|
当前状态:
座谈已结束
|
|||
| [主持人：eccn] | 各位聽眾（網友），下午好！歡迎參加中電網線上座談。今天，我們有幸邀請到美國國家半導體公司的專家就“使用模擬電流模式（ECM）全新的整合型降壓穩壓器系列”舉行線上座談。在座談中，您可就您關心的問題與美國半導體公司的專家線上進行直接、即時的對話交流。中電網衷心希望通過大家的共同努力，不僅能夠增進各位聽眾（網友）對“使用模擬電流模式（ECM）全新的整合型降壓穩壓器系列”的瞭解和掌握，而且能夠為大家事業的發展帶來裨益。 | [2007-4-3 14:46:22] |
| [问：chenjl] | 是不是輸入電壓高低會對轉換效率有響?影響有多大? | |
| [答：Alan] | Yes. Normally, higher Vin has poor efficiency. But there are many things to impact efficiency such as MOSFET, inductor, capacitor. We cannot predict exactlly how much influence based on Vin only. | [2007-4-3 14:47:08] |
| [问：xbd123cn] | 請問使用SIMPLE SWITCHER穩壓器時,什麼條件下需要考慮加散熱器？ | |
| [答：Leon] | 这取决于你可以容许多高的温度，比如国半第4代simple switch LM557x，它的热阻是40度每瓦，那么如果损耗1W的话那么芯片的温度是25度环境温度加40度，如果超过你的容许范围，那么你就需要加点散热措施了，对于国半第4代simple switch LM557x 来说，它有一个Exposed Pad，你可以在它的下面放一块裸铜就可以了。 | [2007-4-3 14:51:44] |
| [问：chenjl] | 請問在開關電源中,設計開關變壓器時應注意那些事項?NS是否有這方面的設計軟體?如何查找? 能否提供鏈結? | |
| [答：Winter] | 不同的架构对变压器的要求都不相同，开关电源的变压器设计也有很多中设计思路。但主要的目的都是满足以下要求， 1。在满载情况下磁心不饱和。 2。选择足够大的磁心以满足热要求。 3。磁心损耗和绕组导线损耗大致相等。 4。磁心窗口尽量占用以提高利用率。 由于设计优化的变压器需要的变量和预先假设很多，所以软体只能作为辅助工具减少计算量，具体设计需要分多个步骤逐次逼近最优设计指标。国半尚未提供这种软体。 | [2007-4-3 14:51:44] |
| [问：xbd123cn] | 能否較詳細介紹散熱器如何設計? | |
| [答：Tony] | 首先要知道IC 的 thermal resistance, 以及 电源的power loss, 然後反算所需heasink thermal resistance 詳請可参考以下ref book: Power Supply Handbook 2nd edition, McGraw Hill | [2007-4-3 14:52:39] |
| [问：chenjl] | 請問要做好SIMPLE SWITCHER穩壓器的電磁相容,一般說來在設計和排版應考慮些什麼? | |
| [答：Sam] | 1. We can add some snubbers to suppress high spike (transient) voltage/current. 2. On the PCB layout, take care of reducing switching node area and ground shielding. ...... There are a lot of considerations, please find related application notes on National Semiconductor website for details. Thanks! www.national.com | [2007-4-3 14:55:39] |
| [问：hclu74] | 開關電源中最難設計、又最難調試的是高頻變壓器,請問NS有什麼好建議? | |
| [答：Winter] | 同意。 高频变压器的设计是一个针对效率，尺寸，成本，热压力作不断折中的过程，所以我采用的方法是利用计算软体（如Excel,MathCAD）将饱和电流与热量损耗作为目标变量，在预设磁心类型，尺寸的基础上，计算出最大磁心占用率下的饱和电流和热量损失。如此反复逼近目标值。最终达到优化的设计。 | [2007-4-3 15:00:00] |
| [问：t7767] | 請問怎樣可以得到SIMPLE SWITCHER穩壓器的資料和相應的開發技術資料? | |
| [答：Janet] | You can go to our website for SIMPLE SWITCHER: http://www.national.com/appinfo/power/switcher.html. For more technical question, also you can submit feedback at here: http://www.national.com/support/ | [2007-4-3 15:00:24] |
| [主持人：eccn] | 各位聽眾（網友），下午好！歡迎參加中電網線上座談。今天，我們有幸邀請到美國國家半導體公司的專家就“使用模擬電流模式（ECM）全新的整合型降壓穩壓器系列”舉行線上座談。在座談中，您可就您關心的問題與美國半導體公司的專家線上進行直接、即時的對話交流。中電網衷心希望通過大家的共同努力，不僅能夠增進各位聽眾（網友）對“使用模擬電流模式（ECM）全新的整合型降壓穩壓器系列”的瞭解和掌握，而且能夠為大家事業的發展帶來裨益。 | [2007-4-3 15:01:14] |
| [主持人：eccn] | 我們已經進入問答階段如果聽眾想重溫演講或內容可以點擊下面“回顧演示”重看演講。 | [2007-4-3 15:01:22] |
| [主持人：eccn] | 在此回答問題的專家是美國國家半導體公司的：Hector Ng、Winter Cheng、Tony Lai、Robert Shen、Janet Wu、Benjamin Zhao、Leon Liang、Morris Li和Betty Lee。 | [2007-4-3 15:01:41] |
| [问：altimate] | switch power supply的雜訊常對ADC電路帶來干擾，貴公司的元件可減少此干擾嗎?why? | |
| [答：Tony] | The noise of switching power supply depends on the converter topologies. Generally, the buck converter have less switching output, because the output current is continuous. Also the PCB layout will also greatly affect the EMI level. Keep the high power current loop as small as possible would really helps to suppress the EMI level. You can browse NS website to view more application for the PCB layout design | [2007-4-3 15:02:47] |
| [问：Andrew10] | 問個一般的問題,DC/DC轉換中調頻控制和調寬控制方式有何不同的優勢? | |
| [答：Benjamin] | PWM Mode has fixed frequency, it"s easier for input and output filters design and also better EMI performance. PFM Mode is widely used in light load appication. In such kind of application, inductor current is discontinuous. PFM mode can get better efficiency. | [2007-4-3 15:05:30] |
| [问：t7767] | 在PCB佈局上如何有利降低EMI? | |
| [答：Sam] | You can try to add a small RC snubber in parallel with wheeling diode to suppress the high spike and reduce the swiching node area. By the way, ground planes on multi-layer PCB are the good shielding. | [2007-4-3 15:06:02] |
| [问：reporter] | what"s different of ECM and current mode? | |
| [答：Alan] | ECM is an enhancement from current mode (CM). CM has good transient performance at input voltage and load change. But disadvantage is layout concern, becasue CM senses current waveform from inductor (or MOSFET) then gets very samll signal. ECM has following advantages: 1. ECM improves the problem on layout, because ECM improves noise influence. 2. If operating frequency is over 1MHz, Ton is very samll, and there is inrush current at MOSFET ON. CM will detect abnormal signal. ECM can ignore the inrush current and give a correct signal for feedback compensation. 3. At high input voltage and lower output voltage, duty cycle is samll also. Same inrush current happens. ECM can offer better perfromance at either higher frequency and samll duty cycle. | [2007-4-3 15:06:41] |
| [问：ralleywu] | 請問NS公司有沒有正負5V轉正負2.5V和1V的晶片？ | |
| [答：Winter] | 正电压降压不是困难。以下芯片都可完成5V转2.5,和1V的要求， LM3670/1/3/4/6/7 , LM2852/3 , LM26400(dual channel) , LM1770/1 , LM3475 , LM2743/4/5/6/7/8 , LM3743 ... 负电压转小的负电压，我们通过Floating Buck的方式来完成，几乎所有的升压芯片，如LM3224，LM27313 , LM2731/3 , LM2703 都可用于这种架构。 | [2007-4-3 15:07:29] |
| [问：ralleywu] | DC-DC 30-60V輸入，14V3A輸出，NS有什麼好晶片或方案嗎？謝謝！ | |
| [答：Sam] | LM5576 is the best solution for your application. http://www.national.com/pf//LM/LM5576.html | [2007-4-3 15:08:16] |
| [问：hclu74] | 還有一個問題,對於不同的頻率,變壓器的漏感有差異,設計高頻變壓器應如何考慮? | |
| [答：Tony] | The leakage inductance can greatly affect the efficiency of the power converter. So we have to minimize the the leakage inductance of the transformer. One of the method, to minimize the leakage inductance is to use the interleaved winding method. The interleaved means use two layers of secondary winding is sandwiched the primary winding or vice visa. And, you can also use active clamp forward converter for high freqency power converter as this topology can inherent absorp the leakage energy & back to input, without adding extra loss snubber network. | [2007-4-3 15:09:50] |
| [问：gunmyj] | 類比電流控制模式與傳統的峰值電流模式相比,最主要的優勢是什麼？ | |
| [答：Janet] | You can refer to our presentation, thanks. | [2007-4-3 15:12:37] |
| [问：rock_lai] | 能否介紹DC/DC轉換器中EMI干擾來源因素?這些干擾頻率處於那個頻率範圍?1 | |
| [答：Leon] | DC/DC转换器EMI的干扰来源是在高di/dt和高dv/dt的地方，比如主控开关管的源级到电感之间，电感，续流二极管。这些干扰频率分为两个部分:1,与DC/DC工作频率成倍数的频率.2，在主控开关开关过程和续流二极管开关的过程中与线路和器件寄生参数震荡频率成倍数的频率。通常这个基频是在MHz. | [2007-4-3 15:13:25] |
| [问：altimate] | 在台灣可否索取貴公司的樣品IC? | |
| [答：Alan] | Yes, of course. You can contact our disty or apply samples on our website. www.nationa.com If you use website, you can find Wenbech simulation also to provide you good solution or analysis at power, op-amp, audio... You put P/N you need first, then choose "Sample and pricing" on top. Then you can choose "24hr sample" for sample sending to you. | [2007-4-3 15:14:28] |
| [问：kittin] | 做了一個DC-DC開關電源，採用PWM控制的BUCK電路，輸入27.6V，輸出20～27V，電流1.5A，在加上類比負載後（9歐電阻），MOS管的D極的PWM脈衝的上升和下降沿各有5.8V的尖峰脈衝，在輸出端（濾波後）的電壓上有1.7V的尖峰紋波，請問專家，這是什麼原因？如何解決？ | |
| [答：Winter] | Buck电路的MOS管如果在Upper Rail上，其D极有PWM脉冲，说明您用的是PMOS。这是开关器件的引脚寄生电感与开关器件寄生电容铃振造成的。 消除的方法是， 1。减小寄生电感，就是缩短PMOS和二极体的引脚长度（包括PCB Trace). 2.减慢开关边沿速度，就是延长Rise time and Fall time 。这需要减小MOS驱动电流。 3。在开关器件两端增加Snubber。一般shi | [2007-4-3 15:15:07] |
| [问：junlu] | 還有一個問題,對於不同的頻率,變壓器的漏感有差異,設計高頻變壓器應如何考慮? | |
| [答：Tony] | To design the high frequency switching converter, we have to minimize the leakage inductance of the transformer as small as possible, otherwise it would contribute the excessive loss. One of the method to minimize the leakage inductance is use interleaved winding method to wound the winding of the transformers. That means two layers of secondary winding is sandwiched to the primary winding & vice visa. And you can also use the active clamp topology to absorpt the leakage inductance back to input source. And, NS has dedicated controllers LM5025, LM5026 for active clamp topology. And you can browse our website power.national.com for more information. | [2007-4-3 15:17:01] |
| [问：gunmyj] | 所採用的類比電流模式(ECM)是如何降低雜訊干擾？ | |
| [答：Sam] | Please find the block diagram in presentation material page 8. The objective is to create a signal that accurately represents the current through the buck switch Q1 without actually making a direct measurement. When we study the characteristics of the buck switch current signal we can note that the signal can be broken down into two parts, a pedestal and a ramp. When the buck switch initially turns on the current level jumps to the same level that was conducting previously in the diode. By taking a sample-and-hold measurement of the diode current just before turning on the buck switch we can establish the pedestal level. A small current sense resistor is placed in series with the diode anode to accomplish this measurement. Once the buck switch is turned on the characteristic of the ramping current is: di/dt = (Vin – Vout) / L This is the basic inductor equation. To emulate the ramping portion of the buck switch signal first we create a current source proportional to the difference between the input and the output voltage. If this current source flows into a capacitor, the ramping voltage across the capacitor will equal: dv/dt = (Vin – Vout) / C If we set the value of the capacitor proportional to the inductor value we can scale the capacitor voltage to match the ramping current signal. The final step is to add the sample and hold diode current level to the capacitor ramp voltage. Now we have recreated the buck switch signal with no delays and no leading edge noise spike. We can now use this signal for pulse-width modulation and current limit purposes as in conventional CM control. Each period after the buck switch turns off the ramp capacitor is discharged in preparation for the next cycle. | [2007-4-3 15:17:45] |
| [问：kittin] | 如何從負壓變換得到更負的壓比如從-100轉到-200？NS公司有沒有成熟的方案？ | |
| [答：Leon] | In theory,you can use positive to negative Buck-boost to implement this function,use the GND as the Positive input,-100 as the GND,this circuit you can refer to national application AN1157,but for so high input voltage range,i recommend you use the isolated solution.National have the LM5020 can implement it. | [2007-4-3 15:21:19] |
| [问：kswang] | 請問專家對於開關電源產生的干擾有沒有好的抑制方法？ | |
| [答：Tony] | Good PCB layout is very critical to suppress EMI. Keep in mind, for every switching converter, you have identified the high di/dt current loop, and always keep the loop as short as possible. You may also have to extra input & output LC filter to express the conducted EMI level. | [2007-4-3 15:21:57] |
| [问：zhoushywan] | 如果出現電流尖峰時怎樣避免PWM的誤判？ | |
| [答：Sam] | In general, additional filtering and / or leading edge blanking is necessary to prevent premature tripping of the PWM. However, the emulated current signal is free of noise and turn-on spikes. | [2007-4-3 15:23:35] |
| [问：zhoushywan] | 電流模式控制怎樣克服傳輸延時和瞬態變化所帶來的影響？ | |
| [答：Alan] | Fed-forward is inherent in current mode. When transient occurs, inductor current changes, controller IC gets this information then modulate to change duty. Propagation delay exists all system. Fed-forward is a factor to improve the transient performance. | [2007-4-3 15:30:10] |
| [问：rock_lai] | 考慮EMC和EMI時，是否需要前置濾波器？前置濾波器的設計要考慮那些因素? | |
| [答：Winter] | 如果在元件摆放，PCB Layout和开关速度都已优化的基础上，依然观察到较大的杂讯在输入输出端，就需要前置滤波器。 需要考虑滤除的目标是共模干扰还是差模干扰。并以此决定使用共模线圈还是差模线圈，或者Ferrite Bead 也有帮助。 | [2007-4-3 15:30:47] |
| [问：zhoushywan] | 請問NS有沒有從1.2V（5號電池）到5V升壓IC？ | |
| [答：Benjamin] | You can choose LM2623A and LM2623. LM2623A has better output current. | [2007-4-3 15:30:53] |
| [问：BanyChang] | 開關電源PCB排版基本要點是什麼？ | |
| [答：Sam] | 1. Good Grounding 2. Reduce the noise source area 3. Keep the signal away from noise source ....... You can go to below link for the related app note. http://www.national.com/an/AN/AN-1229.pdf#page=8 | [2007-4-3 15:34:41] |
| [问：BanyChang] | 請問專家正激電源的變壓器的電感量是怎樣計算? | |
| [答：Hector] | In a forward mode design, inductance of the transformer affects the magnetizing current. Generally speaking, the magnetizing current is one tenth of the primary current. For details, please refer to a switch mode power supply textbook. | [2007-4-3 15:37:40] |
| [问：runzhou] | 對於400HZ的逆變電源產生的噪音有什麼好的解決方法? | |
| [答：Winter] | 开关电源的噪音多数都来源于三种原因， 1. 脉冲电流流经一段导线（包括元件引脚，PCB走线，Jumper)。 2. 开关电压通过容性耦合干扰到邻近高阻抗节点。 3. 磁场耦合。 400Hz逆变电源也不例外。请缩短脉冲电流回路（有功率开关的回路）。隔离敏感的高阻抗节点与大的电压变化节点。并合理拜访磁性元件。适当的吸收电路(Snubber)对减小噪音也是必要的。 | [2007-4-3 15:37:45] |
| [问：BanyChang] | 請問專家電源功率大小由PWM控制晶片+MOSFET的什麼決定？ | |
| [答：Leon] | 首先电源功率大小取决于你的mosfet在一定耐压下的电流能力，功率越大，mosfet的电流要求越大，并且你在要求效率的情况下，会选择RDon小的mosfet,这样就要求大电流的mosfet。但是相对来说，它的栅极电容就比较大，这样对PWM控制晶片来说，它能带的功率就取决于它对mosfet的驱动能力了。 当然这是一般情况了，你可以通过加辅助驱动来解决驱动能力的问题。并且并不是Rdon越小就一定能提高效率，比如在buck电路，就取决于你的输入电压和输出电压的比值。因为驱动损耗也是一个比较大的损耗. | [2007-4-3 15:37:56] |
| [问：BanyChang] | 開關電源中的損耗如何計算？ | |
| [答：Tony] | The power loss of switching converter is mainly divided into following parts: 1) Power switch (including power MOSFET & diode) conduction loss 2) Power switch transition loss. 3) Gate drive switching loss. 4) core loss of magnetic component 5) Ohmic loss of magnetic component. You can visit our website power.national.com to find more application notes regarding how to estimate the power loss. And, for the 4th gen Simple Switcher, we have the Webench tools in our Website, that helps to estimate all power loss bugdets to you. | [2007-4-3 15:38:43] |
| [问：altimate] | 若要同時取得正負雙電源，可否直接將兩個buck converter 串接?或者有更好的方法? | |
| [答：Sam] | You can try one for positive and parallel another one using inverting buck-boost for the negative output. | [2007-4-3 15:44:21] |
| [主持人：eccn] | 由於時間關係，本次中電網“線上座談”馬上就要結束了。雖然各位聽眾（網友）已與美國國家半導體公司的專家討論了許多問題，但是還有許多提問沒有來得及進行交流。本次線上座談結束後，中電網將請美國國家半導體公司的專家繼續答復所有的來自各位聽眾（網友）的提問，然後整理上載到中電網網站上，以便大家查閱。 | [2007-4-3 15:48:34] |
| [主持人：eccn] | 在此，中電網特別感謝給予本次中電網線上座談巨大支持的美國半導體公司，特別感謝專門線上回答各位聽眾（網友）提問的美國半導體公司的各位專家們，特別感謝各位聽眾（網友）積極熱情的參與。 | [2007-4-3 15:48:48] |
| [主持人：eccn] | 祝大家事業有成、生活愉快！歡迎多提寶貴意見，歡迎關注中電網，下次再見。 | [2007-4-3 15:48:57] |
美国国家半导体致力开发各种高能源效率的模拟及混合信号半导体产品。该公司的PowerWise®系列产品旨在降低系统功耗，延长电池寿命，以及减少散热需求。美国国家半导体总部位于美国加州圣塔克拉拉(Santa Clara)，截至2008年5月25日为止的2008年财政年度的营业额达18.9亿美元。欲查询美国国家半导体的公司资料及产品信息，欢迎浏览该公司的网页，网址：www.national.com。
中电网官方微博
