Step 1:

(3.1.1)

Tunnel Diode :

A tunnel diode is a highly doped semiconductor and is mainly used for low voltage high frequency switching applications.

It works on the principle of Tunneling effect.

Circuit Symbol :

The tunnel diode is a two terminal device with p type semiconductor as anode and n-type semiconductor as cathode

The circuit symbol of tunnel diode is shown.

Characteristic Curve :

When the tunnel diode is forward voltage, the current increases and reaches the peak current.

If the voltage is applied to the tunnel diode beyond the peak voltage, the current starts decreasing due to tunneling effect. This is negative resistance region. Thereafter the current after the valley point starts increasing.

In reverse bias condition, tunnel diode conducts reverse bias current.

The V-I characrteristics of the Tunnel diode is

Applications of Tunnel diode :

Used as very high speed switches.

Used as high frequency microwave oscillator.

It is used as an amplifiers and a mixer.

(3.1.2)

Varactor diode :

Varactor diodes or varicap diodes is a voltage controlled variable capacitance  type of semiconductor device.

Circuit Symbol :

A varactor diode uses a p-n junction in reverse and has a structure such that the capacitance of the diode varies with the reverse voltage.

Chraracteristic Curve :

When the varactor diode is forward biased, the diode acts as a p-n junction diode.

When the varactor diode is reverse biased, the depletion region size increases and the capacitance of the diode can be varied.

Applications of Varactor diode :

Varactor diodes is used in RF filters.

Varactor diode as used in voltage controlled oscillators.

Varactor diodes is used as RF phase shifters and resonant circits.

Zener Diode :

Zener diode is a special type of the diode that allows current to flow even reverse bias condition.

Circuit Symbol :

Characteristic Curve :

When a zener diode is forward biased, it operates as a p-n junction diode.

When a zener diode is reverse biased, no current flows until the breakdown voltage is reached. Once the breakdown voltage is reached, there is sharp increase in the reverse current and acquires constant.

Applications of Zener diode :

It is used as Voltage stabilizers or regulators.

It is used as surge suppressors for device protection.

It is used as peak clippers, switching operations, reference elements.

(3.2)

Step 1:

The no-load voltage is 50 v.

The full load voltage is 40 v.

Find the percentage voltage regulation.

Percentage voltage regulation : ,

where is the no load voltage and is the full load voltage.

Percentage voltage regulation is .

Solution:

Percentage voltage regulation is .

(4)

4.1.5 The enhancement type MOSFET has no physical channel between drain and source (true/false)

(4.1.1)

The field effect transistor is less sensitive to the temperature than the ordinary transistor.

Explanation :

Increasing the temperature of FET tends to decrease the mobility of the charge carriers in the channel, reducing the current.

Increasing the temperature of FET aslo narrowsthe temperature coefficient , increasing the drain current.

(4.1.2)

The uni junction transistor can turn ON only when the emitter-to-base 1 is forward biased.

The Uni Junction Transistor is always operating with forward bias voltages. For this purpose the Emitter Base 1 Junction is always kept forward bias w.r.t Base 2.

(4.1.3)

The input impedance of a field effect transistor amplifier is very high.

Explanation : An amplifier must have very high input impedance because it is used to prevent loading effect at the input terminal.

(4.1.4)

The MOSFET is a metal-oxide, semiconductor field effect transistor, whose gate voltage control the drain current.

operating principle a MOSFET is a voltage controlled majority carrier device.

Movement of majority carriers in a MOSFET is controlled by the voltage applied on the control electrode (called gate).

The electric field produced by the gate voltage modulate the conductivity of the semiconductor material in the region between the main current carrying terminals called the Drain (D) and the Source (S).

(4.1.5)

The enhancement type MOSFET has no physical channel between drain and source.

The statement is true.

With no bias voltage applied to the gate terminal, there exists two back-to-back p-n junctions between the drain and the source.

No current flows from drain to source (the resistance will be on the order of 10¹² Ω).

(4.2)

The transconductance characteristics curve of a JFET transistor is the the curve which shows the graph of the drain current, I_D verses the drain-source voltage, V_DS.

The ratio of change in drain current ∆I_D, to the change in gate - source voltage  ∆V_GS is the transconduce g_m.

If Vgs is increased (it\\'s more negative to n-channel), depletion will be immediately generated in the channel so that the current required to pinch off the channel will be decreased.

Below is the characteristic curve for an N-Channel JFET transistor.