Optimizing the charging and discharging of portable power stations

Along with the growth of USB PD, demand for battery-powered electronics creates a need for portable power stations to charge them. In the past, portable power stations powered products such as TVs, radios and small refrigerators, but the expansion of USB PD EPR enables users to charge portable power station batteries for smaller personal electronics such as laptops and speakers with the same USB Type-C cord shown in Figure 5 and Figure 6. In Figure 5, the portable power station battery can be charged with as much as 240 W from the battery charger. Figure 6 shows the reversed power flow. Energy from the portable power station battery provides power out of the USB Type-C port through the cord to charge the laptop.

Achieving the optimized charging and discharging solution shown in Figure 5 and Figure 6 requires a bidirectional buck-boost battery charger. Bidirectional signifies that the battery charger can also perform in buck and boost modes when power flows from the output to the input, which is called reverse mode. To help visualize reverse mode, see Figure 2 and Figure 3. In reverse mode, Figure 2, which was buck mode, is now boost mode. Figure 3, which was boost mode, is now buck mode. Having a bidirectional buck-boost charger enables consumers to use a USB Type-C port to charge an application’s battery and then reverse the power flow to charge another device, such as a laptop.

I have already discussed how a bidirectional battery charger is useful in portable power stations, but are there other applications where bidirectional power flow is useful? One emerging trend is e-bikes using USB Type-C to charge the main battery, and then using the main battery to charge a personal device through the same USB Type-C port. Imagine that you’ve taken your e-bike to the park and want to stream a movie on your smartphone, but it’s only at a 10% charge. Designing the main battery of an e-bike with a bidirectional buck-boost battery charger and USB Type-C allows smartphone charging from the e-bike battery.