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 dictatesState 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
FudFly converter
Started by ●July 25, 2020
Reply by ●July 25, 20202020-07-25
Reply by ●July 25, 20202020-07-25
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
Reply by ●July 25, 20202020-07-25
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. When the switch is on, forward current passes through D1 with only leakage inductance and C1 shaping the current. RL
Reply by ●July 25, 20202020-07-25
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?
Reply by ●July 25, 20202020-07-25
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 statesBut 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 ratioThe 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
Reply by ●July 25, 20202020-07-25
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
Reply by ●July 25, 20202020-07-25
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
Reply by ●July 25, 20202020-07-25
<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/
Reply by ●July 25, 20202020-07-25
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
Reply by ●July 25, 20202020-07-25
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
