On Mon, 26 May 2014 21:50:17 -0400, Phil Hobbs <hobbs@electrooptical.net> wrote:>On 5/26/2014 9:33 PM, John Larkin wrote: >> On Sun, 25 May 2014 18:33:16 +0100, "Ian Field" >> <gangprobing.alien@ntlworld.com> wrote: >> >>> >>> >>> "John Larkin" <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote in message >>> news:e794o9tj2im9tflvlbisagg29g1crl7468@4ax.com... >>>> On Sun, 25 May 2014 17:53:03 +0100, "Ian Field" >>>> <gangprobing.alien@ntlworld.com> wrote: >>>> >>>>> >>>>> >>>>> "Jurd" <guitardorkspamspameggsandham74@gmail.com> wrote in message >>>>> news:llrkq5$hr4$1@news.albasani.net... >>>>>> On 5/24/2014 8:48 PM, John Larkin wrote: >>>>>>> On Sat, 24 May 2014 20:06:45 -0500, Jurd >>>>>> >>>>>>> >>>>>>> That bridge configuration will in theory charge the caps to 1.41 times >>>>>>> the RMS voltage of the transformer secondary, because a sine wave has >>>>>>> a peak voltage 1.41x its RMS. >>>>>>> >>>>>>> In real life you'd typically get more DC than that at light loads and >>>>>>> less at heavy loads. And the "DC" will have ripple, which makes the >>>>>>> voltage dip at 120 Hz (100 Hz in the hinterlands). >>>>>>> >>>>>>> >>>>>> >>>>>> Ah thanks. Good to know about the ripple, as that's certainly something >>>>>> I'd like to avoid. Back to the Googling board! >>>>> >>>>> Search under "active ripple cancelling" - pretty much just an emitter >>>>> follower with some bias and a not quite as huge electrolytic as you'd need >>>>> on its own. >>>> >>>> That doesn't help when you're building a power supply. You may as well >>>> just connect the rectifier caps to the main linear regulator. That's >>>> better, actually; a ripple canceler ahead of the regulator makes >>>> things worse. >>>> >>>> The issue is energy storage. 120 times a second, the transformer >>>> output goes to zero volts. If you want to keep powering the load then, >>>> the energy has to come from somewhere, and in this case it's the >>>> filter caps. >>> >>> I never said don't use reservoir caps - an unregulated emitter follower with >>> a heavily decoupled base does its best to follow the insignificant ripple on >>> its base. >> >> Problem is, it will also follow the significant ripple on its >> collector. >> >> >Nah, that's a capacitance multiplier. As long as you don't let it >saturate, it's the bomb for supply rejection.Sure, as long as the input ripple is small, a few tenths p-p. But the suggestion was to put the c-multiplier between the bridge+filter caps and the main linear regulator, where one might expect amps of current and volts of ripple. -- John Larkin Highland Technology, Inc jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Benchtop Power Supply Options
Started by ●May 7, 2014
Reply by ●May 27, 20142014-05-27
Reply by ●May 27, 20142014-05-27
On Tue, 27 May 2014 06:20:01 +0000 (UTC), mroberds@att.net wrote:>Jurd <guitardorkspamspameggsandham74@gmail.com> wrote: >> On 5/24/2014 8:48 PM, John Larkin wrote: >>> On Sat, 24 May 2014 20:06:45 -0500, Jurd >>> >>> In real life you'd typically get more DC than that at light loads and >>> less at heavy loads. And the "DC" will have ripple, which makes the >>> voltage dip at 120 Hz (100 Hz in the hinterlands). >> >> Ah thanks. Good to know about the ripple, as that's certainly >> something I'd like to avoid. > >Quick version: I am almost certain John is talking about the DC *on C1 >and C2*, not the DC at the output of the supply. > >Long version... > >There will *always* be some ripple "before" the LM317 - across C1 and >C2 in the diagram you posted.* If you had a transformer with a 24 V AC >secondary, and you were drawing 1 A (DC) from the output of the power >supply, and you put an oscilloscope probe across C2, you'd see a DC >voltage varying between about 30 V and 32 V DC. The variation would >be at 120 Hz. You can reduce the amount of this ripple by making C1 and >C2 bigger, but you can never get it to go away completely. > >(* From "Getting Started in Electronics" by Forrest Mims, I think.) > >There will be *much less* ripple "after" the LM317 - across C3 - as long >as you have R1 adjusted to give an output voltage less than about 27 V >(in this example). If you put an oscilloscope probe across C3, you'd >see a DC voltage varying between (say) 27.000 V and 27.005 V. You can >reduce this ripple a little by putting another capacitor across R1 - see >the LM317 data sheet. A lot of things you would run from this power >supply won't care about this. Audio stuff might care a little (you >might hear a 120 Hz hum in the audio), depending on the audio voltage >levels you are using. > >The main reason you have to care about the ripple "before" the LM317 is >that it effectively sets the highest output voltage you can get from >the supply. There will always be a couple of volts of drop "through" >the LM317 - in other words, even if you set the ADJ pin for maximum >output, the OUT pin will always be a couple of volts less than the IN >pin. > >If the voltage on C1 and C2 is rippling between 30 V and 32 V, and you >set R1 for 27 V output or less, then there is always at least 3 V >available to lose in the LM317, and the output will be stable at 27 V. >If you tried to turn up R1 to get 29 V on the output, there would only >be between 1 and 3 V available to lose in the LM317. 1 V isn't enough >for the LM317, so part of the time, you wouldn't get the full 29 V on >the output. > >There is an article by Don Lancaster on how to pick the filter capacitor >size on PDF page 104 of http://www.tinaja.com/glib/hackar1.pdf . In >that article, Figure 1-B is you, the capacitor is the combination of >C1 and C2 in your schematic, and the resistor represents your LM317 and >everything "after" it. > >Matt RoberdsThe full solution involves the copper loss and the leakage inductance of the transformer, the diode characteristics, the capacitance and ESR of the filter capacitors, and maybe the impedance of the AC power line. All that is easier to Spice, or just to test, than to calculate. -- John Larkin Highland Technology, Inc jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●May 27, 20142014-05-27
On Tue, 27 May 2014 06:20:01 +0000 (UTC), mroberds@att.net wrote:>Jurd <guitardorkspamspameggsandham74@gmail.com> wrote: >> On 5/24/2014 8:48 PM, John Larkin wrote: >>> On Sat, 24 May 2014 20:06:45 -0500, Jurd >>> >>> In real life you'd typically get more DC than that at light loads and >>> less at heavy loads. And the "DC" will have ripple, which makes the >>> voltage dip at 120 Hz (100 Hz in the hinterlands). >> >> Ah thanks. Good to know about the ripple, as that's certainly >> something I'd like to avoid. > >Quick version: I am almost certain John is talking about the DC *on C1 >and C2*, not the DC at the output of the supply. > >Long version... > >There will *always* be some ripple "before" the LM317 - across C1 and >C2 in the diagram you posted.* If you had a transformer with a 24 V AC >secondary, and you were drawing 1 A (DC) from the output of the power >supply, and you put an oscilloscope probe across C2, you'd see a DC >voltage varying between about 30 V and 32 V DC. The variation would >be at 120 Hz. You can reduce the amount of this ripple by making C1 and >C2 bigger, but you can never get it to go away completely. > >(* From "Getting Started in Electronics" by Forrest Mims, I think.) > >There will be *much less* ripple "after" the LM317 - across C3 - as long >as you have R1 adjusted to give an output voltage less than about 27 V >(in this example). If you put an oscilloscope probe across C3, you'd >see a DC voltage varying between (say) 27.000 V and 27.005 V. You can >reduce this ripple a little by putting another capacitor across R1 - see >the LM317 data sheet. A lot of things you would run from this power >supply won't care about this. Audio stuff might care a little (you >might hear a 120 Hz hum in the audio), depending on the audio voltage >levels you are using. > >The main reason you have to care about the ripple "before" the LM317 is >that it effectively sets the highest output voltage you can get from >the supply. There will always be a couple of volts of drop "through" >the LM317 - in other words, even if you set the ADJ pin for maximum >output, the OUT pin will always be a couple of volts less than the IN >pin. > >If the voltage on C1 and C2 is rippling between 30 V and 32 V, and you >set R1 for 27 V output or less, then there is always at least 3 V >available to lose in the LM317, and the output will be stable at 27 V. >If you tried to turn up R1 to get 29 V on the output, there would only >be between 1 and 3 V available to lose in the LM317. 1 V isn't enough >for the LM317, so part of the time, you wouldn't get the full 29 V on >the output. > >There is an article by Don Lancaster on how to pick the filter capacitor >size on PDF page 104 of http://www.tinaja.com/glib/hackar1.pdf . In >that article, Figure 1-B is you, the capacitor is the combination of >C1 and C2 in your schematic, and the resistor represents your LM317 and >everything "after" it. > >Matt RoberdsDon's math is pessimistic, because it assumes that the cap is charged instantaneously and discharges for a full half cycle. A real sine wave is mostly flat on top, so the cap doesn't discharge for 8.333 msec. -- John Larkin Highland Technology, Inc jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●May 27, 20142014-05-27
On 5/27/2014 7:21 PM, John Larkin wrote:> On Mon, 26 May 2014 21:50:17 -0400, Phil Hobbs > <hobbs@electrooptical.net> wrote: > >> On 5/26/2014 9:33 PM, John Larkin wrote: >>> On Sun, 25 May 2014 18:33:16 +0100, "Ian Field" >>> <gangprobing.alien@ntlworld.com> wrote: >>> >>>> >>>> >>>> "John Larkin" <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote in message >>>> news:e794o9tj2im9tflvlbisagg29g1crl7468@4ax.com... >>>>> On Sun, 25 May 2014 17:53:03 +0100, "Ian Field" >>>>> <gangprobing.alien@ntlworld.com> wrote: >>>>> >>>>>> >>>>>> >>>>>> "Jurd" <guitardorkspamspameggsandham74@gmail.com> wrote in message >>>>>> news:llrkq5$hr4$1@news.albasani.net... >>>>>>> On 5/24/2014 8:48 PM, John Larkin wrote: >>>>>>>> On Sat, 24 May 2014 20:06:45 -0500, Jurd >>>>>>> >>>>>>>> >>>>>>>> That bridge configuration will in theory charge the caps to 1.41 times >>>>>>>> the RMS voltage of the transformer secondary, because a sine wave has >>>>>>>> a peak voltage 1.41x its RMS. >>>>>>>> >>>>>>>> In real life you'd typically get more DC than that at light loads and >>>>>>>> less at heavy loads. And the "DC" will have ripple, which makes the >>>>>>>> voltage dip at 120 Hz (100 Hz in the hinterlands). >>>>>>>> >>>>>>>> >>>>>>> >>>>>>> Ah thanks. Good to know about the ripple, as that's certainly something >>>>>>> I'd like to avoid. Back to the Googling board! >>>>>> >>>>>> Search under "active ripple cancelling" - pretty much just an emitter >>>>>> follower with some bias and a not quite as huge electrolytic as you'd need >>>>>> on its own. >>>>> >>>>> That doesn't help when you're building a power supply. You may as well >>>>> just connect the rectifier caps to the main linear regulator. That's >>>>> better, actually; a ripple canceler ahead of the regulator makes >>>>> things worse. >>>>> >>>>> The issue is energy storage. 120 times a second, the transformer >>>>> output goes to zero volts. If you want to keep powering the load then, >>>>> the energy has to come from somewhere, and in this case it's the >>>>> filter caps. >>>> >>>> I never said don't use reservoir caps - an unregulated emitter follower with >>>> a heavily decoupled base does its best to follow the insignificant ripple on >>>> its base. >>> >>> Problem is, it will also follow the significant ripple on its >>> collector. >>> >>> >> Nah, that's a capacitance multiplier. As long as you don't let it >> saturate, it's the bomb for supply rejection. > > Sure, as long as the input ripple is small, a few tenths p-p. But the > suggestion was to put the c-multiplier between the bridge+filter caps > and the main linear regulator, where one might expect amps of current > and volts of ripple.Lately I've been using shunt regulators on the base string of cap multipliers. AFAICT the best is the Exar SPX431A. You can adjust that to lop off the ripple if you like, though of course it isn't as efficient as using a huge cap. 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 ●May 28, 20142014-05-28
On Tuesday, May 27, 2014 8:27:19 PM UTC-4, Phil Hobbs wrote:> On 5/27/2014 7:21 PM, John Larkin wrote: > > > On Mon, 26 May 2014 21:50:17 -0400, Phil Hobbs > > > Lately I've been using shunt regulators on the base string of cap > multipliers. AFAICT the best is the Exar SPX431A. You can adjust that > to lop off the ripple if you like, though of course it isn't as > efficient as using a huge cap.That's interesting, the Exar is "best" because it has the least noise to start with? As you've said, the reference/regulator can be the noisiest part of a design. I've got an LT3080 in an instrument. (cap multiplier after it.) And I've regretted it. Much better to just make your own, (reference->opamp->transistor) George H.> > > > 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 ●May 28, 20142014-05-28
On 05/28/2014 10:24 AM, George Herold wrote:> On Tuesday, May 27, 2014 8:27:19 PM UTC-4, Phil Hobbs wrote: >> On 5/27/2014 7:21 PM, John Larkin wrote: >> >>> On Mon, 26 May 2014 21:50:17 -0400, Phil Hobbs >> >> >> Lately I've been using shunt regulators on the base string of cap >> multipliers. AFAICT the best is the Exar SPX431A. You can adjust that >> to lop off the ripple if you like, though of course it isn't as >> efficient as using a huge cap. > > That's interesting, the Exar is "best" because it has the least noise to start with? > > As you've said, the reference/regulator can be the noisiest part of a design. > I've got an LT3080 in an instrument. (cap multiplier after it.) > And I've regretted it. Much better to just make your own, > (reference->opamp->transistor) > > George H. >The Exar is quieter and has a lower minimum cathode current. 0-------*---------RRRR---*---* *-*----------0 | | \ / | R | \ A | R | ------ | R CCC | | R CCC R | | | R R | GND R R | R R | | R | | | *---RRRR---*--RRRR------* | | | | | | | | | CCC /---/ CCC | CCC / \---* CCC *--RRRR--* | --- | | | | GND | | GND | GND | | | GND *-------------* 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 ●May 28, 20142014-05-28
On Wed, 28 May 2014 13:05:31 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>On 05/28/2014 10:24 AM, George Herold wrote: >> On Tuesday, May 27, 2014 8:27:19 PM UTC-4, Phil Hobbs wrote: >>> On 5/27/2014 7:21 PM, John Larkin wrote: >>> >>>> On Mon, 26 May 2014 21:50:17 -0400, Phil Hobbs >>> >>> >>> Lately I've been using shunt regulators on the base string of cap >>> multipliers. AFAICT the best is the Exar SPX431A. You can adjust that >>> to lop off the ripple if you like, though of course it isn't as >>> efficient as using a huge cap. >> >> That's interesting, the Exar is "best" because it has the least noise to start with? >> >> As you've said, the reference/regulator can be the noisiest part of a design. >> I've got an LT3080 in an instrument. (cap multiplier after it.) >> And I've regretted it. Much better to just make your own, >> (reference->opamp->transistor) >> >> George H. >> > >The Exar is quieter and has a lower minimum cathode current. > >0-------*---------RRRR---*---* *-*----------0 > | | \ / | > R | \ A | > R | ------ | > R CCC | | > R CCC R | > | | R R > | GND R R > | R R > | | R > | | | > *---RRRR---*--RRRR------* | > | | | | > | | | | > CCC /---/ CCC | > CCC / \---* CCC *--RRRR--* > | --- | | | | > GND | | GND | GND > | | | > GND *-------------* > >Cheers > >Phil HobbsThat circuit necessarily increases Vce, which has additional benefits. Lots of circuits have good supply rejection at low frequencies and need help at high frequencies. In those cases, just RC power filtering works well. Polymer aluminum caps are great for that. I've also done closed-loop opamp regulators with a huge RC tau on the output. That lops off the HF part of the noise. -- John Larkin Highland Technology, Inc jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●May 28, 20142014-05-28
"John Larkin" <jlarkin@highlandtechnology.com> wrote in message news:ma7ao91fst4isv7k6h2dhc93kuqip6e1i5@4ax.com...> On Mon, 26 May 2014 21:50:17 -0400, Phil Hobbs > <hobbs@electrooptical.net> wrote: > >>On 5/26/2014 9:33 PM, John Larkin wrote: >>> On Sun, 25 May 2014 18:33:16 +0100, "Ian Field" >>> <gangprobing.alien@ntlworld.com> wrote: >>> >>>> >>>> >>>> "John Larkin" <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote in >>>> message >>>> news:e794o9tj2im9tflvlbisagg29g1crl7468@4ax.com... >>>>> On Sun, 25 May 2014 17:53:03 +0100, "Ian Field" >>>>> <gangprobing.alien@ntlworld.com> wrote: >>>>> >>>>>> >>>>>> >>>>>> "Jurd" <guitardorkspamspameggsandham74@gmail.com> wrote in message >>>>>> news:llrkq5$hr4$1@news.albasani.net... >>>>>>> On 5/24/2014 8:48 PM, John Larkin wrote: >>>>>>>> On Sat, 24 May 2014 20:06:45 -0500, Jurd >>>>>>> >>>>>>>> >>>>>>>> That bridge configuration will in theory charge the caps to 1.41 >>>>>>>> times >>>>>>>> the RMS voltage of the transformer secondary, because a sine wave >>>>>>>> has >>>>>>>> a peak voltage 1.41x its RMS. >>>>>>>> >>>>>>>> In real life you'd typically get more DC than that at light loads >>>>>>>> and >>>>>>>> less at heavy loads. And the "DC" will have ripple, which makes the >>>>>>>> voltage dip at 120 Hz (100 Hz in the hinterlands). >>>>>>>> >>>>>>>> >>>>>>> >>>>>>> Ah thanks. Good to know about the ripple, as that's certainly >>>>>>> something >>>>>>> I'd like to avoid. Back to the Googling board! >>>>>> >>>>>> Search under "active ripple cancelling" - pretty much just an emitter >>>>>> follower with some bias and a not quite as huge electrolytic as you'd >>>>>> need >>>>>> on its own. >>>>> >>>>> That doesn't help when you're building a power supply. You may as well >>>>> just connect the rectifier caps to the main linear regulator. That's >>>>> better, actually; a ripple canceler ahead of the regulator makes >>>>> things worse. >>>>> >>>>> The issue is energy storage. 120 times a second, the transformer >>>>> output goes to zero volts. If you want to keep powering the load then, >>>>> the energy has to come from somewhere, and in this case it's the >>>>> filter caps. >>>> >>>> I never said don't use reservoir caps - an unregulated emitter follower >>>> with >>>> a heavily decoupled base does its best to follow the insignificant >>>> ripple on >>>> its base. >>> >>> Problem is, it will also follow the significant ripple on its >>> collector. >>> >>> >>Nah, that's a capacitance multiplier. As long as you don't let it >>saturate, it's the bomb for supply rejection. > > Sure, as long as the input ripple is small, a few tenths p-p. But the > suggestion was to put the c-multiplier between the bridge+filter capsWho suggested that then - I never even mentioned the bridge and filter caps.
Reply by ●May 28, 20142014-05-28
On Wednesday, May 28, 2014 1:05:31 PM UTC-4, Phil Hobbs wrote:> On 05/28/2014 10:24 AM, George Herold wrote: > > On Tuesday, May 27, 2014 8:27:19 PM UTC-4, Phil Hobbs wrote: > >> On 5/27/2014 7:21 PM, John Larkin wrote > >> > >> Lately I've been using shunt regulators on the base string of cap > >> multipliers. AFAICT the best is the Exar SPX431A. You can adjust that > >> to lop off the ripple if you like, though of course it isn't as > >> efficient as using a huge cap. > > > > That's interesting, the Exar is "best" because it has the least noise to start with? > > > > > > The Exar is quieter and has a lower minimum cathode current. >Nice, I like that you've got the cap multiplier inside the feedback path. Thanks, George H. <snipping Phil's circuit>> 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 ●May 28, 20142014-05-28
On Wednesday, May 28, 2014 10:05:31 AM UTC-7, Phil Hobbs wrote:> >> Lately I've been using shunt regulators on the base string of cap >=20 > >> multipliers. AFAICT the best is the Exar SPX431A.=20 > The Exar is quieter and has a lower minimum cathode current.It's possible to get lower (SPX431A wants over 400 uA, and TLV431 wants over 50 uA) but there's some cathode-voltage-range issues, too. Have you considered direct shunt regulation? 0--------*---RRRR---*-----*----------0=20 =A0 =A0 =A0 =A0 =A0| =A0 =A0 =A0 =A0 =A0| =A0|=20 =A0 =A0 =A0 =A0 =A0R =A0 =A0 =A0 =A0| =A0 |=20 =A0 =A0 =A0 =A0 =A0R =A0 =A0 =A0 =A0 =A0| =A0 =A0 *-----*=20 =A0 =A0 =A0 =A0 =A0R =A0 =A0 =A0 =A0 CCC =A0 =A0R | =A0 =A0 =A0 =A0 =A0R =A0 =A0 =A0 =A0 CCC =A0 R C =A0 =A0 =A0 =A0 =A0| =A0 =A0 =A0 =A0 =A0| =A0 =A0 R | =A0 =A0 =A0 =A0 =A0| =A0 =A0 =A0 =A0 =A0|=A0 =A0 =A0*-----*=20 =A0 =A0 =A0 =A0 =A0*--RRRR----* |=20 =A0 =A0 =A0 =A0 =A0| =A0 =A0 =A0 =A0 =A0| =A0=A0=A0 |=20 =A0 =A0 =A0 =A0 =A0| =A0 =A0 =A0 /---/ =A0 |=20 =A0 =A0 =A0 =A0 CCC =A0 =A0 =A0 =A0/ \----* =A0 =A0 =A0 =A0 CCC =A0 =A0 =A0=A0 --- =A0 | =A0 =A0 =A0 =A0 =A0| =A0 =A0 =A0 =A0 | =A0 =A0R =A0 | =A0 | R =A0 =A0 =A0 =A0 GND =A0 =A0 =A0 =A0 | |=20 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0GND =A0 GND
