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2 W Gate Drive Power Supply Design with PCB-Embedded Transformer Substrate

Designed printed circuit board of an integrated transformer
Fig. 1. PCB-embedded transformer structure illustration.
As silicon carbide (SiC) and gallium nitride (GaN) devices become more commercially available, high switching frequency operations become a popular way to increase the power converter efficiency and power density. A key trade-off of these gains is the increasing electromagnetic inference (EMI) noise. In order to attenuate the EMI noise from the power loop into the auxiliary sources, the isolation capacitance in the isolated gate drive power supply is expected to be as small as possible. To this end, a gate drive power supply dedicated to driving two 650 V GaN devices in a phase leg is presented with a PCB-embedded transformer as substrate, thus achieving an ultra-low inter-capacitance of 1.6 pF, a high efficiency of 83% and a high power density of 72 W/in3. The input of the power supply is 15 V and there are two isolated outputs, whose output voltage is 7 V and output power is 1 W each.

To pursue a small inter-capacitance (isolation capacitance) from the primary to the secondary side in the transformer, the primary and secondary windings should be located as far apart as possible. Accordingly, as the transformer volume increases, it exacerbates the difficulty in achieving high power density. The challenge of this work is to find an appropriate design approach, aimed at small converter volume, small inter-capacitance and high efficiency.

To design the targeted gate driver power supply, the paper first presents the circuit design, including the topology selection, operation mode analysis, and active and passive component selections, operation mode analysis, and active and passive component selections. The PCB-embedded transformer structure is then illustrated in Fig. 1, and the core and PCB material selections are addressed. To find a compromise among a low inter-capacitance, low transformer loss, and a small volume, an optimization of the transformer dimensions is performed based on the transformer models. With the optimized dimensions, the transformer is built and shown in Fig. 2, and the fabrication procedures, including the standard lamination process, are introduced. The transformer and the converter hardware are showin in the end and characterized with experimental waveforms, efficiency, isolation voltage, inter-capacitance, and total volume.

Fully designed PCB shown in relation to a quarter (smaller than)
Fig. 2. Active-clamp flyback with the PCB-embedded transformer substrate.
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