John Larkin wrote:> On Wed, 17 Jul 2013 09:16:55 -0700 (PDT), Lasse Langwadt Christensen > <langwadt@fonz.dk> wrote: > >> On Wednesday, July 17, 2013 5:18:25 PM UTC+2, Phil Hobbs wrote: >>> On 07/17/2013 10:00 AM, Joerg wrote: >>> >>>> Phil Hobbs wrote: >>>>> 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.) >>>> That's one of the more serious problems we as a country have. Legal >>>> skirmishes usually have zero productivity from a national perspective >>>> but result in the fattest "payouts". It is the core problem why our >>>> health care system is a mess. Of course, that is never brought up by >>>> body politicus, for obvious reasons :-( >>> >>> >>> You could say much the same thing about the army, but once the shooting >>> >>> starts, you're glad they're there. The case I'm working on today >>> >>> concerns an alleged misappropriation of trade secrets by a big >>> >>> semiconductor company. There's a lot of money at stake, so I'm pretty >>> >>> much in the noise. Designing stuff for start-ups is a bit different. >>> >>> >>> >>>>> <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. ... >>>> They work ok with zero load if you can tolerate the voltage increase. >>>> That would be determined by the turns ratio. If it has to be 45.000V >>>> that's a different story. Then you'll have to let it go into a skipping >>>> mode. >>>>> ... 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. >>>> Yes, needs current control but that's standard even in sub-Dollar chips. >>> >>> >>> I may just make a boost with a two-winding toroid, and return the other >>> >>> end of the second winding to the raw -15V supply. (A lot of the Murata >>> >>> toroids are actually dual-winding, but they expect you to wire them in >>> >>> parallel to get the current handling capacity.) >>> >> they generally spec them both for series and parallel ;) >> >> how about a capacitive coupled boost? >> >> something like this: >> http://obsoletetechnology.wordpress.com/projects/studio-electronics/dc-dc-bipolar-power-supply-for-effect-pedals/ >> >> -Lasse > > That's like my "bubble" (boost-doubler) converter that I posted a few days ago, > except that I didn't use an integrated switching controller and tweaked some > things. > > Rob described it as "a sepic without the second winding." >Bikers would call that a "Bobber SEPIC" :-) https://en.wikipedia.org/wiki/File:Orange-bobber.jpg -- Regards, Joerg http://www.analogconsultants.com/
Flyback vs half-bridge
Started by ●July 16, 2013
Reply by ●July 17, 20132013-07-17
Reply by ●July 17, 20132013-07-17
On 07/17/2013 12:36 PM, Phil Hobbs wrote:> On 07/17/2013 12:16 PM, Lasse Langwadt Christensen wrote: >> On Wednesday, July 17, 2013 5:18:25 PM UTC+2, Phil Hobbs wrote: >>> On 07/17/2013 10:00 AM, Joerg wrote: >>> >>>> Phil Hobbs wrote: >>> >>>>> 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.) >>> >>>>> >>> >>>> >>> >>>> That's one of the more serious problems we as a country have. Legal >>> >>>> skirmishes usually have zero productivity from a national perspective >>> >>>> but result in the fattest "payouts". It is the core problem why our >>> >>>> health care system is a mess. Of course, that is never brought up by >>> >>>> body politicus, for obvious reasons :-( >>> >>> >>> >>> You could say much the same thing about the army, but once the shooting >>> >>> starts, you're glad they're there. The case I'm working on today >>> >>> concerns an alleged misappropriation of trade secrets by a big >>> >>> semiconductor company. There's a lot of money at stake, so I'm pretty >>> >>> much in the noise. Designing stuff for start-ups is a bit different. >>> >>> >>> >>>> >>> >>>> >>> >>>>> <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. ... >>> >>>> >>> >>>> >>> >>>> They work ok with zero load if you can tolerate the voltage increase. >>> >>>> That would be determined by the turns ratio. If it has to be 45.000V >>> >>>> that's a different story. Then you'll have to let it go into a skipping >>> >>>> mode. >>> >>>> >>> >>>> >>> >>>>> ... 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. >>> >>>>> >>> >>>> >>> >>>> Yes, needs current control but that's standard even in sub-Dollar >>>> chips. >>> >>> >>> >>> I may just make a boost with a two-winding toroid, and return the other >>> >>> end of the second winding to the raw -15V supply. (A lot of the Murata >>> >>> toroids are actually dual-winding, but they expect you to wire them in >>> >>> parallel to get the current handling capacity.) >>> >> >> they generally spec them both for series and parallel ;) > > You'd think so, but no. The ones I'm using (Murata 32331C) aren't > called out in the datasheet as anything except a single winding between > pins 1 and 3, whereas in reality there's another independent one between > pins 2 and 4 (the datasheet is at http://tinyurl.com/oyxguho ). >Never mind. I was thinking of a different part--the 32331C has a single two-layer winding, but pins 2 and 4 are also shorted together internally for some reason. 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 ●July 17, 20132013-07-17
On 07/17/2013 12:55 PM, Joerg wrote:> John Larkin wrote: >> On Wed, 17 Jul 2013 09:16:55 -0700 (PDT), Lasse Langwadt Christensen >> <langwadt@fonz.dk> wrote: >> >>> On Wednesday, July 17, 2013 5:18:25 PM UTC+2, Phil Hobbs wrote: >>>> On 07/17/2013 10:00 AM, Joerg wrote: >>>> >>>>> Phil Hobbs wrote: >>>>>> 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.) >>>>> That's one of the more serious problems we as a country have. Legal >>>>> skirmishes usually have zero productivity from a national perspective >>>>> but result in the fattest "payouts". It is the core problem why our >>>>> health care system is a mess. Of course, that is never brought up by >>>>> body politicus, for obvious reasons :-( >>>> >>>> >>>> You could say much the same thing about the army, but once the shooting >>>> >>>> starts, you're glad they're there. The case I'm working on today >>>> >>>> concerns an alleged misappropriation of trade secrets by a big >>>> >>>> semiconductor company. There's a lot of money at stake, so I'm pretty >>>> >>>> much in the noise. Designing stuff for start-ups is a bit different. >>>> >>>> >>>> >>>>>> <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. ... >>>>> They work ok with zero load if you can tolerate the voltage increase. >>>>> That would be determined by the turns ratio. If it has to be 45.000V >>>>> that's a different story. Then you'll have to let it go into a skipping >>>>> mode. >>>>>> ... 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. >>>>> Yes, needs current control but that's standard even in sub-Dollar chips. >>>> >>>> >>>> I may just make a boost with a two-winding toroid, and return the other >>>> >>>> end of the second winding to the raw -15V supply. (A lot of the Murata >>>> >>>> toroids are actually dual-winding, but they expect you to wire them in >>>> >>>> parallel to get the current handling capacity.) >>>> >>> they generally spec them both for series and parallel ;) >>> >>> how about a capacitive coupled boost? >>> >>> something like this: >>> http://obsoletetechnology.wordpress.com/projects/studio-electronics/dc-dc-bipolar-power-supply-for-effect-pedals/ >>> >>> -Lasse >> >> That's like my "bubble" (boost-doubler) converter that I posted a few days ago, >> except that I didn't use an integrated switching controller and tweaked some >> things. >> >> Rob described it as "a sepic without the second winding." >> > > Bikers would call that a "Bobber SEPIC" :-) > > https://en.wikipedia.org/wiki/File:Orange-bobber.jpg >That could get pretty warm on the girlfriend's feet. ;) 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 ●July 17, 20132013-07-17
Phil Hobbs wrote:> On 07/17/2013 12:55 PM, Joerg wrote: >> John Larkin wrote:[...]>>> That's like my "bubble" (boost-doubler) converter that I posted a few >>> days ago, >>> except that I didn't use an integrated switching controller and >>> tweaked some >>> things. >>> >>> Rob described it as "a sepic without the second winding." >>> >> >> Bikers would call that a "Bobber SEPIC" :-) >> >> https://en.wikipedia.org/wiki/File:Orange-bobber.jpg >> > > That could get pretty warm on the girlfriend's feet. ;) >Unless you ride it daredevil-style: http://flathead-bobbers.com/flathead_1937/images-hd0146/Puppy_at_Bear_Butte_by_Mike_Lichterhfb3-468x773.jpg -- Regards, Joerg http://www.analogconsultants.com/
Reply by ●July 17, 20132013-07-17
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 HobbsHave you ever posted the input voltage? I haven't found it in the thread. ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
Reply by ●July 17, 20132013-07-17
Jim Thompson wrote: [...]> Have you ever posted the input voltage? I haven't found it in the > thread. >Probably follows the Hobbs house standard, 19V (laptop supply). -- Regards, Joerg http://www.analogconsultants.com/
Reply by ●July 17, 20132013-07-17
On Wednesday, July 17, 2013 6:36:32 PM UTC+2, Phil Hobbs wrote:> On 07/17/2013 12:16 PM, Lasse Langwadt Christensen wrote: >=20 > > On Wednesday, July 17, 2013 5:18:25 PM UTC+2, Phil Hobbs wrote: >=20 > >> On 07/17/2013 10:00 AM, Joerg wrote: >=20 > >> >=20 > >>> Phil Hobbs wrote: >=20 > >> >=20 > >>>> On 7/16/2013 8:54 PM, Joerg wrote: >=20 > >> >=20 > >>>>> Phil Hobbs wrote: >=20 > >> >=20 > >>>>>> On 7/16/2013 3:53 PM, Joerg wrote: >=20 > >> >=20 > >>>>>>> Phil Hobbs wrote: >=20 > >> >=20 > >>>>>>>> So, I'm goofing off playing with small switchers. (Well, not ex=actly>=20 > >> >=20 > >>>>>>>> goofing off, but there are somewhat more pressing tasks waiting.=...)>=20 > >> >=20 > >>>>>>>> >=20 > >> >=20 > >>>>>>>> As I said in George's thread, "Opamp w/ Vsupply > 36V", I built=a>=20 > >> >=20 > >>>>>>>> small >=20 > >> >=20 > >>>>>>>> half-bridge supply with positive and negative voltage doublers. >=20 > >> >=20 > >>>>>>>> I'm not >=20 > >> >=20 > >>>>>>>> that keen on it, because (a) it uses a fair number of parts for >=20 > >> >=20 > >>>>>>>> what it >=20 > >> >=20 > >>>>>>>> does, and (b) it has a nasty instability. >=20 > >> >=20 > >>>>>>>> >=20 > >> >=20 > >>>>>>> >=20 > >> >=20 > >>>>>>> (a) ... yes. (b) ... why? What happens? Changing to another >=20 > >> >=20 > >>>>>>> architecture >=20 > >> >=20 > >>>>>>> while using the same kind of loop usually doesn't do much to impr=ove>=20 > >> >=20 > >>>>>>> stability. >=20 > >> >=20 > >>>>>>> >=20 > >> >=20 > >>>>>>> >=20 > >> >=20 > >>>>>>>> With a capacitively-coupled half bridge, if you let the transfor=mer>=20 > >> >=20 > >>>>>>>> saturate, it instantly discharges the coupling cap, which about >=20 > >> >=20 > >>>>>>>> doubles >=20 > >> >=20 > >>>>>>>> the volt-seconds on the next half-cycle and guarantee that it wi=ll>=20 > >> >=20 > >>>>>>>> keep >=20 > >> >=20 > >>>>>>>> saturating until the FETs cook themselves. >=20 > >> >=20 > >>>>>>>> >=20 > >> >=20 > >>>>>>> >=20 > >> >=20 > >>>>>>> Not sure what you mean here, but usually current mode control is =the>=20 > >> >=20 > >>>>>>> way >=20 > >> >=20 > >>>>>>> to avoid asymmetrical runaway. >=20 > >> >=20 > >>>>>> >=20 > >> >=20 > >>>>>> The IRS2153D puts a square wave out of a half-bridge--no feedback,=no>=20 > >> >=20 > >>>>>> current limit, nada. If you put that into a transformer via a cap=, all>=20 > >> >=20 > >>>>>> is well until you saturate the transformer. >=20 > >> >=20 > >>>>>> >=20 > >> >=20 > >>>>> >=20 > >> >=20 > >>>>> Ok, the IRS2153D is just a glorified gate driver with an oscillator=in>=20 > >> >=20 > >>>>> there. I'd use a real switcher controller chip, some are in the sam=e>=20 > >> >=20 > >>>>> price category. >=20 > >> >=20 > >>>>> >=20 > >> >=20 > >>>>> >=20 > >> >=20 > >>>>>> Say that happens on the positive half-cycle. >=20 > >> >=20 > >>>>>> At that moment, the voltage on the cap rapidly goes from V_DD/2 to=V_DD.>=20 > >> >=20 > >>>>>> At the next edge, the voltage across the transformer is sudden=ly not>=20 > >> >=20 > >>>>>> V_DD/2 as expected, but V_DD. The transformer saturates in half t=he>=20 > >> >=20 > >>>>>> time it took previously, and the voltage on the cap goes from V_DD=to 0.>=20 > >> >=20 > >>>>>> Then the cycle repeats. It's really obvious on a scope when t=his>=20 > >> >=20 > >>>>>> happens, and it's far from pretty. >=20 > >> >=20 > >>>>>> >=20 > >> >=20 > >>>>> >=20 > >> >=20 > >>>>> Did you use a really big cap? I've never had that happen. Usually >=20 > >> >=20 > >>>>> ferrite saturates softly enough to just "nudge" the cap. >=20 > >> >=20 > >>>> >=20 > >> >=20 > >>>> 1 uF. I can probably post a scope photo tomorrow, if I have time--a >=20 > >> >=20 > >>>> bunch of lawyering has just descended on my head. (Not that I mind =very>=20 > >> >=20 > >>>> much--expert witness work uses a different part of my brain and >=20 > >> >=20 > >>>> generally pays somewhat better than design work.) >=20 > >> >=20 > >>>> >=20 > >> >=20 > >>> >=20 > >> >=20 > >>> That's one of the more serious problems we as a country have. Legal >=20 > >> >=20 > >>> skirmishes usually have zero productivity from a national perspective >=20 > >> >=20 > >>> but result in the fattest "payouts". It is the core problem why our >=20 > >> >=20 > >>> health care system is a mess. Of course, that is never brought up by >=20 > >> >=20 > >>> body politicus, for obvious reasons :-( >=20 > >> >=20 > >> >=20 > >> >=20 > >> You could say much the same thing about the army, but once the shootin=g>=20 > >> >=20 > >> starts, you're glad they're there. The case I'm working on today >=20 > >> >=20 > >> concerns an alleged misappropriation of trade secrets by a big >=20 > >> >=20 > >> semiconductor company. There's a lot of money at stake, so I'm pretty >=20 > >> >=20 > >> much in the noise. Designing stuff for start-ups is a bit different. >=20 > >> >=20 > >> >=20 > >> >=20 > >>> >=20 > >> >=20 > >>> >=20 > >> >=20 > >>>> <snip> >=20 > >> >=20 > >>>>>>> John Larkin has recently used these tiny flyback transformers. No=thing>=20 > >> >=20 > >>>>>>> wrong with hanging two in parallel on the primary and using the 2=nd one>=20 > >> >=20 > >>>>>>> with the secondary flipped around, for the -45V. >=20 > >> >=20 > >>>>>>> >=20 > >> >=20 > >>>>>>> Do you need this isolated? Else you could consider just inverting=and>=20 > >> >=20 > >>>>>>> boost. >=20 > >> >=20 > >>>>>>> >=20 > >> >=20 > >>>>>> >=20 > >> >=20 > >>>>>> Doesn't have to be isolated, but it does need to be quiet, hence t=he>=20 > >> >=20 > >>>>>> toroids. >=20 > >> >=20 > >>>>>> >=20 > >> >=20 > >>>>> >=20 > >> >=20 > >>>>> That usually rules out flybacks. They spew a lot of noise. Then I'd=use>=20 > >> >=20 > >>>>> a half-bridge with CM control and series inductors on the output. >=20 > >> >=20 > >>>> >=20 > >> >=20 > >>>> Fortunately the half-bridge's worst-case condition is zero load, so =it>=20 > >> >=20 > >>>> isn't too hard to control. ... >=20 > >> >=20 > >>> >=20 > >> >=20 > >>> >=20 > >> >=20 > >>> They work ok with zero load if you can tolerate the voltage increase. >=20 > >> >=20 > >>> That would be determined by the turns ratio. If it has to be 45.000V >=20 > >> >=20 > >>> that's a different story. Then you'll have to let it go into a skippi=ng>=20 > >> >=20 > >>> mode. >=20 > >> >=20 > >>> >=20 > >> >=20 > >>> >=20 > >> >=20 > >>>> ... Of course the ungapped ferrite has a prett=y>=20 > >> >=20 > >>>> frightening tempco of mu (it goes down by half when you hit it with =cold>=20 > >> >=20 > >>>> spray), so some sort of current control is going to be required, for=sure.>=20 > >> >=20 > >>>> >=20 > >> >=20 > >>> >=20 > >> >=20 > >>> Yes, needs current control but that's standard even in sub-Dollar chi=ps.>=20 > >> >=20 > >> >=20 > >> >=20 > >> I may just make a boost with a two-winding toroid, and return the othe=r>=20 > >> >=20 > >> end of the second winding to the raw -15V supply. (A lot of the Murat=a>=20 > >> >=20 > >> toroids are actually dual-winding, but they expect you to wire them in >=20 > >> >=20 > >> parallel to get the current handling capacity.) >=20 > >> >=20 > > >=20 > > they generally spec them both for series and parallel ;) >=20 >=20 >=20 > You'd think so, but no. The ones I'm using (Murata 32331C) aren't=20 >=20 > called out in the datasheet as anything except a single winding between==20>=20 > pins 1 and 3, whereas in reality there's another independent one between==20>=20 > pins 2 and 4 (the datasheet is at http://tinyurl.com/oyxguho ). >=20 >=20 >=20 > > >=20 > > how about a capacitive coupled boost? >=20 > > >=20 > > something like this: >=20 > > http://obsoletetechnology.wordpress.com/projects/studio-electronics/dc-=dc-bipolar-power-supply-for-effect-pedals/>=20 > > >=20 > > -Lasse >=20 > > >=20 >=20 >=20 > It's a possibility, for sure. I normally don't think of capacitive=20 >=20 > boosters and hundreds of milliwatts at the same time, but it could work==20>=20 > OK. It's slightly inconvenient due to having to run off +-15 to get the==20>=20 > required output, but not awful. >=20I wouldn't call a capacitive booster, it a normal boost just capacitive cou= pled=20 you can get +/-45V just pick a controller that can handle 45V=20 hacked together from the lt1071 test fixture: Version 4 SHEET 1 2808 1492 WIRE 1600 880 1488 880 WIRE 1824 880 1600 880 WIRE 1872 880 1824 880 WIRE 1984 880 1952 880 WIRE 2144 880 1984 880 WIRE 2160 880 2144 880 WIRE 2272 880 2224 880 WIRE 2320 880 2272 880 WIRE 2416 880 2384 880 WIRE 2528 880 2416 880 WIRE 2640 880 2528 880 WIRE 1488 896 1488 880 WIRE 2528 896 2528 880 WIRE 2640 896 2640 880 WIRE 1600 912 1600 880 WIRE 1824 944 1824 880 WIRE 2416 960 2416 880 WIRE 2272 976 2272 944 WIRE 2528 992 2528 960 WIRE 2640 992 2640 976 WIRE 1488 1008 1488 976 WIRE 1600 1008 1600 976 WIRE 1984 1024 1984 880 WIRE 1984 1024 1952 1024 WIRE 2416 1088 2416 1040 WIRE 2416 1088 1952 1088 WIRE 2416 1104 2416 1088 WIRE 1968 1152 1952 1152 WIRE 2064 1152 2048 1152 WIRE 2064 1168 2064 1152 WIRE 2416 1200 2416 1184 WIRE 1824 1248 1824 1232 WIRE 2064 1248 2064 1232 WIRE 2144 1408 2144 880 WIRE 2304 1408 2208 1408 WIRE 2368 1408 2304 1408 WIRE 2544 1408 2432 1408 WIRE 2656 1408 2544 1408 FLAG 2640 880 OUT FLAG 2416 1200 0 FLAG 2528 992 0 FLAG 2640 992 0 FLAG 2064 1248 0 FLAG 1824 1248 0 FLAG 1600 1008 0 FLAG 1488 1008 0 FLAG 1488 880 IN FLAG 2272 976 0 FLAG 2304 1344 0 FLAG 2656 1328 0 FLAG 2544 1344 0 SYMBOL ind 1856 896 R270 WINDOW 0 32 56 VTop 2 WINDOW 3 5 56 VBottom 2 SYMATTR InstName L1 SYMATTR Value 150=B5 SYMATTR SpiceLine Rser=3D0.02 Rpar=3D5000 SYMBOL schottky 2320 896 R270 WINDOW 0 32 32 VTop 2 WINDOW 3 0 32 VBottom 2 SYMATTR InstName D1 SYMATTR Value MBRS360 SYMBOL RES 2400 944 R0 SYMATTR InstName R1 SYMATTR Value 44K SYMBOL RES 2400 1088 R0 SYMATTR InstName R2 SYMATTR Value 1.24K SYMBOL RES 1952 1168 R270 WINDOW 0 32 56 VTop 2 WINDOW 3 0 56 VBottom 2 SYMATTR InstName R3 SYMATTR Value 1K SYMBOL polcap 2512 896 R0 SYMATTR InstName C1 SYMATTR Value 100=B5 SYMATTR SpiceLine Rser=3D15m SYMBOL CAP 2048 1168 R0 SYMATTR InstName C2 SYMATTR Value 1=B5 SYMBOL VOLTAGE 1488 880 R0 WINDOW 123 0 0 Left 2 SYMATTR InstName V1 SYMATTR Value 19 SYMATTR SpiceLine Rser=3D0.1 SYMBOL polcap 1584 912 R0 SYMATTR InstName C3 SYMATTR Value 100=B5 SYMBOL PowerProducts\\LT1071HV 1824 1088 R0 SYMATTR InstName U1 SYMBOL res 2624 880 R0 SYMATTR InstName Rload SYMATTR Value 2000 SYMBOL schottky 2288 944 R180 WINDOW 0 24 64 Left 2 WINDOW 3 -27 0 Left 2 SYMATTR InstName D2 SYMATTR Value MBRS360 SYMBOL cap 2224 864 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C4 SYMATTR Value 1=B5 SYMATTR SpiceLine V=3D50 Irms=3D0 Rser=3D0.008 Lser=3D0 mfg=3D"TDK" pn=3D"C= 3225X7RlHlO5M" type=3D"X7R" SYMBOL schottky 2432 1392 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName D3 SYMATTR Value MBRS360 SYMBOL schottky 2320 1408 R180 WINDOW 0 24 64 Left 2 WINDOW 3 24 0 Left 2 SYMATTR InstName D4 SYMATTR Value MBRS360 SYMBOL polcap 2528 1344 R0 SYMATTR InstName C6 SYMATTR Value 100=B5 SYMATTR SpiceLine Rser=3D15m SYMBOL res 2640 1312 R0 SYMATTR InstName Rload1 SYMATTR Value 2000 SYMBOL cap 2208 1392 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C5 SYMATTR Value 1=B5 SYMATTR SpiceLine V=3D50 Irms=3D0 Rser=3D0.008 Lser=3D0 mfg=3D"TDK" pn=3D"C= 3225X7RlHlO5M" type=3D"X7R" TEXT 1424 1136 Left 2 !.tran 200m startup -Lasse
Reply by ●July 17, 20132013-07-17
Joerg <invalid@invalid.invalid> writes:> Jim Thompson wrote: > > [...] > > >> Have you ever posted the input voltage? I haven't found it in the >> thread. >> > > Probably follows the Hobbs house standard, 19V (laptop supply).Hmm, most of those use a 3 pin mains connector, does that mean they are free from the high voltage high frequency leakage currents that plague modern wall-warts? Do they earth the DC 0V? -- John Devereux
Reply by ●July 17, 20132013-07-17
On Wed, 17 Jul 2013 09:55:02 -0700, Joerg <invalid@invalid.invalid> wrote:>John Larkin wrote: >> On Wed, 17 Jul 2013 09:16:55 -0700 (PDT), Lasse Langwadt Christensen >> <langwadt@fonz.dk> wrote: >> >>> On Wednesday, July 17, 2013 5:18:25 PM UTC+2, Phil Hobbs wrote: >>>> On 07/17/2013 10:00 AM, Joerg wrote: >>>> >>>>> Phil Hobbs wrote: >>>>>> 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.) >>>>> That's one of the more serious problems we as a country have. Legal >>>>> skirmishes usually have zero productivity from a national perspective >>>>> but result in the fattest "payouts". It is the core problem why our >>>>> health care system is a mess. Of course, that is never brought up by >>>>> body politicus, for obvious reasons :-( >>>> >>>> >>>> You could say much the same thing about the army, but once the shooting >>>> >>>> starts, you're glad they're there. The case I'm working on today >>>> >>>> concerns an alleged misappropriation of trade secrets by a big >>>> >>>> semiconductor company. There's a lot of money at stake, so I'm pretty >>>> >>>> much in the noise. Designing stuff for start-ups is a bit different. >>>> >>>> >>>> >>>>>> <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. ... >>>>> They work ok with zero load if you can tolerate the voltage increase. >>>>> That would be determined by the turns ratio. If it has to be 45.000V >>>>> that's a different story. Then you'll have to let it go into a skipping >>>>> mode. >>>>>> ... 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. >>>>> Yes, needs current control but that's standard even in sub-Dollar chips. >>>> >>>> >>>> I may just make a boost with a two-winding toroid, and return the other >>>> >>>> end of the second winding to the raw -15V supply. (A lot of the Murata >>>> >>>> toroids are actually dual-winding, but they expect you to wire them in >>>> >>>> parallel to get the current handling capacity.) >>>> >>> they generally spec them both for series and parallel ;) >>> >>> how about a capacitive coupled boost? >>> >>> something like this: >>> http://obsoletetechnology.wordpress.com/projects/studio-electronics/dc-dc-bipolar-power-supply-for-effect-pedals/ >>> >>> -Lasse >> >> That's like my "bubble" (boost-doubler) converter that I posted a few days ago, >> except that I didn't use an integrated switching controller and tweaked some >> things. >> >> Rob described it as "a sepic without the second winding." >> > >Bikers would call that a "Bobber SEPIC" :-) > >https://en.wikipedia.org/wiki/File:Orange-bobber.jpgBad-Ass Switcher. -- 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 17, 20132013-07-17
On Wed, 17 Jul 2013 10:51:08 -0700 (PDT), Lasse Langwadt Christensen <langwadt@fonz.dk> wrote:>On Wednesday, July 17, 2013 6:36:32 PM UTC+2, Phil Hobbs wrote: >> On 07/17/2013 12:16 PM, Lasse Langwadt Christensen wrote: >> >> > On Wednesday, July 17, 2013 5:18:25 PM UTC+2, Phil Hobbs wrote: >> >> >> On 07/17/2013 10:00 AM, Joerg wrote: >> >> >> >> >> >>> Phil Hobbs wrote: >> >> >> >> >> >>>> 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.) >> >> >> >> >> >>>> >> >> >> >> >> >>> >> >> >> >> >> >>> That's one of the more serious problems we as a country have. Legal >> >> >> >> >> >>> skirmishes usually have zero productivity from a national perspective >> >> >> >> >> >>> but result in the fattest "payouts". It is the core problem why our >> >> >> >> >> >>> health care system is a mess. Of course, that is never brought up by >> >> >> >> >> >>> body politicus, for obvious reasons :-( >> >> >> >> >> >> >> >> >> >> >> >> You could say much the same thing about the army, but once the shooting >> >> >> >> >> >> starts, you're glad they're there. The case I'm working on today >> >> >> >> >> >> concerns an alleged misappropriation of trade secrets by a big >> >> >> >> >> >> semiconductor company. There's a lot of money at stake, so I'm pretty >> >> >> >> >> >> much in the noise. Designing stuff for start-ups is a bit different. >> >> >> >> >> >> >> >> >> >> >> >>> >> >> >> >> >> >>> >> >> >> >> >> >>>> <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. ... >> >> >> >> >> >>> >> >> >> >> >> >>> >> >> >> >> >> >>> They work ok with zero load if you can tolerate the voltage increase. >> >> >> >> >> >>> That would be determined by the turns ratio. If it has to be 45.000V >> >> >> >> >> >>> that's a different story. Then you'll have to let it go into a skipping >> >> >> >> >> >>> mode. >> >> >> >> >> >>> >> >> >> >> >> >>> >> >> >> >> >> >>>> ... 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. >> >> >> >> >> >>>> >> >> >> >> >> >>> >> >> >> >> >> >>> Yes, needs current control but that's standard even in sub-Dollar chips. >> >> >> >> >> >> >> >> >> >> >> >> I may just make a boost with a two-winding toroid, and return the other >> >> >> >> >> >> end of the second winding to the raw -15V supply. (A lot of the Murata >> >> >> >> >> >> toroids are actually dual-winding, but they expect you to wire them in >> >> >> >> >> >> parallel to get the current handling capacity.) >> >> >> >> >> > >> >> > they generally spec them both for series and parallel ;) >> >> >> >> You'd think so, but no. The ones I'm using (Murata 32331C) aren't >> >> called out in the datasheet as anything except a single winding between >> >> pins 1 and 3, whereas in reality there's another independent one between >> >> pins 2 and 4 (the datasheet is at http://tinyurl.com/oyxguho ). >> >> >> >> > >> >> > how about a capacitive coupled boost? >> >> > >> >> > something like this: >> >> > http://obsoletetechnology.wordpress.com/projects/studio-electronics/dc-dc-bipolar-power-supply-for-effect-pedals/ >> >> > >> >> > -Lasse >> >> > >> >> >> >> It's a possibility, for sure. I normally don't think of capacitive >> >> boosters and hundreds of milliwatts at the same time, but it could work >> >> OK. It's slightly inconvenient due to having to run off +-15 to get the >> >> required output, but not awful. >> > >I wouldn't call a capacitive booster, it a normal boost just capacitive coupled > >you can get +/-45V just pick a controller that can handle 45V > >hacked together from the lt1071 test fixture: > >Version 4 >SHEET 1 2808 1492 >WIRE 1600 880 1488 880 >WIRE 1824 880 1600 880 >WIRE 1872 880 1824 880 >WIRE 1984 880 1952 880 >WIRE 2144 880 1984 880 >WIRE 2160 880 2144 880 >WIRE 2272 880 2224 880 >WIRE 2320 880 2272 880 >WIRE 2416 880 2384 880 >WIRE 2528 880 2416 880 >WIRE 2640 880 2528 880 >WIRE 1488 896 1488 880 >WIRE 2528 896 2528 880 >WIRE 2640 896 2640 880 >WIRE 1600 912 1600 880 >WIRE 1824 944 1824 880 >WIRE 2416 960 2416 880 >WIRE 2272 976 2272 944 >WIRE 2528 992 2528 960 >WIRE 2640 992 2640 976 >WIRE 1488 1008 1488 976 >WIRE 1600 1008 1600 976 >WIRE 1984 1024 1984 880 >WIRE 1984 1024 1952 1024 >WIRE 2416 1088 2416 1040 >WIRE 2416 1088 1952 1088 >WIRE 2416 1104 2416 1088 >WIRE 1968 1152 1952 1152 >WIRE 2064 1152 2048 1152 >WIRE 2064 1168 2064 1152 >WIRE 2416 1200 2416 1184 >WIRE 1824 1248 1824 1232 >WIRE 2064 1248 2064 1232 >WIRE 2144 1408 2144 880 >WIRE 2304 1408 2208 1408 >WIRE 2368 1408 2304 1408 >WIRE 2544 1408 2432 1408 >WIRE 2656 1408 2544 1408 >FLAG 2640 880 OUT >FLAG 2416 1200 0 >FLAG 2528 992 0 >FLAG 2640 992 0 >FLAG 2064 1248 0 >FLAG 1824 1248 0 >FLAG 1600 1008 0 >FLAG 1488 1008 0 >FLAG 1488 880 IN >FLAG 2272 976 0 >FLAG 2304 1344 0 >FLAG 2656 1328 0 >FLAG 2544 1344 0 >SYMBOL ind 1856 896 R270 >WINDOW 0 32 56 VTop 2 >WINDOW 3 5 56 VBottom 2 >SYMATTR InstName L1 >SYMATTR Value 150� >SYMATTR SpiceLine Rser=0.02 Rpar=5000 >SYMBOL schottky 2320 896 R270 >WINDOW 0 32 32 VTop 2 >WINDOW 3 0 32 VBottom 2 >SYMATTR InstName D1 >SYMATTR Value MBRS360 >SYMBOL RES 2400 944 R0 >SYMATTR InstName R1 >SYMATTR Value 44K >SYMBOL RES 2400 1088 R0 >SYMATTR InstName R2 >SYMATTR Value 1.24K >SYMBOL RES 1952 1168 R270 >WINDOW 0 32 56 VTop 2 >WINDOW 3 0 56 VBottom 2 >SYMATTR InstName R3 >SYMATTR Value 1K >SYMBOL polcap 2512 896 R0 >SYMATTR InstName C1 >SYMATTR Value 100� >SYMATTR SpiceLine Rser=15m >SYMBOL CAP 2048 1168 R0 >SYMATTR InstName C2 >SYMATTR Value 1� >SYMBOL VOLTAGE 1488 880 R0 >WINDOW 123 0 0 Left 2 >SYMATTR InstName V1 >SYMATTR Value 19 >SYMATTR SpiceLine Rser=0.1 >SYMBOL polcap 1584 912 R0 >SYMATTR InstName C3 >SYMATTR Value 100� >SYMBOL PowerProducts\\LT1071HV 1824 1088 R0 >SYMATTR InstName U1 >SYMBOL res 2624 880 R0 >SYMATTR InstName Rload >SYMATTR Value 2000 >SYMBOL schottky 2288 944 R180 >WINDOW 0 24 64 Left 2 >WINDOW 3 -27 0 Left 2 >SYMATTR InstName D2 >SYMATTR Value MBRS360 >SYMBOL cap 2224 864 R90 >WINDOW 0 0 32 VBottom 2 >WINDOW 3 32 32 VTop 2 >SYMATTR InstName C4 >SYMATTR Value 1� >SYMATTR SpiceLine V=50 Irms=0 Rser=0.008 Lser=0 mfg="TDK" pn="C3225X7RlHlO5M" type="X7R" >SYMBOL schottky 2432 1392 R90 >WINDOW 0 0 32 VBottom 2 >WINDOW 3 32 32 VTop 2 >SYMATTR InstName D3 >SYMATTR Value MBRS360 >SYMBOL schottky 2320 1408 R180 >WINDOW 0 24 64 Left 2 >WINDOW 3 24 0 Left 2 >SYMATTR InstName D4 >SYMATTR Value MBRS360 >SYMBOL polcap 2528 1344 R0 >SYMATTR InstName C6 >SYMATTR Value 100� >SYMATTR SpiceLine Rser=15m >SYMBOL res 2640 1312 R0 >SYMATTR InstName Rload1 >SYMATTR Value 2000 >SYMBOL cap 2208 1392 R90 >WINDOW 0 0 32 VBottom 2 >WINDOW 3 32 32 VTop 2 >SYMATTR InstName C5 >SYMATTR Value 1� >SYMATTR SpiceLine V=50 Irms=0 Rser=0.008 Lser=0 mfg="TDK" pn="C3225X7RlHlO5M" type="X7R" >TEXT 1424 1136 Left 2 !.tran 200m startup > > > >-LasseCute! That would nicely fit Larkin's needs... with no significant surge. Somewhat similar to my self-charging CD ignition from the late '60's at Philco-Ford and in the early '70's at Dickson electronics... http://www.analog-innovations.com/SED/CD-Ignition-Basic.pdf ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
