在线座谈

热门关键字: 任意波形发生器 扫描仪 射频信号 照明光源 

关于本次座谈

精彩问答

主题:以太网上的功率传输
在线问答:
[问:Dr. Wu] 有时候PSE需要提供更高的电压,比如120V,凌特公司有没有解决方案? 
[答:Terry] 目前我们凌特公司的PSE端控制器最高工作电压达72V。通过变通的设计完全可以使其工作在更高的电压。如果需要,请联系我们。  [2003-11-25 10:29:55]
[问:lq-lh] 2003-11-11 15:06:08 [ Unanswered ] 实际以太网的功率传输和额定值有多大偏差?
[答:Dave] 15.4W at PSE output, 12.95W max at PD input. The extra is lost in the cable.  [2003-11-25 10:31:18]
[问:alter] 请问现在通常的以太网供电的传输距离和功率是多少。 
[答:Dilian] Power is transmitted either over the data pairs of the Ethernet lines or through the spair spares.  Power is 48V.  [2003-11-25 10:33:10]
[问:Dr. Wu] 从目前的标准看,POE技术只能提供13W左右的功率,如果PD设备需要更大功率,怎么办? 
[答:Terry] 按目前IEEE802.3的规范,只允许提供12.95W的功率。如果PD设备需要更大功率意味着不兼容标准,只能用于自行设计的封闭系统里。如果改变设计,凌特公司的相关PSE控制器是可以处理更大功率, 例如利用LTC4255来设计PSE。  [2003-11-25 10:34:15]
[问:willam _gann1] 新的标准下,以太网的传输距离能达到多少?如果扩展距离有何办法? 
[答:Dilian] Power is tranmitted over the Signal Pairs or over the Spare Pairs.  The spare pairs are unused pairs and 48 volts can be directly applied across them.  If power is transmitted over the signal pairs, it must be applied through the common mode of transformers.  [2003-11-25 10:35:21]
[问:snailman] 以太网功率传输的主要问题是什么 
[答:Dilian] One main hurdle of POE is compliance.  Some vendors have designed products before the IEEE standards were finalized.  There are still some legacy devices out in the market.  [2003-11-25 10:37:15]
[问:panqiyong] 传递电源的功率达到多大? 
[答:Dilian] A Power Sourcing Equipment (PSE) device is to provide between 44 Volts to 52 Volts, at 400mA max.  [2003-11-25 10:38:05]
[问:ljfml] 请问有没有关于以太网传输的标准功率? 
[答:Terry] IEEE802.3af has the details  [2003-11-25 10:38:24]
[问:zhj huang] 1.贵公司有PoE的全套解决方案吗?是内嵌于交换机还是做成PowerHub的形式?2.怎样对PoE设备进行管理?3.据我了解,目前做PoE的有很多家,比如PowerDsine,Maxim,TI等。贵公司的PoE方案和其它厂家相比有没有自己的特色? 
[答:Todd] How does LTC compare to PowerDsine, Maxim and TI?LTC offers an automatic mode of operation which does not require a dedicated microcontroller.  Also, LTC offers a version with AC-disconnect.  There are other specifications where LTC is more accurate.  [2003-11-25 10:38:39]
[问:ccdst-7] 能否简介一下以太网上的功率传输的原理? 
[答:Dave] Can you explain the theory of POE in more detail?POE is a standard for applying PD power as well as data over the CAT-5 Ethernet wire. The RX pair is biased at -48V relative to the TX pair. Autopolarity circuits in the PD can accept either polarity. The bias is applied to the center taps of the data isolation transformers. Special detection and classification circuitry prevent applying power to legacy equipment (NIC cards) that cannot tolerate power.  [2003-11-25 10:39:54]
[问:chengpeng] 是否完全符合802。3af标准,对以前cisco的pd设备能否兼容? 
[答:Terry] We fully comply with IEEE802.3af. True Cisco legacy PD discovery is done via the PHY chip, not the PSE chip. There are provisions in the LTC4259 for a PHY that does true Cisco discovery to turn the port on, so it is compatible with Cisco discovery.Some of the other PSE chip vendors have said that their chips can detect Cisco legacy PDs by detecting the input capacitance. This works sometimes but is very dangerous since not all Cisco legacy phones have the same input cap! However, if the customer wants to do it with capacitive detect and not the true Cisco PHY-based method, there is a simple software routine for the LTC4259 that will do capacitive detect.For PD matching with legacy Cisco PSE (lower current limit), our LTC4257-1 can be used which has dual current limit levels.  [2003-11-25 10:40:51]
[问:purch aseguan] 您好!以太网上的功率传输將達到多少訴速率?這個標准同以前的標准IEEE1394,機構上有和區別?/謝謝指教!寶發工業中國有限公司 采購部 管華良 www.professionalhk.com 
[答:Dave] How much power can be transmitted in the POE? What is the difference between this standard and IEEE1394?PoE can transmit up to 12.95W to the PD.PoE works on the standard Ethernet CAT-5 wire with existing building wiring, up to 100M cable. IEEE1394 operates over a proprietary point-to-point connection.  [2003-11-25 10:41:48]
[问:mikelee] PSE和PD能不能直接做在网络设备里?他们之间需要什么接口? 
[答:Terry] Only uses the standard RJ45 connectors.  [2003-11-25 10:43:04]
[问:guo_chunyu] 在安全规范和电磁兼容上是否需要考虑雷击防护和电快速瞬变脉冲群的防护,如果需要,如何设计呢? 
[答:Dilian] A voltage suppressor is required at the output of a Power Sourcing Equiment (PSE) device and at the Input of a Powered Device(PD).  We recommend a 58V voltage suppressor.  Also, a capacitor at the output of a PSE and the input of a PD, typically 0.1uF each.  The input of the PD requires a diode bridge on both spare pairs and signal pairs.  A common mode choke may be used at the PSE output.  [2003-11-25 10:43:54]
[问:Dr. Wu] 凌特为什么不提供八通道器件? 
[答:Terry] 因为这样做对客户和凌特都没有好处。虽然从技术上来说这是可行的,但却并非明智之举。因为所节省的硅片并不太多,原因是基本的和最大的功能单元都必须针对每个端口进行复制。由于硅片尺寸较大,所以产生的损耗会增加,因而有可能导致芯片成本上升。而外形较大的封装也更加昂贵,至少对凌特公司而言的确如此。采用四通道解决方案能够实现较为干净简单的印刷电路板布局。由于受到磁性组件和外围组件实际尺寸的限制,因此对于八通道器件来说,至检测电阻器和FET的印制线将会过长。许多设计工程人员在从事电源设计时都有过这样的教训,即如果至电流检测组件的印制线很长,则会因噪声免疫力较差的缘故而带来问题。我们的客户过去就有过这种经历。根据所使用的磁性材料种类的不同,四通道解决方案可以实现很好的适用性,这最早也是由市场上举足轻重的厂商提出来的。正在推广八通道器件的竞争对手同时也在计划制造四通道器件,那么八通道器件真是大势所趋吗?您现在肯定已经知道答案了。  [2003-11-25 10:46:19]
[问:qin] 对短路或过载保护的能力如何?响应时间有多快?它取决于那些因素?和以太网有关吗? 
[答:Dave] How do we do the short circuit and over-current protection? How fast is the response? What determine those protection factors? Is it related to the Ethernet system?Short circuit current is limited to 450mA after 1ms. Maximum short duration is 75ms before the power must be turned off. The numbers are chosen to keep the power in the switch MOSFET to a safe level. The Ethernet cable can stand more current than this - there is a large safety margin.  [2003-11-25 10:46:58]
[问:fu_zx] 每一路输出功率的限制是什么样的?在以太网上传输功率是否需要比较多的关心它的向外辐射问题
[答:Dilian] What is the limitation on tranmitting power over each port? Do we need to take special attention to EMI issue on the POE?A Power Sourcing Equipment (PSE) device is to provide between 44V to 52V, 400mA max.  A voltage suppressor (58V) and capacitor (0.1uF) are used at the output of a PSE and the input of a PD.  A common mode choke and fuse can be used at the output of a PSE.  [2003-11-25 10:47:43]
[问:chengpeng] 每个端口的最低售价是多少? 
[答:Terry] Please contact eli@linear.com for details  [2003-11-25 10:50:50]
[问:nickelren] 请问有一个设备的功率在12W左右,能不能安全地通过802.3af长时间的供电?Linear公司的LT4259和4257批量价格是多少?国内哪里有供货? 
[答:Dave] If we have a 12W power device, is it reliable to use the 802.3af to provide power for long time?Yes, as long as it never exceeds 12.95W at the input. The system is designed to supply 12.95W continuously.  [2003-11-25 10:51:53]
[问:mikelee] 以太网上用现有电缆提供电源最需要注意的地方在哪?它的应用前景如何?假如想用该技术单独做一产品可以是什么? 
[答:Todd] What is the concern in designing the POE system?How about the development future? What products can be made if we apply such technology?Compatibility with multiple vendors is a concern.  That is why we offer reports from the UNH interoperability tests.  We expect the IEEE standard to be stable for many years, so you can develop parts into the future.  Typical PSE products are hubs, routers and switches but the PD can be many different products: IP phones, wireless access points, PDA or cell phone chargers, security cameras.  We have heard that one company will power electic guitars and other musical instruments.  [2003-11-25 10:52:30]
[问:Kelvin Wong] 我想问一下,在接入PD中,是否设置有优先级?也就是在接入的PD中,对于比较重要的取电设备,主设备有没有一些特殊的措施以保证其可靠供电? 
[答:Dilian] Is there any prioritized power allocation? In other words, once a new  and more important PD is plugged in, how do we deal with this? How can we guaranteed the power allocation?IEEE addresses power prioritization by the optional method of classification.  A Powered Device (PD), in addition to displaying the Signature Resistance of 25kOhm, it has the option of displaying a Class.  There are 4 Classes.  Each class tells the PSE how much power is will require.  Class 1 is a low power device, class 2 is medium power, class 3 is high power.  Class 4 is reserved for future use.  Class 0 is a default if a class is not present and would be full power.  A PSE can decide by the Class how to allocate it"s power.  This way, it is not providing full power to each port.  [2003-11-25 10:53:56]
[问:zhxf00] 请问如果采用这种网络功率截取方法的设备过多,能否对网络的稳定运行构成威胁?网络的运营者会采取哪些应对措施? 
[答:Todd] If there too many system built with POE, will it affect the stability of the network?No, the power is separated from the data so it does not affect the stability.  Special care is needed with Gigabit Ethernet, but it should not affect the stability if done properly.  [2003-11-25 10:54:53]
[问:lixm79] LTC4258/4259是不需要单独供电,而是直接从接口获得电源的吗 
[答:Terry] No, you need to provide a 3.3V for the IC. It is simple to derive the 3.3V from the existing power supply or the 48V power source  [2003-11-25 10:55:00]
[问:gzwy] 以太网功率传输的功率是否要遵循802.3af协议的要求?我想需要更大的功率怎么办? 
[答:Dave] Do we need to follow the 802.3af for POE? How do we do if we want more power?Currently you need to follow 802.3af to be considered compliant. It is possible to get more power either by powering both sets of pairs or by increasing the current limit, but this would not be compliant with the IEEE spec and a PD designed this way would not work with all PSEs. You can also increase the voltage, but this will cause UL compliance problems and is not IEEE compliant.  [2003-11-25 10:55:15]
[问:Kelvin Wong] 可不可以申请样片?有多大? 
[答:Terry] Please contact eli@linear.com for details  [2003-11-25 10:57:07]
[问:rio_hann] 以太网上的功率传输受到哪些限制?关键的技术是什么?如何解决? 
[答:Dave] What is the limitation of the transmitted power? What is the key technology? How to deal with it?Power is limited to 12.95W at the PD. The key technology is a sophisticated technique of detecting a PD that requires power and deciding when to disconnect it. The LTC4259 will take care of all IEEE compliance issues, so the host system just needs to provide a -48V supply.  [2003-11-25 10:57:17]
[问:13823 608335] 已经建设的以太网能向网络终端提供电源吗?如果不能,如何改造。 
[答:Dilian] Can the existing Ethernet network provide the power? If not, how can we modify it?IEEE defines a Midspan Power Sourcing Equipment device.  This device it to go in front of existing Ethernet network devices and provides power to Powered Devices.  The midspan device can be an external box, or even a daughter card that plugs right on top of existing systems.  [2003-11-25 10:58:06]
[问:benz_999] 为何POE的电源选择48V?在企业级应用中有很多是220V交流电源,这种情况如何实现POE? 
[答:Dilian] What the POE use 48V? We usually use 220V ac for the power source, how to we implement the POE?Power across the Ethernet lines is 48V.  A power supply on the Power Sourcing Equipment (PSE) is to provide the 220V AC to 48V DC.  The PSE then provides the 48V to the Powered Devices (PD).  [2003-11-25 11:00:33]
[问:samire] 请介绍25K电阻具体的用途. 
[答:Dave] Please explain the function of the 25K ohm resistor.The 25k resistor identifies the PD as a device that requires power. The PSE controlled (like the LTC4259) must be able to measure the 25K accurately through 100M of cable and up to two series diodes. The PSE must take a two-point measurement and subtract to get the resistor value. The resistance must be between 19k and 26.5k to receive power.  [2003-11-25 11:01:07]
[问:foxtan] 能传送功率?成本增加多少个百分点。 
[答:Todd] How much percentage will the POE add to the existing solution cost?The cost to add POE to an Ethernet switch is a very small percentage.  The power controller (LTC4258 or LTC4259) requires a few additional components but you will also need an isolated 48V supply.  Additional cost will come from software to support the management of this power.  With all this it will still be quite small.  [2003-11-25 11:02:19]
[问:hesixin] 4257-1不满足IEEE802.3AF吗 
[答:Terry] The 4257-1 is also fully compliance with IEEE802.3af  [2003-11-25 11:03:31]
[问:fanchxi] 请问以太网供电,电源噪声会不会对数据传输有影响? 
[答:Dilian] For the POE, will the noise form the power supply affect the data transmission?Yes it may affect the data transmission.  Noise from the power supply may also cause false disconnects.  Make sure the power supply is properly filtered.  [2003-11-25 11:03:39]
[问:anabelle] What is the advanced IEEE standard? How does it work with a good performance in power wiring of internet? 
[答:Dave] 15869: What is the advanced IEEE standard? How does it work with a good performance in power wiring of internet?The most recent standard for PoE is 802.3af-2003. It works with standard CAT-5 wiring and is compatible with 10BASE-T, 100BASE-TX, and 1000BASE-T.  [2003-11-25 11:04:25]
[问:wenlongsh] 我想知道LINEAR的器件与德州的同类产品有那些具体的优势? 
[答:Todd] How do Linear compare its advantage over TI for this kind of product?LTC offers an automatic mode of operation that does not require an external microcontroller.  Even in semi-automatic mode the firmware is very small.  LTC4259 offers AC-disconnect.  Also, LTC specifies the minimum and maximum limits for the precision specifications (detection, classification).  TI does not offer these things.  [2003-11-25 11:04:58]
[问:qin] 如何调整供电功率或对受电设备进行功率管理? 
[答:Dilian] How do we do the power allocation?After a Power Sourcing Equiepment (PSE) device detects a valid Powered Device (PD), it will attempt to read the PD"s class.  By reading the class, the PSE can look at how much power it has left to provide to the ports and decide if it has enough power to turn on the port.  [2003-11-25 11:06:20]
[问:samire] 演示中的LTC4259的功率传输采用以太网上的数据流,请问,最大的功率有多大?检测时对数据信号有无影响?如何克服高频信号对波纹系数的影响? 
[答:Dave] In the presentation, you use the data pairs to transmit the power, what is the max power that can be transmitted? Will it affect the data? How to deal with the high frequency interference on the data?Max power is 12.95W at the PD end, with some additional power lost in the cable. It does not affect the data since it is a common mode signal, and the data is a differential signal. The transformers separate the power from the data. The power supply is required to have low noise to minimize any possible impact on the data.  [2003-11-25 11:06:37]
[问:qin] 能否详细介绍802.3af的标准情况或参考资料? 
[答:Todd] Can you introduce the status of the 802.3af and suggest any reference information?The standard has been ratified which means that it is approved by IEEE.  It can be purchased from the IEEE.org website.  After six months the standard will be available at no charge.  [2003-11-25 11:07:08]
[问:ljp] 以太网上的功率传输,和通常所用的远端供电有何不同? 
[答:Dave] For using POE, what is the difference between this technology and the existing remote powering design?With remote powering, a wall transformer is required at the PD end. With PoE, no wall transformer is needed - only the CAT-5 data cable.  [2003-11-25 11:07:34]
[问:ljp] 以太网上的功率传输,最长的距离有多远? 
[答:Dilian] What is the longest distance for the power transmission?The power transmission distance is limitted by the limits of Ethernet distance.  [2003-11-25 11:08:11]
[问:zhang quan2003] 以太网上的功率传输在国内外的研究现状如何?谢谢 
[答:Todd] How is the current reserach studying on the POE globally?There are market research firms studying POE, but there is very little information available yet.  [2003-11-25 11:08:22]
[问:samire] 能否对受电设备有软起动功能以减小浪涌电流? 
[答:Dave] Can we do soft-start for the PD so as to limit the inrush current?Yes. The IEEE spec mandates a 450mA current limit at start up, and specifies a maximum voltage slew rate. Additional softstart is not required.  [2003-11-25 11:08:39]
[问:hqc415] LTC4259/8 是用在pPse设备上的吧 
[答:Terry] Yes  [2003-11-25 11:09:28]
[问:mai guoliren] 太网上用现有电缆提供电源的方法有几种?贵公司在那些方法上有优势?谢谢! 
[答:Todd] How many POE method are there now? What is our advantage?There were two main methods and both were proprietary.  Our method is compliant with IEEE 802.3af which is not proprietary.  One proprietary method used the data link to manage power but that has been dropped in favor of 802.3af.  The other proprietary method has been dropped in favor of 802.3af, also.  [2003-11-25 11:10:32]
[问:lq-lh] 实际以太网的功率传输和额定值有多大偏差? 
[答:Dave] How much is the max. power and tolerance?The PD is allowed to draw up to 12.95W. Voltage range is 36V min to 57V max.The PSE must supply at least 15.4W to the port. Voltage range is 44V min to 57V max. The extra power at the PSE is to allow for loss due to resistance on a 100M cable - up to 20 ohms round-trip.  [2003-11-25 11:11:11]
[问:guo69] 标准网线可以承受的功率是多少? 
[答:Dave] What is the max. power can the standard power line afford?A PD can draw up to 12.95W.  [2003-11-25 11:11:33]
[问:xxxbbb] 贵公司有没有解决多路PSE端供电的单芯片产品? 
[答:Terry] Our LTC4258/9 is a quard output chip that can support 4 ports. Several chips can be used together and we can at most support up to 64 ports  [2003-11-25 11:11:41]
[问:qin] Linear能否提供成套的参考设计?它的价格如何? 
[答:Todd] Does Linear provide total solution for reference design? How is it priced?The reference design is not priced.  We can provide schematics and BOM as well as an evaluation board.  Our field application engineers can customize the power supply for the 48V and 3.3V supplies based on your system.  [2003-11-25 11:12:01]
[问:ljp] 供电的功率目前有多大?它的阈值是否可编程或配置? 
[答:Dave] How much power can be provided? Is the power level programmable?A PD can draw up to 12.95W. There are two lower power classes for PDs that don"t require as much power:Class 1: up to 3.84WClass 2: up to 6.49WClass 3 or Class 0: up to 12.95W  [2003-11-25 11:13:15]
[问:samire] 受电设备增加以太网功率传输功能,成本会上升多少? 
[答:Todd] How much will be added to the cost if we add the POE to the existing system?It depends on many factors.  You should work with our local sales office for specifics.  It will be somewhat more than $1 or $2 per channel.  [2003-11-25 11:14:13]
[问:shg_mail] 想了解一下其现状及发展方向 
[答:Dave] What is the devlopment situation of POE? What is the development trend of this technology?The IEEE standard 802.3af is finished and retified.There are a few vendors providing chips now, including LTC. Surely more companies will be joining in the future.  [2003-11-25 11:14:34]
[问:zhanhua bin1011] 哪里能得到 IEEE 802.3af 
[答:Terry] You can buy it from IEEE website. www.ieee.org  [2003-11-25 11:14:38]
[问:gyback street] 如何解决脉冲和辐射保护问题? 
[答:Dilian] How do we deal with EMI and surge protection?The output of a Power Sourcing Equipment (PSE) device can have up to 520nF of capacitance.  The input of a Powered Device (PD) must have between 0.05uF to 1.2uF at the input.  Also a voltage suppressor must be placed at the PSE output as well as the PD input.  A common mode choke and poly fuse may also be used at output of a PSE.  [2003-11-25 11:15:33]
[问:wyh 999999] 请介绍一下本次讨论推出的解决方案,有何特点? 
[答:Todd] What is the advantage of this POE solution?It is fully compliant with the IEEE 802.3af standard, it offers several modes of operation including an automatic mode and we offer the choice of AC or DC disconnect methods.  [2003-11-25 11:15:34]
[问:sea258] 以太网供电可以解决那些问题,有多大的应用前景? 
[答:Dave] What problem can we solve using the POE? How is the future of this technology?With PoE, there is no need for a wall transformer at the PD end (the phone, access point, camera, or other). We feel that this technology will grow rapidly until all switches and routers are shipped with PoE as standard equipment.  [2003-11-25 11:16:02]
[问:wuzj] 我做过对绞线上的远供系统,包括远供电源的收,发电路.请问专家:    以太网的远供电源电压应该选多高,直流还是交流,如是交流,频率应该是多少?是带内供电,还是带外供电? 
[答:Terry] DC power is being transmitted.  [2003-11-25 11:17:36]
[问:wills2003] 如何减少供电线路中的高频成分? 
[答:Dilian] How to reduce the high frequency content over such power delivering system?The output of a Power Sourcing Equipment (PSE) allows for up to 520nF of a capacitance during detection.  The input of a PD must have between 0.05uF to 0.12uF of capacitance and up to 100uH of inductance during the Detection.  [2003-11-25 11:18:37]
[问:huazhai] 尊敬的各位专家:请问以太网以怎样的方式传送功率及最高可达到多大,谢谢!!! 
[答:Todd] How does the Ethernet transmit power? How much max. power can be transmitted?48V DC is applied to the common-mode of the cable using the transformer.  A maximum of 12.95W can be used at the receiving end of the cable.  [2003-11-25 11:18:39]
[问:samire] 这种供电对受电设备有和具体要求?是否和现有的设备兼容? 
[答:Todd] What is the requirement of the power device? Is it compatible with the existing system?The powered device (PD) must have a circuit like the LTC4257 to isolate the power until the 48V is delivered.  The PD must look like a 25k ohm resistor to be considered valid.  It must limit the current below 400mA at all times.  The data portion of the PD can use a standard Ethernet PHY chip.  [2003-11-25 11:21:41]
[问:ecnan jing_EBY7E] LTC4259的四路供电电压是否可任意设置? 
[答:Terry] Yes. You can freely set the operation mode independently  [2003-11-25 11:21:43]
[问:lixm79] 以太网上功率传输的损耗主要是由哪些因素决定? 
[答:Dilian] What is the main cause of the powe loss in POE?First, some power is lost over the Ethernet lines.  There is a voltage drop across the input diodes of a Powered Device (PD) which reduces some efficiency.  Linear Tech"s PD Interface Controler consumer very little power and should hardly be an issue.  The rest is up to the efficiencies of whatever regulator is used.  [2003-11-25 11:22:41]
[问:casper] 为什么在贵公司的网站上查不到LTC4258的datasheet 
[答:Todd] Why I can"t search for the datasheet of LTC4258 from your website?Only the LTC4259 is available on our website.  Contact Terry Lo or Echo Li and we can send the LTC4258 datasheet to you.  We expect to have it on our website in several weeks.  [2003-11-25 11:22:57]
[问:wyh 999999] 以太网的RJ45端口中本来就定义了两根电源线完全可以用来传输功率,现讨论的传输功率有何不同,传输的功率容限和距离有何限制?如何抗干扰?个人认为只对微小功耗设备有意义! 
[答:Dave] The original definition of RJ45 use 2 wires to transmit power. What is the different power transmission on this discussion. What is the transmission power limit as well as distance limit? How to take care of noise immunity? My personal feeling is that it is meaningless for low power equipment.The RJ45 connector (for 10Base-T) was originally designed to carry two separate Ethernet connections, but some buildings only wire two pairs (4 wires) through to the jack. The difference with 802.3af is that the power is sent on the same wires as the data, so no extra wires are needed and it will work with buildings that only pass 4 wires through.Power limit is 12.95W at the PD end. Distance is the same as the data: 100M. Noise immunity is taken care of by special 802-3af data transformers. Most large equipment manufacturers now offer 802.3af PoE power as their only method of inline power.  [2003-11-25 11:24:16]
[问:zhanhua bin1011] 贵公司是否能提供关于LTC4258/9得具体使用的设计例子供大家学习使用 
[答:Todd] Can your company provide a real example of using LTC4258/9 so that we can learn from?We have evaluation boards that can be used as a mid-span (receive Ethernet data in, apply 48V and pass the data through with power).  We have the schematics and BOM.  Contact Terry Lo.  [2003-11-25 11:24:34]
[问:wde mail2002] 此次讨论的以太网是在何种带宽下讨论? 
[答:Dave] What bandwidth (speed) of Ethernet are you talking about in the POE seminar?10/100 and Gigabit are all supported.  [2003-11-25 11:24:36]
[问:ecnan jing_EBY7E] 以太网的供电和固话网的远程供电原理是否相同? 
[答:Dave] Is the operation of POE the same as the power for telephone line?No. Telephone power is applied differentially to the twisted pair wire. PoE is applied as a common mode signal between two twisted pairs.  [2003-11-25 11:26:25]
[问:lwz3968] 请问专家:以太网上的功率传输所能达到的峰值是多少?平均值呢?能够传输的电流峰值是多少? 
[答:Dilian] What is the peak power that can be transmitted? How about the typical/average value? How much peak current can it afford?The maximum power of a PD is 12.95W.  The typical value depends on the PD.  Up to 350mA of continuous current can be provided to a PD, and up to 400mA for no more than 50ms.  [2003-11-25 11:27:37]
[问:robin] 对于无线 Hub,发射功率较大的情况,又没有相应的解决方案。 
[答:Dave] Concerning the wireless hub, if the transmission power is relatively high, is there any good POE solution?If the hub runs with less than 12.95W, it can use PoE directly. If it requires more than 12.95W, it must use another technique or include two PD input ports to be compatible with IEEE compliant PSE switches.  [2003-11-25 11:28:16]
[问:ecnan jing_EBY7E] LTC4259/8是否只支持四线方式的传输? 
[答:Terry] if only one chip is used, yes it just support 4 ports. However, several chips can be used together to support up to 64 ports.  [2003-11-25 11:28:40]
[问:zthnuaa] 以太网提供的电源经过调整后最大纹波是多大,能满足微弱信号处理电路的需要吗?比如说0.1毫伏的纹波 
[答:Terry] It all depends on the power supply design. Our chip is not the a power supply, it just manages the power and will not add noise.  [2003-11-25 11:29:29]
[问:ecnan jing_EBY7E] LTC4259对浪涌电压的限制最大为多少伏? 
[答:Dilian] What is the max. inruch current limit for LTC4259?450mA  [2003-11-25 11:29:34]
[问:Dr. Wu] 如何考虑PD端瞬态过电压保护? 
[答:Terry] 对PD端瞬态过电压保护必须加倍小心,除了必要的瞬态过电压滤波和吸收措施外,PD控制器本身要有足够的耐压能力才能可靠工作,这一般要求能承受72V。通常,TVS需要放置在器件之前以提供较好的保护,但是,TVS可能有一个宽箝位范围,例如在极端的情况下,一个58V的箝位TVS可箝位在大约90V,所以选择TVS一定要非常小心。采用一个较大容差的控制器工作电压会有很大帮助,而LTC4257则可允许到100V。  [2003-11-25 11:30:55]
[问:robin] 如何设定供电的电流限制? 
[答:Dave] How do we set the current limit?The current limit required to be set to the IEEE limit in the PSE, and the LTC4259 is set at that limit from the factory.The PD can be set to any limit below 12.95W, and is usually set with a current limit on the switching power supply in the PD. The LTC4257 PD interface device has a 375mA current limit to keep the PD inrush current below the IEEE limit at all times.  [2003-11-25 11:31:51]
[问:ecnan jing_EBY7E] 12。95W的功率可传输多远距离? 
[答:Dave] How long can a 12.95W power be transmitted?12.95W can be transmitted continuously.  [2003-11-25 11:34:41]
[问:robin] 请问专家:对 PD 设备的分类的主要标准是什么? 
[答:Dave] What is the criteria for classifying the PD?Once the PSE has detected the 25K resistor, it applies a constant voltage to the PD, between 15.5V and 20V. The PD must draw a constant current with this voltage applied. The current it draws tells the PSE what class it is, which lets the PSE know how much power the PD will draw when it gets powered up. <4mA = Class 0 = 12.95W9-12mA = Class 1 = 3.84W17-20mA = Class 2 = 6.49W26-30mA = Class 3 = 12.95W  [2003-11-25 11:40:58]
[问:Dr. Wu] 对每个端口进行电流监控重要吗? 
[答:Terry] 这当然不是! 有些竞争对手会这样做并对其优点推崇备至,但究竟是不是确实好我们就需要加以思考了。这样做可能帮助到他们推广CPU/MCU,而软件供应商也可参与这顶目。有些竞争对手则不进行硬件分类,客户需要采用CPU来检查分类电流,并运用软件来进行分类。有些供应商将ADC用于电流监控输出,然而,针对ADC所拟订的技术规格给出的只是典型值,其温度精确度如何就不得而知了。对于IEEE标准而言,这是并不需要的。IEEE标准(IEEE标准文件:802.3af-2003第33.2.9节)并不建议在功率分配中使用电流监控。但是,作为一种服务,凌特公司会在客户确实有需求的时候对相关的工作提供应用支持。  [2003-11-25 11:42:11]
[问:zthnuaa] 提供的电源是交流的?幅值和频率如何?对用电器有干扰吗? 
[答:Terry] It is DC, so not frequency.  [2003-11-25 11:42:27]
[问:DAISY.LUO] 關於HUB&ROUTE的使用,功率的最大值是多少?內部零件需要考慮嗎? 
[答:Dave] Concerning the Hub and Router application, what is the max. power? Do we have any special concern on the component selection?The hub or router must supply at least 15.4W to the port. The -48V power supply must be UL isolated and must supply adequate current. The MOSFET must be 1A, 100V to carry the current and deal with surges. A 58V transorb is required to protect against cable discharge or ESD. Other components are standard - refer to the LTC4259 datasheet or contact Terry Lo at LTC tlo@linear.com  [2003-11-25 11:43:25]
[问:robin] 浪涌保护有什么具体措施? 
[答:Dilian] How do you deal with the inrush? Please explain in detail.On the Power Sourcing Equipment (PSE) side, our LTC4258/LTC4259 goes into current limit if 450mA is exceeded.  On the Powered Device (PD), IEEE requires that a PD should have at least 5uF of capacitance at the Power Interface (PI)under normal operation with full power.   The LTC4257 will isolate this capacitance from the Power Interface until power is switched over to the output when the input voltage is above 42V.  A soft start should be implemented on the switching regulator, if used, to minimize the inrush current when charging the PI capacitance.  [2003-11-25 11:46:25]
[问:xuenet] Some suppliers use MCU to detect the PD, why LTC don"t have such methode?  
[答:Dave] 16041: Some suppliers use MCU to detect the PD, why LTC don"t have such methode?The LTC4259 does all IEEE functions internally, including detection, classification, current limit, and AC disconnect. No MCU is required. An MCU can optionally be used to implement power management if desired.  [2003-11-25 11:46:35]
[问:ecnan jing_EBY7E] Earthnet Very Long 模式传输时LTC4259的-48V供电,是否可行? 
[答:Dave] Is is possible to use LTC4259 to do -48V POE in Earthnet Very Long mode?The LTC4259 can be used as long as the total cable resistance is less than 20 ohms round-trip.  [2003-11-25 11:47:09]
[问:xuenet] What is different between AC disconnect and DC disconnect? Why have 2 detection standard? 
[答:Todd] What is different between AC disconnect and DC disconnect? Why have 2 detection standard?DC disconnect measures continuous DC current, when it drops near zero, it disconnects.  AC disconnects measures AC current.  DC is more robust in most applications.  Some people believe AC is more accurate for very low current applications.  Users can implement either.  [2003-11-25 11:47:26]
[问:xuenet] How important to have the auto detection? Seems other suppliers didn"t provide such method.  
[答:Todd] How important to have the auto detection? Seems other suppliers didn"t provide such method.Automatic detection simplifies the task for the processor and could eliminate the need for a dedicated controller in some cases.  [2003-11-25 11:49:41]
[问:xuenet] It is important for us to implement real-time current detection as it can help proper power allocation and prioritize the PDs. However, you"ve mentioned that this method is not a good idea. Why? 
[答:Dave] 16049: It is important for us to implement real-time current detection as it can help proper power allocation and prioritize the PDs. However, you"ve mentioned that this method is not a good idea. Why?Some PDs will draw low power for a very long time, then draw full power. If the switch is watching the power consumption, it will allocate less power to this kind of PD, then disconnect it when it begins to draw full power. This is why the IEEE spec uses the classification method instead. Older legacy PoE systems used real-time current monitoring, but it was dropped in favor of IEEE classification.  [2003-11-25 11:49:59]
[问:ljp] 请问功率传输以及网接点上的变压器有无特殊要求?? 
[答:Dave] Is there any special requirement on the transformer design in the PSE and PD?Yes, special 802.3af transformers are required that can handle the DC current. Several vendors have transformers available. Contact Echo Li or Terry Lo at LTC for more information eli@linear.com tlo@linear.com  [2003-11-25 11:51:11]
[问:robin] 请介绍 4257的功率良好状态电路的监视功能。 
[答:Dilian] Please explain the power good signal and its detection.Power Good is an Open-Drain output.  This is low-impedance when the LTC4257 input is out of UVLO and power is successfully switched over to the output side.  This can be used to switch on a regulator on the output side.  [2003-11-25 11:51:44]
[问:zthnuaa] 在以太网线上应该是传输的交流电源吧?有关参数? 
[答:Terry] DC power is used, so no AC. Please note this is not talking about the data signal and also it is not talking about the wall-adaptor power. We power up a far end product (Power Device (PD)) with this 48V DC power.  [2003-11-25 11:51:52]
[问:xuenet] Heard that DC disconnect has some law suit issue? It it true or rumour? How it affect the design? 
[答:Todd] Heard that DC disconnect has some law suit issue? It it true or rumour? How it affect the design?Yes, there is a concern with patent infringement on DC disconnect.  It is still pending but not expected to be an issue.  You could start with the LTC4259 and select either AC or DC disconnect.  [2003-11-25 11:54:11]
[问:ecnan jing_EBY7E] 既然提供的电源是直流,那传输过程中如需变压器耦合如何处理? 
[答:Terry] We don"t use transformer to couple the power. The transformer is used for data line which is also used in legacy ethernet equipment. Please note we provide common mode DC over the transformer so the whole transformer is indeed treated as a conductor. So, each signl pair will see a DC common mode voltage and therefore the data is not yet affected.  [2003-11-25 11:54:53]
[问:ljp] 请问热保护在PD和PSE端如何实现?? 
[答:Dilian] How do you do thermal protection in PD and PSE?The LTC4257-1 (PD) will go into thermal protection when the input current is between 350mA to 400mA.  The LTC4257-1 will reduce the current until it is out of current limit.  The LTC4258/LTC4259 (PSE) will go into current limit and reduce the FETs to prevent them from over heating and possibly being damaged in the case of a short circuit at the Power Interface.  [2003-11-25 11:56:06]