Compatibility and Obtainability

Zener diodes, due to their lower cost and greater control, are commonly used in electric devices. They are also compatible with most systems, so they are a preferred method to regulate voltage. They are also used in other applications, such as in solar panels. Though these diodes don't often get damaged due to their current controls, they can still blow out if the current exceeds what they are equipped to handle. If this were to happen, the SCR would also likely blow out and both elements would need to be replaced. Luckily, Zener diodes are fairly easy to obtain due to their common use and low cost.

PERFORMANCE

Zener diodes have a very high performance standard, often more than the electronic device they are placed in needs to operate at maximum efficiency. These diodes are equipped to handle a higher voltage than the standard operating voltage, so they are able to handle more power. These diodes will still operate at standard voltage, but will not blow out if the voltage is still under their threshold. They are also small enough to allow current to flow quickly through their circuits.

ZENER DIODE CONTROL

The ability of the Zener diode to control and reverse part of the current flowing through it means it can be used to regulate and stabilize the voltage in a circuit and prevent problems that can occur when the supply or load voltage varies. Circuit designers can use the Zener voltage of the diode to exactly regulate and stabilize the voltage in the circuit.

ADVANTAGE OF ZENER DIODE

Unlike normal diodes, which allow only forward current, Zener diodes will allow a current to move in reverse when voltage exceeds a specified value, preventing breakdown of the diode. Because of this ability to reverse a portion of the current, Zener diodes offer several advantages in a circuit that normal diodes don't. The idea behind the reverse current used in this diode was proposed by Dr. Clarence Melvin Zener in 1934.

APPLICATION OF TUNNEL DIODE

Although the tunnel diode appeared promising some

years ago, it was soon replaced by other

semiconductor devices like IMPATT diodes for

oscillator applications and FETs when used as an

amplifier. Nevertheless the tunnel diode is a useful

device for certain applications

ADVANTAGE & DISADVANTAGE OF TUNNEL DIODE

One of the main reasons for the early success of the

tunnel diode was its high speed of operation and the

high frequencies it could handle. This resulted from

the fact that while many other devices are slowed

down by the presence of minority carriers, the tunnel

diode only uses majority carriers, i.e. holes in an

n-type material and electrons in a p-type material.

The minority carriers slow down the operation of a

device and as a result their speed is slower. Also

the tunnelling effect is inherently very fast.

The tunnel diode is rarely used these days and this

results from its disadvantages. Firstly they only

have a low tunnelling current and this means that

they are low power devices. While this may be

acceptable for low noise amplifiers, it is a

significant drawback when they are sued in

oscillators as further amplification is needed and

this can only be undertaken by devices that have a

higher power capability, i.e. not tunnel diodes. The

third disadvantage is that they are problems with the

reproducibility of the devices resulting in low

yields and therefore higher production costs.

MODE OF OPERATION

The characteristic curve for a tunnel diode shows an

area of negative resistance. When forward biased the

current in the diode rises at first, but later it can

be seen to fall with increasing voltage, before

finally rising again. The reason for this is that

there are a number of different components to forming

the overall curve. The main two are the normal diode

current across the junction, and the current arising

from the tunnelling effect. It is this last component

that is of interest in a tunnel diode.

Tunnelling is an effect that is caused by quantum

mechanical effects when electrons pass through a

potential barrier. It can be visualised in very basic

terms by them "tunnelling" through the barrier.

The tunnelling only occurs under certain conditions.

This means that it peaks when a certain voltage is

placed across the junction. This results in the

current increasing to a point beyond that which would

be expected for a standard pn junction. As the

voltage across the diode is increased the effect

reduces and the current through the device falls.

This results in a negative resistance region on the

curve of te diode that can be used to provide gain.