| Electronics > Projects, Designs, and Technical Stuff |
| Design of SMPS - Not sure what these spikes are being caused by. |
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| ocset:
top of page 4 of this http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.913.7541&rep=rep1&type=pdf shows how you can measure your tapped inductor coupling coefficient, k. This is important as it affects the duty cycle needed to get from vin to vout......too much leakage and your D max may not be big enough for you to get vout from vin (woops, just realised i accidentlaly wrote "overlap" instead of "overload" in the above simulations annotation, i also accidentally called the "tapped boost" a "tapped buck" simulation...sorry about that) |
| Zog:
I am confused again. After running your new update in LTSpice I see significant changes and was wondering what caused the changes. The original sim had a nice slow startup from zero volts and was stable at 9ms. Original V4 The corrected version shows this. I did turn off the Skip initial operating point solution to show it a little more clearly but is only nearly stable at 30ms. Revised V4 I made up a little voltage divider with these values and replaced V4 in the original with it and it worked well. What benefit is this ? I took it out and it made no obvious difference to the output ? |
| ocset:
So you are comparing the tapped boost with one of the dual boosts.....i confess i havent bothered changing the feedback compensation components for the tapped boost...and the dynamics of the tapped boost are likely to be more complex than the dual_boost.....so i reckon the tapped boost could be speeded up by changing the feedback compensation components...... The LTC6101 based circuit is purely for startup and overload.........it stops the "staircasing" of the inductor cuirrent at startup which is prevalent in many smps's when they are starting up and the vout is well below what it shoudl be.,............its the vout which "discharges" the inductor so if its not high enough you get too high currents in the power stage...therefore i put in the ltc6101 sensor and the extra error amplifier to limit the current........but it will just lie dormant when the converter has got started. It sounds like you have hacked it to be in current limit mode all the time by reducing the 2.8volts to 0.5..........thats isnt what the current limiter is meant for. So also you coudl try clicking the ".ic v(out) = 220v" and make that a comment instead of a spice directive...that may speed it up.......but otherwise i think the complex dynamics of the tapped boost mean the feedback compensation components need changing to make it startup quicker and oscillate less during startup. The little filter inductor L3, is purely to keep the current ripple out of the sense resistor of the ltc6101 current monitor...and of course, this only operates at startup (or overload)...so yes, ususally this doesnt do much...(but woudl be good for emc in a real converter) I dare say the ltc6101 probably works well enough if L3 is omitted. (Apologies for my fat finger typing in places.) |
| Zog:
Thanks again treez, I changed the V4 to a voltage divider in the Dual Boost original. Is that ok ? |
| ocset:
...yes as long as the voltage is the same.....it only goes into an opamp input, and as you yknow, these are very high impednace, so no problems with the divider here.....it just sets the limit that the input current is set to, so that you dont get too much current at startup...after that the error amp concerned just goes dormant. By the way, if you like, there is my free switch mode power supply course which explains a lot about SMPS's.... https://drive.google.com/open?id=0B7aRNbu3Fes4TU92Mkw3YlA3ams {...always interested to here if all course folders from A to Z (sorry, "Y") got sucessfully downloaded, so please say if the download didnt work} Here is also my guide to doing an electronics degree |
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