Switching Power Supply Development History About 1960 About 1965 About 1970 1972 1974 1976 1978 1995 2000 2004 2005 2006 2008 Stabilized power supplies using vacuum tubes were common at this time. America’s NASA began developing switching power supplies for use in space craft. Development of semiconductor elements for switching power supplies begins. TDK and Nippon Electronic Memory Industry Co. Ltd. (predecessor to Nemic-Lambda) enter the switching power supply business. Nippon Electronic Memory Industry Co. Ltd. manufactures and markets Japan’s first standard switching power supply. TDK manufactures and markets switching power supplies. Switching power supplies are adopted for use in commercial television games and the switching power supply market expands. TDK manufactures and markets switching power supply transformers. Nemic -Lambda (predecessor to Densei-Lambda) founded, to take over operations of Nippon Electronic Memory Industry Co. Ltd. TDK begins production of DC-DC converters for use in HEVs. TDK launches the RKW and JBW series of switching power supplies. Densei-Lambda (the predecessor to TDK-Lambda) launches the HWS series of switching power supplies. Densei-Lambda joins the TDK Group. Sales of UPS with lithium-ion batteries (lead-free) begin. Sales of TDK-Lambda brand products begin. TDK and Densei-Lambda market a total of 234 types of EMC filters for power line in 13 series. All models available on the market comply with the RoHS Directive. TDK-Lambda Corporation launched. Advances in Switching Power Supplies (unit type, 150 W comparison) Further miniaturization and higher efficiency 1300cm 3 3800cm 3 Japan’s first standard switching power supply. 3 Next generation 1200cm 3 Power supplies have undergone amazing miniaturization. 4500cm 550cm 3 Fifth generation Fourth generation Second generation ●Compliance with environmental regulations such as the RoHS Third Directive ●Compliance with generation EMC regulations, CE marks, etc. ●Compliance with global standards First generation About 1970 1980 1990 2000 2010 TDK Power Electronics World Date of publication: March 31, 2009 Publisher: TDK Corporation Corporate Communications Dept. 1-13-1 Nihonbashi, Chuo-ku, Tokyo 103-8272 Telephone: +81-3-5201-7102 SGS-COC-004380 Cert no . TDK Power Electronics World Guidebook of TDK Power Electronics Products TDK Power Electronics World Welcome to Power Electronics World Communications and broadcasting equipment Measuring instruments and test equipment Factory automation and control equipment Introductory Section ● What Is Direct Current (DC)? What Is Alternating Current (AC)? 3 ● There Is No Such Thing as Perfect DC or AC・・ 4 ● Why Are Stabilization Circuits Needed?・・・・ 5 ● Power Supply Devices Play a Variety of Different Roles 6 ● What Is Rectification? What Is Smoothing? 7 ● The Functions of Main Components・・・・・・・・ 8 ● Creating Optimal Power Supply Systems・・・ 9 ● Distributed Power Supply Systems and Power Modules 10 Computers and office automation equipment Medical devices Technology Section ● Structure of Linear Power Supplies・・・・・・・ 11 ● Structure of Switching Power Supplies・・・・ 12 ● Basic Circuits of Non-Insulation type DC-DC Converters・・ 13 ・Chopper Type (Back Converter, Boost Converter), Charge Pump Type ● Basic Circuits of Insulation type DC-DC Converters 15 ・Flyback Converter, Forward Converter, RCC Type, Push-Pull Type, Full-Bridge Type ● Technologies for Improving Efficiency・・・・ 17 ・Areas of Loss in Switching Power Supplies, Soft Switching, Power Factor and Harmonic Correction (PFHC) Circuits, Synchronous Rectification Method, Digital Control ● Key Parts That Support Power Supply Performance 19 ・Capacitors, Coils and Transformers ● Noise Countermeasures in Switching Power Supplies 20 ● Uninterruptible Power Supplies・・・・・・・・・・ 21 ● New Power Supply Systems and Batteries 22 ● Switching Power Supply Development History 1 Automobiles and traffic control equipment Household appliances and consumer electronics 2 Introductory Section TDK Power Electronics World What Is Direct Current (DC)? What Is Alternating Current (AC)? Electric current can be direct current (DC) or alternating current (AC). Direct current such as the power from dry cells is characterized by a uniform direction of flow and amount (voltage) of electricity. Alternating current is characterized by direction of flow and amount of electricity that changes cyclically over time. Long ago, static electricity was the only type of electricity known, but when batteries were invented, it became possible to use DC electricity. Generators were later invented, and it became possible to use AC as well. There Is No Such Thing as Perfect DC or AC When the power of a battery (dry cell or rechargeable) falls, electric and electronic devices stop working. This is because the voltage of a battery falls over time. In recent years, the driving voltage of integrated c i r c u i t s h a s d e c l i n e d , s o eve n s m all changes in voltage are a problem. T he vo l t age of a b at te r y falls steadily. The discharge curves vary depending on the type of battery. Voltage ＋ Decreasing battery voltage 0 Direct Current Current ＋ Direct current has uniform direction of flow and amount (voltage) of electricity. Batteries that are used up such Primary Batteries and as dry cells are primary batterSecondary Batteries ies . Batteries that can be recharged and used repeatedly are The symbols used in Lithium-ion secondary batteries (rechargediagrams for batteries battery able batteries). and DC power supplies Lead storage Dry cell cell The commercial AC from outlets is not stable. Commercial AC can become unstable depending on the load (electrical devices and so on) connected to the distribution network. For example, when all the houses in a neighborhood are using the air conditioning during the afternoon in the middle of the summer, the voltage drops. There are also momentary stoppages in distribution and distortion to wave forms caused by the addition of noise. ＜Cases of instability in commercial AC＞ Nicad battery Button battery 0 Time Commercial AC is not stable as a result of a variety of causes. Time When high-frequency AC is added in the form of noise, the waveform can become jagged like this. Key Point Load Alternating Current Current ＋ 0 Alternating current has direction of flow and amount (voltage) of electricity that change cyclically. The symbol used in diagrams for AC power supplies The direction of the electric current that c omes from the two holes of the electric socket alternates. Time 1 cycle AC Frequency How many times the direction of AC changes each second is called the frequency. The unit of frequency is Hertz (Hz).The frequency of commercial AC is 50 Hz in eastern Japan and 60 Hz in western Japan. Voltage drop * Not all AC electric power has a sine wave. There is also AC with a pulse waveform. The difference between DC and AC is fundamental knowledge concerning power electronics. Distorted waveform Large plants, railways, etc. Large buildings, medium-size plants, etc. AC distribution AC plug AC with a relatively low frequency is referred to as low frequency, and that with a high frequency is referred to as high frequency, but generally, high frequency means AC with a frequency in the kilo -Her tz, mega-Hertz, or higher range. Power outage ＜The flow of electricity from generation to distribution＞ Low Frequency and High Frequency Socket The waveform of the commercial AC power supplied by electric power companies is called a sine wave. 3 Things that are connected to power supplies and consume energy are referred to as“ loads. ”Specific ally, loads include resistor s, circuits, connection devices, and so on. Several hundred Power plant (thermal, hydroelectric, nuclear, etc.) V-1 Ultra-high thousand million V or more Primary voltage substation substation When electricity is distributed at high voltage, the electric power losses (thermal losses resulting from the resistance of the power lines) are lower. 60,000 V 150,000 V Distribution substations 6,000V 100V 200V Transformers on utility poles Homes AC has the advantage of being easy to change to a different voltage using a transformer (DC distribution is used for some portions of the distribution route). AC can easily be converted to a different voltage using a transformer. 4 Introductory Section TDK Power Electronics World Why Are Stabilization Circuits Needed? The DC from a battery or converted from commercial AC using an adaptor still has unstable variations in voltage. Changes in voltage can cause sensitive electronic devices to malfunction, so stabilization circuits are used to create DC with stable voltage. Two methods of doing this are the linear method (also called the series method and dropper method) and switching method. Power Supply Devices Play a Variety of Different Roles Most electronic devices operate on direct current. After commercial AC is rectified (the DC is still unstable), a DC-DC converter is used to change the power (change the voltage or current) and stabilization circuits are used to produce extremely stable DC. ＜Power Conversion Devices Inside Electronic Equipment＞ Key Point Linear Method (Series Method) The cut portion of the electric power is lost. ＜Linear Power Supply＞ Voltage variation Electronic equipment uses a wide variety of power supply devices. The linear method cu t s the uneven ness (variation in volt age ) to make the voltage smooth. Key Point ●DC input Electric power converted to thermal energy and discarded using semiconductor resistors devices Voltage and current conversion Unstable Voltage and Stabilized DC-DC converter DC current conversion DC DC Input voltage Output voltage Stabilized DC AC AC rectification and smoothing circuits Commercial AC power supply If the circuit shown to the right is used and the switch is turned ON and OFF quickly, the brightness of the lamp will decrease as if the voltage dropped. Switching power supplies achieve this effect using semiconductor elements. Voltage (V) 0 Key Point DC DC-DC converter DC DC-DC converter DC Because of differences in the operating voltages of circuits, multiple compact DC-DC converters are dispersed in the vicinity of the ICs. AC input/ DC output The switching format is the most commonly used, so such power supplies are called switching power supplies. OFF ON DC-DC converter AC-DC power supply ＜ The idea behind a switching power supply＞ Switch ON DC DC input/DC output Power supply unit Switching Method T h e di f fe r e nt c ir c ui t s of e l e c t r o ni c equipment use different operating voltages, so they contain multiple DC-DC converters. Conversion from DC to AC DC DC-AC inverter Switching power supplies are used as power supply units in desktop PCs, office equipment, factory automation equipment, and many other devices. There are various types including the case type, open frame type, and circuit board type. The same effect Smooth as reducing power the voltage. DC input/ AC output AC High voltages are required to illuminate the backlights of liquid crystal televisions, so current is converted to alternating current and the voltage is stepped up using a transformer. OFF ●AC Input Devices Switching cycle T his is c alle d pulse width modulation (PWM). ON OFF Input voltage Pulse width The pulse width is changed according to the variation in voltage. The switching method uses a cutand-paste like method to produce stable current without losses, making it extremely efficient. Linear Power Supplies Switching Power Supplies Efficiency Stabilized DC Output voltage Radiated heat Low (30%-60%) High (70%-90% or higher) High Low Size and weight Large and heavy Compact and lightweight The current is pulsed at high frequency by switching (ON/OFF) a semiconductor element and is sent to a transformer that changes the voltage. 5 The pulses are controlled so the area of each is the same , producing stable current with uniform voltage. Unstable DC can cause electronic devices to malfunction. Degree of stability Radiated noise High Ordinary None Noise countermeasures are necessary Key Point The main weakness of switching power supplies is the generation of switching noise in conjunction with the high-speed switching of the semiconductor elements. As a result, EMC countermeasures (noise countermeasures) such as noise filters are essential. Devices that convert direct currents to alternating currents are called inverters. 6 Introductory Section TDK Power Electronics World What Is Rectification? What Is Smoothing? Rectification is the conversion of alternating current to direct current. Rectification is performed by a diode that allows current to flow in one direction but not in the opposite direction. Direct current that has only been rectified, however, has various changes in voltage ( ripples ) lingering from the alternating current. Capacitors are used to smooth the current and make it even. The Functions of Main Components In order to understand the structure of a power supply, it is necessary to know the functions of its main components. If you become familiar with the symbols used for circuits, you will be able to decipher the basic structure of a power supply circuit. Capacitors Electrolytic capacitor Coil (Inductor) DC jack Electrolytic capacitor A dashed line (or solid line) shows the core. (the + indicates the polarity) This type of AC adapter and battery charger is heavy because it uses a power supply transformer with an iron core. Multilayer ceramic capacitors are the leading type of surface mounted devices. Coil Iron core Silicon diodes (× 4) Transformer Key Point Silicon diodes (× 4, bridge format) Fuse Electrolytic capacitor Transformer AC 100V + Resistors Transformer Even after rectification by the diodes and smoothing by the capacitor, the direct current is still not stable. DC output Choke and other coils have cores. Storing large amounts of electrical charge is the role of a smoothing capacitor in a power supply. The capacitor functions like a battery that can be charged and discharged instantaneously. They also have the property of allowing alternating current to pass through. Coils allow direct currents to pass through smoothly, but they act as resistors to alternating current and store electrical energy. or Primary winding Secondary winding This symbol is used in school textbooks. There are power supply transformers and high-frequency transformers. Key Point Electrical power on a primary side passes through a core and is sent to the secondary side. At this time, losses known as core losses (mainly thermal losses) occur, and as a result, the properties of the core material have a large impact on the efficiency of the power supply. (unstable direct current) Voltage conversion Rectification Smoothing Discharging Charging ＋ Diodes Transistors Drain Collector 0 There are two types of rectification: half-wave rectification that rectifies the alternating current flowing in one direction, and full-wave rectification that rectifies the current in both directions. The circuit shown above is full-wave rectification using bridge diodes. 7 Gate Base Pulsating current Unstable direct current Smoothing uses the charging and discharging of high-capacity capacitors. Diodes play an important role in rectification circuits, and capacitors are important for smoothing circuits. Integrated Circuits (ICs) MOSFET Ripple Allows current to flow through in one direction only Diodes are elements that have the property of allowing the electric current to flow through in one direction only. They are used in rectification and other circuits. Emitter Source Transistors are semiconductor elements that have amplification functions. They are used in power supply circuits as switching elements that turned the current ON and OFF. A MOSFET is a field effect transistor that uses metal oxide semiconductors. An integrated circuit is made up of multiple transistors, the diodes, resistors, and other components mounted on a semiconductor board (made of silicon or other material). Capacitors allow alternating current to pass through, while coils prevent alternating current from passing. 8 Introductory Section TDK Power Electronics World Creating Optimal Power Supply Systems Switching power supplies (AC-DC power supplies) and DC-DC converters are available in numerous different formats with various sizes, capacities, shapes, and so on. DC-DC converters are broadly divided into insulation types and non-insulation types. Insulation types use transformers (to prevent electric shocks), while non-insulation types are more compact and do not use transformers. Power modules that integrate numerous components onto a single compact board are also frequently used. Non-insulation Used after insulated converters to convert voltage to the voltage necessary to operate circuits. These type Non-insulation type DC-DC converters are often compact SMD (surface mounted device) types. Output of such converters ranges from less than 1 watt to hundreds of watts. DC-DC converter converters are compact and low cost. a transformer and is electrically Insulation Uses insulated. It is difficult to make these type Distributed Power Supply Systems and Power Modules In recent years, ICs have moved to operating at lower voltages and higher currents, resulting in a shift to distributed power supply systems with compact, high-efficiency DC-DC converters installed in the vicinity of the ICs. ＜Earlier Power Supply Systems＞ 《Insulation types》 DC AC-DC DC-DC power supply Problems with Earlier Systems Load converter 48 V, etc. Commercial Unit type, open AC frame type switching power supplies, etc. converters compact or at low cost. ●Using multiple insulation type 5V DC-DC converter 3.3 V DC-DC converter 2.5 V, etc. DC-DC converters is a problem in terms of cost and space. Load ● ICs are operating on lower voltages, but it is not efficient to suddenly reduce the voltage. Load ●At higher frequencies, the wire ＜Distributed Power Supply System＞ Non-insulation type DC-DC converters Commercial AC AC adapter AC-DC power supply (AC/DC conversion) DC input DC output LCD DC Commercial AC Insulation type DC-DC converter CPU HDD DC 48 V, etc. 《Insulation types》 Intermediate 12 V, voltage 5V, etc. DC-DC converter 《Non-insulation type》 ●Only one insulation type I /O CD/DVD drive POL (point of load) What is POL? ●Placement of a compact DC-DC converter near the load (IC) Notebook PCs use multiple compact DC-DC converters to convert voltage to the necessary voltage and supply it to components. These power modules integrate an AC-DC converter and a DC-DC converter. They use conduction cooling and do not need a cooling fan. Output power is in the 50 W to 1000 W range. AC-DC power supplies Unit type Output power ranges from under 10 W to 3000 W and higher. There are various types including wide input and multi-output. Open frame type DC-DC converter Load DC-DC converter Load Key Point High-efficiency non-insulation type DC-DC converters generate little heat and do not require heat sinks, and as a result, can be mounted near ICs on printed circuit boards. 1.8V, 1.5V, 1.3V, 0.8V, etc. ＜Distributed Power Supply Systems and AC-DC Power Modules＞ 116.8mm DC-DC converter Integrated into a compact module Full brick (12.7 mm high) AC-DC power module Unit type (rack-mount type) PFE Series, etc. Non-insulation type DC-DC converters are compact onboard power supplies. Power modules are standardized using units called bricks. ■Brick types and sizes 《Insulation types》 Commercial AC 9 Load AC-DC power modules integrate AC-DC converters, DC-DC converters, PFHC (power factor and harmonic correction) functions (see page 17), and various other power supply circuits. Such power modules make possible a variety of flexible distributed power supply systems. AC-DC power supply AC input DC output Advantages of Distributed Power Supply Systems DC-DC converter 61mm AC-DC power modules Load DC-DC converter is needed. ：DC-DC converters Output ranges from about 1 watt to hundreds of watts resistance to the load and effects of inductance increase. Relay Bus Converter 《Non-insulation type》 DC-DC Load converter DC-DC converter Load DC-DC converter Load Half- Quarter Eighth Sixteenth brick brick brick brick Key Point Power modules are high efficiency and use conduction cooling and as a result do not need a cooling fan. This means that all power supply devices can be mounted on the same printed circuit board. Point of Load means in the immediate vicinity of the load (ICs, etc.) 10 Technology Section TDK Power Electronics World Structure of Linear Power Supplies Structure of Switching Power Supplies Even after commercial AC is rectified and smoothed, the DC that is produced is not stable (see page 7). A stabilization circuit converts this to DC with little variation in voltage. Let’s first examine a linear type stabilization circuit, which was once the most common type of stabilization circuit. Non-stabilized DC power that has been rectified is converted to high-frequency pulses by a switching element (a transistor or MOSFET) using high-speed switching and sent to a transformer. The output voltage is detected and compared and feedback data provided to control the pulse widths to produce stable DC. Switching power supplies are compact, lighter, and higher efficiency than linear power supplies, but the circuits are more complex and the high-speed switching generates noise, so noise countermeasures are essential. ＜Linear Power Supplies Use Three-Terminal ICs＞ Series type stabilization circuits receive DC stabilized by transistors, and as a result, they generate a lot of heat and are low efficiency. Key Point Power supply transformers are big and heavy. Linear Power Supply Non-stabilized Power Supply Unit ※Higher frequencies Key Point Key Point Rectification which is done in the initial phase is different from a linear power supply. Transformers, choke coils, and capacitors can be miniaturized. Stabilized Power Supply Unit Rectification and smoothing circuit (three-terminal regulator) Three-terminal IC Stabilized DC Non-stabilized DC Variations in the input voltage are adjusted by a variable resistor to produce stabilized output voltage. ＜Switching using semiconductor elements＞ Key Point 《Transistor》 Heat sink 《MOS FET》 Zener diode (if current The three-terminal ICs play the same role as the variable resistor. IN OUT is passed through in the opposite direction, a uniform voltage can be achieved) GND Three-terminal ICs are integrated circuits made from transistors, Zener diodes, and other components. They generate heat, so a heat sink is attached. Linear power supplies are fundamentally low efficiency and have high thermal losses. Photo coupler Pulse width modulation See page 5 for the principles of pulse width modulation (PWM). Switch OFF Current Uniform voltage Threeterminal IC The output voltage is detected and compared and feedback information provided. Switch ON Heat is generated, so a heat sink is needed. + Linear power supplies place resistors in series to control Key Point the current, so they are also called series power supplies. They use resistance to reduce the voltage, so they are also called dropper and series dropper power supplies. 11 Switching Heat + + + Load (series regulators) Rectification and smoothing circuit Detection three-terminal ICs Highfrequency transformers 《Rectification》《Smoothing》 Stabilized DC ●Stabilization circuit using stabilization circuits Variable resistor Load 《Smoothing》 Non-stabilized DC with voltage variations ●Principles of series type AC Power Supply AC power supply Threeterminal regulators, etc. + 《Power supply transformer》 《Rectification》 allow transformer cores to be made smaller. Ferrite and other materials with low high-frequency losses are used as the core materials. The switch is turned ON and OFF at the highs and lows of the square voltage waveform. The primary and secondary sides are electrically insulated and a signal is sent. Switching Regulator Unit Principles of Switching Regulators The current is turned ON and OFF by switching elements at set intervals, converted to a pulse wave, and sent to a transformer. A comparison of the timing of the ON status and OFF status (duty ratio, duty cycle) is used to control the output voltage. By controlling the duty ratio (pulse width) in relation to variations in the input voltage, the output voltage is stabilized (PWM method). ON ON ON Duty ratio OFF OFF OFF Time that circuit is ON Switching cycle Switching cycle The key features of switching power supplies are compact size, light weight, and high efficiency. 12 Technology Section TDK Power Electronics World Basic Circuits of Non-Insulation Type DC-DC Converters There are various forms of non-insulation type DC-DC converters also. A form known as the chopper format is a compact onboard type with output power in the range of less than 1 watt to several watts. Types of chopper converters include the step down back converter and the step up boost converter. Each type is suitable for configuring a compact, low-cost local power supply with a low parts count. An even more simple approach is the charge pump type which uses only capacitors but no coils or transformers. Booster Converter (Step Up) Key Point Compact, onboard types with low output Input voltage < Output voltage The energy stored by the choke coil is increased or boosted when the switch is OFF, raising the voltage. Switch OFF The switching element is connected in parallel; this is dif ferent from the step down converter. + ＜Example of component mounting for compact onboard DC-DC converters (chopper type)＞ ＜Switching and Operation of the Coil＞ Switch ON + Switch ON Choke coil Winding Core The choke coil takes up a relatively large area. (Connected to the control circuit) Current Direction of electromotive force When the switch is ON, the coil generates electromotive force in a direction that prevents current from flowing in. Choke coil Coils prevent variations in current and act as resistors (acs cording to Lenz ’ Law). They are called “ chokes ”because they choke off the electric current. Switch OFF When the switch is turned off, the coil generates electromotive force in the direction as if to maintain the current. Input voltage > Output voltage Key Point Switching element Switch ON ❶Switch ON：When energy flows from the input to the output, the choke coil accumulates energy. ❷Switch OFF：The choke coil releases the stored energy in an attempt to maintain the current. * There is also a back boost format that combines the functions of the back converter and the boost converter. This converter is characterized by the ability to reverse the polarity. Low-output type that uses capacitors Diodes, capacitors, control ICs, etc. Back Converter (Step Down) − The coil accumulates energy. Choke coil + Capacitors are also known as condensers because their basic function is to store electric charge. The charge pump type converter makes use of this function. They are compact, simple DC-DC converters that do not use any transformers or coils and use only capacitors to convert voltage. The electric charge stored in the capacitor is carried by switching as if in a bucket relay to increase the voltage. ＜Basic Principles of Charge Pump Type DC-DC Converters (step up type)＞ The chopper converter was named this because it uses switching to chop the current and transmit it. Key Point Input Switch OFF DC input (Connected to control circuit) Diode + DC output S1 S3 Output V Input The charged capacitors are connected in series and switching is performed to raise the voltage. S1 S3 V C1 Capacitor Output 2V C2 C1 C2 − ❶Switch ON：When energy flows from the input to the output, the choke coil accumulates energy. S2 S4 S2 S4 ❷ Switch OFF：The choke coil generates electromotive force in an attempt to maintain the current and current flows through the diode to the output (the switching element is connected in series with the circuit; the needed voltage can be reduced by setting the duty cycle). 13 The choke coil plays an important role in chopper type converters. S1 and S4 are turned ON and C1 is charged (actual switching is performed through IC operation). When S1 and S4 are OFF and S2 and S3 are ON, the charge in C1 is carried to C2 and the output has twice the voltage. Coils and capacitors have the ability to store energy. 14 Technology Section TDK Power Electronics World Basic Circuits of Insulation Type DC-DC Converters Insulation type DC-DC converters actively use transformers and support high output power. Understanding the basic principles and core circuits will deepen your understanding. RCC Type (self-exciting flyback converter) Low Output Power Types ＜Principles of Transformers and Direction of Electromotive Force＞ Symbol indicating the beginning of the windings of the primary winding Magnetic flux from the primary winding Switch ON When Q1 is ON: When Q1 is OFF: Q1 Base winding Load Inductive electromotive force Reverse electromotive force Core ON/ON Types and ON/OFF Types When the switch is ON, magnetic flux is generated by the primary winding, but electromotive force (reverse electroReverse effect motive force) is generated to prevent the magnetic flux magnetic flux from doubling. The magnetic flux from the primary winding the secondary winding from passes through the core and reverse effect magnetic flux from the secondary winding is generated, creating electromotive force (inductive electromotive force) and current Current (inductive current) flows. When the switch is OFF, the current flows in the opposite direction. Key Point *A gap is placed in the transformer core to prevent magnetic saturation (See page 19). The direction of the electromotive force from the primary and secondary windings (reverse electromotive force and inductive electromotive force) is towards the gray circle ( ). Symbol indicating the beginning of the windings of the secondary winding *RCC : Ringing Choke Converter When Q1 is ON as a result of the base current from the base winding, collector current flows. When the base current is insufficient and Q1 is OFF, current flows on the secondary side. The converter is a self-exciting type that performs this operation repeatedly. It requires only a small number of components and can be used as a simple, low output power power supply. DC-DC converters are available in ON/ON types that output energy when the switching elements are on and ON/OFF types that output energy when the switching elements are off. Types by Output Voltage and Power ON/ON Types (Multi-switching types: Push-pull, half-bridge, full-bridge, etc.) ON/OFF Types (RCC, flyback, etc.) Output voltage (V) Medium to high output power types use multiple switching devices which makes the circuit configuration more complex but enables higher efficiency, lower noise, and advanced functionality. Push-Pull Type Medium to High Output Power Types Low and Medium Output Power Types 1000 100 10 0 0 Switch ON Q1 Transformer + Switch OFF + from the generated magnetic flux (energy storage). The direction of the diode is reversed, so no inductive current flows through the secondary winding. − (Connected to control circuit) lated in the core is released and current flows through the diode (→ ). The transformer coil plays a role similar to that of the choke coil. The transformer core stores energy, so no choke coil is needed. B-H Curves of Magnetic Cores When Q1 is ON: When Q2 is ON: Q1 and Q2 are switched in alternation. Push-pull types are commonly used as power supplies up to about 300 W. Switch ON ❶When the switch is ON, electro- + Reverse electromotive force Switch OFF Choke coil Inductive electromotive force + D2 − Q1 Q3 The transformer is the key component of insulation type DC-DC converters. The narrower the curve, the smaller the losses. Comparison of Performance of Core Types DC output Q2 15 H: Magnetic field The half-bridge type replaces Q1 and Q2 with two capacitors. Magnetic permeability Saturation magnetization Q4 ❷ When the switch is OFF, the choke coil generates (Connected to control circuit) Excitation Process The greater the magnetic permeability, the greater the slope. Magnetic permeability Used as high-efficiency, high output power power supplies with outputs of several hundred watts and higher. motive force (reverse electromotive force and inductive electromotive force) is generated in the primary and secondary windings as a result of the transformer principle and current flows through the diode (D1) (→). At this time, energy is stored in the choke coil. electromotive force, preventing changes in the current, the stored energy is released, and current flows through the reverse flow diode (D2) (→ ). B: Magnetic flux density Saturation magnetic flux density Full-Bridge Type Medium to High Output Power Types Medium Output Power Type D1 1000 Power (W) (single-switching forward, etc.) Q2 ❷ When the switch is OFF, the energy accumu- Key Point 100 ON/OFF Types & ON/ON Types DC output ❶ When the switch is ON, current flows in the primary winding (→) and the core is magnetized 10 Iron losses When Q2 and Q3 are ON: When Q1 and Q4 are ON: Manufacturing cost Silicon Ferrite Amorphous Acceptable Good Excellent Excellent Acceptable Acceptable Poor Excellent Excellent Acceptable Excellent Iron cores generate high losses (thermal losses) at high frequencies, so they are not used. Poor 16 Technology Section TDK Power Electronics World Technologies for Improving Efficiency If the efficiency of power supplies could be increased by just one percent, this would have a tremendous energy-saving impact on society as a whole. Some new technologies for improving energy efficiency are discussed below. In the switching power supplies, the semiconductor elements in particular generate high losses. Also, the power supplies are compact, and as a result if the frequency of the switching operation is increased, losses also increase. Research to solve these problems is being conducted on the frontlines of power supply technology. The properties of the transformer core material have a major impact on efficiency. Using accumulated ferrite technologies is one of TDK’ s strengths. ＜Main areas of loss (thermal losses) in AC-DC switching power supplies＞ AC input Rectification and smoothing circuits High-frequency transformer Switching unit DC output Bridge Smoothing diode capacitor Transistor MOSFET High-frequency transformer Rectification Smoothing capacitor diode When multiple losses of less than 1% to several percent are combined, total losses can reach 20%. Synchronous Rectification Type Flyback Converter Conventional Flyback Converter Losses from the resistance of the diode are high. Key Point Voltage induced by a supplementary winding drives the Q2 gate. High-frequency Diode transformer Key Point The losses of semiconductor elements are large, so various circuits have been proposed. IC The orange indicates the main components that generate losses (thermal losses) Comparison and detection circuit DC output DC input (Connected to control circuit) Normal switching (hard switching) Soft Switching Voltage waveform Current waveform Voltage waveform Current waveform ON OFF ON OFF Soft switching is an advanced technology that precisely controls the timing of the ON and OFF switching to reduce switching losses. There is the zero voltage switching (ZVS) method, which performs switching with the voltage at zero, and the zero current switching (ZCS) method, which performs switching with the current at zero. ON Turn-off time The areas of overlap are switching losses (voltage × current). The areas of overlap are reduced and dead times created to reduce switching losses. This technology improves the power factor by rectifying the waveform through control of the high-frequency portions of commercial AC (the portions that are integral multiples of the base frequency). Efficiency and Power Factor of a Power Supply Efficiency = Output power (W) / Input power (W) Power factor = Effective power (W) / Apparent power (VA) Key Point A coil and capacitor store energy in the power supply and return it to the input side, so the power factor is less than one. In response to the use of higher frequencies, a technology known as resonant power supply that uses the resonance of a coil and a capacitor to perform switching is also starting to be applied in practical applications. A power module that integrates an AC-DC converter with PFHC and a DC-DC converter PFE Series (The apparent power is the product of the values obtained from a voltmeter and an ammeter. It is the power that appears to be present.) 17 Power MOSFET (Q2) IC Control Circuit OFF Supplementary winding High-frequency transformer DC output DC input Power MOSFET (Q1) Power transistor OFF A low resistance power MOSFET is used in place of a diode. The linkage between Q1 and Q2 (synchronous rectification) increases efficiency. ＜Example of a Simple Synchronous Rectification Circuit for an Insulation Type DC-DC Converter＞ High-frequency rectification circuit The high-frequency portion of commercial AC reduces the power factor. Digital control of power supplies began in communications fields and is progressing towards full digital control including control circuits. (Connected to control circuit) Two power MOSFETs regulate the flow of current. Example of a DC-DC converter circuit block using digital control for communications functions input and output voltage, output current, and temperature can be displayed on a PC in real time. ● Energy savings are possible through precise control of the output. ●A soft start function to prevent damage to semiconductor elements from inrush current is possible. ●POL power management for the distributed placement of multiple DC-DC converters is beneficial. ● The number of components can be reduced. * In 2005, we launched full digital control DC-DC converters with DSP (Digital Signal Processing). Currently, AC-DC power supplies using digital control are being developed for market introduction in the near future. DC input DC Switching circuit Smoothing output circuit Communications Analog controller Digital interface Benefits of full digital control ●Power supply information such as the Key Point Key Point Communications functions are controlled digitally to enhance functionality. Error amplifier Standard voltage Oscillator The adoption of digital control makes possible incorporation of multiple and advanced functions in power supplies. PWM uses analog control Full Digital Control Example of a DC-DC converter circuit block using full digital control DC input DC Switching circuit Smoothing output circuit Communications Digital interface DSP (digital signal processor) A-D converter Key Point Analog control units are replaced by A-D converters and DSP. Standard voltage Power supplies are making the transition from analog control to digital control. 18 Technology Section TDK Power Electronics World Key Parts That Support Power Supply Performance Switching power supplies contain semiconductor elements such as diodes, transistors, MOSFETs, and ICs, while passive components such as capacitors, coils, and transformers also play important roles. ＜Noise Unique to Switching Power Supplies (AC input)＞ Voltage Since the capacity is high, capacitors are used for smoothing. One of the weak points of switching power supplies is the generation of electromagnetic noise. TDK provides total EMC solutions that support all aspects of noise control from input to output and include various EMC countermeasure components (noise countermeasure components) and noise measurement in anechoic chambers. Voltage Multilayer ceramic chip capacitors are compact and offer high reliability and long life spans. There are also high capacity types that encroach on the territories of film capacitors and electrolytic capacitors. Multilayer ceramic chip capacitors are important as EMC countermeasure components (noise countermeasure components). Such capacitors are characterized by their compact size, high reliability, and longer life spans. They also have excellent highfrequency characteristics. Noise Countermeasures in Switching Power Supplies 0 0 Ripple noise Switching frequency Commercial AC frequency ●Ideal DC Spike noise ● Output waveform of an AC-DC switching power supply Aluminum electrolytic capacitors Multilayer ceramic chip capacitor ＜Examples of EMC countermeasures for switching power supplies (AC input)＞ Switching power supplies use numerous transformers other than the main transformer as well as coils. Mobile phones and other devices use SMD (surface mounted device) type compact power coils. The characteristics of the core material have a substantial impact on making power supplies more efficient as well as making them smaller, slimmer, and lighter. Choke Coils Wire loops become antennas and radiate noise, so the area of such loops must be minimized. The operation of capacitors and resistors can control the switching noise and spike noise of transistors and diodes. Transformers A gap is placed in the core to prevent magnetic saturation. Ferrite Cores Clamp Filters Ferrite absorbs noise to control radiated noise. CR snubber Power Supply EMC Filters Core gap Examples of choke coil cores (toroidal cores) Core gap Winding wire Core Magnetic flux leakage Common mode choke coil AC Input EMC filter Magnetic flux leakage The magnetic flux leaking from the gap can cause noise, so shielding must be used. Active filter choke coil DC input AC Input ● EI Core ● EE Core The characteristics can be controlled by adjusting the gap. Magnetic shielding is needed as a countermeasure against the magnetic flux leaking from the gap. The effects from magnetic flux leakage can be minimized by creating a gap in the center pole. They prevent common mode and differential mode noise and prevent it from flowing in and out. Flexield Control circuit Output rectification and smoothing circuit DC output Comparison and detection circuit A flexible electromagnetic shield material that absorbs radiated noise, converts it to heat, and eliminates it. Main transformer Smoothing choke coil PFHC circuit Key Point Switching power supplies use numerous transformers and coils. 19 ●Noise generated by transistors and diodes is also radiated from heat sinks designed to Power switch circuit Supplementary Switching element drive power supply transformer transformer Control Circuit Current transformer A common mode filter on the output line prevents noise from flowing out. 《EMC Filters for Power Line》 Other Sources of Noise Supplementary power supply circuit Common mode filter release thermal energy. Winding bobbins, transformer exteriors, and ferrite cores (various types including EE cores and EI cores) High-capacity multilayer ceramic chip capacitors are also used for smoothing. Advanced circuit design and simulation technologies are needed. ●Magnetic flux leakage from transformers and choke coils can cause eddy current in metal cases, generating noise. ●Wires and components where large currents are turned ON and OFF. The inductor portion of wire leads can also have an impact, so wiring and leads are made as short as possible. TDK provides Total EMC Solutions. 20 Technology Section TDK Power Electronics World Uninterruptible Power Supplies New Power Supply Systems and Batteries During normal operation AC output Main Power Supply Methods of UPS Rectifier ●Standard commercial type (square wave output) ●Line interactive type (sine wave output) ●Standard inverter type (sine wave output; connection is instantaneous, so there is no interruption of the wave form) Inverter (AC/DC conversion) (DC/AC conversion) AC input Output of a high-quality sine wave with no distortion or noise Power outage During power outage Battery Power Supply Structure Using the Standard Inverter Method UPS operates ＜Method of Calculating UPS Capacity＞ ● Total capacity ＝ (VA) Total capacity of indicated VA of device Total capacity of indicated W of device / 0.6 ● Total capacity ＝ Total capacity of indicated VA of device × Power factor* (W) 10% to 30% additional capacity is added on top of total capacity (VA) and total capacity (W) Total capacity of indicated W of device Select a UPS with a capacity larger than both of the calculated figures. It is necessary to have extra margin during a power outage. If V and A are indicated, multiply them (e.g., 100 V & 1.8 A --> 180 VA) * Power factors will vary depending on the device. They are generally in the range of 0.6 to 0.8. ＜Power supply interruption types and TDK-Lambda UPS categories＞ Key Point Commercial power supply noise Select the UPS that is optimal for the power supply interruption types and the necessary capacity. Recently, UPS batteries have been changing from conventional lead storage cells to lithium-ion batteries, and UPS units are rapidly becoming smaller and lighter and have longer life spans. Batteries will also be the key to the proliferation of electric automobiles such as hybrid electric vehicles (HEV). ＜Energy Density of Secondary Batteries＞ Volume energy density (Wh/R) Uninterruptible power supplies (UPS) are used to prevent unforseen information system downtime caused by various interruptions to power supplies such as power outages, drops in voltages, and distortions to commercial AC waveforms. There are many types of UPS available depending on the application. Nickelhydrogen battery 300 Lithium-ion battery 200 100 NiCd battery 0 40 80 Supplementary battery DC-DC converter Generator 120 High-voltage battery Motor 160 Lithium-ion batteries, nickel hydrogen batteries, and so on are stacked. High voltage of 200 V to 300 V is achieved. Key Point Saving on batteries requires highefficiency onboard DC-DC converters. Electronic devices operate on DC, and there is the idea of supplying offices and homes with DC as well. Floor mount type s HEV DC-DC converter. It converts TDK’ high voltage from the main battery to low voltage. ＜Future Model for Power Electronics＞ Power plants and substations AC distribution AC/DC conversion DC distribution Power router Solar power generation Installed type Voltage drops Overvoltage Rack mount type Level 5 Capacity: Several hundred watts to about 1000 watts ●Line interactive type Surges Energy from wind and solar power is initially stored in lithium-ion batteries. DC distribution Compact, lightweight types Level 3 Capacity: Several dozen watts to several hundred watts ●Standard commercial power supply type The levels according to the number of power supply interruptions that the UPS can protect against and the corresponding power supply formats. A UPS comprises a rectifier, battery, and inverter. Engine Mass energy density (Wh/kg) ●Standard inverter type 21 Inverter for the motor, generator, air conditioner High-capacity installed type Mobile type with casters Variations in Switching High-frequency frequency distortion noise Voltage sags Lights, windshield wipers, etc. 0 Level 9 Power outage ＜Basic Mechanism of an HEV (using a parallel format as an example) and DC-DC Converter＞ Plug-in hybrids that can be charged from a regular outlet are also appearing on the market. Wind power and mini-wind power generation Control board Household devices Highcapacity battery Plug-in electric vehicles Fuel cells Power electronics will play a major role in saving energy and protecting the global environment. 22 Switching Power Supply Development History About 1960 About 1965 About 1970 1972 1974 1976 1978 1995 2000 2004 2005 2006 2008 Stabilized power supplies using vacuum tubes were common at this time. America’s NASA began developing switching power supplies for use in space craft. Development of semiconductor elements for switching power supplies begins. TDK and Nippon Electronic Memory Industry Co. Ltd. (predecessor to Nemic-Lambda) enter the switching power supply business. Nippon Electronic Memory Industry Co. Ltd. manufactures and markets Japan’s first standard switching power supply. TDK manufactures and markets switching power supplies. Switching power supplies are adopted for use in commercial television games and the switching power supply market expands. TDK manufactures and markets switching power supply transformers. Nemic -Lambda (predecessor to Densei-Lambda) founded, to take over operations of Nippon Electronic Memory Industry Co. Ltd. TDK begins production of DC-DC converters for use in HEVs. TDK launches the RKW and JBW series of switching power supplies. Densei-Lambda (the predecessor to TDK-Lambda) launches the HWS series of switching power supplies. Densei-Lambda joins the TDK Group. Sales of UPS with lithium-ion batteries (lead-free) begin. Sales of TDK-Lambda brand products begin. TDK and Densei-Lambda market a total of 234 types of EMC filters for power line in 13 series. All models available on the market comply with the RoHS Directive. TDK-Lambda Corporation launched. Advances in Switching Power Supplies (unit type, 150 W comparison) Further miniaturization and higher efficiency 1300cm 3 3800cm 3 Japan’s first standard switching power supply. 3 Next generation 1200cm 3 Power supplies have undergone amazing miniaturization. 4500cm 550cm 3 Fifth generation Fourth generation Second generation ●Compliance with environmental regulations such as the RoHS Third Directive ●Compliance with generation EMC regulations, CE marks, etc. ●Compliance with global standards First generation About 1970 1980 1990 2000 2010 TDK Power Electronics World Date of publication: March 31, 2009 Publisher: TDK Corporation Corporate Communications Dept. 1-13-1 Nihonbashi, Chuo-ku, Tokyo 103-8272 Telephone: +81-3-5201-7102 SGS-COC-004380 Cert no . TDK Power Electronics World Guidebook of TDK Power Electronics Products