7/28/2019 Exp 2 Single-Phase Rect2

1/6

EEK 471 LAB 2

1

Universiti Sains MalaysiaElectrical Engineering DepartmentAdvanced Power Electronic Laboratory EEK471

The Single-Phase Full-wave RectifierAnd

The Two-Phase Rectifier (Centre-tapped)

OBJECTIVE

To demonstrate the operation of a single-phase bridge rectifier and a full-wave rectifierusing two diodes and a centre-tapped transformer.

INTRODUCTION

Single-phase bridge rectifier

With full-wave rectification, current flow is maintained for both the positive and the negative half-cycles of the source voltage. This can be accomplished using a bridge rectifier. To understandthe operation of this circuit we'll apply the rules of operation for diodes to the circuit andwaveforms of ES and EO shown in Figure 1.

The average voltage of EO can be calculated with the equation:EO = 0.9 ES

Where ES = voltage of the source (Vac)

Figure 1: A bridge rectifier and associated waveforms

7/28/2019 Exp 2 Single-Phase Rect2

2/6

EEK 471 LAB 2

2

Two-phase half-wave rectifier

Figure 2 shows a two-phase half-wave rectifier and some voltage and current waveforms relatedto this circuit. The ac source connected between A and N, diode D 1, and the resistor from asingle-phase half-wave rectifier which is identical to that shown in Figure 2. A second single-phase half-wave rectifier, consisting of another ac source and diode D2, is added to obtain a two-phase half-wave rectifier.

Figure 2: Operation of a two-phase half-wave rectifier

The voltage waveforms EAN and EBN show that the two ac sources have the same voltage and are

180 out of phase. As a result, the two single-phase half-wave rectifiers conduct current in turn.The voltage waveform across the resistor (EO) is identical to that obtain with the single-phase full-

wave rectifier shown in Figure 1. Therefore, the average output voltage of the two phase half-wave rectifier is equal to that of a single-phase full-wave rectifier when ac sources having thesame voltage ES are used in each rectifier.

Figure 3 shows a two-phase half-wave rectifier implemented with a single ac source and a centre-tapped transformer. The instantaneous voltage A-N and B-N at the secondary winding of thetransformer are equal but of opposite polarity. In other words, these voltages are 180 out ofphase. Note that a centre-tapped step-up transformer with a 2:1 turn ratio is required so that thevoltages A-N and B-N are equal to the voltage ES of the ac source connected to the transformerprimary. In such a case, the average output voltage of the two-phase half-wave rectifier is equalto that of a single-phase full-wave rectifier connected to an ac source having the same voltageES.

7/28/2019 Exp 2 Single-Phase Rect2

3/6

EEK 471 LAB 2

3

Figure 3: Two-phase half-wave rectifier implemented with a single source

EQUIPMENTS

EMS 8821 Enclosure Power Supply

EMS 8840-0A PE Power Supply

EMS 8842-1A Power Diodes

EMS 8412-05 Lab-Volt DC Voltmeter/Ammeter

EMS 8311 Variable Resistance

EMS 8325 Smoothing Inductor

EMS 8341 Single-Phase Transformer

EMS 9056-15 and EMS 9056-05 Voltage/Current Isolator

Textronic Oscilloscope

Connection Leads

WARNINGS

The voltages and currents that are used during this lab are larger and rated at 240VACLine-to-Neutralwith current as high as 20 amps (or higher if circuits are improperly connected). Pleasetake the proper precautions and use your head before touching any circuitry. NEVERchange anycircuit connections while the power supply is turned on. Ask the demonstrator to check yourconnections before turning on the switches. And follow the rating of voltmeters and ammetersgiven to prevent equipments from damaged.

7/28/2019 Exp 2 Single-Phase Rect2

4/6

7/28/2019 Exp 2 Single-Phase Rect2

5/6

EEK 471 LAB 2

5

Figure 1b: Z1(b) connection.

7. Set the voltage control knob to the 0 % position then set the main power switch to the Oposition.

8. What is the effect of the inductive load on the operation of the circuit? Compare thecharacteristics of a single-phase bridge rectifier to those of a single-phase half-waverectifier in terms of diode conduction angle, ripple frequency and average output voltageand power.

Figure 1c: Voltage and current waveforms for bridge rectifier.

7/28/2019 Exp 2 Single-Phase Rect2

6/6

EEK 471 LAB 2

6

Experiment: Part IITwo-phase rectifier circuit

1. Make sure that the main power switch of the Power Supply is set to the O (OFF) position.Set the voltage control knob to 0 %. Make sure that the toggle switches on the Resistiveand Inductive Load are all set to the O (open) position.

2. In this part, you will set up different rectifier circuits other using two diodes and a centre-tapped transformer as shown in Figure 2a. Set up the circuit using resistive load. Use thefollowing setting for parameters as in Table 2a. Set the main power switch to 1 (ON), andset the voltage control knob to 90(%).

Figure 2a: Two-phase half-wave rectifier implemented with two diodesand a centre-tapped transformer.

Table 2a: Parameters setting

LineVoltage (V)

I1 dc (A) i1 (A) E1 dc (V) e1, e2 (V) R1

0 - 240 1.5 5 300 600 R=240

3. In this part, Observe the voltage and current waveforms as displayed on the oscilloscope.Explain the operation of this circuit.

4. Measure the average output voltage E1.

Average output voltage E1 = ___________ V

5. Compare this to the output voltage of the full-wave bridge rectifier and explain thedifference.

6. Set the voltage control knob to 0 % then set the main power switch to O (OFF).

REVIEW QUESTIONS

1. Give two differences between a full-wave rectifier and a half-ware rectifier.

2. What will be the ripple frequency of a full-wave rectifier when the ac source frequency is100 Hz?