On Friday, February 3, 2023 at 7:50:52 PM UTC-8, John Larkin wrote:> On Fri, 3 Feb 2023 14:55:32 -0500, Phil Hobbs > <pcdhSpamM...@electrooptical.net> wrote:> >... we're > >kicking around the idea of using a rail splitter on our usual 24V wall > >warts to make +15/-9 or something like that. We'd probably use a > >TCA0372 and a couple of big caps for the job.> This should work: > > https://www.dropbox.com/s/1v66augsxfmlx3f/Rail_Splitter_1.jpg?raw=1Maybe, but if ground-to-minus current is over 5 mA, the negative regulation vanishes (it needs bias current to stabilize the zener voltage).
Rail-splitting a wall wart
Started by ●February 3, 2023
Reply by ●February 4, 20232023-02-04
Reply by ●February 4, 20232023-02-04
On Sat, 4 Feb 2023 09:47:06 -0800 (PST), whit3rd <whit3rd@gmail.com> wrote:>On Friday, February 3, 2023 at 7:50:52 PM UTC-8, John Larkin wrote: >> On Fri, 3 Feb 2023 14:55:32 -0500, Phil Hobbs >> <pcdhSpamM...@electrooptical.net> wrote: > >> >... we're >> >kicking around the idea of using a rail splitter on our usual 24V wall >> >warts to make +15/-9 or something like that. We'd probably use a >> >TCA0372 and a couple of big caps for the job. > > >> This should work: >> >> https://www.dropbox.com/s/1v66augsxfmlx3f/Rail_Splitter_1.jpg?raw=1 > >Maybe, but if ground-to-minus current is over 5 mA, the negative regulation >vanishes (it needs bias current to stabilize the zener voltage).Most situations more V+ than V-. If this circuit won't work for you, don't use it. Or add a dump resistor somewhere.
Reply by ●February 5, 20232023-02-05
On 2023-02-03 16:05, Lasse Langwadt Christensen wrote:> fredag den 3. februar 2023 kl. 21.50.16 UTC+1 skrev John Larkin: >> On Fri, 3 Feb 2023 14:55:32 -0500, Phil Hobbs >> <pcdhSpamM...@electrooptical.net> wrote: >> >>> So we keep being asked for simple TIAs as incidental parts of our >>> consulting work. They're useful to have around anyway. >>> >>> It's a pain getting them to work right if we put SMPSes inside, so we're >>> kicking around the idea of using a rail splitter on our usual 24V wall >>> warts to make +15/-9 or something like that. We'd probably use a >>> TCA0372 and a couple of big caps for the job. >>> >>> Two-wire warts are isolated, of course, so as long as no bright spark >>> decides to try running our box on the same wart as somebody else's, we >>> should be fine, I think, but we haven't done it before. >>> >>> Suggestions? >>> >>> Cheers >>> >>> Phil Hobbs >> I like the little CUI dual-output dc/dc converters. Or one of the >> LM266x inverting charge pumps. But they might be noisy. >> >> The little 3-terminal switchers will invert too. Some are around one >> dollar. >> >> I'd expect that a TIA wouldn't need much current, so a rail splitter >> is sensible. >> >> Wouldn't a negative regulator, an LM337 or a 7905, work as a rail >> splitter? > > Lm317 + LM337 > > https://www.eevblog.com/forum/beginners/lm317-dual-shunt-regulator/msg4632967/#msg4632967 >Yeah, it's possible to bodge regulators to do that sort of thing after a fashion, but getting decent performance in all four quadrants takes a lot of parts AFAICT. I'm leaning towards using a TCA0372 and a voltage divider to do the actual splitting, and then fixing it up for overcurrent with a dual comparator with mega hysteresis and back-to-back MOSFETs to cut the power. Thanks 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 5, 20232023-02-05
søndag den 5. februar 2023 kl. 05.48.59 UTC+1 skrev Phil Hobbs:> On 2023-02-03 16:05, Lasse Langwadt Christensen wrote: > > fredag den 3. februar 2023 kl. 21.50.16 UTC+1 skrev John Larkin: > >> On Fri, 3 Feb 2023 14:55:32 -0500, Phil Hobbs > >> <pcdhSpamM...@electrooptical.net> wrote: > >> > >>> So we keep being asked for simple TIAs as incidental parts of our > >>> consulting work. They're useful to have around anyway. > >>> > >>> It's a pain getting them to work right if we put SMPSes inside, so we're > >>> kicking around the idea of using a rail splitter on our usual 24V wall > >>> warts to make +15/-9 or something like that. We'd probably use a > >>> TCA0372 and a couple of big caps for the job. > >>> > >>> Two-wire warts are isolated, of course, so as long as no bright spark > >>> decides to try running our box on the same wart as somebody else's, we > >>> should be fine, I think, but we haven't done it before. > >>> > >>> Suggestions? > >>> > >>> Cheers > >>> > >>> Phil Hobbs > >> I like the little CUI dual-output dc/dc converters. Or one of the > >> LM266x inverting charge pumps. But they might be noisy. > >> > >> The little 3-terminal switchers will invert too. Some are around one > >> dollar. > >> > >> I'd expect that a TIA wouldn't need much current, so a rail splitter > >> is sensible. > >> > >> Wouldn't a negative regulator, an LM337 or a 7905, work as a rail > >> splitter? > > > > Lm317 + LM337 > > > > https://www.eevblog.com/forum/beginners/lm317-dual-shunt-regulator/msg4632967/#msg4632967 > > > Yeah, it's possible to bodge regulators to do that sort of thing after a > fashion, but getting decent performance in all four quadrants takes a > lot of parts AFAICT. > > I'm leaning towards using a TCA0372 and a voltage divider to do the > actual splitting, and then fixing it up for overcurrent with a dual > comparator with mega hysteresis and back-to-back MOSFETs to cut the power.yeh, an opamp is easiest and it looks like that one is thermally protected so it should be pretty safe maybe add poly fuses to the input supply in case someone does something silly
Reply by ●February 5, 20232023-02-05
On 2023-02-03 16:16, piglet wrote:> On 03/02/2023 7:55 pm, Phil Hobbs wrote: >> So we keep being asked for simple TIAs as incidental parts of our >> consulting work. They're useful to have around anyway. >> >> It's a pain getting them to work right if we put SMPSes inside, so >> we're kicking around the idea of using a rail splitter on our usual >> 24V wall warts to make +15/-9 or something like that. We'd probably >> use a TCA0372 and a couple of big caps for the job. >> >> Two-wire warts are isolated, of course, so as long as no bright spark >> decides to try running our box on the same wart as somebody else's, we >> should be fine, I think, but we haven't done it before. >> >> Suggestions?>> > Wall warts are only isolated at DC! Some have horrible HF noise. > > Only you know the kind of users but a lot of folk have trouble getting > their mind around the idea of the non-positive supply rail not being > ground. The near standard barrel DC jack with center pin positive > encourages that notion so you may want to consider using a non-standard > power connector? > > piglet >We have that problem already, even in products with inverting switchers making the negative supply. Simon has been hacking KiCad to make it easy to plunk in our standard IP blocks, such as cap multipliers for various current ranges, fast quiet PGAs, MCUs with Modbus over RS-485, and so on. We have these nice machined brass boxes with feedthrough caps that we're using for lots of stuff these days. There's a 3D printed section attached that has space for connectors and line filters, so that crap basically never gets inside the box. So filtering the wart's output before letting it into the box is fairly easy. 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 5, 20232023-02-05
søndag den 5. februar 2023 kl. 21.35.16 UTC+1 skrev Phil Hobbs:> On 2023-02-03 16:16, piglet wrote: > > On 03/02/2023 7:55 pm, Phil Hobbs wrote: > >> So we keep being asked for simple TIAs as incidental parts of our > >> consulting work. They're useful to have around anyway. > >> > >> It's a pain getting them to work right if we put SMPSes inside, so > >> we're kicking around the idea of using a rail splitter on our usual > >> 24V wall warts to make +15/-9 or something like that. We'd probably > >> use a TCA0372 and a couple of big caps for the job. > >> > >> Two-wire warts are isolated, of course, so as long as no bright spark > >> decides to try running our box on the same wart as somebody else's, we > >> should be fine, I think, but we haven't done it before. > >> > >> Suggestions? > > >> > > Wall warts are only isolated at DC! Some have horrible HF noise. > > > > Only you know the kind of users but a lot of folk have trouble getting > > their mind around the idea of the non-positive supply rail not being > > ground. The near standard barrel DC jack with center pin positive > > encourages that notion so you may want to consider using a non-standard > > power connector? > > > > piglet > > > We have that problem already, even in products with inverting switchers > making the negative supply. > > Simon has been hacking KiCad to make it easy to plunk in our standard IP > blocks, such as cap multipliers for various current ranges, fast quiet > PGAs, MCUs with Modbus over RS-485, and so on. > > We have these nice machined brass boxes with feedthrough caps that we're > using for lots of stuff these days.you machine the boxes? then machine a separate cavity for the inverter?
Reply by ●February 5, 20232023-02-05
On 2023-02-05 15:46, Lasse Langwadt Christensen wrote:> søndag den 5. februar 2023 kl. 21.35.16 UTC+1 skrev Phil Hobbs: >> On 2023-02-03 16:16, piglet wrote: >>> On 03/02/2023 7:55 pm, Phil Hobbs wrote: >>>> So we keep being asked for simple TIAs as incidental parts of our >>>> consulting work. They're useful to have around anyway. >>>> >>>> It's a pain getting them to work right if we put SMPSes inside, so >>>> we're kicking around the idea of using a rail splitter on our usual >>>> 24V wall warts to make +15/-9 or something like that. We'd probably >>>> use a TCA0372 and a couple of big caps for the job. >>>> >>>> Two-wire warts are isolated, of course, so as long as no bright spark >>>> decides to try running our box on the same wart as somebody else's, we >>>> should be fine, I think, but we haven't done it before. >>>> >>>> Suggestions? >> >>>> >>> Wall warts are only isolated at DC! Some have horrible HF noise. >>> >>> Only you know the kind of users but a lot of folk have trouble getting >>> their mind around the idea of the non-positive supply rail not being >>> ground. The near standard barrel DC jack with center pin positive >>> encourages that notion so you may want to consider using a non-standard >>> power connector? >>> >>> piglet >>> >> We have that problem already, even in products with inverting switchers >> making the negative supply. >> >> Simon has been hacking KiCad to make it easy to plunk in our standard IP >> blocks, such as cap multipliers for various current ranges, fast quiet >> PGAs, MCUs with Modbus over RS-485, and so on. >> >> We have these nice machined brass boxes with feedthrough caps that we're >> using for lots of stuff these days. > > you machine the boxes? then machine a separate cavity for the inverter? > >Yeah, it's pretty cheap to do machined lead brass, because it cuts so easily. (You lot can't use it on account of the regime, but oh well.) We could do separate cavities and all that, but due to the getting-off-the-couch setup charge, it's better to use one box design and hang 3D printed stuff off to the side. (It all looks like DKNY black/gold bling anyway.) 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 5, 20232023-02-05
søndag den 5. februar 2023 kl. 22.26.06 UTC+1 skrev Phil Hobbs:> On 2023-02-05 15:46, Lasse Langwadt Christensen wrote: > > søndag den 5. februar 2023 kl. 21.35.16 UTC+1 skrev Phil Hobbs: > >> On 2023-02-03 16:16, piglet wrote: > >>> On 03/02/2023 7:55 pm, Phil Hobbs wrote: > >>>> So we keep being asked for simple TIAs as incidental parts of our > >>>> consulting work. They're useful to have around anyway. > >>>> > >>>> It's a pain getting them to work right if we put SMPSes inside, so > >>>> we're kicking around the idea of using a rail splitter on our usual > >>>> 24V wall warts to make +15/-9 or something like that. We'd probably > >>>> use a TCA0372 and a couple of big caps for the job. > >>>> > >>>> Two-wire warts are isolated, of course, so as long as no bright spark > >>>> decides to try running our box on the same wart as somebody else's, we > >>>> should be fine, I think, but we haven't done it before. > >>>> > >>>> Suggestions? > >> > >>>> > >>> Wall warts are only isolated at DC! Some have horrible HF noise. > >>> > >>> Only you know the kind of users but a lot of folk have trouble getting > >>> their mind around the idea of the non-positive supply rail not being > >>> ground. The near standard barrel DC jack with center pin positive > >>> encourages that notion so you may want to consider using a non-standard > >>> power connector? > >>> > >>> piglet > >>> > >> We have that problem already, even in products with inverting switchers > >> making the negative supply. > >> > >> Simon has been hacking KiCad to make it easy to plunk in our standard IP > >> blocks, such as cap multipliers for various current ranges, fast quiet > >> PGAs, MCUs with Modbus over RS-485, and so on. > >> > >> We have these nice machined brass boxes with feedthrough caps that we're > >> using for lots of stuff these days. > > > > you machine the boxes? then machine a separate cavity for the inverter? > > > > > Yeah, it's pretty cheap to do machined lead brass, because it cuts so > easily. (You lot can't use it on account of the regime, but oh well.) > > We could do separate cavities and all that, but due to the > getting-off-the-couch setup charge, it's better to use one box design > and hang 3D printed stuff off to the side. (It all looks like DKNY > black/gold bling anyway.)SMD RF shield cans are pretty cheap too
Reply by ●February 5, 20232023-02-05
On 2023-02-05 16:37, Lasse Langwadt Christensen wrote:> søndag den 5. februar 2023 kl. 22.26.06 UTC+1 skrev Phil Hobbs: >> On 2023-02-05 15:46, Lasse Langwadt Christensen wrote: >>> søndag den 5. februar 2023 kl. 21.35.16 UTC+1 skrev Phil Hobbs: >>>> On 2023-02-03 16:16, piglet wrote: >>>>> On 03/02/2023 7:55 pm, Phil Hobbs wrote: >>>>>> So we keep being asked for simple TIAs as incidental parts of our >>>>>> consulting work. They're useful to have around anyway. >>>>>> >>>>>> It's a pain getting them to work right if we put SMPSes inside, so >>>>>> we're kicking around the idea of using a rail splitter on our usual >>>>>> 24V wall warts to make +15/-9 or something like that. We'd probably >>>>>> use a TCA0372 and a couple of big caps for the job. >>>>>> >>>>>> Two-wire warts are isolated, of course, so as long as no bright spark >>>>>> decides to try running our box on the same wart as somebody else's, we >>>>>> should be fine, I think, but we haven't done it before. >>>>>> >>>>>> Suggestions? >>>> >>>>>> >>>>> Wall warts are only isolated at DC! Some have horrible HF noise. >>>>> >>>>> Only you know the kind of users but a lot of folk have trouble getting >>>>> their mind around the idea of the non-positive supply rail not being >>>>> ground. The near standard barrel DC jack with center pin positive >>>>> encourages that notion so you may want to consider using a non-standard >>>>> power connector? >>>>> >>>>> piglet >>>>> >>>> We have that problem already, even in products with inverting switchers >>>> making the negative supply. >>>> >>>> Simon has been hacking KiCad to make it easy to plunk in our standard IP >>>> blocks, such as cap multipliers for various current ranges, fast quiet >>>> PGAs, MCUs with Modbus over RS-485, and so on. >>>> >>>> We have these nice machined brass boxes with feedthrough caps that we're >>>> using for lots of stuff these days. >>> >>> you machine the boxes? then machine a separate cavity for the inverter? >>> >>> >> Yeah, it's pretty cheap to do machined lead brass, because it cuts so >> easily. (You lot can't use it on account of the regime, but oh well.) >> >> We could do separate cavities and all that, but due to the >> getting-off-the-couch setup charge, it's better to use one box design >> and hang 3D printed stuff off to the side. (It all looks like DKNY >> black/gold bling anyway.) > > SMD RF shield cans are pretty cheap too >Yup. We use them a fair amount to control local interference, but just letting a noisy wire into the box creates problems from unknown outside stuff. 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 5, 20232023-02-05
søndag den 5. februar 2023 kl. 22.42.57 UTC+1 skrev Phil Hobbs:> On 2023-02-05 16:37, Lasse Langwadt Christensen wrote: > > søndag den 5. februar 2023 kl. 22.26.06 UTC+1 skrev Phil Hobbs: > >> On 2023-02-05 15:46, Lasse Langwadt Christensen wrote: > >>> søndag den 5. februar 2023 kl. 21.35.16 UTC+1 skrev Phil Hobbs: > >>>> On 2023-02-03 16:16, piglet wrote: > >>>>> On 03/02/2023 7:55 pm, Phil Hobbs wrote: > >>>>>> So we keep being asked for simple TIAs as incidental parts of our > >>>>>> consulting work. They're useful to have around anyway. > >>>>>> > >>>>>> It's a pain getting them to work right if we put SMPSes inside, so > >>>>>> we're kicking around the idea of using a rail splitter on our usual > >>>>>> 24V wall warts to make +15/-9 or something like that. We'd probably > >>>>>> use a TCA0372 and a couple of big caps for the job. > >>>>>> > >>>>>> Two-wire warts are isolated, of course, so as long as no bright spark > >>>>>> decides to try running our box on the same wart as somebody else's, we > >>>>>> should be fine, I think, but we haven't done it before. > >>>>>> > >>>>>> Suggestions? > >>>> > >>>>>> > >>>>> Wall warts are only isolated at DC! Some have horrible HF noise. > >>>>> > >>>>> Only you know the kind of users but a lot of folk have trouble getting > >>>>> their mind around the idea of the non-positive supply rail not being > >>>>> ground. The near standard barrel DC jack with center pin positive > >>>>> encourages that notion so you may want to consider using a non-standard > >>>>> power connector? > >>>>> > >>>>> piglet > >>>>> > >>>> We have that problem already, even in products with inverting switchers > >>>> making the negative supply. > >>>> > >>>> Simon has been hacking KiCad to make it easy to plunk in our standard IP > >>>> blocks, such as cap multipliers for various current ranges, fast quiet > >>>> PGAs, MCUs with Modbus over RS-485, and so on. > >>>> > >>>> We have these nice machined brass boxes with feedthrough caps that we're > >>>> using for lots of stuff these days. > >>> > >>> you machine the boxes? then machine a separate cavity for the inverter? > >>> > >>> > >> Yeah, it's pretty cheap to do machined lead brass, because it cuts so > >> easily. (You lot can't use it on account of the regime, but oh well.) > >> > >> We could do separate cavities and all that, but due to the > >> getting-off-the-couch setup charge, it's better to use one box design > >> and hang 3D printed stuff off to the side. (It all looks like DKNY > >> black/gold bling anyway.) > > > > SMD RF shield cans are pretty cheap too > > > Yup. We use them a fair amount to control local interference, but just > letting a noisy wire into the box creates problems from unknown outside > stuff.would you have the same issue with a wall wart?
