This is a haz V, so SFC protection is required, and 2.2.3 provides the limits.
As for back-light power sources, the models I have done were LCC - which was easy to do because of a very hi-Z load, and as previously stated, were buried under thick plastic. Also the units that I submitted had two current interrupt devices between the battery and/or the Class 2 power source. Note that haptic stuff is typically hi-freq, so you are allowed more current per LCC limits. Brian -----Original Message----- From: emc-p...@ieee.org [mailto:emc-p...@ieee.org]On Behalf Of McInturff, Gary Sent: Wednesday, December 15, 2010 9:39 AM To: Bill Owsley; EMC-PSTC@LISTSERV.IEEE.ORG Subject: RE: [PSES] Need help with safety compliance for a low power, 150 volt circuit inside a cell phone Sounds like a touch screen to me, UL is used to those. The isolation I believe comes from the glass properties and the creepage and clearance distances between the closest point of user contact and the Haptics voltages. From: Bill Owsley [mailto:wdows...@yahoo.com] Sent: Tuesday, December 14, 2010 9:42 PM To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: Re: [PSES] Need help with safety compliance for a low power, 150 volt circuit inside a cell phone you could try it like an old Safety engineer from long ago used to do. Get well grounded and grab the circuit - if he could let go... it was ok. Note he always brought along some help. Bill In the event of a national emergency, click on the following links to provide directions to your duly elected mis-representatives. http://www.usa.gov/Contact/Elected.shtml or... https://writerep.house.gov/writerep/welcome.shtml http://www.senate.gov/general/contact_information/senators_cfm.cfm if really desperate... http://www.usa.gov/Contact/Elected.shtml --- On Tue, 12/14/10, Joe Randolph <j...@randolph-telecom.com> wrote: From: Joe Randolph <j...@randolph-telecom.com> Subject: Need help with safety compliance for a low power, 150 volt circuit inside a cell phone To: "Emc-Pstc" <emc-p...@ieee.org> List-Post: emc-pstc@listserv.ieee.org Date: Tuesday, December 14, 2010, 9:18 PM Hello All: I have been asked to suggest a UL/EN 60950 compliance method for a low power, high voltage circuit that resides inside a cell phone. The circuit activates a piezo-electric transducer that physically vibrates the LCD display at about 300 Hz in 30 mS bursts to provide the sensation of a key "click" when the user touches a virtual key on the touch screen. Note that what the user contacts is the physical vibration, not the actual electrical signal that activates the piezo transducer. Following are some general characteristics of the driver circuit for the piezo transducer: * A non-isolated DC/DC converter powered from the 3.7V cell phone battery generates a 150 VDC driver supply that will deliver about 5 mA into a 2K ohm load. * The 300 Hz AC output of the driver will deliver about 4 mA RMS into a 2K ohm load. * Both the 150 VDC supply and the 300 Hz AC output share the same circuit reference node with the rest of the phone circuits. * This circuit reference node is normally floating with respect to earth ground, but it can become grounded through the USB port. I'm pretty familiar with 60950 and the standard compliance methods for the various circuits that appear in ITE equipment. However, this particular circuit does not fit neatly into any of the standard categories. A brute-force compliance analysis would classify this circuit as a hazardous circuit, and would require an isolation barrier between this circuit and any SELV circuits, such as the USB and headset ports on the phone. The voltage is too high to meet the definition of TNV-2, and the current output, while very small, is too high to qualify as a Limited Current Circuit. My sense is that it may be possible to show compliance by using single-fault testing to demonstrate that under fault conditions, all user-accessible points remain within SELV limits. In particular, I'm looking at the wording of clause 2.2.4, "Connection of SELV Circuits to Other Circuits." I have never attempted to apply the method of 2.2.4 to a product, so I'm looking for feedback on whether the method is appropriate for this application. Any other suggestions or insights would be most welcome. It seems to me that this type of situation may come up in other applications that use high voltage at very low currents, such as CCFL backlights, EL backlights, and possibly camera flashes. Thanks, Joe Randolph Telecom Design Consultant Randolph Telecom, Inc. 781-721-2848 (USA) j...@randolph-telecom.com http://www.randolph-telecom.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://product-compliance.oc.ieee.org/ Graphics (in well-used formats), large files, etc. can be posted to that URL. 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