PN Junction Diode Characteristics EEM LAB

INSTRUCTION MANUAL

FOR

P.N. JUNCTION DIODE CHARACTERISTICS APPARATUS

PN Junction Diode Characteristics Apparatus has been designed to plot the forward & reverse bias characteristics of PN Junction Diode.

The instrument comprises of the following built-in parts:-

1. Two continuously variable DC Regulated power supplies of 0-3 Volts and 0-30 Volts.

Specification of Regulated Power Supply:

Input Voltage :230 v+-10% AC, 50 Hz
Load Regulation :+_0.2%
Line Regulation :+-0.05%
Ripple :Less than 3 mV R.M.S.
Protections :Against Short Circuit & Over Load

2. Two dual range meters to measure voltage & current and range can be selected using SPDT switch are provided on the front panel with connections brought out on sockets/terminals.

3. Two PN Junction Diodes are mounted inside the cabinet with connections brought out on sockets to plot the forward & reverse bias characteristics.

Theory

If a region of n-type semiconductor is in intimate contact with a region of p-type semiconductor, they form p-n junction . A PN Junction is formed at the interface between the indium saturated p-region and the n-type semiconductor. The holes from the p-zone cross over to n zone and electron from n-zone cross over to p-zone. This flow continues - until there are positive and negative layers on both sides of the junction to stop the flow. We call it the depletion layer or the potential barrier. It exists at the junction before any external field is applied.

FORWARD BIASING:

When the positive terminal of the battery is connected to p-type and negative terminal to n-type region of a PN Junction .The PN Junction is said to be forward biased.
This applied potential difference provides the necessary energy for the holes and electrons to diffuse through the junction on barrier. The holes in the p-region are pushed forward toward the n-region and electrons from the n-region because of negative applied potential cross over to p-region. Hence the diode start conducting. As the potential is increased, there is gradual increase in the current initial but then current shoots up. This happens because at this potential almost all the majority carriers (i.e holes and electrons ) cross over.

REVERSE BIASING:

In this case the negative terminal of the battery is connected to the p-region and positive terminal is connected to the n-region . The holes of p-region move towards the -ve terminal and electrons towards the positive terminal of the battery or the deflection layer becomes thick or we can say that the junction barriers gets strengthend. Practically there should be no flow of current but in fact a very small current flows which is called reverse current.
This current is due to the thermally generated electron-hole pairs within both p and n type materials. As the reverse bias is increased to sufficent high value, the covalent bonds near the junction break down and as a result of this large number of electron holes pair are liberated. Thus the current rises abruptly.

PROCEDURE

FOR FORWARD BIAS CHARACTERISTICS:

  1. Make all the connections as shown in fig.(1a).
    Connect +ve of 0-3V DC Power Supply to +ve of Voltmeter & to Anode (A) of PN junction forward biased Diode. Also Connect Cathode (K) of same Diode to +ve of miliammeter, -ve of milliammeter to +ve of Power Supply & to -ve of Voltmeter.
  2. Select 3V range of Voltmeter and 10mA range of Millianmmeter using SPDT switches provided for range selection on the front panel.
  3. Keep power supply potentiometers knob on extreme left & switch ON the instrument.

Increase voltage from the fine voltage control potentiometer in small steps (0.1V) & note down the corresponding current.
Increase voltage further in the steps of 0.1 Volts upto 0.5 Volts & thereafter in the steps of 0.5 VDC up to 3Volts & note down the corresponding current. Note down the observation in Table No. 1
Plot a graph between voltage and current as shown in fig.(1b).
NOTE : If Voltage is not approaches to 3 Volts DC from fine control potentiometer, increase the voltage slightly from coarse control potentiometer (Set Volts).

FOR REVERSE BIAS CHARACTERISTICS:

  1. Make all the connection as shown in fig.(2a).
    Connect +ve of 0-30 VDC Power Supply to +ve of Voltmeter and to Cathode (K) of PN Junction Diode.Also Connect Anode (A) of same Diode to +ve of microammeter to -ve of Power Supply & to -ve of Voltmeter.
  2. Selct 30 V range of Voltmeter and 1.5mA range of ammeter using SPDT switches provided for range selection on the front panel.
  3. Keep power supply potentiometers knob on extreme left & switch ON the instrument.
  4. Increase Voltage in small steps using fine & coarse control potentiometers of power supply and note down the corresponding current.
  5. Plot a graph between voltage and current as shown in fig.2b.

STANDARD ACCESSORIES

  1. Five Single Point Patch cords for Interconnections.
  2. Instruction ManualA

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