Physics help 2

Question

Question 3

3.1 Draw the symbols and characteristic curves of the following diodes. Also give an application of each diode:

3.1.1 Tunnel diode

3.1.2 Varactor diode

3.1.3 Zener diode

 

3.2 A power supply output voltage of 50 V DC when the load is disconnected. When the load is connected the voltage drops to 40 V DC.

Calculate the percentage voltage regulation.

 

 

 

 

 

Question 4

4.1 Choose a word from those in brackets. Write only the word next to the question number (4.1.1 – 4.1.5) in the answer book.

4.1.1 The field effect transistor is (less/more) sensitive to the temperature than the ordinary transistor.

4.1.2 The uni-junction transistor can turn (on/off) only when the emitter-to-base 1 is forward biased.

4.1.3 The input impedance of a field effect transistor amplifier is very (low/high).

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

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

4.2 Draw a neat, labelled characteristic surve of an N-channel, junction field effect transistor.

4.3 A common base amplifier produces an output current change of 4 mA with an input current of 2 µA. The output voltage changes with 6 V by means of 2 V input voltage.

Calculate the following:

4.3.1 hib

4.3.2 hrb

 

Question 5

5.1 Draw neat, labelled circuit diagrams of the following operational amplifiers:

5.1.1 Noninverter

5.1.2 Integrator

5.1.3 Inverter

5.1.4 Diffentiator

 

5.2 Calculate the input resistance of an integrator amplifier if C = 15 µF, Vin = 5 V and the rate of change of the output voltage is 20 v/sec.

 

 

Answer 1

(4.2)

N-Channel Characteristic curve of JFET :

The trans conductance 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 trans conductance g_m.

If V_GS 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.

Answer 2

(4.3)

 

Step 1:

 

The input current is 2 µA.

 

The output current is 4 mA.

 

The input voltage is 2 V.

 

The output voltage is 6 V.

 

Find ou and in common base configuration.

 

Draw the common base configuration.

Observe the figure.

 

Input current is .

 

Output current is .

 

Input voltage is .

 

Output voltage is .

 

Formula for is .

Formula for is .

Therefore the values are and .

Solution :

(4.31)  .

(4.3.2) .