Power Electronics WK4 2a - Efficiency and Loss of a DC-DC Converter - Conduction Losses
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- เผยแพร่เมื่อ 19 ต.ค. 2024
- The conduction losses of a DC-DC buck converter are described. Below are some links for your reference. The 2nd link provides some vendor information on selecting the proper capacitor for your application.
"Ceramic or electrolytic output capacitors
in DC/DC converters-Why not both?" Michael Score
Senior Member Technical Staff, Field Applications Engineering
www.ti.com/lit/...
"MOSFET power losses and how they
affect power-supply efficiency" by By George Lakkas
Product Marketing Manager, Power Management TI
www.ti.com/lit/...
Hi Professor, I hope you are well. Great videos! Just got a question as to why in 6:24 you use Pc= R_ESRC(◇I_o/2_/3)² but when you show the total power loss exluding the switching losses at 11:00 you use R_ESRC(◇I_o²/12). Wasn't this for the losses that we typically ignore in the inductor?
Thank you
Great question. Let's start with the AC term of the current ripple. This current ripple is triangular shaped and therefore the RMS (effective) value is peak amplitude divided by the root(3). Recall for sinusoidal it is peak amplitude divided by root(2). The peak amplitude of the AC term is delta_Io/2 because delta_Io is the total peak-to-peak value. In order to get the power loss in the inductor, you use the square of the DC value of the current and the square of the RMS (AC value of the current). The square of the RMS value will be (delta_Io/2)^2 divided by 3. This results in delta_Io^2/(4*3). Often times, we can ignore the AC power loss in the inductor as it is much smaller than the DC loss. Hope this explanation helps. Best wishes on your designs. -Dr. K
Very good and funny videos bring a great sense of entertainment!
Dear Professor, Thanks for explaining in a simple manner. Could you kindly clarify, how to select ESR value of the inductor? Should it be taken from the datasheet or any calculations involved? Thanks in advance Prof.
Hi Arulmozhi, great question. For a first pass at your design, I would use Rdc for the inductor as the ESR. The value of Rdc should be provided in the data sheet for the inductor. Inductors that are designed for higher ampacities will have larger gauge coil wire and lower Rdc. Note that Rdc is only part of the ESR. There is also a frequency dependent component that is due to hysteresis losses, eddy currents, the skin-effect phenomena, etc. Luckily, this are typically minimal. Again, for the first iteration of your design, use Rdc and then start to incorporate the frequency dependent losses if needed. Hope that helps. Best wishes on your design. -Dr. K
@@powerelectronicswithdr.k1017 Thank You Professor for your detailed reply. It gives me clarity to proceed further with my design.
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Hi, thanks for the video. Where can i find a derivation for the equation at 5:08?
And shouldnt there be a ripple loss term in the conduction loss from the diode and the transistor? Because if i have a higher rms but the same average current those losses should be greater, right?
Hi Mr.Bubblegumx, this is the equation for the mean-squared value of an off-set sawtooth wave. The first term is the average value of the current squared and the second term is due to the saw-tooth nature of the ripple current. The term (delta-Io/2) is the zero-to-peak value of the ripple current and the 1/3 term is used used for the zero-peak value when computing the RMS of a sawtooth wave. Therefore 1/3*(deta-Io/2)^2 results in delta-Io^2/12. Yes, you should multiply deta-Io^2*Rds*D to get the AC power loss in the MOSFET. However, it should be relatively small compared to the DC loss. Your AC loss shouldn't be greater than your DC loss for CCM. For example if we use a 40% allowed ripple, the second term would be (0.4Io)^2/12. Hope this helps and best wishes on your designs. -Dr. K
@@powerelectronicswithdr.k1017 thank you for your comprehensive answer, that really cleared things up
how did you do it can you share with me , thank you
Gustavo, more specific please? How did I produce the videos? How did I study DC-DC converters? Your question is unclear. -Dr K.
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