Electronics > Projects, Designs, and Technical Stuff
Design of SMPS - Not sure what these spikes are being caused by.
Zog:
Still working on this stuff fella's
Tim has got me out of the bog hole I was in.
Will update you on progress as I incorporate his ideas into the new design.
Zog:
This is part of the circuit suggestions I paid Tim (T3sl4co1l) a few bucks for his time for.
I thought I would throw it out there before committing to it.
I see what he means now.
I have a few concerns though.
None of the inductors suggested have very high current Irms(A). The Irms(A) of the torroid I am using is 10A and even that gets hot.
So the question is will the design above still need a high current coupled inductor.
The way I see it is it is still charging the 4.7uf cap and the 10uH inductor so it needs to supply the current, right ?
Will the only thing this circuit do is reduce the ringing with coupled inductor and the snubbers
If that is the case can't I just use the existing circuit and just add the snubbers ?
Edit:...belay that. I have been working on something else for a few days and have not been concentrating on the one project.
The other question I have is if I use a coupled 4.7uH 1:1 inductor why use the extra 10uH one ?
Edit: Because the suggested 1:10 inductor is only 27uH and I will need the extra 10uH ?
If I use a 1:1 I could leave it out ?
Edit: see above. One more question is what advantages or disadvantages are gained or lost by using a ratio of 1:3 or 1:X etc ?
Little bit confusing to me.
Little less confusing to me.
Anyway Tim is obviously an expert and I very much appreciate his work, but rather than pester him with messages privately, I thought it would be better for all, to continue this search for the high power design I am looking for publicly.
Edit: I read this again.
So I "think" I get it.
--- Quote ---Part of the problem is huge input currents and awkward duty cycles, because the circuit attempts to make a large voltage ratio between input and output. The tapped inductor fixes this, making it a very normal (ideally 1:1.5 to 1:3 ratio) converter, as far as everything else is concerned.
--- End quote ---
More Editing:
This is the datasheet for the 6235 1:10 Ratio
Not quite the same circuit example as Tim's above though.
Sorry about the crazy editing ! :P
T3sl4co1l:
--- Quote from: Zog on May 19, 2018, 07:22:18 am ---None of the inductors suggested have very high current Irms(A). The Irms(A) of the torroid I am using is 10A and even that gets hot.
So the question is will the design above still need a high current coupled inductor.
--- End quote ---
*Glances back at the OP*, oh yeah, a couple amps will be needed, won't it. Well, most of these are families, should be able to find something bigger SRF or LPD or whatever. Or that inverter transformer is looking quite good, despite its size and cost. :)
Probably most of the heat in your toroid was core loss, so that it's practically irrelevant if the winding is rated 10A or 100A. With a waveform that peaky, you get a lot of excess heating -- another good reason to use a tapped winding or transformer. ;)
--- Quote ---The other question I have is if I use a coupled 4.7uH 1:1 inductor why use the extra 10uH one ?
Edit: Because the suggested 1:10 inductor is only 27uH and I will need the extra 10uH ?
If I use a 1:1 I could leave it out ?
--- End quote ---
What extra 10?
Inductance depends on operating frequency and desired current ripple. 4.7uH might be enough, or you may need to raise the frequency, or deal with the higher ripple (increased losses, especially in the inductor and main filter caps).
I was looking for values near the original primary inductance, but I didn't check if that was consistent with the controller's operating point. The datasheets for those controllers are very detailed, do take a look and double-check the original author's work. :)
--- Quote ---This is the datasheet for the 6265 1:10 Ratio
Not quite the same circuit example as Tim's above though.
--- End quote ---
--- End quote ---
That's an interesting one. Must be... self-excited oscillator, for single-cell battery or solar or thermopile or energy harvesting purposes? So, the capacitors are there to help shift charge around, without having to put too many different windings on the poor little transformer. Something like that. It's not a good method to use at scale; you can get away with it at low voltages because, with so little voltage to begin with, you're going to get crap efficiency anyway (anything over 50% is good), and since you're only doing this for a couple watts at most, the parts are small and you can afford to overkill them a bit, so they'll tolerate hacks like turn-on switching into a capacitor load.
Notice the current path from MOSFET drain, through the transformer, coupling cap, sync rect, and output filter, back to ground. When the transistor turns on, it delivers a huge gulp of current to charge that capacitor, which means big switching losses.
Tim
Zog:
Thanks for the reply Tim.
I am off to bed ... will analyse your answers after a good snooze.
Marked the 10uH inductor on the hand drawn circuit.
P.S. What inverter transformer ?
T3sl4co1l:
Oh yeah, just for extra filtering (same thing that appears on the other sheet). You'll still want it regardless of switching inductor value, because current is going into and out of the circuit in pulses.
Tim
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