GaN Systems Unveils a 3kW LLC Resonant Converter Reference Design
The full-bridge reference design meets and beats the 80 Plus Titanium standard for switch mode power supplies (SMPS)
Dubbed the GS-EVB-LLC-3KW-GS the new design highlights GaN Systems’ 650 V E-mode transistors. Power densities of better than 100 watts per cubic inch are achieved, as are efficiencies of 96% and more.
Built from GaN Systems’ 3kW LLC Reference Design. Image courtesy of GaN Systems
In today’s data centers, the demand is for power supplies that not only take up less space, but also deliver more power. As GaN Systems describes it, today’s game isn’t so much “Dollars per Watt” as it is “Dollar per Density”. The less space taken up by smaller, more power dense converters, the more room there is for everything else in the rack space that’s freed up.
What is an LLC Converter?
In the diagram below, DC voltage is first turned into a square wave by a switching network. It is fed into a capacitor, and two inductors, hence the moniker “LLC”. Cr, Lr and Lm serve to filter out harmonics and provide a clean, AC-like signal to the transformer. The transformer provides isolation between primary and secondary side, as well as voltage scaling.
The primary side of an LLC converter. Modified image courtesy of EEPower
In an LLC converter, the semiconductors on the primary side, and those on the secondary side (not illustrated) are soft switched, which means that they switch at the zero-voltage crossing (ZVS). This greatly reduces resultant EMI, a critical benefit.
The reference design is specified for an input voltage range of 380 to 420 VDC, with an output of 55 volts at 55 amps. The topology is of a full bridge LLC resonant converter with synchronous rectification. The resonant frequency is 250 kHz, maximum is 450 kHz.
Measurements are 80 x 140 x 30 mm, taking into account the completed unit’s requirement for forced air cooling. The device meets the low profile 1U data center form factor, and features a power density of 146 watts per cubic inches.
The Titanium Standard
The “80 PLUS” Titanium standard means that a power supply achieves:
- 90% efficiency at: 10% of the rated output load
- 94% efficiency at: 20% of the rated output load
- 96% efficiency at: 50% of the rated output load
- 94% efficiency at: 100% of the rated output load
Titanium efficiency standards are outlined in detail by CLEAResult.
The Reference Design
As described in the GS-EVB-LLC-3KW-GS reference design technical manual, there are three main system blocks. The first two are the full bridge LLC power stage and the digital-based MCU control block. The third block holds the auxiliary power supply, which feeds the controller, the driver IC, and forced air cooling fan.
The full resonant behavior of this GaN based LLC resonant converter allows for soft switching turn on over the entire range, from full load to no load. This serves to minimize losses in both power transistors and magnetic components.
A functional look at the GS-EVB-LLC-3KW-GS. Image courtesy of the reference design technical manual
Additionally, standard protections, including those for input undervoltage, output short circuit and overcurrent on both the primary and output are provided.
The new reference design is targeted at SMPS design challenges encountered in:
- Data centers
- Industrial areas