Understanding Buck and Boost Converters and the Capacitors Behind Them

时间： 2023-03-29 来源：Knowles Blogs

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Product designers working on critical applications requiring electrical power must carefully select components that not only supply the appropriate amount of voltage at the right time, but also help mitigate issues such as voltage ripple, ensure system longevity, and improve component reliability.

Buck and boost converters, which are the two most basic DC-to-DC converter topologies used in power supplies, are critical power supply building blocks that require careful component consideration. While a buck converter steps down a system’s main power supply for use in lower voltage components, boost converters conversely ramp up the voltage to a higher value than the input. Buck and boost converters are increasingly being used in switch-mode power supplies (SMPS) for a wide range of important applications such as power delivery networks for military unmanned aerial vehicles (UAVs) and drones, solar panels, electric vehicles, and X-Ray machines.

Additionally, because of their reliability and simplicity, these converters serve as ideal building blocks for more complicated topologies, including the following:

Forward converters
Flyback converters
Buck-boost converters
Half-bridge converters
Full-bridge converters
ZVT full-bridge converters
Push-pull converters

Let’s take a deeper look at the basics of how buck and boost converters work and the components, such as capacitors, inside them.

How It Works: The Buck Converter

The most common switching converter is the buck converter, which is used to down-convert a DC voltage to a lower DC voltage of the same polarity. Buck converters are essential in systems that use distributed power rails (like 24 V to 48 V), which must be locally converted to 15 V, 12V, or 5V with very little power loss.

During operation, the input voltage is connected to the inductor, and the difference between the input and output voltages is then forced across the inductor, causing the current to increase. During this time, the current flows into both the load and the output capacitor, charging the capacitor. When the switch turns off, the capacitor discharges into the load, contributing to the total current – the sum of the inductor and capacitor current – being supplied to the load.

How It Works: The Boost Converter

Conversely, a boost converter takes a DC input voltage and produces a DC output voltage that is higher in value than the input, but of the same polarity. When the switch is turned on, the input voltage is forced across the inductor, causing the current to ramp up. When the switch turns off, the decreasing inductor current forces the switch end of the inductor to swing positive, forward biasing the diode and allowing the capacitor to charge up to a voltage that is higher than the input voltage. During steady-state operation, the inductor current flows into both the output capacitor and the load during the switch-off time. When the switch is on, the load current is supplied only by the capacitor.

Why are Capacitors an Important Component in Buck and Boost Converters?

Good engineering practice requires that additional external capacitance be placed at the input and output of all regulators. This is because capacitors not only help reduce voltage ripple and improve reliability, but these components also increase efficiency compared to linear regulators. A well-designed power supply decoupling network will employ different types of capacitors made from different materials such as ceramic, aluminum, and tantalum.

The Benefits of Using Multilayer Ceramic Capacitors in Converters

Choosing the right capacitor for your converter is a key decision to ensure your final product is as efficient, durable, and reliable as possible. Multilayer ceramic capacitors (MLCCs) are especially helpful since these capacitors provide several layers in a single component, delivering a capacitance level equivalent to using multiple single-layer capacitors (SLCs) connected in parallel.

MLCCs can often be used as the following components that may be included in a buck or boost converter:

Optional input filters – When the frequency is less than 1MHz, MLCCs can be placed in parallel with either a Bulk Aluminum Electrolytic or Polymer Capacitor for maximized filtering. Meanwhile, when the frequency is greater than MHz, MLCCs are ideal filters.
Bypass capacitors - Eliminates voltage drops on the power supply by storing an electric charge that can be released when a voltage spike occurs.
Snubber capacitors – MLCCs help reduce ripple in a switching network.
Output capacitors – Low-value ceramic capacitors (<1μF) can be used when the frequency is greater than 1MHz, or aluminum electrolytic when the frequency is less than 1MHz.

Using MLCCs in these components can help improve ripple-current rating, filtering performance, and longevity for a converter. MLCCs are versatile and are a good option for anything ranging from a simple topology to a more complicated one.

Special Considerations for High-Reliability Applications

For applications requiring high reliability – for example, a military drone’s power supply – additional testing to military standards (MIL-STDS) must be met. When choosing a capacitor for a high-reliability application, it is important to select components that meet more rigorous MIL-STD requirements including being burnt in at elevated voltage and temperature levels and undergoing 100 percent electrical inspections to ensure conformance with strict performance criteria. This will ensure your components are qualified for use in even the most sophisticated and secure military and aerospace applications.

Providing Additional Expertise for Implementing Boost and Buck Converters

KNOWLES Precision Devices employs a highly experienced Applications and Product team that can help you choose the right capacitors for your buck and boost converters or even the more complicated DC-DC converter topologies as mentioned above. As an expert in developing MLCCs and power supply applications, our components are thoroughly tested to the most stringent levels to ensure reliability, accuracy, and success for our customers.

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型号- A 738411,A 738410,FELSIC DI,PRORELSIC 145,A 738418,A 738417,A 738416,A 738415,SNAPSIC 125,A 738414,PRORELSIC,A 738413,A 738412,A691055,A 691915,A 691914,A 691913,CI FRS,A691065,A 728848,CUBISIC LP,A 738433,A 738432,A 738431,A 738430,FELSIC 105 TFRS BC,FELSIC 105 TFRS BD,RELSIC,A 738438,A 738437,A 738436,A 738435,A 738434,VACSIC 150,FELSIC 105 BD,FELSIC 105 BC,A 691907,ALSIC 20G,PROMISIC,FELSIC 85,A 691905,FELSIC HC,A 728807,A 728806,A 728808,A 738840,FELSIC O39,FELSIC O37,A 728360,A 728481,A 728480,A 738848,A 738847,A 738846,A 738845,A 738844,A 738843,A 738842,FELSIC HP BC – BD,A 738841,A 728801,A 728800,A 728803,A 728802,FELSIC 85 M BD,A 728805,A 728804,FELSIC 125 RS,A 728362,A 728483,A 728361,A 728482,A 728364,FELSIC 85 M BC,A 728484,A 728366,A 728487,A 728365,A 728368,A 728367,A 728488,FELSIC 039,SNAPSIC 105 LP,VACSIC,FELSIC 037,FELSIC BD,CUBISIC,FELSIC BC,A 728832,A 728831,A 728834,A 728833,A 728836,A 728835,A 728837,ALSIC 145,A 728830,A 728380,A 728382,A 728381,FELSIC HV BD,FELSIC 85 LP,FELSIC HV BC,A 728384,A 728383,A 728386,A 728385,A 728388,A 728387,A 738378,A 738377,A 738498,A 738376,A 738497,FELSIC LP,A 738375,A 738374,A 738494,A 738372,A 738493,A 738371,A 738492,ALSIC HV,A 738815,A 738814,A 738813,A 738812,A 738811,A 738810,FELSIC 105 LP,A 738808,ALSIC,SNAPSIC HC,A 738370,A 738491,A 738490,A 728331,A 728332,SNAPSIC HV,SICAL,ALSIC IR,FELSIC 125 FRS,A 728447,FELSIC 85 BD,A 728446,FELSIC 85 BC,A 728448,A 728441,A 728440,A 728322,A 728443,A 728321,A 728442,A 728445,A 728444,A 738398,A 738397,FELSIC,A 738396,A 738395,A 738394,A 738393,A 691060,FELSIC 125 FRS BC,CO 37,CO 39,A 691062,A 691061,A 691057,A 691059,A 738392,A 738391,A 738390,A 691071,A 691070,A 728347,ALSIC 145 20G,A 738817,A 738816,A 728340,A 728342,A 728341,A 728344,A 728343,A 728346,A 728345,A 738455,A 738454,A 738453,A 738452,A 738451,A 738450,FELIC O37,FELSIC HV,A 738458,A 738457,A 738456,FELSIC 105,PROMISIC 031,A 728403,A 728402,A 728405,A 728404,A 728407,A 728406,A 728408,SNAPSIC 4P,A 728401,A 728400,A 738356,A 738355,PRORELSIC 125,A 738354,SNAPSIC 105,A 738353,RELSIC 033,A 738352,A 738351,A 738350,A 738357,PRORELSIC 105 TFRS,FELSIC HC BC,SNAPSIC,FELSIC HC BD,SICAL CO 42,CUBISIC 125,SNAPSIC 105 4P,A 728425,A 728424,A 728427,A 728426,A 728428,A 728421,A 728420,A 728423,A 728422

01/19 - EXXELIA - 数据手册 - Revision 01/19 代理服务技术支持批量订货

Knowles（楼氏电子）符合AEC-Q200标准的汽车级电容器选型指南

目录- AUTOMOTIVE GRADE CAPACITORS INTRODUCTION GENERAL AND TECHNICAL INTRODUCTION MLC CAPACITORS SM EMI FILTERS

型号- 1808JA250102JCTSP,1808JA250102JXTPY2,1808JA250102GJTSYS,2220YA300563KSTS3X,085J2500101JHT,1812Y1000334MXTE03,1812Y5000474KJTWS2,1206Y1000473KNT,1206Y0500224KXT---,2220JA250102JXTB16,1206Y1000103MXTE07,1808JA250102KJTSYX,0805Y1000103KST---,1210Y2000103KCT---,1808JA250102GJTS2X

09282022 - KNOWLES - 选型指南 - R12.3 代理服务技术支持批量订货

Capacitors for External Defibrillators

Defibrillators are designed to deliver electric current to the heart, in the form of a controlled shock to the myocardium, to treat arrhythmias and restore the heartbeat back to normal. Capacitors play an important role in the function of these life-saving devices. Here, we’ll cover the basic components of a defibrillator circuit and explore the role of capacitor selection in defibrillator system design.

2024-08-31 - 技术探讨代理服务技术支持批量订货