Electronics > Projects, Designs, and Technical Stuff
Design of SMPS - Not sure what these spikes are being caused by.
Zog:
Ok .. I now have 125 mA's out as per your instructions Tim,
Well done on picking that up for me.
The gate still shows ringing of course but the FET run's very cool now which is a big plus.
Zero missing pulses.
The guys design runs at slightly below the recommended chip frequency.
I might try to up that a bit. His reasoning was the gate charge even though pretty low would lower the efficiency.
What's your opinion ? I would rather up it and use smaller inductors.
I am now experimenting with different winding ratios and will report back.
Once I have got that down I will start implementing the rest of your suggestions.
After that I will continue with the suggestions on layout posted before.
The dirty ground net naming trick is a good one I have never seen anywhere else.
You were also right about that other signal. It is all over the board anywhere you poke the probe. Layout of course.
Cheers mate.
T3sl4co1l:
Gate charge is a tiny part of overall switching loss, far more significant is the stray inductance causing RF to blast out of everywhere!
As the leakage inductance is part of that switching loss (unless clamped and recycled -- an advanced topic), you can't reduce losses terrifically far in this type of design. A good transformer is required. Still, it should be able to run at 200kHz easily, given improved layout and an okay transformer.
Adding gate resistor(s) is necessary with the layout as-is, as this reduces the switching speed. You must slow it to below the rate of that ringing, so as not to excite it. Then your waveforms will look alright.
Tim
Zog:
Thanks Tim,
Yes a gate resistor was mentioned by someone else too.
Is that in addition to the snubber on the gate or can that be the "gate" resistor. I am assuming it can be/is.
BTW A Zero poster called Carlotta sent me a PM pushing their "prototyping" service.
https://www.smart-prototyping.com/. You can also contact me at carlota@smart-prototyping.com
Anyone else heard of this crowd ?.
I am pretty happy with my current manufacturer, so doubt I will change.
T3sl4co1l:
--- Quote from: Zog on May 21, 2018, 08:31:33 pm ---Thanks Tim,
Yes a gate resistor was mentioned by someone else too.
Is that in addition to the snubber on the gate or can that be the "gate" resistor. I am assuming it can be/is.
--- End quote ---
Some kind of gate resistance, yes. If it's two resistors and a diode, or just a resistor, whatever, that's just different ways of getting there, more options.
--- Quote ---BTW A Zero poster called Carlotta sent me a PM pushing their "prototyping" service.
<snip free advertising> You can also contact me at carlota@SPAM
Anyone else heard of this crowd ?.
I am pretty happy with my current manufacturer, so doubt I will change.
--- End quote ---
Same. Mods, if you would please -- discipline said account for PM spam?
Tim
Zog:
Roger roger,
Thanks Tim.
I will "go dark" on this topic for a few weeks now.
Need to get a new board layout done for testing.
Source parts etc.
Will be back once this is done.
Cheers,
Phill
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