PFCs are a key power stage in HVAC systems, and the most common PFC topology used in HVAC systems is the boost PFC. The boost PFC topology utilizes a full-bridge rectifier to first rectify the AC line voltage, and then a boost converter is used to step up the rectified voltage to a desired DC bus voltage. This topology consists of a single FET referenced to ground, requiring a low-side gate driver. Figure 2-1 shows an example of the boost PFC.

Figure 2-1 Boost PFC with UCC5714x

Selecting a gate driver to drive the FET in HVAC PFC circuits requires careful consideration. Parasitic inductance and electromagnetic interference in HVAC systems can potentially cause damaging or destructive negative voltages that can affect gate drivers. To help circumvent this issue, it is important to select a gate driver with negative voltage capability to increase the robustness of the system. Another requirement to consider when designing high efficiency HVAC PFC circuit is peak drive current. A high peak drive current helps to achieve fast rise and fall time of the FET. This reduces voltage and current overlapping, which reduces switching losses to help HVAC systems achieve higher efficiency. Another consideration is the size of the gate driver IC. A smaller package allows the gate driver IC to be placed closer to the power FET, which reduces parasitic inductance due to PCB traces.

The UCC5714x can be used to drive the FET in a boost PFC for HVAC systems. The UCC5714x has peak output current of 3A source and 3A sink and is rated up to 30V VDD. Furthermore, the driver has a rise time of 8ns, fall time of 14ns, and propagation delay of 26ns for fast and efficient switching in HVAC systems. The UCC5714x also has negative voltage capability, under-voltage lockout (UVLO), and integrated over-current protection (OCP) for added robustness. Refer to this app note for a greater explanation of how OCP benefits end systems.Table 2-1 features a comparison between UCC5714x and the leading competitors.