dc/dc converterrippleripple-currentvoltage
This is a followup of my previous question.
Boost IC = NCV3063
Vin = 8V
Vout = 23V
Iout(max) = 250mA – (Load is a constant current circuit which is enabled at 200Hz)
Schematic
Mentioned the points where I have probed
Waveforms (Same waveform, only varying the timescale) :
Why is there a dip in output current and increase in output ripple voltage at the marked areas?
And which waveform describes the right Peak to Peak ripple voltage measurement?
This :
Or
Or
TLRD: your calculations are fine. I got myself confused by checking them against a different calculator that targeted DCM not CCM. I'm not gonna change the stuff below because Arsenal replied to it, and it might also be useful to you to compare the two modes.
Your inductor looks an order of magnitude too big vs what I get at https://learn.adafruit.com/diy-boost-calc/the-calculator
And it does look like your inductor is far too big:
@Arsenal N.B.: I figured out the difference between these two calculators. The adafruit one gives you a DCM (discountinous current mode) solution, whereas TI's gives a CCM solution.
Which one is preferable depends on various factors. Basically at high output currents you want CCM to lower the losses and stresses on the components, but DCM has better transient response. A lot more about that can be read here, including a side-by-side power efficiency calculation example.
There is no one answer about how much ripple is too much, because that depends on the devices being powered.
Yes, LDOs don't attenuate high frequency ripple much, but much of it can be filtered out before the LDO with a chip inductor in series followed by the LDO input cap to ground.
All that said, 20 mV ripple on a 3.3 V supply should not cause trouble for an ordinary microcontroller or digital logic.
Best Answer
Ripple voltage for a switching regulator circuit is usually (normally if you prefer) made under static load conditions and this means that you might only be interested in the part of the waveform shown in red below: -
In other words, the load effects are unchanging in the red area.
However, in purple is the change in output voltage when you change the load conditions. You apply this transient load change every 5 milli seconds but, it doesn't settle down to constant waveform and so this cannot (in my book) be regarded as a full picture of ripple voltage; you can see that the waveform is exponentially rising over the 1 milli second that you apply the load change but you don't apply the load change for long-enough of a period of time to let it settle.
This means you cannot accurately deduce the ripple voltage because the load change effect hasn't settled. If you allowed the load change to settle (maybe for 5 milliseconds) then switched back to the default loading scenario for 5 milliseconds you will likely be in a better position to deduce ripple voltage because, the waveforms will have stabilized.
Paramount is the effect of poor regulation (causing a long-term shift in the average value of the waveform following a transient load change) AND actual ripple superimposed on that average waveform change. You have to distinguish between the two and, at the moment, your waveform pictures (and testing method) don't allow that differentiation.
If, at the end of the day you tell me that you cannot change the load envelope (1 ms every 5 ms) then YOU have to make your mind up what is important to you. I can only advise what I feel is the right condition to determine ripple voltage and differentiate this from regulation quality effects.