4 Low-Cost, High-Performance Auxiliary Power Solution

The LLC converter has high efficiency. TI's UCC25800-Q1 transformer driver is open-loop control, so it is necessary to add a pre-voltage pre-regulator between the low-voltage 12V battery and the auxiliary power circuit to make the UCC25800-Q1 work at a fixed input voltage, commonly used pre-voltage pre-regulator circuits are Boost or Sepic circuits. The research scope of this article is to use a low-voltage 12V battery as the input. Considering the fluctuation of the input voltage range, the input voltage range is generally 6-18V. The Sepic circuit is suitable for occasions where there is a need for Boost and Buck. Compared with the Boost converter, the Sepic converter has an additional energy storage inductor and a DC blocking capacitor. The system BOM cost is higher and the design is more complex. The input voltage range of UCC25800-Q1 is 9-34V. Under the condition of 34V input voltage, the power of UCC25800-Q1 can up to 9W. This solution selects UCC2803-Q1 as the Boost converter to increase the 12V voltage of the low-voltage battery to 34V as the front-stage voltage pre-regulator.

The block diagram of this solution is shown in Figure 4-1. The peripheral circuit design of this solution is simple, the efficiency can reach 85%-90%, and the output voltage adjustment accuracy can reach ±5%.

The system BOM cost of this solution is shown in Table 4-1.

The pros and cons of this solution are shown in Table 4-2.

The radar chart is shown in Figure 4-2.