FudFly converter...

[Klaus Kragelund]

Yeah, the negative rail is the flyback part

Was is the idea of this converter was really my point. You cannot regulate both rails at the same time except for a sweet spot?

 

[server]

On Sat, 25 Jul 2020 12:10:02 -0700 (PDT), klaus.kragelund@gmail.com
wrote:

>State space is used to calculate the transfer function from converter states

But what does it dictate?

I\'d use Spice anyhow. Real life is nonlinear.

Have you ever seen a forward converter without output inductance, a cap and freewheeling diodes?

Sure. Sold thousands. Of course there are output caps.

Sketch what you are thinking about.

Without it, it\'s just a DC transformer like the Royer and converts not according to a duty cycle, but rather a turns ratio

The forward direction works like that. The direction that regulates is
the flyback side.



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[server]

On Sat, 25 Jul 2020 15:59:01 -0400, legg <legg@nospam.magma.ca> wrote:

On Sat, 25 Jul 2020 07:55:54 -0700 (PDT), klaus.kragelund@gmail.com
wrote:

Does this really work

I haven\'t simulated it or dug deeper, but is seems the positive rail is standard flyback, regulated with Ipeak squared like normally, while the negative path is a forward style converter, with no inductor in the buck part, so more or less just the input voltage and turns ratio?

Conventional dots preserve voltage polarity, so the flyback portion
is neg through D2.

The output part is symmetric, so the dots don\'t actually matter. They
are just talking points.

When the switch is on, forward current passes through D1 with
only leakage inductance and C1 shaping the current.

RL

--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[server]

On Sat, 25 Jul 2020 14:05:50 -0700 (PDT), Klaus Kragelund
<klauskvik@hotmail.com> wrote:

Yeah, the negative rail is the flyback part

Was is the idea of this converter was really my point. You cannot regulate both rails at the same time except for a sweet spot?

There\'s only one output.



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[Tim Williams]

<jlarkin@highlandsniptechnology.com> wrote in message
news:ipkohfhebuu5uf9p5d0b0cha04n4bc9819@4ax.com...

On Sat, 25 Jul 2020 10:09:48 -0500, \"Tim Williams\"
tiwill@seventransistorlabs.com> wrote:

*Charge pump.

You\'re missing two diodes and inductors for that.

Tim

Don\'t follow that. Got a sketch?

This is a charge pump. Vout = Vin * N2/N1. Regulation not possible.
Transistors sink huge peak currents during startup.
https://i.pinimg.com/originals/b3/2a/3f/b32a3f81363866c64fe69aa1dfe17d3b.gif
(this is an automotive amplifier DC-DC converter, a very typical example)

This is a forward converter. Vout = Vin * D * N2/N1 (give or take DCM/CCM).
Eminently regulable. Transistor sinks trapezoidal current corresponding to
inductor charge.
https://upload.wikimedia.org/wikipedia/commons/7/7d/Schematic_of_a_forward_converter.png

This monstrosity might be better deserving of such a name,
https://www.seventransistorlabs.com/Images/Flyward_Converter.png
but I don\'t know why anyone would ever build it.
(The effect is to drive L1 with two pulses per cycle; in analogy to steam
engines, it might be called double-acting. The forward pulse amplitude is
set by VIN - Vds(sat); D1 is required to set the flyback pulse amplitude to
some maximum value, otherwise you would have two inductors fighting it out,
and a waste of voltage. Like the half-wave forward converter, D must be
limited to 50% or less.)

Tim

--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Design
Website: https://www.seventransistorlabs.com/

 

[server]

On Sat, 25 Jul 2020 16:57:27 -0500, \"Tim Williams\"
<tiwill@seventransistorlabs.com> wrote:

jlarkin@highlandsniptechnology.com> wrote in message
news:ipkohfhebuu5uf9p5d0b0cha04n4bc9819@4ax.com...
On Sat, 25 Jul 2020 10:09:48 -0500, \"Tim Williams\"
tiwill@seventransistorlabs.com> wrote:

*Charge pump.

You\'re missing two diodes and inductors for that.

Tim

Don\'t follow that. Got a sketch?

This is a charge pump. Vout = Vin * N2/N1. Regulation not possible.

What charge is being pumped?

>Transistors sink huge peak currents during startup.

The LT chip senses and limits peak fet current. As I noted, startup is
interesting.

https://i.pinimg.com/originals/b3/2a/3f/b32a3f81363866c64fe69aa1dfe17d3b.gif
(this is an automotive amplifier DC-DC converter, a very typical example)

This is a forward converter. Vout = Vin * D * N2/N1 (give or take DCM/CCM).
Eminently regulable. Transistor sinks trapezoidal current corresponding to
inductor charge.
https://upload.wikimedia.org/wikipedia/commons/7/7d/Schematic_of_a_forward_converter.png

This monstrosity might be better deserving of such a name,
https://www.seventransistorlabs.com/Images/Flyward_Converter.png
but I don\'t know why anyone would ever build it.

That one\'s not isolated.



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[legg]

On Sat, 25 Jul 2020 14:18:53 -0700, jlarkin@highlandsniptechnology.com
wrote:

On Sat, 25 Jul 2020 12:10:02 -0700 (PDT), klaus.kragelund@gmail.com
wrote:

State space is used to calculate the transfer function from converter states

But what does it dictate?

I\'d use Spice anyhow. Real life is nonlinear.


Have you ever seen a forward converter without output inductance, a cap and freewheeling diodes?

Sure. Sold thousands. Of course there are output caps.

Sketch what you are thinking about.


Without it, it\'s just a DC transformer like the Royer and converts not according to a duty cycle, but rather a turns ratio

The forward direction works like that. The direction that regulates is
the flyback side.

You don\'t need the first CD pair in the regulation loop.
It will simply increase fet loss at turn-on (which is
going to be pretty severe anyways).

It\'s not a forward converter without an energy storage element -
it\'s just a switched capacitor DC-DC.

RL

 

[legg]

On Sat, 25 Jul 2020 14:18:53 -0700, jlarkin@highlandsniptechnology.com
wrote:

On Sat, 25 Jul 2020 12:10:02 -0700 (PDT), klaus.kragelund@gmail.com
wrote:

State space is used to calculate the transfer function from converter states

But what does it dictate?

I\'d use Spice anyhow. Real life is nonlinear.


Have you ever seen a forward converter without output inductance, a cap and freewheeling diodes?

Sure. Sold thousands. Of course there are output caps.

Sketch what you are thinking about.


Without it, it\'s just a DC transformer like the Royer and converts not according to a duty cycle, but rather a turns ratio

The forward direction works like that. The direction that regulates is
the flyback side.

Shorting the drain capacitor and using a slow diode on the primary
peak clamping/regulation node could allow clamp current to be
included in the transformed secondary flyback delivery, through
the slow diode\'s Trr, rather than just being burnt in the clamp\'s
load.

Active clamp circuits use a switch in that diode position and
the induced reverse/recovery current that it produces allows
potentially lower switch turn-on losses as the drain voltage
falls naturally - but it won\'t work in a discontinuos (complete
energy transfer) circuit, at fizxed frequency.

If a switch is used, it can be translated to a ground-referenced
pmos, using the ~ same drive as the main switch (with suitable
negative dc offset).

RL

 

[server]

On Sat, 25 Jul 2020 22:49:51 -0400, legg <legg@nospam.magma.ca> wrote:

On Sat, 25 Jul 2020 14:18:53 -0700, jlarkin@highlandsniptechnology.com
wrote:

On Sat, 25 Jul 2020 12:10:02 -0700 (PDT), klaus.kragelund@gmail.com
wrote:

State space is used to calculate the transfer function from converter states

But what does it dictate?

I\'d use Spice anyhow. Real life is nonlinear.


Have you ever seen a forward converter without output inductance, a cap and freewheeling diodes?

Sure. Sold thousands. Of course there are output caps.

Sketch what you are thinking about.


Without it, it\'s just a DC transformer like the Royer and converts not according to a duty cycle, but rather a turns ratio

The forward direction works like that. The direction that regulates is
the flyback side.

You don\'t need the first CD pair in the regulation loop.
It will simply increase fet loss at turn-on (which is
going to be pretty severe anyways).

The dual diode thing on the grounded side makes it feed back on the
primary peak-to-peak voltage, which tracks the secondary, which also
rectifies peak-to-peak.

The LTC3803 is a peak current limiter, so the startup current is
pretty much always the same, regardless of topology.

Interestingly, at current limit in the flyback topology, it is pretty
much constant power vs voltage. That can be useful.

It\'s not a forward converter without an energy storage element -
it\'s just a switched capacitor DC-DC.

That\'s just terminology. I call the non-flyback side a forward
converter, because fet turn-on drives the load with no specific energy
storage.

I think of \"switched capacitor\" as something else, an actual switched
capacitor.




--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[server]

On Sat, 25 Jul 2020 23:08:08 -0400, legg <legg@nospam.magma.ca> wrote:

On Sat, 25 Jul 2020 14:18:53 -0700, jlarkin@highlandsniptechnology.com
wrote:

On Sat, 25 Jul 2020 12:10:02 -0700 (PDT), klaus.kragelund@gmail.com
wrote:

State space is used to calculate the transfer function from converter states

But what does it dictate?

I\'d use Spice anyhow. Real life is nonlinear.


Have you ever seen a forward converter without output inductance, a cap and freewheeling diodes?

Sure. Sold thousands. Of course there are output caps.

Sketch what you are thinking about.


Without it, it\'s just a DC transformer like the Royer and converts not according to a duty cycle, but rather a turns ratio

The forward direction works like that. The direction that regulates is
the flyback side.

Shorting the drain capacitor and using a slow diode on the primary
peak clamping/regulation node could allow clamp current to be
included in the transformed secondary flyback delivery, through
the slow diode\'s Trr, rather than just being burnt in the clamp\'s
load.

Active clamp circuits use a switch in that diode position and
the induced reverse/recovery current that it produces allows
potentially lower switch turn-on losses as the drain voltage
falls naturally - but it won\'t work in a discontinuos (complete
energy transfer) circuit, at fizxed frequency.

If a switch is used, it can be translated to a ground-referenced
pmos, using the ~ same drive as the main switch (with suitable
negative dc offset).

RL

Got a circuit?



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[Piotr Wyderski]

Tim Williams wrote:

This is a charge pump.  Vout = Vin * N2/N1.  Regulation not possible.
Transistors sink huge peak currents during startup.

The lack of the inductor is a regular implementation at low power, e.g.
see the SN6501. For lower ripple level is commonly being implemented as
two interleaved forwards, i.e. the push-pull.

I was also considering that topology in my multi-output slew-rate
limited low-power auxiliary PSU; perhaps you remember the thread. But
the added complexity and dependence on the transistor model turned out
not to be worth further exploration. The LT3439 did it better. But then
I am still using to feed two groups of independent, interleaved
half-wave rectifiers. The loads are quite symmetric, so there is no
noticeable flux imbalance, all is within the current-mode regulation
capabilities of the controller. It works very well at power level
200-500mW per channel.

This monstrosity might be better deserving of such a name,
https://www.seventransistorlabs.com/Images/Flyward_Converter.png

Just to note: there *is* a topology called flyback-forward.

Best regards, Piotr

 

[Piotr Wyderski]

legg wrote:

If a switch is used, it can be translated to a ground-referenced
pmos, using the ~ same drive as the main switch (with suitable
negative dc offset).

Or a high-side depletion-mode N FET due to its correct body diode
direction. I did it once and the results were very OK. The V_IN range
was just right to use this trick.

Best regards, Piotr

 

[server]

On Sun, 26 Jul 2020 09:05:12 +0200, Piotr Wyderski
<peter.pan@neverland.mil> wrote:

Tim Williams wrote:

This is a charge pump.  Vout = Vin * N2/N1.  Regulation not possible.
Transistors sink huge peak currents during startup.

The lack of the inductor is a regular implementation at low power, e.g.
see the SN6501. For lower ripple level is commonly being implemented as
two interleaved forwards, i.e. the push-pull.

I was also considering that topology in my multi-output slew-rate
limited low-power auxiliary PSU; perhaps you remember the thread. But
the added complexity and dependence on the transistor model turned out
not to be worth further exploration. The LT3439 did it better. But then
I am still using to feed two groups of independent, interleaved
half-wave rectifiers. The loads are quite symmetric, so there is no
noticeable flux imbalance, all is within the current-mode regulation
capabilities of the controller. It works very well at power level
200-500mW per channel.

This monstrosity might be better deserving of such a name,
https://www.seventransistorlabs.com/Images/Flyward_Converter.png

Just to note: there *is* a topology called flyback-forward.

Best regards, Piotr

It occurs to me that my circuit is functionally equivalent to a
discontinuous boost or flyback converter driving a voltage doubler or
a C-W multiplier. Fet ON makes a low impedance voltage pulse of Vcc*N
volts into the capacitive load, and fet off is flyback in the opposite
direction. All the sophisticated objections to my circuit apply to the
flyback/C-W case too.

I guess my only innovation is the p-p detector in the lowside feedback
loop, which only a few thousand people invented before me.

Never mind.



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[server]

On Sun, 26 Jul 2020 10:29:52 -0400, legg <legg@nospam.magma.ca> wrote:

On Sat, 25 Jul 2020 20:07:47 -0700, jlarkin@highlandsniptechnology.com
wrote:

On Sat, 25 Jul 2020 22:49:51 -0400, legg <legg@nospam.magma.ca> wrote:

On Sat, 25 Jul 2020 14:18:53 -0700, jlarkin@highlandsniptechnology.com
wrote:

On Sat, 25 Jul 2020 12:10:02 -0700 (PDT), klaus.kragelund@gmail.com
wrote:

State space is used to calculate the transfer function from converter states

But what does it dictate?

I\'d use Spice anyhow. Real life is nonlinear.


Have you ever seen a forward converter without output inductance, a cap and freewheeling diodes?

Sure. Sold thousands. Of course there are output caps.

Sketch what you are thinking about.


Without it, it\'s just a DC transformer like the Royer and converts not according to a duty cycle, but rather a turns ratio

The forward direction works like that. The direction that regulates is
the flyback side.

You don\'t need the first CD pair in the regulation loop.
It will simply increase fet loss at turn-on (which is
going to be pretty severe anyways).

The dual diode thing on the grounded side makes it feed back on the
primary peak-to-peak voltage, which tracks the secondary, which also
rectifies peak-to-peak.

The transformer, tied to the positive rail, already supplies half
of the pk-pk being sensed, without the need (or interference of)
the CD parts in question.

Not necessarily half. The positive flyback voltage depends on the
load. Sensing p-p for feedback forces the p-p to be constant.

The LTC3803 is a peak current limiter, so the startup current is
pretty much always the same, regardless of topology.

The fet current waveform, is a combination of the series Llk/Cout
(reflected) and the primary mag current. The former portion of
that peaks early and is resonant. Though the chip may have a
spike suppressor on it\'s sense pin (a delay), it can\'t regulate
on a waveform with current that varies early in this manner.

It regulates on the voltage feedback it sees.

Interestingly, at current limit in the flyback topology, it is pretty
much constant power vs voltage. That can be useful.

It\'s one of the basic features (and hazards) of a flyback - the output
current being uncontrolled when shorted. In your case, this current
will be capacitively limited by the output structure - but may involve
output (or at least output cap) polarity reversal.


It\'s not a forward converter without an energy storage element -
it\'s just a switched capacitor DC-DC.

That\'s just terminology. I call the non-flyback side a forward
converter, because fet turn-on drives the load with no specific energy
storage.

When you use \'terminology\', you should stick to definitions of the
terms, which DO exist. We know what you mean, but you should stick
to simple switch-on and switch-off terms to describe the operating
periods.

Yes sir. Please don\'t punish me much.

I think of \"switched capacitor\" as something else, an actual switched
capacitor.

Your \'forward\' operation is basic switched capacitor with (ideally)
a \'DC transformer\' separating the elements.

Which cap is being switched?

It is a switch shorting two voltage sources, something usually
tolerable only at very low power levels, where efficiencies below 50%
can be ignored.

Efficiency can be almost 100% once everything gets to steady-state.
It\'s low during startup.

RL

--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[legg]

On Sat, 25 Jul 2020 20:07:47 -0700, jlarkin@highlandsniptechnology.com
wrote:

On Sat, 25 Jul 2020 22:49:51 -0400, legg <legg@nospam.magma.ca> wrote:

On Sat, 25 Jul 2020 14:18:53 -0700, jlarkin@highlandsniptechnology.com
wrote:

On Sat, 25 Jul 2020 12:10:02 -0700 (PDT), klaus.kragelund@gmail.com
wrote:

State space is used to calculate the transfer function from converter states

But what does it dictate?

I\'d use Spice anyhow. Real life is nonlinear.


Have you ever seen a forward converter without output inductance, a cap and freewheeling diodes?

Sure. Sold thousands. Of course there are output caps.

Sketch what you are thinking about.


Without it, it\'s just a DC transformer like the Royer and converts not according to a duty cycle, but rather a turns ratio

The forward direction works like that. The direction that regulates is
the flyback side.

You don\'t need the first CD pair in the regulation loop.
It will simply increase fet loss at turn-on (which is
going to be pretty severe anyways).

The dual diode thing on the grounded side makes it feed back on the
primary peak-to-peak voltage, which tracks the secondary, which also
rectifies peak-to-peak.

The transformer, tied to the positive rail, already supplies half
of the pk-pk being sensed, without the need (or interference of)
the CD parts in question.

The LTC3803 is a peak current limiter, so the startup current is
pretty much always the same, regardless of topology.

The fet current waveform, is a combination of the series Llk/Cout
(reflected) and the primary mag current. The former portion of
that peaks early and is resonant. Though the chip may have a
spike suppressor on it\'s sense pin (a delay), it can\'t regulate
on a waveform with current that varies early in this manner.

Interestingly, at current limit in the flyback topology, it is pretty
much constant power vs voltage. That can be useful.

It\'s one of the basic features (and hazards) of a flyback - the output
current being uncontrolled when shorted. In your case, this current
will be capacitively limited by the output structure - but may involve
output (or at least output cap) polarity reversal.

It\'s not a forward converter without an energy storage element -
it\'s just a switched capacitor DC-DC.

That\'s just terminology. I call the non-flyback side a forward
converter, because fet turn-on drives the load with no specific energy
storage.

When you use \'terminology\', you should stick to definitions of the
terms, which DO exist. We know what you mean, but you should stick
to simple switch-on and switch-off terms to describe the operating
periods.

I think of \"switched capacitor\" as something else, an actual switched
capacitor.

Your \'forward\' operation is basic switched capacitor with (ideally)
a \'DC transformer\' separating the elements.

It is a switch shorting two voltage sources, something usually
tolerable only at very low power levels, where efficiencies below 50%
can be ignored.

RL

 

[legg]

On Sat, 25 Jul 2020 20:13:07 -0700, jlarkin@highlandsniptechnology.com
wrote:

On Sat, 25 Jul 2020 23:08:08 -0400, legg <legg@nospam.magma.ca> wrote:

On Sat, 25 Jul 2020 14:18:53 -0700, jlarkin@highlandsniptechnology.com
wrote:

On Sat, 25 Jul 2020 12:10:02 -0700 (PDT), klaus.kragelund@gmail.com
wrote:

State space is used to calculate the transfer function from converter states

But what does it dictate?

I\'d use Spice anyhow. Real life is nonlinear.


Have you ever seen a forward converter without output inductance, a cap and freewheeling diodes?

Sure. Sold thousands. Of course there are output caps.

Sketch what you are thinking about.


Without it, it\'s just a DC transformer like the Royer and converts not according to a duty cycle, but rather a turns ratio

The forward direction works like that. The direction that regulates is
the flyback side.

Shorting the drain capacitor and using a slow diode on the primary
peak clamping/regulation node could allow clamp current to be
included in the transformed secondary flyback delivery, through
the slow diode\'s Trr, rather than just being burnt in the clamp\'s
load.

Active clamp circuits use a switch in that diode position and
the induced reverse/recovery current that it produces allows
potentially lower switch turn-on losses as the drain voltage
falls naturally - but it won\'t work in a discontinuos (complete
energy transfer) circuit, at fizxed frequency.

If a switch is used, it can be translated to a ground-referenced
pmos, using the ~ same drive as the main switch (with suitable
negative dc offset).

RL

Got a circuit?

http://ve3ute.ca/query/active_clamp_-_switched_snubber.zip

I\'ve already admitted that, at low power levels, you can get
away with murder. That doesn\'t mean that you should\'t admit to
your crime . . .

Getting away with it is just part of the fun, and any circuit
that can survive on parasitic components is bound to end up
cheaper ( at thr BOMaterials level, anyways) than one requiring
a purchase order and schematic entry.

RL

 

[legg]

On Sun, 26 Jul 2020 07:45:29 -0700, jlarkin@highlandsniptechnology.com
wrote:

<snip>

The dual diode thing on the grounded side makes it feed back on the
primary peak-to-peak voltage, which tracks the secondary, which also
rectifies peak-to-peak.

The transformer, tied to the positive rail, already supplies half
of the pk-pk being sensed, without the need (or interference of)
the CD parts in question.

Not necessarily half. The positive flyback voltage depends on the
load. Sensing p-p for feedback forces the p-p to be constant.

By half, I meant the input voltage ( \'forward\' ) share of the
sensed voltage.

The LTC3803 is a peak current limiter, so the startup current is
pretty much always the same, regardless of topology.


The fet current waveform, is a combination of the series Llk/Cout
(reflected) and the primary mag current. The former portion of
that peaks early and is resonant. Though the chip may have a
spike suppressor on it\'s sense pin (a delay), it can\'t regulate
on a waveform with current that varies early in this manner.

It regulates on the voltage feedback it sees.

Chaotically, and not necessarily safely, if at all possible, when
a silly nodal waveform appears within the regulation loop.

Interestingly, at current limit in the flyback topology, it is pretty
much constant power vs voltage. That can be useful.

It\'s one of the basic features (and hazards) of a flyback - the output
current being uncontrolled when shorted. In your case, this current
will be capacitively limited by the output structure - but may involve
output (or at least output cap) polarity reversal.


It\'s not a forward converter without an energy storage element -
it\'s just a switched capacitor DC-DC.

That\'s just terminology. I call the non-flyback side a forward
converter, because fet turn-on drives the load with no specific energy
storage.

When you use \'terminology\', you should stick to definitions of the
terms, which DO exist. We know what you mean, but you should stick
to simple switch-on and switch-off terms to describe the operating
periods.

Yes sir. Please don\'t punish me much.



I think of \"switched capacitor\" as something else, an actual switched
capacitor.

Your \'forward\' operation is basic switched capacitor with (ideally)
a \'DC transformer\' separating the elements.

Which cap is being switched?

Input (cap) and C1.

It is a switch shorting two voltage sources, something usually
tolerable only at very low power levels, where efficiencies below 50%
can be ignored.

Efficiency can be almost 100% once everything gets to steady-state.
It\'s low during startup.

There\'s a TI chip that regulates a switched cap. You should check out
it\'s efficiency plots. TPS60121.

Switched cap light load efficiency usually depends on reduced
frequency ie no load / no loss.

I stuck an old switched cap clamp sim, late, into the download.
This shows the commonly used pfet transposition to common drive gnd,
with common gate drive voltage offset.

RL

 

[Klaus Kragelund]

On Sunday, July 26, 2020 at 4:45:35 PM UTC+2, jla...@highlandsniptechnology.com wrote:

On Sun, 26 Jul 2020 10:29:52 -0400, legg <legg@nospam.magma.ca> wrote:

On Sat, 25 Jul 2020 20:07:47 -0700, jlarkin@highlandsniptechnology.com
wrote:

On Sat, 25 Jul 2020 22:49:51 -0400, legg <legg@nospam.magma.ca> wrote:

On Sat, 25 Jul 2020 14:18:53 -0700, jlarkin@highlandsniptechnology.com
wrote:

On Sat, 25 Jul 2020 12:10:02 -0700 (PDT), klaus.kragelund@gmail.com
wrote:

State space is used to calculate the transfer function from converter states

But what does it dictate?

I\'d use Spice anyhow. Real life is nonlinear.


Have you ever seen a forward converter without output inductance, a cap and freewheeling diodes?

Sure. Sold thousands. Of course there are output caps.

Sketch what you are thinking about.


Without it, it\'s just a DC transformer like the Royer and converts not according to a duty cycle, but rather a turns ratio

The forward direction works like that. The direction that regulates is
the flyback side.

You don\'t need the first CD pair in the regulation loop.
It will simply increase fet loss at turn-on (which is
going to be pretty severe anyways).

The dual diode thing on the grounded side makes it feed back on the
primary peak-to-peak voltage, which tracks the secondary, which also
rectifies peak-to-peak.

The transformer, tied to the positive rail, already supplies half
of the pk-pk being sensed, without the need (or interference of)
the CD parts in question.

Not necessarily half. The positive flyback voltage depends on the
load. Sensing p-p for feedback forces the p-p to be constant.


The LTC3803 is a peak current limiter, so the startup current is
pretty much always the same, regardless of topology.


The fet current waveform, is a combination of the series Llk/Cout
(reflected) and the primary mag current. The former portion of
that peaks early and is resonant. Though the chip may have a
spike suppressor on it\'s sense pin (a delay), it can\'t regulate
on a waveform with current that varies early in this manner.

It regulates on the voltage feedback it sees.




Interestingly, at current limit in the flyback topology, it is pretty
much constant power vs voltage. That can be useful.

It\'s one of the basic features (and hazards) of a flyback - the output
current being uncontrolled when shorted. In your case, this current
will be capacitively limited by the output structure - but may involve
output (or at least output cap) polarity reversal.


It\'s not a forward converter without an energy storage element -
it\'s just a switched capacitor DC-DC.

That\'s just terminology. I call the non-flyback side a forward
converter, because fet turn-on drives the load with no specific energy
storage.

When you use \'terminology\', you should stick to definitions of the
terms, which DO exist. We know what you mean, but you should stick
to simple switch-on and switch-off terms to describe the operating
periods.

Yes sir. Please don\'t punish me much.

Terminology is important, otherwise you cannot communicate in any sensible manor.

I think of \"switched capacitor\" as something else, an actual switched
capacitor.

Your \'forward\' operation is basic switched capacitor with (ideally)
a \'DC transformer\' separating the elements.

Which cap is being switched?

The FET turns on in forward fashion, with the voltage on the secondary side determined by VDC in times turns ratio. That voltage is imposed directly on the output cap. Thus switch cap, since you have a cap on the VDC input as always

It is a switch shorting two voltage sources, something usually
tolerable only at very low power levels, where efficiencies below 50%
can be ignored.

Efficiency can be almost 100% once everything gets to steady-state.
It\'s low during startup.

Switch cap converters with non-ideal transfer ratios are not very efficient

Cheers

Klaus

 

[server]

On Sun, 26 Jul 2020 08:51:49 -0700 (PDT), Klaus Kragelund
<klauskvik@hotmail.com> wrote:

On Sunday, July 26, 2020 at 4:45:35 PM UTC+2, jla...@highlandsniptechnology.com wrote:
On Sun, 26 Jul 2020 10:29:52 -0400, legg <legg@nospam.magma.ca> wrote:

On Sat, 25 Jul 2020 20:07:47 -0700, jlarkin@highlandsniptechnology.com
wrote:

On Sat, 25 Jul 2020 22:49:51 -0400, legg <legg@nospam.magma.ca> wrote:

On Sat, 25 Jul 2020 14:18:53 -0700, jlarkin@highlandsniptechnology.com
wrote:

On Sat, 25 Jul 2020 12:10:02 -0700 (PDT), klaus.kragelund@gmail.com
wrote:

State space is used to calculate the transfer function from converter states

But what does it dictate?

I\'d use Spice anyhow. Real life is nonlinear.


Have you ever seen a forward converter without output inductance, a cap and freewheeling diodes?

Sure. Sold thousands. Of course there are output caps.

Sketch what you are thinking about.


Without it, it\'s just a DC transformer like the Royer and converts not according to a duty cycle, but rather a turns ratio

The forward direction works like that. The direction that regulates is
the flyback side.

You don\'t need the first CD pair in the regulation loop.
It will simply increase fet loss at turn-on (which is
going to be pretty severe anyways).

The dual diode thing on the grounded side makes it feed back on the
primary peak-to-peak voltage, which tracks the secondary, which also
rectifies peak-to-peak.

The transformer, tied to the positive rail, already supplies half
of the pk-pk being sensed, without the need (or interference of)
the CD parts in question.

Not necessarily half. The positive flyback voltage depends on the
load. Sensing p-p for feedback forces the p-p to be constant.


The LTC3803 is a peak current limiter, so the startup current is
pretty much always the same, regardless of topology.


The fet current waveform, is a combination of the series Llk/Cout
(reflected) and the primary mag current. The former portion of
that peaks early and is resonant. Though the chip may have a
spike suppressor on it\'s sense pin (a delay), it can\'t regulate
on a waveform with current that varies early in this manner.

It regulates on the voltage feedback it sees.




Interestingly, at current limit in the flyback topology, it is pretty
much constant power vs voltage. That can be useful.

It\'s one of the basic features (and hazards) of a flyback - the output
current being uncontrolled when shorted. In your case, this current
will be capacitively limited by the output structure - but may involve
output (or at least output cap) polarity reversal.


It\'s not a forward converter without an energy storage element -
it\'s just a switched capacitor DC-DC.

That\'s just terminology. I call the non-flyback side a forward
converter, because fet turn-on drives the load with no specific energy
storage.

When you use \'terminology\', you should stick to definitions of the
terms, which DO exist. We know what you mean, but you should stick
to simple switch-on and switch-off terms to describe the operating
periods.

Yes sir. Please don\'t punish me much.


Terminology is important, otherwise you cannot communicate in any sensible manor.

People who can\'t draw schematics have to communicate circuit concepts
by typing words. Lots of words. Then they can debate about what the
words mean.

I think of \"switched capacitor\" as something else, an actual switched
capacitor.

Your \'forward\' operation is basic switched capacitor with (ideally)
a \'DC transformer\' separating the elements.

Which cap is being switched?


The FET turns on in forward fashion, with the voltage on the secondary side determined by VDC in times turns ratio. That voltage is imposed directly on the output cap. Thus switch cap, since you have a cap on the VDC input as always

Now THAT is some bizarre terminology! The circuit has a switch, and it
has some caps somewhere, so it\'s a switched-capacitor converter!

Incidentally, I don\'t put bypass caps across my power supplies in
Spice. Do you?

It is a switch shorting two voltage sources, something usually
tolerable only at very low power levels, where efficiencies below 50%
can be ignored.

Efficiency can be almost 100% once everything gets to steady-state.
It\'s low during startup.


Switch cap converters with non-ideal transfer ratios are not very efficient

Switched cap converters (which this isn\'t one of) can approach 100%
efficiency if not asked to do goofy voltage ratios.



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard

 

[server]

On Sun, 26 Jul 2020 11:54:10 -0400, legg <legg@nospam.magma.ca> wrote:

On Sun, 26 Jul 2020 07:45:29 -0700, jlarkin@highlandsniptechnology.com
wrote:

snip
The dual diode thing on the grounded side makes it feed back on the
primary peak-to-peak voltage, which tracks the secondary, which also
rectifies peak-to-peak.

The transformer, tied to the positive rail, already supplies half
of the pk-pk being sensed, without the need (or interference of)
the CD parts in question.

Not necessarily half. The positive flyback voltage depends on the
load. Sensing p-p for feedback forces the p-p to be constant.

By half, I meant the input voltage ( \'forward\' ) share of the
sensed voltage.



The LTC3803 is a peak current limiter, so the startup current is
pretty much always the same, regardless of topology.


The fet current waveform, is a combination of the series Llk/Cout
(reflected) and the primary mag current. The former portion of
that peaks early and is resonant. Though the chip may have a
spike suppressor on it\'s sense pin (a delay), it can\'t regulate
on a waveform with current that varies early in this manner.

It regulates on the voltage feedback it sees.

Chaotically, and not necessarily safely, if at all possible, when
a silly nodal waveform appears within the regulation loop.

Silly nodal waveform? Where?

I\'ve Spiced this topology and it can be made perfectly stable. It
gives decent regulation on the load side without the usual
optocouplers. I\'ll actually build it if my customer will give me a
little more info about his needs.

Interestingly, at current limit in the flyback topology, it is pretty
much constant power vs voltage. That can be useful.

It\'s one of the basic features (and hazards) of a flyback - the output
current being uncontrolled when shorted. In your case, this current
will be capacitively limited by the output structure - but may involve
output (or at least output cap) polarity reversal.


It\'s not a forward converter without an energy storage element -
it\'s just a switched capacitor DC-DC.

That\'s just terminology. I call the non-flyback side a forward
converter, because fet turn-on drives the load with no specific energy
storage.

When you use \'terminology\', you should stick to definitions of the
terms, which DO exist. We know what you mean, but you should stick
to simple switch-on and switch-off terms to describe the operating
periods.

Yes sir. Please don\'t punish me much.



I think of \"switched capacitor\" as something else, an actual switched
capacitor.

Your \'forward\' operation is basic switched capacitor with (ideally)
a \'DC transformer\' separating the elements.

Which cap is being switched?


Input (cap) and C1.

My Spice circuit has no input cap and it works fine. I have never
considered power rail bypass caps as \"switched\". Output filters
neither.

But use the words that you like. I just build circuits.

It is a switch shorting two voltage sources, something usually
tolerable only at very low power levels, where efficiencies below 50%
can be ignored.

Efficiency can be almost 100% once everything gets to steady-state.
It\'s low during startup.

There\'s a TI chip that regulates a switched cap. You should check out
it\'s efficiency plots. TPS60121.

Switched cap light load efficiency usually depends on reduced
frequency ie no load / no loss.

I stuck an old switched cap clamp sim, late, into the download.
This shows the commonly used pfet transposition to common drive gnd,
with common gate drive voltage offset.

RL

Of course if you have two caps at very different voltages, and slap
them in parallel, energy is lost. So don\'t do that.



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard