Any modification done to an existing power unit that bears the label of another company and/or the mark of an accredited lab can result in one or more of following.
1. a fire hazard 2. a shock hazard 3. an unreliable power converter 4. litigation by the OEM for placing a modified unit on the market that bears their company name 5. a unit that no longer meets any 'special' requirements (LPS, LCC, Class 2/3, Class II/III, TNV-x, etc) 6. a unit that no longer meets EMC immunity and/or emissions. It cannot be over-stated that power converters that are depended on for the system's galvanic isolation and/or for providing a safe output voltage or power level should never be modified by anyone other than the original mfr. Brian -----Original Message----- From: Rob Oglesbee [mailto:[email protected]] Sent: Tuesday, December 02, 2014 5:59 AM To: [email protected] Subject: Re: [PSES] Noisy DC / DC converter Amund, Here are a few more generic things you can look at... - RC snubber across diodes (output rectifiers, primary-side snub diode) - Change the gate drive of the switching FET, if discrete, by adding small resistance between the driver and the gate (sometimes a diode is added across the resistor to have different turn on/turn off time). Be careful with this one, it can really nail your efficiency and cause your switch to fail thermally. - RC snubber across the switch. - If you can change the layout, take a look to make sure the main switching path and return are optimized. - Sometimes adding in a little discrete inductance between the switch and the transformer can help (another way to slow the switching edges). - Resonances in the transformer due to parasitics (leakage inductance interwinding capacitances) can be snubbed out with RC's, but that takes a bit more work. Regards, Rob Oglesbee Radian Research (765) 449-5505 This message, and any attachments to it, may contain information that is privileged, confidential, and exempt from disclosure under applicable law. If the reader of this message is not the intended recipient, you are notified that any use, dissemination, distribution, copying, or communication of this message is strictly prohibited. If you have received this message in error, please notify the sender immediately by return e-mail or call 765-449-5500 and delete the message and any attachments. Thank you. -----Original Message----- From: Amund Westin [mailto:[email protected]] Sent: Monday, December 01, 2014 2:48 PM To: [email protected] Subject: [PSES] Noisy DC / DC converter Got a DC / DC converter in an ITE. >From a radiated emission plot, I can see lot of spikes with spacing 330kHz in >the region 30-80MHz. The DC / DC converter datasheet tells that the switching frequency is 330kHz. No suppression components around the converter. I assume a common mode choke could block some on the noise, so it does not enter the power supply cable, which may act as an antenna in this case. Any other "tricks" for EMI suppression of DC / DC converters? #Amund - ---------------------------------------------------------------- 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 <[email protected]> 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://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
