5 High Voltage Isolation

The distance between the high-voltage area at the primary side, and low-voltage area at the secondary side, must have enough creepage and clearance to comply with standards such as IEC 60664-1. For creepage design criteria as example, with 800 Vrms working voltage and pollution degree 2, the working voltage for material group I is 4 mm for basic isolation, and 8 mm for reinforce isolation. Therefore, the PCB layout between primary and secondary side and the transformer pin-out needs to follow the guideline.

The ground of the low-voltage side can be connected to a 12-V battery or vehicle chassis, which a user can come in contact with. Therefore, a transformer with reinforced isolation and AEC-Q200 Grade 1 compliance is recommended for this application.

With internal error amplifier and reference, the UCC28C5x family can be configured as a primary-side regulated solution by using an auxiliary winding for feedback, so that it can avoid the need to use optocoupler across isolation and eliminate the CTR degradation from the optocoupler life time issue