EXPERIMENTS
PN Junction Diode:
Pin Diagram:
Circuit Symbol:
Circuit Diagram:
Forward Bias:
Reverse Bias:
Ex. No.: ____ Date: _ _ / _ _ / _ _ _ _
CHARACTERISTICS OF PN AND ZENER DIODES
Aim:
(i) To plot the forward and reverse VI characteristics of PN junction diode (Silicon diode) and calculate its cut – in voltage, static resistance and dynamic resistance.
(ii) To study and plot the forward and reverse VI characteristics of Zener diode and calculate its breakdown voltage, static resistance and dynamic resistance.
Apparatus Required:
S. No. / Components / Specification / Quantity1. / Silicon PN diode / 1N4007 / 1
2. / Zener diode / 3Z 6.1 / 1
3. / Voltmeter / 0-20 V / 1
4. / Ammeter / 0-200 mA / 1
5. / Ammeter / 0-200 µA / 1
6. / Power Supply / 0-30 V / 2A / 1
7. / Bread board / - / 1
8. / Connecting Wires / - / As necessary
Formula Used:
Change in Voltage ΔV
Dynamic Resistance, Rd = =
Resulting Change in Current ΔI
Tabulation:
Forward Bias: Reverse Bias:
Forward VoltageVf (V) / Forward Current
If (mA)
Reverse Voltage
Vr (V) / Reverse Current
Ir (µA)
Model Graph:
Theory:
PN Diode:
When a P – type and an N – type semiconductor are joined together, a junction diode is created. It has the unique ability to allow current only in one direction. The lead connected to the P – type semiconductor is called anode and that connected to the N – type is called cathode. The P – type and N – type semiconductors are electrically neutral before the junction is formed. As soon as the junction is formed, the majority carriers are trying to diffuse through the junction. This happens due to the concentration gradient of holes and electrons existing inside the diode. Due to the diffusion of majority carriers from P – region to N- region and vice – versa, neutrality ends and a potential barrier forms across the junction. The barrier potential is 0.6 V for Silicon. The region thus created is due to the majority carriers. It has a depth of about 1 µm and is called depletion region.
(i) Forward Bias:
If the anode of the diode is connected to the positive terminal of a battery and cathode to the negative terminal, the set up is called forward bias. The diode does not pass any current till the battery voltage exceeds the potential barrier. Once the battery potential exceeds the barrier potential, high forward current in the order of mA flows through the diode due to the movement of holes and electrons.
(ii) Reverse Bias:
When the positive terminal of a battery is connected to the N – type and negative terminal is connected to the P – type, the diode is said to be reverse biased. This connection makes the majority carriers in the semiconductor move away from the junction. So the depletion region gets more widened. The minority carriers move towards the junction and cause a minute current flow through the diode which is in the order of µA in Germanium diodes and nA in Silicon diodes.
(iii) Static and Dynamic Resistances of the Diode:
When the diode is forward biased, it offers a definite resistance in the circuit. The static resistance or DC resistance is the ratio of DC voltage across the diode to the DC current flows through it. Dynamic resistance or AC resistance of the diode at any point is the reciprocal of the slope of the tangent of the characteristic curve at that point.
Change in Voltage ΔV
Dynamic Resistance = =
Resulting Change in Current ΔI
Zener Diode:
Pin Diagram:
Circuit Symbol:
Circuit Diagram:
1. Forward Bias:
2. Reverse Bias:
Zener Diode:
An ordinary diode will not permit current when it is reverse biased. If the reverse bias voltage exceeds the peak inverse voltage rating, diode may get destroyed due to avalanche breakdown. Zener diodes are special kinds of diodes designed to operate in the breakdown region without causing the damage to them. When a diode is heavily doped, its depletion layer becomes very narrow. When the applied reverse bias voltage across the diode is increased, the electric field across the depletion layer becomes very intense and electrons get pulled out from covalent bonds, generating electron – hole pairs. Thus heavy reverse current flows. This phenomenon is called Zener Breakdown.
Zener diode behaves like an ordinary diode in the forward bias mode. In the V – I characteristics of the Zener diode, it can be seen that the voltage across the diode remains constant and independent of the current through it. This property is utilized in voltage regulation.
Procedure:
For PN Junction Diode:
1. The circuit is set up on breadboard keeping the supply voltage at the minimum position (say 0V).
2. The supply voltage is varied so that the voltmeter readings vary from 0 to 0.7 V or 0.8 V in steps of 0.1 V. Take the readings of voltmeter and ammeter and enter it in the tabular column for the forward bias connection.
3. For reverse bias connection, the input voltage is varied from 0 to 10V in steps of 1V and enters the ammeter and voltmeter readings.
4. To measure forward static resistance, consider a point on the forward characteristics and note the corresponding voltage and current. The ratio of voltage to current is the static resistance. To measure reverse static resistance, repeat this step by considering another point on reverse characteristics.
5. To measure dynamic forward resistance, for a particular DC current, find out the reciprocal of the slope at the point corresponding to that current. It is extremely high because the slope is almost zero.
For Zener Diode:
1. The circuit connection is given after testing the components.
Tabulation:
Forward Bias: Reverse Bias:
Forward VoltageVf (V) / Forward Current
If (mA)
Reverse Voltage
Vr (V) / Reverse Current
Ir (mA)
Model Graph:
2. The input voltage is varied and the ammeter and voltmeter readings are noted down and entered in the tabular column.
3. The reverse characteristics on a graph sheet with voltage along x – axis and current along y – axis is in the third quadrant. The static resistance is calculated by taking the ratio of voltage to current at any particular voltage.
4. The dynamic Zener resistance is calculated by taking the ratio of change in voltage to resulting change in current at a point on the graph after the breakdown point.
Questions for Discussion:
1. Define peak inverse voltage of a diode.
2. Why Silicon diodes are more popular than Germanium diodes?
3. What do you mean by ‘1N’ in 1N4007?
4. Differentiate Zener and Avalanche breakdown.
5. Write down the applications of PN Junction and Zener diodes.
Result:
(i) Thus the forward and reverse VI characteristics of PN diode are plotted and the following parameters are obtained.
a) Cut – in Voltage of PN junction diode =______V.
b) Dynamic Forward Resistance at 10 mA=______Ω.
c) Static Forward Resistance at 10 mA =______Ω.
(ii) Thus the forward and reverse characteristics of Zener diode are plotted and the following parameters are obtained.
a) Breakdown Voltage of Zener diode =______V.
b) Dynamic Zener Resistance at 10 mA =______Ω.
c) Static Zener resistance at 10 mA =______Ω.
Pre – lab test (20) / Remarks & Signature with DateSimulation (20)
Circuit connection (30)
Result (10)
Post-lab test (20)
Total (100)
Pin Diagram:
Circuit Symbol:
Circuit Diagram:
Ex. No.: ____ Date: _ _ / _ _ / _ _ _ _
CHARACTERISTICS OF CE CONFIGURATION
Aim:
To plot the input and output characteristics of an NPN transistor in common emitter configuration and to find out the dynamic input resistance, dynamic output resistance and common emitter current gain.
Apparatus Required:
S. No. / Components / Specification / Quantity1. / RPS / (0 – 30) V / 1
2. / Ammeters / (0 – 200)mA, (0 – 200 )µA / Each 1
3. / Voltmeter / (0 – 20) V / 2
4. / Resistor / 1 KΩ / 1
5. / Transistor / BC 107 / 1
6. / Bread Board / - / 1
7. / Connecting Wires / - / As necessary
Theory:
Transistor can be connected in a circuit in any one of the three different configurations namely common emitter, common base and common collector. In this configuration input is applied between base and emitter, and output is taken from collector and emitter. Here, emitter of the transistor is common to both input and output circuits and hence the name common emitter configuration. It is also called grounded emitter configuration. The bias voltage forward biases the base-emitter junction and Vcc is used to reverse bias the collector-base junction. The input voltage in the CE configuration is the base-emitter and the output voltage is the collector-emitter voltage. The input current is IB and the output current is Ic.
Tabulation:
Input Characteristics:
VCE = 0V / VCE = V / VCE = VVBE (V) / IB (µA) / VBE (V) / IB (µA) / VBE (V) / IB (µA)
Output Characteristics:
IB = 0 µA / IB = µA / IB = µAVCE (V) / IC (mA) / VCE (V) / IC (mA) / VCE (V) / IC (mA)
For audio frequency applications common emitter is used. Common emitter is the most frequently used configuration because it provides voltage, current and power gain always greater than unity.
(i) Dynamic Input Resistance (ri):
Dynamic input resistance can be calculated from the input characteristic curves. It is given by the ratio of small change in base to emitter voltage to corresponding change in base current, keeping collector to emitter voltage constant.
ri = DVBE/DIB keeping VCE constant.
(i) Dynamic Output Resistance (rO):
Dynamic output resistance can be calculated from the output characteristic curves. It is given by the ratio of small change in collector to emitter voltage to corresponding change in collector current, keeping base current constant.
ro = DVCE/DIC keeping IB constant.
(iii) Common Emitter Current Gain (b):
It is the ratio of the change in collector current to the corresponding change in base current, keeping the collector to emitter voltage constant.
b = DIC /DIB keeping VCE constant.
Procedure:
Input Characteristics:
1. The circuit connections are made as shown in figure.
2. Keeping the VCE as 0 V, the input voltage VBE is varied from 0 to 0.8 V in step of 0.1 and the corresponding input current IB is noted.
3. Step 2 is repeated for several values of output voltage VCE (Say 3V, 6V, etc.).
4. All the readings are tabulated.
5. The V-I characteristics curve is plotted by taking VBE along X – axis and IB along Y axis for each value of VCE.
6. The dynamic input resistance is calculated by taking the ratio of change in VBE to the resulting change in IB at any point (say 10 µA), which is the inverse of the slope of the tangent of a curve at that point.
Model Graph:
Input Characteristics: Output Characteristics:
Calculations:
(i) Dynamic Input Resistance, ri = DVBE/DIB
(ii) Dynamic Output Resistance, ro = DVCE/DIC
(iii) Common Emitter Current Gain, b = DIC /DIB
Output Characteristics:
1. The circuit connections are made as shown in figure.
2. Keeping the input current IB as 0 µA, the output voltage VCE is varied from 0 to 10 V in steps of 0.5 V and the corresponding output current IC is noted until it becomes zero.
3. Step 2 is repeated for several values of the input current IB (say 50 µA, 100 µA).
4. All the readings are tabulated.
5. The V-I characteristics curve is plotted by taking the output voltage VCE along X – axis and output current IC along Y – axis for each value of IB.
6. The dynamic output resistance is calculated by taking the ratio of change in VCE to the resulting change in IC at any specific point on the curve, say 10 mA.
7. The common emitter current gain is calculated by using the formulae.
Questions for Discussion:
1. What are the regions of operation of a transistor? Mention its uses.
2. Why CE configuration is preferred as a switch?
3. What is indicated by B, C and 107 in BC 107?
4. Why common collector stage is also called as an emitter follower?
5. Mention the importance of CE amplifier.
Result:
Thus the input and output characteristics of an NPN transistor in CE configuration is plotted and the following parameters are calculated.
a) Dynamic Input Resistance, ri =______Ω.
b) Dynamic Output Resistance, ro =______Ω.
c) Common Emitter Current Gain, b =______.
Pre – lab test (20) / Remarks & Signature with DateSimulation (20)
Circuit connection (30)
Result (10)
Post-lab test (20)
Total (100)
Pin Diagram:
Circuit Symbol:
Circuit Diagram:
Ex. No.: ____ Date: _ _ / _ _ / _ _ _ _
CHARACTERISTICS OF CB CONFIGURATION
Aim:
To plot the input and output characteristics of an NPN transistor in common base configuration and calculate its dynamic input resistance, dynamic output resistance and common base current gain.
Apparatus Required:
S. No. / Components / Specification / Quantity1. / RPS / (0 – 30) V / 1
2. / Ammeters / (0 – 100)mA / 2
3. / Voltmeter / (0 – 1) V, (0 – 30) V / Each 1
4. / Resistors / 1 KΩ, 10 KΩ / Each 1
5. / NPN Transistor / BC 107 / 1
6. / Bread Board / - / 1
7. / Connecting Wires / - / As necessary
Theory: