On 17/02/2018 07:18, bloggs.fredbloggs.fred@gmail.com wrote:> On Friday, February 16, 2018 at 12:51:24 PM UTC-5, John Larkin wrote: >> On Fri, 16 Feb 2018 08:57:05 -0800 (PST), >> bloggs.fredbloggs.fred@gmail.com wrote: >> >>> On Thursday, February 15, 2018 at 8:32:35 PM UTC-5, John Larkin wrote: >>>> LM317's like some ESR in their output capacitors. I don't want any >>>> electrolytic or tantalum caps in my new thing, just ceramics, and the >>>> sim sure rings: >>>> >>>> https://www.dropbox.com/s/11b3w42nsvpliki/317_nocomp.jpg?raw=1 >>>> >>>> But this fixes it: >>>> >>>> https://www.dropbox.com/s/9q80heyfbwh5frp/317_comp.jpg?raw=1 >>>> >>>> This ain't rocket science, but I haven't seen it done before. >>> >>> 317 needs no such ESR compensation. >> >> The data sheet says it does. >> >>> The ringing looks suspiciously like excitation of the SRF of an output capacitor. >> >> The frequency is low, and is different on the rising and falling edges >> of the load current pulse. It's the chip pseudo-inductance resonating, >> not the cap's ESL. If the ringing were local to the caps, my damping >> on ADJ wouldn't fix that. >> >> Cap series L makes a different waveform than paralleled inductance. >> >> >>> Did your model give it any ESL? And your solution merely reduces the shunt resistance by a factor of 20x which probably has more to do with damping than anything else. >> >> With a big cap from ADJ to ground, it rings badly, too. It has to be >> the *right* capacitor to damp the ringing. >> >> I tried this with two different LM317 models; the ringing is somewhat >> different (the LT317 is better), but the damping idea is the same. >> >> It's amazing that LT ever made a 317. I think they did that early on, >> when they needed some revenue. They want $4 for it! I'm paying less >> than a tenth of that for TI. > > I doubt you're going to see this energetic resonance on anything other than the LT part. >I doubted it too, but found out the hard way when: my 337's all oscillated, and the 317s rang so badly that the oscillation ripple on the positive rails was even bigger than on the negative rails. The 317s wouldn't oscillate by themselves, but they would ring like a bell even after I cured the 337's of oscillation. I had to scratch off a lot of solder mask and tack on many tantalums to cure my boards. Quite embarassing.
LM317 compensation
Started by ●February 15, 2018
Reply by ●February 18, 20182018-02-18
Reply by ●February 18, 20182018-02-18
On Mon, 19 Feb 2018 00:08:55 +1100, Chris Jones <lugnut808@spam.yahoo.com> wrote:>On 16/02/2018 17:47, David Eather wrote: >> On Fri, 16 Feb 2018 14:46:33 +1000, John Larkin >> <jjlarkin@highlandtechnology.com> wrote: >> >>> On Thu, 15 Feb 2018 22:31:09 -0500, bitrex >>> <bitrex@de.lete.earthlink.net> wrote: >>> >>>> On 02/15/2018 08:32 PM, John Larkin wrote: >>>>> >>>>> >>>>> LM317's like some ESR in their output capacitors. I don't want any >>>>> electrolytic or tantalum caps in my new thing, just ceramics, and the >>>>> sim sure rings: >>>>> >>>>> https://www.dropbox.com/s/11b3w42nsvpliki/317_nocomp.jpg?raw=1 >>>>> >>>>> But this fixes it: >>>>> >>>>> https://www.dropbox.com/s/9q80heyfbwh5frp/317_comp.jpg?raw=1 >>>>> >>>>> This ain't rocket science, but I haven't seen it done before. >>>>> >>>>> >>>> >>>> Straight Darlington output emitter follower voltage regulators are meh, >>>> maybe relics of when you couldn't make a decent high beta PNP on a chip >>> >>> I'm regulating +48 down to to +30, which few LDOs will do, and I have >>> the 317's in stock. >>> >>> I thought this was a cute trick, but everybody's a critic. >>> >>> >> >> >> I have never heard of a 317 ringing in a properly designed real >> application. Anyone seen it? >> > >Yes, a 317 will ring with ceramic output capacitors, and a 337 will even >oscillate with ceramic output capacitors. (Unless you mean by "properly >designed" that it doesn't ring, in which case of course not.) > >Can be cured with big tantalums on the output, or series resistors >between the regulator and output capacitors. > >I guess this problem has not been well known in the past because in the >past it was very expensive to buy ceramic capacitors with high enough >values to replace the electrolytic output capacitor.The other problem is that a minority of data sheets quantlfy cap ESR requirements and effects, and many don't mention it at all, especially older ones. I derate tantalums 3:1 on voltage if they are on a bus with significant current capability. That's not practical on a high-current 30 volt rail. -- John Larkin Highland Technology, Inc trk jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●February 18, 20182018-02-18
On Mon, 19 Feb 2018 00:14:26 +1100, Chris Jones <lugnut808@spam.yahoo.com> wrote:>On 17/02/2018 07:18, bloggs.fredbloggs.fred@gmail.com wrote: >> On Friday, February 16, 2018 at 12:51:24 PM UTC-5, John Larkin wrote: >>> On Fri, 16 Feb 2018 08:57:05 -0800 (PST), >>> bloggs.fredbloggs.fred@gmail.com wrote: >>> >>>> On Thursday, February 15, 2018 at 8:32:35 PM UTC-5, John Larkin wrote: >>>>> LM317's like some ESR in their output capacitors. I don't want any >>>>> electrolytic or tantalum caps in my new thing, just ceramics, and the >>>>> sim sure rings: >>>>> >>>>> https://www.dropbox.com/s/11b3w42nsvpliki/317_nocomp.jpg?raw=1 >>>>> >>>>> But this fixes it: >>>>> >>>>> https://www.dropbox.com/s/9q80heyfbwh5frp/317_comp.jpg?raw=1 >>>>> >>>>> This ain't rocket science, but I haven't seen it done before. >>>> >>>> 317 needs no such ESR compensation. >>> >>> The data sheet says it does. >>> >>>> The ringing looks suspiciously like excitation of the SRF of an output capacitor. >>> >>> The frequency is low, and is different on the rising and falling edges >>> of the load current pulse. It's the chip pseudo-inductance resonating, >>> not the cap's ESL. If the ringing were local to the caps, my damping >>> on ADJ wouldn't fix that. >>> >>> Cap series L makes a different waveform than paralleled inductance. >>> >>> >>>> Did your model give it any ESL? And your solution merely reduces the shunt resistance by a factor of 20x which probably has more to do with damping than anything else. >>> >>> With a big cap from ADJ to ground, it rings badly, too. It has to be >>> the *right* capacitor to damp the ringing. >>> >>> I tried this with two different LM317 models; the ringing is somewhat >>> different (the LT317 is better), but the damping idea is the same. >>> >>> It's amazing that LT ever made a 317. I think they did that early on, >>> when they needed some revenue. They want $4 for it! I'm paying less >>> than a tenth of that for TI. >> >> I doubt you're going to see this energetic resonance on anything other than the LT part. >> > >I doubted it too, but found out the hard way when: >my 337's all oscillated, and >the 317s rang so badly that the oscillation ripple on the positive rails >was even bigger than on the negative rails. > >The 317s wouldn't oscillate by themselves, but they would ring like a >bell even after I cured the 337's of oscillation. > >I had to scratch off a lot of solder mask and tack on many tantalums to >cure my boards. Quite embarassing. >I can't persuade a TI LM317 to oscillate on a breadboard, with ceramic caps, but it does ring. -- John Larkin Highland Technology, Inc trk jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●February 18, 20182018-02-18
On 02/18/2018 08:14 AM, Chris Jones wrote:> On 17/02/2018 07:18, bloggs.fredbloggs.fred@gmail.com wrote: >> On Friday, February 16, 2018 at 12:51:24 PM UTC-5, John Larkin wrote: >>> On Fri, 16 Feb 2018 08:57:05 -0800 (PST), >>> bloggs.fredbloggs.fred@gmail.com wrote: >>> >>>> On Thursday, February 15, 2018 at 8:32:35 PM UTC-5, John Larkin wrote: >>>>> LM317's like some ESR in their output capacitors. I don't want any >>>>> electrolytic or tantalum caps in my new thing, just ceramics, and the >>>>> sim sure rings: >>>>> >>>>> https://www.dropbox.com/s/11b3w42nsvpliki/317_nocomp.jpg?raw=1 >>>>> >>>>> But this fixes it: >>>>> >>>>> https://www.dropbox.com/s/9q80heyfbwh5frp/317_comp.jpg?raw=1 >>>>> >>>>> This ain't rocket science, but I haven't seen it done before. >>>> >>>> 317 needs no such ESR compensation. >>> >>> The data sheet says it does. >>> >>>> The ringing looks suspiciously like excitation of the SRF of an >>>> output capacitor. >>> >>> The frequency is low, and is different on the rising and falling edges >>> of the load current pulse. It's the chip pseudo-inductance resonating, >>> not the cap's ESL. If the ringing were local to the caps, my damping >>> on ADJ wouldn't fix that. >>> >>> Cap series L makes a different waveform than paralleled inductance. >>> >>> >>>> Did your model give it any ESL? And your solution merely reduces the >>>> shunt resistance by a factor of 20x which probably has more to do >>>> with damping than anything else. >>> >>> With a big cap from ADJ to ground, it rings badly, too. It has to be >>> the *right* capacitor to damp the ringing. >>> >>> I tried this with two different LM317 models; the ringing is somewhat >>> different (the LT317 is better), but the damping idea is the same. >>> >>> It's amazing that LT ever made a 317. I think they did that early on, >>> when they needed some revenue. They want $4 for it! I'm paying less >>> than a tenth of that for TI. >> >> I doubt you're going to see this energetic resonance on anything other >> than the LT part. >> > > I doubted it too, but found out the hard way when: > my 337's all oscillated, and > the 317s rang so badly that the oscillation ripple on the positive rails > was even bigger than on the negative rails. > > The 317s wouldn't oscillate by themselves, but they would ring like a > bell even after I cured the 337's of oscillation. > > I had to scratch off a lot of solder mask and tack on many tantalums to > cure my boards. Quite embarassing. > >Check out the Erroll Dietz article I posted upthread. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Reply by ●February 18, 20182018-02-18
"M Philbrook" <jamie_ka1lpa@charter.net> wrote in message news:MPG.34f28ed5eec53b3998a0b1@news.eternal-september.org...> "fuckoff" I don't remember learning about that metric when I was in > school some 45 years ago. my how you can fall behind if you don't pay > attention!It's not quite as big as a metric shitload. :-) Tim -- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website: https://www.seventransistorlabs.com/
Reply by ●February 18, 20182018-02-18
On Sun, 18 Feb 2018 23:08:55 +1000, Chris Jones <lugnut808@spam.yahoo.com> wrote:> On 16/02/2018 17:47, David Eather wrote: >> On Fri, 16 Feb 2018 14:46:33 +1000, John Larkin >> <jjlarkin@highlandtechnology.com> wrote: >> >>> On Thu, 15 Feb 2018 22:31:09 -0500, bitrex >>> <bitrex@de.lete.earthlink.net> wrote: >>> >>>> On 02/15/2018 08:32 PM, John Larkin wrote: >>>>> >>>>> >>>>> LM317's like some ESR in their output capacitors. I don't want any >>>>> electrolytic or tantalum caps in my new thing, just ceramics, and the >>>>> sim sure rings: >>>>> >>>>> https://www.dropbox.com/s/11b3w42nsvpliki/317_nocomp.jpg?raw=1 >>>>> >>>>> But this fixes it: >>>>> >>>>> https://www.dropbox.com/s/9q80heyfbwh5frp/317_comp.jpg?raw=1 >>>>> >>>>> This ain't rocket science, but I haven't seen it done before. >>>>> >>>>> >>>> >>>> Straight Darlington output emitter follower voltage regulators are >>>> meh, >>>> maybe relics of when you couldn't make a decent high beta PNP on a >>>> chip >>> >>> I'm regulating +48 down to to +30, which few LDOs will do, and I have >>> the 317's in stock. >>> >>> I thought this was a cute trick, but everybody's a critic. >>> >>> >> I have never heard of a 317 ringing in a properly designed real >> application. Anyone seen it? >> > > Yes, a 317 will ring with ceramic output capacitors, and a 337 will even > oscillate with ceramic output capacitors. (Unless you mean by "properly > designed" that it doesn't ring, in which case of course not.) > > Can be cured with big tantalums on the output, or series resistors > between the regulator and output capacitors. > > I guess this problem has not been well known in the past because in the > past it was very expensive to buy ceramic capacitors with high enough > values to replace the electrolytic output capacitor. >OK. Something new I learnt about a chip I've used for years. By 'properly' I only meant that it fulfilled the basic requirements laid out in the spec sheet - and as was pointed out many older sheets have little to nothing to say about the interactions of size and type of capacitor on the output. -- I look forward to the day when a chicken can cross the road without having its motives questioned.
Reply by ●February 19, 20182018-02-19
On Thu, 15 Feb 2018 17:32:30 -0800, John Larkin <jjlarkin@highlandtechnology.com> wrote:> > >LM317's like some ESR in their output capacitors. I don't want any >electrolytic or tantalum caps in my new thing, just ceramics, and the >sim sure rings: > >https://www.dropbox.com/s/11b3w42nsvpliki/317_nocomp.jpg?raw=1 > >But this fixes it: > >https://www.dropbox.com/s/9q80heyfbwh5frp/317_comp.jpg?raw=1 > >This ain't rocket science, but I haven't seen it done before.The original LM117 data sheet shows a 10uF elec cap on the adjustment pin, with its effect illustrated in the typical performance plots. I don't know what the A version is intended to improve, but if you vary from recommended decoupling, you're bound to see performance that is non-optimal in some respect. The fact that you're using ceramics simply by preference, may be the only issue with this circuit. I don't know about the model, or what you can expect from it, but you should probably suspect anything that responds to 'tuning'. RL
Reply by ●February 19, 20182018-02-19
Den søndag den 18. februar 2018 kl. 14.09.05 UTC+1 skrev Chris Jones:> On 16/02/2018 17:47, David Eather wrote: > > On Fri, 16 Feb 2018 14:46:33 +1000, John Larkin > > <jjlarkin@highlandtechnology.com> wrote: > > > >> On Thu, 15 Feb 2018 22:31:09 -0500, bitrex > >> <bitrex@de.lete.earthlink.net> wrote: > >> > >>> On 02/15/2018 08:32 PM, John Larkin wrote: > >>>> > >>>> > >>>> LM317's like some ESR in their output capacitors. I don't want any > >>>> electrolytic or tantalum caps in my new thing, just ceramics, and the > >>>> sim sure rings: > >>>> > >>>> https://www.dropbox.com/s/11b3w42nsvpliki/317_nocomp.jpg?raw=1 > >>>> > >>>> But this fixes it: > >>>> > >>>> https://www.dropbox.com/s/9q80heyfbwh5frp/317_comp.jpg?raw=1 > >>>> > >>>> This ain't rocket science, but I haven't seen it done before. > >>>> > >>>> > >>> > >>> Straight Darlington output emitter follower voltage regulators are meh, > >>> maybe relics of when you couldn't make a decent high beta PNP on a chip > >> > >> I'm regulating +48 down to to +30, which few LDOs will do, and I have > >> the 317's in stock. > >> > >> I thought this was a cute trick, but everybody's a critic. > >> > >> > > > > > > I have never heard of a 317 ringing in a properly designed real > > application. Anyone seen it? > > > > Yes, a 317 will ring with ceramic output capacitors, and a 337 will even > oscillate with ceramic output capacitors. (Unless you mean by "properly > designed" that it doesn't ring, in which case of course not.)afaict the LM337 is more like an LDO, output is collector rather than emitter
Reply by ●February 19, 20182018-02-19
John Larkin wrote...> > LM317's like some ESR in their output capacitors. > I don't want any electrolytic or tantalum caps in > my new thing, just ceramics, and the sim sure rings:I hate the way LTSpice hides added parasitic elements, if any, to the passive components. It's better to manually add these explicitly, so others (and yourself) can see them, and evaluate reasonableness of the chosen values. John, please be aware that ceramic capacitors certainly do not have zero esr. I measured 1210-size Murata, Samsung and Yageo caps, with an HP 4192A LCR meter, and got values between 2.5 and 60 m-ohms for 47uF 16V caps at 5V bias, and 9 to 30 m-ohms for 10uF 35V caps at 15V. As expected for MLCC, the capacitance dropped severely with voltage, but esr didn't change. These resistances help to stabilize regulators of all types, but also defeat ideal filtering. -- Thanks, - Win
Reply by ●February 19, 20182018-02-19
On Mon, 19 Feb 2018 02:04:45 -0800 (PST), Lasse Langwadt Christensen <langwadt@fonz.dk> wrote:>Den s�ndag den 18. februar 2018 kl. 14.09.05 UTC+1 skrev Chris Jones: >> On 16/02/2018 17:47, David Eather wrote: >> > On Fri, 16 Feb 2018 14:46:33 +1000, John Larkin >> > <jjlarkin@highlandtechnology.com> wrote: >> > >> >> On Thu, 15 Feb 2018 22:31:09 -0500, bitrex >> >> <bitrex@de.lete.earthlink.net> wrote: >> >> >> >>> On 02/15/2018 08:32 PM, John Larkin wrote: >> >>>> >> >>>> >> >>>> LM317's like some ESR in their output capacitors. I don't want any >> >>>> electrolytic or tantalum caps in my new thing, just ceramics, and the >> >>>> sim sure rings: >> >>>> >> >>>> https://www.dropbox.com/s/11b3w42nsvpliki/317_nocomp.jpg?raw=1 >> >>>> >> >>>> But this fixes it: >> >>>> >> >>>> https://www.dropbox.com/s/9q80heyfbwh5frp/317_comp.jpg?raw=1 >> >>>> >> >>>> This ain't rocket science, but I haven't seen it done before. >> >>>> >> >>>> >> >>> >> >>> Straight Darlington output emitter follower voltage regulators are meh, >> >>> maybe relics of when you couldn't make a decent high beta PNP on a chip >> >> >> >> I'm regulating +48 down to to +30, which few LDOs will do, and I have >> >> the 317's in stock. >> >> >> >> I thought this was a cute trick, but everybody's a critic. >> >> >> >> >> > >> > >> > I have never heard of a 317 ringing in a properly designed real >> > application. Anyone seen it? >> > >> >> Yes, a 317 will ring with ceramic output capacitors, and a 337 will even >> oscillate with ceramic output capacitors. (Unless you mean by "properly >> designed" that it doesn't ring, in which case of course not.) > >afaict the LM337 is more like an LDO, output is collector rather than emitterRight. That makes it a current source, which forms an integrator into low-ESR output caps. -- John Larkin Highland Technology, Inc trk jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
