1ECEN3250

ECEN3250 Lab 4Rectifiers and Power Supplies

AC-DC Power Supplies

ECE DepartmentUniversity of Colorado, Boulder

PlusExtra Credit Lab Assignment:Voltage Doublers and Inverters

(Starts on Slide 17)

2ECEN3250

Prelab Assignment

Objectives:Use diodes to design practical rectifiers and power supply circuits: an unregulated DC power supply, a regulated DC power supply, and circuits that double or invert voltage. This lab will extend over 5 lab sessions.

Prelab assignment:a) Read Section 3.5 (Rectifier Circuits) from the Sedra/Smith textbook 5th

edition (Section 3.7 of the 4th edition), and do Exercise problem D3.24 on page 183 of the 5th edition (problem D3.30 on page 191 of the 4th edition). Turn in your solution - show complete work. Use PSpice transient (.tran) simulation to verify your solution. Print the output voltage waveform and label the DC output voltage and the output voltage ripple in steady state. Use the 1N4148 diode model from the 3250 library. Compare the results obtained by simulation to the results obtained by hand calculation.

b) Read the complete Lab procedure AC-DC Power Supply Design and the textbook Example 3.10 starting on page 213 of the 5th edition (Example 3.11 starting on page 202 of the 4th edition). Using the results shown in Figure 3.55 of the 5th edition (Figure 3.54 of the 4th edition) for Rload=250Ohm and Rload=200Ohm, compute an estimate for the Load-regulation of the power supply designed in this textbook example. Explain how you got the result.

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Introduction• Objective: given an unregulated AC voltage source, design a DC power supply

+

VCC

_

Load

ICC

AC-DC Power SupplyvAC(t)

• AC source• vAC(t) = VAC,peak sin (ωt); for sine-wave, • AC power-line voltage: f = ω/(2π) = 60 Hz, VAC,rms = 120 V (± 10%)• A transformer can be used to scale VAC,rms down or up

• Load• Usually requires a precisely regulated DC supply voltage VCC

• Ideally, VCC is independent of variations in the load current ICC or variations in the input rms voltage VAC,rms

rmsACpeakAC VV ,, 2=

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AC-DC Power Supply

• AC line voltage source is available, f = 60 Hz, VAC,rms = 120 V (± 10%)• A transformer scales the AC line voltage, vs (t) = vAC (t) /n• A diode circuit rectifies the AC voltage vs (t) into vr(t)• A low-pass filter keeps the DC component vDC and attenuates AC harmonics in

vr(t)• A voltage regulator circuit keeps the DC output voltage VCC independent of

variations in the load current ICC or variations in the input RMS voltage VAC,rms

• Reference: Textbook, Section 3.5, 5th edition (Section 3.7, 4th edition)

+

VCC

_

Load

ICC

AC-DC Power Supply

vAC(t) Rectifier Low-PassFilter

VoltageRegulator

Transformer

AC linevoltage

+

vs

_

+

vr

_

+

vDC

_

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Power Supply Performance Measures(1) Output Voltage Ripple

• The output voltage vcc(t) includes an AC ripple component:vcc(t) = VCC + vripple(t)

• Ideally, vripple(t) = 0• In practice, it is desirable to design the power supply so

that the peak-to-peak value (Vr) of vripple(t) is as small as possible

• In this lab, you will measure the ripple voltage obtained with a half-wave peak rectifier, a full-wave peak rectifier, and a peak rectifier followed by a Zener shunt voltage regulator

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Power Supply Performance Measures(2) Line Voltage Regulation

• Ideally, the DC output voltage VCC should be independent of variations in the input voltage RMS value

• In practice, a change ΔVAC,rms in the input RMS value results in a change ΔVCC of the DC output voltage

• Line voltage regulation is defined as:Line-regulation = ΔVCC / ΔVAC,rms

• It is desirable to design the power supply with Line-regulation as small as possible

• In this lab, you will measure the line regulation obtained with a half-wave peak rectifier, a full-wave peak rectifier, and a peak rectifier followed by a Zener shunt regulator

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Power Supply Performance Measures(3) Load Regulation

• Ideally, the DC output voltage VCC should be independent of variations in the load current ICC

• In practice, a change ΔICC in the load current results in a change ΔVCC of the DC output voltage

• Load regulation is defined as:Load-regulation = ΔVCC / ΔICC

• It is desirable to design the power supply with Load-regulation as small as possible

• In this lab, you will measure the load regulation obtained with a half-wave peak rectifier, a full-wave peak rectifier, and a peak rectifier followed by a Zener shunt regulator

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Power Supply Performance Measures(4) Efficiency and Size

• The power dissipation Ploss on the components of the power supply circuit should be as small as possible

• Efficiency η, defined as η = Pout / Pin = Pout/(Pout + Ploss)

is ideally equal to 100%. In practice, efficiency can be significantly lower than 100%.

• In addition to achieving high efficiency, it is usually desirable to design a power supply using small-size components

• In this lab, you will find the power losses in a power supply having a Zener shunt regulator. The effects of the size of a filter capacitor on the output ripple voltage will be observed.

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LAB4 Part 1: Power Supply Design Specifications

• VAC,rms can vary ± 10% from a selected nominal value• VCC = 4.7 V (nominal DC output voltage)• Load current range: ICC,max ≥ ICC ≥ ICC,min

• ICC,min = 0 mA• ICC,max = 20 mA

• Available components:– Bench AC supply with adjustable RMS voltage and a step-

down isolation transformer to get VAC,rms (up to 6 Vrms)– 1N4148 diodes– 1N4732 (4.7 V) Zener diode– C = 470 μF or C = 220 μF filter capacitor– Miscellaneous resistors and capacitors

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LAB4 Part 1: Power Supply Design Procedure

1. Construct and test a half-wave rectifier without and with a filter capacitor

2. Construct and test a full-wave rectifier without and with a filter capacitor

3. Design, construct and test a complete regulated power supply using the full-wave rectifier with the filter capacitor (the full-wave “peak rectifier”) and a Zener shunt regulator

References:• Textbook Section 3.5: Rectifier Circuits (Section 3.7 of 4th edition)• Textbook Section 3.4.2: Zener shunt regulator (Section 3.6 of 4th edition)• Textbook Example 3.10 on page 213 of the 5th edition: Design of a

Regulated Power Supply (Example 3.11 on page 202 of the 4the edition)

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1.1 Half-Wave Rectifier

Note: VAC,rms is the RMS value of vac(t). Use a bench multi-meter on AC voltage setting to measure this RMS voltage.

The 10 KΩ resistor R will be used in all parts of this lab assignment.a) Using two channels on the scope, measure the peak of vr(t) as a function of

VAC,rms, in the range from 1 Vrms, to 6 Vrms, in 1 Vrms steps. In the report, include a plot of the measured data and a plot of the results that would be obtained with an ideal diode (use Excel). Comment on the results.

b) Adjust VAC,rms so that the peak of vr(t) equals 6 V.In the report, record VAC,rms and include an annotated plot of the waveforms vr(t) and vac(t)

VAC

60 Hz

Bench Variable AC Supply

+

vac(t)

_

+

vr(t)

_

D1

R10 kΩ

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1.2 Half-Wave “Peak Rectifier”

Add the filter capacitor C. Note the value you are using. Use the scope (AC coupled) to measure the ripple in vout(t). Use DC multi-meters to measure the DC output voltage VCC and the DC load current ICC. For ICC ≈ 22 mA(Rload = 220 Ω), adjust VAC,rms so that the DC output voltage equals 5 V.

a) Measure and report the peak-to-peak ripple Vr in vout(t). Compare the measured value to the result obtained by analysis (see textbook Eq.(3.29a), ((3.71) of the 4th edition)). Include an annotated plot of the vout(t) waveform.

b) Measure and report the Load-regulation for the specified load range (see pages 6 and 8 of this Lab Procedure). Comment on the results.

c) Using Rload = 220 Ω, measure and report the Line-regulation for the specified range of VAC,rms (see pages 5 and 8 of this Lab procedure). Comment on the results.

VAC

60 Hz

Bench Variable AC Supply

+

vac(t)

_

D1

RC

Iout

Rload

+

Vout

_10 kΩ

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2.1 Full-Wave Rectifier

Note: in this setup it is not possible to use two channels of the scope to observe vr(t) and vac(t) at the same time. Why? Discuss with the TA.

a) Using the scope, measure the peak of vr(t) as a function of VAC,rms, in the range from 1 Vrms, to 6 Vrms, in 1 Vrms steps.

In the report, include a plot of the measured data and a plot of the results that would be obtained with an ideal diode (use Excel). Comment on the results. Compare to the results you obtained with the half-wave rectifier (part 1.1.a)

b) Adjust VAC,rms so that the peak of vr(t) equals 6 V.In the report, record VAC,rms and include an annotated plot of the waveform vr(t).

VAC

60 Hz

Bench Variable AC Supply

+

vac(t)

_

+

vr(t)

_

D1

R

D2

D3 D4

10 kΩ

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2.2 Full-Wave “Peak Rectifier”

Add the filter capacitor C. Make a note of the value you are using. Use the scope (AC coupled) to measure the ripple in vout(t). Use DC multi-meters to measure the DC output voltage VCC and the DC load current ICC. For ICC ≈ 22 mA (Rload = 220 Ω), adjust VAC,rms so that the DC output voltage equals 5 V.

a) Measure and report the peak-to-peak ripple Vr in vout(t). Compare the measured value to the result obtained by analysis (see textbook Eq.(3.33) ((3.75) of the 4th

edition)). Include an annotated plot of the vout(t) waveform.b) Measure and report the Load-regulation for the specified load range (see pages 6

and 8 of this Lab Procedure). Comment on the results.c) Using Rload = 200 Ω, measure and report the Line-regulation for the specified range

of VAC,rms (see pages 5 and 8 of this Lab procedure). Comment on the results.d) Compare the results in this section to the results obtained with the Half-Wave “Peak

Rectifier.”

VAC

60 Hz

Bench Variable AC Supply

+

vac(t)

_

D1

RC

ICC

Rload

D2

D3 D4

+

VCC

_10 kΩ

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3. Complete Voltage Regulator

Design considerations (see class notes and Example 3.10 on page 213 (Example 3.11 of the 4th edition):• The circuit has two design parameters:

The unregulated DC voltage VDC at the output of the full-wave “peak-detection” rectifier can be adjusted by changing VAC,rmsThe resistor RZ can be used to adjust the current IR

• VDC should be as low as possible to minimize the power dissipation on RZ and get the best possible efficiency for the power supply. Explain this statement in the report!

• The minimum value of vDC(t) should be greater than VCC by at least 1-2 V. Explain why in the report. Therefore, VDC has to be sufficiently greater than VCC to allow for the worst-case VAC,rms (nominal−10%), and the worst-case peak ripple Vr in vdc(t).

• Once VDC and the minimum value of vDC(t) have been selected, choose RZ so that the minimum value of the Zener diode current IZ under worst-case conditions is about 5 mA. This ensures that the Zenerdiode operates on the steep portion of the breakdown region and improves Line and Load regulation of the power supply.

VAC

60 Hz

Bench Variable AC Supply

+

vac(t)

_

+

vDC(t)

_

D1

RC

ICC

Rload

D2

D3 D4

+

VCC

_

RZ

DZ

IZ

IR

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3.1 Design and test

Select VAC,rms and RZ. In the report, give a detailed explanation of how you selected the values. All tests in this Section should be performed using the values of VAC,rms and RZ you selected. If the power supply fails to operate correctly (i.e. if VCC goes significantly “out of regulation” under any operating conditions), you have to re-examine your selection of VAC,rms and RZ. You may start testing your design by using a DC supply to generate VDC. Once you have verified that the Zener shunt regulator operates correctly with the DC input, you can use the full-wave peak rectifier to generate vDC(t).

Use the scope (AC coupled) to measure the ripple in vCC(t). Use DC multi-meters to measure the DC output voltage VCC and the DC load current ICC. Testing of the power supply should include the following:

a) Measure and report the peak-to-peak ripple Vrcc in vCC(t). Compare the measured value to the result obtained without theZener shunt regulator (in part 2.2). Include an annotated plot of the vCC(t) waveform.

b) Measure and report the Load-regulation for the specified load range (see pages 6 and 8 of this Lab Procedure). Comment on the results.

c) Using Rload = 220 Ω, measure and report the Line-regulation for the specified range of VAC,rms (see pages 5 and 8 of this Lab procedure). Comment on the results.

d) Compare the results in this section to the results obtained without the Zener shunt regulator (in part 2.2).e) In the report, find and give the maximum and the minimum power dissipated on RZ and DZ, as well as the power delivered to

the load Rload. Find the efficiency η of the Zener shunt regulator for maximum ICC = 22 mA, ICC = 10 mA, and ICC = 0.

VAC

60 Hz

Bench Variable AC Supply

+

vac(t)

_

+

vDC(t)

_

D1

RC

ICC

Rload

D2

D3 D4

+

VCC

_

RZ

DZ

IZ

IR

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ECEN3250 Lab 4Rectifiers and Power Supplies

Diode-CapacitorVoltage Doublers and Inverters

Extra Credit Lab Assignment

ECE DepartmentUniversity of Colorado, Boulder

18ECEN3250

IntroductionIn many electronic systems, the available DC voltage sources do not meet supply-voltage requirements of various sub-systems. For example, in a typical cell phone, a single Lithium-Ion battery is available to supply all parts of the system: microprocessor, audio amplifier, display, RF power amplifier, modulators and demodulators, etc. A Lithium-Ion battery voltage VCC is between about 4.2 V, when the battery is fully charged, and about 3 V, when the battery is fully charged. On the other hand, the display lighting or the RF power amplifier may require a power supply of about 5 V, while analog amplifiers may require both positive and negative supply voltages. In this case, and in may other applications, there is a need to to generate supply voltages greater than the available voltage source VCC or of opposite polarity.

The question is: how can we generate a DC supply voltage greater than the available battery voltage, or a DC supply voltage of opposite polarity?

Using linear components, it is not possible to increase or invert a DC supply voltage. Using diodes and capacitors, however, it is possible to do that. The purpose of this lab is to construct and test simple diode-capacitor voltage doublers and voltage inverters.

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Introduction• Objective: given a DC power supply VCC, generate a DC supply voltage VOUT

having:– VOUT = ≈ 2VCC (voltage doubler), or – VOUT ≈ – VCC (voltage inverter)

• In this part of the lab, you will construct the required DC-DC power supply using diodes, capacitors and a pulse generator

+

VOUT

_

Load

IOUT

DC-DC Power SupplyVCC+–

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Diode-capacitor voltage doubler

• VCC is the available DC voltage source• The waveform generator produces a 0-to-VCC pulsating waveform• Depending on Rload, the output voltage can be as high as 2VCC

• This circuit is a diode-capacitor voltage doubler

D1

RloadD2

+–

+–

C1

C2

+

Vout

_

VCC Cdc-decouple

Waveformgenerator

+

vp

_

50 Ω_ +

+

_

+

_

1 μF

1 μF

10 μF

10 kΩ

1N4148

1N4148

5 V

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Voltage doubler operation: subinterval 1

• When the pulsating source is close to 0:• C1 is charged up from the DC source VCC through D1 to approximately VCC = 5 V• Diode D2 is reverse-biased• C2, which is discharged by the load current, maintains the voltage Vout across the

load approximately constant

D1

RloadD2

+–

+–

C1

C2

+

Vout

_

VCC Cdc-decouple

Waveformgenerator

+

vp

_

50 Ω_ +

+

_

+

_

1 μF

1 μF

10 μF

10 kΩ

1N4148

1N4148

5 V

≈ 0

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Voltage doubler operation: subinterval 2

• When the pulsating source is close to VCC:• C1 discharges through D2 to charge up C2 to approximately VCC+VCC = 2 VCC

• Diode D1 is reverse-biased• C2, which is still discharged by the load current, maintains the voltage Vout of

approximately 2 VCC across the load

D1

RloadD2

+–

+–

C1

C2

+

Vout

_

VCC Cdc-decouple

Waveformgenerator

+

vp

_

50 Ω_ +

+

_

+

_

1 μF

1 μF

10 μF

10 kΩ

1N4148

1N4148

5 V

≈ VCC

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Voltage doubler experiment

• Adjust the waveform generator to produce a 0-to-5 V pulsating waveform at the frequency of 10 KHz across a 10 kΩ load

• Construct the doubler circuit, measure and report:• The DC output voltage with and without Rload• The AC output voltage ripple with and without Rload• Waveforms at vp and at the anode of D2

• Comments about the operation of the circuit: why is the output voltage lower than 10 V? Why do the output voltage and the ripple depend on the load current? Does the frequency of vp affect the results?

D1

RloadD2

+–

+–

C1

C2

+

Vout

_

VCC Cdc-decouple

Waveformgenerator

+

vp

_

50 Ω_ +

+

_

+

_

1 μF

1 μF

10 μF

10 kΩ

1N4148

1N4148

5 V

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Voltage inverter

• Using a DC voltage source VCC, a 0-to-VCC pulsating voltage source, two diodes and two capacitors, it is possible to construct a circuit to invert the DC voltage source VCC

• In the report• Sketch the voltage inverter circuit• Construct the voltage inverter and repeat the experiment/report tasks you

did with the voltage doubler