This topology with the extra mosfet inverting the phase would work like a charm on lower frequencies but as frequency must be high to avoid monster size inductors, mosfet gate miniscule capacitance becomes a factor because gate must change voltage state as fast as possible to keep efficiency high, and exact timing is really important for among other reasons to avoid shoot through currents. Dedicated buck drivers can do all that very fast at speeds over 1Mhz nowdays on low RdsON ie high gate capacitance mosfets. If on the other hand you have infinite board space and funds for inductors then OK.
The reason specialized controllers are used with synchronous rectification is that they prevent forced continuous current mode (CCM) operation. While forced CCM has some advantages, it has a very big disadvantage in applications where high efficiency must be maintained at low load current. Without proper control the sync rectifier will begin to discharge the output capacitor through the inductor at the point where the inductor has just fully discharged. A typical buck converter will be designed to make the transition from discontinuous current mode to CCM at something in the range of 30 to 40% of full rated output current. Forced CCM in such a design swings a lot of current around for no benefit and usually detrimentally. You can push the DCM/CCM transition current down by increasing the inductance, but that comes with penalties, too - efficiency, volume and cost. You also have to be careful to be sure that the rectifier FET and high-side FET are never on at the same time or you can get very high magnitude shoot-through current that degrades efficiency and generates a lot of noise. This is almost impossible to assure with a simple inverter circuit. In fact a simple inverter will pretty much assure that it _will_ happen.
Very nicely explained. Good for anyone at a more advanced level to understand why this isn't done in real world power supplies. This was good though as a chance to show a beginner how you can invert signals without using logic gates.
@@mendiarapi I don't understand what you mean. Can you elaborate at bit. The actual "main" part of a power MOSFET can conduct in either direction. However, all real-world power MOSFETs have a diode in parallel with the main FET structure. With an N-channel FET the cathode of the diode connects to the drain and the anode to the source. This diode isn't made deliberately, it is there because of the way the main part of the FET is made (it is sometimes called "parasitic"). In some circumstances you can make good use of this diode by connecting the FET "backwards." If you never turn the FET ON, it just acts like an ordinary diode - not a very good diode but not terrible. If you turn the FET ON at the time when the diode would normally be conducting you can reduce the voltage drop that you'd normally get with the diode - current flows through the main channel of the FET. This can be really useful in circuits where you would normally use just a diode but the voltage drop of an ordinary or even a Shottky diode is too high. One such application is for "synchronous rectification" in a switching power supply. Another is "ORing" of multiple power supplies.
Am o întrebare legata de inversarea semnalului. Pare ca rezistenta aia cam consuma curent pentru ca da la masa prin mosfet. Dacă e asa asta înseamnă că reduce eficienta circuitului din cauza ca acea rezistenta se poate încălzi?
Slowly raise current Diana plz :) you every time send it full speed on that potentiometer I am scared something will explode just waiting to see bOOM ! :D LOL Nice!
I understand your point of using electronics but when designing a circuit it is cheaper to use a chip with two PWM than using more components and these components are taking more space on PCB so you have extra expenses on components and PCB with more space
They call it "not logic gate" that actually reverse the signal from logic 1 to logic 0. An indeed you cannot find it easy on google such a solution with a mosfet. In general they use another chip to reverse the signal and again this is not ideal.
Thank you SORIN & DIANA for this educational and entertaining video series! Great! 🥰👍
your hair i very nice on this day , Diana, thank you Sorin for sharing your wisdom , 🙂
This is best so far. it is sort of Digital Electronics fundamentals which are lectured on Electronics Engineering faculties... Great Content!
Glad to see where you get MOSFETs from. Useful when I want to copy your practical work. Thanks.
This topology with the extra mosfet inverting the phase would work like a charm on lower frequencies but as frequency must be high to avoid monster size inductors, mosfet gate miniscule capacitance becomes a factor because gate must change voltage state as fast as possible to keep efficiency high, and exact timing is really important for among other reasons to avoid shoot through currents. Dedicated buck drivers can do all that very fast at speeds over 1Mhz nowdays on low RdsON ie high gate capacitance mosfets.
If on the other hand you have infinite board space and funds for inductors then OK.
The reason specialized controllers are used with synchronous rectification is that they prevent forced continuous current mode (CCM) operation. While forced CCM has some advantages, it has a very big disadvantage in applications where high efficiency must be maintained at low load current. Without proper control the sync rectifier will begin to discharge the output capacitor through the inductor at the point where the inductor has just fully discharged.
A typical buck converter will be designed to make the transition from discontinuous current mode to CCM at something in the range of 30 to 40% of full rated output current. Forced CCM in such a design swings a lot of current around for no benefit and usually detrimentally. You can push the DCM/CCM transition current down by increasing the inductance, but that comes with penalties, too - efficiency, volume and cost.
You also have to be careful to be sure that the rectifier FET and high-side FET are never on at the same time or you can get very high magnitude shoot-through current that degrades efficiency and generates a lot of noise. This is almost impossible to assure with a simple inverter circuit. In fact a simple inverter will pretty much assure that it _will_ happen.
Very nicely explained. Good for anyone at a more advanced level to understand why this isn't done in real world power supplies.
This was good though as a chance to show a beginner how you can invert signals without using logic gates.
i am confused about the mosfet beeing a bidirectional device
@@mendiarapi
I don't understand what you mean. Can you elaborate at bit.
The actual "main" part of a power MOSFET can conduct in either direction. However, all real-world power MOSFETs have a diode in parallel with the main FET structure. With an N-channel FET the cathode of the diode connects to the drain and the anode to the source. This diode isn't made deliberately, it is there because of the way the main part of the FET is made (it is sometimes called "parasitic"). In some circumstances you can make good use of this diode by connecting the FET "backwards." If you never turn the FET ON, it just acts like an ordinary diode - not a very good diode but not terrible. If you turn the FET ON at the time when the diode would normally be conducting you can reduce the voltage drop that you'd normally get with the diode - current flows through the main channel of the FET. This can be really useful in circuits where you would normally use just a diode but the voltage drop of an ordinary or even a Shottky diode is too high. One such application is for "synchronous rectification" in a switching power supply. Another is "ORing" of multiple power supplies.
Ciao Sorin,
In this moment 23:15 (high voltage) Diana (i don't know what you mean a divorce...) 😂😂😂
God bless you ❤
Am o întrebare legata de inversarea semnalului. Pare ca rezistenta aia cam consuma curent pentru ca da la masa prin mosfet. Dacă e asa asta înseamnă că reduce eficienta circuitului din cauza ca acea rezistenta se poate încălzi?
Am reusit sa testez circuitul si e OK pentru ca se consuma foarte putin curent prin acea rezistenta.
bine
more videossss :,)
Slowly raise current Diana plz :) you every time send it full speed on that potentiometer I am scared something will explode just waiting to see bOOM ! :D LOL Nice!
I understand your point of using electronics but when designing a circuit it is cheaper to use a chip with two PWM than using more components and these components are taking more space on PCB so you have extra expenses on components and PCB with more space
of course, but here we are speaking strictly about DIY
yeah but Sorin want to learn Diana fully to understand everything. from 0
They call it "not logic gate" that actually reverse the signal from logic 1 to logic 0. An indeed you cannot find it easy on google such a solution with a mosfet. In general they use another chip to reverse the signal and again this is not ideal.
so simple so simple no one is using it lol 🤣