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Yes, good observation. Often that diode is replaced with a MOSFET. This is called a synchronous converter. It has lower loss (improved efficiency) but requires a more complex controller. There is still switching loss in the MOSFETs, but if the frequency is low enough, the overall loss will be better. There are converters such as resonant converters that utilize zero-voltage, zero-current (ZVZC) conditions and have even better efficiency. Best wishes on your designs. -Dr. K

@@powerelectronicswithdr.k1017 thanks for your kind response! Sync buck do need a complex controller, that's why I mention the dead-time. During the dead-time, the body diode of MOS will conduct firstly. That will cause an extra power loss: Vdiode✖️Io✖️（dead-time/T）, but body diode dosen't have a ton and toff time, it exists automatically, so I think the rectifier MOS will cause a body diode power loss, but has almost no switch loss.

Lower loss when the diode conducts. The other selection would be a fast recovery diode. Many converters are also synchronous and use a MOSFET instead of a diode. Great question and best wishes on your design.

Hi! The links for the equations can be found in the video description. Best wishes. -Dr. K

Great question which applies to high-side driving of typically a P-channel MOSFET. The answer is yes. However, the switching frequency range is relatively broad and will partially determine the value of boot-strap capacitor used. As an example, it is impossible to never switch because the boot-strap capacitor requires charge and this capacitor charges up when one side is switched to ground either through the driver or through the low-side switch. Once charged, the boost-capacitor can then be used to drive the MOSFET and acts like a floating voltage supply. However, the capacitor will eventually discharge over time and the result is Vgs will slowly decrease to an in operable point. If the switching frequency is to high, the boot-strap capacitor never fully charges up or takes too long to charge. Often the high-side gate drive datasheet will provide information on selecting the boot-strap capacitor based on your switching frequency. Best wishes on your design. -Dr. K

@@powerelectronicswithdr.k1017 thanks for perfect explanation. one more question about gate drive. Gate drive require high current for a moment ,(say 500 mA), due to Cgs. If we use bootstrap, does bootstrap capacitor can deliver such a high current?

Yes, that is correct. I do not show the gate-driver circuitry or control for this. That would be another video. N-channel MOSFETs require special circuitry for high-side driving. There are h-bridge topologies in which the two high-side switches are P-channel MOSFETs. This makes for easier switching. Best wishes on your design. - Dr. K

Hi Ziadfawzi. Great question and the answer is that it depends. For example, will you try to maintain a constant output power at all voltage ranges? If so, then the output current will be maximum at the smaller output voltage values and minimum at the larger output voltage values. It would be a good practice too look at both extremes and see which values will "stress" your components the most. Sorry it is not as easy as just the highest output voltage. Best wishes on your design. -Dr. K

Hi Jviccii, the resistance is not part of the design of the Buck Converter. It is an easy way (although not always accurate) to implement a load on the power supply. You can set the value to Vo/Io. However, please take caution as not all loads are purely resistive. Great question and best wishes on your design. -Dr. K

Hi Gan-rc2im, yes you are correct. I am using these terms liberally. On the datasheet, the rise time is actually the amount of time it takes to turn the MOSFET "off". This is the time duration where Vds rises from near 0 V to the supply value Vdc. The fall time is the duration it takes to turn the MOSFET "on". The is the duration where Vds drops from Vdc to near 0V. Please note that the datasheets use very specific testing parameters and your application of rise and fall times will vary. Great observation and thank you for watching. -Dr. K

Hi, I developed those graphics using MS Visio, MS Power point and some of the simulations were done in LTspice.

Lol... You do know you can skip past the introduction. Have a great day MrSummitville and best wishes on your designs. - Dr. K

@@powerelectronicswithdr.k1017 LOL - You do know, that adding crap noise to your video does not make it better? Have a nice day...

Yes, that would be correct. The units would be 100 Vpp (volts peak-to-peak) or 50 Vp (volts peak).

You’re welcome.

Often one assumes the load is resistive and because the output voltage is relatively constant ( with the exception of the voltage ripple), the average output current is constant. The output capacitor is therefore used to store and provide charge to help maintain that constant voltage assumption. Thank you for the question and best wishes on your design. -Dr. K

Thank you.

Pablo, YES! Great catch. The voltage should be in the range of -0.5V to -0.65V. Luckily we have a low forward voltage drop and it will not impact the results drastically. Also, you are correct, the average value of Vds during that period will be (Io/D)* Rds and that is 2/3*Rds. Best wishes on our design. -Dr. K

@@powerelectronicswithdr.k1017 thank you very much

That's actually the peak value of the current on the secondary side. This comes from the computation of the average value of a fully rectified sine wave. The average value of |Apk*sin(wt)| is 2*Apk/pi, where Apk is the peak value. In this case it Is. Solving for Is using the average, one gets Io*pi/2. If only 1/2 wave rectification is used, then the equation would change to Io*pi. Hope this helps. Best wishes on your design. -Dr. K

@@powerelectronicswithdr.k1017Thank you Dr. K! That makes more sense. I think you mispoke in the video by mistake and I took it literally😅😂. Thank you for your lecture too! Have a great day!

Please do not confuse my audience. You only switch with a 50% duty cycle for a resonant converter. You are correct in that gate drivers are required. This video is not about MOSFET gate drivers. This an explanation of how resonant converter functions and has soft switching. Best wishes on your designs.

You are right. I do need to re-edit that video. It is one of the more popular ones and the audio terrible. My summer project. Thank you for the feedback. -Dr. K

The IR2101 has both a high-side and low-side gate driver. Are you doing a synchronous buck converter? Also the IRF3205 N-channel MOSFET needs about 10V for the gate-to-source pin. What is the voltage you are using on the Vcc pin for the IR2101. This needs to be anywhere from 10-15V. I would probably use a regulator specifically designed for buck converting that has a built in gate-driver. Infineon does make switching regulators for buck converters. Best wishes on your design. - Dr. K

Hi Professor, Thank You for the response. I have tried Power Mosfet driver IR2101 for high side Buck Converter with Vcc between 12 to 15V. But Mosfet is not going to off state. Hence the required output voltage is not observed across the load. @@powerelectronicswithdr.k1017

Ts is the total switching period. For example, if the switching frequency is 10kHz, then Ts = 0.10ms. The switches are only activated for a portion of that period (i.e. the duty cycle D) and we can control the voltage by adjusting the duty cycle. Hope this helps and best wishes on your design. -Dr. K

You are welcome. Best wishes on your design.

The switching loss can be estimated if you know the max turn-on and turn-off power values. It would then then be 0.5*(p_max_on*t_on + p_max_off*t_off)*fswx, where fswx is the frequency of your sawtooth carrier wave. The tricky part will be estimating the turn on and off times and the max power values.