TI - 电源管理电路介绍.ppt
《TI - 电源管理电路介绍.ppt》由会员分享,可在线阅读,更多相关《TI - 电源管理电路介绍.ppt(37页珍藏版)》请在得力文库 - 分享文档赚钱的网站上搜索。
1、1,f,Introduction to Power Management,Dr Ali Shirsavar Biricha Digital Power Ltd Parkway Drive Reading RG4 6XG Dec - 2013,2,Introduction to Power Management,The voltage of the power supply and/or battery feeding our PCB is seldom at the correct level that we need for our circuitry: Example: A standar
2、d desktop PC in Europe is fed with 230V but the motherboard needs: +12V, -12V, +5V and +3.3V We need to step up and step down (convert) our voltage levels ALL THE TIME depending on the voltage available to us at our input connector and what the circuitry actually needs There are two major methods to
3、 do this: Linear Regulators (also known as series pass regulator, series regulator or LDOs) and Switching Regulators (known as switch mode power supplies, or switching power supplies and power “converters” ) Note that (beyond very low currents) zener diodes or potential dividers are not good choices
4、 for this purpose!,3,Introduction to Power Management,LDO Switching Regulator,12V,5V 100mA,(12 5) = 7V,12V,5V 100mA,4,Why Do We Need a Converter/Regulator,Of course the first job of the converter/regulator is to convert our input voltage to the output voltage level that our circuit requires e.g. Inp
5、ut voltage Vin = 12V but we actually need 5V for our ICs The second job is to regulate! If there is a increase/decrease in the amount of current that we draw, the output voltage should not fall/rise This is called Load Regulation If there is a change in the input voltage of our power supply the outp
6、ut voltage should not change This is called Line Regulation There are other desirable characteristics such as: transient response, efficiency, EMI, cost, size, etc but we will talk about these later,5,Linear Regulators,Two major types (even though many people call all of them LDOs): Standard e.g. LM
7、78LXX Requires higher input voltage of around 2V; e.g. LM78L05 will give you a regulated output of 5V 100mA but Vin must be 7V Low Drop Out (LDO): e.g. TPS793xx Requires less dropout voltage than “standard type”. The input voltage typically needs to be only 0.6V higher than the output voltage They w
8、ork by operating a transistor in the linear region (i.e. like a variable resistor), sensing the output voltage (Vout) and automatically changing this variable resistor value such that Vout remains constant Advantages: Cheap works well for Buck but not suitable for CCM Boost, Buck-Boost, Flyback or S
9、EPIC Poor/slow transient performance under DCM conditions Current mode Faster transient response than voltage mode during line voltage transients Good performance in both DCM and CCM Ideal for Boost, Buck-Boost, Flyback and SEPIC in CCM Poor performance when duty is small (e.g. if you step-down too
10、much) Needs slope compensation and leading edge blanking (i.e. bit of a pain!) Emulated current mode Similar to current mode but can operate under low duties But based on a mathematic model which will not be perfect Constant On Time Cheap and easy and always stable with fast response Better efficien
11、cy under low loads (unless pulse skipping used in other control methods) But will have more ripple than other control methods Variable frequency so unpredictable EMI spectrum + harder to design EMI filter,18,Choosing the Right Switching Frequency,Our switching frequency (Fs) directly impacts the siz
12、e of our power supply We saw earlier that the higher the switching frequency the smaller the current ripple on our inductor i.e. the higher the switching frequency, the smaller the inductor This also applies to our output capacitor, so the entire power supply will get smaller This is why the switchi
13、ng frequency of the PSU for small hand held devices needs to be so high There is a limit as to the ripple we can have on our inductor as you must not saturate the inductor WEBENCH automatically selects a correctly sized inductor Our switching frequency directly impacts our efficiency The higher the
14、switching frequency the poorer the efficiency Every time we turn a switch on or off we will waste some energy; these are called Switching Losses if we switch faster we will have higher switching losses Every time we magnetize and de-magnetize our inductor we will lose some energy in the magnetic mat
15、erial of our inductor; these are called Core Losses if we switch faster we will have higher core losses Of course both of the above will have an impact on cost,19,Which Device is Best for Your Application,Switching Modules (e.g. LMZ14203) Complete solution with internal switch and inductor in one pa
16、ckage Very small foot print + everything optimized Some come with EMC compliance,* Images taken from i.e. no internal switch or inductor Largest foot print + most have gate driver inside but not optimized with the switch You have to select the right switch yourself (or use WEBENCH) V cheap but need
17、an extra switch/inductor/compensation etc Gives you complete flexibility in terms of your design at the expense of more development time, larger foot print, extra components & routing etc,* Images taken from & device datasheet,22,Quick Summary to Selection Guide,Which topologies to use for various a
18、pplications: LDOs Small currents and limited/fixed voltages, poor efficiency Buck most common step down Boost most common step up Buck-Boost/SEPIC most common for battery operation / step up and down Flyback when you need multiple voltage or need to step down from large input voltage Which control m
19、ode to use for various applications? COT cheap and easy, always stable but variable frequency & ripple Voltage mode most common in Buck, cheap and easy low component count Current mode most common for CCM in Boost, Buck-Boost, SEPIC, Flyback, very good performance but needs slope compensation and le
20、ading edge blanking (a bit of a pain), not great if duty is very small Emulated Current Mode like current mode but solved the low duty issue, but model based so it all depends on how accurate the model is,23,Quick Summary to Selection Guide,Selecting the switching frequency The higher our Fs, the sm
21、aller the PSU but the poorer the efficiency The higher the Fs the smaller the ripple on the inductor large ripple on inductor could cause saturation and a blown up power supply WEBENCH allows you to automatically optimize this Which Device to Select? Switching Modules (almost) everything internal, s
- 配套讲稿:
如PPT文件的首页显示word图标,表示该PPT已包含配套word讲稿。双击word图标可打开word文档。
- 特殊限制:
部分文档作品中含有的国旗、国徽等图片,仅作为作品整体效果示例展示,禁止商用。设计者仅对作品中独创性部分享有著作权。
- 关 键 词:
- TI 电源管理电路介绍 电源 管理 电路 介绍
限制150内