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
FudFly converter
Started by ●July 25, 2020
Reply by ●July 26, 20202020-07-26
Reply by ●July 26, 20202020-07-26
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
Reply by ●July 26, 20202020-07-26
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). > >RLGot a circuit? -- John Larkin Highland Technology, Inc Science teaches us to doubt. Claude Bernard
Reply by ●July 26, 20202020-07-26
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.pngJust to note: there *is* a topology called flyback-forward. Best regards, Piotr
Reply by ●July 26, 20202020-07-26
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
Reply by ●July 26, 20202020-07-26
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, PiotrIt 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
Reply by ●July 26, 20202020-07-26
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
Reply by ●July 26, 20202020-07-26
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
Reply by ●July 26, 20202020-07-26
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
Reply by ●July 26, 20202020-07-26
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
