RE: ferrite transient voltage/current response
While I was at Agilent in Spokane, one of the engineers or technicians claimed that he had changed the RF characteristics of a 6-hole ferrite bead (wound with 2 1/2 turns) used on a power supply trace to a noisy assembly. The normal current was about 1 amp, but he accidently shorted the power supply voltage after the inductor. This caused a current spike as the power supply filter capacitor discharged (and then the supply current limited at about 10 amps). After this, there was a problem with RF leakage from the assembly. Replacing the inductor fixed the problem. Apparently the effect was repeatable. I didn't observe this personally, so I can't guarantee it. Don Borowski Schweitzer Engineering Labs Sorry that I wasn't clear; I typically try to keep my questions general so not to get too detailed about the specific application. And thanks to Bob, Chris and Mike who have responded ... putting it into Chris's words ... I was just trying to find out if ferrites had ratings to prevent them from j ust plain blowing the ferrite to smithereens. Also, I was looking for a shortcut if someone else had faced this question rather than reading through all of the vendor web sites. I understand and have used ferrites quite often for typical EMI suppression; the ferrites typically being rated for the application currents, voltages, etc. In this case, the program is trying to protect a power supply input from the DO-160 waveform 5B pin injected lightning pulse of 300 volts open circuit 300A short circuit. If the Gas Discharge Tube is located past (closer to the supply which was done for packaging limitations) than the T EMI filter, a question was raised as to whether the ferrite properties would be altered by the lightning pulse. Most of the standard literature on the use of ferrites does not address these types of transients. Susan Beard Robert Wilson robert_wil...@tirsys.com@majordomo.ieee.org on 06/04/2002 02:16:48 PM Please respond to Robert Wilson robert_wil...@tirsys.com Sent by:owner-emc-p...@majordomo.ieee.org To:shbe...@rockwellcollins.com, emc-p...@ieee.org cc: Subject:RE: ferrite transient voltage/current response Your question is not all that clear. It appears to imply that transients have an affect on the ferrite beads, but it is the other way around (maybe that is what you meant). But in general, small ferrite beads have little effect, except at very high frequencies (hundreds of MHz), unless they are no longer beads (i.e. they are very large). Have a look at the various magnetics vendors data sheets and app notes. Magnetics Inc: www.mag-inc.com Fair-Rite Inc: www.fair-rite.com (whoever came up with THAT name should be shot! Steward Inc: www.steward.com Ferroxcube: www.ferroxcube.com Epcos (was Siemens): www.epcos.com Bob Wilson TIR Systems Ltd. Vancouver. -Original Message- From: shbe...@rockwellcollins.com [mailto:shbe...@rockwellcollins.com] Sent: June 4, 2002 8:57 AM To: emc-p...@ieee.org Subject: ferrite transient voltage/current response Could someone point me to some good App Note information on the response of and affect on ferrite beads to transient voltage current waveforms? The waveforms are based on the indirect lightning pulses specified in Section 22 of DO-160. Thanks in advance, Susan Beard This e-mail may contain SEL confidential information. The opinions expressed are not necessarily those of SEL. Any unauthorized disclosure, distribution or other use is prohibited. If you received this e-mail in error, please notify the sender, permanently delete it, and destroy any printout. Thank you. --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list
RE: ferrite transient voltage/current response
Heat buildup in a ferrite is self-limiting. Once temperature reaches the material's Curie point, it looses its magnetic properties, and heat buildup essentially stops. Mind you, this temperature can be as high as 200°C for some power ferrites, so it may get rather toasty. There is no actual rating as such, that I am aware of because there are far too many variables. Hysteresis heating can be estimated from the usual curves of specific power loss-vs-excitation frequency-vs-flux density that most manufacturers provide for each material. But this only tells you how much heat is being generated due to hysteresis losses. It still won't tell you the heat generated by resistive losses in a lossy type of ferrite (which is what is commonly used for this purpose). It also won't tell you what the thermal resistance of the ferrite is (i.e. how easily it can lose the heat being generated). The latter is sometimes available for ferrite E-E cores (and other transformer shapes), but for small beads, I suspect there is nothing available. Finally, a lot depends on the harmonic content you are hitting the ferrite bead with, and this is obviously impossible for a ferrite manufacturer to know. The answer, I suspect, is to try it. At least, the thing will not blow itself to smithereens, but it might get mighty hot before it hits the self-limiting Curie point. Bob Wilson TIR Systems Ltd. Vancouver. -Original Message- From: shbe...@rockwellcollins.com [mailto:shbe...@rockwellcollins.com] Sent: June 5, 2002 10:09 AM To: emc-p...@ieee.org Subject: RE: ferrite transient voltage/current response Sorry that I wasn't clear; I typically try to keep my questions general so not to get too detailed about the specific application. And thanks to Bob, Chris and Mike who have responded ... putting it into Chris's words ... I was just trying to find out if ferrites had ratings to prevent them from j ust plain blowing the ferrite to smithereens. Also, I was looking for a shortcut if someone else had faced this question rather than reading through all of the vendor web sites. I understand and have used ferrites quite often for typical EMI suppression; the ferrites typically being rated for the application currents, voltages, etc. In this case, the program is trying to protect a power supply input from the DO-160 waveform 5B pin injected lightning pulse of 300 volts open circuit 300A short circuit. If the Gas Discharge Tube is located past (closer to the supply which was done for packaging limitations) than the T EMI filter, a question was raised as to whether the ferrite properties would be altered by the lightning pulse. Most of the standard literature on the use of ferrites does not address these types of transients. Susan Beard Robert Wilson robert_wil...@tirsys.com@majordomo.ieee.org on 06/04/2002 02:16:48 PM Please respond to Robert Wilson robert_wil...@tirsys.com Sent by:owner-emc-p...@majordomo.ieee.org To:shbe...@rockwellcollins.com, emc-p...@ieee.org cc: Subject:RE: ferrite transient voltage/current response Your question is not all that clear. It appears to imply that transients have an affect on the ferrite beads, but it is the other way around (maybe that is what you meant). But in general, small ferrite beads have little effect, except at very high frequencies (hundreds of MHz), unless they are no longer beads (i.e. they are very large). Have a look at the various magnetics vendors data sheets and app notes. Magnetics Inc: www.mag-inc.com Fair-Rite Inc: www.fair-rite.com (whoever came up with THAT name should be shot! Steward Inc: www.steward.com Ferroxcube: www.ferroxcube.com Epcos (was Siemens): www.epcos.com Bob Wilson TIR Systems Ltd. Vancouver. -Original Message- From: shbe...@rockwellcollins.com [mailto:shbe...@rockwellcollins.com] Sent: June 4, 2002 8:57 AM To: emc-p...@ieee.org Subject: ferrite transient voltage/current response Could someone point me to some good App Note information on the response of and affect on ferrite beads to transient voltage current waveforms? The waveforms are based on the indirect lightning pulses specified in Section 22 of DO-160. Thanks in advance, Susan Beard --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list
Re: CCFT Backlight Circuits
Hi Chris: We use similar circuits. The circuit is an inverter powered from SELV. The inverter output is hazardous voltage. Usually, the output is floating, but not always. The output MAY be hazardous energy ONLY IF the SELV is hazardous energy. If the SELV is hazardous energy, the inverter circuit may provide either hazardous energy or non-hazardous energy output. If the SELV is not hazardous energy, then the inverter output is not hazardous energy (applying the conservation of energy theorem). While the output is hazardous voltage, it may not be hazardous current, i.e., it may be a limited current circuit. A limited current circuit is one where the maximum current does not exceed 0.5 mA peak times the frequency in kilohertz. Since you are at 60 kHz, then the maximum current into a 2 kohm resistor is 30 mA peak, under both normal and single-fault conditions. Most faults in the inverter circuit cause it to shut down, so the output is zero, and the circuit qualifies as a limited current circuit. Even if the circuit does not shut down under single- fault conditions, the impedance of the transformer is often so high that the output remains as limited current. The advantage of the limited current circuit is that it is considered the equivalent of SELV, and you do not need Basic, Double, or Reinforced insulation between the circuit and the body of an operator. Also, you do not need an electrical enclosure. If the circuit is not a limited current circuit, then you must apply the rules for Basic, Double, or Reinforced insulation. If the circuit is floating, then any one fault in Basic Insulation will not cause a shock hazard. This creates an interesting conundrum in evaluating the insulation required for protection. The inverter transformer is subject to - normal temperature tests (for Class A insulation); - output short-circuit tests (max temperture or the cheesecloth test). Since the transformer is not an isolating transformer, there is no hi-pot test. As for start-up voltage, you should determine whether the output is limited current during the start-up. If it is, then there are no further requirements. Standards experts are still considering the problem of start-up conditions in general. There are no guide- lines at the moment. All we can say is that if your circuit complies during startup, then there are no further requirements. If you design for safety during startup conditions, then you have an acceptable construction. If you have hazardous conditions during startup, and non-hazardous conditions during run, then you will need to negotiate with your certification house. Some warnings... The HV, HF output easily creates arcs. These arcs can lead to tracking across the surface of insulators, including printed wiring boards, which can then lead to ignition. Test for tracking using a small hand- held screwdrive drawn across the board from the HV trace to a ground or LV trace. Also, while the HV is limited current and is therefore not a shock hazard, the HV and HF combine to arc to the skin. This creates a deep burn that takes a long time to heal. So, stay away from the HV. Enjoy! And best regards, Rich --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list
RE: ferrite transient voltage/current response
Hi Susan, Your response makes it much clearer. Sorry about the Ferrites 101 in my previous response. Hope I didn't insult your intelligence. Now that I see the true nature of your question, I only have one tidbit to offer from experience. In one telecom circuit we had (starting from the connector): A ferrite bead, a 1206 zero ohm resistor (used as a jumper where a current limiting resistor could be placed) a fuse (1.25A, fast acting), a sidactor (across from one line to the other, not to ground). In this application, the ITU K.20 and ITU K.21 lightning pulses blew the 1206 ferrite chips off of the board before the fuses would activate. This also happened to a MOV which we had originally used; that's why we ended up with a sidactor. The ferrite chips were rated for 150mA steady state. I, like you, was unsure of their pulse current capability. I could find no specification for it in the ferrite data sheets.The fact that they disintigrated gave us some idea that they were probably a little under-rated. We replaced them with PREM part number SPG-104 (a multi-turn bead on a lead part with higher current rating). These parts worked. These parts had a steady-state current rating similar to the in-line fuse. Coincidence? Maybe. So, in our caseyes our lightning pulse did alter the properties of the ferrite (and how). I know that you have a different circuit and a different lightning requirement; so take my advice with a grain of salt (as always). I hope that you can find some bit of information there that you can extrapolate to your situation. Chris -Original Message- From: shbe...@rockwellcollins.com [SMTP:shbe...@rockwellcollins.com] Sent: Wednesday, June 05, 2002 1:09 PM To: emc-p...@ieee.org Subject: RE: ferrite transient voltage/current response Sorry that I wasn't clear; I typically try to keep my questions general so not to get too detailed about the specific application. And thanks to Bob, Chris and Mike who have responded ... putting it into Chris's words ... I was just trying to find out if ferrites had ratings to prevent them from j ust plain blowing the ferrite to smithereens. Also, I was looking for a shortcut if someone else had faced this question rather than reading through all of the vendor web sites. I understand and have used ferrites quite often for typical EMI suppression; the ferrites typically being rated for the application currents, voltages, etc. In this case, the program is trying to protect a power supply input from the DO-160 waveform 5B pin injected lightning pulse of 300 volts open circuit 300A short circuit. If the Gas Discharge Tube is located past (closer to the supply which was done for packaging limitations) than the T EMI filter, a question was raised as to whether the ferrite properties would be altered by the lightning pulse. Most of the standard literature on the use of ferrites does not address these types of transients. Susan Beard --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list
RE: ferrite transient voltage/current response
Sorry that I wasn't clear; I typically try to keep my questions general so not to get too detailed about the specific application. And thanks to Bob, Chris and Mike who have responded ... putting it into Chris's words ... I was just trying to find out if ferrites had ratings to prevent them from j ust plain blowing the ferrite to smithereens. Also, I was looking for a shortcut if someone else had faced this question rather than reading through all of the vendor web sites. I understand and have used ferrites quite often for typical EMI suppression; the ferrites typically being rated for the application currents, voltages, etc. In this case, the program is trying to protect a power supply input from the DO-160 waveform 5B pin injected lightning pulse of 300 volts open circuit 300A short circuit. If the Gas Discharge Tube is located past (closer to the supply which was done for packaging limitations) than the T EMI filter, a question was raised as to whether the ferrite properties would be altered by the lightning pulse. Most of the standard literature on the use of ferrites does not address these types of transients. Susan Beard Robert Wilson robert_wil...@tirsys.com@majordomo.ieee.org on 06/04/2002 02:16:48 PM Please respond to Robert Wilson robert_wil...@tirsys.com Sent by:owner-emc-p...@majordomo.ieee.org To:shbe...@rockwellcollins.com, emc-p...@ieee.org cc: Subject:RE: ferrite transient voltage/current response Your question is not all that clear. It appears to imply that transients have an affect on the ferrite beads, but it is the other way around (maybe that is what you meant). But in general, small ferrite beads have little effect, except at very high frequencies (hundreds of MHz), unless they are no longer beads (i.e. they are very large). Have a look at the various magnetics vendors data sheets and app notes. Magnetics Inc: www.mag-inc.com Fair-Rite Inc: www.fair-rite.com (whoever came up with THAT name should be shot! Steward Inc: www.steward.com Ferroxcube: www.ferroxcube.com Epcos (was Siemens): www.epcos.com Bob Wilson TIR Systems Ltd. Vancouver. -Original Message- From: shbe...@rockwellcollins.com [mailto:shbe...@rockwellcollins.com] Sent: June 4, 2002 8:57 AM To: emc-p...@ieee.org Subject: ferrite transient voltage/current response Could someone point me to some good App Note information on the response of and affect on ferrite beads to transient voltage current waveforms? The waveforms are based on the indirect lightning pulses specified in Section 22 of DO-160. Thanks in advance, Susan Beard --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list
CCFT Backlight Circuits
Hi all, Historically, we have made products with CCFT (Cold Cathode Flourescent Tube) Backlight for the Liquid Crystal Displays. These backlight circuits run from SELV, usually 12VDC; and then they create 1000VAC @ 60Khz (typical). These circuits typically use a small transformer with really small gauge secondary wiring (around 40AWG). The voltage is high; but the current capability is about 10mA. For safety testing, I have always submitted specifications for parts within this circuit. I have also always provided color coded artworks of the circuitboard showing the high voltage traces. We have never had a problem with these circuits during safety testing. In a way, that's bad. Why? Because no failures means that I don't have anything to fix and I don't learn how to get the circuit to pass.So, in essence, I don't know why we're passing. We throw the circuit on the board with almost no regard for creepage and clearance. Maybe we've just been getting lucky? That's nice; but it doesn't give me a warm fuzzy about how we design our next CCFT circuit. Specific questions: 1. Are these circuits considered as energy limited? For instance, I know that the lab performs short circuit testing on this circuit; but, since its current capability is so low, nothing ever happens. 2. Should we design to the Creepage and Clearance distances for Double Insulation (our chassis is ungrounded); or do we just need to meet functional insulation requirements. 3. How are the startup transients considered? For instance, our CCFTs run at about 900VAC steady state; but during startup the voltage can climb above 2KV while the tube is warming up. Do we just consider the 900VAC and ignore the transients? Sorry for the rambling nature of this email; but such rambliness typifies my thoughts on this subject; hence my appeal to the group for some insight. Any thoughts are appreciated. Chris Maxwell | Design Engineer - Optical Division email chris.maxw...@nettest.com | dir +1 315 266 5128 | fax +1 315 797 8024 NetTest | 6 Rhoads Drive, Utica, NY 13502 | USA web www.nettest.com | tel +1 315 797 4449 | --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list
Re: Japan mains voltage
Yes, we have experienced similar problems at some sites in Japan. This is one of the reasons why we specify our power supplies (we buy them in) to cover the range from 85 V. Regards, Neil Helsby ** This email and any files transmitted with it are confidential and intended solely for the use of the individual or entity to whom they are addressed. If you have received this email in error please notify the system manager. This footnote also confirms that this email message has been swept by MIMEsweeper for the presence of computer viruses. www.mimesweeper.com ** --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on browse and then emc-pstc mailing list
