Den torsdag den 8. september 2016 kl. 21.30.53 UTC+2 skrev John Larkin:> On 08 Sep 2016 10:29:39 GMT, Allan Herriman > <allanherriman@hotmail.com> wrote: > > >On Wed, 07 Sep 2016 20:53:51 -0700, John Larkin wrote: > > > >> On Wed, 7 Sep 2016 21:12:42 -0500, "Tim Williams" > >> <tiwill@seventransistorlabs.com> wrote: > >> > >>>"John Larkin" <jjlarkin@highlandtechnology.com> wrote in message > >>>news:gp11tbt58a7n4hjd8gc3kglcugqf7pgnah@4ax.com... > >>>> The convention is Z at 100 MHz. That bead has a low-frequency > >>>> inductance of a few uH. > >>> > >>>Unfortunately it saturates by 20-50mA or thereabouts (a few 100s mA for > >>>the biggest multilayer beads), so it's useless for power applications. > >> > >> We have some 1206 power beads in stock. The chunkiest one is 33 ohms, > >> 6 amps. > > > > > >I'm going to bet that 6A is the thermal rating, not the saturation > >current. > > > > > >Allan > > The data sheet doesn't say anything about saturation. We used it to > reduce EMI hazards in the drive to an NMR sample heater. Beads work on > RFI the same sort of way that garlic keeps vampires away. >https://youtu.be/xSVqLHghLpw
Reducing SMPS noise
Started by ●September 6, 2016
Reply by ●September 8, 20162016-09-08
Reply by ●September 8, 20162016-09-08
On Thu, 8 Sep 2016 12:33:22 -0700 (PDT), Lasse Langwadt Christensen <langwadt@fonz.dk> wrote:>Den torsdag den 8. september 2016 kl. 21.30.53 UTC+2 skrev John Larkin: >> On 08 Sep 2016 10:29:39 GMT, Allan Herriman >> <allanherriman@hotmail.com> wrote: >> >> >On Wed, 07 Sep 2016 20:53:51 -0700, John Larkin wrote: >> > >> >> On Wed, 7 Sep 2016 21:12:42 -0500, "Tim Williams" >> >> <tiwill@seventransistorlabs.com> wrote: >> >> >> >>>"John Larkin" <jjlarkin@highlandtechnology.com> wrote in message >> >>>news:gp11tbt58a7n4hjd8gc3kglcugqf7pgnah@4ax.com... >> >>>> The convention is Z at 100 MHz. That bead has a low-frequency >> >>>> inductance of a few uH. >> >>> >> >>>Unfortunately it saturates by 20-50mA or thereabouts (a few 100s mA for >> >>>the biggest multilayer beads), so it's useless for power applications. >> >> >> >> We have some 1206 power beads in stock. The chunkiest one is 33 ohms, >> >> 6 amps. >> > >> > >> >I'm going to bet that 6A is the thermal rating, not the saturation >> >current. >> > >> > >> >Allan >> >> The data sheet doesn't say anything about saturation. We used it to >> reduce EMI hazards in the drive to an NMR sample heater. Beads work on >> RFI the same sort of way that garlic keeps vampires away. >> > >https://youtu.be/xSVqLHghLpwExactly. FBs do sometimes kill resonances in PCB traces and cables and such. They are cheap, so why not? -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●September 8, 20162016-09-08
On Thursday, September 8, 2016 at 12:05:12 AM UTC-4, John Larkin wrote:> On Wed, 7 Sep 2016 18:40:14 -0700 (PDT), George Herold > <gherold@teachspin.com> wrote: > > >On Wednesday, September 7, 2016 at 5:34:44 PM UTC-4, John Larkin wrote: > >> On Wed, 7 Sep 2016 05:35:23 -0700 (PDT), George Herold > >> <gherold@teachspin.com> wrote: > >> > >> >On Tuesday, September 6, 2016 at 4:11:46 PM UTC-4, John Larkin wrote: > >> >> On Tue, 6 Sep 2016 09:46:13 -0700 (PDT), hondgm@yahoo.com wrote: > >> >> > >> >> >I'm working on a PCB that contains nearly 30 resistors in a ladder configuration, each step switched in or out by a SMT solid state relay. It's essentially a decade box for a specific application. The relays are controlled by a micro and all is powered by a boardmount enclosed CUI AC/DC switching converter, supplying up to 400mA. > >> >> > > >> >> >The resistors are electrically isolated from the SMPS, however I see a lot of noise on the resistance output that can be from nothing other than the SMPS. I'm assuming the power planes on the board are inducing all kinds of noise into the traces that connect the resistors and solid state relays. > >> >> > > >> >> >Replacing the SMPS with a linear would be ideal, but the amount of space required is a big problem. So I'm looking at filtering the output of the SMPS. I'm a digital and DC analog guy, so this switching noise scares me. Some research and an educated guess tells me to try an LC filter on the SMPS output. I'm looking for any first hand experience with this and dumbed-down advice that will hopefully get me a solution without days of headaches. > >> >> > > >> >> >The SMPS claims a 100kHz switching frequency, and spikes on the scope confirm that. I've already tried putting several MLCC 1uF caps across the SMPS output but that didn't change anything. > >> >> > >> >> If the noise is in-plain-sight conducted, adding a ferrite bead, or a > >> >> small inductor, and a cap, can help a lot. I just tried that this > >> >> morning. > >> >> > >> >> https://dl.dropboxusercontent.com/u/53724080/Parts/VREGS/CUI_P7805.zip > >> > > >> >What's 600 ohms on the FB. Is that it's impedance at 10 or 100 MHz? > >> > >> The convention is Z at 100 MHz. That bead has a low-frequency > >> inductance of a few uH. > >Thanks, is a bead better than an inductor?.. lower Q or something. > >(I always worry about making a low pass with a high Q. Resistors > >are safer that way.) > > Ferrite beads are low-Q by design. Still, the inductance would > resonate with a biggish cap at low frequencies. > > LT Spice includes a bunch of Wurth bead models, for playing with.Huh OK. I should just download a spec sheet...but... Are the beads toroidally wound like the through hole ones.. and do some they have multiple turns? That would be awesome, filter inductorwise. George H.> > > > >> > >> > >> > > >> >I figured out yesterday how to do the ground for a board with multiple > >> >CUI smps's. Shunting everyone's noise to ground, made the local gnd > >> >"bad". A star gnd should work but I want to test that today. > >> > >> One can cut a ground peninsula out of the PCB ground plane and locate > >> things such as to keep switcher ground loop currents out of the rest > >> of the board. > >OK I could try that... I've got 5 supplies, five peninsula's looks > >like a star. :^) > > > >The HF crud in my lab seems to get nothing but worse. > >~20 mV @ ~100 MHz. (with a 60 MHz 'scope, x1 probe) I made a little > >pomona box LP filter to stick on 'scope. A little active > >box with some gain would be nice. > > We're in a wooden building in plain sight of this: > > https://dl.dropboxusercontent.com/u/53724080/SF/Sutrotower1.jpg > > so we are sort of an EMI horror lab. > > > -- > > John Larkin Highland Technology, Inc > > lunatic fringe electronics
Reply by ●September 8, 20162016-09-08
On Thu, 8 Sep 2016 17:34:16 -0700 (PDT), George Herold <gherold@teachspin.com> wrote:>On Thursday, September 8, 2016 at 12:05:12 AM UTC-4, John Larkin wrote: >> On Wed, 7 Sep 2016 18:40:14 -0700 (PDT), George Herold >> <gherold@teachspin.com> wrote: >> >> >On Wednesday, September 7, 2016 at 5:34:44 PM UTC-4, John Larkin wrote: >> >> On Wed, 7 Sep 2016 05:35:23 -0700 (PDT), George Herold >> >> <gherold@teachspin.com> wrote: >> >> >> >> >On Tuesday, September 6, 2016 at 4:11:46 PM UTC-4, John Larkin wrote: >> >> >> On Tue, 6 Sep 2016 09:46:13 -0700 (PDT), hondgm@yahoo.com wrote: >> >> >> >> >> >> >I'm working on a PCB that contains nearly 30 resistors in a ladder configuration, each step switched in or out by a SMT solid state relay. It's essentially a decade box for a specific application. The relays are controlled by a micro and all is powered by a boardmount enclosed CUI AC/DC switching converter, supplying up to 400mA. >> >> >> > >> >> >> >The resistors are electrically isolated from the SMPS, however I see a lot of noise on the resistance output that can be from nothing other than the SMPS. I'm assuming the power planes on the board are inducing all kinds of noise into the traces that connect the resistors and solid state relays. >> >> >> > >> >> >> >Replacing the SMPS with a linear would be ideal, but the amount of space required is a big problem. So I'm looking at filtering the output of the SMPS. I'm a digital and DC analog guy, so this switching noise scares me. Some research and an educated guess tells me to try an LC filter on the SMPS output. I'm looking for any first hand experience with this and dumbed-down advice that will hopefully get me a solution without days of headaches. >> >> >> > >> >> >> >The SMPS claims a 100kHz switching frequency, and spikes on the scope confirm that. I've already tried putting several MLCC 1uF caps across the SMPS output but that didn't change anything. >> >> >> >> >> >> If the noise is in-plain-sight conducted, adding a ferrite bead, or a >> >> >> small inductor, and a cap, can help a lot. I just tried that this >> >> >> morning. >> >> >> >> >> >> https://dl.dropboxusercontent.com/u/53724080/Parts/VREGS/CUI_P7805.zip >> >> > >> >> >What's 600 ohms on the FB. Is that it's impedance at 10 or 100 MHz? >> >> >> >> The convention is Z at 100 MHz. That bead has a low-frequency >> >> inductance of a few uH. >> >Thanks, is a bead better than an inductor?.. lower Q or something. >> >(I always worry about making a low pass with a high Q. Resistors >> >are safer that way.) >> >> Ferrite beads are low-Q by design. Still, the inductance would >> resonate with a biggish cap at low frequencies. >> >> LT Spice includes a bunch of Wurth bead models, for playing with. > >Huh OK. I should just download a spec sheet...but...Few bead spec sheets mention inductance, although you can usually estimate it from the Z/F curves. The LT Spice models include the baseline L.>Are the beads toroidally wound like the through hole ones.. >and do some they have multiple turns?Most are some sort of planar ferrite brick, surface mount. I don't know what's inside. They cost a few cents, so they must be bulk manufactured. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●September 8, 20162016-09-08
On Wed, 7 Sep 2016 21:12:42 -0500, "Tim Williams" <tiwill@seventransistorlabs.com> wrote:>"John Larkin" <jjlarkin@highlandtechnology.com> wrote in message >news:gp11tbt58a7n4hjd8gc3kglcugqf7pgnah@4ax.com... >> The convention is Z at 100 MHz. That bead has a low-frequency >> inductance of a few uH. > >Unfortunately it saturates by 20-50mA or thereabouts (a few 100s mA for the >biggest multilayer beads), so it's useless for power applications. > >A ferrite bead that's rated for DC bias is called an inductor. Yes, they do >actually make that distinction. Even though the ferrite bead technically >has higher quality material (high purity = high mu), and they're both >inductive components.Huh? The Murata BLMxxPG series is rated for power applications. Some of the 0603s are rated for up to 3A. http://search.murata.co.jp/Ceramy/image/img/PDF/ENG/L0110S0100BLM18P.pdf> >Inductors have higher Q, so you usually need to dampen the filter resonance >with an R+C. (Or something with ESR, like tantalum, but really, who puts >tants on supply rails? Use a ceramic plus resistor for goodness sake.) > >Tim
Reply by ●September 8, 20162016-09-08
On Thursday, September 8, 2016 at 8:55:36 PM UTC-4, John Larkin wrote:> On Thu, 8 Sep 2016 17:34:16 -0700 (PDT), George Herold > <gherold@teachspin.com> wrote: > > >On Thursday, September 8, 2016 at 12:05:12 AM UTC-4, John Larkin wrote: > >> On Wed, 7 Sep 2016 18:40:14 -0700 (PDT), George Herold > >> <gherold@teachspin.com> wrote: > >> > >> >On Wednesday, September 7, 2016 at 5:34:44 PM UTC-4, John Larkin wrote: > >> >> On Wed, 7 Sep 2016 05:35:23 -0700 (PDT), George Herold > >> >> <gherold@teachspin.com> wrote: > >> >> > >> >> >On Tuesday, September 6, 2016 at 4:11:46 PM UTC-4, John Larkin wrote: > >> >> >> On Tue, 6 Sep 2016 09:46:13 -0700 (PDT), hondgm@yahoo.com wrote: > >> >> >> > >> >> >> >I'm working on a PCB that contains nearly 30 resistors in a ladder configuration, each step switched in or out by a SMT solid state relay. It's essentially a decade box for a specific application. The relays are controlled by a micro and all is powered by a boardmount enclosed CUI AC/DC switching converter, supplying up to 400mA. > >> >> >> > > >> >> >> >The resistors are electrically isolated from the SMPS, however I see a lot of noise on the resistance output that can be from nothing other than the SMPS. I'm assuming the power planes on the board are inducing all kinds of noise into the traces that connect the resistors and solid state relays. > >> >> >> > > >> >> >> >Replacing the SMPS with a linear would be ideal, but the amount of space required is a big problem. So I'm looking at filtering the output of the SMPS. I'm a digital and DC analog guy, so this switching noise scares me. Some research and an educated guess tells me to try an LC filter on the SMPS output. I'm looking for any first hand experience with this and dumbed-down advice that will hopefully get me a solution without days of headaches. > >> >> >> > > >> >> >> >The SMPS claims a 100kHz switching frequency, and spikes on the scope confirm that. I've already tried putting several MLCC 1uF caps across the SMPS output but that didn't change anything. > >> >> >> > >> >> >> If the noise is in-plain-sight conducted, adding a ferrite bead, or a > >> >> >> small inductor, and a cap, can help a lot. I just tried that this > >> >> >> morning. > >> >> >> > >> >> >> https://dl.dropboxusercontent.com/u/53724080/Parts/VREGS/CUI_P7805.zip > >> >> > > >> >> >What's 600 ohms on the FB. Is that it's impedance at 10 or 100 MHz? > >> >> > >> >> The convention is Z at 100 MHz. That bead has a low-frequency > >> >> inductance of a few uH. > >> >Thanks, is a bead better than an inductor?.. lower Q or something. > >> >(I always worry about making a low pass with a high Q. Resistors > >> >are safer that way.) > >> > >> Ferrite beads are low-Q by design. Still, the inductance would > >> resonate with a biggish cap at low frequencies. > >> > >> LT Spice includes a bunch of Wurth bead models, for playing with. > > > >Huh OK. I should just download a spec sheet...but... > > Few bead spec sheets mention inductance, although you can usually > estimate it from the Z/F curves. The LT Spice models include the > baseline L. > > > >Are the beads toroidally wound like the through hole ones.. > >and do some they have multiple turns? > > Most are some sort of planar ferrite brick, surface mount. I don't > know what's inside. They cost a few cents, so they must be bulk > manufactured.Have you (or anyone here) ground one down and looked at the cross-section? You could lay down stripes of metal in the ferrite, you'd then need some edge metalization to connect 'em. George H.> > > -- > > John Larkin Highland Technology, Inc > picosecond timing precision measurement > > jlarkin att highlandtechnology dott com > http://www.highlandtechnology.com
Reply by ●September 8, 20162016-09-08
"John Larkin" <jjlarkin@highlandtechnology.com> wrote in message news:lse3tb1nbk45712s587v85la91h3jj6bu3@4ax.com...> The data sheet doesn't say anything about saturation. We used it to > reduce EMI hazards in the drive to an NMR sample heater. Beads work on > RFI the same sort of way that garlic keeps vampires away.Larkin once again affirming his design process involves neither theoretical design, nor quantitative testing... See Fig.8: http://www.digikey.com/Web%20Export/Supplier%20Content/TDK_445/PDF/TDK_InCompliance_Aug2010.pdf It's rare to actually find such a graph in a datasheet. Most of the time, they're hidden away in the manufacturer's database tool (i.e. TDK SEAT 2013). When's the last time you had a product pass emissions tests, first time in the lab, zero mods? When's the last time you had a product tested in a lab? Tim -- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website: http://seventransistorlabs.com
Reply by ●September 8, 20162016-09-08
"krw" <krw@somewhere.com> wrote in message news:dv14tbdt8on30bl8ldg72kkd47ohjoiop7@4ax.com...> Huh? The Murata BLMxxPG series is rated for power applications. Some > of the 0603s are rated for up to 3A. > > http://search.murata.co.jp/Ceramy/image/img/PDF/ENG/L0110S0100BLM18P.pdfShow me where it says those impedance curves are valid at Idc = 3.0A. You can't. Some of Murata's parts have DC ratings (or they did, back when their data was accessible in an offline application), but the saturation is dismal. Tim -- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website: http://seventransistorlabs.com
Reply by ●September 8, 20162016-09-08
On Thu, 8 Sep 2016 21:07:05 -0500, "Tim Williams" <tiwill@seventransistorlabs.com> wrote:>"krw" <krw@somewhere.com> wrote in message >news:dv14tbdt8on30bl8ldg72kkd47ohjoiop7@4ax.com... >> Huh? The Murata BLMxxPG series is rated for power applications. Some >> of the 0603s are rated for up to 3A. >> >> http://search.murata.co.jp/Ceramy/image/img/PDF/ENG/L0110S0100BLM18P.pdf > >Show me where it says those impedance curves are valid at Idc = 3.0A. > >You can't.They certainly work.> >Some of Murata's parts have DC ratings (or they did, back when their data >was accessible in an offline application), but the saturation is dismal.They work fine as ferrites (frequency dependent resistors, really). I certainly don't use them as inductors.
Reply by ●September 9, 20162016-09-09
On Thursday, September 8, 2016 at 10:07:06 PM UTC-4, Tim Williams wrote:> "krw" <krw@somewhere.com> wrote in message > news:dv14tbdt8on30bl8ldg72kkd47ohjoiop7@4ax.com... > > Huh? The Murata BLMxxPG series is rated for power applications. Some > > of the 0603s are rated for up to 3A. > > > > http://search.murata.co.jp/Ceramy/image/img/PDF/ENG/L0110S0100BLM18P.pdf > > Show me where it says those impedance curves are valid at Idc = 3.0A. > > You can't. > > Some of Murata's parts have DC ratings (or they did, back when their data > was accessible in an offline application), but the saturation is dismal. > > Tim > > -- > Seven Transistor Labs, LLC > Electrical Engineering Consultation and Contract Design > Website: http://seventransistorlabs.comTim, I know next to nothing about the details of magnetic materials. (It might be a fun field to study.) But obviously a low Q means energy loss somewhere. I've got two knobs hysteresis and saturation to play with, so I don't see how it can be anything but a crappy inductor. But good for the task, like high k ceramic caps. George h.
