ELECTRICAL TECHNOLOGY

POWER SUPPLY SBA

LAB #2
Power Supply

Name: Alrae Jackson

Candidate Number: 100047

Centre Number: 100047

TITLE: Connect and test Full-wave rectifier with smoothing choke and

capacitors Objectives: (Use oscilloscope/multi-meter.)

The candidate will be required to:

 Determine from tests undesirable characteristics of D.C. output.

 Connect bridge rectifier circuits using solid state diodes into smoothing

circuit.

 Procedures

 The full-wave bridge was connected.

Questions:

What effect is there on the circuit when?

1. The capacitor C1 is removed?

2. The choke is removed?

3. The diode D2 is removed?

4. One (1) diode is reversed?

Schematic Diagrams:
 Relevant Theory for Power Supply Lab in
Multisim
In the context of a power supply lab conducted in Multisim, a combination of electrical theory
and practical circuit design principles is essential to understand the lab's objectives.

Below is an explanation of relevant theories and laws, along with the tools used to create a power
supply circuit.

1. Ohm's Law:

Ohm's Law is a fundamental principle in electronics that defines the relationship between voltage,
current, and resistance in a circuit. It states that:

V=I×RV = I \times RV=I×R

Where:

 V is the voltage (in volts, V),

 I is the current (in amperes, A),
 R is the resistance (in ohms, Ω).

Ohm’s Law is crucial when analysing power supply circuits, as it helps determine the amount of
current that will flow through a component based on the voltage across it and its resistance. This
law is applied in various parts of the circuit, such as calculating load current or determining
appropriate resistor values to control current flow in the power supply.

2. Kirchhoff's Laws:

Two important laws that help analyse complex circuits are Kirchhoff's Current Law (KCL) and
Kirchhoff's Voltage Law (KVL).

 Kirchhoff’s Current Law (KCL): KCL states that the total current entering a junction in
a circuit is equal to the total current leaving the junction. This law is important in the
power supply lab for analysing parallel circuits and ensuring that the current is properly
distributed.

 Kirchhoff’s Voltage Law (KVL): KVL states that the sum of the voltages around any
closed loop in a circuit is equal to zero. This is essential for analysing series circuits where
voltages across various components must sum up to the source voltage. This law is useful
 for ensuring that voltage is properly distributed across all elements in the power supply
circuit.

3. The Power Formula:

In electrical circuits, power is the rate at which energy is transferred or used. The power in an
electrical circuit can be calculated using the following formula:

P=V×IP = V \times IP=V×I

Where:

 P is the power (in watts, W),

 V is the voltage (in volts, V),
 I is the current (in amperes, A).

For resistive loads, power can also be expressed in terms of resistance using Ohm’s Law.
Understanding power is essential in a power supply circuit to ensure that the circuit can deliver
the required power to the load and that components are not overloaded.

Capacitance and Filtering (for Power Supply Smoothing):

In a power supply, especially in rectifiers, capacitors are used to smooth the output. The role of
the capacitor in smoothing is based on its ability to charge during the peak of the waveform and
discharge during the trough, reducing ripple and providing more stable DC output. The
capacitance value determines how effectively the capacitor filters out high-frequency ripples.

Transformer Theory (for AC-DC Conversion):

In an AC to DC power supply, a transformer is often used to step down or step up the AC voltage
to a level suitable for the load. The transformer operates on the principle of electromagnetic
induction.

The transformer allows efficient voltage conversion and is an essential part of AC-DC conversion
in power supply circuits.
Tools Used in Multisim for Power Supply Circuit
Design (Simulated):
In Multisim, the following tools and components are used to design and simulate a power supply
circuit:

1. Power Source:
o AC voltage sources are used to provide the required electrical input for the circuit. For
rectifiers, an AC source is commonly used, and for DC power supplies, a DC source is
used.

2. Diodes:
o Diodes are used in rectifier circuits to convert AC into pulsating DC. In the power supply
lab, a full-wave bridge rectifier typically uses four diodes to convert both positive and
negative halves of the AC waveform into DC.

3. Transformer:
o A transformer is used to step up or step down the AC voltage. In a typical power supply,
an AC voltage is first stepped down to a desired level by the transformer before
rectification.

4. Capacitors:
o Capacitors are used for filtering the pulsating DC output from the rectifier. In the lab,
different capacitor values can be tested to see how they affect the smoothness of the DC
output.

5. Resistors:
o Resistors are used to limit current, set biasing conditions, or simulate load in the power
supply circuit. They follow Ohm's Law and are crucial in controlling the circuit
behaviour.

6. Inductors (Optional):
o Inductors are sometimes used in power supplies to filter high-frequency noise. They help
smooth the DC output further in combination with capacitors.

7. Oscilloscope:
o An oscilloscope is used to observe the waveform of the output. It helps in visualizing the
ripple in the DC voltage and determining the effectiveness of the filtering components.

8. Multimeter:
o A multimeter is used to measure voltage, current, and resistance in the circuit. This is
useful for verifying the performance of the power supply and ensuring it meets design
specifications.
 9. Simulation and Analysis Tools:
o Multisim provides simulation tools to analyse the circuit’s behaviour before physically
constructing it. This allows you to verify whether the design works correctly by
simulating voltage, current, and power waveforms, as well as making adjustments to
components in real-time.

Observation:
A p-type semiconductor is created by introducing a trivalent impurity, such as boron, into a pure
semiconductor (like silicon), while an n-type semiconductor is formed by doping with
pentavalent impurities, such as phosphorus. A full-wave rectifier converts the entire AC cycle
into DC by allowing current to flow in only one direction through a load. Diodes, made from p-
type and n-type materials, create a junction that ensures current flows in one direction. In a bridge
rectifier, diodes rectify both halves of the AC cycle, but the resulting DC still contains ripples.
These ripples are smoothed using inductors and capacitors, which filter the current and voltage.

This experiment requires knowledge of NI Multisim and diode operation. Diodes function as one-
way switches that convert AC into pulsating DC. The two biasing states of a diode are forward
(when current flows) and reverse (when current is blocked). The full-wave bridge rectifier uses
four diodes to rectify the AC, while the inductor and capacitor act as filters to stabilize the output
DC.
1. The capacitor C1 is removed

Without the capacitor, the output from the bridge rectifier is still pulsating DC, but the ripple
(the fluctuations in voltage) are much higher. The voltage varies more significantly, and the
output is less smooth, with noticeable fluctuations that are undesirable for most electronic
applications that require stable DC power.

2. The choke is removed

Ans: The choke was removed from the circuit, leaving no component to provide filtering. As a
result, maximum ripples were observed, as indicated by the oscilloscope.
3. The diode D2 is removed

Ans: In the case that Diode 2 is removed from the circuit the A.C wave form as seen
above would continue to be produced.

4. One (1) diode is reversed?

Ans: If one diode in the circuit is reversed, half of the AC cycle will result in a short circuit,
while the other half will be blocked. This is reflected in the oscilloscope, which displays an error
message. When the circuit was connected according to the specified requirements and powered
on, the DC voltage exhibited significant ripples due to the absence of a filter.

In this lab, we assembled and tested a full-wave rectifier with a smoothing choke and capacitors.
Based on oscilloscope readings, an unfiltered DC output would display rippling waveforms.
Since many electronic circuits require direct current to function properly, this circuit is designed
to convert alternating current into direct current to meet their requirements.

Conclusion:

In this power supply lab, we explored the principles and components necessary for designing and
analysing an efficient power supply circuit using Multisim. By applying fundamental electrical
laws such as Ohm's Law, Kirchhoff’s Laws, and the power formula, we were able to understand
the behaviour of the circuit, calculate important values, and predict how each component would
influence the overall performance.

The bridge rectifier, constructed using diodes, allowed us to convert AC into pulsating DC, while
the capacitor and, optionally, the inductor were used to filter the output and reduce ripple, thus
providing a smoother DC voltage. We also learned how transformers are essential in stepping
down or stepping up AC voltage levels to meet the requirements of the load.

Through the use of simulation tools in Multisim, we were able to visualize and test the behaviour
of the power supply before physical implementation, ensuring the design met its intended
specifications. By examining the effects of various components, such as different capacitor values
and resistor placements, we could fine-tune the power supply for optimal performance.

In conclusion, this lab provided valuable insights into the design and analysis of power supplies,
reinforcing our understanding of key electrical concepts and showing how simulations can
significantly enhance the learning and development of electronic circuits. The ability to model,
test, and iterate on a circuit in a virtual environment not only saves time but also strengthens the
comprehension of circuit dynamics and the interactions between components.