FudFly converter...

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I guess this is pretty obvious, but when the fet turns on, it\'s a
forward converter charging C1, and when it turns off it\'s a flyback
charging C2.

https://www.dropbox.com/s/4vsi3a5r3ky0wv0/FudFly_Conv.jpg?raw=1



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard
 
On a sunny day (Fri, 24 Jul 2020 21:23:42 -0700) it happened
jlarkin@highlandsniptechnology.com wrote in
<2mcnhftioe6o3qsp0lh71gdnm2if4nltps@4ax.com>:

I guess this is pretty obvious, but when the fet turns on, it\'s a
forward converter charging C1, and when it turns off it\'s a flyback
charging C2.

https://www.dropbox.com/s/4vsi3a5r3ky0wv0/FudFly_Conv.jpg?raw=1
Click to expand...

Yes, in principle.
One thing to take into account is that for a high ratio of flyback to forward
so a very short flyback pulse, is transformer winding heating
A shorter pulse for the same power means more current during the flyback into the output.
i * tflyback

However the ohmic losses in the coil go up with i^2 * Rcoil * tflyback
This heating limits what you can do with reasonable wire gauge.

To get a decent size transformer a few more turns and a bit less flyback is simpler.
Slower switching is easier on the driver too.

?
 
On a sunny day (Fri, 24 Jul 2020 21:23:42 -0700) it happened
jlarkin@highlandsniptechnology.com wrote in
<2mcnhftioe6o3qsp0lh71gdnm2if4nltps@4ax.com>:

I guess this is pretty obvious, but when the fet turns on, it\'s a
forward converter charging C1, and when it turns off it\'s a flyback
charging C2.

https://www.dropbox.com/s/4vsi3a5r3ky0wv0/FudFly_Conv.jpg?raw=1
Click to expand...

Yes, in principle.
One thing to take into account is that for a high ratio of flyback to forward
so a very short flyback pulse, is transformer winding heating
A shorter pulse for the same power means more current during the flyback into the output.
i * tflyback

However the ohmic losses in the coil go up with i^2 * Rcoil * tflyback
This heating limits what you can do with reasonable wire gauge.

To get a decent size transformer a few more turns and a bit less flyback is simpler.
Slower switching is easier on the driver too.

?
 
On a sunny day (Fri, 24 Jul 2020 21:23:42 -0700) it happened
jlarkin@highlandsniptechnology.com wrote in
<2mcnhftioe6o3qsp0lh71gdnm2if4nltps@4ax.com>:

I guess this is pretty obvious, but when the fet turns on, it\'s a
forward converter charging C1, and when it turns off it\'s a flyback
charging C2.

https://www.dropbox.com/s/4vsi3a5r3ky0wv0/FudFly_Conv.jpg?raw=1
Click to expand...

Yes, in principle.
One thing to take into account is that for a high ratio of flyback to forward
so a very short flyback pulse, is transformer winding heating
A shorter pulse for the same power means more current during the flyback into the output.
i * tflyback

However the ohmic losses in the coil go up with i^2 * Rcoil * tflyback
This heating limits what you can do with reasonable wire gauge.

To get a decent size transformer a few more turns and a bit less flyback is simpler.
Slower switching is easier on the driver too.

?
 
jlarkin@highlandsniptechnology.com wrote:
I guess this is pretty obvious, but when the fet turns on, it\'s a
forward converter charging C1, and when it turns off it\'s a flyback
charging C2.

https://www.dropbox.com/s/4vsi3a5r3ky0wv0/FudFly_Conv.jpg?raw=1
Click to expand...

LOL, I have just invented something similar and wanted to share. My idea
is to use the L output pin of a synchronous buck converter to supply a
floating MOSFET gate driver elsewhere in the system using the same
charge pump principle. Provided the PWM duty cycle is reasonable, it
works like a charm -- just prototyped that to source 1mA.

It needs one more part than a flybuck (two diodes and one capacitor
instead of an additional winding and a diode), but a cheap off-the-shelf
inductor can be used, which is a big advantage.

Best regards, Piotr
 
jlarkin@highlandsniptechnology.com wrote:
I guess this is pretty obvious, but when the fet turns on, it\'s a
forward converter charging C1, and when it turns off it\'s a flyback
charging C2.

https://www.dropbox.com/s/4vsi3a5r3ky0wv0/FudFly_Conv.jpg?raw=1
Click to expand...

LOL, I have just invented something similar and wanted to share. My idea
is to use the L output pin of a synchronous buck converter to supply a
floating MOSFET gate driver elsewhere in the system using the same
charge pump principle. Provided the PWM duty cycle is reasonable, it
works like a charm -- just prototyped that to source 1mA.

It needs one more part than a flybuck (two diodes and one capacitor
instead of an additional winding and a diode), but a cheap off-the-shelf
inductor can be used, which is a big advantage.

Best regards, Piotr
 
Piotr Wyderski wrote:

> using the same charge pump principle.

I was referring to the doubler network connected to the drain, not to
your secondary.

Best regards, Piotr
 
Piotr Wyderski wrote:

> using the same charge pump principle.

I was referring to the doubler network connected to the drain, not to
your secondary.

Best regards, Piotr
 
On Fri, 24 Jul 2020 21:23:42 -0700, jlarkin@highlandsniptechnology.com
wrote:

I guess this is pretty obvious, but when the fet turns on, it\'s a
forward converter charging C1, and when it turns off it\'s a flyback
charging C2.

https://www.dropbox.com/s/4vsi3a5r3ky0wv0/FudFly_Conv.jpg?raw=1
Click to expand...

You get very peaky current in the forward converter if there\'s no
output inductor, and it\'s unregulated.

There IS a converter that regulates both, with a conventional filter
on the forward section. The forward stage is PWM, while the flyback
section is PFM. There\'s some interaction between the two, if current
mode is employed. This was documented in the mid-80s by Steigerwald
at GE and I think there\'s a control chip for it.

Another uses a fixed frequency, but modulates the active clamping
network for the forward converter, from the mid 90s.

https://www.researchgate.net/publication/274370275_Designing_a_Cost_Effective_Single_Switch_Isolated_Multiple_Output_Flyback_Converter

A third uses two transformers, which is sort of silly if the
switch and controller costs less than the magnetics - which is
the current reality.

At low power, of course, you can get away with murder.

Your circuit appears to not regulate only the negative voltage
generated by the flyback period - your waveform suggests
complete energy transfer; so a designed rather than fudged
magnetic part. If so, then why not just add another flyback
winding?

RL
 
On Fri, 24 Jul 2020 21:23:42 -0700, jlarkin@highlandsniptechnology.com
wrote:

I guess this is pretty obvious, but when the fet turns on, it\'s a
forward converter charging C1, and when it turns off it\'s a flyback
charging C2.

https://www.dropbox.com/s/4vsi3a5r3ky0wv0/FudFly_Conv.jpg?raw=1
Click to expand...

You get very peaky current in the forward converter if there\'s no
output inductor, and it\'s unregulated.

There IS a converter that regulates both, with a conventional filter
on the forward section. The forward stage is PWM, while the flyback
section is PFM. There\'s some interaction between the two, if current
mode is employed. This was documented in the mid-80s by Steigerwald
at GE and I think there\'s a control chip for it.

Another uses a fixed frequency, but modulates the active clamping
network for the forward converter, from the mid 90s.

https://www.researchgate.net/publication/274370275_Designing_a_Cost_Effective_Single_Switch_Isolated_Multiple_Output_Flyback_Converter

A third uses two transformers, which is sort of silly if the
switch and controller costs less than the magnetics - which is
the current reality.

At low power, of course, you can get away with murder.

Your circuit appears to not regulate only the negative voltage
generated by the flyback period - your waveform suggests
complete energy transfer; so a designed rather than fudged
magnetic part. If so, then why not just add another flyback
winding?

RL
 
On Fri, 24 Jul 2020 21:23:42 -0700, jlarkin@highlandsniptechnology.com
wrote:

I guess this is pretty obvious, but when the fet turns on, it\'s a
forward converter charging C1, and when it turns off it\'s a flyback
charging C2.

https://www.dropbox.com/s/4vsi3a5r3ky0wv0/FudFly_Conv.jpg?raw=1
Click to expand...

I guess I missed the point - this is a single output, so one
regulation is as good as another.

Current mode control, or even simple limiting may be an issue.

RL
 
On Fri, 24 Jul 2020 21:23:42 -0700, jlarkin@highlandsniptechnology.com
wrote:

I guess this is pretty obvious, but when the fet turns on, it\'s a
forward converter charging C1, and when it turns off it\'s a flyback
charging C2.

https://www.dropbox.com/s/4vsi3a5r3ky0wv0/FudFly_Conv.jpg?raw=1
Click to expand...

I guess I missed the point - this is a single output, so one
regulation is as good as another.

Current mode control, or even simple limiting may be an issue.

RL
 
jlarkin@highlandsniptechnology.com wrote:
I guess this is pretty obvious, but when the fet turns on, it\'s a
forward converter charging C1, and when it turns off it\'s a flyback
charging C2.

https://www.dropbox.com/s/4vsi3a5r3ky0wv0/FudFly_Conv.jpg?raw=1
Click to expand...

LOL, I have just invented something similar and wanted to share. My idea
is to use the L output pin of a synchronous buck converter to supply a
floating MOSFET gate driver elsewhere in the system using the same
charge pump principle. Provided the PWM duty cycle is reasonable, it
works like a charm -- just prototyped that to source 1mA.

It needs one more part than a flybuck (two diodes and one capacitor
instead of an additional winding and a diode), but a cheap off-the-shelf
inductor can be used, which is a big advantage.

Best regards, Piotr
 
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?
 
*Charge pump.

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

Tim

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

<jlarkin@highlandsniptechnology.com> wrote in message
news:2mcnhftioe6o3qsp0lh71gdnm2if4nltps@4ax.com...
I guess this is pretty obvious, but when the fet turns on, it\'s a
forward converter charging C1, and when it turns off it\'s a flyback
charging C2.

https://www.dropbox.com/s/4vsi3a5r3ky0wv0/FudFly_Conv.jpg?raw=1



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard
Click to expand...
 
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
Click to expand...

Don\'t follow that. Got a sketch?



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard
 
I think Tim hints at that you need an inductor to have a buck part and diodes for the freewheeling part. Otherwise it won\'t act as the state space model dictates
 
On Sat, 25 Jul 2020 11:34:41 -0700 (PDT), klaus.kragelund@gmail.com
wrote:

>I think Tim hints at that you need an inductor to have a buck part and diodes for the freewheeling part. Otherwise it won\'t act as the state space model dictates

State space model dictates?

The turn-on phase isn\'t a buck, it\'s a forward converter. Turnoff is
conventional flyback. It might like a snubber on the primary, mostly
for cosmetics.

I admit the dynamics is interesting, especially at startup. If I
decide to use it, I\'ll certainly Spice it first.

Anybody with another idea could post a sketch.



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

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

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

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

Cheers

Klaus
 
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?
Click to expand...

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

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

RL
 
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