On Thu, 15 Feb 2018 21:19:21 -0500, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.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. >> >> >I do that reasonably routinely with LDOs and higher-current cap >multipliers--a zero-ohm jumper in series with the output cap to make it >look like we did it on purpose. ;) > >With cap multipliers I usually put the resistor in series with the >output, but with LDOs I usually put it in series with the cap so that it >mimics a small ESR. > >Cheers > >Phil HobbsAre you referring to the 1u resistor? That's just there to conveniently snoop the current in the sim. It's the RC from ADJ to ground that kills the ringing. I expect big, fast current spikes in my load, so I don't want to add ESR to my output bypass caps. Aluminums would have too much ESR anyhow, but they would be too tall too. -- John Larkin Highland Technology, Inc lunatic fringe electronics
LM317 compensation
Started by ●February 15, 2018
Reply by ●February 16, 20182018-02-16
Reply by ●February 16, 20182018-02-16
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 chipI'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. -- John Larkin Highland Technology, Inc lunatic fringe electronics
Reply by ●February 16, 20182018-02-16
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 soThe 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. The 1117 is a nice part, but limited to 15 volts in:out. (They typically die around 60.) Anyway, my thing seems to work. If you don't approve, don't use it. -- John Larkin Highland Technology, Inc lunatic fringe electronics
Reply by ●February 16, 20182018-02-16
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? -- I look forward to the day when a chicken can cross the road without having its motives questioned.
Reply by ●February 16, 20182018-02-16
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. It works pretty well with discretes. As far as I can tell design work on high power non-LDO voltage regulators ceased around 1980 they pretty much all seem to be variants on the LMxxx LMxxxx topologies.> The 1117 is a nice part, but limited to 15 volts in:out. (They > typically die around 60.) > > Anyway, my thing seems to work. If you don't approve, don't use it. > >Easy John Wayne, the LM317 is meatloaf not filet mignon but sometimes meatloaf works just fine
Reply by ●February 16, 20182018-02-16
On 02/16/2018 01:47 AM, 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? >How would you know if one did? Do all LM317s communicate with u telepathically
Reply by ●February 16, 20182018-02-16
>Are you referring to the 1u resistor? That's just there to >conveniently snoop the current in the sim. It's the RC from ADJ to >ground that kills the ringing.Normally a 317 running at high CL gain is pretty stable IME, but I can imagine that a bit of lead/lag could help the load transient response. I use the lead network a bit like that in buck switchers with cap multipliers--take the DC feedback from the cap mult and AC from the switcher output. Cheers Phil Hobbs
Reply by ●February 16, 20182018-02-16
"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=1Urhhhh...... the 1 uohm resister is finger nails down a blackboard for me. For a regular spice engine on regular doubles, numbers can't span more than 12 digits and have it solve correctly. So, 1 uohm means 1 Meg max. Don't use smaller than 1m ohm er... This ain't rocket science. And alternatively, ... you could put a low value resister in the ic output prior to the feedback, and use a feedback cap direct from the ic output to its input. Effectively, if configured correctly, the output resister does the job of an out of loop esr, but without the dc error. -- 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 04:09:14 -0800 (PST), pcdhobbs@gmail.com wrote:> >>Are you referring to the 1u resistor? That's just there to >>conveniently snoop the current in the sim. It's the RC from ADJ to >>ground that kills the ringing. > >Normally a 317 running at high CL gain is pretty stable IME, but I can imagine that a bit of lead/lag could help the load transient response. > >I use the lead network a bit like that in buck switchers with cap multipliers--take the DC feedback from the cap mult and AC from the switcher output. > >Cheers > >Phil HobbsOne way to get a stiff programmable power rail is to drive the ADJ pin of a 3T regulator with an opamp, open-loop. Maybe that could benefit from some sort of damping too. For a stiff bipolar rail, the TCA0372 opamp (dual, 1 amp per, 50 cents) is great, but it sure doesn't like low-ESR caps on its output. A tenth of an ohm in series with the output fixes that. -- John Larkin Highland Technology, Inc lunatic fringe electronics
Reply by ●February 16, 20182018-02-16
Den fredag den 16. februar 2018 kl. 16.24.59 UTC+1 skrev John Larkin:> On Fri, 16 Feb 2018 04:09:14 -0800 (PST), pcdhobbs@gmail.com wrote: > > > > >>Are you referring to the 1u resistor? That's just there to > >>conveniently snoop the current in the sim. It's the RC from ADJ to > >>ground that kills the ringing. > > > >Normally a 317 running at high CL gain is pretty stable IME, but I can imagine that a bit of lead/lag could help the load transient response. > > > >I use the lead network a bit like that in buck switchers with cap multipliers--take the DC feedback from the cap mult and AC from the switcher output. > > > >Cheers > > > >Phil Hobbs > > One way to get a stiff programmable power rail is to drive the ADJ pin > of a 3T regulator with an opamp, open-loop. Maybe that could benefit > from some sort of damping too. > > For a stiff bipolar rail, the TCA0372 opamp (dual, 1 amp per, 50 > cents) is great, but it sure doesn't like low-ESR caps on its output. > A tenth of an ohm in series with the output fixes that.that aussie guy had some fun with that recently https://youtu.be/1VlKoR0ldIE tldw: A new batch of boards with virtual ground made with an opamp oscillates at certain loads, even though it has 270R resistor on the output. Turns out the opamp with the same part number from a different manufacturer wasn't quite identical
