SLUAAU2 January 2024 UCC21551 , UCC27517A , UCC27624 , UCC27714
In PFC circuits, the switching components (diodes and MOSFETs) account for around 20% of all losses, therefore, careful selection of the power switch is important, as well as the driver that controls the power switch to optimize performance. To minimize losses, a MOSFET with low RDS(ON) conduction losses and a low gate charge (QG) is important. To compare FETs, a rating is created that is a scalar value with the loss contributing parameters of RDS(ON) multiplied by QG. This scalar result is a figure of merit that creates a rating scale to compare FETs where the lowest rating yields the most efficient power switch. For most of these topologies, Si MOSFETs are an excellent choice and operate as needed, but SiC or GaN FETs are needed for the high switching frequencies required by the highest efficiency applications.
Table 3-1 shows some examples of the power switches that have been used in reference designs for PFC circuits.
| Topology | Boost | Boost | Bridgeless Boost | Interleaved Boost | Interleaved Boost | Totem Pole | Totem Pole | |
|---|---|---|---|---|---|---|---|---|
| Power (W) | 1000 | 1000 | 300 | 1500 | 700 | 6600 | 3000 | |
| Type | Si | SiC | Si | Si | Si | SiC | SiC | Si |
| VDS (V) | 650 | 900 | 550 | 600 | 650 | 1000 | 750 | 600 |
| VGS(th) (V) | 4 | 2.1 | 3 | 3 | 3 | 2.1 | 4.8 | 3.5 |
| Rg (Ω) | 3.5 | 3.5 | 2.2 | 0.85 | 1.3 | 3.5 | 4.5 | 0.45 |
| rDS(on) (Ω) | 0.171 | 0.065 | 0.22 | 0.063 | 0.22 | 0.065 | 0.018 | 0.015 |
| Coss (pF) | 76 | 66 | 63 | 215 | 54 | 70 | 217 | 200 |
| Qg (nC) | 37 | 30 | 27 | 170 | 26 | 37 | 37.8 | 340 |
| Rating | 6.327 | 1.95 | 5.94 | 10.71 | 5.72 | 2.405 | 0.6504 | 3.6 |
| Gate Driver | UCC27614 | UCC21520 | UCC27624 | UCC27517A (2) | UCC27524 | UCC21520 | UCC21551 | UCC27714 |
Table 3-1 also highlights some of the gate drivers used for these various switches. For SiC switching, isolated gate drivers such as the UCC21551 and the UCC21520 are used. This is due to the high voltage, power and switching frequencies needed for SiC FETs. For Si power switches, single or dual-channel gate drivers can be utilized depending on the topology. As seen for a boost circuit, a single-channel device such as the UCC27517A or the UCC27614 is needed to drive these power transistors. For dual-channel gate driver scenarios, the UCC27524 and the UCC27624 are often used. These scenarios include bridgeless boost and interleaved boost PFCs. For applications where GaN FETs are utilized, drivers such as the UCC27517A, the UCC27624, and the UCC21222 are all capable of driving GaN FETs.