APEC 2015 – using the Fly-Buck™ converter for IGBT gate drive bias

This year’s Applied Power Electronics Conference and Exposition (APEC) is coming up very soon in Charlotte, North Carolina. I’m sure many attendees like me are looking forward to experiencing the technical sessions, touring the exhibitions, and finding out about the newest developments and research in the power-electronics industry.

Besides visiting TI’s demonstrations in the exhibition hall, be sure to check out the poster sessions as well. We are presenting a paper, “Isolated Bias Power Supply for IGBT Gate Drives Using the Fly-Buck™ Converter” in the Dialogue Session on Thursday, March 19. I have been working on Fly-Buck power-supply designs for two years. It is very exciting to me to have the chance to bring Fly-Buck to APEC and have discussions with my fellow power professionals.

The Fly-Buck, a topology that uses a coupled inductor in a buck converter to generate multiple output voltages, has proven its versatility as an isolated power supply in various industrial applications and is renowned for its ease of design and compactness. In AC motor drive applications, dedicated isolated bias supplies are often required to power insulated gate bipolar transistor (IGBT) gate drivers. Compared to the whole motor system, which handles power ranging from kilowatt to megawatt levels, the bias power for each IGBT driver is “pea-sized” in the order of a few watts. However, this is no small issue for the bias-supply designs. The high voltage and current swing in the motor operation pose serious challenges to the gate-drive bias, and providing stable bias voltages is critical to the reliable switching of the IGBT.

Another challenge is the requirement for multiple isolation outputs. One single IGBT driver usually needs bipolar biasing (one positive and one negative rail) for turn-on and turn-off, and each high-side IGBT in a multiphase configuration needs separate supplies isolated from one another. The Fly-Buck is a suitable solution to meet these challenges. Figure 1 shows an example of using Fly-Buck in a typical three-phase motor-drive application.

Figure 1: Four-output Fly-Buck bias supply for two IGBT drivers in a three-phase motor drive

Push-pull, flyback and forward converters are popular isolation-power topologies used in this area, where the output regulation is often realized with open-loop control or auxiliary-winding feedback control. On the other hand, the Fly-Buck has the natural primary-side regulation, which uses the primary non-isolated buck-output voltage as the feedback to clamp the isolated output. This feature keeps the Fly-Buck design simple and offers flexibility in creating multiple outputs. Performance wise, it provides good cross-regulation, line-transient response and low-noise interference.

In our APEC paper, we explore the use and the design of the Fly-Buck as an IGBT driver-bias supply. We used a four-output Fly-Buck reference design with TI’s LM5017 buck regulator as an example in the paper, which can power two IGBT drivers in half bridge, as shown in Figure 2. There are actually different ways to configure the Fly-Buck for either single or multiple IGBTs.

We will bring another example to APEC as well: an eight-output Fly-Buck bias reference design for three-phase IGBTs (six IGBTs) with TI’s latest, higher-current-capable LM5160 buck regulator, as seen in Figure 3.

Figure 2: Four-output Fly-Buck gate-driver bias reference board (PMP9460)

Figure 3: Eight-output Fly-Buck gate-driver bias reference board (PMP10531)


Please come visit me in the Dialogue Session, Poster Area 1, from 11:30 a.m.-2:00 p.m. on Thursday, March 19. In the meantime, you can also check out more Fly-Buck design resources at ti.com/fly-buck, as well as these related Fly-Buck reference designs for IGBT gate driver bias: