Download Experiment # 1: pn junction diode and zener diode

Experiment # 1: p-n junction diode
Aim: To study the I-V characteristics of a p-n junction diode
Equipment & components required: Power Supply (0-30V), Voltmeter (0-30V),
Ammeter (μA & mA range), resistors, p-n junction diode
Theory
Circuit diagrams:
220
Fig: 1.1 Forward Biased diode
220
Fig: 1.2 Reverse Biased diode
Procedure:
1. Wire up the circuit shown in figure 1.1
2. Record the voltage across the diode (V) and current (I) through it as a function
of input voltage.
3. Repeat the experiment of the reverse biased diod (ckt 1.2).
4. Plot the relevant graphs.
5. Find the equation of dc load line and plot it along with I-V characteristics of fig
1.1
Experiment # 2: zener diode
1. a) Aim: To study the I-V characteristics of a zener diode.
Equipment & components required: Power Supply (0-30V), Voltmeter (0-30V),
Ammeter (μA & mA range), resistors, zener diode.
Theory
Circuit diagrams:
470/2W
Fig: 2.1 Reverse Biased (zener) diode
diode
470/2W
Fig: 2.2 Voltage regulation by Zener
Procedure:
1. Wire up the circuit shown in figure 2.1
2. Record the voltage across the diode (V) and current (I) through it as a function
of input voltage. Find Zenar Voltage
3. Connect the circuit shown in figure 2.2. Keep the load resistance R L at 3.3 kΏ.
Vary the input voltage in short steps and record the voltage across the zener and
current flowing through the zener. Repeat the above step for various RL values.
4. Plot the relevant graphs.
Experiment # 3: Transistor characteristics BJT
Aim: 1. To study the input and output characteristics of a PNP/ NPN transistors in
common base configuration
Equipment: Power Supply ( 0-15V), DMMs and potentiometer and other components.
Theory
Circuit Diagrams:
VCC
transistor used CK100
Fig: 3.1 Common Base Configuration of PNP transistor
Procedure:
A. Common Base configuration
1. For the input characteristics of common base configuration, set-up the ckt of fig
4.1. Set VEE around 5-6 V and do not change it during the experiment (why?).
Now vary VEB with the potentiometer and record IE keeping VCB at zero volt.
Observations may be recorded up to a maximum of 30mA emitter current. Repeat
the observations (for four sets) for various values of VCB from 0 to 10 V.
2. For output characteristics follow the ckt of fig 4.1. Set VEE around 5-6 V and do
not change it during the experiment. Set IE =0 with the pot and record the IC as a
function of VCB (from 0-10V). Record at least four sets of O/p curve by varying IE
from 0-20mA.
3. Plot all the curves. Plot the load line. Find input and output resistances and current
gain dc.
Experiment # 4 Photovoltaic effect: Solar cell
Objective:
To study (i) the variation of the open circuit voltage as a function of incident light
intensity and (ii) the load characteristics under the illumination of a solar cell module.
Theory:
The depletion region of a p-n junction has a built-in electric field under which
negative charges drift towards the n-side and positive charges drift towards the p-side. If the pn junction is illuminated by light with photon energy greater than the band gap energy of the
material, then this will result in the creation of electron-hole pairs. Electron and hole pairs thus
created in the depletion region by the incident light, get separated generating a photo voltage
under open-circuit conditions (photovoltaic mode, fig. 1) or a photocurrent under some load.
If I is the intensity of light of frequency ν incident on the solar cell with a sensitive area
A, and all this light is absorbed by the solar cell to create electron-hole pairs with a quantum
efficiency η, then the number of electron-hole pairs created in the cell per second is
Representing the solar cell as a constant current source, the source current (photocurrent) is
given by
Thus the photocurrent is directly proportional to the intensity of the incident radiation.
Fig. 1 shows the equivalent circuit of the solar cell with the current source giving a
current iν, the ideal diode D and a shunt resistance Rp, all in parallel, together with a series
resistance rs. For open circuit (Iext = 0) the voltage across the cell is nearly equal to the voltage
across the diode. From the usual ideal diode equation, we can thus write
where Iso is the reverse saturation current of the diode. For the usual operating conditions,
i ν>> Iso. With Iso ≈ 0.01 µA, Rp ≈ 108 Ω and V ≈ 0.6V, we have the approximation relation
Thus the photovoltage V is a logarithmic function of the intensity I. Under some load RL eqn.
3 modifies to
Fig. 2 shows a sketch of the current-voltage characteristics of a p-n junction solar cell under
illumination with light. Maximum power will be delivered by the solar cell when the product
iext×V is a maximum. The optimum load is determined by the point (Vm , im) corresponding
to the enclosed rectangle having largest area as shown in fig. 2.
Circuit Diagram
Procedure:
1. Illuminate the photovoltaic cell with a suitable light source and record the open circuit
voltage (toggle switch should be in “ no load “ position) as a function of intensity (you
can change the intensity by placing filter plates. Transmission of each plate is given.
2. Keep the switch in “with load” position. Record the variation of voltage as a function of
load current for various intensities..
3. Plot a suitable curve to verify Eq. 4.
4. Plot variation of load current as a function of voltage and determine the optimum operating
point for various intensities.
Experiment # 3: Rectifier and voltage regulation circuits
Aim: To construct Half wave, Full wave and Bridge Rectifier circuits using diodes
study the regulation with various filter circuits.
Equipment & components required: Step down transformer with centre tap (12-012V) or (9-0-9V), C.R.O., diodes, capacitor and resistors, regulator chips (IC 7809
and IC 7909)..
Circuit diagrams:
Fig: 3.1 Half Wave Rectifier Circuit
Fig 3.2 Half wave rectifier with filter RC circuit
Procedure:
1.
Connect the circuit as shown Fig. 3.1 for an half wave rectifier. You may
assemble the circuit by using the function generator (set for 50 Hz) also instead of
transformer. Check the waveform across the secondary of the transformer (or the
function generator) by displaying on one of the channel of oscilloscope. After
setting the oscilloscope to observe the above wave forms, connect the other
channel of the oscilloscope to the output resistor of the circuit. Trace the output
and input (secondary of the transformer) waveforms Measure peak to peak
voltages and dc voltage if any.
2. Connect the first filter circuits of fig 3.2.
3. Display the input and out put voltages both on the scope. Measure the dc voltages
and peak to peak ripple voltages. Also measure the time elapsed between two
consecutive cycles of diode conduction. Compare the results with the theoretical
estimates. (you might have to put input coupling to ac mode for some of these
measurements.
4. Vary R and C values and observe the changes.
5. Connect the second filter circuit of fig 3.2 and measure (and trace) the voltage
drop across 56 resistance. Estimate the current through the capacitor from this
and explain the observations.
6. Make the full wave rectifier circuit as shown in the fig.3.3. Measure the peak to
peak input and out put voltages using the oscilloscope. Trace the output signal
across the resistor using the oscilloscope.
7. Make the bridge wave rectifier circuit as shown in fig.3.4. Trace and measure the
peak to peak voltages of input and output signals.
8. Make the ckt of fig 3.5 for full wave rectifier with filter. Trace the output both
with the capacitor disconnected and connected. Measure the ac and dc voltages
and compre with th ehalf wave rectifier of fig 3.2.
9. Connect the dual power supply circuit as shown in fig. 3.6. 78xx and 79xx series
IC’s are positive and negative voltage 3-pin regulators respectively. Measure the
wave forms at the input and output ac and dc(both the positive and negative
voltages).
10. Assemble the voltage doubler circuit of fig 3.7 and observe th einput and output
wave form.
Try to modify the circuit in fig. 3.6 to produce on output that gives variable + Ve or
–Ve regulated outputs. Read the manufacturer’s manual on 3-pin regulator chips.