How to control a DC-DC buck converter by an MCU (ESP32) to choose between two fixed voltage outputs?

Question

I made this post a day before about controlling a DC-DC buck converter’s output voltage with an ESP32 DAC output.

Is it possible to control a Dc Dc buck converter output voltage by the DAC of an Esp32?

But in fact what I need is to control the output voltage of the DC-DC buck converter between a max voltage (for me 30 V) and a fixed lower one (18 V), from an MCU. In my case an ESP32. I don’t need to swing between the voltages, just need to choose between then when needed it.

I read about it in this post below:

Changing output voltage of a buck converter by electronically swapping the feedback resistors

I need some help on how to implement it on the feedback pin of the DC-DC controller. In my case, the XL4005.

Thanks

Answer 1

You can use the diagram in the answer you linked almost directly. You only need one MOSFET to switch between two voltages, like so:

^{simulate this circuit – Schematic created using CircuitLab}

First calculate Ra and Rb2 for 18V operation. Then calculate Rb1 so that Rb1 in parallel with Rb2 has the correct value for 30V operation.

Answer 2

Modify the answer I gave in your previous question to replace the DAC and buffer op-amp with a GPIO pin to the FET gate. Done.