Looking at Continuous and Discontinuous Conduction Mode

#214 In this video I analyze and look at the main differences between the main conductions modes found in switch mode power supplies - continuous and discontinuous conduction mode. I look at what the exact difference is between the 2 modes as well as look at how the performance of the circuit is finally impacted.
More on Power supplies:
PSU Static Output: • Power supply parameter...
PSU Dynamic Output: • Power Supply parameter...
PSU Output Noise: • Power Supply parameter...
PSU Loop response: • Power Supply parameter...
CCM/DCM: • Looking at Continuous ...
Further reading:
www.ti.com/download/trng/docs...
www.monolithicpower.com/en/th...
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[@biswajit681]

I would like to request you to make video on following topics 1. Magnetics design for SMPS 2.Designing Control loop 3. Modelling of the converter

[@al-moutazbillah3693]

I would ask you a favour... Please clarify to us how did you get this amount of knowledge in such a young age 💪, I think you have one of the best knowledge structure among other KZbin engineers, please clarify the way you have followed, or the steps you have walked through to reach here 😊

[@InTimeTraveller]

University education and working in the field most probably.

[@m1geo]

Agreed. But also working in a structured way in the field. Working with people who know their stuff, too, and every day is a learning day.

[@mihaelabortos4696]

Actually he has a 4 year special video where he speaks about how he got interested into electronics and how he got better at it. kzbin.info/www/bejne/joi3l3h7f9l8a5o&ab_channel=FesZElectronics

[@Banchev]

Very straightforward and easy to understand!

[@MatthewStainton]

Just spot on, great listening and learning from you

[@andrewmcfarland57]

You are a power conversion guru. 🙂 Your use of the simulator in your explanations is very helpful.

[@VoidElectronics]

Top quality explanation as always! 😁

[@alaricsnellpym]

I thought discontinuous conduction was caused by insufficient load current - so the output capacitor remains charged to the target voltage, the PWM feedback loop cranks the duty cycle down, and the inductor is "charged" with less energy so empties out before the next cycle. So you sort of need to design for a minimum load current if you want to avoid discontinuous current. Is that a correct understanding? Thanks!

[@FesZElectronics]

Indeed, you will run the risk of DCM under low load conditions - its not avoidable.. But if you design to move the DCM lower and lower (like use a very large inductor), the supply will react slower to fast transients. In the end you need to find the usual real life load, and design for that - and accept that extreme cases are rare... stability should still be ensured under extreme conditions, but things like low emissions can sometimes be skipped :D

[@m1geo]

Nice one, Fesz! I've been on a project at work designing some complex SMPS regulators. The output voltage was desired to vary with high slew rates, and forcing continuous mode allowed for much faster negative slew, since continuous mode can sink current from the load back to the source (albeit not efficiently).

[@FesZElectronics]

I also noticed this in some converters where there is the option to enable or disable FPWM ; with the option disabled, the converter reaction is quite slow, especially when going from very small loads; but with FPWM enabled, the reaction time is much smaller.

[@m1geo]

@@FesZElectronics the problem in our case was we had nearly 1000uF of output capacitance and needed to drop the voltage from say 1.2V to 1.1V very quickly. And then jump back up again.

[@ghlscitel6714]

Enlightening! Thanks!

[@bob_mosavo]

Thanks, FesZ 👍

[@joejane9977]

thanks again explains a lots

[@SergiuCosminViorel]

what do you mean?

[@joejane9977]

i found the video helpful in my understanding of selecting diodes and inductors depending on mode of operation of power supply@@SergiuCosminViorel

[@mohameddrissi1075]

So synchronous converters making the inductor current going backward is primarly to prevent the oscillation in DCM ?

[@ivanlam1304]

Could you use an electronic switch to discharge the residual capacitance and prevent the LC oscillation and consequent EMI?

[@andrew-qf4xl]

Where do u suggest we learn power electronics

[@ranaharsh365]

Why the DCM is used then? Why not to use CCM in every converter? Is the choice application dependent?

[@ahmedzafar-xp3kb]

ccm usually require very big inductor sizes.

[@thewhitedragon4184]

If you are using non-synchronous converters at low current, they'll tend to be run at DCM. So it's more of a "it just goes into it naturally" then of a "I want it in DCM". Another reason you might want DCM is that it algebraically degenerates the coil, reducing the system order by 1. Running a converter in DCM is a headache but a lower order system (which should be a first order system in this case) is easier to stabilize. Finally, DCM is just more efficient at low currents but its efficiency drops off at higher currents. The opposite goes for CCM. The down side of course is the fact that DCM is highly dependent on the load current, it's ripple is higher, and it radiates EMI so you win some of you lose some.

[@InTimeTraveller]

@@thewhitedragon4184 can you explain a bit more on how it reduces the order of the system? How does DCM affect the transfer function of the system?

[@thewhitedragon4184]

@@InTimeTraveller In DCM operation coil current goes to 0 and starts from 0 each cycle. This means that in DCM the coil has fixed starting conditions, and thus doesn't add a pole to the system. Basically, a coil in DCM is a coil with a current source of value 0 in series. Analogous to a capacitor with a voltage source in parallel, such a circuit does not add poles to the overall transfer function

[@thewhitedragon4184]

It should be noted that the pole isn't really gone but it is pushed closer to the switching frequency which means that we can usually neglect it in averaged models of converters

[@cyrus-music]

And boundary mode?

[@SergiuCosminViorel]

more accurate, to say it is damped oscillation, not oscillation

[@BartKus]

69th thumbs up. aww yiis.