DENE 3353 APPLIED ELECTRONICS CHAPTER 5 REGULATED POWER SUPPLIES
Oct 22, 2014
DENE 3353APPLIED ELECTRONICS
CHAPTER 5REGULATED POWER
SUPPLIES
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
OutlineOutline
• Introduction• Filter Voltage Regulation & Ripple• Capacitor Filter• RC Filter• Discrete Transistor Voltage Regulation• Integrated Circuit Regulator
22
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
Power Supply DiagramPower Supply Diagram
33
Fig. 15.1: Block Diagram Showing Parts of a Power Supply
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
Filter CircuitsFilter Circuits
• The output from the rectifier section is a pulsating DC.
• The filter circuit reduces the peak-to-peak pulses to a small ripple voltage.
44
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
Ripple FactorRipple Factor
After the filter circuit a small amount of AC is still remaining. The amount of ripple voltage can be rated in terms of ripple factorripple factor (r).
100V
)V
voltage dc
(rms) voltage ripple%r
dc
r(rms
55
Fig. 15.2: Filter Voltage Waveform Showing dc and Ripple Voltages.
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
Example 15.1Example 15.1
Using a dc and ac voltmeter to measure the output signal from a filter circuit, we obtain readings of 25V dc and 1.5 V rms. Calculate the ripple of the filter output voltage.
100V
)V
voltage dc
(rms) voltage ripple%r
dc
r(rms
66
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
Example 15.2Example 15.2
A dc voltage supply provides 60V when the output is unloaded. When connected to a load, the output drops to 56V. Calculate the value of voltage regulation.
77
100V
V-V
voltageload full
voltageload full- voltageload-no%VR
FL
FLNL
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
Rectifier Ripple FactorRectifier Ripple Factor
mdc 0.636VV
%481000.636
0.308
100V
V%r
Vm
Vm
dc
r(rms)
mr(rms) 0.308VV
mdc 0.318VV
mr(rms) 0.385VV
121%1000.318V
0.385V
100V
V%r
m
m
dc
r(rms)
88
Half-WaveHalf-Wave
DC output:
AC ripple output:
Ripple factor:
Full-WaveFull-Wave
DC output:
AC ripple output:
Ripple factor:
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
Types of Filter CircuitsTypes of Filter Circuits
Capacitor FilterCapacitor Filter
RC FilterRC Filter
99
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
Capacitor FilterCapacitor Filter
The larger the capacitor the smaller the ripple voltage.
CR
2.4V
C
2.4I
fC34
IV
L
dcdcdcr(rms)
Ripple voltageRipple voltage
C
4.17IV
4fC
IVV dc
mdc
mdc
DC outputDC output
100RLC
2.4100
CV
2.4I100
V
V%r
dc
dc
dc
r(rms)
Ripple factorRipple factor
1010
Fig. 15.4: Capacitor Filter Operation
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
Example 15.3Example 15.3
Calculate the ripple voltage of a full-wave rectifier with a 100µF filter capacitor connected to a load drawing 50mA.
1111
CR
2.4V
C
2.4I
fC34
IV
L
dcdcdcr(rms)
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
Example 15.4Example 15.4
If the peak rectified voltage for the filter circuit of Example 15.3 is 30V, calculate the filter dc voltage.
1212
C
4.17IV
4fC
IVV dc
mdc
mdc
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
Example 15.5Example 15.5
Calculate the ripple voltage of a capacitor filter for a peak rectified voltage of 30V, capacitor C = 50µF, and a load current of 50mA.
1313
100RLC
2.4100
CV
2.4I100
V
V%r
dc
dc
dc
r(rms)
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
Voltage Regulation CircuitsVoltage Regulation Circuits
There are two common types of circuitry for voltage regulation:
• Discrete Transistors• IC’s
1414
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
Discrete-Transistor RegulatorsDiscrete-Transistor Regulators
Series voltage regulatorSeries voltage regulatorCurrent-limiting circuitCurrent-limiting circuitShunt voltage regulatorShunt voltage regulator
1515
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
Series Voltage Regulator CircuitSeries Voltage Regulator Circuit
The series element controls the amount of the input voltage that gets to the output.
If the output voltage increases (or decreases), the comparator circuit provides a control signal to cause the series control element to decrease (or increase) the amount of the output voltage.
1616
Fig. 15.12: Series Regulator Block Diagram
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
Example 15.8Example 15.8
Calculate the output voltage and the Zener current in the regulator circuit of Fig. 15.14 for RL =1kΩ.
1717
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
Series Voltage Regulator CircuitSeries Voltage Regulator Circuit
When the output increases:When the output increases:
1. The voltage at V2 and VBE of Q2 increases
2. The conduction of Q2 increases3. The conduction of Q1 decreases4. The output voltage decreases
• R1 and R2 act as the sampling circuit• Zener provides the reference voltage• Q2 controls the base current to Q1
• Q1 maintains the constant output voltage
When the output decreases:When the output decreases:
1. The voltage at V2 and VBE of Q2 decreases
2. The conduction of Q2 decreases3. The conduction of Q1 increases4. The output voltage increases
1818
Fig. 15.15: Improved Series Regulator Circuit
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
Example 15.9Example 15.9What regulated output voltage is provided by the circuit of Fig. 15.15 for the circuit elements R1=20kΩ, R2 = 30kΩ, and VZ = 8.3V?
1919
)(2
2
21BEZo VV
R
RRV
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
Series Voltage Regulator CircuitSeries Voltage Regulator Circuit
The op-amp compares the Zener diode voltage with the output voltage (at R1 and R2) and controls the conduction of Q1.
2020
Fig. 15.16: Op-amp Series Regulator Circuit
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
Example 15.10Example 15.10
Calculate the regulated output voltage in the circuit of Fig. 15.17
2121
Zo VR
RV
2
11
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
Current-Limiting CircuitCurrent-Limiting Circuit
When IL increases:
• The voltage across RSC increases• The increasing voltage across RSC drives Q2 on• Conduction of Q2 reduces current for Q1 and the load
2222
Fig. 15.18: Current-Limiting Voltage Regulator
Short-circuit / overload protection
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
Example (Floyd)Example (Floyd)
Determine the maximum current that the regulator in Figure 15.18 can provide to a load.
2323
Fig. 15.18: Current-Limiting Voltage Regulator
scL R
I7.0
(max)
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
The load voltage is sampled and fed back to a comparator circuit. If the load voltage is too high, control circuitry shunts more current away from the load.
Shunt Voltage Regulator CircuitShunt Voltage Regulator Circuit
The shunt voltage regulator shunts current away from the load.
2424
Fig. 15.20: Block Diagram of Shunt Voltage Regulator
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
Example 15.11Example 15.11
Determine the regulated voltage and circuit currents for the shunt regulator of Fig. 15.22
2525
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
When the output voltage increases:
• The Zener current increases• The conduction of Q2 increases• The voltage drop at Rs increases• The output voltage decreases
Shunt Voltage Regulator CircuitShunt Voltage Regulator Circuit
When the output voltage decreases:
• The Zener current decreases• The conduction of Q2 decreases• The voltage drop at Rs decreases• The output voltage increases
2626
Fig. 15.24: Improved Shunt Voltage Regulator Circuit
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
Shunt Voltage Regulator CircuitShunt Voltage Regulator Circuit
2727
Fig. 15.24: Shunt Voltage Regulator Using an Op-amp
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
Example of shunt regulatorExample of shunt regulator
2828
Fig. 15.24: Shunt Voltage Regulator Using an Op-amp
In Figure 15.24, what power rating must Rs have if the maximum input voltage is 12.5V?
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
IC Voltage RegulatorsIC Voltage Regulators
Regulator ICs contain:
• Comparator circuit• Reference voltage• Control circuitry• Overload protection
Types of three-terminal IC voltage regulators
• Fixed positive voltage regulator• Fixed negative voltage regulator• Adjustable voltage regulator
2929
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
Three-Terminal Voltage RegulatorsThree-Terminal Voltage Regulators
The specifications for this IC indicate:
• The range of input voltages that can be regulated for a specific range of output voltage and load current
• Load regulation—variation in output voltage with variations in load current
• Line regulation—variation in output voltage with variations in input voltage
3030
Fig. 15.25: Block Representation of Three-Terminal Voltage Regulator
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
Fixed Positive Voltage Regulator
These ICs provide a fixed positive output voltage.
3131
Fig. 15.26: Connection of a 7812 Voltage Regulator
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
These ICs output a fixed negative output voltage.
Fixed Negative Voltage RegulatorFixed Negative Voltage Regulator
3232
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
Quiz 4Quiz 4
Draw a schematic for voltage supply using a full-wave bridge rectifier, capacitor filter, and IC regulator to provide an output of +5V
3333
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
Example 15.13Example 15.13
For a transformer output of 15V and a filter capacitor of 250µF, calculate the minimum input voltage when connected to a load drawing 400mA.
3434
IC Part Output Voltage (V)
Minimum Vi (V)
7805 +5 7.3
7806 +6 8.3
7808 +8 10.5
7810 +10 12.5
7812 +12 14.6
7815 +15 17.7
7818 +18 21.0
7824 +24 27.1
Table 15.1: Positive-voltage regulators in the 7800 Series
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
Example 15.14Example 15.14
Determine the maximum value of load current at which regulation is maintained for the circuit of Fig. 15.29.
3535
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
Adjustable Voltage RegulatorAdjustable Voltage Regulator
These regulators have adjustable output voltages.
The output voltage is commonly selected using a potentiometer.
3636
Fig. 15.30: Connection of LM317 adjustable-voltage regulator
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
Example 15.15Example 15.15
Determine the regulated voltage in the circuit of Fig. 15.30 with R1 = 240Ω and R2 = 2.4kΩ.
3737
Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.
Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky
Example 15.16Example 15.16
Determine the regulated output voltage of the circuit in Fig. 15.31
3838