Optimal Design of Switching Power Supply
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Preface xiii
Introduction xv
1 Overview on Switching-Mode Power Supply (SMPS) 1
1.1 Classification of Integrated Regulated Power Supply 1
1.2 Characteristics of SMPS 5
1.3 New Development Trend of SMPS 6
1.4 Basic Principles of SMPS 13
1.5 Control Mode Type of SMPS 16
1.6 Working Mode of SMPS 20
1.7 Feedback Type of SMPS 22
1.8 Load Characteristics of SMPS 27
2 New Technology and Its Application of SMPS 31
2.1 Single-Chip Integration of SMPS 31
2.2 Computer-Based SMPS Design 33
2.3 Internal Protection Circuit of SMPS 39
2.4 Synchronous Rectification (SR) Technology 41
2.5 Active Clamp Technology 43
2.6 Magnetic Amplifier Regulator Technology 45
2.7 Programmable Voltage Regulator Technology 49
2.8 Digital Power Supply System 56
2.9 Energy-Saving and Environment-Friendly Technology of SMPS 66
3 Topologies of the DC/DC Converter 69
3.1 Topologies of the DC/DC Converter 69
3.2 Basic Principle of Buck Converter 75
3.3 Basic Principle of Boost Converter 78
3.4 Basic Principle of Buck-Boost Converter 79
3.5 Basic Principle of Charge Pump Converter 80
3.6 Basic Principle of SEPIC 81
3.7 Basic Principle of Flyback Converter 82
3.8 Basic Principle of Forward Converter 86
3.9 Basic Principle of Push-Pull Converter 87
3.10 Basic Principle of Half/Full Bridge Converter 89
3.11 Basic Principle of Soft Switching Converter 90
3.12 Basic Principle of Half-Bridge LLC Resonant Converter 93
3.13 Basic Principle of the 2-Switch Forward Converter 97
4 Method for Selecting Key Peripheral Components of SMPS 99
4.1 Selection Method for Fixed Resistor 99
4.2 Selection Method for Capacitors 105
4.3 Inductor Characteristics and Selection Method for Magnetic Beads 111
4.4 Selection Method for EMI Filter 116
4.5 Selection Method for Input Bridge Rectifier 128
4.6 Selection Method for Output Rectifier 130
4.7 Selection Method for Transient Voltage Suppressor (TVS) 137
4.8 Selection Method for Power Switching Tube 142
4.9 Selection Method for Optical Coupler 149
4.10 Selection Method for Adjustable Precision Shunt Regulator 152
4.11 Selection Method for SMPS Protection Elements 159
5 Power Factor Correction Circuit Design of SMPS 167
5.1 Brief Introduction to Power Factor Correction (PFC) 167
5.2 Basic Principle of Passive PFC Circuit 170
5.3 Design Examples of Passive PFC Circuit 175
5.4 Basic Principle of Active PFC Circuit 177
5.5 Design Examples of Active PFC Circuit 184
5.6 Principle and Application of High-Power PFC 188
5.7 Measures to Suppress PFC Electromagnetic Interference 197
5.8 PFC Configuration Scheme 200
6 Design of High-Frequency Transformer 205
6.1 Selection Method for Magnetic Cores by the Empirical Formula or Output Power Table 205
6.2 Waveform Parameters of the High-Frequency Transformer Circuit 211
6.3 Formula Derivation of Selecting High-Frequency Transformer Magnetic Core Based on AP Method 212
6.4 Design of Flyback High-Frequency Transformer 217
6.5 Design of Forward High-Frequency Transformer 225
6.6 Loss of High-Frequency Transformer 227
7 Examples of SMPS Optimization Design 231
7.1 Multioutput SMPS Design 231
7.2 Methods to Improve the Cross-Load Regulation of Multioutput SMPS 236
7.3 Design of PC SMPS with Magnetic Amplifier 238
7.4 Design of Synchronous Rectification DC/DC Converter 241
7.5 Design of SMPS for Peak-Power-Output Audio Power Amplifier 243
7.6 Design of Industrial Control Power Supply Based on Voltage-Doubling Rectifier 246
7.7 Design of Industrial Control Power Supply Based on Suspension High-Voltage Constant Current Source 248
7.8 Design of StackFETTM Technology-Based Micro-SMPS 250
7.9 Design of Power Supply for the Digital TV Set-Top Box 252
7.10 Design of Mobile Phone Charger with USB Interface 254
8 Key Design Points of SMPS 257
8.1 SMPS Design Requirements 257
8.2 Design of High-Efficiency SMPS 260
8.3 Methods of Reducing No-Load and Standby Power Consumption of SMPS 265
8.4 Stability Design of Optocoupler Feedback Control Loop 274
8.5 SMPS Layout and Wiring 282
8.6 Design of Constant Voltage/Current SMPS 288
8.7 Design of Precision Constant Voltage/Current SMPS 292
8.8 Design of Remote Turn-Off Circuit for SMPS 297
8.9 Typical Application and Printed Circuit Design of New Single-Chip SMPS 299
8.10 Electromagnetic Interference Waveform Analysis and Safety Code Design of SMPS 307
8.11 Radiator Design of Single-Chip SMPS 313
8.12 Radiator Design of Power Switching Tube (MOSFET) 321
8.13 Common Troubleshooting Methods of SMPS 327
9 SMPS Testing Technology 329
9.1 Parameter Testing of SMPS 329
9.2 Performance Testing of SMPS 333
9.3 SMPS Measurement Skills 336
9.4 Accurate Measurement Method of Duty Ratio 343
9.5 Method to Detect the Magnetic Saturation of High-Frequency Transformer with Oscilloscope 345
9.6 Digital Online Current/Resistance Meter 348
9.7 Electromagnetic Compatibility Measurement of SMPS 354
9.8 Waveform Test and Analysis of SMPS 359
10 Protection and Monitoring Circuit Design of SMPS 367
10.1 Design of Drain Clamp Protection Circuit 367
10.2 Overvoltage Protection Circuit Constituted by Discrete Components 371
10.3 Application of Integrated Overvoltage Protector 377
10.4 Design of Undervoltage Protection Circuit 381
10.5 Design of Overcurrent and Overpower Protection Circuit 384
10.6 Design of Soft-Start Circuit 389
10.7 Mains Voltage Monitor 392
10.8 Transient Interference and Audio Noise Suppression Technology of SMPS 396
10.9 Design of Overheating Protection Component and Cooling Control System 400
References 407
Index 409
Chapter 1
Overview on Switching-Mode Power Supply (SMPS)
1.1 Classification of Integrated Regulated Power Supply
There are tens of thousands of integrated voltage regulators in the market, which can be roughly classified into linear regulators and switching regulators. See Table 1.1 for the classification and characteristics of integrated regulated power supply.
Table 1.1 Classification and Characteristics of Integrated Regulated Power Supply
Integrated regulated power supply Linear power supply Standard linear regulator Fixed type Three-terminal fixed type Positive voltage output, negative voltage output Multiple-terminal fixed type Positive voltage output, negative voltage output Adjustable type Three-terminal adjustable type Positive voltage output, negative voltage output, tracking mode Multiple-terminal adjustable type Positive voltage output, negative voltage output, tracking mode Low dropout linear regulator Low dropout regulator (LDO) Three-terminal or multiple-terminal fixed/adjustable type Positive voltage output, negative voltage output, tracking mode Quasi low dropout regulator (QLDO) Very low dropout regulator (VLDO) Switching mode power supply (SMPS) Pulse width modulator (PWM) With relatively low integration level and complicated peripheral circuit with constitutes high-power SMPS Pulse frequency modulator (PFM) With relatively low integration level, complicated peripheral circuit, switching frequency may reach over 1 MHz, and high efficiency Switching regulator With relatively high integration level and power switch tube inside, which needs to be equipped with industrial frequency transformer Single-chip SMPS With pretty high integration level and simple peripheral circuit, which constitutes SMPS of medium and small power1.1.1 Optimal Design of SMPS
The linear regulator, also known as series regulated integrated regulator, is named for its internal regulating tube, which works in the linear working area and is in series connection with load. It has advantages such as sound voltage regulation performance, low-output ripple voltage, simple circuit, and low cost, while its main disadvantages include relatively bigger voltage drop and high power consumption of the regulating tube with relatively low efficiency of the regulated power supply at about 45%. The linear regulator mainly consists of two types, namely, standard linear regulator using NPN regulating tube, which is also known as NPN linear regulator, and PNP low-dropout (LDO) regulator using PNP regulating tube. Besides, there are quasi low-dropout (QLDO) regulator and very low-dropout (VLDO) regulator. According to the characteristics of output voltage, linear regulators can be divided into different types such as fixed output, adjustable output, positive pressure output, negative pressure output, and multiplexed-output (including tracking output). The efficiency of traditional standard linear regulators is only around 45%, while that of LDO and VLDO can reach 80-90% under low voltage output.
The switching-mode power supply (SMPS) is known as a highly energy-efficient power supply. It leads the development direction of regulated power supply and now has become the leading product of regulated power supply. With the internal key components working under high-frequency switch status, the SMPS consumes quite low energy so that its power efficiency may reach up to 70-90%, twice as high as that of the standard linear regulated power supply. The SMPS integrated circuit mainly consists of the following four types: pulse width modulator (PWM), pulse frequency modulator (PFM), switching regulator, and single-chip SMPS.
According to the circuit principle, regulators can be divided into three types including series regulated linear regulator, shunt regulated linear regulator, and switching regulator. Their equivalent circuits are respectively shown in Figure 1.1(a)-(c). In this figure, refers to the equivalent resistance of regulating tube and S the power switch tube. As its output voltage is highly stable and output current is very small, shunt regulated linear regulator is generally used as reference voltage source. The main characteristics of various products are described in the following sections.
Figure 1.1 Equivalent circuits of the three kinds of regulators: (a) series regulated linear regulator; (b) shunt regulated linear regulator; and (c) switching regulator
1.1.1.1 Three-Terminal Fixed Regulator
Fairchild Semiconductor Corporation firstly launched 7800 and A7900 series three-terminal fixed regulators in the beginning of the 1970s. It is a big revolution for integrated circuits of power supply, which greatly simplifies the design and application of power supply. The three-terminal fixed regulator can be placed in the circuits via the simplest way (such as a transistor) and has relatively complete overcurrent protection (OCP), overvoltage protection (OVP), and overheat protection (OTP) functions. At present, A7800 and A7900 series three-terminal fixed regulators have become universal ones in the world, with the widest application and largest sale volume. Such a three-terminal fixed regulator is easy to operate and needs no adjustment. It has a simple peripheral circuit and operates reliably and safely, and therefore is applicable to make general or nominal-output regulated power supply. However, it cannot regulate the output voltage or directly output non-nominal voltage, and its voltage is not stable enough.
1.1.1.2 Three-Terminal Adjustable Regulator
Three-terminal adjustable regulator was developed in the late 1970s and the early 1980s, which was the second-generation three-terminal regulator initiated by National Semiconductor (NSC). It not only reserves the advantage of simple structure the three-terminal fixed regulator has but also overcomes the disadvantage that the voltage could not be regulated. Moreover, its voltage stability is increased by one order of magnitude. Therefore, three-terminal adjustable regulator can be used to make laboratory power supply and DC regulated power supply. In addition, it can also be designed as fixed type to replace the three-terminal fixed regulator, to further improve the voltage regulation performance.
1.1.1.3 Low-Dropout (LDO) Regulator
LDO is a high-efficiency linear integrated regulator, whose input-output dropout voltage is about 500 mV, with power efficiency obviously higher than that of NPN linear regulator. VLDO is a new linear integrated regulator developed based on LDO in the beginning of the twenty-first century. VLDO uses the field-effect tube with very low specific on-resistance instead of the power tube that PNP uses, and its input-output dropout voltage can be as low as .
1.1.1.4 Multiterminal Integrated Regulator
With plenty of pins, the multiterminal integrated regulator is flexible to use but with complicated connections. It can also be classified into fixed type and adjustable type.
1.1.1.5 Tracking Positive-Negative Balanced Output Integrated Regulator
Its characteristic is that when the positive voltage changes for some reasons, the negative voltage output may track automatically and make corresponding change to keep the absolute values of the two equal. The tracking function is particularly important for a precision operational amplifier powered by two supplies, which can prevent the operational amplifier from zero drift rising out of the unbalance between positive voltage and negative voltage.
1.1.1.6 Transformer SMPS without Power Frequency
The SMPS is also known as a low-loss power supply. As its internal parts operate under high-frequency switch status, the SMPS consumes low energy but with power efficiency twice that of ordinary linear regulated power supply.
1.1.1.7 Switching Regulator
A switching regulator is a switch integrated voltage regulator developed in the 1980s and 1990s. With PWM, power output, and protection circuit integrated on the same chip, the switching regulator has efficiency of over 90%. In addition, some switching regulators can even regulate output voltage continuously that can be used to SMPS with dozens to hundreds of wattage.
1.1.1.8 Single-Chip SMPS
With the main circuits (including MOSFET, required analog and digital circuits) of SMPS integrated on chip, the single-chip SMPS with the highest integration level can realize output isolation, PWM, and many other protection functions. A single-chip SMPS fits AC current of 85-265 V and 47-400 Hz via an input rectifier filter; it is thus an AC/DC power converter. The single-chip SMPS integrated circuit has displayed strong vitality since its appearance in the...
