Features

• Up to 50% Lower Switch Cost

• Up to 4x Less Switching Loss

• Up to 8x Lower Temperature Rise

• Up to 75% Smaller Inductor

• Up to 1% Increase in Efficiency

• Up to 9x Lower EMI Noise

1kW Bridgeless Totem-Pole PFC Comparison

The advantages of ICERGi technologies are clear when compared to conventional PFC approaches based on conventional topologies. However, incremental steps in the efficiency are no longer enough and the global trend requires a leap. In order to do this, the industry is adapting the Bridgeless Totem-Pole PFC topology. Unfortunately, Bridgeless Totem-Pole is a hard-switched topology and Superjunction MOSFETs are not suited for this task. This is where GaN comes in, with the promise of very low ON resistance (further boost in efficiency) and much faster switching frequency (allow using smaller inductor).

ICERGi PFC designs use MOSFETs in a 5x6mm SMD package. This is an industry standard package and many transistors from various manufacturers are available for multisourcing. GaN Systems Inc. produce GaN FETs in a 5x6mm SMD package and therefore have been selected for a like-to-like comparison with ICERGi.

A lot of messages about GaN mention increase in efficiency and increase in switching frequency (reduced inductor size) which may lead people to believe that both hold true for any scenario. However, the loss breakdown reveals that in a hard-switched topology these advantages do not come together. ICERGi design overcomes this and offers highest efficiency together with reduced inductor size.

Fourier theory states that the amplitudes of the harmonics are reversely proportional to square of the harmonic order. This means that the third harmonic will be 9 times smaller than the first (fundamental) harmonic.**

** B. Lu, W. Dong, S. Wang and F. C. Lee, "High frequency investigation of single-switch CCM power factor correction converter," Nineteenth Annual IEEE Applied Power Electronics Conference and Exposition, 2004. APEC '04., Anaheim, CA, USA, 2004, pp. 1481-1487 Vol.3.

260kHz implementation will face significant EMI challenges because the first harmonic has to be suppressed. This will result in a complex and costly EMI filter. This observation applies to any conventional design with switching frequency above 150kHz.

ICERGi Si implementation has two significant EMI advantages:

• It is much easier to filter out 390kHz noise as compared to 195kHz or even 260kHz.

• Third harmonic has 9 times lower amplitude than the fundamental harmonic.

Aside from reduced cost of current sensing, ICERGi has implemented a cycle-by-cycle control on a low cost, low memory variant of an ARM® Cortex™-M0 microcontroller. An M0 is limited to 48MHz operation and in order to implement similar control strategy on a GaN converter running 4x faster switching frequency one would have to upgrade to a much faster microcontroller. Some industry examples use a much more expensive Cortex™-M4. An M4 comes with a many advanced peripherals and lots of memory, all of which are not necessary and were never intended for SMPS applications. So if one needs a faster core, one must bear the extra cost of all the unnecessary functionality too.

ICERGi Si implementation enables significantly cooler operation of power switches resulting in various benefits such as:

• Longer life span

• Higher reliability

• Capability to handle higher power - lower cost per Watt

• Easier thermal management

• Improved convection-cooled performance

It is worth noting that this could be a much worse scenario for GaN implementations because other manufacturers use much, much smaller packaging which results in very low surface area and multiple times higher thermal impedance, making it very difficult to keep the switching devices cool.