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. -- John Larkin Highland Technology, Inc lunatic fringe electronics
LM317 compensation
Started by ●February 15, 2018
Reply by ●February 15, 20182018-02-15
You can put resistors in series with ceramics... Tim -- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website: https://www.seventransistorlabs.com/ "John Larkin" <jjlarkin@highlandtechnology.com> 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 > > 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. > > > -- > > John Larkin Highland Technology, Inc > > lunatic fringe electronics >
Reply by ●February 15, 20182018-02-15
On Thu, 15 Feb 2018 19:46:44 -0600, "Tim Williams" <tiwill@seventransistorlabs.com> wrote:>You can put resistors in series with ceramics... > >TimSure, but that raises the bus impedance, and I expect load current pulses. Putting resistors in series with just some of the caps still rings. This takes less parts. Actually, it's pretty good without R6. -- John Larkin Highland Technology, Inc lunatic fringe electronics
Reply by ●February 15, 20182018-02-15
"John Larkin" <jjlarkin@highlandtechnology.com> wrote in message news:t3ec8dppc7rm0hh03fcv04pkc79m11b451@4ax.com...> Sure, but that raises the bus impedance, and I expect load current > pulses. Putting resistors in series with just some of the caps still > rings. > > This takes less parts. Actually, it's pretty good without R6.Well, your way raises the bus impedance rather more significantly. You can't do "some", you need to do >2/3rds of total capacitance. Example: 3uF worth of 0.1's scattered around the board, 10uF + (0.1R or whatever works best) "bulk" cap. If you need low bus impedance, you have to do both! Tim -- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website: https://www.seventransistorlabs.com/
Reply by ●February 15, 20182018-02-15
Den fredag den 16. februar 2018 kl. 02.51.57 UTC+1 skrev John Larkin:> On Thu, 15 Feb 2018 19:46:44 -0600, "Tim Williams" > <tiwill@seventransistorlabs.com> wrote: > > >You can put resistors in series with ceramics... > > > >Tim > > Sure, but that raises the bus impedance, and I expect load current > pulses. Putting resistors in series with just some of the caps still > rings. > > This takes less parts. Actually, it's pretty good without R6.from the data sheet: The adjustment terminal can be bypassed to ground on the LM317-N to improve ripple rejection. This bypass capacitor prevents ripple from being amplified as the output voltage is increased. With a 10-μF bypass capacitor, 80-dB ripple rejection is obtainable at any output level. Increases over 10 μF do not appreciably improve the ripple rejection at frequencies above 120 Hz. If the bypass capacitor is used, it is sometimes necessary to include protection diodes to prevent the capacitor from discharging through internal low current paths and damaging the device.
Reply by ●February 15, 20182018-02-15
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 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 15, 20182018-02-15
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
Reply by ●February 15, 20182018-02-15
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 chipapart from the dropout, whats meh about them?
Reply by ●February 16, 20182018-02-16
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
Reply by ●February 16, 20182018-02-16
On Thu, 15 Feb 2018 18:05:23 -0800 (PST), Lasse Langwadt Christensen <langwadt@fonz.dk> wrote:>Den fredag den 16. februar 2018 kl. 02.51.57 UTC+1 skrev John Larkin: >> On Thu, 15 Feb 2018 19:46:44 -0600, "Tim Williams" >> <tiwill@seventransistorlabs.com> wrote: >> >> >You can put resistors in series with ceramics... >> > >> >Tim >> >> Sure, but that raises the bus impedance, and I expect load current >> pulses. Putting resistors in series with just some of the caps still >> rings. >> >> This takes less parts. Actually, it's pretty good without R6. > >from the data sheet: > >The adjustment terminal can be bypassed to ground on the LM317-N to improve ripple rejection. This bypass >capacitor prevents ripple from being amplified as the output voltage is increased. With a 10-?F bypass capacitor, >80-dB ripple rejection is obtainable at any output level. Increases over 10 ?F do not appreciably improve the >ripple rejection at frequencies above 120 Hz. If the bypass capacitor is used, it is sometimes necessary to >include protection diodes to prevent the capacitor from discharging through internal low current paths and >damaging the device.Sure, everybody knows that. If you use a big cap from ADJ to ground, and use low ESR output caps, it still rings wildly on a load step. -- John Larkin Highland Technology, Inc lunatic fringe electronics
