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The writers of the above article in top post are villifying the single switch offline flyback...they wrongly accuse it of having a primary clamp which dissipates 15-20% of the output power.
Also, there are absolutely no application notes, across the world, from any semico, of an application getting a 100-200W Offline isolated Flyback applied to it.....when a 100-200W Flyback is often a great solution.
There are also loads of application notes which start off by saying, above 100W, an offline isolated converter cannot use a single switch flyback because of blah blah blah.........and its all nonsense...just further villification.
In this way, it suffers discrimination , and is villified.
I did once go to a big company who had had a 100W offline single stage, single switch flyback LED driver designed as a prototype. They had made the stupid mistake of using a primary clamp consisting of nothing more than an ultrafast diode into an SMA TVS (SMA!!).
….Some years later, I was describing this to a Leading Consultant SMPS designer over a beer at a meeting……expecting him to baulk at the SMA….but all he said was “what on earth were they using a Flyback for 100W for?”
Thanks, yes, but i believe the alleged level is closer to 200W...as this 200W offline SMPS flyback shows...As power level goes up, then you'll find that moving to a two-switch design can save cost and size. That threshold is, allegedly, around ~100W
I think you’ll find it will depend on the target market and application. Areas which demand low noise such as aerospace, medical and military may typically choose a low noise topology from the start as it will give an easier life further down the line. Theres no precise line in the sand. As the design engineer its your prerogative to chose the appropriate topology for your application based on your experience (good and bad). Unfortunately you learn from failures and that will set your boundaries.Thanks, yes, but i believe the alleged level is closer to 200W...as this 200W offline SMPS flyback shows...
I believe cost is the main driver, and the reduction in parts count that a flyback gives you means its nearer 200W for offline , unless output current is really high
...Thanks, yes, and its cheaper. My colleague runs a consultancy, and he says the Semico's are totally out of touch with reality.....they are peddling there 150W 2TFC's and 150W LLC's when real companies want "cheap as chips"....and thus Flyback.......not efficiency , and pleasing Greta Thunberg is way way down their priority list.Using just an RFI /EMI argument though - it is hard to beat the single or 2 switch flyback up to 250 watts in QR - valley switched - mode
...Thanks, do you mean sometimes triple interleaving is needed when above 100W?...to really cut down the leakage inductance?this pre-supposes and engineer who can design a transformer with low enough lakage and will meet mains safety regulations.
If you can get away with direct offline, then i agree flybacks are good however meeting harmonic distortion (sub 5% THD) requirements will be a challenge without high turns ratio of the transformer which can result in high secondary currents. If you have to go down the route of a boost preregulator the differences between a flyback and forward converter becomes much less so this is also a consideration. It is possible to shape the voltage reference of a PFC controller to give better harmonic distortion with a lower turns ratio transformer but it can be a bit of a pain to setup.Thanks, yes, but i believe the alleged level is closer to 200W...as this 200W offline SMPS flyback shows...
I believe cost is the main driver, and the reduction in parts count that a flyback gives you means its nearer 200W for offline , unless output current is really high
I agree that this only achieves good power factor but at 200W but won't harmonics be a requirement? I work in Aerospace where harmonics content comes in above 30W. A flyback will likely fail power quality tests on THD if they are a consideration. If he needs good harmonics and good power factor you have to push more of the energy transfer to the peak of the havesine by either using a higher turns ratio or shaping the line voltage reference to modulate less at low line than would normally be necessary. The shaping via modulation can only be done with IC's that uses the line voltage reference.you don't need to change the turns ratio from optimal for a flyback - just modulate the gate drive to achieve in input current closer to a sine wave - the Vout of the flyback Tx will always be the Vout on the o/p cap ... if you want higher power factor.
Ok, To clarify i think what i'm stating is you won't get a PF of 0.999 with a standard offline flyback without doing one of the following:all your assumptions are non sequitur, also 0.999 PF = very low THD ...
Thank you, you confirmed my thoughts.1. modulation has already been mentioned.
2. the flyback volts will be approx constant, they add to Vin at turn off.
Thanks thats very interesting, and consider without even the divider from the half-sine DC bus to "guide" it...would that give good enough harmonics performance to get through EN61000-3-2 etc?if you operate a flyback in DCM, then, with a slow feedback volt loop ( i.e. almost fixed pwm ), you will get very good power factor - without any other fancy control.if you operate a flyback in DCM, then, with a slow feedback volt loop ( i.e. almost fixed pwm ), you will get very good power factor - without any other fancy control.
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