Transphorm and Microchip Highlight the Virtues of GaN for Bridgeless Totem-Pole PFCApril 07, 2020 by Gary Elinoff
The new evaluation board opens a discussion on the pros and cons of continuous conduction mode PFC circuits and bridgeless totem-pole PFC circuits. What's your take?
Transphorm and Microchip are teaming up to push the widespread adoption of GaN ever further. Combining Transphorm's GaN power semiconductors and Microchip's digital signal processing technology, the two companies hope to empower designers with limited skills in embedded design.
The collaboration has combined Transphorm’s 4 kW AC-DC bridgeless totem-pole power factor correction (PFC) evaluation board, the TDTTP4000W066C-KIT, with Microchip's digital signal controller board, the dsPIC33CK. The Microchip controller is a plug-in module (PIM) that controls the PFC powertrain.
The Transphorm bridgeless totem-pole PFC evaluation board and Microchip digital signal controller board. Image used courtesy of Transphorm
Transphorm and Microchip explain that the result is an evaluation board with 99% efficiency and pre-programmed, off-the-shelf firmware.
A "Game-Changing" Bridgeless Totem-Pole PFC
Philip Zuk, Transphorm's VP of worldwide technical marketing and North American sales, calls the collaboration a "gamechanger" because of its GaN bridgeless totem-pole PFC.
Typical efficiency of Transphorm's TDTTP4000W066C-KIT with Microchip’s dsPIC digital power PIM. Image used courtesy of Transphorm
“The control requirements of GaN power systems using the bridgeless totem-pole power factor correction is different than what is used to control traditional CCM boost PFCs which has long been a new challenge for some OEMs. Today, two industry leaders have partnered to reduce that knowledge gap. We’re giving customers access to a disruptive GaN solution backed by a world-class global support team.”
PFC Inductor and input line current waveforms in continuous conduction mode. Image used courtesy of Infineon
To explore that "knowledge gap" Zuk refers to, it may be helpful to briefly review the advantages and disadvantages of traditional CCM PFC circuits and bridgeless totem-pole PFC circuits.
Continuous Conduction Mode PFC Circuits
The great selling point of continuous conduction mode (CCM) power factor correction (PFC) circuits is that ∆iL, the change in current across inductor L, is small. According to Lazar Rozenblat from PowerFactor, the result is decreased conduction losses and a smaller EMI filter. Rozenblat explains that the drawback of CCM PFC circuits is the "hard reverse recovery of the free-wheeling diode."
CCM PFC circuit. Image used courtesy of Lazar Rozenblat, Powerfactor
In a PFC boost converter design guide from Infineon, the company explains that a boost topology is the most popular option for PFC applications since a line voltage can range from a zero to approximately 375 V, and a designer must use a step-up converter to boost the output DC bus voltage to 380 V or more.
Infineon also explains that because a boost converter has a filter inductor on the input side, it "provides a smooth continuous input current waveform as opposed to the discontinuous input current of the buck or buck-boost topology." This, the company explains, simplifies filtering, which decreases the cost and reduces the power factors associated with the capacitive loading of the line.
Bridgeless Totem-Pole PFC Circuit
A great advantage of the bridgeless totem-pole PFC circuit is in the name itself—it has no bridge circuit. This eliminates the losses normally encountered as the current transverses the bridge diodes.
In a review of GaN totem-pole bridgeless PFC, authors Qingyun Huang and Alex Q. Huang conclude that a soft-switching GaN totem-pole PFC is superior to traditional CCM PFCs because of its high efficiency, high power density, and low switching and driver losses. It also eliminates reverser recovery.
Bridgeless totem-pole PFC circuit. Image used courtesy of Infineon
This arrangement is possible because of the intrinsic lack of body diodes in gallium nitride (GaN) devices.
We might better see the advantages of bridgeless totem-pole PFC circuits by assessing the key specifications of the Transphorm-Microchip evaluation kit.
The Transphorm Kit and Microchip's PIM Control Card
Here are some highlights of the new evaluation kit that elucidates the virtues of GaN bridgeless totem-pole PFC circuits:
- P65H035G4WS 650 volt, 35 mΩ GaN FETs
- Input voltage range of 85 VAC to 265 VAC at 47 Hz to 63 Hz
- Programmable output voltage up to 387 VDC ± 5 VDC
- Input current of 18 Arms; 2 kW at 115 VAC, 4 kW at 230 VAC
- PWM frequency of 66 kHz
- Power factor of greater than 0.99
Transform’s TDTTP4000W066C-KIT. Image used courtesy of Transphorm
The smaller PCB in the picture’s foreground is Microchip’s dsPIC33CK PIM control card. This collaboration between Transphorm and Microchip enables OEMs to work with Transphorm’s 650 V 35 mΩ Gen IV TP65H035G4WS GaN FETs.
The PIM is AEC-Q100 qualified. It operates at 100 MIPS in order to quickly evaluate and control time-critical functions. Dual flash panels will make live code updates possible even while the power section is operating. Designers will be able to find firmware updates for the dsPIC33CK at Microchip’s website.
If you're a non-power specialist designing power circuitry, especially power circuitry in the kilowatt and higher range, you may find yourself on unexpected trips down technological “rabbit holes.” Both Transphorm and Microchip stress that users of Transphorm’s TDTTP4000W066C-KIT can expect ample support.
This will certainly take away much of the pain of designing with gallium nitride and will help designers take advantage of all this transformative power technology has to offer.
What are your thoughts on the pros and cons of continuous conduction mode PFC circuits and bridgeless totem-pole PFC circuits? Share your thoughts in the comments below.