GaN technology evaluation board converts AC to DC power up to 4kW

Article By : Maurizio Di Paolo Emilio

Transphorm's TDTTP4000W065AN evaluation board features its latest SuperGaN Gen IV GaN technology to convert single-phase AC to DC power up to 4kW.

The new TDTTP4000W065AN evaluation board from Transphorm is now available and it features its latest SuperGaN Gen IV GaN technology to convert single-phase AC to DC power up to 4 kilowatts (kW), together with bridgeless totem-pole power factor correction (PFC) with traditional analog control.

In addition to providing a higher than 99% level of efficiency, GaN technology ensures the required performance as per data sheet without developing any control firmware as in solutions with digital signal controllers (DSC).

In an interview with EE Times, Philip Zuk VP of Worldwide Technical Marketing and NA Sales, Transphorm, said this board will hit more than 99% efficiency with a highline input (230 Vac) similar to the digital solution.

The evaluation kit offers a GaN-based platform, thus providing the reliability of wide bandgap semiconductor physics and ensuring ease of design driveability and high-volume reproducibility (RDDR). Efficiency, as Transphorm highlights, offers designers a more efficient power supply system than standard CCM Boost PFC designs using super junction MOSFETs.

Bridgeless totem-pole power factor correction (PFC) topology

PFC circuits are used for AC-DC conversion and include a full-wave diode bridge rectifier and a boost circuit. The input voltage drops on the bridge and the boost stage determines the quality of the system efficiency. The bridgeless PFC totem-pole converter shows the smallest conduction loss among all bridgeless PFC topologies and needs a minimum number of components. Efficiency is obtained by removing the high voltage diode bridge rectifier and using the bi-directional current flow capability that GaN offers through hard-switching synchronous rectification and either single phase or interleaved control methods.

Transphorm examined a family of bridgeless PFC converters, including Dual Boost Bridgeless PFC, Two boost-circuit bridgeless PFC, Bi-directional Bridgeless PFC, and Totem-pole bridgeless PFC to eliminate the input diode bridge.

With the two-chip normally off GaN FET solution using a low voltage silicon MOSFET and a depletion mode GaN HEMT, the solution offers additional low switching losses, low Qrr, and low capacitance. This allows having simple and efficient power conversion circuits.

totem-pole bridgeless PFC boost converte

Figure 1: totem-pole bridgeless PFC boost converter based on GaN HEMT (a) Diode for line rectification (b) MOSFET for line rectification (Source: Transphorm)

Figure 1: totem-pole bridgeless PFC boost converter based on GaN HEMT (a) Diode for line rectification (b) MOSFET for line rectification (Source: Transphorm)

Figure 1 illustrates a bridgeless PFC totem-pole converter with GaN HEMT in two configurations. The configuration shown in Figure 1b increases efficiency by replacing the diodes shown in Figure 1a with two MOSFETs.

operation principle of totem-pole bridgeless PFC

Figure 2: Operation principle of totem-pole bridgeless PFC (a) positive half-cycle (b) negative half cycle (Source: Transphorm)

The operating principle of the PFC totem-pole is shown in figure 2. In the positive half-cycle of the AC line, D2 leads and connects the AC signal to the output ground. S2 is the active boost switch and S1 releases the inductor current and discharges the inductor energy to power the output. S1 will be complementary to the ignition in tune with the inductor to reduce conduction loss. In the negative half-cycle, D1 leads and connects the AC source to the output DC bus. S1 is the active boost switch and S2 releases the inductor current. The operating mode changes with each cycle. In the positive half, the PWM determined by the boost load ratio is conducting the S2 switch, while it is conducting the S1 switch in the negative half. The operation of the MOSFET version is the same, except that the MOSFET is actively activated for line straightening at half cycle.

GaN Board Evaluation

The 4 kW highline (180-260 V) and 2 kW lowline (90-120 V) evaluation kit does not require any DSP firmware programming, thus adapting to standard CCM boost AC-to-DC PFC power stages.

“Power electronic engineers have always used analog control standard CCM/CRM boost PFC converters. In order to use the digital totem-pole, firmware development is required. Many tier 2/3/4 power supply companies do not have this capability nor the resource(s), so we are enabling them with the analog solution. They can gain access to the high performing totem-pole PFC with the analog control solution without any firmware required. Quick time to market…the analog board helps designs get to market faster. It is also a great steppingstone to the digital solution if they want to move in that direction in the future. Lastly, this solution also gives a direct competitor to the traditional boost PFC that uses Silicon,” said Zuk.

Engineers who need more flexibility in the design process can use the TDTTP4000W066C 4 kW TDTTP4000W066C board with a pre-programmed Microchip dsPIC33CK in addition to the bridgeless totem pole PFC of Transphorm’s SuperGaN FETs.

The TDTTP4000W065AN uses the SuperGaNTM Gen IV TP65H035G4WS SuperGaNTM FETs as support for fast switching and with low resistance silicon MOSFETs and soft-switching support. SuperGaNTM FETs can be driven with a threshold voltage (Vth) of 4 volts and a standard off-the-shelf gate driver operating from 0 to 12 volts.

“This board does not offer any customization like the digital design. It gives the designer a direct replacement for the standard, Silicon boost PFC with higher efficiency. That efficiency is due to a combination of our GaN platform and the analog control. Maintenance or auxiliary power is basically constant no matter what the system power level is. Since the analog board does not use a DSP, its auxiliary power could be less depending on the boards circuitry design. This could result in a slightly improved efficiency at lower powers where the auxiliary power draw becomes a higher percentage of the overall loss of the solution. This in fact could be an advantage for the designer in determining whether our analog control solution is the preferred design choice. But, as stated above—there are other variables to consider, as well,” said Philip Zuk.

The TP65H035G4WS is a 650-volt device with a resistance of 35 milliohm in a TO-247 package with an intrinsically high thermal dissipation capacity that offers the possibility to eliminate any additional device in parallel if more power is required.

This article was originally published on EEWeb.

Maurizio Di Paolo Emilio holds a Ph.D. in Physics and is a telecommunication engineer and journalist. He has worked on various international projects in the field of gravitational wave research. He collaborates with research institutions to design data acquisition and control systems for space applications. He is the author of several books published by Springer, as well as numerous scientific and technical publications on electronics design.

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