Zener Diode And Tunnel Diode

Zener Diode:

It is also a p-n junction diode. Its safe inverse voltage or break down voltage is kept lower than that of an ordinary diode and each diode is designed to have a specific brake down voltage. The amount of leakage current increases suddenly by increasing the reverse bias. The current flowing through the zener diode on break down voltage is called avalanche current or zener current.

A zener diode is used in voltage regulator circuits. A zener diode is connected across the voltage to be regulated with a series registers in opposite polarity. The load register is connected in parallel to the zener diode.

When the input voltage rises beyond the Break down voltage of the zener diode, the conduction of current is started through the series resistor Rs. The magnetic of current conducting through the resistor Rs is equal to the sum of zener plus load current. The magnitude of Rs resistors current will increase further for increase in input voltage. 

But, due to decreased zener resistance, only the magnitude of zener current will increase and not the magnitude of load current. Now, the will be more voltage drop across Rs and the output voltage will remain unchanged. In this way, the circuit can effectively work for small changes of even less than one volt.

The break down voltage of zener diodes in printed on them eg.12 v, 27v etc.

TUNNEL DIODE:

In this diode a P-N junction is made in such a way that the electrons passing through the junction have to cross a very narrow junction region and they have to managing any how to cross the junction.

In forward bias state, the magnitude of current reaches at its maximum value at a very low voltage, whereas the flow of current doesn’t start in an ordinary diode at a voltage. On increasing the forward bias, the current will decrease and it will be reduced to a minimum value at a certain high forward bias. The property of tunnel diode is termed as its negative resistance characteristic. If the forward bias is increased further, the magnitude of current will start to increase again.

A tunnel diode is used in amplifiers and oscillators of gigahertz frequency and range and in flip-flop gates.