Phil Hobbs wrote:> On 7/16/2013 5:10 PM, Joerg wrote: >> Phil Hobbs wrote: >>> On 07/16/2013 03:52 PM, Jim Thompson wrote: >>>> On Tue, 16 Jul 2013 15:08:24 -0400, Phil Hobbs >>>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>>> >>>>> So, I'm goofing off playing with small switchers. (Well, not exactly >>>>> goofing off, but there are somewhat more pressing tasks waiting....) >>>>> >>>>> As I said in George's thread, "Opamp w/ Vsupply > 36V", I built a >>>>> small >>>>> half-bridge supply with positive and negative voltage doublers. >>>>> I'm not >>>>> that keen on it, because (a) it uses a fair number of parts for >>>>> what it >>>>> does, and (b) it has a nasty instability. >>>>> >>>>> With a capacitively-coupled half bridge, if you let the transformer >>>>> saturate, it instantly discharges the coupling cap, which about >>>>> doubles >>>>> the volt-seconds on the next half-cycle and guarantee that it will >>>>> keep >>>>> saturating until the FETs cook themselves. >>>>> >>>>> The particular little ISDN transformers I'm using have really >>>>> amazingly >>>>> low leakage inductance, so I'm thinking about using a current-mode >>>>> flyback instead. The UCC28C45 bicmos controller chip looks pretty >>>>> suitable--it's about the same price as the IRS2153D, needs one less >>>>> FET, >>>>> runs up to 1 MHz, and with such a low leakage inductance I wouldn't >>>>> expect to need much snubbing, if any. Plus I can run the transformer >>>>> right up to its maximum volt-seconds without worrying. >>>>> >>>>> Ideally I'd like it to give me +-45 V at about 20 mA each. >>>>> >>>>> Any words of wisdom? >>>>> >>>>> Cheers >>>>> >>>>> Phil Hobbs >>>> >>>> Do you have a decent Spice model for the ISDN transformer? >>>> >>>> ...Jim Thompson >>>> >>> >>> It's 2.2 mH CT : 8.8 mH CT. >>> >>> On the 9 mH side, with the 2 mH side shorted, my trusty Heathkit HD1250 >>> dip meter ... >> >> >> Hey, I've got the same one. Since childhood. >> >> >>> ... shows it resonating at 2.1 MHz with 4.9 nF in parallel, which >>> is 1.2 uH. ... >> >> >> Careful. You've got tons of winding capacitance in there which can >> seriously fool one into believing a much too small number. You have to >> measure the leakage inductance at frequency-of-interest, using an >> impedance analyzer or do it in a more pedestrian fashion via generator >> and meter. > > I sort of doubt that there are nanofarads of distributed capacitance in > that tiny transformer, though, because otherwise its open-circuit > resonance would be way too low. It works as a transformer up to well > over 1 MHz, so at 9 mH, the winding capacitance has to be down in the > lowish picofarads. >Not nanofarads but I bet the transformer is far from a 0.99986 coupling factor. [...] -- Regards, Joerg http://www.analogconsultants.com/
Flyback vs half-bridge
Started by ●July 16, 2013
Reply by ●July 16, 20132013-07-16
Reply by ●July 16, 20132013-07-16
On 7/16/2013 8:42 PM, Joerg wrote:> Phil Hobbs wrote: >> On 7/16/2013 5:10 PM, Joerg wrote: >>> Phil Hobbs wrote: >>>> On 07/16/2013 03:52 PM, Jim Thompson wrote: >>>>> On Tue, 16 Jul 2013 15:08:24 -0400, Phil Hobbs >>>>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>>>> >>>>>> So, I'm goofing off playing with small switchers. (Well, not exactly >>>>>> goofing off, but there are somewhat more pressing tasks waiting....) >>>>>> >>>>>> As I said in George's thread, "Opamp w/ Vsupply > 36V", I built a >>>>>> small >>>>>> half-bridge supply with positive and negative voltage doublers. >>>>>> I'm not >>>>>> that keen on it, because (a) it uses a fair number of parts for >>>>>> what it >>>>>> does, and (b) it has a nasty instability. >>>>>> >>>>>> With a capacitively-coupled half bridge, if you let the transformer >>>>>> saturate, it instantly discharges the coupling cap, which about >>>>>> doubles >>>>>> the volt-seconds on the next half-cycle and guarantee that it will >>>>>> keep >>>>>> saturating until the FETs cook themselves. >>>>>> >>>>>> The particular little ISDN transformers I'm using have really >>>>>> amazingly >>>>>> low leakage inductance, so I'm thinking about using a current-mode >>>>>> flyback instead. The UCC28C45 bicmos controller chip looks pretty >>>>>> suitable--it's about the same price as the IRS2153D, needs one less >>>>>> FET, >>>>>> runs up to 1 MHz, and with such a low leakage inductance I wouldn't >>>>>> expect to need much snubbing, if any. Plus I can run the transformer >>>>>> right up to its maximum volt-seconds without worrying. >>>>>> >>>>>> Ideally I'd like it to give me +-45 V at about 20 mA each. >>>>>> >>>>>> Any words of wisdom? >>>>>> >>>>>> Cheers >>>>>> >>>>>> Phil Hobbs >>>>> >>>>> Do you have a decent Spice model for the ISDN transformer? >>>>> >>>>> ...Jim Thompson >>>>> >>>> >>>> It's 2.2 mH CT : 8.8 mH CT. >>>> >>>> On the 9 mH side, with the 2 mH side shorted, my trusty Heathkit HD1250 >>>> dip meter ... >>> >>> >>> Hey, I've got the same one. Since childhood. >>> >>> >>>> ... shows it resonating at 2.1 MHz with 4.9 nF in parallel, which >>>> is 1.2 uH. ... >>> >>> >>> Careful. You've got tons of winding capacitance in there which can >>> seriously fool one into believing a much too small number. You have to >>> measure the leakage inductance at frequency-of-interest, using an >>> impedance analyzer or do it in a more pedestrian fashion via generator >>> and meter. >> >> I sort of doubt that there are nanofarads of distributed capacitance in >> that tiny transformer, though, because otherwise its open-circuit >> resonance would be way too low. It works as a transformer up to well >> over 1 MHz, so at 9 mH, the winding capacitance has to be down in the >> lowish picofarads. >> > > Not nanofarads but I bet the transformer is far from a 0.99986 coupling > factor. > > [...] >So what's wrong with the measured values? I can do it over with e.g. 3300 and 5000 pF, and compare the two estimated inductances. That should be fairly diagnostic, unless I'm missing something ultra-important. That sort of coupling coefficient is similar to large mains transformers, for instance. 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 USA +1 845 480 2058 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●July 16, 20132013-07-16
Phil Hobbs wrote:> On 7/16/2013 3:53 PM, Joerg wrote: >> Phil Hobbs wrote: >>> So, I'm goofing off playing with small switchers. (Well, not exactly >>> goofing off, but there are somewhat more pressing tasks waiting....) >>> >>> As I said in George's thread, "Opamp w/ Vsupply > 36V", I built a small >>> half-bridge supply with positive and negative voltage doublers. I'm not >>> that keen on it, because (a) it uses a fair number of parts for what it >>> does, and (b) it has a nasty instability. >>> >> >> (a) ... yes. (b) ... why? What happens? Changing to another architecture >> while using the same kind of loop usually doesn't do much to improve >> stability. >> >> >>> With a capacitively-coupled half bridge, if you let the transformer >>> saturate, it instantly discharges the coupling cap, which about doubles >>> the volt-seconds on the next half-cycle and guarantee that it will keep >>> saturating until the FETs cook themselves. >>> >> >> Not sure what you mean here, but usually current mode control is the way >> to avoid asymmetrical runaway. > > The IRS2153D puts a square wave out of a half-bridge--no feedback, no > current limit, nada. If you put that into a transformer via a cap, all > is well until you saturate the transformer. >Ok, the IRS2153D is just a glorified gate driver with an oscillator in there. I'd use a real switcher controller chip, some are in the same price category.> Say that happens on the positive half-cycle. > At that moment, the voltage on the cap rapidly goes from V_DD/2 to V_DD. > At the next edge, the voltage across the transformer is suddenly not > V_DD/2 as expected, but V_DD. The transformer saturates in half the > time it took previously, and the voltage on the cap goes from V_DD to 0. > Then the cycle repeats. It's really obvious on a scope when this > happens, and it's far from pretty. >Did you use a really big cap? I've never had that happen. Usually ferrite saturates softly enough to just "nudge" the cap.> On each half cycle, roughly 0.5 C_coup*V_DD**2 gets dissipated in one of > the FETs, which gradually cook themselves. >More than once have I had that, SMT parts slowly sliding down the board because the solder melted :-)>>> The particular little ISDN transformers I'm using have really amazingly >>> low leakage inductance, so I'm thinking about using a current-mode >>> flyback instead. The UCC28C45 bicmos controller chip looks pretty >>> suitable--it's about the same price as the IRS2153D, needs one less FET, >>> runs up to 1 MHz, and with such a low leakage inductance I wouldn't >>> expect to need much snubbing, if any. Plus I can run the transformer >>> right up to its maximum volt-seconds without worrying. >>> >>> Ideally I'd like it to give me +-45 V at about 20 mA each. >>> >>> Any words of wisdom? >>> >> >> ISDN transformers don't have much air gap, and you need air gap for a >> flyback. Plus ISDN is on the way out in many areas so if this has to >> remain in production until the cows come home I wouldn't. > > So I'm discovering. The actual amount of energy I can store in that > toroid isn't very large, so to get any power out of it I have to run it > pretty fast. With 2.2 mH of primary inductance, that takes quite a bit > of voltage, which makes the whole flyback thing sort of moot. > >> >> John Larkin has recently used these tiny flyback transformers. Nothing >> wrong with hanging two in parallel on the primary and using the 2nd one >> with the secondary flipped around, for the -45V. >> >> Do you need this isolated? Else you could consider just inverting and >> boost. >> > > Doesn't have to be isolated, but it does need to be quiet, hence the > toroids. >That usually rules out flybacks. They spew a lot of noise. Then I'd use a half-bridge with CM control and series inductors on the output. -- Regards, Joerg http://www.analogconsultants.com/
Reply by ●July 16, 20132013-07-16
On Tue, 16 Jul 2013 20:46:37 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>On 7/16/2013 8:42 PM, Joerg wrote: >> Phil Hobbs wrote: >>> On 7/16/2013 5:10 PM, Joerg wrote: >>>> Phil Hobbs wrote: >>>>> On 07/16/2013 03:52 PM, Jim Thompson wrote: >>>>>> On Tue, 16 Jul 2013 15:08:24 -0400, Phil Hobbs >>>>>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>>>>> >>>>>>> So, I'm goofing off playing with small switchers. (Well, not exactly >>>>>>> goofing off, but there are somewhat more pressing tasks waiting....) >>>>>>> >>>>>>> As I said in George's thread, "Opamp w/ Vsupply > 36V", I built a >>>>>>> small >>>>>>> half-bridge supply with positive and negative voltage doublers. >>>>>>> I'm not >>>>>>> that keen on it, because (a) it uses a fair number of parts for >>>>>>> what it >>>>>>> does, and (b) it has a nasty instability. >>>>>>> >>>>>>> With a capacitively-coupled half bridge, if you let the transformer >>>>>>> saturate, it instantly discharges the coupling cap, which about >>>>>>> doubles >>>>>>> the volt-seconds on the next half-cycle and guarantee that it will >>>>>>> keep >>>>>>> saturating until the FETs cook themselves. >>>>>>> >>>>>>> The particular little ISDN transformers I'm using have really >>>>>>> amazingly >>>>>>> low leakage inductance, so I'm thinking about using a current-mode >>>>>>> flyback instead. The UCC28C45 bicmos controller chip looks pretty >>>>>>> suitable--it's about the same price as the IRS2153D, needs one less >>>>>>> FET, >>>>>>> runs up to 1 MHz, and with such a low leakage inductance I wouldn't >>>>>>> expect to need much snubbing, if any. Plus I can run the transformer >>>>>>> right up to its maximum volt-seconds without worrying. >>>>>>> >>>>>>> Ideally I'd like it to give me +-45 V at about 20 mA each. >>>>>>> >>>>>>> Any words of wisdom? >>>>>>> >>>>>>> Cheers >>>>>>> >>>>>>> Phil Hobbs >>>>>> >>>>>> Do you have a decent Spice model for the ISDN transformer? >>>>>> >>>>>> ...Jim Thompson >>>>>> >>>>> >>>>> It's 2.2 mH CT : 8.8 mH CT. >>>>> >>>>> On the 9 mH side, with the 2 mH side shorted, my trusty Heathkit HD1250 >>>>> dip meter ... >>>> >>>> >>>> Hey, I've got the same one. Since childhood. >>>> >>>> >>>>> ... shows it resonating at 2.1 MHz with 4.9 nF in parallel, which >>>>> is 1.2 uH. ... >>>> >>>> >>>> Careful. You've got tons of winding capacitance in there which can >>>> seriously fool one into believing a much too small number. You have to >>>> measure the leakage inductance at frequency-of-interest, using an >>>> impedance analyzer or do it in a more pedestrian fashion via generator >>>> and meter. >>> >>> I sort of doubt that there are nanofarads of distributed capacitance in >>> that tiny transformer, though, because otherwise its open-circuit >>> resonance would be way too low. It works as a transformer up to well >>> over 1 MHz, so at 9 mH, the winding capacitance has to be down in the >>> lowish picofarads. >>> >> >> Not nanofarads but I bet the transformer is far from a 0.99986 coupling >> factor. >> >> [...] >> > >So what's wrong with the measured values? I can do it over with e.g. >3300 and 5000 pF, and compare the two estimated inductances. That >should be fairly diagnostic, unless I'm missing something ultra-important. > >That sort of coupling coefficient is similar to large mains >transformers, for instance. > >Cheers > >Phil HobbsBifalar 1:1 transformers are often spec'd 0.998. We measured a 1:1:2:2 ISDN at 0.99997! -- John Larkin Highland Technology, Inc jlarkin at highlandtechnology dot com http://www.highlandtechnology.com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser drivers and controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation
Reply by ●July 16, 20132013-07-16
On Tue, 16 Jul 2013 17:54:06 -0700, Joerg <invalid@invalid.invalid> wrote:>Phil Hobbs wrote: >> On 7/16/2013 3:53 PM, Joerg wrote: >>> Phil Hobbs wrote: >>>> So, I'm goofing off playing with small switchers. (Well, not exactly >>>> goofing off, but there are somewhat more pressing tasks waiting....) >>>> >>>> As I said in George's thread, "Opamp w/ Vsupply > 36V", I built a small >>>> half-bridge supply with positive and negative voltage doublers. I'm not >>>> that keen on it, because (a) it uses a fair number of parts for what it >>>> does, and (b) it has a nasty instability. >>>> >>> >>> (a) ... yes. (b) ... why? What happens? Changing to another architecture >>> while using the same kind of loop usually doesn't do much to improve >>> stability. >>> >>> >>>> With a capacitively-coupled half bridge, if you let the transformer >>>> saturate, it instantly discharges the coupling cap, which about doubles >>>> the volt-seconds on the next half-cycle and guarantee that it will keep >>>> saturating until the FETs cook themselves. >>>> >>> >>> Not sure what you mean here, but usually current mode control is the way >>> to avoid asymmetrical runaway. >> >> The IRS2153D puts a square wave out of a half-bridge--no feedback, no >> current limit, nada. If you put that into a transformer via a cap, all >> is well until you saturate the transformer. >> > >Ok, the IRS2153D is just a glorified gate driver with an oscillator in >there. I'd use a real switcher controller chip, some are in the same >price category. > > >> Say that happens on the positive half-cycle. >> At that moment, the voltage on the cap rapidly goes from V_DD/2 to V_DD. >> At the next edge, the voltage across the transformer is suddenly not >> V_DD/2 as expected, but V_DD. The transformer saturates in half the >> time it took previously, and the voltage on the cap goes from V_DD to 0. >> Then the cycle repeats. It's really obvious on a scope when this >> happens, and it's far from pretty. >> > >Did you use a really big cap? I've never had that happen. Usually >ferrite saturates softly enough to just "nudge" the cap. > > >> On each half cycle, roughly 0.5 C_coup*V_DD**2 gets dissipated in one of >> the FETs, which gradually cook themselves. >> > >More than once have I had that, SMT parts slowly sliding down the board >because the solder melted :-) > > >>>> The particular little ISDN transformers I'm using have really amazingly >>>> low leakage inductance, so I'm thinking about using a current-mode >>>> flyback instead. The UCC28C45 bicmos controller chip looks pretty >>>> suitable--it's about the same price as the IRS2153D, needs one less FET, >>>> runs up to 1 MHz, and with such a low leakage inductance I wouldn't >>>> expect to need much snubbing, if any. Plus I can run the transformer >>>> right up to its maximum volt-seconds without worrying. >>>> >>>> Ideally I'd like it to give me +-45 V at about 20 mA each. >>>> >>>> Any words of wisdom? >>>> >>> >>> ISDN transformers don't have much air gap, and you need air gap for a >>> flyback. Plus ISDN is on the way out in many areas so if this has to >>> remain in production until the cows come home I wouldn't. >> >> So I'm discovering. The actual amount of energy I can store in that >> toroid isn't very large, so to get any power out of it I have to run it >> pretty fast. With 2.2 mH of primary inductance, that takes quite a bit >> of voltage, which makes the whole flyback thing sort of moot. >> >>> >>> John Larkin has recently used these tiny flyback transformers. Nothing >>> wrong with hanging two in parallel on the primary and using the 2nd one >>> with the secondary flipped around, for the -45V. >>> >>> Do you need this isolated? Else you could consider just inverting and >>> boost. >>> >> >> Doesn't have to be isolated, but it does need to be quiet, hence the >> toroids. >> > >That usually rules out flybacks. They spew a lot of noise. Then I'd use >a half-bridge with CM control and series inductors on the output.In my IRS2153D thing, I used big gate resistors and gave up some efficiency. It's a couple inches away from a 12-bit, 250 MHz ADC. -- John Larkin Highland Technology, Inc jlarkin at highlandtechnology dot com http://www.highlandtechnology.com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser drivers and controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation
Reply by ●July 16, 20132013-07-16
On 7/16/2013 8:54 PM, Joerg wrote:> Phil Hobbs wrote: >> On 7/16/2013 3:53 PM, Joerg wrote: >>> Phil Hobbs wrote: >>>> So, I'm goofing off playing with small switchers. (Well, not exactly >>>> goofing off, but there are somewhat more pressing tasks waiting....) >>>> >>>> As I said in George's thread, "Opamp w/ Vsupply > 36V", I built a small >>>> half-bridge supply with positive and negative voltage doublers. I'm not >>>> that keen on it, because (a) it uses a fair number of parts for what it >>>> does, and (b) it has a nasty instability. >>>> >>> >>> (a) ... yes. (b) ... why? What happens? Changing to another architecture >>> while using the same kind of loop usually doesn't do much to improve >>> stability. >>> >>> >>>> With a capacitively-coupled half bridge, if you let the transformer >>>> saturate, it instantly discharges the coupling cap, which about doubles >>>> the volt-seconds on the next half-cycle and guarantee that it will keep >>>> saturating until the FETs cook themselves. >>>> >>> >>> Not sure what you mean here, but usually current mode control is the way >>> to avoid asymmetrical runaway. >> >> The IRS2153D puts a square wave out of a half-bridge--no feedback, no >> current limit, nada. If you put that into a transformer via a cap, all >> is well until you saturate the transformer. >> > > Ok, the IRS2153D is just a glorified gate driver with an oscillator in > there. I'd use a real switcher controller chip, some are in the same > price category. > > >> Say that happens on the positive half-cycle. >> At that moment, the voltage on the cap rapidly goes from V_DD/2 to V_DD. >> At the next edge, the voltage across the transformer is suddenly not >> V_DD/2 as expected, but V_DD. The transformer saturates in half the >> time it took previously, and the voltage on the cap goes from V_DD to 0. >> Then the cycle repeats. It's really obvious on a scope when this >> happens, and it's far from pretty. >> > > Did you use a really big cap? I've never had that happen. Usually > ferrite saturates softly enough to just "nudge" the cap.1 uF. I can probably post a scope photo tomorrow, if I have time--a bunch of lawyering has just descended on my head. (Not that I mind very much--expert witness work uses a different part of my brain and generally pays somewhat better than design work.)> ><snip>>>> John Larkin has recently used these tiny flyback transformers. Nothing >>> wrong with hanging two in parallel on the primary and using the 2nd one >>> with the secondary flipped around, for the -45V. >>> >>> Do you need this isolated? Else you could consider just inverting and >>> boost. >>> >> >> Doesn't have to be isolated, but it does need to be quiet, hence the >> toroids. >> > > That usually rules out flybacks. They spew a lot of noise. Then I'd use > a half-bridge with CM control and series inductors on the output.Fortunately the half-bridge's worst-case condition is zero load, so it isn't too hard to control. Of course the ungapped ferrite has a pretty frightening tempco of mu (it goes down by half when you hit it with cold spray), so some sort of current control is going to be required, for sure. 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 USA +1 845 480 2058 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●July 17, 20132013-07-17
On Tuesday, July 16, 2013 9:53:11 PM UTC+2, Joerg wrote:> Phil Hobbs wrote: > > > So, I'm goofing off playing with small switchers. (Well, not exactly > > > goofing off, but there are somewhat more pressing tasks waiting....) > > > > > > As I said in George's thread, "Opamp w/ Vsupply > 36V", I built a small > > > half-bridge supply with positive and negative voltage doublers. I'm not > > > that keen on it, because (a) it uses a fair number of parts for what it > > > does, and (b) it has a nasty instability. > > > > > > > (a) ... yes. (b) ... why? What happens? Changing to another architecture > > while using the same kind of loop usually doesn't do much to improve > > stability. > > > > > > > With a capacitively-coupled half bridge, if you let the transformer > > > saturate, it instantly discharges the coupling cap, which about doubles > > > the volt-seconds on the next half-cycle and guarantee that it will keep > > > saturating until the FETs cook themselves. > > > > > > > Not sure what you mean here, but usually current mode control is the way > > to avoid asymmetrical runaway. > >You need to be careful about that. Even if you have primary current mode peak limit, then inequalities in the secondary diodes forward drops can let the xformer go into staircasing, saturating the xformer. Cheers Klaus
Reply by ●July 17, 20132013-07-17
On Tue, 16 Jul 2013 14:08:39 -0700, John Larkin wrote:> On Tue, 16 Jul 2013 15:08:24 -0400, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >>So, I'm goofing off playing with small switchers. (Well, not exactly >>goofing off, but there are somewhat more pressing tasks waiting....) >> >>As I said in George's thread, "Opamp w/ Vsupply > 36V", I built a small >>half-bridge supply with positive and negative voltage doublers. I'm not >>that keen on it, because (a) it uses a fair number of parts for what it >>does, and (b) it has a nasty instability. >> >>With a capacitively-coupled half bridge, if you let the transformer >>saturate, it instantly discharges the coupling cap, which about doubles >>the volt-seconds on the next half-cycle and guarantee that it will keep >>saturating until the FETs cook themselves. >> >>The particular little ISDN transformers I'm using have really amazingly >>low leakage inductance, so I'm thinking about using a current-mode >>flyback instead. The UCC28C45 bicmos controller chip looks pretty >>suitable--it's about the same price as the IRS2153D, needs one less FET, >>runs up to 1 MHz, and with such a low leakage inductance I wouldn't >>expect to need much snubbing, if any. Plus I can run the transformer >>right up to its maximum volt-seconds without worrying. >> >>Ideally I'd like it to give me +-45 V at about 20 mA each. >> >>Any words of wisdom? >> >>Cheers >> >>Phil Hobbs > > The ISDNs work to pretty low frequencies, so a high frequency driver and > a small cap might fix the saturation problem. > > I recently saw a chip with an oscillator, flipflop, and two open-drain > outputs. You could drive a center-tapped primary winding with one of > those. The ISDN trannies caome in all sorts of ratios, like 1:1:2:2 for > example.Ya know, it seems that are proving to be a really useful SMPS transformer. A lot of small to moderate volume (different use) applications may keep them in production for a long time. ??-)
Reply by ●July 17, 20132013-07-17
On a sunny day (Tue, 16 Jul 2013 15:08:24 -0400) it happened Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote in <buSdne_Xk7O0B3jMnZ2dnUVZ_sudnZ2d@supernews.com>:>Ideally I'd like it to give me +-45 V at about 20 mA each.I have used simple sine wave oscillator and small E core (or potcore if you can get those), you know 1 transistor, feedback turn to base or emitter, tuning cap. Takes 5 minutes to wind it (1 turn per volt works usually). couple of 1N4148 diodes, some elcos. The advantage is that it does not radiate like a switcher, if that means anything to you. At 20 mA who cares about 99 % efficiency jive.
Reply by ●July 17, 20132013-07-17
On Tuesday, July 16, 2013 6:12:17 PM UTC-4, Phil Hobbs wrote:> On 7/16/2013 3:53 PM, Joerg wrote: > > > Phil Hobbs wrote:<snip original question>> >> Any words of wisdom? > > >> > > > > > > ISDN transformers don't have much air gap, and you need air gap for a > > flyback. Plus ISDN is on the way out in many areas so if this has to > > remain in production until the cows come home I wouldn't. > > So I'm discovering. The actual amount of energy I can store in that > toroid isn't very large, so to get any power out of it I have to run it > pretty fast. With 2.2 mH of primary inductance, that takes quite a bit > of voltage, which makes the whole flyback thing sort of moot. >Sorry for the diverting question, but help me out here. (I find magnet material a bit magical.) So I thought the energy in an inductor was 1/2*L*i^2. But your and Joerg's comments seem to imply the energy is mostly in the gap. Now my very limited understanding of making a gap in an inductor was that the gap sorta sets the inductance... the actual value isn't so dependent on the magnetic material. And doesn't the gap reduce the inductance? I seem to be missing something fundamental. Thanks, George H.> > > > > > John Larkin has recently used these tiny flyback transformers. Nothing > > > wrong with hanging two in parallel on the primary and using the 2nd one > > > with the secondary flipped around, for the -45V. > > > > > > Do you need this isolated? Else you could consider just inverting and boost. > > > > > > > Doesn't have to be isolated, but it does need to be quiet, hence the > > toroids. > > > > Thanks > > > > 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 USA > > +1 845 480 2058 > > > > hobbs at electrooptical dot net > > http://electrooptical.net
