SSZTAW3 september 2016 LMG3410R070 , UCC21520
Remember the blog with an interesting analogy between power factor correction (PFC) and beer earlier this year? I think it is brilliant! In that case, the beer in a glass represented the “real power” that an electronic device actually requires, the foam at the top represented “reactive power,” and the entire glass of beer plus the foam represented the “apparent power.” Today, I’m taking on the challenge of proposing a related analogy to explain the role that a gate driver plays in PFC designs.
Let’s briefly talk about the different types of PFC circuits first. In general, PFC circuits are either passive or active. To create passive PFC circuits, you add passive components like capacitors and inductors to increase the current conduction angle and smooth down the pulse, which helps reduce the current’s harmonic distortion. This approach is simple and reliable, but the size and cost of the passive components becomes a big problem when the power level is high. A passive PFC design can also only achieve a power factor (PF) up to 0.9 and is affected by frequency, load change and input voltage.
Active PFC uses a DC/DC circuit, which contains MOSFETs, insulated-gate bipolar transistors (IGBTs) or other active components to force the current to follow the voltage in both shape and phase. Compared to passive PFC, active PFC can achieve higher PF and does not have strict requirements on the input voltage. Drawbacks of active PFC include comparatively complex circuitry; also, the efficiency can be affected by the losses of active components.
There are different topologies to realize active PFC circuits, such as boost PFC (also known as traditional PFC), dual boost bridgeless PFC and totem-pole bridgeless PFC. Each topology contains a different number of active components and has its own pros and cons. When designing a PFC, you should consider the efficiency and power ratings of each topology and then determine which type of controller to use. However, one part many designers ignore is the gate driver that’s connected to the controller to switch the FETs. Gate drivers seem too common to bother with, but they play an important role in the performance of the system.
A gate driver is essentially an amplifier that boosts the logic signal to a high current and high-voltage signal that turns the MOSFET or IGBT on and off quickly, with the least switching loss. To make an analogy also related to beer, power-switch MOSFETs or IGBTs are like the beer-tap handle, the gate drive is like the muscles in the bartender’s hand and the controller is the brain. The skills of the bartender and the quality of the tap handle can both impact how much beer you actually get in a glass.
In PFC circuits, gate drivers switch the transistors in the boost stage to regulate the current and force it to be in phase with the sine-wave voltage. So how does the gate driver affect PFC circuit performance? Several parameters and features play a vital role:
PFC will be used more and more in various applications as regulations make higher efficiency mandatory in more countries. Pick your topologies and components wisely so that your PFC can work efficiently and fit your needs. And don’t forget gate drivers – the muscle.
Gate driver’s importance should be clear now, but the brain plays an even more important role in PFC designs. Texas Instruments offers a broad range of PFC controller solutions, including analog and digital controllers for both single and multiphase interleave PFCs.
Explore all the PFC controllers and high voltage gate drivers from Texas Instruments.