I made a boost converter based on the below schematic. I want to use this to create 18V.
When I connect a 12V powersupply to the connector P3IN, I only measure the same 12V at the output on connector PWR3. Changing the potmeter R52 seems not to change anything.
I have 2 PCB's (ordered via JLCPCB - minimum qty for SMT assembly is 2), so I tried both. Unfortunately, on my second board the MT3608L blew up. So there must definitely be something wrong.
Does somebody has a clue?
Some more information as requested in the below comments:
- The inductor is SWPA6045S220MT. I choose it directly from the JLCPCB components, which shows chinese data sheet. But when I google, you can also find it at DigiKey.
- The layout of my PCB is shown below. As this was only an experimental PCB, the boost convertor is just a complete separate section on my PCB. Just ignore the USB connector DC1. I only show 2 layers, but this is a 4 layer board. One of the mid-layers is GND, which is not visible, but that obviously does connect all the GND together. The GND pins of connectors P3IN and PWR3 are connected through that inner layer.
Good news, the boost convertor works as a charm. It was a matter of tuning the potmeter correctly. I removed the potmeter from the my PCB, measured a correct 63.8kOhm, and connected it with some wires back in the circuit in such way that R52 becomes 63.8kOhm, and FB is connected between R51 and R52. After that, I got almost exactly 18V.
The circuit I made is indeed very dangerous, because if the resistor wiper gets to close to the output, you might exceed the max 6V rating on the FB pin, which destroys the chip (which was the case in my first test). As Verbal Kint commented, it's indeed better to use a fixed resistor divider if I only want one fixed voltage.
Also worth mentioning is that I didn't need any extra load to make it work.
Consider this as solved.