Klaus Kragelund wrote: ---------------------------> > > No staircasing, and very simple filter >** The "staircasing" story is 100% bogus in the example under discussion. .... Phil
class D amp
Started by ●August 11, 2017
Reply by ●August 12, 20172017-08-12
Reply by ●August 12, 20172017-08-12
On 12/08/2017 01:13, John Larkin wrote:> > Driving the toroid from a 50 ohm fungen, at 400 Hz, it only takes 10s > of mA of DC to make serious distortion. It will be better driven from > a low-Z source, but I'm thinking that DC is bad. > > https://www.dropbox.com/s/0bl6jdkw4ljx4e2/400_Hz_Toroid.JPG?raw=1 > > > The TI part has a lot of nice features and protections. >Your sketch circuit is completely open loop. Perhaps feedback would reduce your distortion and DC offset worries ? piglet --- This email has been checked for viruses by AVG. http://www.avg.com
Reply by ●August 12, 20172017-08-12
On Sat, 12 Aug 2017 10:13:13 +0100, Piglet wrote:> On 12/08/2017 01:13, John Larkin wrote: >> >> Driving the toroid from a 50 ohm fungen, at 400 Hz, it only takes 10s >> of mA of DC to make serious distortion. It will be better driven from a >> low-Z source, but I'm thinking that DC is bad. >> >> https://www.dropbox.com/s/0bl6jdkw4ljx4e2/400_Hz_Toroid.JPG?raw=1 >> >> >> The TI part has a lot of nice features and protections. >> >> > Your sketch circuit is completely open loop. Perhaps feedback would > reduce your distortion and DC offset worries ? > > pigletThere's feedback inside the TPA3251. Allan
Reply by ●August 12, 20172017-08-12
On 12/08/2017 11:52, Allan Herriman wrote:> On Sat, 12 Aug 2017 10:13:13 +0100, Piglet wrote: >> Your sketch circuit is completely open loop. Perhaps feedback would >> reduce your distortion and DC offset worries ? >> >> piglet > > > There's feedback inside the TPA3251. > > Allan > > --- > This email has been checked for viruses by AVG. > http://www.avg.com >Sure, but JL was talking about the chip adding 60mV offset causing 1A primary current. External overall feedback could bring that to mere microvolts and better reduce distortion introduced by LC filter resistance. piglet
Reply by ●August 12, 20172017-08-12
On 08/11/2017 10:28 PM, Phil Allison wrote:> George Herold wrote: > > ---------------------- > > > >>>> >>>> I don't know the TPA3251... Says 13.2 V_max?, maybe you mean the >>>> tpa3221? >>>> >>> >>> >>> ** FFS learn to READ !!! >>> >>> 13.2V is the *analog* supply. >>> >>> The class D power stage spec is 36V !! >> >> Ouch, sorry Phil, no need to yell. > > > ** Hardly your first such offence - pal. > > > >>>> >>>> Is it a one of? (I would do class A, a heat sink and fan... >>>> ('cause that's what I know.) >>> >>> ** Class A ??? WTF for ? >>> >>> Class AB not good enough for you ? >> >> Sorry, my own hammer/nail problem. I've used someone else's >> AB and complained about the cross-over. >> > > > ** This class AB amplifier IC from ST is my weapon of choice: > > http://www.st.com/content/ccc/resource/technical/document/datasheet/4f/18/a6/c8/21/33/41/8d/CD00001887.pdf/files/CD00001887.pdf/jcr:content/translations/en.CD00001887.pdf > > > > > ..... Phil >You can get the bare board from you know who for $3.45 delivered: <http://www.ebay.com/itm/New-TDA7293-AC-12-50V-100W-Mono-Single-Channel-Digital-Audio-Amplifier-Board-/142277453807?hash=item212065a7ef:g:6SkAAOSw-itXqBqT>
Reply by ●August 12, 20172017-08-12
On Sat, 12 Aug 2017 01:22:16 -0700 (PDT), Phil Allison <pallison49@gmail.com> wrote:>Klaus Kragelund wrote: > >--------------------------- >> >> >> No staircasing, and very simple filter >> > > >** The "staircasing" story is 100% bogus in the example under discussion. > > >Why? -- John Larkin Highland Technology, Inc lunatic fringe electronics
Reply by ●August 12, 20172017-08-12
"Phil Hobbs" <pcdhSpamMeSenseless@electrooptical.net> wrote in message news:gJKdnUUGRLAIhBPEnZ2dnUU7-R3NnZ2d@supernews.com...> The caps will force the volt-seconds to average to zero, but not > necessarily within a cycle. There may be some DC on the caps because > once the average current in the core gets off zero, it'll walk in the > direction of increasing magnetization. It does have to stop on account > of the capacitor, but maybe there could be a bit of distortion as a > result. >Ferromagnetism is weird. Once had a 10kW, "high frequency" (low kHz) stripwound toroid in an induction heater. The inverter (just simple square wave output) wasn't quite balanced, so it went into saturation (audible with the loud, harsh noise) pretty quickly.. So we put a coupling capacitor in, and ran it again. DC is gone, but it's still saturating. Huh. Even stranger, it's fine for a few seconds, then "walks" over to saturation. Put in transformer #2. No problem, nice and quiet (well, relatively speaking). Some ferromagnetic materials have saturation and history problems: NiZn ferrite often warns not to saturate the material (though I don't know why; I haven't tested that yet). I've seen the same behavior, the long time constant, "flux walking" saturation, with square permalloy cores. Those transformers were interesting. We quoted a dozen transformer shops across the country. Most "no quote". A few came back with unrealistic designs, like, a 24" wide toroid. Guessing their "designer" was using winding and loss tables for 60Hz. ;-) The place we finally bought from, gave us something about $800 and 10" o.d., with a copper tube in the middle for cooling water, exactly what I was expecting. Couldn't find any thermal problems with them. As far as I know, those units are still in service at LANL. Some sort of material processing system. Something about a rare, toxic metal -- probably nothing interesting. :^) Tim -- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website: http://seventransistorlabs.com
Reply by ●August 12, 20172017-08-12
On Saturday, August 12, 2017 at 10:31:12 PM UTC+2, Tim Williams wrote:> "Phil Hobbs" <pcdhSpamMeSenseless@electrooptical.net> wrote in message > news:gJKdnUUGRLAIhBPEnZ2dnUU7-R3NnZ2d@supernews.com... > > The caps will force the volt-seconds to average to zero, but not > > necessarily within a cycle. There may be some DC on the caps because > > once the average current in the core gets off zero, it'll walk in the > > direction of increasing magnetization. It does have to stop on account > > of the capacitor, but maybe there could be a bit of distortion as a > > result. > > > > Ferromagnetism is weird. > > Once had a 10kW, "high frequency" (low kHz) stripwound toroid in an > induction heater. The inverter (just simple square wave output) wasn't > quite balanced, so it went into saturation (audible with the loud, harsh > noise) pretty quickly.. > > So we put a coupling capacitor in, and ran it again. DC is gone, but it's > still saturating. Huh. Even stranger, it's fine for a few seconds, then > "walks" over to saturation. > > Put in transformer #2. No problem, nice and quiet (well, relatively > speaking). > > Some ferromagnetic materials have saturation and history problems: NiZn > ferrite often warns not to saturate the material (though I don't know why; I > haven't tested that yet). I've seen the same behavior, the long time > constant, "flux walking" saturation, with square permalloy cores. > > Those transformers were interesting. We quoted a dozen transformer shops > across the country. Most "no quote". A few came back with unrealistic > designs, like, a 24" wide toroid. Guessing their "designer" was using > winding and loss tables for 60Hz. ;-) The place we finally bought from, > gave us something about $800 and 10" o.d., with a copper tube in the middle > for cooling water, exactly what I was expecting. Couldn't find any thermal > problems with them. > > As far as I know, those units are still in service at LANL. Some sort of > material processing system. Something about a rare, toxic metal -- probably > nothing interesting. :^) >Staircase saturation can be difficult to manage with full confidence Until recently I only looked at the primary side control, but you also need to consider unbalance on the secondary. Typically on the primary the staircase is prevented by a series capacitor, but that only works for voltage mode control systems For the secondary, one could have say a halfbridge converter with primary series capacitor, but secondary could be what is called a current doubler type: http://www.encyclopedia-magnetica.com/doku.php/current_doubler The problem with that type is that if the diodes are not equal (and they never are), then different volt seconds are presented to positive and negative cycles leading to staircasing. In the halfbridge, the staircasing can be mitigated by series resistance which offers negative feedback. But staircasing exists for sure Cheers Klaus
Reply by ●August 12, 20172017-08-12
On Saturday, August 12, 2017 at 11:49:31 PM UTC+2, Klaus Kragelund wrote:> On Saturday, August 12, 2017 at 10:31:12 PM UTC+2, Tim Williams wrote: > > "Phil Hobbs" <pcdhSpamMeSenseless@electrooptical.net> wrote in message > > news:gJKdnUUGRLAIhBPEnZ2dnUU7-R3NnZ2d@supernews.com... > > > The caps will force the volt-seconds to average to zero, but not > > > necessarily within a cycle. There may be some DC on the caps because > > > once the average current in the core gets off zero, it'll walk in the > > > direction of increasing magnetization. It does have to stop on account > > > of the capacitor, but maybe there could be a bit of distortion as a > > > result. > > > > > > > Ferromagnetism is weird. > > > > Once had a 10kW, "high frequency" (low kHz) stripwound toroid in an > > induction heater. The inverter (just simple square wave output) wasn't > > quite balanced, so it went into saturation (audible with the loud, harsh > > noise) pretty quickly.. > > > > So we put a coupling capacitor in, and ran it again. DC is gone, but it's > > still saturating. Huh. Even stranger, it's fine for a few seconds, then > > "walks" over to saturation. > > > > Put in transformer #2. No problem, nice and quiet (well, relatively > > speaking). > > > > Some ferromagnetic materials have saturation and history problems: NiZn > > ferrite often warns not to saturate the material (though I don't know why; I > > haven't tested that yet). I've seen the same behavior, the long time > > constant, "flux walking" saturation, with square permalloy cores. > > > > Those transformers were interesting. We quoted a dozen transformer shops > > across the country. Most "no quote". A few came back with unrealistic > > designs, like, a 24" wide toroid. Guessing their "designer" was using > > winding and loss tables for 60Hz. ;-) The place we finally bought from, > > gave us something about $800 and 10" o.d., with a copper tube in the middle > > for cooling water, exactly what I was expecting. Couldn't find any thermal > > problems with them. > > > > As far as I know, those units are still in service at LANL. Some sort of > > material processing system. Something about a rare, toxic metal -- probably > > nothing interesting. :^) > > > Staircase saturation can be difficult to manage with full confidence > > Until recently I only looked at the primary side control, but you also need to consider unbalance on the secondary. Typically on the primary the staircase is prevented by a series capacitor, but that only works for voltage mode control systems > > For the secondary, one could have say a halfbridge converter with primary series capacitor, but secondary could be what is called a current doubler type: > > http://www.encyclopedia-magnetica.com/doku.php/current_doubler > > The problem with that type is that if the diodes are not equal (and they never are), then different volt seconds are presented to positive and negative cycles leading to staircasing. In the halfbridge, the staircasing can be mitigated by series resistance which offers negative feedback. But staircasing exists for sure > > Cheers > > KlausOh, forgot to link that to Larkins shcematics, is secondary unbalance possible? Bytheway John, nice idea, good use of the IC if it works Cheers Klaus
Reply by ●August 12, 20172017-08-12
On Friday, August 11, 2017 at 1:27:25 PM UTC-7, 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... > 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=1Annoyingly, you can't feed low-impedance input to those digital amps, you gotta DC-block with capacitors. So, that pic has some issues (won't bias the inputs right). That also means that if you have a toroid doing voltage-boosting, and care about DC, you can't correct the DC level at those input terminals. You might, however, run a second winding on the toroid with a modulated load, that would let you balance the induction with a resistor-to-small-voltage load that opposes the (DC-offset) current.
