"bitrex" wrote in message news:oBzhC.33534$iZ2.30856@fx29.iad... On 02/15/2018 11:54 PM, John Larkin wrote:> On Thu, 15 Feb 2018 23:11:05 -0500, bitrex > <bitrex@de.lete.earthlink.net> wrote: > >> On 02/15/2018 10:39 PM, Lasse Langwadt Christensen wrote: >>> Den fredag den 16. februar 2018 kl. 04.31.28 UTC+1 skrev bitrex: >>>> 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 >>> >>> apart from the dropout, whats meh about them? >>> >> >> All things being equal the quasi-complimentary/Sziklai topology is >> better in just about all respects than the straight Darlington; the >> complex output impedance of a straight Darlington has an inductive >> component that increases rapidly with frequency (hence stability >> problems), the complimentary less so > > The emitter follower is basically low output impedance. The PNP starts > with high output impedance. Sziklai types, like the LM1117, have > plenty of ESR constraints too. There are few regs around that are > stable down to zero ESR, and most are low-voltage parts.A Sziklai output as I'm thinking of would have a PNP in line with the output and an NPN driving the base; it would be the functional equivalent of just a regular NPN emitter follower, "in disguise.">Unfortunately for high power regulators that's also a non-starter because >IIRC you can't make a high power monolithic PNP to pass the current, >either.Your 40 years out of date, probably. Decent, high current, very fast complementary bipolar processes are available. The X-Fab XTO18 SOI is a pretty good 0.18u BiCMOS process. It has good low noise mosfets and fully isolated, fast npn/pnp, and is very affordable. -- Kevin Aylward http://www.anasoft.co.uk - SuperSpice http://www.kevinaylward.co.uk/ee/index.html
LM317 compensation
Started by ●February 15, 2018
Reply by ●February 16, 20182018-02-16
Reply by ●February 16, 20182018-02-16
"John Larkin" wrote in message news:k32e8d5g65854goltcuc8uk6asimkvcnej@4ax.com... On Fri, 16 Feb 2018 15:05:40 -0000, "Kevin Aylward" <kevinRemovAT@kevinaylward.co.uk> wrote:>"John Larkin" wrote in message >news:vecc8dt14p89hcaeb09rd3mkplt5vergrb@4ax.com... > > > >>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 > >Urhhhh...... the 1 uohm resister is finger nails down a blackboard for me.>That's there to let me snoop the current. I find it hard to aim the LT >Spice current probe at device pins, so I'll stick in a resistor here >and there to make current snooping easy.>I usually use 1m, but I wanted an accurate sim of regulator ringing >and 1m might have affected that a little.>I suppose I could use 0 ohms... tries it... no, LT Spice will not >probe the current in a 0 ohm resistor. Pity.The "correct" way to probe currents in Spice if the data is not otherwise available, is to use a zero voltage dc source. In fact, in basic Spice3 AC currents are not available for say, bipolars, so you have to do that if you want that data. In SuperSpice to get transparent current probing in .subckts, I automatically add 0V sources into the pins. -- Kevin Aylward http://www.anasoft.co.uk - SuperSpice http://www.kevinaylward.co.uk/ee/index.html
Reply by ●February 16, 20182018-02-16
On Fri, 16 Feb 2018 20:21:56 -0000, "Kevin Aylward" <kevinRemovAT@kevinaylward.co.uk> wrote:>"John Larkin" wrote in message >news:k32e8d5g65854goltcuc8uk6asimkvcnej@4ax.com... > >On Fri, 16 Feb 2018 15:05:40 -0000, "Kevin Aylward" ><kevinRemovAT@kevinaylward.co.uk> wrote: > >>"John Larkin" wrote in message >>news:vecc8dt14p89hcaeb09rd3mkplt5vergrb@4ax.com... >> >> >> >>>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 >> >>Urhhhh...... the 1 uohm resister is finger nails down a blackboard for me. > >>That's there to let me snoop the current. I find it hard to aim the LT >>Spice current probe at device pins, so I'll stick in a resistor here >>and there to make current snooping easy. > >>I usually use 1m, but I wanted an accurate sim of regulator ringing >>and 1m might have affected that a little. > >>I suppose I could use 0 ohms... tries it... no, LT Spice will not >>probe the current in a 0 ohm resistor. Pity. > >The "correct" way to probe currents in Spice if the data is not otherwise >available, is to use a zero voltage dc source.OK, big round 0 ohm resistors! -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●February 16, 20182018-02-16
On 02/16/2018 12:51 PM, 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 was going to ask what in the world is so special about a 317 that one would need a gilded version of it
Reply by ●February 16, 20182018-02-16
On Fri, 16 Feb 2018 16:08:55 -0500, bitrex <bitrex@de.lete.earthlink.net> wrote:>On 02/16/2018 12:51 PM, 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 was going to ask what in the world is so special about a 317 that one >would need a gilded version of itOnly that LT Spice had a model already. I tried an independent LM317 model (can't recall where I got it) and the overall situation was similar... lots of ringing with ceramic caps, and the right RC helped a lot. I'm borderline over using a switcher to get from +48 to +30. Not many switchers will handle 48 in. We have LM2576HV in stock, an ancient 50 KHz SimpleSwitcher, which has its own issues, so I'll go linear and dump the heat. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●February 16, 20182018-02-16
<bloggs.fredbloggs.fred@gmail.com> wrote in message news:fc7f7804-2fef-4483-8faa-1ee21724ebe4@googlegroups.com...> > Right, any single pole rolloff has an effective inductance as output > impedance, but the Q is generally too low (<1) to support ringing. His > waveform shows a Q of approximately 10. >Right, so what does that tell you about the output impedance of the model in question? :-) (To go much farther, this thread needs waveforms from a real part. Or an R+C and being done with it. ;-) ) Tim -- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website: https://www.seventransistorlabs.com/
Reply by ●February 16, 20182018-02-16
On Fri, 16 Feb 2018 12:16:52 -0800 (PST), bloggs.fredbloggs.fred@gmail.com wrote:>On Friday, February 16, 2018 at 12:19:07 PM UTC-5, Tim Williams wrote: >> <bloggs.fredbloggs.fred@gmail.com> wrote in message >> news:d4f2ca9f-ff53-44fd-8877-51c55e3b1f1c@googlegroups.com... >> >317 needs no such ESR compensation. The ringing looks suspiciously like >> >excitation of the SRF of an output capacitor. 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. >> > >> >> The output has an inductive characteristic at higher frequencies. It's >> stable as you can see, but that doesn't mean the impedance is great. > >Right, any single pole rolloff has an effective inductance as output impedance, but the Q is generally too low (<1) to support ringing. His waveform shows a Q of approximately 10. >Why would the Q be low? Active filters have Qs in the hundreds. 3T regulators are notorious for oscillating into low-ESR output caps. Opamps, too. A minority of opamps are c-load stable, and that's usually not determinable from the data sheets. Many opamps are stable with small capacitive loads and with giant ones, unstable between. My LT317 sim, without the fix, is starting to look decently damped with 300,000 uF of zero-ESR caps. The internal pole must be a few 10s of Hz. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●February 16, 20182018-02-16
On Friday, February 16, 2018 at 6:32:58 PM UTC-5, John Larkin wrote:> On Fri, 16 Feb 2018 12:16:52 -0800 (PST), > bloggs.fredbloggs.fred@gmail.com wrote: > > >On Friday, February 16, 2018 at 12:19:07 PM UTC-5, Tim Williams wrote: > >> <bloggs.fredbloggs.fred@gmail.com> wrote in message > >> news:d4f2ca9f-ff53-44fd-8877-51c55e3b1f1c@googlegroups.com... > >> >317 needs no such ESR compensation. The ringing looks suspiciously like > >> >excitation of the SRF of an output capacitor. 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. > >> > > >> > >> The output has an inductive characteristic at higher frequencies. It's > >> stable as you can see, but that doesn't mean the impedance is great. > > > >Right, any single pole rolloff has an effective inductance as output impedance, but the Q is generally too low (<1) to support ringing. His waveform shows a Q of approximately 10. > > > > Why would the Q be low? Active filters have Qs in the hundreds. > > 3T regulators are notorious for oscillating into low-ESR output caps. > Opamps, too. A minority of opamps are c-load stable, and that's > usually not determinable from the data sheets. Many opamps are stable > with small capacitive loads and with giant ones, unstable between. > > My LT317 sim, without the fix, is starting to look decently damped > with 300,000 uF of zero-ESR caps. The internal pole must be a few 10s > of Hz.LOL- 300,000u ??? Hahaha- what does that tell you? The simulation is not credible.> > > -- > > John Larkin Highland Technology, Inc > picosecond timing precision measurement > > jlarkin att highlandtechnology dott com > http://www.highlandtechnology.com
Reply by ●February 16, 20182018-02-16
On Fri, 16 Feb 2018 15:54:56 -0800 (PST), bloggs.fredbloggs.fred@gmail.com wrote:>On Friday, February 16, 2018 at 6:32:58 PM UTC-5, John Larkin wrote: >> On Fri, 16 Feb 2018 12:16:52 -0800 (PST), >> bloggs.fredbloggs.fred@gmail.com wrote: >> >> >On Friday, February 16, 2018 at 12:19:07 PM UTC-5, Tim Williams wrote: >> >> <bloggs.fredbloggs.fred@gmail.com> wrote in message >> >> news:d4f2ca9f-ff53-44fd-8877-51c55e3b1f1c@googlegroups.com... >> >> >317 needs no such ESR compensation. The ringing looks suspiciously like >> >> >excitation of the SRF of an output capacitor. 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. >> >> > >> >> >> >> The output has an inductive characteristic at higher frequencies. It's >> >> stable as you can see, but that doesn't mean the impedance is great. >> > >> >Right, any single pole rolloff has an effective inductance as output impedance, but the Q is generally too low (<1) to support ringing. His waveform shows a Q of approximately 10. >> > >> >> Why would the Q be low? Active filters have Qs in the hundreds. >> >> 3T regulators are notorious for oscillating into low-ESR output caps. >> Opamps, too. A minority of opamps are c-load stable, and that's >> usually not determinable from the data sheets. Many opamps are stable >> with small capacitive loads and with giant ones, unstable between. >> >> My LT317 sim, without the fix, is starting to look decently damped >> with 300,000 uF of zero-ESR caps. The internal pole must be a few 10s >> of Hz. > > >LOL- 300,000u ??? Hahaha- what does that tell you? The simulation is not credible.It tells me that the 317 internal pole is at a few 10s of Hz. Most opamps start to roll off at similar frequencies. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●February 16, 20182018-02-16
On Friday, February 16, 2018 at 7:06:54 PM UTC-5, John Larkin wrote:> On Fri, 16 Feb 2018 15:54:56 -0800 (PST), > bloggs.fredbloggs.fred@gmail.com wrote: > > >On Friday, February 16, 2018 at 6:32:58 PM UTC-5, John Larkin wrote: > >> On Fri, 16 Feb 2018 12:16:52 -0800 (PST), > >> bloggs.fredbloggs.fred@gmail.com wrote: > >> > >> >On Friday, February 16, 2018 at 12:19:07 PM UTC-5, Tim Williams wrote: > >> >> <bloggs.fredbloggs.fred@gmail.com> wrote in message > >> >> news:d4f2ca9f-ff53-44fd-8877-51c55e3b1f1c@googlegroups.com... > >> >> >317 needs no such ESR compensation. The ringing looks suspiciously like > >> >> >excitation of the SRF of an output capacitor. 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. > >> >> > > >> >> > >> >> The output has an inductive characteristic at higher frequencies. It's > >> >> stable as you can see, but that doesn't mean the impedance is great. > >> > > >> >Right, any single pole rolloff has an effective inductance as output impedance, but the Q is generally too low (<1) to support ringing. His waveform shows a Q of approximately 10. > >> > > >> > >> Why would the Q be low? Active filters have Qs in the hundreds. > >> > >> 3T regulators are notorious for oscillating into low-ESR output caps. > >> Opamps, too. A minority of opamps are c-load stable, and that's > >> usually not determinable from the data sheets. Many opamps are stable > >> with small capacitive loads and with giant ones, unstable between. > >> > >> My LT317 sim, without the fix, is starting to look decently damped > >> with 300,000 uF of zero-ESR caps. The internal pole must be a few 10s > >> of Hz. > > > > > >LOL- 300,000u ??? Hahaha- what does that tell you? The simulation is not credible. > > > It tells me that the 317 internal pole is at a few 10s of Hz. Most > opamps start to roll off at similar frequencies.How do you get 10Hz, 10^-2 sec. from 300uF? (where's the ~30 ohms) I like your circuit, I've never had any issue's with the '317, but I think I've always used it with a tant or Al cap. George H.> > > -- > > John Larkin Highland Technology, Inc > picosecond timing precision measurement > > jlarkin att highlandtechnology dott com > http://www.highlandtechnology.com
