On Sun, 13 Aug 2017 14:51:28 -0700 (PDT), Klaus Kragelund <klauskvik@hotmail.com> wrote:>On Sunday, August 13, 2017 at 7:23:05 PM UTC+2, Tim Williams wrote: >> "Klaus Kragelund" <klauskvik@hotmail.com> wrote in message >> news:ecfdc33d-636b-40d6-be9a-22eae6bf760d@googlegroups.com... >> > Staircase saturation can be difficult to manage with full confidence >> >> FYI, nothing is staircasing. At least, whoever came up with it, chose a >> terrible name. >> >> Staircase flux would only happen if you apply "pulsed DC" (i.e., a unipolar, >> constant voltage source) to a zero-resistance winding. >> > >Staircasing, or a better name for it flux walking. The name staircasing comes AFAIK from push pull converters, when if you observe the current in one winding, it will show a semi staircase look cycle to cycle (envelope) > >It is not an effect caused by the magnetics, but caused by unequal volt seconds product by the converter control. For example in a push pull converter with non equal duty cycle for push and pull, or from other non-linear effect (RDSon, matching of push/pull paths etc) > >It can be remedied by deadtime and negative feedback of the paths (increasing resistances, bifilar windings etc) > >A current mode converter can also remedy the effect, but also cause it to be worse, due to interaction of the coupling capacitor and the current mode control, which makes the problem a lot worse > >See page 7 for explanation: > >http://www.ti.com/lit/an/sprabw0b/sprabw0b.pdf > >Cheers > >KlausAssume a sinewave voltage source driving a saturable inductor. The inductor current waveform will be a sine wave, steady-state. If you add a small DC offset to the source, there will be a slow ramp of current superimposed on the current sinewave. This will eventually push the inductor towards saturation. As it approaches saturation, the sine wave gets lopsided, with current peaks in the Isat direction. The combined current waveform can look like a stairstep. In my case, series capacitance breaks up any long-term current integration. Adding diodes across the cap is probably OK, as it disconnects the amplifier offset and adds volt-seconds in the proper direction to discharge the DC current ramp. If the user applies an out-of-spec low frequency signal, the diodes protect the caps from overvoltage. That's a whole nother issue. Maybe I could use a supercap, keep the phase shift down. I've been looking for a reason to use one of them. I'd simulate it, but I don't have a suitable saturable inductor model, and it would take a bunch of time. I'll lay out the board with some options, in case I do get into trouble. It would probably be safe without the diodes. -- John Larkin Highland Technology, Inc lunatic fringe electronics
class D amp
Started by ●August 11, 2017
Reply by ●August 14, 20172017-08-14
Reply by ●August 14, 20172017-08-14
On Sun, 13 Aug 2017 22:13:18 -0700 (PDT), Phil Allison <pallison49@gmail.com> wrote:>bill....@ieee.org wrote: > > >> >> 250mH would resonate with 0.63uf at 400Hz, 1.62uF at 250Hz. >> >> > >** JL's inductance figure is a nonsense, the tranny is toriodal with no effective air gap so the L value varies widely with magnetisation.I measured it with a 50-ohm function generator, by finding the 3dB point. That let me measure it in the low audio range, where it will work. Most L meters will report nonsense when connected to a big power transformer. I measured the primary and secondary independently, and the ratio was very close to n-squared. This is a custom toroid designed to work in the 300-5K Hz range, not a 60 Hz part. Of course L will vary with excitation, but I measured it in about the expected operating range.> >https://dl.dropboxusercontent.com/content_link/Ha8ZedbZ7p6bz2cb30TWJveulbmmOMzeuMNXGdd73SiJiEhGWoWygBm56ro1c12g/file404 error.> >If JL just used a coupling cap, say two 1000uF 35V electros back to back, all DC offset issues disappear.That's only 500 uF, lots of phase shift. Big caps, too. I want at least a few millifarads. Maybe a supercap is the best thing to use, say 0.47 farad at 5 volts.> >If he clipped the input signal so the amp never clips and followed that by even a 6dB/oct HPF set at 300Hz - another bogey is gone.And massive phase shift. The max DC offset of the amp is 60 mV and the tranny primary is 70 mohms; that's almost an amp of static current. Filtering the amp input doesn't fix that.> >The final bogey, inrush surges, can be *eliminated* by using a tranny with double the primary voltage rating at 300Hz his class D amp can deliver.The TI amp claims to be pop and click free. What's the difference between pop and click?> >Yep, AC supply transformers do not surge at switch of if run at half rated voltage or less. Fact.They surge, but the AC line doesn't much care. There's an entire power grid available to demagnetize it. I want all the power I can get in the volume (and budget) available. And any iron-core transformer will saturate if you put enough DC across it, and 60 mV is "enough" here. It's not a matter of being within 2:1 of safety; it's a couple of orders of magnitude. -- John Larkin Highland Technology, Inc lunatic fringe electronics
Reply by ●August 14, 20172017-08-14
On Mon, 14 Aug 2017 08:24:05 -0700, John Larkin <jjlarkin@highlandtechnology.com> wrote: [snip]> >I'd simulate it, but I don't have a suitable saturable inductor model, >and it would take a bunch of time. I'll lay out the board with some >options, in case I do get into trouble. It would probably be safe >without the diodes.See "Inductor_with_Saturation.zip " on the Device Models & Subcircuits Page of my website. Doesn't have hysteresis modeled... but as I posted recently, I've devised a way to do Analog hysteresis... adding to the Inductor Model RSN ;-) ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | STV, Queen Creek, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I'm looking for work... see my website. Thinking outside the box...producing elegant & economic solutions.
Reply by ●August 14, 20172017-08-14
On Fri, 11 Aug 2017 13:27:11 -0700, John Larkin <jjlarkin@highland_snip_technology.com> wrote:> >I want to build an AC source to test synchros/resolvers/RVDTs. The >target is 400 Hz 30 VRMS at maybe 30 VA, but we might want to simulate >aircraft "wild power" and drive LVDTs, so maybe 250 Hz to a few KHz. > >I'm thinking of using half of a TPA3251 audio amp and a step-up >transformer. Like this maybe: > >https://www.dropbox.com/s/eikiu79jv4cjxqp/P548_WB_1.JPG?raw=1 > >The transformer DCR is low, so a blocking cap might be prudent to >prevent DC current in the primary. I have a cute little 1000 uF 2.5V >polymer cap in stock, so I could use a few of those in parallel. The >diodes keep the cap from exploding if the h-bridge ever rails. > >How does that look? Any advice? > >I've heard horror stories about "the devil's staircase" progressive >saturation, which I don't really understand. The transformer is a >toroid, low resistance and pretty dramatic saturation behavior.I tried it on the TI eval board, with 4000 uF plus two diodes in series with the transformer primary. Seems to work fine. I did a bunch of sloppy stuff and didn't damage the TI chip. It does make funny noises some time. It's putting 33 volts RMS 400 Hz into 25 ohms, 87% efficient after the transformer. Nice chip. https://www.dropbox.com/s/ybjj14i0302vb1y/TPS3251_Eval_1.JPG?raw=1 I put some questions about this chip on the TI forum. No answers so far. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●August 14, 20172017-08-14
John Larkin massively bullshitted -------------------------------------> > >bill....@ieee.org wrote: > > > > > >> > >> 250mH would resonate with 0.63uf at 400Hz, 1.62uF at 250Hz. > >> > >> > > > >** JL's inductance figure is a nonsense, the tranny is toriodal with no effective air gap so the L value varies widely with magnetisation. > > > I measured it with a 50-ohm function generator, by finding the 3dB > point.** Useless and meaningless. The L value is not constant.> >https://dl.dropboxusercontent.com/content_link/Ha8ZedbZ7p6bz2cb30TWJveulbmmOMzeuMNXGdd73SiJiEhGWoWygBm56ro1c12g/file > > 404 error.** The link is to YOUR pic a that small toroidal.> > > >If JL just used a coupling cap, say two 1000uF 35V electros back to back, all DC offset issues disappear. > > That's only 500 uF, lots of phase shift.** It's actually very little.> > >If he clipped the input signal so the amp never clips and followed that by even a 6dB/oct HPF set at 300Hz - another bogey is gone. > > And massive phase shift.** Bad luck and you are raising a new issue you should have mentioned in your first post.> The max DC offset of the amp is 60 mV and the tranny primary is 70 > mohms; that's almost an amp of static current. Filtering the amp input > doesn't fix that.** Wrong issue !!! Try following the context - you bullshitting fuckhead.> >The final bogey, inrush surges, can be *eliminated* by using a > > tranny with double the primary voltage rating at 300Hz his > > class D amp can deliver. > > > The TI amp claims to be pop and click free. What's the difference > between pop and click?** Where is the relevance to my post? Is JL on illegal drugs ??> >Yep, AC supply transformers do not surge at switch of if run at half > > rated voltage or less. Fact. > > They surge, but the AC line doesn't much care. There's an entire power > grid available to demagnetize it.** We all know that, no point in stating the obvious. My information means you can easily eliminate them altogether.> I want all the power I can get in the volume (and budget) available. > And any iron-core transformer will saturate if you put enough DC > across it, and 60 mV is "enough" here.** Totally off with the fairies. That small issue was long ago addressed. JL is well out of his depth and bullshitting wildly. His only REAL skill. .... Phil
Reply by ●August 15, 20172017-08-15
On Mon, 14 Aug 2017 17:00:36 -0700 (PDT), Phil Allison <pallison49@gmail.com> wrote:>John Larkin massively bullshitted > >------------------------------------- >> >> >bill....@ieee.org wrote: >> > >> > >> >> >> >> 250mH would resonate with 0.63uf at 400Hz, 1.62uF at 250Hz. >> >> >> >> >> > >> >** JL's inductance figure is a nonsense, the tranny is toriodal with no effective air gap so the L value varies widely with magnetisation. >> >> >> I measured it with a 50-ohm function generator, by finding the 3dB >> point. > >** Useless and meaningless.Seems like a reasonable measurement to me. But in this case, it's interesting but not very important.> > The L value is not constant.No, that's the problen with measuring power transformer inductance; it varies with frequency and excitation. So the measurement is only ballpark.> > > >> >https://dl.dropboxusercontent.com/content_link/Ha8ZedbZ7p6bz2cb30TWJveulbmmOMzeuMNXGdd73SiJiEhGWoWygBm56ro1c12g/file >> >> 404 error. > > >** The link is to YOUR pic a that small toroidal.???> > >> > >> >If JL just used a coupling cap, say two 1000uF 35V electros back to back, all DC offset issues disappear. >> >> That's only 500 uF, lots of phase shift. > > >** It's actually very little.500 uF has a reactance of 0.8 ohms at 400 Hz, twice that at 200 Hz. The transformer primary looks like maybe 5 ohms. This isn't audio, it's aircraft synchros and resolvers and stuff where precision matters.> > >> >> >If he clipped the input signal so the amp never clips and followed that by even a 6dB/oct HPF set at 300Hz - another bogey is gone. >> >> And massive phase shift. > > >** Bad luck and you are raising a new issue you should have mentioned in your first post. > > > >> The max DC offset of the amp is 60 mV and the tranny primary is 70 >> mohms; that's almost an amp of static current. Filtering the amp input >> doesn't fix that. > >** Wrong issue !!! > >Try following the context - you bullshitting fuckhead. > > > > >> >The final bogey, inrush surges, can be *eliminated* by using a >> > tranny with double the primary voltage rating at 300Hz his >> > class D amp can deliver. >> >> >> The TI amp claims to be pop and click free. What's the difference >> between pop and click? > >** Where is the relevance to my post? > > Is JL on illegal drugs ?? > > > >> >Yep, AC supply transformers do not surge at switch of if run at half >> > rated voltage or less. Fact. >> >> They surge, but the AC line doesn't much care. There's an entire power >> grid available to demagnetize it. > > >** We all know that, no point in stating the obvious. > > My information means you can easily eliminate them altogether. > > > >> I want all the power I can get in the volume (and budget) available. >> And any iron-core transformer will saturate if you put enough DC >> across it, and 60 mV is "enough" here. > > >** Totally off with the fairies. > > That small issue was long ago addressed. > > JL is well out of his depth and bullshitting wildly.Real electronic design sometimes gets complex. That's one reason it's fun.> > His only REAL skill. > > >.... PhilMy skill is designing aerospace gear and selling it for a lot more than your wah-wah pedal repairs. -- John Larkin Highland Technology, Inc lunatic fringe electronics
Reply by ●August 15, 20172017-08-15
On 14 Aug 2017 08:22:43 -0700, Winfield Hill <hill@rowland.harvard.edu> wrote:>John Larkin wrote... >> >>I want to build an AC source to test synchros/resolvers/RVDTs. The >>target is 400 Hz 30 VRMS at maybe 30 VA, but we might want to simulate >>aircraft "wild power" and drive LVDTs, so maybe 250 Hz to a few kHz. >> >>I'm thinking of using half of a TPA3251 audio amp and a step-up >>transformer. Like this maybe: > > Skip the transformer, get a proper higher-voltage > class D. I like the IRS2092 chip, +/- 100V range. > Lots of assembled PCBs on eBay, free shipping from > China, two-three weeks. Just search on IRS2092. > Choose from among the smallest wimpiest ones.I do want isolated output, and if I ever want to do, say, a 120 volt version, I can buy a new transformer. The transformer lets me use full-bridge drive. Half-bridge can do interesting things driving reactive loads. Full-bridge also lets me run the box off a single 24 volt wart. I would never use potentially counterfeit Chinese parts in aerospace gear, or actually in anything that we make. -- John Larkin Highland Technology, Inc lunatic fringe electronics
Reply by ●August 15, 20172017-08-15
John Larkin bullshitted again: -------------------------------> >> > > >> >> > >> >> 250mH would resonate with 0.63uf at 400Hz, 1.62uF at 250Hz. > >> >> > >> >> > >> > > >> >** JL's inductance figure is a nonsense, the tranny is toriodal with no effective air gap so the L value varies widely with magnetisation. > >> > >> > >> I measured it with a 50-ohm function generator, by finding the 3dB > >> point. > > > >** Useless and meaningless. > > Seems like a reasonable measurement to me. >** Says a lot about you, nothing else.> > > > The L value is not constant. > > No, that's the problen with measuring power transformer inductance; it > varies with frequency and excitation. So the measurement is only > ballpark. >** With a wound core toroidal it is worthless since applied voltage and resulting current hardly differ in phase, series resonance with cap is not possible.> > > >** The link is to YOUR pic a that small toroidal. > > ???** Go to the link yourself.> >> > >> That's only 500 uF, lots of phase shift. > > > > > >** It's actually very little. > > 500 uF has a reactance of 0.8 ohms at 400 Hz, twice that at 200 Hz. > The transformer primary looks like maybe 5 ohms. >** Makes the phase shift what, 10 degrees ?> This isn't audio, it's aircraft synchros and resolvers and stuff > where precision matters.** So you claim now, but not previously. My point remains good cos I was not telling you what to do.> > > >> The max DC offset of the amp is 60 mV and the tranny primary is 70 > >> mohms; that's almost an amp of static current. Filtering the amp input > >> doesn't fix that. > > > >** Wrong issue !!! > > > >Try following the context - you bullshitting fuckhead. > > > > > > > > > >> >The final bogey, inrush surges, can be *eliminated* by using a > >> > tranny with double the primary voltage rating at 300Hz his > >> > class D amp can deliver. > >> > >> > >> The TI amp claims to be pop and click free. What's the difference > >> between pop and click? > > > >** Where is the relevance to my post? > > > > Is JL on illegal drugs ?? > > > > > > > >> >Yep, AC supply transformers do not surge at switch of if run at half > >> > rated voltage or less. Fact. > >> > >> They surge, but the AC line doesn't much care. There's an entire power > >> grid available to demagnetize it. > > > > > >** We all know that, no point in stating the obvious. > > > > My information means you can easily eliminate them altogether. > >> > > >> I want all the power I can get in the volume (and budget) available. > >> And any iron-core transformer will saturate if you put enough DC > >> across it, and 60 mV is "enough" here. > > > > > >** Totally off with the fairies. > > > > That small issue was long ago addressed. > > > > JL is well out of his depth and bullshitting wildly. > > > Real electronic design sometimes gets complex.** Leaves a dope like you in it's dust then.> > His only REAL skill. > > > > My skill is ...** Lying, bullshitting, talking irrational garbage and being a complete arsehole. Plus self aggrandising to an insane degree. FYI: You don't what to hear good advice, so don't ask for it. You vile, fucking egomaniac. .... Phil
Reply by ●August 15, 20172017-08-15
On 08/13/17 23:29, Phil Allison wrote:> > ** The scheme JL posted *IS* a common audio circuit - the fact the amp is class D seems to have you all going in tiny circles and thinking about SMPS topologies. > > An audio power amp coupled directly to a iron core transformer is something I am very familiar with and so KNOW the issues. > > IMO JD would be wise to drop the class D IC as it creates additional problems and use a class AB linear amp. > > It is obvious that none of you here have a clue. > > > .... Phil >That was my suggestion as well, but why design it if you can buy a s/hand audio amp for peanuts on ebay, then drive it with an audio oscillator ?. Dunno, why do some people always want to do stuff the hard way ?... Chris
Reply by ●August 15, 20172017-08-15
On Mon, 14 Aug 2017 21:47:51 -0700 (PDT), Phil Allison <pallison49@gmail.com> wrote:>John Larkin bullshitted again: > >------------------------------- > >> >> > >> >> >> >> >> >> 250mH would resonate with 0.63uf at 400Hz, 1.62uF at 250Hz. >> >> >> >> >> >> >> >> > >> >> >** JL's inductance figure is a nonsense, the tranny is toriodal with no effective air gap so the L value varies widely with magnetisation. >> >> >> >> >> >> I measured it with a 50-ohm function generator, by finding the 3dB >> >> point. >> > >> >** Useless and meaningless. >> >> Seems like a reasonable measurement to me. >> > >** Says a lot about you, nothing else.The alternative is to declare it unmeasurable amd not know what the inductive load will be on the h-bridge. Actually, I did a number of measurements on the transformer. Ballpark numbers are better than no numbers. Why would you not want to know the inductance? -- John Larkin Highland Technology, Inc lunatic fringe electronics
