On 25/07/2020 23:07, jlarkin@highlandsniptechnology.com wrote:
> On Sat, 25 Jul 2020 16:57:27 -0500, "Tim Williams"
>> 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.
>
>
On Sun, 26 Jul 2020 22:38:58 +0200, Piotr Wyderski
<peter.pan@neverland.mil> wrote:
>jlarkin@highlandsniptechnology.com wrote:
>
>> I call that an autotransformer flyback. I usually use the DRQ127-type
>> dual inductors and as much voltage multiplier as needed.
>
>Here is a good introduction to these:
>
>https://www.youtube.com/watch?v=mr3sCPnsOas
>
> Best regards, Piotr
My very first switcher was a center-tapped-inductor buck. It converted
+24 to +5 for a military control system, on the LHA ships. I tapped
the inductor because we couldn't get a 24 volt schottky diode. I might
even have the board still.
The ripple current into the output cap went way up, so it fried caps.
N*I is constant and the tap changes N every cycle.
--
John Larkin Highland Technology, Inc
Science teaches us to doubt.
Claude Bernard
Reply by Piotr Wyderski●July 26, 20202020-07-26
jlarkin@highlandsniptechnology.com wrote:
> I call that an autotransformer flyback. I usually use the DRQ127-type
> dual inductors and as much voltage multiplier as needed.
> Yes, at low power you don't care about crap efficiency
True, but even then the efficiency is not that bad. 70% or so, very
close to a regular flyback.
> and the current can be limited by relatively high Rds(on) or hFE-limited transistors.
Adding insult to injury, the SN6501 uses R_DS_ON(temperature) to balance
the flux. But at that power level any dishonourable trick is acceptable.
For example, a series of 100mW flybacks I use in quantity for gate
driving purposes are based on a 6mm OD ungapped toroid. There are enough
volt-seconds available that allow me not to care. It is super-tiny and
reliable, f^Hignore the rules.
Best regards, Piotr
>"Piotr Wyderski" <peter.pan@neverland.mil> wrote in message
>news:rfj9v9$1hauu$1@portraits.wsisiz.edu.pl...
>> 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. :-)
>
>Yes, at low power you don't care about crap efficiency and the current can
>be limited by relatively high Rds(on) or hFE-limited transistors.
>Here's another example of that:
>https://www.seventransistorlabs.com/Images/Deadbug_Sch.png
>
I call that an autotransformer flyback. I usually use the DRQ127-type
dual inductors and as much voltage multiplier as needed.
It's not inherently inefficient.
--
John Larkin Highland Technology, Inc
Science teaches us to doubt.
Claude Bernard
Reply by Tim Williams●July 26, 20202020-07-26
"Piotr Wyderski" <peter.pan@neverland.mil> wrote in message
news:rfj9v9$1hauu$1@portraits.wsisiz.edu.pl...
> 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. :-)
Yes, at low power you don't care about crap efficiency and the current can
be limited by relatively high Rds(on) or hFE-limited transistors.
Here's another example of that:
https://www.seventransistorlabs.com/Images/Deadbug_Sch.png
I know the PP drivers as MAX253, same thing more or less.
I recall a bunch of ADuM isolator parts having PP drivers in them, though I
think they're actually current mode and suggest^H^Hrequire output filter
inductors?
> Just to note: there *is* a topology called flyback-forward.
Hmm, I get very few search results. One patent that's some sort of
quasi-resonant C-clamped-flyback hybrid.
It seems obscure enough that I wouldn't feel bad creating yet another
definition for it...
Tim
--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Design
Website: https://www.seventransistorlabs.com/
Reply by legg●July 26, 20202020-07-26
On Sun, 26 Jul 2020 09:57:25 -0700, jlarkin@highlandsniptechnology.com
wrote:
>On Sun, 26 Jul 2020 10:45:09 -0400, legg <legg@nospam.magma.ca> wrote:
>
>>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 . . .
>
>How do you define "low power levels"? Nanowatts? Kilowatts?
>
>>
>>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.
>
>What are the parasitic components in my circuit?
Zin, Llk are the main ones, but it's hard to tell without
an actual model or measured waveforms from which they can
be enumerated or derived.
Doodling on a pad isn't building circuits, so there's a
limit to how they can be evaluated.
I doubt very much, for a start, that the chip can be induced
to produce the illustrated pulse-widths, except under very
specific external conditions - something that nature is very
lax in ensuring.
I'm not going to flog topology or applications on newsnet -
I learned some years ago that there was little profit or
satisfaction in doing so.
Have fun.
RL
Reply by ●July 26, 20202020-07-26
On Sun, 26 Jul 2020 10:11:38 -0700 (PDT), klaus.kragelund@gmail.com
wrote:
>On Sunday, 26 July 2020 19:43:53 UTC+3, jla...@highlandsniptechnology.com wrote:
>> 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 do not know where you are going with this. You used the wrong terminology
Sez you. I drew a schematic that was unambiguous. And a bunch of
people here want to argue about words.
My circuits don't give a damn what you call them.
Can't people draw any more?
--
John Larkin Highland Technology, Inc
Science teaches us to doubt.
Claude Bernard
Reply by ●July 26, 20202020-07-26
On Sunday, 26 July 2020 06:07:54 UTC+3, jla...@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 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
Reply by ●July 26, 20202020-07-26
On Sunday, 26 July 2020 19:43:53 UTC+3, jla...@highlandsniptechnology.com wrote:
> 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 do not know where you are going with this. You used the wrong terminology
> >
> >> >
> >> >>
> >> >>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?
>
No, but I am quite confident that you do in real 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.
> >>
> >
> >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.
>
That's just a rewrite of my statement above :-)
Cheers
Klaus