Quote:
Originally Posted by NiHaoMike
Most of the losses are on the low voltage side. Using Litz wire, oversizing the windings, and using synchronous rectification all help efficiency. Low switching frequencies also reduce switching losses but increase size of parts.
Getting high efficiency at low voltages is a big challenge. Nonetheless, 95% efficiency is certainly possible at low voltages. The PTV08T250W is 95% efficient when outputting 3.3v at 50A from a 12v supply. Getting that kind of efficiency when outputting 14.4v from a 20v+ source should be a piece of cake by comparison.

Okay a team of engineers came up with a module using a 3 phase buck converter can hit 95% at 3.3V when used with huge caps that have an ESR of 0.005 Ohms. Good luck finding caps rated at 16V with an ESR that low.
Coming up with a suitable and efficient inductor for this application is going to take more than just throwing thick wire at it or using Litz wire. With larger windings you have magnetic leakage between the coils. Also the outer windings have a larger distance to travel potentially increasing resistive losses. Litz wire is only good for high frequencies. An inductors job is to resist change in the flow of current. In a proper buck converter the change in current in the inductor is minuscule compared to the current of the load. The inductor's current is essentially DC and Litz wire won't help. You would have to go with wire made of silver.
Dropping the frequency of switching speed also increases the output ripple voltage. An increase in ripple voltage increases the loss in the capacitors caused by the capacitors' ESR.
In short, designing an efficient switch DC to DC converter takes careful matching of the efficiency curves of all the components and operating parameters. Don't expect to just slap one together. My hat is off to the TI engineers that hit 95% efficiency as it is a true work of engineering.