P-n Junction Diode

Topics: Diode, P-n junction, Schottky diode Pages: 5 (821 words) Published: March 31, 2014
1 CHARACTERISTICS AND OTHER DIODE APPLICATIONS
AIM:-To observe and draw the Forward and Reverse bias V-I Characteristics of a P-N Junction diode and diode applications .
APPARATUS:P-N Diode 1N914
Regulated Power supply (0-30v)
Resistor 1KΩ
Ammeters (0-200 mA,
Voltmeter (0-2V/200 V)
Bread board
Connecting wires
THEORY:A p-n junction diode conducts only in one direction. The V-I characteristics of the diode are curve between voltage across the diode and current through the diode. When external voltage is zero, circuit is open and the potential barrier does not allow the current to flow. Therefore, the circuit current is zero. When Ptype (Anode is connected to +ve terminal and n- type (cathode) is connected to –ve terminal of the supply voltage, is known as forward bias. The potential barrier is reduced when diode is in the forward biased condition. At some forward voltage, the potential barrier

altogether eliminated and current starts flowing through the diode and also in

the circuit. The diode is said to be in ON state. The current increases with increasing forward voltage.
When N-type (cathode) is connected to +ve terminal and P-type (Anode) is connected

–ve terminal of the supply voltage is known as reverse bias and

the potential barrier across the junction increases. Therefore, the junction resistance becomes very high and a very small current (reverse saturation current) flows in the circuit. The diode is said to be in OFF state. The reverse bias current due to minority charge carriers.

1

CIRCUIT DIAGRAM:FORWARD BIAS:-

Fig.1 (a) Forward Bias Diode

REVERSE BIAS:-

Fig.1 (b) Reverse Bias Diode

MODEL WAVEFORM:-

2

PROCEDURE:FORWARD BIAS:1. Connections are made as per the circuit diagram. 2. For forward bias, the RPS +ve is connected to the anode of the diode and RPS –ve

is connected to the cathode of the diode,

3. Switch on the power supply and increases the input voltage (supply voltage) in Steps.
4. Note down the corresponding current flowing through the diode and voltage across the diode for each and every step of the input voltage. 5. The reading of voltage and current are tabulated.
6. Graph is plotted between voltage and current.

3

OBSERVATION:-

S.NO

APPLIED VOLTAGE (V)

VOLTAGE
DIODE(V)

ACROSS CURRENT
THROUGH
DIODE(mA)

4

PROCEDURE:REVERSE BIAS:1. Connections are made as per the circuit diagram 2 . For reverse bias, the RPS +ve is connected to the cathode of the diode and RPS –ve is connected to the anode of the diode.

3. Switch on the power supply and increase the input voltage (supply voltage) in Steps
4. Note down the corresponding current flowing through the diode voltage across the diode for each and every step of the input voltage. 5. The readings of voltage and current are tabulated
6. Graph is plotted between voltage and current.
OBSEVATION:S.NO

APPLIEDVOLTAGE VOLTAGE

CURRENT

ACROSSDIODE(V)

ACROSS

THROUGH

DIODE(V)

DIODE(mA)

5

Applications of Diode:
(a) Clipper circuit :
A circuit which removes the peak of a waveform is known as a clipper. A negative clipper is shown in Figure below.
During the positive half cycle of the 5 V peak input, the diode is reversed biased. The diode does not conduct. It is as if the diode were not there. The positive half cycle is unchanged at the output V(2) in Figure below. Since the output positive peaks actually overlays the input sinewave V(1)

During the negative half cycle of sinewave input of figure above, the diode is forward biased, that is, conducting. The negative half cycle of the sinewave is shorted out. The negative half cycle of V(2) would be clipped at 0 V for an ideal diode. The waveform is clipped at -0.7 V due to the forward voltage drop of the silicon diode.

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Closer examination of the negative clipped peak (Figure above) reveals that it follows the input for a slight period of time while the sinewave is moving toward -0.7 V. The clipping...
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