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Abusing the LM386

Started by bitrex April 11, 2018
Use two bridged to drive say a little PCB-mount 2k - 8 ohm audio 
transformer "backwards" to charge a HV capacitor, current feedback from 
each side of the "primary" inductance keeps the drive current waveform 
from going all sloppy, cross-coupling the G1 pins boosts each 
amplifier's "open loop" gain.

<https://imgur.com/a/RaXU3>

On Wed, 11 Apr 2018 11:39:44 -0400, bitrex
<bitrex@de.lete.earthlink.net> wrote:

>Use two bridged to drive say a little PCB-mount 2k - 8 ohm audio >transformer "backwards" to charge a HV capacitor, current feedback from >each side of the "primary" inductance keeps the drive current waveform >from going all sloppy, cross-coupling the G1 pins boosts each >amplifier's "open loop" gain. > ><https://imgur.com/a/RaXU3>
Seems complex. Why not just poke a sine wave into the primary through a DC block capacitor? -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
On 04/11/2018 12:47 PM, John Larkin wrote:
> On Wed, 11 Apr 2018 11:39:44 -0400, bitrex > <bitrex@de.lete.earthlink.net> wrote: > >> Use two bridged to drive say a little PCB-mount 2k - 8 ohm audio >> transformer "backwards" to charge a HV capacitor, current feedback from >> each side of the "primary" inductance keeps the drive current waveform >>from going all sloppy, cross-coupling the G1 pins boosts each >> amplifier's "open loop" gain. >> >> <https://imgur.com/a/RaXU3> > > Seems complex. Why not just poke a sine wave into the primary through > a DC block capacitor? > >
Yep, but unless you want to wait all afternoon for your capacitor to charge up you need push powah to do that. Hence what you might call a "power amplifier" made out of some cheap parts. Or you could use a HV switcher/boost converter. That's cool. Switchers are cool. Boosting 12 volts to ~250 at more than a few mA has its own fun time design probs tho
On Wed, 11 Apr 2018 13:31:12 -0400, bitrex
<bitrex@de.lete.earthlink.net> wrote:

>On 04/11/2018 12:47 PM, John Larkin wrote: >> On Wed, 11 Apr 2018 11:39:44 -0400, bitrex >> <bitrex@de.lete.earthlink.net> wrote: >> >>> Use two bridged to drive say a little PCB-mount 2k - 8 ohm audio >>> transformer "backwards" to charge a HV capacitor, current feedback from >>> each side of the "primary" inductance keeps the drive current waveform >>>from going all sloppy, cross-coupling the G1 pins boosts each >>> amplifier's "open loop" gain. >>> >>> <https://imgur.com/a/RaXU3> >> >> Seems complex. Why not just poke a sine wave into the primary through >> a DC block capacitor? >> >> > >Yep, but unless you want to wait all afternoon for your capacitor to >charge up you need push powah to do that. Hence what you might call a >"power amplifier" made out of some cheap parts.
Sure, but it could be a lot simpler.
> >Or you could use a HV switcher/boost converter. That's cool. Switchers >are cool. Boosting 12 volts to ~250 at more than a few mA has its own >fun time design probs tho
The LT3803 and one of those cheap dual-winding inductors works pretty well. https://www.dropbox.com/s/priqv9f5jm5gx13/HP_PS_5.jpg?raw=1 https://www.dropbox.com/s/sokhhr8yibzdkt6/T840_A13_PS.pdf?raw=1 -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
On 04/11/2018 03:23 PM, John Larkin wrote:
> On Wed, 11 Apr 2018 13:31:12 -0400, bitrex > <bitrex@de.lete.earthlink.net> wrote: > >> On 04/11/2018 12:47 PM, John Larkin wrote: >>> On Wed, 11 Apr 2018 11:39:44 -0400, bitrex >>> <bitrex@de.lete.earthlink.net> wrote: >>> >>>> Use two bridged to drive say a little PCB-mount 2k - 8 ohm audio >>>> transformer "backwards" to charge a HV capacitor, current feedback from
This paper presents a new and novel technique for speed control of a brushed DC motor without employing any direct shaft transducer in its feedback mechanism. This method uses the current/voltage variation produced on the motor main input power lines as the brushes move from collector blade to the next. The frequency of variation is proportional to the motor speed and the rotor position can also be detected by monitoring the changes for each collector blade. The performance of the motor torque speed characteristic using this system as its feedback has been evaluated through laboratory testing. This configuration is very suitable for harsh environment and places with not enough space for the motor with discrete sensors.
>>>> each side of the "primary" inductance keeps the drive current waveform >>> >from going all sloppy, cross-coupling the G1 pins boosts each >>>> amplifier's "open loop" gain. >>>> >>>> <https://imgur.com/a/RaXU3> >>> >>> Seems complex. Why not just poke a sine wave into the primary through >>> a DC block capacitor? >>> >>> >> >> Yep, but unless you want to wait all afternoon for your capacitor to >> charge up you need push powah to do that. Hence what you might call a >> "power amplifier" made out of some cheap parts. > > Sure, but it could be a lot simpler. > >> >> Or you could use a HV switcher/boost converter. That's cool. Switchers >> are cool. Boosting 12 volts to ~250 at more than a few mA has its own >> fun time design probs tho > > The LT3803 and one of those cheap dual-winding inductors works pretty > well. > > https://www.dropbox.com/s/priqv9f5jm5gx13/HP_PS_5.jpg?raw=1 > > https://www.dropbox.com/s/sokhhr8yibzdkt6/T840_A13_PS.pdf?raw=1 > >
I could probably tack on a few CW multiplier stages to the output and make an anode supply for a small CRT. Talk about complicated, just look at this thing this is nuts! <http://www.seekic.com/uploadfile/ic-circuit/s201141331219442.jpg>
On 04/11/2018 03:57 PM, bitrex wrote:
> On 04/11/2018 03:23 PM, John Larkin wrote: >> On Wed, 11 Apr 2018 13:31:12 -0400, bitrex >> <bitrex@de.lete.earthlink.net> wrote: >> >>> On 04/11/2018 12:47 PM, John Larkin wrote: >>>> On Wed, 11 Apr 2018 11:39:44 -0400, bitrex >>>> <bitrex@de.lete.earthlink.net> wrote: >>>> >>>>> Use two bridged to drive say a little PCB-mount 2k - 8 ohm audio >>>>> transformer "backwards" to charge a HV capacitor, current feedback >>>>> from > This paper presents a new and novel technique for speed control of a > brushed DC motor without employing any direct shaft transducer in its > feedback mechanism. This method uses the current/voltage variation > produced on the motor main input power lines as the brushes move from > collector blade to the next. The frequency of variation is proportional > to the motor speed and the rotor position can also be detected by > monitoring the changes for each collector blade. The performance of the > motor torque speed characteristic using this system as its feedback has > been evaluated through laboratory testing. This configuration is very > suitable for harsh environment and places with not enough space for the > motor with discrete sensors.
Whoops, IDK how that got pasted in there. Hey, but the paper looks pretty cool though
On Wednesday, April 11, 2018 at 3:58:02 PM UTC-4, bitrex wrote:
> On 04/11/2018 03:23 PM, John Larkin wrote: > > On Wed, 11 Apr 2018 13:31:12 -0400, bitrex > > <bitrex@de.lete.earthlink.net> wrote: > > > >> On 04/11/2018 12:47 PM, John Larkin wrote: > >>> On Wed, 11 Apr 2018 11:39:44 -0400, bitrex > >>> <bitrex@de.lete.earthlink.net> wrote: > >>> > >>>> Use two bridged to drive say a little PCB-mount 2k - 8 ohm audio > >>>> transformer "backwards" to charge a HV capacitor, current feedback from > This paper presents a new and novel technique for speed control of a > brushed DC motor without employing any direct shaft transducer in its > feedback mechanism. This method uses the current/voltage variation > produced on the motor main input power lines as the brushes move from > collector blade to the next. The frequency of variation is proportional > to the motor speed and the rotor position can also be detected by > monitoring the changes for each collector blade. The performance of the > motor torque speed characteristic using this system as its feedback has > been evaluated through laboratory testing. This configuration is very > suitable for harsh environment and places with not enough space for the > motor with discrete sensors. > > >>>> each side of the "primary" inductance keeps the drive current waveform > >>> >from going all sloppy, cross-coupling the G1 pins boosts each > >>>> amplifier's "open loop" gain. > >>>> > >>>> <https://imgur.com/a/RaXU3> > >>> > >>> Seems complex. Why not just poke a sine wave into the primary through > >>> a DC block capacitor? > >>> > >>> > >> > >> Yep, but unless you want to wait all afternoon for your capacitor to > >> charge up you need push powah to do that. Hence what you might call a > >> "power amplifier" made out of some cheap parts. > > > > Sure, but it could be a lot simpler. > > > >> > >> Or you could use a HV switcher/boost converter. That's cool. Switchers > >> are cool. Boosting 12 volts to ~250 at more than a few mA has its own > >> fun time design probs tho > > > > The LT3803 and one of those cheap dual-winding inductors works pretty > > well. > > > > https://www.dropbox.com/s/priqv9f5jm5gx13/HP_PS_5.jpg?raw=1 > > > > https://www.dropbox.com/s/sokhhr8yibzdkt6/T840_A13_PS.pdf?raw=1 > > > > > > I could probably tack on a few CW multiplier stages to the output and > make an anode supply for a small CRT. Talk about complicated, just look > at this thing this is nuts! >
Those are CW multipliers... maybe you didn't look at the last pic? GH
> <http://www.seekic.com/uploadfile/ic-circuit/s201141331219442.jpg>
On 04/11/2018 07:49 PM, George Herold wrote:
> On Wednesday, April 11, 2018 at 3:58:02 PM UTC-4, bitrex wrote: >> On 04/11/2018 03:23 PM, John Larkin wrote: >>> On Wed, 11 Apr 2018 13:31:12 -0400, bitrex >>> <bitrex@de.lete.earthlink.net> wrote: >>> >>>> On 04/11/2018 12:47 PM, John Larkin wrote: >>>>> On Wed, 11 Apr 2018 11:39:44 -0400, bitrex >>>>> <bitrex@de.lete.earthlink.net> wrote: >>>>> >>>>>> Use two bridged to drive say a little PCB-mount 2k - 8 ohm audio >>>>>> transformer "backwards" to charge a HV capacitor, current feedback from >> This paper presents a new and novel technique for speed control of a >> brushed DC motor without employing any direct shaft transducer in its >> feedback mechanism. This method uses the current/voltage variation >> produced on the motor main input power lines as the brushes move from >> collector blade to the next. The frequency of variation is proportional >> to the motor speed and the rotor position can also be detected by >> monitoring the changes for each collector blade. The performance of the >> motor torque speed characteristic using this system as its feedback has >> been evaluated through laboratory testing. This configuration is very >> suitable for harsh environment and places with not enough space for the >> motor with discrete sensors. >> >>>>>> each side of the "primary" inductance keeps the drive current waveform >>>>> >from going all sloppy, cross-coupling the G1 pins boosts each >>>>>> amplifier's "open loop" gain. >>>>>> >>>>>> <https://imgur.com/a/RaXU3> >>>>> >>>>> Seems complex. Why not just poke a sine wave into the primary through >>>>> a DC block capacitor? >>>>> >>>>> >>>> >>>> Yep, but unless you want to wait all afternoon for your capacitor to >>>> charge up you need push powah to do that. Hence what you might call a >>>> "power amplifier" made out of some cheap parts. >>> >>> Sure, but it could be a lot simpler. >>> >>>> >>>> Or you could use a HV switcher/boost converter. That's cool. Switchers >>>> are cool. Boosting 12 volts to ~250 at more than a few mA has its own >>>> fun time design probs tho >>> >>> The LT3803 and one of those cheap dual-winding inductors works pretty >>> well. >>> >>> https://www.dropbox.com/s/priqv9f5jm5gx13/HP_PS_5.jpg?raw=1 >>> >>> https://www.dropbox.com/s/sokhhr8yibzdkt6/T840_A13_PS.pdf?raw=1 >>> >>> >> >> I could probably tack on a few CW multiplier stages to the output and >> make an anode supply for a small CRT. Talk about complicated, just look >> at this thing this is nuts! >> > Those are CW multipliers... maybe you didn't look at the last pic? > GH >> <http://www.seekic.com/uploadfile/ic-circuit/s201141331219442.jpg> >
Ok, I see now. JL didn't say what kind of power output he's getting from that circuit, the one I drew will charge up a 4.7uF cap to over 250 volts in a little over 250 mS in the simulation at least. I'm gonna use it to fire a small xenon strobe repeatedly, I'd like to see what kind of flash rate I can get before the ICs melt down. I don't feel too bad about destroying a couple 20 cent LM386es...
On Thursday, April 12, 2018 at 3:31:17 AM UTC+10, bitrex wrote:
> On 04/11/2018 12:47 PM, John Larkin wrote: > > On Wed, 11 Apr 2018 11:39:44 -0400, bitrex > > <bitrex@de.lete.earthlink.net> wrote: > > > >> Use two bridged to drive say a little PCB-mount 2k - 8 ohm audio > >> transformer "backwards" to charge a HV capacitor, current feedback from > >> each side of the "primary" inductance keeps the drive current waveform > >>from going all sloppy, cross-coupling the G1 pins boosts each > >> amplifier's "open loop" gain. > >> > >> <https://imgur.com/a/RaXU3> > > > > Seems complex. Why not just poke a sine wave into the primary through > > a DC block capacitor? > > > > > > Yep, but unless you want to wait all afternoon for your capacitor to > charge up you need push powah to do that. Hence what you might call a > "power amplifier" made out of some cheap parts. > > Or you could use a HV switcher/boost converter. That's cool. Switchers > are cool. Boosting 12 volts to ~250 at more than a few mA has its own > fun time design probs tho
It's a well-known problem, with at least one well-known solution. http://sophia-elektronica.com/0344_001_Baxandal.pdf Peter Baxandall apparently invented the circuit to deal the problems created by inter-windng capacitance in the secondary of a high-turns ratio step-up transformer. He seems to have been generating about 1mA at 1kV to drive photomultiplier tubes, but while I worked with a guy who had worked with him, I never met the man myself. http://sophia-elektronica.com/Baxandall_parallel-resonant_Class-D_oscillator1.htm The circuit at the bottom of the page is my speculation about how you'd do it today. http://sophia-elektronica.com/PMT-transformer.html talks about the interwinding capacitance in the transformer shown in the circuit diagram and in the .asc file. -- Bill Sloman, Sydney
On Thursday, April 12, 2018 at 5:23:55 AM UTC+10, John Larkin wrote:
> On Wed, 11 Apr 2018 13:31:12 -0400, bitrex > <bitrex@de.lete.earthlink.net> wrote: > > >On 04/11/2018 12:47 PM, John Larkin wrote: > >> On Wed, 11 Apr 2018 11:39:44 -0400, bitrex > >> <bitrex@de.lete.earthlink.net> wrote: > >> > >>> Use two bridged to drive say a little PCB-mount 2k - 8 ohm audio > >>> transformer "backwards" to charge a HV capacitor, current feedback from > >>> each side of the "primary" inductance keeps the drive current waveform > >>>from going all sloppy, cross-coupling the G1 pins boosts each > >>> amplifier's "open loop" gain. > >>> > >>> <https://imgur.com/a/RaXU3> > >> > >> Seems complex. Why not just poke a sine wave into the primary through > >> a DC block capacitor? > >> > >> > > > >Yep, but unless you want to wait all afternoon for your capacitor to > >charge up you need push powah to do that. Hence what you might call a > >"power amplifier" made out of some cheap parts. > > Sure, but it could be a lot simpler. > > > > >Or you could use a HV switcher/boost converter. That's cool. Switchers > >are cool. Boosting 12 volts to ~250 at more than a few mA has its own > >fun time design probs tho > > The LT3803 and one of those cheap dual-winding inductors works pretty > well. > > https://www.dropbox.com/s/priqv9f5jm5gx13/HP_PS_5.jpg?raw=1 > > https://www.dropbox.com/s/sokhhr8yibzdkt6/T840_A13_PS.pdf?raw=1
John Larkin seems to have been frightened by a coil-winding machine as a child. You can design your own transformers and get them wound for you at your local coil-winding shop. TDK/EPCOS sell a large range of ferrite cores and formers (quite a few of which you can buy off the shelf from Mouser). There are quite a few parameters you can play with when you design your own transformers and inductors, so it's not an entirely trivial exercise, but you end up with lot more options than if you confine yourself to inductors that you can buy ready-wound off the shelf, as John likes to. -- Bi9ll Sloman, Sydney