On Thu, 8 Sep 2016 21:04:44 -0500, "Tim Williams" <tiwill@seventransistorlabs.com> wrote:>"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...I did reduce the EMI suceptability of a temperature controller by about 30 dB by adding beads. The thermocouple front-end was rectifying RF. The sensitivity was in narrow RF bands where things resonated, and the beads killed the Q. The product from the competitor, the previous English vendor, could be shut down from across the room with a GR signal generator and a banana-lead antenna. Plus, they had lost the source code and couldn't make any firmware mods. I use theory when it is available and necessary. We design and sell a lot of electronics. Instinct and a little experimenting or simulation are really efficient ways to get creative things done fast... if your instincts are good enough. Tennis players don't do a lot of calculus: they just hit the ball. And we do test everything. Hard. First-article, then production test. We put a lot of effort into automated testing, tester boards and test sets and Python. It's a heap of work, but it pays off. https://dl.dropboxusercontent.com/u/53724080/PCBs/Tester_Boards/D169_Laser_Driver_Test.JPG https://dl.dropboxusercontent.com/u/53724080/PCBs/Tester_Boards/P951_E1.JPG https://dl.dropboxusercontent.com/u/53724080/PCBs/Tester_Boards/Z388_ESM_Test.JPG How do you test your designs?> >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?We took all our Varian/Agilent OEM products through full CE/UL/etc NRTL certifications. We didn't have any EMI problems. We did have to modify some ground lugs and wire colors on the AC inlet side, and change some fuse types. We had to add one internal fuse once, for a small auxiliary power transformer. The VME aerospace and semiconductor fab gear doesn't need certifications. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reducing SMPS noise
Started by ●September 6, 2016
Reply by ●September 9, 20162016-09-09
Reply by ●September 9, 20162016-09-09
On 9/8/2016 8:34 PM, George Herold 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... > Are the beads toroidally wound like the through hole ones.. > and do some they have multiple turns? > > That would be awesome, filter inductorwise.It might, but when you add turns you increase the self capacitance which can act to short the inductor at high frequencies. Also, at parallel resonance it will become a very high impedance. -- Rick C
Reply by ●September 10, 20162016-09-10
"George Herold" <gherold@teachspin.com> wrote in message news:b766d0ad-9641-4adc-8bf6-38733321c275@googlegroups.com...> Tim, 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.What do you get when you saturate a crappy inductor? A crappy piece of wire. :) Not kidding -- Laird has an unusually helpful catalog: http://cdn.lairdtech.com/home/brandworld/files/Catalog_EMI%20Filtering%20&%20RF%20Inductors.pdf e.g. p.18 for the 1206's. Since it's a two-terminal device, you can use Kramers�Kronig to solve for R + jX. It would be handy if they had plotted log(|Z|), so that a 1:1 (inductive or capacitive) slope is apparent. But oh well. In any case, they all start at low |Z| and go up along a nice curve, roughly exponentially (as one should expect for a ~pure inductance, on a semilog plot). Then the curve flattens out (as R dominates), and eventually peaks (pure R), and then it falls off again (capacitive). For example, the LI1206H151R-10 is rated 0.15 ohm DCR and 0.8A. The 0 and 100mA curves are pretty close together (e.g., 100 ohms vs. 92 ohms at 40MHz), which is encouraging. But it's already -3dB at 200mA. And at ratings, it's down to maybe 22 ohms (40MHz), equivalent to about four inches of wire. Clearly, you aren't getting the impedance ("150 ohm @ 100MHz") you thought you were paying for, if you use this anywhere near rated current! The dropoff is considerably worse than X7R caps, with respect to voltage. Though if you want an equally grotesque capacitor, Z5U is certainly very available... And LI1206H151R-10 is one of the best here. Check out the nearby plots. MI1206L501R-10 has the peak frequency rising considerably with bias, and the bandwidth of that peak, falling equally fast. (That's not entirely fair, because the zero-bias FWHM is 170MHz wide, versus maybe 160MHz at rated current. The bandwidth is constant, so the Q is rising proportionally. So much for a lossy inductor!) Look at how sensitive it is: half its value, at just 10% of ratings! Indeed, the saturation depends more on part size, than current rating. If you need a lossy inductor, you're /far, far better off/ constructing one yourself. Not only are you guaranteed the inductance you need, under any condition, but you can design the resistance to be precisely what you need! Related: how much flux does it take to saturate a ferrite bead? Simply: Phi = L * I_sat In turn, for a square pulse, say: Phi = V_pk * t_pw So one of these 1206s that saturates at ~200mA, and has an inductance of maybe 0.52uH (take |Z| at a very low frequency, where R is small and X is dominant -- it looks like an inductor down here!), does so with about 0.1uWb of flux, which is equivalent to, say, a 20ns * 5V pulse. The reason Joerg is fond of using FBs for gate resistors, from time to time, is this: _they're cheap saturable reactors._ The gate driver chip has completed its output swing, just as the FB saturates; upon saturation, a huge gulp of current flows into the gate, causing its voltage to rise quickly; then as the voltage overshoots (only slightly, because saturated inductance is small -- very little energy is stored), it pops out of saturation and dampens the ringing. Meanwhile, the lossiness is back, preventing the transistor from making naughty oscillations. Tim -- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website: http://seventransistorlabs.com
Reply by ●September 10, 20162016-09-10
On Sat, 10 Sep 2016 17:20:42 -0500, "Tim Williams" <tiwill@seventransistorlabs.com> wrote:>"George Herold" <gherold@teachspin.com> wrote in message >news:b766d0ad-9641-4adc-8bf6-38733321c275@googlegroups.com... >> Tim, 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. > >What do you get when you saturate a crappy inductor? > >A crappy piece of wire. :) > >Not kidding -- Laird has an unusually helpful catalog: >http://cdn.lairdtech.com/home/brandworld/files/Catalog_EMI%20Filtering%20&%20RF%20Inductors.pdf >e.g. p.18 for the 1206's. >Several of those parts hold up well at 1 amp, and even 3 amps. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●September 10, 20162016-09-10
On 09/10/2016 06:20 PM, Tim Williams wrote:> > If you need a lossy inductor, you're /far, far better off/ constructing > one yourself.Sometimes. Power supplies are super slow compared with signal nodes, so you don't have to worry too much about the additional capacitance and length of trace (i.e. antenna) due to building up a discrete RLC network. If you're living in that world, great, but many of us aren't. For example, the Murata 0603 beads are super nice for stabilizing microwave transistors in baseband circuits, where they can do some amazing things. Beads are also useful insurance against board turns--you can replace an unneeded bead with a zero ohm jumper just by changing the BOM, and of course those are always useful for debugging since you can isolate circuit blocks by removing them. ;) Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●September 11, 20162016-09-11
"John Larkin" <jjlarkin@highlandtechnology.com> wrote in message news:c649tbdk8tot755c202ioa441fccai26sd@4ax.com...> Several of those parts hold up well at 1 amp, and even 3 amps.Really? I'd love to see the VNA plots. Tim -- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website: http://seventransistorlabs.com
Reply by ●September 11, 20162016-09-11
"Phil Hobbs" <pcdhSpamMeSenseless@electrooptical.net> wrote in message news:fe9caa14-dc46-cd6d-70c8-efafc06fadb1@electrooptical.net...> Sometimes. Power supplies are super slow compared with signal nodes, so > you don't have to worry too much about the additional capacitance and > length of trace (i.e. antenna) due to building up a discrete RLC network. > If you're living in that world, great, but many of us aren't. For example, > the Murata 0603 beads are super nice for stabilizing microwave transistors > in baseband circuits, where they can do some amazing things.Yeah, but you go from "power supply" to "small signal" in one paragraph. You know what I'm talking about, Phil, and I know you know better than to equate them. The whole point, that I've apparently been a complete and utter failure at communicating, over the last four posts, is that power supplies are "large signal" and small signals aren't! People can't even read, and this is a text-only forum... sigh.> Beads are also useful insurance against board turns--you can replace an > unneeded bead with a zero ohm jumper just by changing the BOM, and of > course those are always useful for debugging since you can isolate circuit > blocks by removing them. ;)Let's just put in extra tee and pi networks of DNPs and 0-ohms on every trace ever. You'll never have to rev the board again, hell, you can use the same board for a hundred other designs just with assembly variants. ;) I try to avoid jumpers and terminators, if I can. It clutters the design, which causes real delays in layout, for customers who request 100% nodal coverage. Which is often. They have their place, but not every friggin' pin needs it. Use them prudently, not pervasively. Tim -- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website: http://seventransistorlabs.com
Reply by ●September 11, 20162016-09-11
On 09/10/2016 11:47 PM, Tim Williams wrote:> "Phil Hobbs" <pcdhSpamMeSenseless@electrooptical.net> wrote in message > news:fe9caa14-dc46-cd6d-70c8-efafc06fadb1@electrooptical.net... >> Sometimes. Power supplies are super slow compared with signal nodes, >> so you don't have to worry too much about the additional capacitance >> and length of trace (i.e. antenna) due to building up a discrete RLC >> network. If you're living in that world, great, but many of us aren't. >> For example, the Murata 0603 beads are super nice for stabilizing >> microwave transistors in baseband circuits, where they can do some >> amazing things. > > Yeah, but you go from "power supply" to "small signal" in one paragraph. > You know what I'm talking about, Phil, and I know you know better than > to equate them. > > The whole point, that I've apparently been a complete and utter failure > at communicating, over the last four posts, is that power supplies are > "large signal" and small signals aren't!Sure thing--I was agreeing with you about power supply filters, where you do have the luxury of slowness.> People can't even read, and this is a text-only forum... sigh. > > >> Beads are also useful insurance against board turns--you can replace >> an unneeded bead with a zero ohm jumper just by changing the BOM, and >> of course those are always useful for debugging since you can isolate >> circuit blocks by removing them. ;) > > Let's just put in extra tee and pi networks of DNPs and 0-ohms on every > trace ever. You'll never have to rev the board again, hell, you can use > the same board for a hundred other designs just with assembly variants. ;) > > I try to avoid jumpers and terminators, if I can. It clutters the > design, which causes real delays in layout, for customers who request > 100% nodal coverage. Which is often. They have their place, but not > every friggin' pin needs it. Use them prudently, not pervasively.Sure. I usually put a space for one in the base of every transistor whose f_T > 2 GHz, and add places for extra filter components at the power entry, even though I may not need them. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●September 11, 20162016-09-11
On Sun, 11 Sep 2016 14:26:51 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>On 09/10/2016 11:47 PM, Tim Williams wrote: >> "Phil Hobbs" <pcdhSpamMeSenseless@electrooptical.net> wrote in message >> news:fe9caa14-dc46-cd6d-70c8-efafc06fadb1@electrooptical.net... >>> Sometimes. Power supplies are super slow compared with signal nodes, >>> so you don't have to worry too much about the additional capacitance >>> and length of trace (i.e. antenna) due to building up a discrete RLC >>> network. If you're living in that world, great, but many of us aren't. >>> For example, the Murata 0603 beads are super nice for stabilizing >>> microwave transistors in baseband circuits, where they can do some >>> amazing things. >> >> Yeah, but you go from "power supply" to "small signal" in one paragraph. >> You know what I'm talking about, Phil, and I know you know better than >> to equate them. >> >> The whole point, that I've apparently been a complete and utter failure >> at communicating, over the last four posts, is that power supplies are >> "large signal" and small signals aren't! > >Sure thing--I was agreeing with you about power supply filters, where >you do have the luxury of slowness. > > >> People can't even read, and this is a text-only forum... sigh. >> >> >>> Beads are also useful insurance against board turns--you can replace >>> an unneeded bead with a zero ohm jumper just by changing the BOM, and >>> of course those are always useful for debugging since you can isolate >>> circuit blocks by removing them. ;) >> >> Let's just put in extra tee and pi networks of DNPs and 0-ohms on every >> trace ever. You'll never have to rev the board again, hell, you can use >> the same board for a hundred other designs just with assembly variants. ;) >> >> I try to avoid jumpers and terminators, if I can. It clutters the >> design, which causes real delays in layout, for customers who request >> 100% nodal coverage. Which is often. They have their place, but not >> every friggin' pin needs it. Use them prudently, not pervasively. > >Sure. I usually put a space for one in the base of every transistor >whose f_T > 2 GHz, and add places for extra filter components at the >power entry, even though I may not need them. > >Cheers > >Phil HobbsI just did a diff pair of BFQ18's driving a diff pair of BFQ149's driving, well, more stuff. I was shocked that everything just worked... no oscillations, no weirdness. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●September 11, 20162016-09-11
On 09/11/2016 04:31 PM, John Larkin wrote:> On Sun, 11 Sep 2016 14:26:51 -0400, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> On 09/10/2016 11:47 PM, Tim Williams wrote: >>> "Phil Hobbs" <pcdhSpamMeSenseless@electrooptical.net> wrote in message >>> news:fe9caa14-dc46-cd6d-70c8-efafc06fadb1@electrooptical.net... >>>> Sometimes. Power supplies are super slow compared with signal nodes, >>>> so you don't have to worry too much about the additional capacitance >>>> and length of trace (i.e. antenna) due to building up a discrete RLC >>>> network. If you're living in that world, great, but many of us aren't. >>>> For example, the Murata 0603 beads are super nice for stabilizing >>>> microwave transistors in baseband circuits, where they can do some >>>> amazing things. >>> >>> Yeah, but you go from "power supply" to "small signal" in one paragraph. >>> You know what I'm talking about, Phil, and I know you know better than >>> to equate them. >>> >>> The whole point, that I've apparently been a complete and utter failure >>> at communicating, over the last four posts, is that power supplies are >>> "large signal" and small signals aren't! >> >> Sure thing--I was agreeing with you about power supply filters, where >> you do have the luxury of slowness. >> >> >>> People can't even read, and this is a text-only forum... sigh. >>> >>> >>>> Beads are also useful insurance against board turns--you can replace >>>> an unneeded bead with a zero ohm jumper just by changing the BOM, and >>>> of course those are always useful for debugging since you can isolate >>>> circuit blocks by removing them. ;) >>> >>> Let's just put in extra tee and pi networks of DNPs and 0-ohms on every >>> trace ever. You'll never have to rev the board again, hell, you can use >>> the same board for a hundred other designs just with assembly variants. ;) >>> >>> I try to avoid jumpers and terminators, if I can. It clutters the >>> design, which causes real delays in layout, for customers who request >>> 100% nodal coverage. Which is often. They have their place, but not >>> every friggin' pin needs it. Use them prudently, not pervasively. >> >> Sure. I usually put a space for one in the base of every transistor >> whose f_T > 2 GHz, and add places for extra filter components at the >> power entry, even though I may not need them. >> >> Cheers >> >> Phil Hobbs > > > I just did a diff pair of BFQ18's driving a diff pair of BFQ149's > driving, well, more stuff. I was shocked that everything just > worked... no oscillations, no weirdness.Interesting. Why cascade two pairs of 1-W-class transistors? Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
