Some additional ideas for the SZBK07 DC-DC converter
In this video, I will show you two interesting things that you can use to control the SZBK07 DC-DC controller. First, I show you how to control the output voltage of the DC-DC converter without removing the built in trimmer potentiometer (CV). This is realized by adding an extra rheostat which injects a certain amount of current. If we add two extra potentiometers, we can control the output voltage of the DC-DC converter within a certain lower and upper limit. I show two examples, 6-12 V and 4-8 V.
In the second experiment I replace the original 100 kOhm potentiometer with several different (smaller) potentiometers and see what happens. The potentiometer -which is wired as a rheostat- is part of a voltage divider which is ultimately connected to the feedback pin of the LM25116. Therefore having too low values for the potentiometer, would not allow the buck controller to work properly.
A typical application circuit for the LM25116 buck controller. The voltage divider which controls the output voltage is highlighted with a red rectangle. In the SZBK07 DC-DC converter, the R3 = 3.74 kOhm resistor is replaced by a 100 kOhm trimmer potentiometer and the R4 = 1.21 kOhm resistor is replaced by a 3.9 kOhm resistor.
The highlighted parts belong to the voltage divider. In the SZBK07 DC-DC converter, the R3 = 3.74 kOhm resistor is replaced by a 100 kOhm trimmer potentiometer and the R4 = 1.21 kOhm resistor is replaced by a 3.9 kOhm resistor. The output voltage can be adjusted with the RFB1 (R4) and RFB2 (R3) values.
The voltage divider with some typical potentiometer values in the SZBK07 circuit. The voltage values represent the maximum output voltages that can be achieved on the SZBK07 DC-DC converter.
The input of the rheostat network (50 kOhm potentiometer) is connected to a 5 V voltage source in my demonstration. It can be a different value, but it has to be a fix voltage! For example the input power supply of the DC-DC converter is supposed to be a stable and fixed supply, so you can connect the network to it. The output of the network is connected to the CV potentiometer’s 2-3 pin. These pins are connected together for the CV potentiometer because it is also used as a rheostat.
