This is my first time playing with one of those $2 Chinese voltage boosters. This one in particular uses what I think is an SBD628, which has a Vref=600mV. The actual circuit has the output divider consists of a 100K trim pot from Vout, with a 2K2 fix resistor to groung on the other end.
I set it up on a breadboard, with a 235R load, trying to get 18V on the output. I started turning the trim pot while measuring voltage. After quite some turns, the voltage started to increase, with a reasonable sensitivity, but as voltage increased, the sensitivity grew exponentially, making it hard to set a value. I soldered a few wires for voltage monitoring on the trim pot, and took a few measurement points.
Eventually I looked for the IC datasheet and found the voltage setting formula. With it I went to excel and created a spreadsheet with 1% adjustment steps of the trim pot. It is incredible how badly it behaves as the pot goes up. When the Vout at 6V, the Vout sensitivity is around 11% for a 1% trim increment. At Vout=10, it is 20%; at Vout=12V, 25%; at Vout=14.7V, 31%. A one% change takes it from 14.65V to 19.23V, making it very hard to adjust.
Are there any tricks to deal with this? I may hack it replacing the 100K trim pot with two fix resistors and a 5K or 10K one.
Any ideas will be appreciated.