltage for voltage regulators, or to protect other semiconductor devices from momentary voltage pulses.

There are two different effects that are used in Zener diodes. The only practical difference is that the two types have temperature coefficients of opposite polarities.

·         Zener breakdown – Occurs for breakdown voltages greater than approximately 6V when the electric field across the diode junction pulls the electrons from the atomic valence band into the conduction band, causing a current to flow.

·         Impact ionization (also called avalanche breakdown) – Occurs at lower breakdown voltages when the reverse electric field across the p-n junction causes a cascading ionization, similar to an avalanche, that produces a large current.

A reference diode is a special Zener diode designed to use both conduction modes, which cancels the temperature coefficients and produces a temperature stable breakdown voltage.

If we connect a diode with a series voltage source DC so that the diode is forward biased, having voltage diodes will tend to a constant voltage supplynya power though increased steadily as in Figure 1a.

The current that flows in the forward bias diodes, proportionate to the rank of the voltage. Because of the linear or proposrional with the rank of voltage, then just a little increase in voltage a diode at the moment could go ahead, the current that flows tend to rise higher. Or in other words, the increase in the flow of very large diodes not too affect voltage diode. Circuit in Figure 1a, the current diodes a diode is determined by the power supply voltage, the resistance of the resistor, and the voltage on the diode (Silicon diodes amounted to 0.7 V). When the power supply voltage is raised, then the resistor voltage is also rising in almost the same amount, while voltage diode only go up just a little. Similarly, if we reduce the voltage of the power supply voltage of the diode, then decreased a little bit. In conclusion, the diode on the circuit of Figure 1a functions as a voltage regulator for the diode voltage drop is likely to be a constant equal to 0.7 V power supply voltage though personalised way.

As long as battery voltage is V who used 12.3 not less than 7 V, then the output of 10 diodes it will still be worth 7 V.

If we need to provide a higher voltage again, then we can get it by using a Silicon diode even more, of course this is not practical. The other method that we can do is reverse breakdown voltage using diode. At the time of diode reverse bias experienced (reverse biased), the diode will not siphon off electricity. However, there is limitation of voltage that can be held by a diode. When the voltage is raised, then continue turning the diode should not conduct current, because it is too large, the diode voltage having break down (broke) so that it can drain currents although his condition reversed biased.Reverse breakdown voltage for a Silicon diode that is commonly used is approximately 100 V. we can provide a constant voltage of 100 V reverse voltage, by making use of this breakdown is most notably shown in Figure 2a. Note the placement of a Silicon diode in Figure 2a. These diodes are conditioned in order to experience the reverse bias.