Electronics > Beginners

Weird switching topologies you don't see anymore

<< < (5/6) > >>

Circlotron:
One topology I independently invented myself about 15 years ago (I'm not imagining that someone else hasn't also done elsewhere) Is a boost reg +12V nominal to +16V where there is a pair of boost inductors running antiphase driven by a SG3525 (yeah, I know  ::) ) and the tops of  the inductors, instead of being fed directly from +12V were instead attached to either end of a centre tapped single winding transformer. The idea was that if the left side inductor was charging, the right side inductor would be discharging, but at the same time the right side inductor would be being fed with somewhat more than +12V because of the transformer action of the tranny feeding it. At the same time, the left side inductor would be charging from somewhat less than +12V. The whole purpose was to reduce the slope of the inductor charge and discharge currents and consequently the input and output ripple currents. Never did follow through with it. I should do that.

T3sl4co1l:
No shame in the SG3525, matter of fact it's kind of surprising come to think of it, that there aren't more applications/notes out there proposing such dual-phase controllers for phase-interleave purposes instead.  That said, major downside: <50% max duty cycle (per output) limitation.  (Well, that and the lack of tracking (e.g., for average current mode, independent current error amps) per channel, basically limiting this operation to voltage mode as well.  Which wouldn't be outside the scope of their original intent, but is decidedly passe for good reason.)

Your proposal works in CCM, but falls over badly in DCM I think?  Because, one inductor can't charge into the other when it's not carrying any current.  I should probably draw it out to get a better feel for behavior.  It may be the kind of thing that works well in a narrow range of conditions; maybe not exactly the conditions you were considering, but some low-numbered ratio between Vin and Vout, I think, and preferably where CCM is maintained.

The DCM-CCM transition should almost act like a "swinging choke" in a choke-input filter does, I think?  Because in DCM, the transformer (magnetizing inductance) dominates, but in CCM the transformer acts to unify the two chokes as acting in series.

Tim

Circlotron:
Okay, this is a sim of it running in continuous mode 12 Volts in, 18 volts out, 220mH inductors, 20kHz, but with no feedback so the current is ratcheting up... but you get the idea. Red is the switch voltage, green is the left side inductor current 330mA min, 540mA max, and blue is the left diode current going right down to zero with the red switch voltage then follows the inductor current. Interesting part is where the left side inductor and diode current turns back and starts to rise again while the left side switch is still off because the right side switch is now on.

In discontinuous mode it might be a bit of a flop but I think it then acts more like a forward converter because for example if the left side switch turns on the top of the right side inductor is pulled up to double the supply voltage. Less so in continuous mode.

MagicSmoker:

--- Quote from: Circlotron on July 25, 2019, 01:34:05 pm ---Okay, this is a sim of it running in continuous mode...

--- End quote ---

Looks like a "dual inductor boost" converter except with the DC feed via a coupled choke; if you are interested in comparing the two just delete the coupled choke and tie the two boost inductors directly together.

Circlotron:
Put together a real version of the above cct and it's a bit lame... You cannot wind the input voltage down as far as you can using two normally connected boost inductors. Maybe an interesting mod might be to wind a step-up secondary onto the transformer and feed it via a full wave rectifier straight to the output with no filter inductors of course because it would be a current source with a current related to the boost inductor current.

Navigation

[0] Message Index

[#] Next page

[*] Previous page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod