Research on Power Topology Structure Based on DC-DC Converter

Modern telecommunication systems require wider bandwidth, faster data rates, tighter security measures, newer performance, more users and a wide range of user characteristics, which motivates the design of power supplies that provide dc voltage and current for modern telecommunication systems, Transforming from traditional forms to new technological forms, the new generation of power systems based on dc-dc converters must work in a wide input voltage range, sometimes up to 30″ 100V. At the same time, the power systems are ASICs, DSPs and DSPs for high-performance communication systems. Microprocessors designed in a floating submicron CMO process provide several low-level dc voltages.

Modern telecommunication systems require wider bandwidth, faster data rates, tighter security measures, newer performance, more users and a wide range of user characteristics, which motivates the design of power supplies that provide dc voltage and current for modern telecommunication systems, Transforming from traditional forms to new technological forms, the new generation of power systems based on dc-dc converters must work in a wide input voltage range, sometimes up to 30″ 100V. At the same time, the power systems are ASICs, DSPs and DSPs for high-performance communication systems. Microprocessors designed in a floating submicron CMO process provide several low-level dc voltages.

In communications and network server applications, this means not only converting the 48V input voltage to the traditional 5V and 3.3V, but also to the new lower voltages (ranging from sub-1V to 2.5V with a load current of 10″ 35V) Additionally, the power supply system must maintain tight tolerances and generate minimal noise to maintain signal integrity. These increased requirements occur in environments where space is constrained and thermal management is a major consideration.

To meet these requirements, power system architectures are changing from earlier centralized offerings of lower voltages and currents to today’s distributed approaches. Instead of a single power supply generating all the necessary voltage levels, the power supply is now distributed along the 2nd and 3rd bus lines to dc-dc converters that step down to voltage levels appropriate for each circuit or subsystem.

At each level, designers can design or purchase dc-dc converters that provide the necessary voltages and currents for several ICs, ASICs, warm-signal devices, or complete printed circuit boards. Each dc-dc converter will have a special topology that depends on many factors of the circuit it supplies and the system in which it operates, such as efficiency, noise level, physical factors (height, weight, size), desired output voltage quantity, power consumption and heat dissipation. This article will discuss specific tradeoffs and the best topologies to meet different system power design goals.

distributed power

In a distributed power architecture (Figure 1), the front-end power supply converts ac power to dc and distributes the dc voltage (usually -48V in telecom systems) to a dc-to-dc intermediate bus converter (IBC) through the first stage bus. The purpose of the IBC is first to provide isolation and to reduce the voltage distributed on the ac-dc front end to a lower voltage level. This should happen by sending it to the final non-isolated dc-dc (step-down) converter through the 2nd stage distribution bus to provide the required voltage and current for the system.

Research on Power Topology Structure Based on DC-DC Converter
Figure 1 12V intermediate bus of communication power system

Figure 2 shows how a dc-dc isolated current module and a POL point-of-load converter can be configured into a typical distributed power system, providing multiple output voltages and currents. The DC voltage (-36″ 72V) from the front-end ac-dc power supply is fed into an isolated power module, which represents a bus converter. The module is a completely isolated ac-dc converter, available in different forms (full brick, half brick, 1/4 brick), with standard footprint, pin-to-pin output and heat dissipation capability. POL converters can be a combination of switching regulators (buck or boost regulators) and linear regulators or only are line regulators, depending on the requirements of the circuit being powered. Sensitive circuits require low noise linear regulators, and high efficiency switching regulators are the choice for power systems that must have minimal power dissipation.

Research on Power Topology Structure Based on DC-DC Converter
Figure 2 Traditional -48V Communication Distributed Power Architecture

-48V Telecom Distributed Power System

Figure 3 shows a block diagram of a -48V distributed power system for telecom applications. The diagram illustrates the process of power supply from the input ac line to the low voltage ac-dc POL converter. The battery (48V) is the backup ac-dc converter in case of power failure. The -48V Interchange Controller (IC) provides intelligent control of the power connection when plugging and unplugging the circuit board under power, which includes inrush current control, short circuit protection and other protection functions to protect the power system. The first ac-dc converter was an isolated converter, which meant that the input ac power ground was isolated from the output ac power ground, usually with converter isolation, and isolation was specified to prevent dangerous voltages from presenting under failure conditions Levels endanger people. However, the isolation circuit makes the converter more expensive and affects efficiency. POL converters supplying power to the system unit circuits do not require isolation because they are protected by an isolated power module that provides them with ac input power.

Research on Power Topology Structure Based on DC-DC Converter
Figure 3 -48V distributed power conversion

Hybrid Power System

Basic DC-DC Conversion Topology

All ac-dc converters can be divided into linear regulators and switching regulators. The advantages of linear regulators are simplicity, lower output ripple voltage and noise, and simple line and load regulation. Switching regulators have high efficiencies, up to 95% (linear regulators are about 50% efficient or less), and have large power densities (power-to-volume ratio, measured in W/in3). Switching converters are more efficient for wide input-to-output level ratios than linear converters because switching converters utilize output filtering components. Figure 4 shows block diagrams of linear and switching regulators.Non-Isolated Buck Topology

Research on Power Topology Structure Based on DC-DC Converter
Figure 4 Two basic types of voltage regulators are popular

Buck converters are the basic topology that forms the basis of most switching converter architectures. It is the most common topology and is used in distributed power systems because the high ac voltage (48V) must be converted to a lower voltage, and the power consumption is small. A switch is a power transistor (usually a MOSFET) whose gate is driven by an IC that performs Pulse Width Modulation (PWM). Figure 5 shows a non-isolated buck topology.

Research on Power Topology Structure Based on DC-DC Converter
Figure 5 Non-isolated buck topology

The buck converter characteristics are:

・Without isolation
・Only drop the voltage
・Only single output
・Very high efficiency
・Low output ripple current
・High input ripple current
・High-side gate drive required
・Large duty cycle range
・Wide voltage regulation range

low power topology

Single transistor topologies (Figure 6) such as buck, boost, forward, and flyback are dc-dc converters designed for fairly low power loads in distributed systems (up to 100W). Buck and boost circuits are non-isolated, while forward and flyback converters provide transformer isolation.

Research on Power Topology Structure Based on DC-DC Converter
Figure 6 General single-transistor switching DC-DC power supply topology

Research on Power Topology Structure Based on DC-DC Converter
Figure 7 2-transistor switch DC-DC power topology

High Power Topology

Push-pull, half-bridge, and full-bridge dc-dc converters are isolated switching topologies that provide higher power output than single-transistor types. The advantage of the 2-transistor topology is that it provides twice as much power as the single-transistor type with the same size transformer. The transistors in the bridge topology only pay attention to the lesser voltage carrying in the half or forward (or push-pull) configuration. Therefore, the transistor voltage rating is a fraction of what other topologies require. Half-bridge and full-bridge converters are often used in off-line applications, operating with very high 400V ac input voltages (ac input line voltage from rectification and power factor correction).

Forward and flyback converters are also used in lower power (less than 100W) offline applications. Unlike forward and flyback converters, bridge converters provide high efficiency in high power dc-dc applications up to 1500W, push-pull converters are particularly effective at low input voltages, it can generate multiple output voltages, some of which output voltage, which can be of opposite polarity.

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