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elektroda.net NewsGroups Forum Index - Electronics Design - Baxandall class-D oscillator squegging and the VBIC model
Bill Sloman
Guest
Guest
Sat Jan 14, 2012 3:31 am
The Baxandall parallel class-D oscillator "squegs" in real life if you
build it with a high value inductance in the current feed and bipolar
switches. An LTSpice circuit using the Gummel-Poon model for the
bipolar transistors doesn't show this - it settles down to a stable
sinusoidal oscillation within less than a hundred cycles.
The obvious effect of using a high value inductor is that the current
through the inductor over-shoots dramatically at start-up and actually
reverses polarity as it recovers, so the bipolar transistors briefly
run inverted (emitter and collector diffusions swap roles). In real
life this clearly makes the circuit behave very oddly, but the Gummel-
Poon model equally clearly doesn't capture this particular oddness.
VBIC might do better, but it doesn't with the model parameters that
I bodged out of Gummel-Poon parameters. Somebody who had a better -
some - understanding of the VBIC parameters might well be able to do
better.
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--
Bill Sloman, Nijmegen
Tim Wescott
Guest
Guest
Sat Jan 14, 2012 5:36 am
On Fri, 13 Jan 2012 17:44:04 -0800, Bill Sloman wrote:
Quote:
The Baxandall parallel class-D oscillator "squegs" in real life if you
build it with a high value inductance in the current feed and bipolar
switches. An LTSpice circuit using the Gummel-Poon model for the bipolar
transistors doesn't show this - it settles down to a stable sinusoidal
oscillation within less than a hundred cycles.
The obvious effect of using a high value inductor is that the current
through the inductor over-shoots dramatically at start-up and actually
reverses polarity as it recovers, so the bipolar transistors briefly run
inverted (emitter and collector diffusions swap roles). In real life
this clearly makes the circuit behave very oddly, but the Gummel- Poon
model equally clearly doesn't capture this particular oddness.
VBIC might do better, but it doesn't with the model parameters that I
bodged out of Gummel-Poon parameters. Somebody who had a better - some -
understanding of the VBIC parameters might well be able to do better.
(LTSpice _schematic_ (Phil) snipped)
build it with a high value inductance in the current feed and bipolar
switches. An LTSpice circuit using the Gummel-Poon model for the bipolar
transistors doesn't show this - it settles down to a stable sinusoidal
oscillation within less than a hundred cycles.
The obvious effect of using a high value inductor is that the current
through the inductor over-shoots dramatically at start-up and actually
reverses polarity as it recovers, so the bipolar transistors briefly run
inverted (emitter and collector diffusions swap roles). In real life
this clearly makes the circuit behave very oddly, but the Gummel- Poon
model equally clearly doesn't capture this particular oddness.
VBIC might do better, but it doesn't with the model parameters that I
bodged out of Gummel-Poon parameters. Somebody who had a better - some -
understanding of the VBIC parameters might well be able to do better.
(LTSpice _schematic_ (Phil) snipped)
Since it's balanced, why do you need a monster inductor there? Why not
use a resistor, or put a resistor in series with the L to dampen the
squegging?
--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?
Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com
John Larkin
Guest
Guest
Sat Jan 14, 2012 5:36 am
On Fri, 13 Jan 2012 17:44:04 -0800 (PST), Bill Sloman
<bill.sloman_at_ieee.org> wrote:
Quote:
The Baxandall parallel class-D oscillator "squegs" in real life if you
build it with a high value inductance in the current feed and bipolar
switches. An LTSpice circuit using the Gummel-Poon model for the
bipolar transistors doesn't show this - it settles down to a stable
sinusoidal oscillation within less than a hundred cycles.
The obvious effect of using a high value inductor is that the current
through the inductor over-shoots dramatically at start-up and actually
reverses polarity as it recovers, so the bipolar transistors briefly
run inverted (emitter and collector diffusions swap roles). In real
life this clearly makes the circuit behave very oddly, but the Gummel-
Poon model equally clearly doesn't capture this particular oddness.
VBIC might do better, but it doesn't with the model parameters that
I bodged out of Gummel-Poon parameters. Somebody who had a better -
some - understanding of the VBIC parameters might well be able to do
better.
build it with a high value inductance in the current feed and bipolar
switches. An LTSpice circuit using the Gummel-Poon model for the
bipolar transistors doesn't show this - it settles down to a stable
sinusoidal oscillation within less than a hundred cycles.
The obvious effect of using a high value inductor is that the current
through the inductor over-shoots dramatically at start-up and actually
reverses polarity as it recovers, so the bipolar transistors briefly
run inverted (emitter and collector diffusions swap roles). In real
life this clearly makes the circuit behave very oddly, but the Gummel-
Poon model equally clearly doesn't capture this particular oddness.
VBIC might do better, but it doesn't with the model parameters that
I bodged out of Gummel-Poon parameters. Somebody who had a better -
some - understanding of the VBIC parameters might well be able to do
better.
It seems to wobble a bit on startup, but doesn't actually squegg even
with a full henry as the feed inductor.
Oscillators sure simulate slowly.
John
John Devereux
Guest
Guest
Sat Jan 14, 2012 11:09 am
Bill Sloman <bill.sloman_at_ieee.org> writes:
Quote:
On Jan 14, 5:36Â am, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Fri, 13 Jan 2012 17:44:04 -0800 (PST), Bill Sloman
bill.slo...@ieee.org> wrote:
The Baxandall parallel class-D oscillator "squegs" in real life if you
build it with a high value inductance in the current feed and bipolar
switches. An LTSpice circuit using the Gummel-Poon model for the
bipolar transistors doesn't show this - it settles down to a stable
sinusoidal oscillation within less than a hundred cycles.
The obvious effect of using a high value inductor is that the current
through the inductor over-shoots dramatically at start-up and actually
reverses polarity as it recovers, so the bipolar transistors briefly
run inverted (emitter and collector diffusions swap roles). In real
life this clearly makes the circuit  behave very oddly, but the Gummel-
Poon model equally clearly doesn't capture this particular oddness.
VBIC might do better, but it doesn't with the model parameters that
I Â bodged out of Gummel-Poon parameters. Somebody who had a better -
some - understanding of the VBIC parameters might well be able to do
better.
It seems to wobble a bit on startup, but doesn't actually squeg even
with a full henry as the feed inductor.
That's what I'm complaining about. A real circuit would almost
certainly squeg.
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Fri, 13 Jan 2012 17:44:04 -0800 (PST), Bill Sloman
bill.slo...@ieee.org> wrote:
The Baxandall parallel class-D oscillator "squegs" in real life if you
build it with a high value inductance in the current feed and bipolar
switches. An LTSpice circuit using the Gummel-Poon model for the
bipolar transistors doesn't show this - it settles down to a stable
sinusoidal oscillation within less than a hundred cycles.
The obvious effect of using a high value inductor is that the current
through the inductor over-shoots dramatically at start-up and actually
reverses polarity as it recovers, so the bipolar transistors briefly
run inverted (emitter and collector diffusions swap roles). In real
life this clearly makes the circuit  behave very oddly, but the Gummel-
Poon model equally clearly doesn't capture this particular oddness.
VBIC might do better, but it doesn't with the model parameters that
I Â bodged out of Gummel-Poon parameters. Somebody who had a better -
some - understanding of the VBIC parameters might well be able to do
better.
It seems to wobble a bit on startup, but doesn't actually squeg even
with a full henry as the feed inductor.
That's what I'm complaining about. A real circuit would almost
certainly squeg.
Well there's one way to find out isn't there? :)
--
John Devereux
Bill Sloman
Guest
Guest
Sat Jan 14, 2012 11:56 am
On Jan 14, 5:36 am, John Larkin
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
Quote:
On Fri, 13 Jan 2012 17:44:04 -0800 (PST), Bill Sloman
bill.slo...@ieee.org> wrote:
The Baxandall parallel class-D oscillator "squegs" in real life if you
build it with a high value inductance in the current feed and bipolar
switches. An LTSpice circuit using the Gummel-Poon model for the
bipolar transistors doesn't show this - it settles down to a stable
sinusoidal oscillation within less than a hundred cycles.
The obvious effect of using a high value inductor is that the current
through the inductor over-shoots dramatically at start-up and actually
reverses polarity as it recovers, so the bipolar transistors briefly
run inverted (emitter and collector diffusions swap roles). In real
life this clearly makes the circuit behave very oddly, but the Gummel-
Poon model equally clearly doesn't capture this particular oddness.
VBIC might do better, but it doesn't with the model parameters that
I bodged out of Gummel-Poon parameters. Somebody who had a better -
some - understanding of the VBIC parameters might well be able to do
better.
It seems to wobble a bit on startup, but doesn't actually squeg even
with a full henry as the feed inductor.
bill.slo...@ieee.org> wrote:
The Baxandall parallel class-D oscillator "squegs" in real life if you
build it with a high value inductance in the current feed and bipolar
switches. An LTSpice circuit using the Gummel-Poon model for the
bipolar transistors doesn't show this - it settles down to a stable
sinusoidal oscillation within less than a hundred cycles.
The obvious effect of using a high value inductor is that the current
through the inductor over-shoots dramatically at start-up and actually
reverses polarity as it recovers, so the bipolar transistors briefly
run inverted (emitter and collector diffusions swap roles). In real
life this clearly makes the circuit behave very oddly, but the Gummel-
Poon model equally clearly doesn't capture this particular oddness.
VBIC might do better, but it doesn't with the model parameters that
I bodged out of Gummel-Poon parameters. Somebody who had a better -
some - understanding of the VBIC parameters might well be able to do
better.
It seems to wobble a bit on startup, but doesn't actually squeg even
with a full henry as the feed inductor.
That's what I'm complaining about. A real circuit would almost
certainly squeg.
--
Bill Sloman, Nijmegen
Bill Sloman
Guest
Guest
Sat Jan 14, 2012 11:56 am
On Jan 14, 5:36 am, Tim Wescott <t...@seemywebsite.com> wrote:
Quote:
On Fri, 13 Jan 2012 17:44:04 -0800, Bill Sloman wrote:
The Baxandall parallel class-D oscillator "squegs" in real life if you
build it with a high value inductance in the current feed and bipolar
switches. An LTSpice circuit using the Gummel-Poon model for the bipolar
transistors doesn't show this - it settles down to a stable sinusoidal
oscillation within less than a hundred cycles.
The obvious effect of using a high value inductor is that the current
through the inductor over-shoots dramatically at start-up and actually
reverses polarity as it recovers, so the bipolar transistors briefly run
inverted (emitter and collector diffusions swap roles). In real life
this clearly makes the circuit behave very oddly, but the Gummel- Poon
model equally clearly doesn't capture this particular oddness.
VBIC might do better, but it doesn't with the model parameters that I
bodged out of Gummel-Poon parameters. Somebody who had a better - some -
understanding of the VBIC parameters might well be able to do better.
(LTSpice _schematic_ (Phil) snipped)
Since it's balanced, why do you need a monster inductor there? Why not
use a resistor, or put a resistor in series with the L to dampen the
squegging?
The Baxandall parallel class-D oscillator "squegs" in real life if you
build it with a high value inductance in the current feed and bipolar
switches. An LTSpice circuit using the Gummel-Poon model for the bipolar
transistors doesn't show this - it settles down to a stable sinusoidal
oscillation within less than a hundred cycles.
The obvious effect of using a high value inductor is that the current
through the inductor over-shoots dramatically at start-up and actually
reverses polarity as it recovers, so the bipolar transistors briefly run
inverted (emitter and collector diffusions swap roles). In real life
this clearly makes the circuit behave very oddly, but the Gummel- Poon
model equally clearly doesn't capture this particular oddness.
VBIC might do better, but it doesn't with the model parameters that I
bodged out of Gummel-Poon parameters. Somebody who had a better - some -
understanding of the VBIC parameters might well be able to do better.
(LTSpice _schematic_ (Phil) snipped)
Since it's balanced, why do you need a monster inductor there? Why not
use a resistor, or put a resistor in series with the L to dampen the
squegging?
Using a big inductor reduces the level of odd harmonics (3rd, 5th etc)
in the sine wave generated. Using an inductor at all is the kern of
the Class-D oscillator
http://home.planet.nl/~sloma000/0344_001_Baxandal.pdf
Adding more resistance in series with the inductor makes the circuit
less efficient. Jim William's versions get over 90% efficiency -
Linear Technology application notes AN45, AN49, AN51, AN55, AN61,
AN65.
If it were big enough, it might damp the overshoot on start-up enough
to prevent the initial reversal of current in the inductor, which
might - in turn - stop the squegging from starting.
--
Bill Sloman, Nijmegen
Bill Sloman
Guest
Guest
Sat Jan 14, 2012 1:00 pm
On Jan 14, 11:09 am, John Devereux <j...@devereux.me.uk> wrote:
Quote:
BillSloman<bill.slo...@ieee.org> writes:
On Jan 14, 5:36 am, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Fri, 13 Jan 2012 17:44:04 -0800 (PST),BillSloman
bill.slo...@ieee.org> wrote:
The Baxandall parallel class-D oscillator "squegs" in real life if you
build it with a high value inductance in the current feed and bipolar
switches. An LTSpice circuit using the Gummel-Poon model for the
bipolar transistors doesn't show this - it settles down to a stable
sinusoidal oscillation within less than a hundred cycles.
The obvious effect of using a high value inductor is that the current
through the inductor over-shoots dramatically at start-up and actually
reverses polarity as it recovers, so the bipolar transistors briefly
run inverted (emitter and collector diffusions swap roles). In real
life this clearly makes the circuit behave very oddly, but the Gummel-
Poon model equally clearly doesn't capture this particular oddness.
VBIC might do better, but it doesn't with the model parameters that
I bodged out of Gummel-Poon parameters. Somebody who had a better -
some - understanding of the VBIC parameters might well be able to do
better.
It seems to wobble a bit on startup, but doesn't actually squeg even
with a full henry as the feed inductor.
That's what I'm complaining about. A real circuit would almost
certainly squeg.
Well there's one way to find out isn't there?
On Jan 14, 5:36 am, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Fri, 13 Jan 2012 17:44:04 -0800 (PST),BillSloman
bill.slo...@ieee.org> wrote:
The Baxandall parallel class-D oscillator "squegs" in real life if you
build it with a high value inductance in the current feed and bipolar
switches. An LTSpice circuit using the Gummel-Poon model for the
bipolar transistors doesn't show this - it settles down to a stable
sinusoidal oscillation within less than a hundred cycles.
The obvious effect of using a high value inductor is that the current
through the inductor over-shoots dramatically at start-up and actually
reverses polarity as it recovers, so the bipolar transistors briefly
run inverted (emitter and collector diffusions swap roles). In real
life this clearly makes the circuit behave very oddly, but the Gummel-
Poon model equally clearly doesn't capture this particular oddness.
VBIC might do better, but it doesn't with the model parameters that
I bodged out of Gummel-Poon parameters. Somebody who had a better -
some - understanding of the VBIC parameters might well be able to do
better.
It seems to wobble a bit on startup, but doesn't actually squeg even
with a full henry as the feed inductor.
That's what I'm complaining about. A real circuit would almost
certainly squeg.
Well there's one way to find out isn't there?
The last one I built with an over-sized oscillator (which was the
first one I ever built, more than forty years ago) certainly squegged.
Building another just to prove the point would be something of a waste
of time. An example with a diode to prevent the current through the
inductor going the wrong way might make more sense.
--
Bill Sloman, Nijmegen
John Devereux
Guest
Guest
Sat Jan 14, 2012 3:41 pm
Bill Sloman <bill.sloman_at_ieee.org> writes:
Quote:
On Jan 14, 11:09Â am, John Devereux <j...@devereux.me.uk> wrote:
BillSloman<bill.slo...@ieee.org> writes:
On Jan 14, 5:36Â am, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Fri, 13 Jan 2012 17:44:04 -0800 (PST),BillSloman
bill.slo...@ieee.org> wrote:
The Baxandall parallel class-D oscillator "squegs" in real life if you
build it with a high value inductance in the current feed and bipolar
switches. An LTSpice circuit using the Gummel-Poon model for the
bipolar transistors doesn't show this - it settles down to a stable
sinusoidal oscillation within less than a hundred cycles.
The obvious effect of using a high value inductor is that the current
through the inductor over-shoots dramatically at start-up and actually
reverses polarity as it recovers, so the bipolar transistors briefly
run inverted (emitter and collector diffusions swap roles). In real
life this clearly makes the circuit  behave very oddly, but the Gummel-
Poon model equally clearly doesn't capture this particular oddness.
VBIC might do better, but it doesn't with the model parameters that
I Â bodged out of Gummel-Poon parameters. Somebody who had a better -
some - understanding of the VBIC parameters might well be able to do
better.
It seems to wobble a bit on startup, but doesn't actually squeg even
with a full henry as the feed inductor.
That's what I'm complaining about. A real circuit would almost
certainly squeg.
Well there's one way to find out isn't there? :)
The last one I built with an over-sized oscillator (which was the
first one I ever built, more than forty years ago) certainly squegged.
Building another just to prove the point would be something of a waste
of time. An example with a diode to prevent the current through the
inductor going the wrong way might make more sense.
BillSloman<bill.slo...@ieee.org> writes:
On Jan 14, 5:36Â am, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Fri, 13 Jan 2012 17:44:04 -0800 (PST),BillSloman
bill.slo...@ieee.org> wrote:
The Baxandall parallel class-D oscillator "squegs" in real life if you
build it with a high value inductance in the current feed and bipolar
switches. An LTSpice circuit using the Gummel-Poon model for the
bipolar transistors doesn't show this - it settles down to a stable
sinusoidal oscillation within less than a hundred cycles.
The obvious effect of using a high value inductor is that the current
through the inductor over-shoots dramatically at start-up and actually
reverses polarity as it recovers, so the bipolar transistors briefly
run inverted (emitter and collector diffusions swap roles). In real
life this clearly makes the circuit  behave very oddly, but the Gummel-
Poon model equally clearly doesn't capture this particular oddness.
VBIC might do better, but it doesn't with the model parameters that
I Â bodged out of Gummel-Poon parameters. Somebody who had a better -
some - understanding of the VBIC parameters might well be able to do
better.
It seems to wobble a bit on startup, but doesn't actually squeg even
with a full henry as the feed inductor.
That's what I'm complaining about. A real circuit would almost
certainly squeg.
Well there's one way to find out isn't there? :)
The last one I built with an over-sized oscillator (which was the
first one I ever built, more than forty years ago) certainly squegged.
Building another just to prove the point would be something of a waste
of time. An example with a diode to prevent the current through the
inductor going the wrong way might make more sense.
Well of course the next step is to fix the squegging. But if it does not
show up in the simulation, then the simulation is not going to be much
use for fixing it!
--
John Devereux
Tim Wescott
Guest
Guest
Sat Jan 14, 2012 5:36 pm
On Sat, 14 Jan 2012 01:56:59 -0800, Bill Sloman wrote:
Quote:
On Jan 14, 5:36Â am, Tim Wescott <t...@seemywebsite.com> wrote:
On Fri, 13 Jan 2012 17:44:04 -0800, Bill Sloman wrote:
The Baxandall parallel class-D oscillator "squegs" in real life if
you build it with a high value inductance in the current feed and
bipolar switches. An LTSpice circuit using the Gummel-Poon model for
the bipolar transistors doesn't show this - it settles down to a
stable sinusoidal oscillation within less than a hundred cycles.
The obvious effect of using a high value inductor is that the current
through the inductor over-shoots dramatically at start-up and
actually reverses polarity as it recovers, so the bipolar transistors
briefly run inverted (emitter and collector diffusions swap roles).
In real life this clearly makes the circuit  behave very oddly, but
the Gummel- Poon model equally clearly doesn't capture this
particular oddness.
VBIC might do better, but it doesn't with the model parameters that I
bodged out of Gummel-Poon parameters. Somebody who had a better -
some - understanding of the VBIC parameters might well be able to do
better.
(LTSpice _schematic_ (Phil) snipped)
Since it's balanced, why do you need a monster inductor there? Â Why not
use a resistor, or put a resistor in series with the L to dampen the
squegging?
Using a big inductor reduces the level of odd harmonics (3rd, 5th etc)
in the sine wave generated. Using an inductor at all is the kern of the
Class-D oscillator
http://home.planet.nl/~sloma000/0344_001_Baxandal.pdf
Adding more resistance in series with the inductor makes the circuit
less efficient. Jim William's versions get over 90% efficiency - Linear
Technology application notes AN45, AN49, AN51, AN55, AN61, AN65.
If it were big enough, it might damp the overshoot on start-up enough to
prevent the initial reversal of current in the inductor, which might -
in turn - stop the squegging from starting.
On Fri, 13 Jan 2012 17:44:04 -0800, Bill Sloman wrote:
The Baxandall parallel class-D oscillator "squegs" in real life if
you build it with a high value inductance in the current feed and
bipolar switches. An LTSpice circuit using the Gummel-Poon model for
the bipolar transistors doesn't show this - it settles down to a
stable sinusoidal oscillation within less than a hundred cycles.
The obvious effect of using a high value inductor is that the current
through the inductor over-shoots dramatically at start-up and
actually reverses polarity as it recovers, so the bipolar transistors
briefly run inverted (emitter and collector diffusions swap roles).
In real life this clearly makes the circuit  behave very oddly, but
the Gummel- Poon model equally clearly doesn't capture this
particular oddness.
VBIC might do better, but it doesn't with the model parameters that I
bodged out of Gummel-Poon parameters. Somebody who had a better -
some - understanding of the VBIC parameters might well be able to do
better.
(LTSpice _schematic_ (Phil) snipped)
Since it's balanced, why do you need a monster inductor there? Â Why not
use a resistor, or put a resistor in series with the L to dampen the
squegging?
Using a big inductor reduces the level of odd harmonics (3rd, 5th etc)
in the sine wave generated. Using an inductor at all is the kern of the
Class-D oscillator
http://home.planet.nl/~sloma000/0344_001_Baxandal.pdf
Adding more resistance in series with the inductor makes the circuit
less efficient. Jim William's versions get over 90% efficiency - Linear
Technology application notes AN45, AN49, AN51, AN55, AN61, AN65.
If it were big enough, it might damp the overshoot on start-up enough to
prevent the initial reversal of current in the inductor, which might -
in turn - stop the squegging from starting.
You might also consider putting diodes in series with the transistor
collectors, to force the transistors to only work one way.
--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com
Tim Wescott
Guest
Guest
Sat Jan 14, 2012 5:38 pm
On Sat, 14 Jan 2012 01:56:59 -0800, Bill Sloman wrote:
Quote:
On Jan 14, 5:36Â am, Tim Wescott <t...@seemywebsite.com> wrote:
On Fri, 13 Jan 2012 17:44:04 -0800, Bill Sloman wrote:
The Baxandall parallel class-D oscillator "squegs" in real life if
you build it with a high value inductance in the current feed and
bipolar switches. An LTSpice circuit using the Gummel-Poon model for
the bipolar transistors doesn't show this - it settles down to a
stable sinusoidal oscillation within less than a hundred cycles.
The obvious effect of using a high value inductor is that the current
through the inductor over-shoots dramatically at start-up and
actually reverses polarity as it recovers, so the bipolar transistors
briefly run inverted (emitter and collector diffusions swap roles).
In real life this clearly makes the circuit  behave very oddly, but
the Gummel- Poon model equally clearly doesn't capture this
particular oddness.
VBIC might do better, but it doesn't with the model parameters that I
bodged out of Gummel-Poon parameters. Somebody who had a better -
some - understanding of the VBIC parameters might well be able to do
better.
(LTSpice _schematic_ (Phil) snipped)
Since it's balanced, why do you need a monster inductor there? Â Why not
use a resistor, or put a resistor in series with the L to dampen the
squegging?
Using a big inductor reduces the level of odd harmonics (3rd, 5th etc)
in the sine wave generated. Using an inductor at all is the kern of the
Class-D oscillator
http://home.planet.nl/~sloma000/0344_001_Baxandal.pdf
Adding more resistance in series with the inductor makes the circuit
less efficient. Jim William's versions get over 90% efficiency - Linear
Technology application notes AN45, AN49, AN51, AN55, AN61, AN65.
If it were big enough, it might damp the overshoot on start-up enough to
prevent the initial reversal of current in the inductor, which might -
in turn - stop the squegging from starting.
On Fri, 13 Jan 2012 17:44:04 -0800, Bill Sloman wrote:
The Baxandall parallel class-D oscillator "squegs" in real life if
you build it with a high value inductance in the current feed and
bipolar switches. An LTSpice circuit using the Gummel-Poon model for
the bipolar transistors doesn't show this - it settles down to a
stable sinusoidal oscillation within less than a hundred cycles.
The obvious effect of using a high value inductor is that the current
through the inductor over-shoots dramatically at start-up and
actually reverses polarity as it recovers, so the bipolar transistors
briefly run inverted (emitter and collector diffusions swap roles).
In real life this clearly makes the circuit  behave very oddly, but
the Gummel- Poon model equally clearly doesn't capture this
particular oddness.
VBIC might do better, but it doesn't with the model parameters that I
bodged out of Gummel-Poon parameters. Somebody who had a better -
some - understanding of the VBIC parameters might well be able to do
better.
(LTSpice _schematic_ (Phil) snipped)
Since it's balanced, why do you need a monster inductor there? Â Why not
use a resistor, or put a resistor in series with the L to dampen the
squegging?
Using a big inductor reduces the level of odd harmonics (3rd, 5th etc)
in the sine wave generated. Using an inductor at all is the kern of the
Class-D oscillator
http://home.planet.nl/~sloma000/0344_001_Baxandal.pdf
Adding more resistance in series with the inductor makes the circuit
less efficient. Jim William's versions get over 90% efficiency - Linear
Technology application notes AN45, AN49, AN51, AN55, AN61, AN65.
If it were big enough, it might damp the overshoot on start-up enough to
prevent the initial reversal of current in the inductor, which might -
in turn - stop the squegging from starting.
I know that putting a resistor in makes things less efficient -- but what
do you want? An astonishingly efficient oscillator that wastes some
power, but still works? Or an oscillator that is is astonishingly
efficient and useless?
--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com
Bill Sloman
Guest
Guest
Sat Jan 14, 2012 5:40 pm
On Jan 14, 3:41 pm, John Devereux <j...@devereux.me.uk> wrote:
Quote:
BillSloman<bill.slo...@ieee.org> writes:
On Jan 14, 11:09 am, John Devereux <j...@devereux.me.uk> wrote:
BillSloman<bill.slo...@ieee.org> writes:
On Jan 14, 5:36 am, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Fri, 13 Jan 2012 17:44:04 -0800 (PST),BillSloman
bill.slo...@ieee.org> wrote:
The Baxandall parallel class-D oscillator "squegs" in real life if you
build it with a high value inductance in the current feed and bipolar
switches. An LTSpice circuit using the Gummel-Poon model for the
bipolar transistors doesn't show this - it settles down to a stable
sinusoidal oscillation within less than a hundred cycles.
The obvious effect of using a high value inductor is that the current
through the inductor over-shoots dramatically at start-up and actually
reverses polarity as it recovers, so the bipolar transistors briefly
run inverted (emitter and collector diffusions swap roles). In real
life this clearly makes the circuit behave very oddly, but the Gummel-
Poon model equally clearly doesn't capture this particular oddness..
VBIC might do better, but it doesn't with the model parameters that
I bodged out of Gummel-Poon parameters. Somebody who had a better -
some - understanding of the VBIC parameters might well be able to do
better.
It seems to wobble a bit on startup, but doesn't actually squeg even
with a full henry as the feed inductor.
That's what I'm complaining about. A real circuit would almost
certainly squeg.
Well there's one way to find out isn't there? :)
The last one I built with an over-sized oscillator (which was the
first one I ever built, more than forty years ago) certainly squegged.
Building another just to prove the point would be something of a waste
of time. An example with a diode to prevent the current through the
inductor going the wrong way might make more sense.
Well of course the next step is to fix the squegging. But if it does not
show up in the simulation, then the simulation is not going to be much
use for fixing it!
On Jan 14, 11:09 am, John Devereux <j...@devereux.me.uk> wrote:
BillSloman<bill.slo...@ieee.org> writes:
On Jan 14, 5:36 am, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Fri, 13 Jan 2012 17:44:04 -0800 (PST),BillSloman
bill.slo...@ieee.org> wrote:
The Baxandall parallel class-D oscillator "squegs" in real life if you
build it with a high value inductance in the current feed and bipolar
switches. An LTSpice circuit using the Gummel-Poon model for the
bipolar transistors doesn't show this - it settles down to a stable
sinusoidal oscillation within less than a hundred cycles.
The obvious effect of using a high value inductor is that the current
through the inductor over-shoots dramatically at start-up and actually
reverses polarity as it recovers, so the bipolar transistors briefly
run inverted (emitter and collector diffusions swap roles). In real
life this clearly makes the circuit behave very oddly, but the Gummel-
Poon model equally clearly doesn't capture this particular oddness..
VBIC might do better, but it doesn't with the model parameters that
I bodged out of Gummel-Poon parameters. Somebody who had a better -
some - understanding of the VBIC parameters might well be able to do
better.
It seems to wobble a bit on startup, but doesn't actually squeg even
with a full henry as the feed inductor.
That's what I'm complaining about. A real circuit would almost
certainly squeg.
Well there's one way to find out isn't there? :)
The last one I built with an over-sized oscillator (which was the
first one I ever built, more than forty years ago) certainly squegged.
Building another just to prove the point would be something of a waste
of time. An example with a diode to prevent the current through the
inductor going the wrong way might make more sense.
Well of course the next step is to fix the squegging. But if it does not
show up in the simulation, then the simulation is not going to be much
use for fixing it!
If the problem is the current going the wrong way through the inductor
- which is what the simulations seem to suggest - then one extra diode
might well fix it. If this were to work, I'd have found something -
thanks to the simulation - which Peter Baxandall (amongst many others,
including me and Tony Williams) had missed. If it were that simple,
someone should have found it out earlier, so it probably won't work.
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John Larkin
Guest
Guest
Sat Jan 14, 2012 5:47 pm
On Sat, 14 Jan 2012 01:56:34 -0800 (PST), Bill Sloman
<bill.sloman_at_ieee.org> wrote:
Quote:
On Jan 14, 5:36 am, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Fri, 13 Jan 2012 17:44:04 -0800 (PST), Bill Sloman
bill.slo...@ieee.org> wrote:
The Baxandall parallel class-D oscillator "squegs" in real life if you
build it with a high value inductance in the current feed and bipolar
switches. An LTSpice circuit using the Gummel-Poon model for the
bipolar transistors doesn't show this - it settles down to a stable
sinusoidal oscillation within less than a hundred cycles.
The obvious effect of using a high value inductor is that the current
through the inductor over-shoots dramatically at start-up and actually
reverses polarity as it recovers, so the bipolar transistors briefly
run inverted (emitter and collector diffusions swap roles). In real
life this clearly makes the circuit behave very oddly, but the Gummel-
Poon model equally clearly doesn't capture this particular oddness.
VBIC might do better, but it doesn't with the model parameters that
I bodged out of Gummel-Poon parameters. Somebody who had a better -
some - understanding of the VBIC parameters might well be able to do
better.
It seems to wobble a bit on startup, but doesn't actually squeg even
with a full henry as the feed inductor.
That's what I'm complaining about. A real circuit would almost
certainly squeg.
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Fri, 13 Jan 2012 17:44:04 -0800 (PST), Bill Sloman
bill.slo...@ieee.org> wrote:
The Baxandall parallel class-D oscillator "squegs" in real life if you
build it with a high value inductance in the current feed and bipolar
switches. An LTSpice circuit using the Gummel-Poon model for the
bipolar transistors doesn't show this - it settles down to a stable
sinusoidal oscillation within less than a hundred cycles.
The obvious effect of using a high value inductor is that the current
through the inductor over-shoots dramatically at start-up and actually
reverses polarity as it recovers, so the bipolar transistors briefly
run inverted (emitter and collector diffusions swap roles). In real
life this clearly makes the circuit behave very oddly, but the Gummel-
Poon model equally clearly doesn't capture this particular oddness.
VBIC might do better, but it doesn't with the model parameters that
I bodged out of Gummel-Poon parameters. Somebody who had a better -
some - understanding of the VBIC parameters might well be able to do
better.
It seems to wobble a bit on startup, but doesn't actually squeg even
with a full henry as the feed inductor.
That's what I'm complaining about. A real circuit would almost
certainly squeg.
I doubt it. The whole thing is domnated by the Q of the tuned circuit.
It's not a higher-order system. A cap in the base bias network could
push it over the edge, like a super-regen receiver.
But why don't you build one and see?
John
John Larkin
Guest
Guest
Sat Jan 14, 2012 7:16 pm
On Sat, 14 Jan 2012 03:00:55 -0800 (PST), Bill Sloman
<bill.sloman_at_ieee.org> wrote:
Quote:
On Jan 14, 11:09 am, John Devereux <j...@devereux.me.uk> wrote:
BillSloman<bill.slo...@ieee.org> writes:
On Jan 14, 5:36 am, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Fri, 13 Jan 2012 17:44:04 -0800 (PST),BillSloman
bill.slo...@ieee.org> wrote:
The Baxandall parallel class-D oscillator "squegs" in real life if you
build it with a high value inductance in the current feed and bipolar
switches. An LTSpice circuit using the Gummel-Poon model for the
bipolar transistors doesn't show this - it settles down to a stable
sinusoidal oscillation within less than a hundred cycles.
The obvious effect of using a high value inductor is that the current
through the inductor over-shoots dramatically at start-up and actually
reverses polarity as it recovers, so the bipolar transistors briefly
run inverted (emitter and collector diffusions swap roles). In real
life this clearly makes the circuit behave very oddly, but the Gummel-
Poon model equally clearly doesn't capture this particular oddness.
VBIC might do better, but it doesn't with the model parameters that
I bodged out of Gummel-Poon parameters. Somebody who had a better -
some - understanding of the VBIC parameters might well be able to do
better.
It seems to wobble a bit on startup, but doesn't actually squeg even
with a full henry as the feed inductor.
That's what I'm complaining about. A real circuit would almost
certainly squeg.
Well there's one way to find out isn't there? :)
The last one I built with an over-sized oscillator (which was the
first one I ever built, more than forty years ago) certainly squegged.
Building another just to prove the point would be something of a waste
of time.
BillSloman<bill.slo...@ieee.org> writes:
On Jan 14, 5:36 am, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Fri, 13 Jan 2012 17:44:04 -0800 (PST),BillSloman
bill.slo...@ieee.org> wrote:
The Baxandall parallel class-D oscillator "squegs" in real life if you
build it with a high value inductance in the current feed and bipolar
switches. An LTSpice circuit using the Gummel-Poon model for the
bipolar transistors doesn't show this - it settles down to a stable
sinusoidal oscillation within less than a hundred cycles.
The obvious effect of using a high value inductor is that the current
through the inductor over-shoots dramatically at start-up and actually
reverses polarity as it recovers, so the bipolar transistors briefly
run inverted (emitter and collector diffusions swap roles). In real
life this clearly makes the circuit behave very oddly, but the Gummel-
Poon model equally clearly doesn't capture this particular oddness.
VBIC might do better, but it doesn't with the model parameters that
I bodged out of Gummel-Poon parameters. Somebody who had a better -
some - understanding of the VBIC parameters might well be able to do
better.
It seems to wobble a bit on startup, but doesn't actually squeg even
with a full henry as the feed inductor.
That's what I'm complaining about. A real circuit would almost
certainly squeg.
Well there's one way to find out isn't there? :)
The last one I built with an over-sized oscillator (which was the
first one I ever built, more than forty years ago) certainly squegged.
Building another just to prove the point would be something of a waste
of time.
If the behavior of this oscillator is a waste of time, give it up.
If it were interesting to me, I'd have one running in about 30
minutes, on a handsome, dremeled, labeled slice of copperclad.
John
Bill Sloman
Guest
Guest
Sat Jan 14, 2012 8:59 pm
On Jan 14, 7:16 pm, John Larkin
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
Quote:
On Sat, 14 Jan 2012 03:00:55 -0800 (PST),BillSloman
bill.slo...@ieee.org> wrote:
On Jan 14, 11:09 am, John Devereux <j...@devereux.me.uk> wrote:
BillSloman<bill.slo...@ieee.org> writes:
On Jan 14, 5:36 am, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Fri, 13 Jan 2012 17:44:04 -0800 (PST),BillSloman
bill.slo...@ieee.org> wrote:
The Baxandall parallel class-D oscillator "squegs" in real life if you
build it with a high value inductance in the current feed and bipolar
switches. An LTSpice circuit using the Gummel-Poon model for the
bipolar transistors doesn't show this - it settles down to a stable
sinusoidal oscillation within less than a hundred cycles.
The obvious effect of using a high value inductor is that the current
through the inductor over-shoots dramatically at start-up and actually
reverses polarity as it recovers, so the bipolar transistors briefly
run inverted (emitter and collector diffusions swap roles). In real
life this clearly makes the circuit behave very oddly, but the Gummel-
Poon model equally clearly doesn't capture this particular oddness..
VBIC might do better, but it doesn't with the model parameters that
I bodged out of Gummel-Poon parameters. Somebody who had a better -
some - understanding of the VBIC parameters might well be able to do
better.
It seems to wobble a bit on startup, but doesn't actually squeg even
with a full henry as the feed inductor.
That's what I'm complaining about. A real circuit would almost
certainly squeg.
Well there's one way to find out isn't there? :)
The last one I built with an over-sized oscillator (which was the
first one I ever built, more than forty years ago) certainly squegged.
Building another just to prove the point would be something of a waste
of time.
If the behavior of this oscillator is a waste of time, give it up.
If it were interesting to me, I'd have one running in about 30
minutes, on a handsome, dremeled, labeled slice of copperclad.
bill.slo...@ieee.org> wrote:
On Jan 14, 11:09 am, John Devereux <j...@devereux.me.uk> wrote:
BillSloman<bill.slo...@ieee.org> writes:
On Jan 14, 5:36 am, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Fri, 13 Jan 2012 17:44:04 -0800 (PST),BillSloman
bill.slo...@ieee.org> wrote:
The Baxandall parallel class-D oscillator "squegs" in real life if you
build it with a high value inductance in the current feed and bipolar
switches. An LTSpice circuit using the Gummel-Poon model for the
bipolar transistors doesn't show this - it settles down to a stable
sinusoidal oscillation within less than a hundred cycles.
The obvious effect of using a high value inductor is that the current
through the inductor over-shoots dramatically at start-up and actually
reverses polarity as it recovers, so the bipolar transistors briefly
run inverted (emitter and collector diffusions swap roles). In real
life this clearly makes the circuit behave very oddly, but the Gummel-
Poon model equally clearly doesn't capture this particular oddness..
VBIC might do better, but it doesn't with the model parameters that
I bodged out of Gummel-Poon parameters. Somebody who had a better -
some - understanding of the VBIC parameters might well be able to do
better.
It seems to wobble a bit on startup, but doesn't actually squeg even
with a full henry as the feed inductor.
That's what I'm complaining about. A real circuit would almost
certainly squeg.
Well there's one way to find out isn't there? :)
The last one I built with an over-sized oscillator (which was the
first one I ever built, more than forty years ago) certainly squegged.
Building another just to prove the point would be something of a waste
of time.
If the behavior of this oscillator is a waste of time, give it up.
If it were interesting to me, I'd have one running in about 30
minutes, on a handsome, dremeled, labeled slice of copperclad.
A bit extravagant for a 16kHz oscillator. If I get enthusiastic enough
to build one I'll put it on a perforated prototyping board. I rather
like the one Farnell sells that comes with a "collander ground plane"
on the component side of the board. The copper rings around the holes
on the track side can be chopped up to support surface mount parts if
you want to mix and match.
It will take a bit longer than half an hour - winding transformers is
tedious, even when you've got access to a coil winding machine.
--
Bill Sloman
Bill Sloman
Guest
Guest
Sat Jan 14, 2012 9:00 pm
On Jan 14, 5:47 pm, John Larkin
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
Quote:
On Sat, 14 Jan 2012 01:56:34 -0800 (PST),BillSloman
bill.slo...@ieee.org> wrote:
On Jan 14, 5:36 am, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Fri, 13 Jan 2012 17:44:04 -0800 (PST),BillSloman
bill.slo...@ieee.org> wrote:
The Baxandall parallel class-D oscillator "squegs" in real life if you
build it with a high value inductance in the current feed and bipolar
switches. An LTSpice circuit using the Gummel-Poon model for the
bipolar transistors doesn't show this - it settles down to a stable
sinusoidal oscillation within less than a hundred cycles.
The obvious effect of using a high value inductor is that the current
through the inductor over-shoots dramatically at start-up and actually
reverses polarity as it recovers, so the bipolar transistors briefly
run inverted (emitter and collector diffusions swap roles). In real
life this clearly makes the circuit behave very oddly, but the Gummel-
Poon model equally clearly doesn't capture this particular oddness.
VBIC might do better, but it doesn't with the model parameters that
I bodged out of Gummel-Poon parameters. Somebody who had a better -
some - understanding of the VBIC parameters might well be able to do
better.
It seems to wobble a bit on startup, but doesn't actually squeg even
with a full henry as the feed inductor.
That's what I'm complaining about. A real circuit would almost
certainly squeg.
I doubt it. The whole thing is dominated by the Q of the tuned circuit.
It's not a higher-order system. A cap in the base bias network could
push it over the edge, like a super-regen receiver.
bill.slo...@ieee.org> wrote:
On Jan 14, 5:36 am, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Fri, 13 Jan 2012 17:44:04 -0800 (PST),BillSloman
bill.slo...@ieee.org> wrote:
The Baxandall parallel class-D oscillator "squegs" in real life if you
build it with a high value inductance in the current feed and bipolar
switches. An LTSpice circuit using the Gummel-Poon model for the
bipolar transistors doesn't show this - it settles down to a stable
sinusoidal oscillation within less than a hundred cycles.
The obvious effect of using a high value inductor is that the current
through the inductor over-shoots dramatically at start-up and actually
reverses polarity as it recovers, so the bipolar transistors briefly
run inverted (emitter and collector diffusions swap roles). In real
life this clearly makes the circuit behave very oddly, but the Gummel-
Poon model equally clearly doesn't capture this particular oddness.
VBIC might do better, but it doesn't with the model parameters that
I bodged out of Gummel-Poon parameters. Somebody who had a better -
some - understanding of the VBIC parameters might well be able to do
better.
It seems to wobble a bit on startup, but doesn't actually squeg even
with a full henry as the feed inductor.
That's what I'm complaining about. A real circuit would almost
certainly squeg.
I doubt it. The whole thing is dominated by the Q of the tuned circuit.
It's not a higher-order system. A cap in the base bias network could
push it over the edge, like a super-regen receiver.
Doubt all you like. It squegs anyway, and always has, if you make the
feed inductor too big
http://home.planet.nl/~sloma000/0344_001_Baxandal.pdf
See Baxandall's footnote on page 752.
Quote:
But why don't you build one and see?
I've built several over the years. I've got no urgent need to build
one now.
--
Bill Sloman, Nijmegen
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