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| Design of SMPS - Not sure what these spikes are being caused by. |
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| T3sl4co1l:
C8 charges when Q2 turns on, which will probably defeat the peak current mode operation of the controller. They also don't document it very well, but TPS40210 goes into hiccup mode (/SS pulls low, stays off until crosses rising threshold) rather than current limiting. It's rather dumb. The combination will probably frustrate operation of this circuit enough that it never starts up, or doesn't maintain the full output you were expecting, or isn't able to recover from a momentary overload condition. You can use multiple secondaries as their own flyback outputs, and connect the DC outputs in series. Then you don't need C8 charging on the "down stroke", energy gets delivered to the output only in the flyback period (Q2 off). Probably use N = 2-3 of say MSS12xx dual-winding inductors, with the primaries in parallel, and the secondaries wired accordingly. (Choose inductance to be N times higher per inductor, because for uncoupled inductors, the value reduces in parallel.) Tim |
| Zog:
Thanks Tim, That explains why it never started up. Will look at implementing your new suggestions. The circuit is wired correctly though right ? --- Quote ---You can use multiple secondaries as their own flyback outputs, and connect the DC outputs in series. Then you don't need C8 charging on the "down stroke", energy gets delivered to the output only in the flyback period (Q2 off). Probably use N = 2-3 of say MSS12xx dual-winding inductors, with the primaries in parallel, and the secondaries wired accordingly. (Choose inductance to be N times higher per inductor, because for uncoupled inductors, the value reduces in parallel.) --- End quote --- Could you perhaps provide a hand drawn circuit explaining to us non engineers just what you mean by that ? --- Quote ---C8 charges when Q2 turns on, which will probably defeat the peak current mode operation of the controller. --- End quote --- It did not do that on the original circuit ? Little confused now ? :-// (original is the original post) |
| T3sl4co1l:
Other than that, yeah I think so. There was an appnote I think from TI's "flybuck" documentation that showed the connection, I can't seem to find it offhand. Try giving that a look. Yes, the original circuit would have the same problem. Tim |
| Zog:
I thought these files might help other beginners like me at how to layout SMPS. treez layout instructions are very good. https://www.eevblog.com/forum/projects/design-of-smps-not-sure-what-these-spikes-are-being-caused-by/msg2622906/#msg2622906 The TPS40210 Datasheet http://www.ti.com/lit/ds/slus772f/slus772f.pdf is good but kind of difficult to follow given that the example circuit does not match the layout. The example layout is just the bottom and the top, so I got creative in photoshop and merged them together and added component references so it's a little easier to follow. Pretty sure it's a hexfet package used for Q1. Top and Bottom layers merged. Top Layer Bottom Layer I do have a question though. What are the R1,R2 and the jumper for ? |
| T3sl4co1l:
Looks to be routed to EN. Don't know why it's not on the schematic. Tim |
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