EXPERIMENT 1 SINGLE-PHASE FULL-WAVE RECTIFIER AND LINEAR REGULATOR

YEDITEPE UNIVERSITY

ENGINEERING & ARCHITECTURE FACULTY INDUSTRIAL ELECTRONICS LABORATORY

EE 432 – INDUSTRIAL ELECTRONICS

EXPERIMENT 1

SINGLE-PHASE FULL-WAVE RECTIFIER AND LINEAR

REGULATOR

Introduction:

In this experiment groups will perform the construction of a basic AC-DC converter (rectifier) circuit. This is a simple example of a regulated DC power supply. You will see an application of one of the basic switching elements (diode) studied in the course. Employing a basic regulator integrated circuit (IC), the output voltage is kept constant at value of 15 VDC, 1 A regardless of loading conditions and input voltage variations.

Equipments:

Table 1. List of Equipments

726 88 AC/DC Stabilizer, 220V Transformer

537 34 Variable Load Resistor (0-100Ω, 1.8A)

735 01 Bridge rectifier 735 095 Capacitor, 1000µF 578 37 Capacitor, 10µF 35V 7815 15V Linear Regulator 100n, 20V Capacitors 1kΩ, 1/4W Resistor

LED Light Emitting Diode

Heatsink for TO-220 package Breadboard

Metra Hit 25S Multi-Meter (x3) Fluke 66 Infrared Thermometer

DW-6060 AC Power Wattmeter

Note: It may be useful to have copies of datasheets of semiconductor components given in Table 1.

General Information:

Power is distributed to consumers through AC distribution lines. Almost all electronic equipment like computers, TV, hi-fi equipment and instruments are powered by DC power sources, either by batteries or DC power supplies obtained from an AC source. Most electronic equipment requires not only DC voltage but voltage that is also filtered and well regulated. Regulated AC-to-DC converters have a wide range of use as power supplies in many industrial and consumer applications.

Deniz Yildirim

Digitally signed by Deniz Yildirim DN: CN = Deniz Yildirim, C = TR, O = Istanbul Technical University, OU = Electrical Engineering Reason: I am the author of this document Date: 2011.10.10 07:12:13 +03'00'

A power supply converting AC line voltage to DC power is expected to perform the following functions at high efficiency with a very low cost:

• Voltage Transformation: Reduce the incoming AC utility voltage to lower AC voltage values.

• Rectification: Converting the reduced AC line voltage to pulsating DC voltage. • Filter: Smooth the ripple of the rectified voltage.

• Regulation: Control of the output voltage to a constant value regardless of variations in AC line, load and temperature changes.

• Isolation: Electrical separation (isolation) of output voltage from the input source. • Protection: Prevent damaging voltage surges from reaching the output; provide safe

shut down during a brown-out or high load.

An ideal power supply would be characterized by supplying a smooth and constant output voltage regardless of variations in line voltage, load current or ambient temperature at 100% conversion efficiency.

There are two types of AC-DC converters; Linear Converters and Switch-Mode Converters. In this experiment, groups will perform a single-phase full-wave rectifier with a linear regulator. Figure 1 shows a typical schematic for this circuit.

A transformer, a bridge rectifier, low and high frequency filters, a Blue LED, and a linear regulator are depicted. The transformer reduces the input AC line voltage to the desired

lower voltage level. Diodes D1 to D4 form a bridge rectifier where this circuit topology is

called an uncontrolled rectifier. Diodes D1 and D4 work together to rectify the positive half

cycle of the sinusoidal waveform while diodes D2 and D3 rectify the negative half cycles.

Capacitor Cf filters the 100 Hz ripple component of the rectified voltage. Even though the

voltage has been rectified and regulated, there may be some high frequency spikes on the DC

output. A high frequency ceramic or mica capacitor may be connected in parallel with Cf in

order to filter these high frequency spikes (harmonics). The linear voltage regulator behaves as a variable resistance between the

LED R_led C_f

+

+

v

Figure 1. Single-Phase Full-Wave Rectifier with Linear Regulator

input and the output as it provides the precise and well regulated output voltage. One of the limitations to the efficiency of this circuit is due to the fact that the linear device must drop the difference in voltage between the input and output. While these supplies have many desirable characteristic, such as simplicity, low output ripple, excellent line and load

regulation, fast response time to load or line changes and EMI, they suffer from low efficiency. A Blue Light Emitting Diode (LED) at the output of bridge rectifier is used as an

indicator. Resistor Rled is used to limit the current going through the LED which is typically

20mA. You should calculate the value of this resistor considering the output voltage of the bridge rectifier and forward voltage drop of LED.

Procedure of Experiment:

Before coming to the laboratory students are advised to make a small research about single-phase full-wave rectifiers with linear regulators as a preliminary work. Students can find the necessary information from either text books or from data sheets of linear regulator.

Please note that the power supply that you are testing will have a constant DC output voltage at 15V and 1A rated current values from a utility input voltage of 220V, 50Hz AC voltage.

Note: When capturing oscilloscope screen and include in your report, you have to specify the time base (… ms/div) and scale of voltages (…V/div).

1. Voltage Transformation and Rectification

Circuit Set-up:

Assemble the circuit shown in Figure 2. Adjust the load resistor such that rated current flows through load resistor.

+

+

v

Figure 2. Voltage Transformation and Rectifier

• Using a multimeter measure the input voltage Vs, the transformer voltage Vsec and output voltage Vdc. Write down the measured values to the Table 3 given below.

• With the help of an oscilloscope obtain the time waveforms (two complete cycles of input voltage frequency) of Vsec and Vdc using the save screen feature of oscilloscope. Determien peak-to-peak values and fill in Table 3.

2. Filtering the 100 Hz AC Ripple Component

Circuit Set-up:

Assemble the circuit shown in Figure 3. Adjust the load resistor such that rated current flows through load resistor.

• By adding a filter capacitor Cf you shall reduce the voltage ripple as much as possible. C_f

v

+

+

Figure 3. Filtering the 100 Hz Component

• Try three different capacitor values (10µF, 500µF and 1000µF) and observe their effects on the voltage ripple. Comment on your observations in your report. Include oscilloscope images supply voltage and output voltage.

• Draw the voltage Vdc with the help of an oscilloscope on the scope sheet for two different capacitor values. Measure the output voltage ripple and write values in Table 4..

• Measure and write down the voltage Vdc and Vdc,ripple with a multimeter and write values in Table 4.

Please note that output voltage is DC with small AC ripple riding on it. Select proper type on the multimeter for ripple measurement (select VDC for DC, and select VAC for ripple).

3. Visual Indicator

Circuit Set-up:

Assemble the circuit shown in Figure 4. Adjust the load resistor such that rated current flows through load resistor.

• Calculate the value of resistor Rled to limit the current passing through the led to 20 mA. Write down the value in Table 4.Show calculations in your report.

LED Rled Cf

+

+

v

4. Placement of the Linear Regulator and Its Effects

Circuit Set-up:

Set the circuit shown in Figure 5.

LED R_led Cf

+

+

v

Figure 5. Single-Phase Full-Wave Rectifier with Linear Regulator and Resistive Load

• Connect the linear regulator IC and the variable resistor to the circuit.

• Adjust the load resistor such that rated current flows through load resistor. It may be necessary to place a heatsink on the regulator as it will get very hot.

• To measure the overall efficiency of the regulator, do the following steps:

a) By setting the variable resistor to 10 different values, measure: Iout, Vout, Vdc, Pac and case temperature and fill in the values in Table 6 where Pac is the real power input from the utility. Case temperature measurements should be performed using infrared thermometer, please direct laser guided sighting system (red dot) onto the plastic case of the regulator as illustrated in Figure 6.

NOTE: Please be careful not to short the circuit the output by adjusting

the variable resistor resistance to 0 Ω.

b) Calculate the regulator, rectifier bridge and rectifier efficiencies from the measured values: out reg dc P P η = dc bridge ac P P η = out rec ac P P η =

where Pout, Pdc, and Pac are the DC output, bridge output, and input powers, respectively.

• Plot all of the above measurements as a function of Iout (plots are required for report).

Measure the no–load and rated load output voltages and fill in the values in Table 5. Calculate Voltage Regulation of your rectifier

c) Obtain the time waveforms of Vdc and Vout at full output power (i.e., 1A) and copy the screen to a file using save screen feature of the oscilloscope.

7815 metal case temperature probe 35 oC

measure temperature on the surface of regulator case

Deniz Yildirim Feb 14, 2010 e1regtemp.eps

Figure 6. Measurement of case temperature for the linear regulator Conclusion:

This experiment gives operational characteristics of a basic AC-DC converter by construct a simple rectifier. Four diodes are used to rectify the incoming AC line voltage. Instead of diodes, controllable solid-state switching devices such as thyristors can also be employed where the use of thyristors will give the opportunity to control the output voltage without the use of a linear regulator. This type of circuit containing controllable switches is called as a controlled rectifier and is mainly used for speed control of DC motors. The experimental analysis for such a circuit is the same as the one you have performed in this experiment. However, the triggering circuit is a bit tricky and a proper design of a feedback control circuit is necessary.

You must write a full report about what you have observed and what procedures you have done to obtain these results. Compare your results with data sheets and other resources (text book or references given below) or simulation analysis.

References:

[1] Introduction to Power Supplies, National Semiconductors Application Note 556, September 2002.

[2] B. K. Bose, Modern Power Electronics and AC Drives, Prentice Hall 2002

[3] T. E. Kissell, Industrial Electronics: Applications for Programmable Controllers,

Instrumentation and Process Control and Electrical Machines and Motor Controls,

Prentice Hall, 3rd. ed., 2002.

[4] M. Brown, Power Supply Cookbook, Newnes 2nd. ed., 2001.

[5] D. W. Hart, Introduction to Power Electronics, Prentice Hall, 1997.

[6] J. W. Motto, Introduction to Solid State Power Electronics, Powerex |Inc., 1977. [7] A. Kilian, Modern Control Technology: Components and Systems, 2nd ed., Delmar

E X P E R I M E N T R E S U L T S H E E T

This form must be filled in using a PEN. Use of PENCIL IS NOT ALLOWED

EXPERIMENT 1:SINGLE-PHASE FULL-WAVE RECTIFIER AND LINEAR

REGULATOR

STUDENT NO STUDENT NAME SIGNATURE DATE

1

2 INSTRUCTOR APPROVAL

3 4

Table 3

Multimeter Measurements Oscilloscope Measurements

Vs (V) Vsec (V) Vdc (V) Vsec (Vp-p) Vdc (Vp-p)

Table 4

Oscilloscope Measurements (ripple voltage peak–to–peak)

Multimeter Measurements (ripple voltage RMS value) Vdc,ripple (V) 10 µF Vdc,ripple (V) 500 µF Vdc,ripple (V) 1000 µF Vdc,ripple (V) 10 µF Vdc,ripple (V) 500 µF Vdc,ripple (V) 1000 µF Table 5

Rled (Ω) No–Load Output Voltage Vout,noload (V)

Rated Load Output Voltage

Vout,ratedload (V)

Table 6: Data for the rectifier from no load (0A) to full load (1000mA)