[PSES] USB output limitation
Dear experts, What would be the limit of USB output? I know IEC 60950-1 requires only that it complies with limited power source, but there might be some other requirements to limit power from USB? In particular, I am talking about power supply with USB connector. Can it go up to 5Vd.c./3A? Best regards, Bostjan Glavic SIQ - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to emc-p...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas emcp...@radiusnorth.net Mike Cantwell mcantw...@ieee.org For policy questions, send mail to: Jim Bacher: j.bac...@ieee.org David Heald: dhe...@gmail.com
Re: [PSES] IEC 61000-4-4 test setup for EUT which have casters
On Fri, 24 May 2013 17:24:35 +0100, John Woodgate j...@jmwa.demon.co.uk wrote: It's known that this clause is inadequate and it will be reviewed, but probably not very swiftly. It has been pointed out that the capacitance between the EUT and the ground plane depends on the permittivity of the support, which is not controlled. Thanks both for the responses. Actually, I didn't mind of permittivity of the insulating material so much, which is plastic or rubber wheel of the casters/rollers in this case. However, I mind of the possible ambiguities, such as: o If non conductive roller/casters part of the EUT can be used as the insulating support, how about commonplace casters like this? http://commons.wikimedia.org/wiki/File:Absolex_san.jpg If such casters can still be used as the insulating support, how about machine rollers like these ones, http://www.machineroller.com/ which are mostly metal but surface of the wheels are covered by plastic or rubber? o If such casters/rollers can be used as the insulating support, which position of the rollers/casters should positioned at the specified height of about 0.1m? Top of the caster/roller, or bottom of its metal component? o This standard didn't use the term may about this. However, if it is an option, it would be expected that one laboratory may put an EUT on the GRP without 0.1m support, and other laboratory may put the same EUT on 0.1m support. This will alter the distance between EUT's bottom surface and GRP, and can cause additional inconsistency of the test results between laboratories, I thought. At this time, we would need to put such EUTs on 0.1m insulating support for some other 61000-4-* standards anyway, and I think it would far easier to put such EUTs on 0.1m insulating support as far as possible also for 61000-4-4 testing. Regards, Tom -- Tomonori Sato vef00...@nifty.ne.jp URL: http://homepage3.nifty.com/tsato/ - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to emc-p...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas emcp...@radiusnorth.net Mike Cantwell mcantw...@ieee.org For policy questions, send mail to: Jim Bacher: j.bac...@ieee.org David Heald: dhe...@gmail.com
Re: [PSES] USB output limitation
Hello Bostjan, There are a number of considerations regarding power from standard USB ports. There are USB ports designed to supply power over an additional set of contacts. I would recommend using one of these connector types where you intend to deliver more power than normally supplied by a USB port. The powered USB ports are designed for up to 30W at 5V. http://en.wikipedia.org/wiki/Powered_USB The standard USB connector will typically be designed for a maximum continuous current of 1.5A. Drawing more current through a standard connector may raise temperatures beyond what IEC 60950-1 would allow. The temperatures of the plastics of the connector body may exceed their RTI, or the temperatures of the circuit board supporting the connector might exceed the board's maximum rating. Although the USB standard doesn't limit the size of conductors in USB cables, the specification recommends making cable conductors as small as possible to enhance the flexibility of the cable. If you have a standard USB port, you have no control of what the user connects beyond instructional safeguards. The designers of many USB devices presume a limited current from USB ports. Their designs assume that under fault conditions, the USB port will limit the current enough that a short circuit in their device will not result in overheating or other issues. This could be a problem if such a device experiences a fault when connected to the USB port you propose. Ted Eckert Compliance Engineer Microsoft Corporation ted.eck...@microsoft.com The opinions expressed are my own and do not necessarily reflect those of my employer. -Original Message- From: Boštjan Glavič [mailto:bostjan.gla...@siq.si] Sent: Monday, May 27, 2013 5:30 AM To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: USB output limitation Dear experts, What would be the limit of USB output? I know IEC 60950-1 requires only that it complies with limited power source, but there might be some other requirements to limit power from USB? In particular, I am talking about power supply with USB connector. Can it go up to 5Vd.c./3A? Best regards, Bostjan Glavic SIQ - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to emc-p...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas emcp...@radiusnorth.net Mike Cantwell mcantw...@ieee.org For policy questions, send mail to: Jim Bacher: j.bac...@ieee.org David Heald: dhe...@gmail.com - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to emc-p...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas emcp...@radiusnorth.net Mike Cantwell mcantw...@ieee.org For policy questions, send mail to: Jim Bacher: j.bac...@ieee.org David Heald: dhe...@gmail.com
Re: [PSES] Capacitor Discharge Test IEC 61010-1 - A little history
Brian, et al, A histerical, er - historical, review... In an internationally harmonized standard all expected issues must be considered. The primary driving factor for the cap discharge test on the power input pins has been driven by the British over the years. The large, 13A British power plug behaves differently than the North American or Euro (or similar) plugs. When you pull a NA plug from the wall and drop it in your hand the pins are parallel to your palm and spaced away from you hand by the plug insulation (envision it in your mind as it is described). Whether or not a voltage exists on the pin is not usually important, the person holding the plug will not know if the voltage exists there. The large, flat British plug seems to follow the 'perversity of nature' rule and drop 'butter side down' with the pins in the palm of your hand most of the time - thereby providing the shocking experience which is deemed adequate to need mitigation. Hence the test to limit the sensation to that which is acceptable. I remember British colleagues on the committee pressing to have this requirement properly included during standards harmonization discussion in another standard. History has never been a strong interest among most engineers so I'm not surprised that small facts such as this fall away with time. :) br, Pete Peter E Perkins, PE Principal Product Safety Engineer PO Box 23427 Tigard, ORe 97281-3427 503/452-1201 fone/fax p.perk...@ieee.org - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to emc-p...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas emcp...@radiusnorth.net Mike Cantwell mcantw...@ieee.org For policy questions, send mail to: Jim Bacher: j.bac...@ieee.org David Heald: dhe...@gmail.com
Re: [PSES] Capacitor Discharge Test IEC 61010-1 - A little history
In message 34C449781DB0418B8509F64FA4FA3967@Pete97219Compaq, dated Mon, 27 May 2013, Pete Perkins peperkin...@cs.com writes: The large, flat British plug seems to follow the 'perversity of nature' rule and drop 'butter side down' with the pins in the palm of your hand most of the time - thereby providing the shocking experience which is deemed adequate to need mitigation. It needs mitigation because consumers complained about it and often tried to reject the product as 'unsafe'. It's not only our lovely 13 A plug that drops 'butter side down', the Continental Schuko plug and its relatives do it. -- OOO - Own Opinions Only. See www.jmwa.demon.co.uk Why does everything require an odd number of opamps? John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to emc-p...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas emcp...@radiusnorth.net Mike Cantwell mcantw...@ieee.org For policy questions, send mail to: Jim Bacher: j.bac...@ieee.org David Heald: dhe...@gmail.com
Re: [PSES] USB output limitation
All, Regardless of a connector's ampacity, you should always refer to the USB specification and its limits. I cannot vouch for how much current a manufacturer may decide to put on the port, but if they exceed the USB standard, they are outside the spec. Conversely manufacturers sometimes provide dual USB ports, with the available current split between the two. http://www.usb.org/developers/docs/ On a side note, I have seen a number of manufactures push the specs, especially when used as cell phone chargers. They will push the upper tolerance of the voltage spec and make a claim of fast charging. Doug Douglas E Powell http://www.linkedin.com/in/dougp01 -Original Message- From: Ted Eckert ted.eck...@microsoft.com Date: Mon, 27 May 2013 14:59:41 To: EMC-PSTC@LISTSERV.IEEE.ORG Reply-To: Ted Eckert ted.eck...@microsoft.com Subject: Re: [PSES] USB output limitation Hello Bostjan, There are a number of considerations regarding power from standard USB ports. There are USB ports designed to supply power over an additional set of contacts. I would recommend using one of these connector types where you intend to deliver more power than normally supplied by a USB port. The powered USB ports are designed for up to 30W at 5V. http://en.wikipedia.org/wiki/Powered_USB The standard USB connector will typically be designed for a maximum continuous current of 1.5A. Drawing more current through a standard connector may raise temperatures beyond what IEC 60950-1 would allow. The temperatures of the plastics of the connector body may exceed their RTI, or the temperatures of the circuit board supporting the connector might exceed the board's maximum rating. Although the USB standard doesn't limit the size of conductors in USB cables, the specification recommends making cable conductors as small as possible to enhance the flexibility of the cable. If you have a standard USB port, you have no control of what the user connects beyond instructional safeguards. The designers of many USB devices presume a limited current from USB ports. Their designs assume that under fault conditions, the USB port will limit the current enough that a short circuit in their device will not result in overheating or other issues. This could be a problem if such a device experiences a fault when connected to the USB port you propose. Ted Eckert Compliance Engineer Microsoft Corporation ted.eck...@microsoft.com The opinions expressed are my own and do not necessarily reflect those of my employer. -Original Message- From: Boštjan Glavič [mailto:bostjan.gla...@siq.si] Sent: Monday, May 27, 2013 5:30 AM To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: USB output limitation Dear experts, What would be the limit of USB output? I know IEC 60950-1 requires only that it complies with limited power source, but there might be some other requirements to limit power from USB? In particular, I am talking about power supply with USB connector. Can it go up to 5Vd.c./3A? Best regards, Bostjan Glavic SIQ - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to emc-p...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas emcp...@radiusnorth.net Mike Cantwell mcantw...@ieee.org For policy questions, send mail to: Jim Bacher: j.bac...@ieee.org David Heald: dhe...@gmail.com - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to emc-p...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas emcp...@radiusnorth.net Mike Cantwell mcantw...@ieee.org For policy questions, send mail to: Jim Bacher: j.bac...@ieee.org David Heald: dhe...@gmail.com - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion
[PSES] USB charging
http://blog.circuitprotection.com/blognews/the-new-usb-charging-specification-increased-user-experience-in-the-world-of-power-hungry-devices/ Curt - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to emc-p...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas emcp...@radiusnorth.net Mike Cantwell mcantw...@ieee.org For policy questions, send mail to: Jim Bacher: j.bac...@ieee.org David Heald: dhe...@gmail.com
Re: [PSES] USB charging
Nice article. It begs the question, is this the new de facto standard for powering digital appliances? Doug Douglas E Powell http://www.linkedin.com/in/dougp01 -Original Message- From: Curt McNamara mcnam...@umn.edu Date: Mon, 27 May 2013 12:39:08 To: EMC-PSTC@LISTSERV.IEEE.ORG Reply-To: Curt McNamara mcnam...@umn.edu Subject: [PSES] USB charging http://blog.circuitprotection.com/blognews/the-new-usb-charging-specification-increased-user-experience-in-the-world-of-power-hungry-devices/ Curt - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to emc-p...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas emcp...@radiusnorth.net Mike Cantwell mcantw...@ieee.org For policy questions, send mail to: Jim Bacher: j.bac...@ieee.org David Heald: dhe...@gmail.com - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to emc-p...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas emcp...@radiusnorth.net Mike Cantwell mcantw...@ieee.org For policy questions, send mail to: Jim Bacher: j.bac...@ieee.org David Heald: dhe...@gmail.com
Re: [PSES] USB output limitation
The USB specification gives a lower limit, defining the minimum current that must be available. However, it has no upper limit. In addition, the USB specification is written to ensure minimum functionality and interoperability. It does not directly address safety issues. Compliance with the specification means that you will have a product that can be eligible for the USB logo; it does not mean you will comply with IEC 60950-1. Conversely, it is quite possible to have a product that violates the USB specification yet meets all of the IEC 60950-1 requirements. Ted Eckert Compliance Engineer Microsoft Corporation ted.eck...@microsoft.com The opinions expressed are my own and do not necessarily reflect those of my employer. -Original Message- From: doug...@gmail.com [mailto:doug...@gmail.com] Sent: Monday, May 27, 2013 9:58 AM To: Ted Eckert; EMC-PSTC Subject: Re: [PSES] USB output limitation All, Regardless of a connector's ampacity, you should always refer to the USB specification and its limits. I cannot vouch for how much current a manufacturer may decide to put on the port, but if they exceed the USB standard, they are outside the spec. Conversely manufacturers sometimes provide dual USB ports, with the available current split between the two. http://www.usb.org/developers/docs/ On a side note, I have seen a number of manufactures push the specs, especially when used as cell phone chargers. They will push the upper tolerance of the voltage spec and make a claim of fast charging. Doug Douglas E Powell http://www.linkedin.com/in/dougp01 -Original Message- From: Ted Eckert ted.eck...@microsoft.com Date: Mon, 27 May 2013 14:59:41 To: EMC-PSTC@LISTSERV.IEEE.ORG Reply-To: Ted Eckert ted.eck...@microsoft.com Subject: Re: [PSES] USB output limitation Hello Bostjan, There are a number of considerations regarding power from standard USB ports. There are USB ports designed to supply power over an additional set of contacts. I would recommend using one of these connector types where you intend to deliver more power than normally supplied by a USB port. The powered USB ports are designed for up to 30W at 5V. http://en.wikipedia.org/wiki/Powered_USB The standard USB connector will typically be designed for a maximum continuous current of 1.5A. Drawing more current through a standard connector may raise temperatures beyond what IEC 60950-1 would allow. The temperatures of the plastics of the connector body may exceed their RTI, or the temperatures of the circuit board supporting the connector might exceed the board's maximum rating. Although the USB standard doesn't limit the size of conductors in USB cables, the specification recommends making cable conductors as small as possible to enhance the flexibility of the cable. If you have a standard USB port, you have no control of what the user connects beyond instructional safeguards. The designers of many USB devices presume a limited current from USB ports. Their designs assume that under fault conditions, the USB port will limit the current enough that a short circuit in their device will not result in overheating or other issues. This could be a problem if such a device experiences a fault when connected to the USB port you propose. Ted Eckert Compliance Engineer Microsoft Corporation ted.eck...@microsoft.com The opinions expressed are my own and do not necessarily reflect those of my employer. -Original Message- From: Boštjan Glavič [mailto:bostjan.gla...@siq.si] Sent: Monday, May 27, 2013 5:30 AM To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: USB output limitation Dear experts, What would be the limit of USB output? I know IEC 60950-1 requires only that it complies with limited power source, but there might be some other requirements to limit power from USB? In particular, I am talking about power supply with USB connector. Can it go up to 5Vd.c./3A? Best regards, Bostjan Glavic SIQ - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to emc-p...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas emcp...@radiusnorth.net Mike Cantwell mcantw...@ieee.org For policy questions, send mail to: Jim Bacher: j.bac...@ieee.org David Heald: dhe...@gmail.com - This message is from the IEEE Product Safety
Re: [PSES] USB output limitation
I've understood from the USB 2.0 spec quoted below the maximum current provided should be no more than 5A. Has this changed? I've also noted that it isn't hard to find hubs that allow more than 5A to individual ports. Gary Tornquist Director of Product Safety MICROSOFT CONFIDENTIAL: This email message may contain confidential and proprietary information. Any unauthorized use is prohibited. If you are not the intended recipient, please contact the sender by reply email and destroy all copies of the original message. *** 7.2.1.2.1 Over-current Protection The host and all self-powered hubs must implement over-current protection for safety reasons, and the hub must have a way to detect the over-current condition and report it to the USB software. Should the aggregate current drawn by a gang of downstream facing ports exceed a preset value, the over-current protection circuit removes or reduces power from all affected downstream facing ports. The over-current condition is reported through the hub to Host Controller, as described in Section 11.12.5. The preset value cannot exceed 5.0 A and must be sufficiently above the maximum allowable port current such that transient currents (e.g., during power up or dynamic attach or reconfiguration) do not trip the over-current protector. If an over-current condition occurs on any port, subsequent operation of the USB is not guaranteed, and once the condition is removed, it may be necessary to reinitialize the bus as would be done upon power-up. The over-current limiting mechanism must be resettable without user mechanical intervention. Polymeric PTCs and solid-state switches are examples of methods, which can be used for over-current limiting. -Original Message- From: Ted Eckert [mailto:ted.eck...@microsoft.com] Sent: Monday, May 27, 2013 4:43 PM To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] USB output limitation The USB specification gives a lower limit, defining the minimum current that must be available. However, it has no upper limit. In addition, the USB specification is written to ensure minimum functionality and interoperability. It does not directly address safety issues. Compliance with the specification means that you will have a product that can be eligible for the USB logo; it does not mean you will comply with IEC 60950-1. Conversely, it is quite possible to have a product that violates the USB specification yet meets all of the IEC 60950-1 requirements. Ted Eckert Compliance Engineer Microsoft Corporation ted.eck...@microsoft.com The opinions expressed are my own and do not necessarily reflect those of my employer. -Original Message- From: doug...@gmail.com [mailto:doug...@gmail.com] Sent: Monday, May 27, 2013 9:58 AM To: Ted Eckert; EMC-PSTC Subject: Re: [PSES] USB output limitation All, Regardless of a connector's ampacity, you should always refer to the USB specification and its limits. I cannot vouch for how much current a manufacturer may decide to put on the port, but if they exceed the USB standard, they are outside the spec. Conversely manufacturers sometimes provide dual USB ports, with the available current split between the two. http://www.usb.org/developers/docs/ On a side note, I have seen a number of manufactures push the specs, especially when used as cell phone chargers. They will push the upper tolerance of the voltage spec and make a claim of fast charging. Doug Douglas E Powell http://www.linkedin.com/in/dougp01 -Original Message- From: Ted Eckert ted.eck...@microsoft.com Date: Mon, 27 May 2013 14:59:41 To: EMC-PSTC@LISTSERV.IEEE.ORG Reply-To: Ted Eckert ted.eck...@microsoft.com Subject: Re: [PSES] USB output limitation Hello Bostjan, There are a number of considerations regarding power from standard USB ports. There are USB ports designed to supply power over an additional set of contacts. I would recommend using one of these connector types where you intend to deliver more power than normally supplied by a USB port. The powered USB ports are designed for up to 30W at 5V. http://en.wikipedia.org/wiki/Powered_USB The standard USB connector will typically be designed for a maximum continuous current of 1.5A. Drawing more current through a standard connector may raise temperatures beyond what IEC 60950-1 would allow. The temperatures of the plastics of the connector body may exceed their RTI, or the temperatures of the circuit board supporting the connector might exceed the board's maximum rating. Although the USB standard doesn't limit the size of conductors in USB cables, the specification recommends making cable conductors as small as possible to enhance the flexibility of the cable. If you have a standard USB port, you have no control of what the user connects beyond instructional safeguards. The designers of many USB devices presume a limited current from USB ports. Their designs assume that under fault conditions, the
