Development history and direction of communication switching power supply technology

zbz0529

Development history and direction of communication switching power supply technology [Copy link]

In the 1980s, high-power AC/DC switching power supplies (400V AC input, 48V DC output, 500W-6kW) became the mainstream product of the primary power supply of the communication system, called the switching rectifier SMR (Switching-mode Rectifier). Equipped with 48/±5, ±12V DC-DC switching converter modules and ring current modules, it is called the secondary power supply. Compared with the phase-controlled rectifier, the switching rectifier is superior in terms of volume, weight and efficiency (Table 1).

? As the size of microprocessor ULSI continues to decrease, the size of the power supply is much larger than that of the microprocessor, and it is necessary to develop a small and lightweight power supply (see Table 2); the miniaturization and lightweight of the power supply are more important for portable communication equipment (such as mobile phones, etc.). In order to achieve high power density, the operating frequency of the switching power supply must be increased. The next generation of microprocessors also requires a switching power supply with a lower output voltage (≤1V). ? The requirements for communication switching power supplies are: high power density, small size, high efficiency, high performance, high reliability, high power factor (AC input end), as well as intelligence, low cost, low EMI, manufacturability, distributed power architecture, etc.

? The main technologies that promoted the continuous improvement of switching power supply performance and quality in the 20th century are:

? 1. New high-frequency power semiconductor devices

? For example, power MOSFET and IGBT can completely replace power transistors and small and medium current thyristors, so that the operating frequency of switching power supplies can reach 400kHz (AC-DC switching converter) and 1MHZ (DC-DC) switching converter, making it possible to realize high frequency switching power supplies. The development of ultra-fast recovery power diodes and MOSFET synchronous rectification technology has also created conditions for the development of high-efficiency low-voltage output (≤3V) switching power supplies.

? 2. Soft switching technology? PWM switching power supplies work in hard switching mode (during the on/off process, the voltage drop/rise/drop waveforms overlap), so the switching loss is large. High frequency switching power supply can reduce the volume and weight, but the switching loss is greater (power consumption is proportional to frequency). To this end, it is necessary to study the technology of non-overlapping switching voltage/current waveforms, namely the so-called zero voltage (ZVS)/zero current (ZCS) switching technology, or soft switching technology (relative to PWM hard switching technology). In the mid-1990s, the 30A/48V switching rectifier module weighed 7? after adopting the phase-shifted full bridge (Phase-shifted Full Bridge) ZVS-PWM technology. Compared with similar products using PWM technology, the weight is reduced by 40%. The development and application of soft switching technology has improved the efficiency of switching power supplies. It is said that the total power of foreign small-power DC-DC switching power supply modules (48/12V) can reach 96%; the efficiency of 48/5V DC-DC switching power supply modules can reach 92-93%. At the end of the 20th century, the efficiency of domestically produced 50-100A output, full-bridge phase-shifted ZV-ZCS-PWM switching power supply modules exceeded 93%.

? 3. Control technology? Current control and multi-loop control have been widely used; the development of technologies such as charge control, one-cycle control, digital signal processor (DSP) control and the development of corresponding dedicated integrated control chips have greatly improved the dynamic performance of the switching power supply and greatly simplified the circuit.

? 4. Active power factor correction technology? Due to the rectifier element and filter capacitor at the input end, the power factor of the grid side (input end) of the single-phase AC-DC switching power supply and a large class of electronic equipment powered by rectifier power supply is only 0.65. Using active power correction technology (Active Power Factor Correction), referred to as APPC, it can be increased to 0.95-0.99, which not only controls the harmonic "pollution" of the power grid, but also improves the overall efficiency of the switching power supply. Single-phase APFC is a specific application of DC-DC switching converter topology and power factor control technology, while three-phase APFCA is a combination of three-phase PWM rectifier switch topology and power factor control technology.

? Domestic communication power supply professional factories have applied active power factor correction technology to AC-DC switching power supplies for communication with an output of 6kW and 100A, and the input power factor can reach 0.92-0.93.

? 5. Magamp post-regulator technology? In the 1980s, due to the development of high-frequency magnetic materials, such as amorphous soft magnetic alloys (Amorphous) and nano-crystalline soft magnetic alloys (Nano-crystalline alloy), it was possible to use high-frequency magnetic amplifiers (Magamp), that is, controlled saturable inductors (Controlled Saturable Indutor) in multi-channel high-frequency (>100kHz) switching power supplies as the voltage regulator (Output Regulator) of one of the outputs, called post-regulators. Its advantages are: simple circuit, low EMI, reliable, high efficiency, and can adjust the output voltage more accurately. It is particularly suitable for switching power supplies with output currents of 1A to tens of amperes.

? 6. Saturated inductor technology? Saturated inductor is a coil with an iron core (no gap), and its characteristics are: the saturation degree and inductance of the iron core change with the current passing through. If the magnetic characteristics of the iron core are ideal (for example, rectangular), the saturated inductor works like a switch. In the switching power supply, the application of saturated inductor can absorb surges, suppress spikes, eliminate parasitic oscillations, and reduce the loss of the rectifier tube when connected in series with the fast recovery rectifier tube.

? Application of saturated inductor in switching power supply

? a) Used as the resonant inductor of the phase-shifted full-bridge ZVS-PWM switching power supply, thereby expanding the range of the switching power supply meeting the ZVS condition under light load.
? b) Eliminate the secondary parasitic oscillation of the switching power supply? Connected in series with the secondary output rectifier tube of the isolation transformer of the switching power supply, it can eliminate the secondary parasitic oscillation (Secondary parasitic ringing), reduce the circulating energy, and minimize the duty ratio loss of the phase-shifted full-bridge ZVS-PWM switching power supply.
c) Realizing ZV-ZCS in the phase-shifted full-bridge ZVS-PWM switching power supply? The capacitor is connected in series to the primary side of the phase-shifted full-bridge ZVS-PWM switching power supply transformer, and the leading arm switch tube works according to ZVS; when the load current approaches zero, the inductance increases to prevent the current from changing in the opposite direction; the ZCS condition of the lagging arm switch tube is created, and the phase-shifted full-bridge ZV-ZCS PWM switching power supply is realized.

7. Distributed power supply technology, parallel current sharing technology? Distributed power supply technology (Distributeb Power Technipue) is to supply the 48V bus voltage (Distributed Bus) generated by the 250-425/48V DC-DC converter to the load board (Board), and then through several parallel low-profile (Low Profile) DC-DC converters on the board (On board), the 48V is converted into the 3.3-5V voltage required by the load. Generally, the power density of the DC-DC converter reaches 100W/in3, the efficiency is 90%, and it should be parallelable (Parallelable). The distributed power supply system is suitable for large workstations (such as image processing stations) and large digital electronic switching systems composed of very high speed integrated circuits (VHSIC). Its advantages are: it can reduce the current and voltage drop on the 48V bus; it is easy to achieve N 1 redundancy (Redundancy), improving system reliability; it is easy to expand the load capacity; it has good heat dissipation; it has good transient response; it reduces the number of electrolytic capacitors; it can realize the modularity of DC-DC converter components (Modularity); it is easy to use plug-in connection; it can replace the failed module online (On line), etc.

? 8. Power supply intelligent technology and system integration technology? Switching power supply microprocessor monitoring, power system internal communication, power system intelligent technology and power electronic system integration and packaging technology, etc.

? The above briefly reviews the development process and achievements of communication switching power supplies in the 20th century. The application of the above technologies, especially the development of high power density, high efficiency, high performance, high reliability and intelligent power supply systems, will still be the development direction of communication switching power supply technology in the future.

? Entering the 21st century, China's industry, academia, power electronics, electronic power supply, communication, materials and other industries should also jointly develop the following products and technologies related to communication switching power supplies.

? 1. Explore and develop high-temperature resistant high-performance silicon carbide (SiC) power semiconductor devices? It can be foreseen that silicon carbide will be the most likely new power semiconductor material to be successfully applied in the 21st century. The advantages of silicon carbide are: wide bandgap, high operating temperature (up to 600℃), low on-state resistance, good thermal conductivity, extremely small leakage current, high PN junction withstand voltage, etc.

? 2. Planar core and planar transformer technology? The development of planar core can realize ultra-thin transformers and ultra-thin switching converters. It is suitable for portable electronic equipment power supplies and on-board power supplies. Because of its wide and flat structure and large heat dissipation area, it is more suitable for high-frequency transformers.

? Planar transformers require magnetic cores, windings, copper foil windings, etc. It is reported that many foreign companies have developed planar transformers. A suitcase can hold a total power of tens of kW and more than a dozen planar transformers. Efficiency 97-99%; operating frequency 50/Payton's 5W-20kW transformer has a volume and power density of only 20% of traditional high-frequency transformers. A suitcase can hold a total power of tens of kW and more than a dozen planar transformers. Efficiency 97-99%; operating frequency 50kHz-2MHz; leakage inductance <0.2%; low EMI.

? 3. Integrated high-frequency magnetic component technology and array (Matrix) magnetic component technology integrate multiple magnetic components (such as multiple inductors, transformers and inductors) on a magnetic core. It can reduce the volume of the converter and reduce the loss of magnetic components. There have been reports of integrated magnetics converters abroad: 50W output, 5V and 15V two-way, 100kHz, DC-DC forward converter, transformer and output filter inductor are implemented on one magnetic core, referred to as IM converter. Array magnetic element technology is to discretize the magnetic elements in the circuit to form a distributed array arrangement, or to form a "magnetic structure layer" so that the magnetic structure is closely matched with the circuit board or other devices and integrated.

? 4. Magneto-electric hybrid integration technology ? Including the integration of magnetic core and transistor silicon wafer, and the use of distributed capacitance between inductor foil winding layers to achieve hybrid integration of magnetic elements and capacitors.

? 5. New capacitors. ? Research and develop new capacitors suitable for energy and power systems, requiring large capacitance, small equivalent series resistance (ESR), small size, etc. It is reported that KEMET Electronics in South Carolina, USA, has developed a new 330μF solid (Solid Tantalum) capacitor in the late 1990s, and its ESR has dropped from the original 500mΩ to 30mΩ.

? 6. S4 Power Factor Corrected (PF Corrected) AC-DC Switching Conversion Technology Generally, high power factor AC-DC switching power supplies require two power electronic circuits to be operated in cascade, and a pre-stage power factor corrector is added before the DC-DC switching converter. For low-power PWM switching power supplies, at least two main switching tubes and two sets of control drive circuits are required, with low overall efficiency and high cost.

? Using a single-stage AC-DC switching converter to achieve a low-power voltage-stabilized or current-stabilized power supply and correct the input power factor (PF) to above 0.8 is called a single-tube single-stage (Single Switch Stage), referred to as S4 power factor corrected (PF Corrected) AC-DC switching converter. For example, the pre-stage power factor correction uses DCM operation; the two-stage circuits share one main switching tube, and because the flyback circuit has an isolated converter, it is called an S4 power factor corrected isolated AC-DC switching converter. Of course, if active clamping or other soft switching technologies are added, an auxiliary switch tube is also required, called single stage (S2) with isolated positive soft switching power supply experimental results; efficiency 86.5%, power factor 0.98, THD13%, switching frequency 150kHz, input 155VAC, output 28V, 80W.

? 7. Output 1V/50A low voltage and high current DC-DC converter.

? In order to meet the power supply needs of the next generation of fast microprocessors, portable communication equipment, servers (Server), etc., it is required to develop low output voltage and high current DC-DC switching converters, or voltage regulator modules VRM (Voltage Regulator Module). Its output voltage is 1.1-1.8V, the output current is 50-100A, and the current conversion rate is 5A/ns.

? Because the circuit has high-frequency parasitic parameters, when the current changes greatly, it causes output voltage disturbances. In order to prevent this disturbance, the method of increasing the output filter capacitor and inductor was used in the past, but there are many disadvantages. Foreign countries have developed a multi-channel or multi-phase DC-DC converter as a server power supply. The output adopts a waveform interleaving scheme to ensure that the VRM output ripple is small, improve the output transient response, and reduce the output filter inductance and capacitance.

Table 3 compares two solutions for reducing VRM output ripple:

8. Design and testing technology of communication switching power supply Mainly the development, research and application of power supply thermal design and testing, EMI design and testing, reliability design and testing and other technologies.