PCB Tech - What is the use of gate driver in PFC circuit design

This article mainly talks about the role of the gate driver in PFC design, and there will be an image metaphor to help you understand.

To create a passive PFC circuit, it is necessary to use passive components such as capacitors and inductors to increase the current conduction angle and smooth the pulse to reduce the harmonic distortion of the current. This method is simple and reliable, but when the power is high, the size and cost of the passive components will become a big problem. The power factor (PF) obtained by passive PFC design can only reach 0.9, and it will be affected by frequency, load changes and input voltage.

Different topologies can be used to implement 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 advantages and disadvantages. When designing a PFC, one should consider the efficiency and power rating of each topology,

and then decide which type of controller to use. However, the part that many designers overlook is the gate driver connected to the controller switching FET. The gate driver is too common to be noticed, but the gate driver plays an important role in system performance.

The gate driver is essentially an amplifier that uses the least switching loss to increase the logic signal to a high current and high voltage signal to quickly turn on and turn off the MOSFET or IGBT. Similarly with beer-related things, the power switch MOSFET or IGBT is like the handle of a beer faucet, the gate drive is like the muscles of the bartender's hand, and the controller is like the bartender's brain. The skill of the bartender and the quality of the tap handle will affect the actual amount of beer that can be obtained in the glass.

In the PFC circuit, the gate driver switches the transistors in the boost stage to adjust the current, forcing the current to maintain the same phase as the sine wave voltage. So, how does the gate driver affect the performance of the PFC circuit? Several parameters and functions play a vital role:

Drive current.

Although not every application requires a strong current drive (large transient currents may cause electromagnetic interference (EMI) problems), higher power applications will require a stronger current drive to simultaneously drive multiple field effect transistors (FET) . Therefore, the high drive current provides flexibility for a wide range of power applications.

Switch characteristics.

Including propagation delay, delay matching, and signal rise and fall times. The switching time will greatly affect the speed of the power switch, making the control more predictable and accurate. Short delay matching also reduces the risk of breakdown and makes design easier.

Interlock function.

Breakdown protection, also known as the interlock function, is very important in some applications that use half-bridge or full-bridge circuits. In totem pole PFC, two power switches (a high-side FET and a low-side FET) alternately turn on and off. If the two switches are turned on at the same time, current will flow through the two FETs, which may damage the system. The interlock function can prevent breakdown, turn off both FETs, and turn on one of them in a short time. As described in Texas Instruments’ "GaN FET-based CCM Totem Pole Bridgeless PFC" power supply design seminar paper, this design uses two silicon MOSFETs and two gallium nitride (GaN) high electron mobility transistors (HEMT) to reduce Conduction loss. Two drivers are required: one half-bridge driver drives conventional silicon MOSFETs, and the other half-bridge driver drives GaN transistors. TI's 600V LMG3410 GaN power stage integrates bridge drivers and GaN transistors into one package, further reducing power consumption and improving EMI. In order to drive the silicon FET, a bridge driver with interlocking function improves the reliability of the design.

As more countries' regulations mandate higher efficiency, PFC will be used more and more in various applications. Choosing topologies and components wisely can make PFC more efficient and meet demand. And don't forget the gate driver-the muscles of the bartender's hands.

The importance of gate drivers is now understood, but the brain plays a more important role in PFC design.