Isolated DC-DC Converters with eGaN® FETs

  

Darnell’s Power Forum
September 19 – 21, 2012

"GaN as a Displacement Technology for Silicon in Power Management"
Speaker: Johan Strydom, PhD; VP Applications Engineering, Efficient Power Conversion Corporation
Location: San Jose, CA
 

Abstract:
The intermediate bus architecture (IBA) is currently the most popular power system architecture in computing and telecommunications equipment. It typically consists of a +48 V system power distribution bus that feeds on-board isolated converters, which in turn supply power to a 12 V power bus.

In this presentation we demonstrate substantial performance gains achieved in isolated DC-DC converters using enhancement mode gallium nitride power transistors that have been commercially available for over three years. These transistors, also known as eGaN® FETs are making significant inroads replacing the aging silicon power MOSFET

Two topologies are explored; a full bridge topology [1] and a soft-switched resonant topology [2] (See figures 1 and 2).

 


Figure 2: High frequency resonant converter

The eGaN FET-based phase shifted full bridge topology (PSFB) is able to operate at much higher frequencies
and produce higher power densities than corresponding isolated converters using power MOSFETs as shown in figure 3.


Figure 3: Efficiency comparison between 48 VIN – 12 VOUT eighth brick converters showing an eGaN FET based EPC9102 reference design vs. a commercial MOSFET based solution.

 

This presentation will also demonstrate the ability of the eGaN FET to improve efficiency and output power density in a high frequency soft switching application, as compared to what is achievable with existing power MOSFET devices. An isolated 48 V intermediate bus converter (IBC) with a 12 V output utilizing a resonant topology operating above 1 MHz is presented. Figure 4 shows an efficiency comparison with dotted lines for three different power losses. If we assume a 14 W loss is acceptable in an eighth-brick format, the eGaN FET-based converter is able to deliver over 375 W compared with 310 W for the silicon-based resonant circuit.



Figure 4: Efficiency comparison between 48 VIN – 12 VOUT soft-switched resonant converters operating at 1.2 MHz. The eGaN FET solution can deliver more than 20% greater output power in the same (or smaller) footprint.

A significant savings can be realized by adopting the new generation of isolated DC-DC converters that use gallium nitride-based transistors. The two examples presented here each enable a 20 percent efficiency improvement in addition to tighter regulation, faster transient response, and higher power density.

References:

[1] A. Lidow, J. Strydom, M. deRooij, and Y. Ma, “Gallium Nitride Transistors for Efficient Power Conversion”, Power Conversion Publications 2012, Chapter 6.

[2] D. Reusch and J. Strydom, The eGaN® FET-Silicon Power Shoot-Out Vol. 10: High Frequency Resonant Converters, Power Electronics Technology, September 2012