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Efficiency is an important dc-dc converter characteristic, particularly for virtually every battery-based or embedded system. It impacts the thermal and electrical losses in the system, as well as the cooling required. Also, it affects the physical package sizes of both the power supply and the entire system. Plus, it has a direct effect on the system’s operating temperatures and reliability. These factors contribute to the total system cost, both in hardware and field support.
Battery-based dc-dc converter efficiency determines battery life and run time. These converters must be small and lightweight as well as efficient, so they usually employ analog techniques. This will probably continue because of size and cost limitations. Most handheld battery-based systems have a built-in dc-dc converter integrated with other circuits（看 ”DC-DC Converter Systems Glossary”）。
The德州仪器公司TPS8267xis a complete dc-dc converter for low-power applications. Housed in a compact, low-profile ball-grid array (BGA) package, it suits automated assembly. Its IC-like package includes the switching regulator, inductor, and I/O capacitors, so it doesn’t require any additional components.
TPS8267X是一种同步的，降低的转换器，可与2.3至4.8V输入一起使用。它以5.5 MHz的速度运行，最多可提供600 ma输出，并且具有良好的负载和线路变量响应。它的〜17 µA静态电流有助于在光负载下保持高效率，同时为需要严格的输出调节的应用保留快速的瞬态响应。
如果负载电流减小，转换器将自动进入功率传递模式，在该模式下以不连续电流（DCM），单脉冲脉冲频率调制（PFM）模式运行。当无法在PFM模式下支持输出电流时，转换器将退出PFM模式并进入脉冲宽度调制（PWM）模式。结果，直流输出电压通常位于标称输出电压高约0.5％。PFM和PWM之间存在无缝的过渡。
Digitally Based Design
Digital control is now appearing in embedded systems to augment or supplant analog techniques. Point-of-load (POL) converters in embedded systems are among the first to incorporate digital technology. Because embedded systems usually use several POLs, they have been good candidates for efficiency optimization.
GE Power’sdlynx分布式功率开放标准联盟（DOSA）模块是以数字为导向的POL。这些模块仅需要三个外部组件，并提供离散功率设计密度的两倍。他们基于标准的DOSA足迹和与现有电路板设计的模拟/数字兼容性缩小了大小，降低了成本并提高了DC-DC转换器的性能。
Digital control provides the ability to monitor load power consumption. The DLynx modules deliver optimized current derating and 96% efficiency. Also, adaptive voltage scaling (AVS) leverages silicon performance to reduce power consumption through tight digital control (±0.4%) of the output voltage and a ±1% controller setpoint reference.
这些模块包括可调循环技术，该技术通过修改POL的控制带宽来改善转换器的瞬态响应。随着控制带宽的增加，固定外部电容的瞬态响应会提高。增加对照带宽和外部电容将共同提高瞬态响应。
However, these parameters are interdependent. Increasing the external capacitance degrades the system’s control bandwidth. With the Tunable Loop, the control loop can be retuned to compensate for the additional external capacitance, which yields the best possible transient response.
The Tunable Loop employs an external network consisting of a resistor and capacitor in series connected across the TRIM and VOUT(or SENSE) pins of the POL module(Fig. 1)。These networks use resistors of up to a few kilohms and capacitors from a few hundred picofarads to a few hundred nanofarads. This allows a single POL module to be externally optimized across multiple applications of significantly varying demands and yields the optimum board area, cost, response, and reliability.
Transients and surges applied to system power supplies can affect associated loads and cause system and component failure. To combat this,线性技术的LTC4366“surge stopper” IC interfaces between a system power supply and its loads, protecting the loads from the supply’s input-voltage surges.
The LTC4366 protects loads by controlling the gate of an external N-channel MOSFET to absorb the surge(Fig. 2)。Normally, the IC and MOSFET allow the power supply to service its loads with minimal insertion loss. But if the power-supply input receives a surge or transient, the LTC4366 and MOSFET clamp the voltage applied to the loads to protect them from damage or failure.
浮动拓扑允许LTC4366从9 V到500 V的输入运行。其可调节的，受调节的输出夹具电压不会影响系统操作。
TheEricsson PowerModules 3E series BMR462转换器还使用数字控制来提供广泛的监视功能(Fig. 3)。It operates with a 4.5- to 14-V input and produces an output from 0.6 to 5 V. At half-load, 5 VINand 3.3 VOUT, typical efficiency is 97.1%.
PMBUS命令可以在灯负载条件下自动控制电源耗散，从而最大程度地减少电流排水和开关损耗。在低负载电流下，BMR462在其同步整流器输出中关闭其低侧MOSFET门驱动器，从而提高效率。
Isolated POL
In a departure from most conventional non-isolated POLs,Vicor的Picor Division developed thePI3106，具有高效率，软开关功率架构的孤立pol转换器。该拓扑允许PI3106在分布式功率架构中运行，而无需隔离电源输入(Fig. 4)。
The PI3106’s 16- to 50-V dc input range and 334-W/in.3power density enable it to deliver ~50 W (12 VOUT在4.2 a）。安装在储蓄0.87 x 0.65 x 0.265英寸的空间中。与传统的转换器拓扑相比，表面安装（SMT）软件包可将空间降低约50％。
900千赫的切换频率允许PI3106use small input and output filter components, further reducing the total system size and cost. Its output voltage is sensed and fed back to an internal controller using a proprietary isolated magnetic feedback scheme that allows high bandwidth and good common-mode noise immunity. It requires no external feedback compensation.
The PI3106 feature set includes output-voltage trim capability, output overvoltage protection, adjustable soft-start, overcurrent protection with auto-restart, and over and under input-voltage lockout. Also, its temperature monitoring and protection function provides an analog voltage proportional to the die temperature as shutdown and alarm capabilities.
Another type of dc-dc converter developed byCUI Inc.employs the Solus Power Topology, which combines a single-ended primary-inductor converter (SEPIC) with a buck converter to form a SEPIC-fed buck converter. Increased efficiency is accomplished by reducing both the conduction and switching losses at several critical points within the converter circuit.
减少损失是如此重要，以至于给定功率包装大小的输出电流可以增加40％。相反，与传统的雄鹿拓扑相比，给定输出电流和包装大小的损失减少可以提高效率几％。
单独的拓扑结构包括一个磁性组件, one control switch, and two commutation switches that are optimally PWM-controlled. The magnetic component consists of four inductively coupled inductors wound on the same core. This translates to a level simplicity on par with a traditional buck converter.
另外，Solus减少了我2R losses by channeling the operating currents into multiple paths. When the input current enters the converter, the topology branches that input into multiple paths, with each path carrying a lower current. This reduces conduction losses to a level that's significantly less than the losses within a standard buck converter.
Multi-current paths also reduce the voltage stresses on components by nearly 50%. With lower applied currents and voltages, the Solus topology reduces high-side MOSFET turn-on losses by better than 75% compared to the traditional buck.
The first product based on the Solus topology is CUI’s NQB series isolated dc-dc quarter brick（图5）。This 720-W intermediate bus converter will initially support an input range of 36 to 60 V with a 12-V output and efficiency greater than 96%.
Brick Converters
Brick converters are a defined physical size, but their efficiency can depend on whether power MOSFETs, gallium-nitride (GaN) transistors, or silicon-carbide (SiC) transistors are in the output stage（请参阅表）。所有第八砖将具有非常相似的最大功率损失数，在12到14 W之间，因为可以从模块中去除的热量纯粹取决于大小。
A typical eighth-brick converter that's 90% efficient at full load will have a maximum output power of no more than 125 W (assuming 14-W loss). Improving the efficiency by just 2% increases the available output power to 160 W, a 28% improvement.
It’s possible to reduce the power loss in the magnetic components (up to a point) by increasing their operating frequency. However, this isn’t normally done because the increase in frequency-dependent semiconductor losses outweighs that potential improvement. Usually, the operating frequency is reduced to maximize the magnetic structure size within the brick’s physical size constraints.
It’s difficult to compare an isolated brick converter using power MOSFETs with one using a GaN FET. Even when limiting the comparison to a regulated 12-V output for an eighth brick, there are still variations between commercial designs. The resultant structure, layout, and topology may differ at the same power level. Efficiency achieved in a specific brick converter, as good as it may be, can be improved easily simply by allowing the converter to increase in size.
Johan Strydom and others atEfficient Power Conversion (EPC)设计并构建了48至12-V增强模式GAN（EGAN）FET的第八砖转换器。它使用具有全桥同步整流器拓扑的相移全桥转换器。
EPC’s goal was to show that, due to their relatively small device size, a significant number of eGaN FETs can be used within the restrictive eighth-brick size limitations. The choice of transformer turns ratio (6:3) meant that, at 75 VIN，次级绕组电压为38 V，对于40V设备而言，它太近了。因此，在输出阶段的主要和次要侧都使用了100V设备。
Strydom said the eGaN FET-based converter wasn’t necessarily an optimal solution. Its design goal was to deliberately push the operating frequency much higher than current commercial systems to show that eGaN devices can produce a more efficient power-supply design.
将基于EGAN FET的原型完全调节的第八砖转换器与类似的基于MOSFET的转换器进行了比较。Egan FET版本的效率提高，开关频率提高33％。
设计支持
The design of dc-dc converters can get an assist fromMaxim’sMAX15301controller IC, which uses digital power technology to automatically compensate the converter(Fig. 6)。It accomplishes this by constructing an internal mathematical model of the supply, including its external components.
The result is a switching power-supply design that achieves excellent dynamic performance with guaranteed stability. Furthermore, this power-supply model optimizes a converter’s efficiency across a wide range of operating conditions.
This IC relies on mixed-signal design techniques to control the power system efficiently and precisely. It doesn't require any software to configure or initialize the device. The MAX15301 can regulate and perform power-management tasks without any programming. Using standard PMBus commands, its functions can be monitored and optimized through an SMBus interface, resulting in ease of design and flexibility.
You could also use Powervation’s (now part ofROHM Semiconductor) PV3012 controller IC for a dc-dc converter design. This dual-phase digital synchronous buck controller IC for POL design applications is PMBus- and DOSA-compliant and provides features to improve a converter design’s efficiency and reliability.
The PV3012’s Auto-Control technology offers real-time adaptive loop compensation for converter designs. This patented digital control-loop technology optimizes the tradeoffs between dynamic performance and system stability on a cycle-by-cycle basis without requiring any noise injection or other drawbacks of part-time measurement techniques. This is a key advantage for converter designs that drive imprecise or variable loads.
Auto-Control also compensates for the power-supply component parameter drift that occurs over temperature and time, as well as for tolerances seen in production- or component-level variation. It relieves power-supply designers of the burden of compensation and plant characterization, while reducing total design iterations as well. Furthermore, Auto-Control readily enables efficiency maximization mode changes such as phase add/drop and light-load modes, again, without sacrificing transient performance and cost.
电力连接与Murata Power Solutions为Murata Power Solutions 45-A电源块共同开发参考板。Murata的CEB019数字DC-DC转换器使用PV3012来克服与外部组件，温度和用户布局变化有关的问题。
