23-03-2012, 10:39 AM
Electron Devices and Circuits lab
63461320-Electronic-Device-and-Circuits.pdf (Size: 3.1 MB / Downloads: 96)
CUT IN VOLTAGE:
Even though voltage is applied to the diode during forward bias,
initially there is no current flowing through the diode till a particular forward
voltage is applied. The forward voltage at which the diode current starts to
increase is called as cut-in voltage. For silicon 0.7V, for germanium 0.3V.
PROCEDURE:
FORWARD CHARACTERISTICS:
1. Connections are made as per the circuit diagram.
2. Keep the RPS in minimum value and switch ON the power supply.
3. Gradually increase the forward voltage in step by step of variation, Note down
the forward voltage and current values and graph is plotted.
REVERSE CHARACTERISTICS:
1. Connections are made as per the circuit diagram.
2. Keep the RPS in minimum value and switch ON the power supply.
3. Gradually increase the reverse voltage in step by step of variation, Note down
the reverse voltage and current values and graph is plotted.
The characteristics of diode are drawn between Voltage
and Current with forward characteristics on first quadrant and reverse
characteristics on third quadrant.
DISCUSSION QUESTIONS:
1. What is semiconductor material? How does it differ from a conductor?
A semiconductor is a material whose conductivity lies somewhere between
that of a conductor and insulator. The typical value of conductivity is 100Ω/cm3.
Germanium and silicon are most commonly used as semiconductor materials.
2. Why do we prefer extrinsic semiconductor than intrinsic semiconductors?
Extrinsic semiconductor has high electrical conductivity which depends on the
number of doping atoms and has high operating temperature. But in the intrinsic
semiconductor the electrical conductivity is very small and is not a constant at
different temperature.
3. Define the term drift current?
When an electrical field is applied across the semiconductor, the holes move
towards the negative terminal of the battery and electrons more towards the positive
terminal of the batter. This combine effect causes a current flow in the circuit. This
current is called as drift current.
4. Define the term diffusion current?
Diffusion current is due to the movement of charge carriers by concentration
gradients of charges by applied electrified d strength.
5. What is PN junction diode?
A PN junction diode is a two terminal device consisting of a PN junction
formed either in germanium or silicon crystal. A PN junction is formed from a piece
of semiconductor by diffusing P-type material to one half sides and N type material to
other half side.
6. What is depletion region in a PN junction diode?
The region around the junction from which the charge carriers are depleted is
called as depletion region.When a PN junction is forward biased, the depletion region
width decreases
When a PN junction is reversed biased the depletion region width increase.
7. Define the term transition capacitance CT of a diode?
When a PN junction is reverse biased the depletion layer acts like a dielectric
material while P and N type region on either side have low resistance acts as the
plates. In reverse biased PN junction may be regarded as parallel plate capacitor.